RU2300515C2 - Method of production of methacrylic acids by catalytic oxidation of propylene or isobutylene (versions), method of decomposition of by-product (versions) and plant for realization of this method - Google Patents

Abstract

FIELD: industrial production of methacrylic acids at reduced amount of industrial wastes.

SUBSTANCE: proposed method is performed by catalytic oxidation of propane, propylene or isobutylene in vapor phase at separation of final product and forming of high-boiling mixture as by-product which contains (according to Michaels addition) water, alcohol or methacrylic acid added to methacrylic group. By-product is decomposed in thermal decomposition reactor at simultaneous distillation of decomposition products in distilling column from which methacrylic acid is taken in form of distillate. Flow of liquid decomposition residue is forced for peripheral direction by means of mixing blades before withdrawal from reactor. Peripheral direction is obtained with the aid of liquid fed from the outside of decomposition reactor; to this end use is made of initial high-boiling material or flow of liquid discharged from decomposition reactor. If necessary, etherification stage is performed through interaction with alcohol for obtaining methecrylic ester. Decomposition of by-product formed at obtaining methacrylic acid by oxidation of propylene or isobutylene or at obtaining methacrylic acid by interaction of acid with alcohol by alcohol through introduction of by-product into thermal decomposition reactor provided with distilling column which has plates made in form of disks and toroids for simultaneous decomposition and distillation. Plant proposed for realization of this method includes thermal decomposition reactor and distilling column, level meters and lines for discharge of liquid containing easily polymerized compounds. Level indicator mounted at area of accumulation of liquid shows pressure differential. Line for detecting the side of high pressure of this level meter is connected with accumulated liquid discharge line.

EFFECT: updated technology; increased yield of target products.

38 cl, 14 dwg, 2 tbl, ex

Description

FIELD OF TECHNOLOGY

This invention relates to a method of producing (meth) acrylic acids that is advantageous for industrial production at a high extraction rate while reducing the amount of industrial waste by decomposition of by-products, such as Michael addition products of (meth) acrylic acids or meth (acrylic) esters formed as by-products in the preparation of (meth) acrylic acids, and the recovery of various compounds such as (meth) acrylic acid, esters of (meth) acrylic acid and alcohols.

As used herein, the term “(meth) acrylic acid” is a generic term for acrylic acid and methacrylic acid and may mean either one or both of them. Further, the term “(meth) acrylic acids” is a general term for these acids and esters of (meth) acrylic acids derived from such acids and alcohols, and this term refers to at least one of these compounds.

State of the art

but. As a method for the decomposition of Michael addition reaction products formed as by-products during the preparation of acrylic acid or acrylic acid esters, a catalyst-free thermal decomposition method is usually used in the case of the method for producing acrylic acid (JP-A-11-12222), whereas in the case of a method for producing an acrylic acid ester, decomposition by heating in the presence of a Lewis acid or Lewis base is known (Japanese Patents JP-A-49-55614, JP-B-7-68168, JP-A-9-110791, JP-A-9 -124552, JP-A-10-45670). Further, as a reactive decomposition system for Michael addition products, a reactive distillation system is usually used in which the desired decomposed reaction product is distilled off by distillation during the decomposition reaction. Further, there is also known a method in which the Michael reaction addition products formed as by-products in the acrylic acid production step and the Michael reaction addition products formed as by-products in the acrylic acid ester preparation stage are combined together with subsequent thermal decomposition. A known method of thermal decomposition using a chemically active distillation system in the absence of any catalyst (JP-A-8-225486) and a decomposition method using a highly concentrated acid catalyst (JP-A-9-183753).

To increase the rate of extraction of acrylic acid, acrylic acid ester or alcohol used as a product or as a starting material for the reaction, it is necessary to increase the decomposition reaction temperature in the upper part of such a decomposition reaction column and reduce the amount of discharge from the lower part, due to which So far, there has been a problem in that the liquid of the lower part tends to be a highly viscous liquid; when the decomposition temperature is high, it is likely that an oligomer or polymer of acrylic acid or an ester of acrylic acid is formed, which is an easily polymerizable substance; and some of the substances contained in the starting material for this reaction tend to precipitate, whereby a solid is deposited at the bottom of the decomposition reaction column, a polymer is formed due to the presence of liquid contained in this deposit (sludge), and such sludge will flow into line fluid discharge; and therefore, there was no suitable way by which the decomposition reaction column could operate continuously for a long time. Mainly, in the case where a solid is deposited in the lower part of the decomposition reaction column, the easily polymerizable liquid absorbed in the deposited solid tends to be extremely polymerizable since it cannot flow and the decomposition reaction temperature is relatively high, which therefore leads to the phenomenon when the amount of sludge will increase even more with this polymerization. Thus, it is desirable to solve this problem.

b. As an example of solving this problem, a method is possible in which the diameter of the lower fluid transfer pipe is reduced to transfer this fluid at a high volumetric flow rate, but it was not possible to use such a method, since a pump for such transfer should be a type of high pressure pump which is economically disadvantageous for the industrial production method. Further, it is also possible a method in which to reduce the viscosity of the liquid of the lower part, the spent liquid can be added from the production step or water can be added again, but this will lead to a decrease in the temperature of the liquid, whereby the blockage tends to accelerate somewhat or require the addition of such water to a large number. Thus, the use of such a method is practically impossible.

from. On the other hand, as is well known, there is a method of oxidation in the vapor phase of propylene as a reaction for the formation of acrylic acid. For such a method for producing acrylic acid by oxidation of propylene, there is a two-stage oxidation method in which oxidation to acrolein and the next oxidation step to acrylic acid are carried out in separate reactors, respectively, since the oxidation conditions are different, and a method in which oxidation to acrylic acid is carried out directly in a single-stage oxidation.

Fig. 9 shows an example of a scheme for the formation of acrylic acid by two-stage oxidation followed by reaction with alcohol to form an acrylic acid ester. Namely, propylene, steam and air are subjected to two-stage oxidation using the first and second reactors filled, for example, with a molybdenum type catalyst, to form a gas containing acrylic acid. This gas containing acrylic acid is reacted with water in a collecting column to obtain an aqueous solution of acrylic acid, which is extracted in the extraction column by adding a suitable extraction solvent, after which the extraction solvent is separated in a solvent separation column. Acetic acid is then separated in an acetic acid separation column to obtain crude acrylic acid, and a by-product is separated from this crude acrylic acid in a fractionation column to obtain a purified acrylic acid product. Further, this acrylic acid (purified product) is esterified in an esterification reaction column, and then, using an extraction column and a light component separation column, a crude acrylic acid ester is obtained. A by-product (high boiling point product) is separated from this crude acrylic acid ester in a fractionation column to obtain a purified acrylic acid ester product.

Here, depending on the type of acrylic acid ester, there may be a case in which the flow chart will be as shown in FIG. 10. In this case, the by-product is obtained as residues (undercuts) in an acrylic acid separation column.

In the method for producing the acrylic acid ester of FIG. 10, acrylic acid, alcohol, recovered acrylic acid and recovered alcohol are respectively fed to the esterification reactor. This esterification reactor is filled with a catalyst, such as a strongly acidic ion exchange resin. The esterification reaction mixture containing the formed ester, unreacted acrylic acid, unreacted alcohol, formed water, etc., withdrawn from this reactor, is fed to the acrylic acid separation column.

From the bottom of this acrylic acid separation column, the bottom liquid containing unreacted acrylic acid is withdrawn and recycled to the esterification reactor. A portion of this lower portion liquid is fed to a high boiling component separation column, whereby the high boiling component is separated from the bottom and fed to the decomposition reactor of the high boiling component and decomposed (not shown). The decomposition product containing the valuable substance formed by the decomposition will be recycled to the process. The place in this process where this decomposition product is recycled varies depending on the process conditions. High boiling impurities, such as polymers, will be discharged from the decomposition reactor of the high boiling component to the outside of this system.

Acrylic ester, unreacted alcohol, and water formed are distilled off from the top of this acrylic acid separation column. Part of this distillate is recycled as a reflux liquid to the acrylic acid separation column, and the remainder is fed to the extraction column.

Water is extracted into this extraction column for alcohol extraction. Water containing alcohol flowing from the bottom is fed to the alcohol recovery column. The distilled alcohol will be recycled to the esterification reactor.

The crude ester of acrylic acid from the top of the extraction column will be fed to the separation column of low boiling components, and the low boiling material is removed from the upper part and it is recycled to the process. The place in this process where it is recycled varies depending on the process conditions. The crude acrylic acid ester containing the removed low boiling material will be fed to a purification column for the acrylic acid ester product, whereby high purity acrylic ester will be obtained from the top. The bottom fluid contains a large amount of acrylic acid and, therefore, is recycled in this process. The place in this process where it is recycled varies depending on the process conditions.

Further, in recent years, instead of a solvent extraction method in which the extraction of acrylic acid from the above aqueous solution of acrylic acid is carried out by a solvent extraction method, an azeotropic separation method is carried out in which distillation is carried out using water and an azeotropic solvent, so that from the top of the azeotropic separation column an azeotropic mixture containing water and an azeotropic solvent is distilled off, and acrylic acid is recovered from the bottom.

Further, a method in which acrylic acid is prepared using propane instead of propylene and using a mixed oxide catalyst of the Mo-V-Te type or a mixed oxide catalyst of the Mo-V-Sb type is also practically used. In the case of methacrylic acid and methacrylic acid ester, isobutylene or tert-butyl alcohol is used instead of propylene, and the purified methacrylic acid product and the purified methacrylic acid ester product are obtained through a similar oxidation process and subsequent esterification process.

Further, as a method of forming an (meth) acrylic acid ester (acrylic acid ester or methacrylic acid ester), a method is used in which the (meth) acrylic acid ester of a lower alcohol and a higher alcohol is subjected to a transesterification reaction using, for example, an acid as a catalyst with obtaining the ester of (meth) acrylic acid of higher alcohol. The crude (meth) acrylic acid ester obtained by the transesterification reaction is subjected to such steps as separation of the catalyst, concentration and fractionation to obtain the purified (meth) acrylic acid ester.

A useful by-product, such as a Michael addition product, is contained in a fraction separated by distillation and purification of the above crude acrylic acid, crude methacrylic acid, crude acrylic ester or crude methacrylic ester. Thus, this by-product is destroyed to regenerate the (meth) acrylic acid or its ester or alcohol of the starting material.

To date, the methods described above in a. were known as methods for the decomposition of the Michael addition product formed by-products during the production of acrylic acid or acrylic acid ester. Thus, it has previously been customary to decompose the Michael addition product, which is formed by-product during the production of an acrylic acid ester, for regeneration by this valuable substance such as acrylic acid, acrylic ester or alcohol. As such a decomposition and regeneration method, reactive (chemically active) distillation systems are usually used, in which distillation is carried out during the decomposition reaction.

To carry out a system of chemically active distillation, a reactor equipped with a distillation column in its upper part is used. As such a distillation column, a plate-containing column provided internally with various plates or a packed column filled with various packed materials is typically used to produce fractionation effects. These plates may be, for example, cap plates, single-flow plates, flexible plates, ballast plates, perforated plates (mesh plates), exhaust plates, rippled plates, double-flow double plates or bubble plates. The packing material may be, for example, ring type packing material, such as Raschig rings (contact material for packed columns), spiral rings or Pall metal rings, or saddle type packing material, such as Burl saddle packing for packed columns, or an inner seat, or other materials, such as the Goodloe nozzle, the Dixon ring, the McMagon saddle mesh nozzle, or the vertically adjustable flat plate nozzle material.

However, in both methods for producing acrylic acid and acrylic ester, the starting material to be fed to the decomposition step of the by-product is the fraction obtained by concentrating the high boiling point component formed in the reaction system or purification system. In addition, acrylic acid and acrylic acid esters are very readily polymerizable materials and, therefore, the starting material for the decomposition reaction contains the resulting polymers. Further, the decomposition reaction is carried out at a high temperature and, therefore, a polymer will form during the decomposition reaction. Thus, it is likely that a solid is already present in the starting material to be decomposed, and even if there is no solid in the starting material, it can be re-deposited or a solid can be formed during the operation of the distillation separation or in the decomposition stage, where a chemical reaction is carried out simultaneously . In this case, adhesion, deposition or accumulation of such a solid substance takes place on plates or in the free spaces of the packed material in a distillation column, whereby, for example, an increase in excessive pressure (pressure drop), violation of the gas / liquid contact state and additional blockage can occur. Thus, there was a problem in that all this tends to impede the production of a high rate of extraction of a valuable substance or impede continuous continuous operation.

Thus, in both methods for producing acrylic acid and an ester of acrylic acid, it is desirable to solve the above problems and to develop a method for decomposing the addition product according to Michael, by which a high extraction rate can be continuously achieved.

d. Further, in the method for the regeneration of (meth) acrylic acid or (meth) acrylic ester, the decomposition reaction of the Michael addition reaction product formed by-products during the process of producing (meth) acrylic acid or (meth) acrylic ester if the decomposition reaction temperature is made high in order to obtain a high regeneration rate for such (meth) acrylic acid, (meth) acrylic acid ester or alcohol, an oligomer or polymer of (meth) acrylic acid or (meth) acrylic acid ester will be formed which is Xia easily polymerizable substance. To prevent such polymerization, the addition of molecular oxygen is contemplated, in addition to the polymerization inhibitor, such as hydroquinone, methoxyhydroquinone, phenothiazine or hydroxylamine, to the decomposition reactor (for example, the aforementioned Japanese patent JP-A-10-45670, paragraphs 0012 and 0019).

However, when using such a method, a case can be observed in which not only can an adequate effect not be obtained with respect to preventing the polymerization of (meth) acrylic acid or of the (meth) acrylic acid ester in the decomposition product by oxygen, but polymerization can also be accelerated and therefore there may be a case in which the above decomposition reaction cannot continue continuously for a long time.

e. Further, a gas containing acrylic acid obtained by catalytic vapor phase oxidation with molecular oxygen of propylene and / or acrolein typically contains maleic acid as one of the by-products in an amount of about 0.2-1.6 wt.% based on acrylic acid. Maleic acid is a dicarboxylic acid represented by HOCO-CH = CH-CO ₂ H, and it is in equilibrium with a carboxylic acid anhydride having one water molecule dehydrated in its molecule in its solution. Further, unless otherwise indicated, maleic acid and maleic anhydride will be referred to together as maleic acid. When a gas containing acrylic acid is collected with a solvent in the form of a solution containing acrylic acid, maleic acid will be collected simultaneously. The boiling point of maleic acid is high compared to the boiling point of acrylic acid, and in the purification step by distillation, maleic acid will be concentrated in the residues.

When two molecules of acrylic acid are exposed to Michael addition, an acrylic acid dimer will form. There are no ways to prevent the formation of such an acrylic acid dimer in an acrylic acid solution, and the rate of this formation increases as the temperature becomes high. Further, a higher oligomer, such as an acrylic acid trimer, will be successively formed by acrylic acid and an acrylic acid dimer. In the acrylic acid purification step, a dimer (or oligomer) of acrylic acid will be formed mainly in a distillation column where heating is carried out, in particular in the lower region where the temperature is high and the retention time is long.

To improve the acrylic acid regeneration rate, acrylic acid is usually regenerated from the formed acrylic acid oligomer in the purification step.

As a method of regenerating from an oligomer of acrylic acid, for example, a method can be used in which thermal decomposition is carried out under reduced pressure in the presence or absence of a catalyst, and acrylic acid is regenerated in the form of a distilled gas or distilled liquid, as described in JP-B -45-19281. In such a case, the distilled gas and the distilled liquid of acrylic acid contain a large number of high boiling compounds, other than regenerated acrylic acid, such as maleic acid. In the case where the operation temperature is increased to increase the rate of acrylic acid regeneration, the concentration of maleic acid in the regenerated acrylic acid will also increase.

As a method of reducing such maleic acid in the method described in JP-A-11-12222, crude acrylic acid containing 3-10 wt.% Maleic acid and other acrylic acid oligomers is introduced into an acrylic acid recovery column and acrylic the acid is distilled from the upper part, and the liquid of the lower part is thermally decomposed and such a liquid of the lower part is recycled to the regeneration column, the amount of maleic acid can be reduced to a level of 0-3 wt.%.

In this method for the thermal decomposition of an acrylic acid oligomer, maleic acid is removed as an impurity in the form of precipitates from a thermal decomposition reaction device or a distillation device. At this time, if the amount of maleic acid contained in the recoverable acrylic acid is large, the amount of maleic acid recycled in this system will increase, whereby the equipment and heat load will increase at this stage of purification. The easiest way to prevent this is to reduce the amount of acrylic acid oligomer recovered by thermal decomposition, but the acrylic acid recovery rate at this stage of purification will thereby decrease and economic efficiency will deteriorate.

To achieve an improvement in the degree of extraction of acrylic acid and to reduce the recycle amount of maleic acid, there is a method for adding a distillation column, as described in the method disclosed in JP-A-11-1222. However, since acrylic acid is an easily polymerizable compound, distillation under reduced pressure is usually carried out to prevent polymerization by lowering the working temperature, but since the boiling point of maleic acid is higher than the melting point of acrylic acid, even if the working pressure decreases, the working temperature does not increase can be fixed. This will not only facilitate clogging of the distillation device as a result of polymerization, but tends to accelerate the formation of an acrylic acid oligomer in acrylic acid recoverable by thermal decomposition. Further, to increase the degree of rarefaction of the distillation plant, the diameter of the distillation column is increased, as a result of which the load will also increase during design and operation.

Further, concentrated maleic acid is discharged from the bottom of the column. However, maleic acid is a solid at room temperature and, therefore, there is a problem in that the viscosity of this liquid tends to increase from the bottom to the bottom of the distillation column and there will likely be a deterioration in separation ability due to contamination or polymer deposition or clogging. .

Such problems are observed when maleic acid, an impurity, is separated in the form of a high-boiling substance by distillation.

In order not to include the stage of maleic acid concentration by distillation and to improve the efficiency of acrylic acid extraction by thermal decomposition, it is necessary to carry out without imparting high heating, as is the case with distillation, or (1) decrease the concentration of maleic acid in the solution of acrylic acid supplied to the device for a thermal decomposition reaction, or (2) reducing maleic acid in an acrylic acid solution recovered from the thermal decomposition reaction device.

f. Further, first in an apparatus for producing acrylic acid or the like. it was common to carry out a pressure measurement by mounting the detecting portion of the high pressure side of a liquid level meter directly connected to the main body of the installation. However, using a generally accepted method for mounting a liquid level meter, a polymerization inhibitor that should be used to produce a readily polymerizable compound or formed polymer enters the detecting portion of the high pressure side of the liquid level meter and the solid should probably accumulate, resulting in erroneous operation of the level meter fluid commonly used to observe levels.

Thus, it is usually difficult to accurately measure continuously with a liquid level meter, making it difficult to continuously operate such an installation for a long period of time.

DESCRIPTION OF THE INVENTION

but. The aim of the present invention is to overcome the problems in the conventional decomposition reaction of the Michael addition product of acrylic acid or acrylic ester, so as to prevent deposits from remaining in the column of the decomposition reaction, to prevent the formation of polymer in the column of the decomposition reaction, and to prevent unexpected clogging of the discharge pipe so as to ensure stable way of operation.

b. Further, it is an object of the present invention to provide a method for decomposing a by-product during the production of (meth) acrylic acids, by which during the regeneration of a valuable substance by decomposition by means of a reactive distillation system, the formation of a Michael addition product is formed by-product during the production of (meth) acrylic acid ester of (meth) acrylic acid, adhesion, deposition or accumulation of such a solid is prevented, high extraction rate of (meth) acrylic acid, ether and (meth) acrylic acid and alcohol can be maintained continuously and continuous continuous operation can be carried out over a long period of time.

from. Further, an object of the present invention is to provide a method for eliminating maleic acid recycling in an acrylic acid purification system, comprising thermally decomposing and recovering an acrylic acid oligomer in a distillation purification step containing an acrylic acid liquid, and easily performing purification without the problem of polymerization of acrylic acid or clogging of equipment on this purification stages.

d. Further, an object of the present invention is to provide a method for mounting a liquid level meter in an apparatus for producing an easily polymerizable compound by which an accurate measurement can be continuously performed by preventing the formation and accumulation of solids from the liquid to be measured in the detecting portion of the high pressure side of the liquid level meter.

The authors of this invention have conducted various studies to achieve the above objectives and as a result have completed the invention having the following main aspects.

(1) A method for producing (meth) acrylic acids, which comprises decomposing in a decomposition reactor a high boiling point mixture formed as a by-product during the production of (meth) acrylic acids, characterized in that this high boiling point mixture contains a Michael addition product containing water, alcohol or (meth) acrylic acid attached to a (meth) acryloyl group; while by forcing the liquid to flow peripherally to the liquid reaction residue in the decomposition reactor, this liquid reaction residue is unloaded and (meth) acrylic acid or (meth) acrylic acid ester is recovered.

(2) The method according to paragraph (1), characterized in that the fluid flow in the peripheral direction is supplied by the mixing blades installed in the decomposition reactor.

(3) The method according to paragraph (1), characterized in that the fluid flow in the peripheral direction is provided by the fluid supplied from the outside of the decomposition reactor.

(4) The method according to paragraph (3), characterized in that the liquid supplied from the outside of the decomposition reactor is a high boiling material supplied as the starting material, or the liquid returned by the liquid of the reaction residue discharged from the decomposition reactor.

(5) The method according to any one of paragraphs (1) to (4), characterized in that the liquid reaction residue is periodically discharged from the decomposition reactor.

(6) The method according to any one of paragraphs (1) to (5), characterized in that during the distillation of the valuable substance and the thermal decomposition of the high-boiling mixture, the distillation is carried out using a distillation column, which is equipped with disk-and-type plates inside toroids.

(7) The method according to any one of paragraphs (1) to (6), characterized in that oxygen-containing gas is added to the distillate from the decomposition reactor.

(8) The method according to any one of items (1) to (7), characterized in that from the liquid to be added to the thermal decomposition reactor, or from the liquid extracted from the thermal decomposition reactor, maleic acid contained in said liquid is precipitated and separated .

(9) The method according to any one of (1) to (8), characterized in that a liquid level meter is installed on the thermal decomposition reactor and a high pressure side detection line of the liquid level meter is connected to a liquid discharge line of the decomposition reactor.

The present invention has the following preferred options (a) to (f).

a1. A method for producing (meth) acrylic acids, which is a method for producing acrylic acid or (meth) acrylic acid (they are also called hereinafter in general terms also (meth) acrylic acid) or (meth) acrylic acid ester ((meth) acrylic acid and ether ( Hereinafter, meth) acrylic acid may also be generically referred to as (meth) acrylic acids) by means of a reaction step involving catalytic oxidation in the vapor phase of propylene, propane or isobutylene and then, if necessary, a reaction step including an esterification step, o characterized in that while the high boiling mixture (hereinafter referred to as high boiling material) containing the Michael addition product is decomposed in a decomposition reactor to recover (meth) acrylic acids, the liquid residue of this reaction is discharged by forcing the liquid to flow in a peripheral direction to this liquid reaction residue in the decomposition reactor.

a2. The method according to paragraph A1, wherein the fluid flow in the peripheral direction is imparted by mixing blades mounted in the decomposition reactor.

a3. The method according to paragraphs A1 or A2, where the mixing blades are anchor blades, multi-stage bladed blades, multi-stage inclined bladed blades or trellised blades.

a4. The method according to a1 or a2, where the design of the mixing blades is such that on a rotational shaft mounted vertically in the central part of the reactor, the flow type radial blades are attached in two or more steps in the direction of the axis of rotation, so that the blades adjacent in the direction of the axis of rotation, arranged with respect to the rotation axis so that their phases are offset from each other by not more than ⁹⁰ and the lowermost portion of one of the upper-stage blades adjacent in the rotation axis direction, location with ene below the highest part of the lower-stage blade.

a5. The method according to A1, wherein a fluid flow in the peripheral direction is imparted by fluid supplied from the outside of the decomposition reactor.

a6. The method according to a1 or a5, wherein the liquid supplied from the outside of the decomposition reactor is a high boiling material supplied as a starting material, or the liquid returned from the liquid reaction residue discharged from the decomposition reactor.

b1. A method for producing (meth) acrylic acid, which is a method for producing acrylic acid, (meth) acrylic acid or (meth) acrylic acid ester by means of a reaction step comprising catalytic vapor phase oxidation of propylene, propane or isobutylene and then, if necessary, a reaction step comprising an esterification step, characterized in that while the high boiling mixture (hereinafter referred to as high boiling material) containing the Michael addition product is decomposed in the decomposition reactor for extraction of (meth) acrylic acids, the liquid reaction residue is periodically discharged from the decomposition reactor.

b2. The method according to paragraph b1, where the unloading stop time is from 5 seconds to 5 minutes and the unloading time is from 2 seconds to 5 minutes.

b3. The method according to paragraphs b1 or b2, wherein the liquid high boiling material is continuously fed to the decomposition reactor and the (meth) acrylic acids are continuously discharged from the vapor phase.

c1. In a process that involves introducing a by-product formed during the production of (meth) acrylic acid and / or a by-product formed during the production of an (meth) acrylic acid ester into a reactor equipped with a distillation column to thermally decompose this by-product and simultaneously distillation to extract a valuable substance, the method of decomposition of a by-product formed during the production of (meth) acrylic acids, characterized in that as the specified distillation to The columns use a distillation column, which is provided internally with disk-and-toroid plates.

c2. The method of claim C1, wherein the by-product formed during the production of (meth) acrylic acid is the liquid of the bottom of the fractionation column of the final stage of the production of (meth) acrylic acid, and the by-product formed during the preparation of the (meth) acrylic acid ester is the liquid of the lower part of the fractionation column to separate the high boiling fraction of the purification step of the (meth) acrylic acid ester.

c3. The method of c1 or c2, wherein the by-product formed during the preparation of (meth) acrylic acid and / or the by-product formed during the preparation of the (meth) acrylic acid ester comprises a Michael addition product containing water, alcohol or (meth ) acrylic acid attached to a (meth) acryloyl group.

c4. A method according to any one of c1-c3, where the thermal decomposition reaction temperature is 120-280 C and ^the thermal decomposition reaction time is 0.5 to 50 hours.

d1. A method for decomposing a by-product formed during the production of (meth) acrylic acids, comprising decomposing in a decomposition reactor a by-product formed during the preparation of (meth) acrylic acid and / or a by-product formed during the preparation of the (meth) acrylic acid ester, and distillation of the decomposed product from the decomposition reactor, characterized in that oxygen-containing gas is added to the distillate from the decomposition reactor.

d2. The method according to d1, wherein the by-product formed during the production of (meth) acrylic acid is the liquid of the bottom of the fractionation column of the final stage of the production of (meth) acrylic acid, and the by-product formed during the preparation of the (meth) acrylic acid ester is a liquid the bottom of the fractionation column of the final stage of the production of (meth) acrylic acid ester or column precipitates to separate the (meth) acrylic acid.

d3. The method of d1 or d2, wherein the by-product to be decomposed comprises the Michael addition product.

d4. The method according to any one of d1-d3, wherein the oxygen-containing gas is air or oxygen diluted with an inert gas.

d5. The method according to any one of d1 to d4, wherein the oxygen-containing gas is added to the discharge line for the distillate from the decomposition reactor or to the top of the decomposition reactor.

e1. In a method for producing acrylic acid, which comprises reacting with a solvent an acrylic acid-containing gas obtained by catalytic oxidation of propane or propylene, to collect acrylic acid in the form of an acrylic acid-containing solution and purify acrylic acid by distillation of the obtained acrylic acid-containing solution, the method for recovering acrylic acid, characterized the fact that the residues obtained from the bottom of the fractionation column for acrylic acid, or the liquid obtained is heated by the concentration and concentration of such residues, it is fed into the thermal decomposition reactor to decompose the acrylic acid oligomer in this liquid, and the obtained acrylic acid is recovered in a purification step in which from the liquid supplied to the thermal decomposition reactor or from the liquid extracted from the thermal reactor decomposition, precipitated and separated maleic acid contained in this liquid.

e2. The method according to e1, where the composition of the liquid supplied to the thermal decomposition reactor, or the liquid extracted from the thermal decomposition reactor, is adjusted to obtain a solution containing at least 70 wt.% Acrylic acid, 1.6-28 wt.% Maleic acid and / or maleic anhydride and water having a molar ratio:

Water

-------------------------- (molar ratio) less than or equal to 1.0

maleic acid +

maleic anhydride x 2

and maleic acid is precipitated at 20-70 ^{° C} in the range of 0.5-5 hours, followed by filtration and separation.

e3. The method according to e1 or e2, where during the operation for the separation of maleic acid add an aliphatic or aromatic hydrocarbon in a 0.5-4-fold volume ratio.

e4. The method according to e3, wherein the added hydrocarbon is a solvent that must be used to collect the gas containing acrylic acid, or an azeotropic agent that must be used for the dehydration distillation purification of acrylic acid.

f1. A method of establishing a liquid level meter in the case where a liquid level meter is installed in a place where liquid containing an easily polymerizable compound is accumulated, in an installation for producing an easily polymerizable compound, characterized in that the detection line of the high pressure side of this liquid level meter is connected to a discharge line for accumulated liquid .

f2. The method according to f1, where the angle of attachment α between the detection line of the high pressure side and the liquid discharge line is 5-90 ^about .

f3. The method according to f1, where the aspect ratio D ₂ / D ₁ is 1-20, where D ₁ is the diameter of the pipeline of the detection line of the high pressure side, and D ₂ is the diameter of the pipeline of the liquid discharge line.

f4. The method according to f1, wherein the liquid discharge line is connected to a distillation column, a reflux recovery tank of a distillation column, a decomposition reaction column, a film evaporator, a condensed gas liquid tank of the top of the column, a vertical storage tank, a horizontal storage tank or a tank.

f5. The method according to any one of f1 to f4, wherein the high pressure side detection line and / or the low pressure side detection line of the liquid level meter is heated or heated.

f6. The method according to any one of f1 to f5, wherein the high pressure side detection line and / or the low pressure side detection line of the liquid level meter are connected to the gas and / or liquid inlet.

f7. The method according to any one of f1-f6, wherein the readily polymerizable compound is (meth) acrylic acid or its ester and the liquid to be measured by a liquid level meter comprises at least one compound selected from a dimer of acrylic acid, β- (meth) acryloxypropionic acid esters , β-alkoxypropionic acid esters, β-hydroxypropionic acid and β-hydroxypropionic acid esters.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows an example of a production line through a thermal decomposition reaction (a spiral flow is formed by the liquid returned to the decomposition reactor).

Figure 2 shows an example of a production line by a thermal decomposition reaction (a spiral flow is formed by a liquid of a feed material fed to a decomposition reactor).

Figure 3 shows an example of a production line through a thermal decomposition reaction (a spiral flow is formed by mixing blades).

4 is a view showing a horizontal cross-sectional view of a decomposition reactor A and a positional relationship for connecting to these lines to form a spiral flow.

5 is a view schematically showing a solid accumulating in the lower part of the decomposition reactor A (cross-sectional view in the longitudinal direction of the column).

6 shows an example of a production line by a thermal decomposition reaction.

7 (a) is a schematic cross-sectional view showing a distillation column equipped with flat plate disks and toroids suitable for carrying out the decomposition method of a by-product formed during the production of (meth) acrylic acids in accordance with this invention.

Fig. 7 (b) is an enlarged perspective view of the main parts of Fig. 7 (a).

Fig. 8 (a) is a schematic cross-sectional view showing a distillation column equipped with beveled disk disks and toroids suitable for carrying out the decomposition process of a by-product formed during the production of (meth) acrylic acids in accordance with this invention.

Fig. 8 (b) is an enlarged perspective view of the main parts of Fig. 8 (a).

Fig.9 is an example of a scheme for producing acrylic acid and an ester of acrylic acid.

Figure 10 is another example of a scheme for producing an ester of acrylic acid.

11 is a decomposition diagram of a high boiling liquid.

12 is a view showing an entire installation where the method of installing a liquid level meter of the present invention is applied to a decomposition reaction column (high boiling material) and an upper reservoir of gas-cooled liquid to produce acrylic acid.

FIG. 13 is a partial enlarged view showing a liquid level meter mounted on a decomposition reaction column (high boiling material) of FIG. 11.

Fig. 14 is a partial enlarged view showing a liquid level meter mounted on a decomposition reaction column (high boiling material) of Fig. 11.

Reference character explanation

A: decomposition reactor

B: bottom pump

C: Heat exchanger for heating

D: Agitator

E: Deposition

F: Periodic discharge control valve

1: High-boiling material feed line

2: bottom liquid discharge line

2-1, 2-2: Residual Liquid Discharge Lines

3: Supply line for heat exchanger for heating

3-2: Return line for heating

4: Reaction residue discharge line

5: Return line forming a spiral flow

6: The line of regeneration (extraction) of a valuable substance

7: coolant supply line

8: coolant discharge line

31, 33: Distillation columns

31D, 33D: Residue discharge holes

32A, 34A: Disc Plates

32B, 34B: Toroidal plates

35: Switchgear

41: Column decomposition reaction

42, 46: Pumps

43: Heat exchanger for heating

44a: Pipeline top

44, 47: Heat exchangers

45: Chilled fluid reservoir

6A: Column of decomposition reaction (high boiling material)

6E: Tank with gas-cooled liquid at the top of the column

H ₁ , H ₂ : liquid level meters

62: bottom discharge line

62a: Short bottom discharge line

62b: bottom discharge pipe

65: bottom liquid discharge line

65a: Short bottom discharge line

65b: bottom discharge line

11, 13: High pressure side detection line

11a, 13a: Short high pressure side detection conduits

11b, 13b: High pressure side detection pipelines

12, 14: Low pressure side detection line

12a, 14a: Short low pressure side detection pipelines

12b, 14b: Low pressure side detection pipelines

α: Angle of connection between the high pressure side detection line and the liquid discharge line

BEST MODE FOR CARRYING OUT THE INVENTION

Option a

This option was achieved on the basis of the discovery of the fact that in the decomposition reaction of the product of addition of Michael acrylic acid or acrylic acid ester is very effective is the implementation of the flow of liquid in the lower part of the column in the peripheral direction to prevent the accumulation of solids in the lower part of the column for the decomposition reaction and thereby eliminating polymerization due to such accumulation.

1. (Meth) acrylic acid and (meth) acrylic acid ester

The present invention can be applied to treat the decomposition of a high boiling mixture (high boiling material) obtained during the preparation of (meth) acrylic acid or (meth) acrylic acid ester. For example, it can be applied to a method for producing (meth) acrylic acid by catalytic oxidation in the vapor phase of propylene or isobutylene in the presence of a mixed oxide of the Mo-Bi type as a catalyst to form acrolein or methacrolein followed by catalytic oxidation in the vapor phase in the presence of a mixed oxide of the type Mo-V as a catalyst. In this case, a preliminary reaction with the formation of acrolein or methacrolein by oxidation of propylene or the like. and a later reaction to form mainly (meth) acrylic acid by oxidation of acrolein or methacrolein can be carried out in separate reactors, respectively, or such reactions can be carried out in a single reactor filled with both a catalyst for the preliminary reaction and a catalyst for the later reaction. Further, the invention is also applicable to a method for producing acrylic acid by vapor-phase oxidation of propane using a mixed oxide of the Mo-V-Te type as a catalyst or a complex oxide of the Mo-V-Sb type as a catalyst. Further, it is also applicable to a method for producing an acrylic acid ester by reacting an alcohol with (meth) acrylic acid.

The high boiling mixture (high boiling material) obtained after separation of the desired product in these methods is an object to be decomposed using the present invention. As the acrylic acid ester, a C _1-8 alkyl or cycloalkyl ether may be mentioned. For example, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate or methoxyethyl acrylate may be mentioned. With respect to the (meth) acrylic acid ester, esters similar to the aforementioned esters may also be mentioned.

Michael Accession Product

The Michael addition product contained in the high boiling material as subject to decomposition is an object of the present invention is a product having an active hydrogen compound such as water, alcohol or (meth) acrylic acid, attached as an ion to the carbon-carbon (meth) double bond acrylic acid or ester of (meth) acrylic acid. Specifically, the Michael addition product in the case of producing acrylic acid may be, for example, an acrylic acid dimer (hereinafter referred to as a dimer), an acrylic acid trimer (hereinafter referred to as a trimer), acrylic acid tetramer (hereinafter referred to as tetramer) or β-osipropionic acid, as shown below.

Dimer: H ₂ C = CH — C (= O) —O — CH ₂ —CH ₂ —C (= O) —OH

Trimer: H ₂ C = CH — C (= O) —O — CH ₂ —CH ₂ —C (= O) —CH ₂ —CH ₂ —C (= O) —OH

Tetramer: H ₂ C = CH — C (= O) —O — CH ₂ —CH ₂ —C (= O) —CH ₂ —CH ₂ —C (= O) —O — CH ₂ —CH ₂ —C ( = O) -OH

β-hydroxypropionic acid: HO-CH ₂ -CH ₂ -C (= O) -OH

On the other hand, the Michael addition product in the case of producing an acrylic acid ester can be, for example, the Michael addition product of acrylic acid to the aforementioned acrylic acid ester, in particular β-aryloxypropionic acid ester (dimer ether); the product of Michael addition of an alcohol, in particular an ester of this dimer, trimer or tetramer, β-hydroxypropionic acid, β-hydroxypropionic acid esters or β-hydroxypropionic acid esters.

Ether of β-acryloxypropionic acid: H ₂ C = CH — C (= O) —O — CH ₂ —CH ₂ —C (= O) —OR

Β-alkoxypropionic acid ester: RO-CH ₂ -CH ₂ -C (= O) -OR

The trimer ether: H ₂ C = CH — C (= O) —O — CH ₂ —CH ₂ —C (= O) —O — CH ₂ —CH ₂ —C (= O) —OR

Ether of β-hydroxypropionic acid: HO-CH ₂ -CH ₂ -C (= O) -OR

β-hydroxypropionic acid: HO-CH ₂ -CH ₂ -C (= O) -OH

As for methacrylic acid and methacrylic acid ester, essentially the same as described above is also used. The only difference is that as a result of replacing the hydrogen in position α with a methyl group, propionic acid (ether) becomes isobutyric acid (ether).

The high boiling material to be fed to the decomposition reactor is a high boiling mixture containing the Michael addition product described above. The content of the Michael addition product may vary significantly depending on the preparation method. However, it is common to use a high boiling material containing a Michael addition product in an amount of 1-90 wt.%, Preferably 2-70 wt.%. This high-boiling material also contains a compound formed side-by-side in the preparation of (meth) acrylic acids, or a substance to be used as an auxiliary agent in this method. Specifically, for example, (meth) acrylic acid, esters of (meth) acrylic acid, maleic acid, maleic esters, furfural, benzaldehyde, polymers, oligomers, alcohols used as materials for producing esters, or polymerization inhibitors, in particular copper acrylate, copper dithiocarbamate, phenol compound (derivative) or phenothiazine compound (derivative).

Copper dithiocarbamate may be, for example dialkyl copper, such as dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate copper or dibutyl copper, cyclic alkilenditiokarbamatom copper, such as etilenditiokarbamat copper tetrametilenditiokarbamat copper pentamethylenedithiocarbamate copper or geksametilenditiokarbamat copper, or cyclic oksidialkilenditiokarbamatom copper, such as oksidietilenditiokarbamat copper.

The phenol compound may be hydroquinone, methoxyhydroquinone (methoxyquinone), pyrogallol, resorcinol, phenol or cresol. The phenothiazine compound may be, for example, phenothiazine, bis (α-methylbenzyl) phenothiazine, 3,7-doctylphenothiazine or bis (α-dimethylbenzyl) phenothiazine. In some cases, substances other than those mentioned above may be contained depending on the process without adversely affecting the invention.

The method of obtaining (meth) acrylic acids

The above high boiling material can, for example, be obtained by a purification step, such as extraction or distillation, after contacting the gas (meth) acrylic acid obtained by catalytic oxidation in the vapor phase of propylene or acrolein with water or an organic solvent to collect (meth) acrylic acid in the form of a solution. A method for producing an (meth) acrylic acid ester includes, for example, a step for the esterification reaction of the interaction of (meth) acrylic acid with an alcohol in the presence of an organic acid or cation exchange resin or the like, as a catalyst, and a purification step, carrying out extraction, evaporation or distillation as a single operation for concentrating a solution of the crude (meth) acrylic acid ester obtained by this reaction. Each such operation is suitably selected depending on the ratio of (meth) acrylic acid and alcohol of the starting material in this esterification reaction, the type of catalyst used for the esterification reaction, or the physical properties of the starting materials, reaction by-products, etc.

The reaction scheme of the thermal decomposition of high-boiling material

The description will use links to graphic illustrations. Figure 1 is an example of a production line (production line) using the thermal decomposition reaction of the present invention. The high boiling material is fed via line 1 to the decomposition reactor A. The feed to the decomposition reactor A may be continuous or batchwise (semi-continuous), but continuous feed is preferred. The valuable substance formed in the decomposition reactor, and part of the materials that make up the high-boiling material, will be continuously discharged in the gaseous state along the extraction line 6 and will be returned to this in-line process as is, in the gaseous state, or upon cooling in the liquid state. In the case where decomposition reactor A is a column type reactor, part of the cooled liquid can be returned as reflux liquid to the upper part of the decomposition reactor.

Residual liquid will be discharged through line 2 of the discharge of residual liquid to the pump. At the bottom, part of it will be fed to heat exchanger C for heating using line 3 and returned to decomposition reactor A. The remainder will be discharged from this system through line 4. The ratio between the amount of returned liquid and the amount of discharge can be suitably set depending on various factors, such as thermal equilibrium in the heat exchanger for heating and retention time in the decomposition reactor. A peripheral flow (hereinafter sometimes referred to as a spiral flow) in the decomposition reactor of the present invention is formed by the liquid return line 5 in FIG. 1. Line 5 is located in a tangential direction relative to the main body of the decomposition reactor, and a spiral flow will be formed in the reactor by the flow of fluid supplied from line 5. The amount of return fluid of line 5 is usually selected in a 0.2-5-fold range by weight based on the amount of starting material supplied from line 1. If the amount of liquid returned is less than the above range, an adequate spiral flow is unlikely to form. The liquid returned for heating, flowing through line 3-2, is not associated with the formation of a spiral flow and its flow rate is determined depending, for example, on thermal equilibrium.

FIG. 2 is an example in which the peripheral flow is produced by the source material liquid supplied to the decomposition reactor and this fluid is conducted by line 1. Line 1 is located in the tangential direction relative to the main body of the decomposition reactor, and a spiral flow will be formed in the reactor by the liquid supplied from line 1. In this case, line 1 should be controlled so that the surface of this liquid is lower than the surface of the reaction liquid held in the decomposition reactor .

Figure 3 is an example of a device for forming a spiral flow in a decomposition reactor using stirring blades.

High-boiling material is fed through line 1 to decomposition reactor A. The valuable substance and some of the materials that make up the high-boiling material decomposed in decomposition reactor A will be discharged along extraction line 6 and will be returned to the in-line process as is, in a gaseous state, or when they are cooled, in a liquid state. In the case where decomposition reactor A is a column type reactor, part of the cooled liquid can be returned as reflux liquid to the upper part of the decomposition reactor. Residual liquid will be discharged from line 4 from this system. The coolant supply line 7 and the coolant discharge line 8 are exemplary and, depending on the type of coolant, the positions of the supply line and the discharge line can be changed.

The peripheral flow (spiral flow) in this decomposition reactor of the present invention is performed by the residual liquid mixing means D in FIG. 3. The stirring means D comprises stirring blades (blades), a stirring bar and a stirring motor, whereby the internal liquid of the decomposition reactor is capable of forming a fluid flow in the peripheral direction. The rotational speed of the mixing blades is usually chosen appropriately depending on the shape or diameter of the blades so that the speed of the leading edge of the blades will usually be 0.2-5 m / s. Residual fluid forming a spiral flow will be discharged along lines 2-1 or 2-2 of the residual fluid discharge. Residual liquid discharge line 2-1 is an example in which it is located in the tangential direction (tangentially) of the decomposition reactor main body, and line 2-2 is an example in which it is located in the central part of the decomposition reactor. In the case of a discharge line 2-1, a good spiral flow can be maintained along with the mixing action of the blades.

FIG. 4 is a view showing a cross section of decomposition reactor A. Line 5 (return line 5 forming a spiral flow) in FIG. 1 or line 1 (supply line 1 of high boiling material) in FIG. 2 are located in a tangential direction relative to the main reactor vessel decomposition, whereby a peripheral flow (spiral flow) can be formed in the decomposition reactor. Further, the residual liquid discharge line 2-1 in FIG. 3 is located in a tangential direction relative to the main body of the decomposition reactor, whereby a good spiral flow can be maintained together with the mixing action of the blades.

FIG. 5 is a view (longitudinal cross-sectional view of a column) schematically showing solid matter accumulated in the lower part of decomposition reactor A. If the left and right accumulated products are connected, the discharge openings will be plugged, thereby removing liquid from the lower part will be impossible and the pump at the bottom may be subjected to cavitation.

The decomposition reaction of high-boiling material

The Michael addition product contained in the high boiling material can be decomposed to a monomer containing (meth) acrylic acid as the main component. When a (meth) acrylic acid ester is contained in a high boiling material, it can be hydrolyzed to (meth) acrylic acid and alcohol, or it can be recovered as is, in the form of ether, without decomposition, depending on the conditions.

The temperature of the decomposition reaction was adjusted to 110-250 ^C, preferably 120-230 ^C. In Figure 1 the high boiling material is heated in a heat exchanger for heating and controlling the temperature. In another case than this case, in which the heater is installed outside of decomposition reactor A, as shown in FIG. 1, an internal steam coil type heater installed in the decomposition reactor or a jacket type heater installed around the decomposition reactor is suitable and may any type of heating device may also be used.

The retention time for the decomposition reaction varies depending on the presence or absence of catalyst and the temperature of the decomposition reaction. In the case where the temperature of the decomposition reaction is low, this time is relatively long, such as 10-50 hours, and in the case where the temperature of the decomposition reaction is high, it is 30 minutes to 10 hours. The reaction pressure may be either reduced pressure conditions or atmospheric pressure conditions.

The decomposition reaction can be carried out using only high-boiling material as a reaction object. However, for the purpose of accelerating the decomposition reaction, it can be carried out in the presence of an acid catalyst or in the presence of water. The catalyst used for the decomposition reaction is mainly Lewis acid or acid, such as sulfuric acid, phosphoric acid, methanesulfonic acid, para-toluenesulfonic acid or aluminum chloride. The catalyst and / or water may be premixed with high boiling material or may be fed to decomposition reactor A separately from the high boiling material. When a polymer, a polymerization inhibitor, a catalyst, etc. are contained in a high-boiling material, they usually remain and are concentrated in the decomposition residue without degradation.

Decomposition reactor design

The design of decomposition reactor A may be any structure, such as a column type structure or a tank type structure. In the case of a column type reactor, plates or filling materials (packing) that are typically used in a distillation column can be installed as the contents, whereby not only a decomposition reaction can be carried out, but also a distillation operation can be carried out, which is preferred. As the filling material, such filling material may be used, for example, SULZER PACKING manufactured by SULZER BROTHERS LTD., SUMITOMO SULZER PACKING or MELLAPACK manufactured by SUMITOMO HEAVY INDUSTRIES, LTD., GEMPAK manufactured by GLITSCH, MONTZ PACKZ, GOOD MON PACKING manufactured by TOKYO TOKUSHU KANAAMI KK, HONEYCOMB PACKING manufactured by NGK INSULATORS, LTD. or IMPULSE PACKING manufactured by NAGAOKA INTERNATIONAL CORPORATION.

As an unusual filler, for example, INTALOX SADDLE manufactured by NORTON, TELLERETTE manufactured by Nittetu Chemical Engineering Ltd., PALL RING manufactured by BASF, CASCADE MINI-RING manufactured by MASS TRANSFER or FLEXIRING manufactured by JGC CORPORATION may be mentioned. Any of these excipients may be used, or several may be used in combination.

The plates may be, for example, cap plates, perforated plates, bubble trays, ultra-flow plates or maximum flow plates having a drain pipe, or double plates or disk type and toroid type plates without a drain pipe. These plates or filling materials may be used in combination or such contents may not be present in the decomposition reactor.

In the present invention, the peripheral fluid flow (spiral flow) is a forced flow, and this can be accomplished by supplying high boiling material or liquid returned from the sludge (bottoms) (sludge liquid) from the tangential direction of the reactor. In the case where the feed inlet from the tangential direction is absent, the spiral flow is formed by the mixing blades provided in this reactor, both of which can be used in combination.

In the case of a stirred tank type reactor, a sparging can be used if required. The mixing blades can be any type of blades as long as they are capable of generating a peripheral flow. Specifically, anchor blades (at least one step), multi-stage blade vanes, multi-stage oblique blade blades, trellised blades, MAXLEND blades (trade name manufactured by SUMITOMO HEAVY INDUSTRIES, LTD.), FULLZONE VANES (trade name manufactured by SHINKO PANTEC CO., LTD) etc. and at least one type may be used in at least one step. FULLZONE blades are such that the radial flow-type blades are attached in two steps in the direction of the axis of rotation so that the blades adjacent to the direction of the axis of rotation are located relative to the direction of the axis of rotation so that their phases are offset from each other by no more than 90 ^° , and the lower part of one of the blades of the upper stage, adjacent in the direction of the axis of rotation, is located below the highest part of the blade of the lower stage (see JP-A-7-33804). Particularly preferred as mixing blades are anchor blades, trellised blades or FULLZONE blades.

As for the bubble trays (hereinafter referred to as flaps) mounted together with the mixing blades, in this invention there are no restrictions on them. Any type may be used or spargers may not be installed. Specifically, for example, a rod type, a plate type, a comb type can be mentioned, and at least one type and at least one connection can be installed. It is particularly preferred to establish one type of rod or one type of plate.

Unloading the remainder of the decomposition reactor

The residue of decomposition can be discharged from the decomposition reactor in a suitable manner. The discharge position of the lower part of the decomposition reactor can be located anywhere while it is in the part of the lower end of the column. It is preferably within 1/2 the diameter of the column from the lowest part of this lower part of the reactor. If it is located above the end portion, a solid will accumulate in this end portion. This residue is stored, for example, in a tank and then recycled to a combustion treatment or to a production process. Acrylic acid, methacrylic acid, alcohol, etc., on the other hand. as Michael’s decomposition products, Michael’s addition products or ether will be continuously discharged from the upper part (top of the column) of the decomposition reactor. They are diverted to the treatment system or recycled to a suitable position in this in-line process.

Option b

This option was achieved on the basis of the discovery of the fact that the decomposition reaction of the product of addition of Michael (meth) acrylic acids can be carried out without clogging for a long time by means of a pulse discharge, i.e. periodic discharge of liquid from the lower part instead of continuous discharge from the lower part of the reactor. The reason why clogging can be effectively prevented has not been fully elucidated. However, based on experimental facts, the authors of this invention believe that clogging in a pipeline with a constant flow will be disrupted by the fluid flow through a periodic flow and, due to the disturbing action of such a fluid flow, clogging can be extremely effectively suppressed, despite the fact that the fluid flow will temporarily stop.

The terms “(meth) acrylic acid and (meth) acrylic ester”, “Michael addition product” and “method for the preparation of (meth) acrylic acids” have the same meanings as in case of variant a.

Flow line diagram using the thermal decomposition reaction of high boiling material

6 is an example of a flow line using the thermal decomposition reaction of the present invention, which is the same as in case of option a, except that C is a heat exchanger for heating, F is a periodic discharge control valve, and 3 is a feed line into a heat exchanger for heating.

High boiling material is fed from line 1 to decomposition reactor A. The feed to the decomposition reactor A may be continuous or batchwise (semi-continuous), but continuous feed is preferred. The valuable substance and part of the materials constituting the high-boiling material formed in the decomposition reactor will be continuously discharged in the gaseous state from the extraction line 6 and will be returned to this in-line process as is, in the gaseous state, or upon cooling in the liquid state. In the case where decomposition reactor A is a column type reactor, a portion of the cooled liquid may be returned as reflux liquid to the top of the column for the decomposition reaction. The liquid of the lower part is discharged from line 2 and through pump B and part of it is supplied to heat exchanger C for heating and returned to decomposition reactor A. The remainder will be discharged from this system from line 4 through the periodic discharge control valve D as one of the advantages of this invention. Reference numeral 5 denotes a pipeline for transporting to a storage tank.

The terms "decomposition reaction of high-boiling material" and "design of the decomposition reactor" are the same as in the case of option a.

Periodic Unloading

In option b, the most significant feature is that the decomposition residue is periodically discharged from the decomposition reactor. This periodic discharge is carried out by the periodic discharge control valve D. The closed state of valve D is usually 5 seconds to 5 minutes, preferably 10 seconds to 2 minutes, and the open time of valve D is usually 2 seconds to 5 minutes, preferably 3 seconds to 2 minutes. The proportion of the open state of the control valve D (percentage of open state time / (open state time + closed state time)) is preferably in the range of 2-50%, more preferably 5-30%. If the closed state time is shorter and the open state time is longer than the above range, the clogging suppression effect may be insufficient due to the inertia of the decomposition residue stream. If the time of the closed state is long and the time of the open state is short, then clogging of the pipeline is likely to occur due to the influence of the static state of this liquid in the pipeline, which is undesirable. With continuous unloading (degree of open state: 100%), clogging of the pipeline will take place, as is also evident from the comparative example below.

Acrylic acid, methacrylic acid, alcohol, etc., on the other hand. as Michael’s decomposition products, Michael’s addition products or ether will be continuously discharged from the upper part (top of the column) of the decomposition reactor. They are diverted to the purification system or recycled to a suitable position in the production method.

Option c

In embodiment c, disk and toroidal plates are used as trays for the distillation column, whereby the problems of adhesion, deposition and accumulation of solids can be solved. Namely, the disk and toroid plates are such that the disk plates and toroid plates are alternately mounted at a suitable interval and, as shown in FIGS. 7 and 8, this structure is very simple and the opening is extremely large, whereby problems can be solved. adhesion, deposition and accumulation of solids.

Thus, using a distillation column equipped with plates such as disks and toroids, the decomposition of a by-product and the extraction of a valuable substance during the production of (meth) acrylic acids can be carried out continuously. Plates such as discs and toroids have a design that is extremely simple. Thus, in comparison with a distillation column using conventional plates or conventional filler material, there is an advantage in that the cost of producing this distillation column and the construction costs, such as the costs of plate installation, can be very low.

Now will be described in detail a practical version of the method of decomposition of a by-product formed during the production of (meth) acrylic acids in accordance with option c. First, with reference to FIGS. 7 and 8, a design of a distillation column equipped with plates such as disks and toroids suitable for embodiment c will be described. FIG. 7 (a) is a schematic cross-sectional view showing a distillation column provided with flat plate disks and toroids, and FIG. 7 (b) is an enlarged perspective view of the main parts of FIG. 7 (a). Further, FIG. 8 (a) is a schematic cross-sectional view showing a distillation column provided with disk and toroidal plates of the type of inclined plates, and FIG. 8 (b) is an enlarged perspective view of the main parts of FIG. 8 (a).

Disks and toroid-type plates are such that a plurality of disk-shaped and toroid-shaped plates are alternately arranged with a suitable distance between them in this distillation column, and in the distillation column 31 of FIG. 7, in this column are alternately arranged plates in the form disks 32A and toroid-shaped plates 32B of the flat-plate type, while in the distillation column 3 of FIG. 8, plates in the form of disks 34A and toroid-shaped plates 34B of the type of inclined plates are alternately arranged. In the distillation columns 31 and 33 of FIGS. 7 and 8, there are liquid inlets, and 31B and 33B are steam inlets. Further, 31C and 33C are steam vents, and 31D and 33D are bottom vents. 35 in FIG. 8 is a dispensing device (dispersing device).

The distance between the disk-shaped trays 32A and 34A and the toroid-shaped trays 32B and 34B (L in FIGS. 7 and 8) is preferably at least 250 mm in order to suppress fluid entrainment. If this distance L is excessively large, the height of the distillation column should be increased, and therefore it is preferably equal to a maximum of 500 mm.

The shape of the top view of the disk-shaped plate 32A or 34A is preferably an exact circle and its center is preferably located in the center of the distillation column. Likewise, the top view shape of the toroid-shaped plate 32B or 34B is preferably an exact annular circle, and the outer periphery of the toroid-shaped plate 32B or 34B is preferably in close contact with the inner wall of the distillation column 31 or 33.

The diameter of the disk-shaped disk 32A or 33A (D ₁ in FIGS. 7 and 8) and the diameter of the disk-shaped disk hole 32B or 34B (D ₂ in FIGS. 7 and 8) (hereinafter sometimes referred to as the “inner diameter”) are suitably selected in the range of 55-74% of the inner diameter of the distillation column 31 or 33. This size corresponds to the range of 30-55%, represented by the ratio of the open zone in the distillation column 31 or 33.

In order to avoid a short path (short conduit) of the downward flow of liquid in the distillation column 31 or 33, the diameter D _{1 of the} disk-shaped disk 32A or 34A is preferably slightly larger than the inner diameter D _{2 of the} disk-shaped disk 32B or 34B.

Regarding the shape of the plates, plates 32A and 32B of the type of flat plates are preferred, as shown in FIG. However, as shown in FIG. 8, using trays 34A and 34B slightly inclined with respect to the direction of flow of the liquid, the accumulation of solids can be further reduced. The angle of inclination in this case is not particularly limited, but is usually set in the range of 5-45 ^{° C} to a horizontal direction.

The method of establishing plates in the form of disks 32A and 34A and plates in the form of toroids 32B and 34B in the distillation column 31 or 33 can be in any way. It can be, for example, a way to fix them using holders protruding from the walls of the distillation columns, a method of welding them to the walls of the distillation column, or a method in which the corresponding disk-shaped plates and toroid-shaped plates are completely fixed with a vertical holder and mounted in the distillation column in the form of an integrated structure.

The number of disk-shaped plates of plates and toroid-shaped plates to be installed in the distillation column is not particularly limited, and it is selected appropriately so that the separation performance required for this particular method can be achieved. If the number of plates is too low, the distilled amount of the high boiling component tends to be large, and the amount of the recycle component will increase and the processing ability of this decomposition reactor will decrease, which is undesirable. On the other hand, if the number of plates increases more than necessary, the design cost will not only increase, but the concentration during distillation in the upper part of the polymerization inhibitor contained in the liquid of the starting material will also decrease, as a result of which, probably, an undesired distillate polymerization reaction takes place that is undesirable. Thus, the number of disk-shaped and toroid-shaped plates to be installed is preferably selected in the range of 5-20 plates (for this number of plates, one disk-shaped plate or one toroid-shaped plate will be considered one plate).

The (meth) acrylic acid in embodiment c is preferably a (meth) acrylic acid obtained by the catalytic oxidation reaction of the vapor phase of propane, propylene, acrolein, isobutylene, tert-butyl alcohol or the like, and the gaseous product of the oxidation reaction is rapidly cooled and quenched water. Then, water and (meth) acrylic acid are separated by azeotropic distillation using an azeotropic solvent, or by an extraction method using a solvent. Further, low boiling compounds, such as acetic acid, are separated and then a heavy component, such as the Michael addition product, is separated to give high purity (meth) acrylic acid. Alternatively, water and acetic acid can be separated simultaneously using an azeotropic agent. The above Michael addition product will be concentrated in a high boiling fraction, and preferably this fraction, i.e. the liquid of the bottom of the fractionation column is mixed with the by-product formed during the production of the (meth) acrylic acid ester, so that they are treated together.

The ester of (meth) acrylic acid in Example C is not particularly limited and may be, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-hexyl (meth) ) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, methoxyethyl (meth) acrylate, isononyl (meth) acrylate or isodecyl (meth) acrylate.

The Michael addition product is a by-product formed during the reaction or in the purification step in the process for producing (meth) acrylic acid and (meth) acrylic acid ester, and it is a substance containing (meth) acrylic acid, acetic acid, alcohol or water attached by the Michael reaction at the α-position or β-position of a compound having a group of (meth) acrylic acid present in this preparation process. A compound containing a group of (meth) acrylic acid present in this preparation process may be, for example, (meth) acrolein, (meth) acrylic acid, carboxylic acid having a (meth) acryloyl group such as β-aryloxypropionic acid or β -methacryloxyisobutyric acid (hereinafter, both may be generically referred to as a dimer) containing (meth) acrylic acid Michael attached to such (meth) acrylic acid, a trimer of (meth) acrylic acid (hereinafter referred to as a trimer) having (meth) acrylic acid joined by Micah to such a dimer, or a (meth) acrylic acid tetramer (hereinafter referred to as a tetramer) having (meth) acrylic acid attached by Michael to such a trimer, or a corresponding (meth) acrylic acid ester having such a carboxylic acid having (meth) an acryloyl group esterified with alcohol. Further, a compound containing (meth) acrylic acid Michael attached to (meth) acrolein may also be contained in a similar manner. Specifically, the Michael addition product of the present invention includes β-aryloxypropionic acid or β-methacryloxyisobutyric acid and their ester or aldehyde compound (β-aryloxypropanal or β-methacryloxyisobutanal), β-acoxypropionic acid or esters, β-hydroxypropionic acid or β-hydroxypropionic acid or β-hydroxypropionic acid or , and their esters or aldehydes, as well as their dimers, trimers, tetramers, etc. and their β-acryloxy compound, β-acetoxy compound, β-alkoxy compound and β-hydroxy compound. Further, there is a compound containing acetic acid attached by Michael to the (meth) acryloyl group, although it may be in very small amounts.

In embodiment c, as a method for producing an (meth) acrylic acid ester, a method for reacting an alcohol with (meth) acrylic acid for esterification or a method for producing a higher alcohol acrylic acid ester by reacting a lower alcohol acrylic acid ester with a higher alcohol for transesterification is usually used. Further, this production method can be either a periodic system or a continuous system. An acid catalyst is usually used as a catalyst for such esterification or transesterification.

The method for producing the (meth) acrylic acid ester preferably includes a reaction step and a purification step for washing, extraction, evaporation, distillation or the like. in a single operation for separation from the catalyst, concentration, purification, etc. the crude ester of (meth) acrylic acid obtained in this reaction step. The molar ratio of the starting material of (meth) acrylic acid or ester of (meth) acrylic acid to alcohol in the reaction step may be suitably selected depending on the type and amount of catalyst used for this reaction, the reaction system, the reaction conditions, or the type of alcohol used in quality of the source material.

The Michael addition product, mainly by-produced by this reaction, will be concentrated at the bottom of the distillation column (fractionation column) to separate the high boiling fraction. Thus, in the present invention, this lower part liquid, as an object to be treated, is thermally decomposed together with a by-product from the previous step for producing (meth) acrylic acid, and the obtained valuable component will be extracted for the reaction step for ether (meth) acrylic acid or purification steps.

In this case, the distillation column for separating the high boiling fraction may vary depending on the type of (meth) acrylic acid ester obtained or the method used, but it is usually a separation column for (meth) acrylic acid and a high boiling fraction or column for separating the (meth) acrylic acid ester and high boiling fraction or column for the separation of (meth) acrylic acid, alcohol and ether (meth) acrylic acid and high boiling fraction. This invention can be applied to all of them.

The above-mentioned Michael addition product is concentrated in the liquid of the lower part of the high-boiling fraction separation column, but in addition, significant amounts of (meth) acrylic acid and / or (meth) acrylic acid ester are contained and, in addition, high boiling components, such as a polymerization inhibitor, are contained used in this method, the oligomer or polymer formed in this method, high-boiling impurities in the starting material or their reaction products. Further, in some cases, the catalyst used for the esterification or transesterification step may be contained.

As mentioned above, the Michael addition product by-produced during the (meth) acrylic acid production step will usually be concentrated at the bottom of the distillation column (fractionation column) to separate the (meth) acrylic acid product from the heavy fraction. This lower portion liquid also contains a significant amount of (meth) acrylic acid and, in addition, also contains the polymerization inhibitor used in this method, the oligomer formed in this method, or high boiling components.

In embodiment c, any system, such as a continuous system, a batch system, a semi-batch system or a batch discharge system, can be used as a chemically active distillation system in which both the decomposition reaction of the Michael addition product and the distillation and recovery of a valuable substance are carried out a continuous system is preferred. Further, the type of reactor may be any one selected from a full mixing reactor with a stirred tank-reactor, a circulation type reactor with a full mixing tank or a simple hollow reactor without being limited to any particular type.

As a catalyst, a known catalyst, which is a Lewis acid or Lewis base, can be used, but simple thermal decomposition without using a catalyst can be used. As conditions for the decomposition reaction, the temperature is usually 120-280 ° C., preferably 140-240 ° C., and the retention time of the liquid based on the discharge liquid is 0.5-50 hours, preferably 1-20 hours. Regarding the reaction pressure, the conditions are chosen so that most of the (meth) acrylic acid, ester of (meth) acrylic acid, alcohol, etc., which must be recovered, is distilled off at the reaction temperature.

In a variant with a distillation column equipped with plates such as disks and toroids, shown in Figs. 7 or 8, are installed in a reactor for carrying out chemically active distillation. This portion of the distillation column may be a column directly connected to the reactor, or an independent column system that is connected to a steam piping system from the reactor and a liquid piping system from the distillation column, and therefore this system is not particularly limited. Further, the heating system for reactive distillation is not particularly limited and may be a coil type system in a reactor, such as an internal multi-tube heat exchanger, an external jacket type system, or an external heat exchanger type system.

In the case where the reactive distillation is carried out in a continuous system, the starting material can be fed to a part of the distillation column or to a part of the reactor in the lower part, but it is preferable to supply it to a part of the distillation column.

Further, in this invention, the by-product formed during the preparation of (meth) acrylic acid containing the Michael addition product and the by-product formed during the preparation of the (meth) acrylic acid ester can be separately subjected to thermal decomposition treatment or they can be mixed and subjected thermal decomposition processing.

Option d

Option d is a variant in which oxygen or an oxygen-containing gas is supplied directly to a distillate containing a decomposition product formed by the decomposition reaction of the above by-product, and an option for suppressing the polymerization of an easily polymerizable compound in the decomposition product by the action of such oxygen. As a result of numerous studies, it was found that the polymerization of the easily polymerizable compound in the decomposition product can be sufficiently suppressed by the addition of such oxygen or an oxygen-containing gas. This is due to the fact that the added oxygen will increase the polymerization inhibitory effect of the polymerization inhibitor typically contained in the decomposition reaction feed.

In Embodiment d, (meth) acrylic acid ester is not particularly limited, but esters similar to those described in Embodiment c may be mentioned. Further, with regard to the Michael addition product, products similar to those described in embodiment c may be mentioned.

The feed liquid (hereinafter sometimes referred to as high boiling liquid), which must be fed to the decomposition reaction column, also contains substances used or generated in the process of producing acrylic acid or acrylic esters. Specifically, they are acrylic acid, acrylic acid esters, maleic acid, maleic acid esters, furfural, benzaldehyde, polymers, oligomers, alcohols used as materials for the production of esters, and a polymerization inhibitor (copper acrylate, copper dithiocarbamate, compound (derivative) phenol or a compound (derivative) of phenothiazine, etc.).

The above copper dithiocarbamate may be as described in embodiment a. Further, the above phenol compound may be as described in embodiment a.

Depending on the particular method, substances other than those described above may be contained.

The (meth) acrylic acid in embodiment d is the same as that described in embodiment c. Further, the method for producing the (meth) acrylic acid ester in embodiment d includes, for example, a step for reacting the alcohol with (meth) acrylic acid for esterification using a cation exchange resin as a catalyst and a step for purifying washing, extraction, evaporation, distillation, or t .P. for separation of the catalyst, concentration, purification, etc. a crude solution of acrylic acid ester obtained in the reaction step. The molar ratio of the starting material of (meth) acrylic acid or ether (meth) acrylic acid to alcohol in the reaction stage, type and amount of catalyst used for this reaction, reaction system, reaction conditions, etc. may be suitably selected depending on the type of alcohol used as starting material. The Michael addition product, mainly by-produced in the esterification reaction step, will be concentrated as a heavy fraction in the lower part of the reaction column to recover the variable component.

The by-product formed during the preparation of acrylic acid and the by-product formed during the preparation of the acrylic acid ester can be decomposed together.

In embodiment d, any system, such as a continuous system, a batch system, a semi-batch system, or a batch system, can be used to carry out the decomposition reaction of the Michael addition product, but a continuous system is preferred. The type of reactor is also not particularly limited, and any type can be used, such as a flow-through tube reactor, a thin-film flow-through reactor with a descent, a stirred reactor-tank type of a full mixing tank, and a reactor of a complete mixing tank type of a circulation type. To obtain valuable components contained in the decomposition reaction product, a method for producing them by evaporation or distillation during the reaction or a method for producing them by evaporation or distillation after the decomposition reaction can be used. However, to obtain a high yield, the first reactive distillation system is preferred.

If a reactive distillation system is used, the reaction pressure mainly depends on the reaction temperature indicated below and such pressure is used that most of the valuable components, such as acrylic acid, acrylic ester, alcohol, etc., obtained in the decomposition reaction and contained in the starting material for the decomposition reaction, it will evaporate.

The catalyst may be selected from a Lewis acid, Lewis base, an inorganic acid such as sulfuric acid or phosphoric acid, and an organic acid such as methanesulfonic acid or para-toluenesulfonic acid. Water can be supplied to the decomposition reaction column, so that decomposition can be carried out in the presence of a high boiling fraction and water.

The concentration of the acid catalyst is preferably 0.1-1.0% by weight, particularly preferably 0.2-0.8% by weight, based on the loading liquid.

The temperature of the decomposition reaction is preferably 110 -250 ^{° C,} particularly preferably 120-230 ° ^C. The retention time of the liquid on the basis of the liquid discharge is preferably 0.5-50 hours. Further, in the case where the temperature of the decomposition reaction is lower, the time is preferably 10-50 hours, and in the case where the temperature of the decomposition reaction is higher, it is preferably 0.5-10 hours. Further, in the case where the decomposition reaction is carried out in the form of a continuous reaction, with respect to the reaction time, the retention time of the liquid, calculated from the discharged liquid, can be considered as the reaction time. For example, in the case when the liquid capacity in the reactor is 500 l and the amount of liquid discharged is 100 l / h, the retention time will be 5 hours.

To distill from the decomposition reaction column, oxygen or an oxygen-containing gas (hereinafter sometimes referred to as “oxygen or the like”) is added to prevent polymerization. As "oxygen or the like" for example, pure oxygen, a gas containing oxygen diluted with an inert gas, air or a gas containing air diluted with an inert gas can be used. The inert gas may be, for example, nitrogen, carbon dioxide, argon or neon. The addition of an inert gas should prevent the formation of explosive gas. The inert gas is preferably present in a 3.76-18.05-fold amount by volume relative to oxygen, and in the case of air, the inert gas is preferably present in a 0.3-3-fold amount by volume relative to air. In terms of cost, it is obvious that air is cheaper than oxygen. Oxygen or the like preferably added in a volume ratio of 0.0001-0.01, in particular in a volume ratio of 0.0005-0.005, calculated as the ratio of oxygen to distilled gas.

Further, in the present invention, the addition of oxygen or the like. to the distilled gas of the column for the decomposition reaction may be carried out in line after discharge from the column for the decomposition reaction or oxygen or the like. can be added to the top of the column for the decomposition reaction, where mainly distilled gas is formed.

11 is a diagram showing a decomposition reaction process. A high boiling liquid is supplied to the decomposition reaction column 41 and is thermally decomposed. Here, this decomposition reaction column 41 may be provided with a stirrer to mix the liquid in the column. Further, the decomposition reaction column 41 may be provided with a jacket to heat the water vapor or organic heat carrier used as a heat source.

The liquid of the lower part in the decomposition reaction column 41 is withdrawn using a pump 42 and part of it using a recirculation line 43a is heated using a heat exchanger 43 for heating and recycled, and the rest is discharged from this system.

The distillate formed by the decomposition reaction is distilled from the top of the decomposition reaction column 41 even after the addition of oxygen or the like. through the gas pipe 44a, the top of the column is cooled and fluidized using a heat exchanger 44 and introduced into the chilled liquid reservoir 5. However, in the case of a reflux line, the chilled fluid reservoir 45 may be absent. 11, the gaseous component in the chilled fluid tank 45 is withdrawn from the chilled fluid tank 45 to the heat exchanger 7 and cooled, whereby the valuable substance will liquefy. Non-condensed gas is supplied to a plant for recovering a valuable substance or to a vacuum plant (not shown). The liquid in the chilled fluid reservoir 45 is withdrawn through the pump 46 and part of it, after the addition of the polymerization inhibitor, is recycled through the heat exchanger 44 to the chilled fluid reservoir 45, and the rest is discharged as a decomposition product. This decomposition product is returned to the process for producing acrylic acid or acrylic ester, as mentioned above.

The decomposition reactor 41 may be provided with trays or filling (packing) material, which is usually used in a distillation column. In this case, it will work as a reactive distillation column for decomposition. As the filling material, conventional filling material may be mentioned, such as, for example, SULZER PACKING manufactured by SULZER BROTHERS LTD., SUMITOMO SULZER PACKING manufactured by SUMITOMO HEAVY INDUSTRIES, LTD., MELLAPACK manufactured by SUMITOMO HEAVY INDUSTRIES, LTD. GLITSCH, MONTZ PACK, manufactured by MONTZ, GOODROLL PACKING, manufactured by TOKYO TOKUSHU KANAAMI KK, HONEYCOMB PACKING, manufactured by NGK INSULATORS, LTD., Or IMPULSE PACKING, manufactured by NAGAOKA INTERNATIONAL CORPORATION, or by an unusual TELLER, such as INTELLETERELLELL, such as EXTERNAL TELLERELL manufactured by Nittetu Chemical Engineering Ltd., PALL RING, manufactured by BASF, CASCADE MINI-RING, manufactured branded MASS TRANSFER, or FLEXIRING, manufactured by JGC CORPORATION. Any of these excipients may be used, or several may be used in combination.

The plates may be, for example, cap plates, plates in the form of perforated plates, bubble plates, ultra-flow plates, maximum flow plates having a drain pipe, or double plates, etc., without a drain pipe. These plates or packing materials may be used in combination.

Further, such contents may not be present in the column for the decomposition reaction. In this case, a distillation column or the like. can be mounted as required in a particular case.

In the case where the decomposition reaction column 41 is provided with a mixing means, the mixing blades can be of any type, and for example, they can be anchor blades (at least one step), multi-stage inclined blade blades, as special blades, MAXLEND blades (manufactured by SUMITOMO HEAVY INDUSTRIES, LTD.) or FULLZONE blades (manufactured by SHINKO PANTEC CO., LTD). Several types can be used in more than one stage, i.e. in multi-stage design. Especially preferred are anchor blades or trellised blades.

Bubble plates (flaps), installed together with the mixing blades, can be of any type. Specifically, they can be, for example, a rod type, a plate type, a comb type, and more than one type and more than one plate can be installed. However, bubbling plates may not be available.

The fraction enriched in (meth) acrylic acid, (meth) acrylic acid ester and alcohol, obtained by the decomposition reaction, is recovered completely for the step of producing an acrylic acid ester. The place where the recovered fraction is to be recycled is not particularly limited. However, this fraction contains a small amount of the light fraction and, therefore, it is preferable to recycle it together before the stage of separation of the light fraction.

Option e

The invention of this embodiment e relates to a method for the extraction of acrylic acid. In particular, in a method that involves reacting acrylic acid containing maleic acid, in particular an acrylic acid-containing gas obtained by catalytic oxidation in the vapor phase of propylene, with a solvent for collecting acrylic acid in the form of an acrylic acid-containing solution, distilling the low boiling component from the containing acrylic acid of the solution by azeotropic distillation or direct distillation, then the production of acrylic acid by fractionation during thermal decomposition of the oligomer of acrylic acid of the residues (bottoms) of the bottom of the distillation column, and the extraction of acrylic acid and its recycling to the purification step, the invention of embodiment e relates to a method for effectively removing maleic acid as a contaminant from a liquid to be fed to a thermal decomposition reactor, or from the distillate.

The invention of option e was made on the basis of the discovery by the authors of this invention of the following fact:

- Maleic acid, formed together with acrylic acid in an oxidation reactor, is present in the form of a dicarboxylic acid having two carboxylic groups in an aqueous solution, but in acrylic acid it can be in the form of maleic anhydride having one water molecule dehydrated from its molecule. Maleic acid and maleic anhydride are in equilibrium and in a solution of acrylic acid, which must be supplied to the installation to extract the reaction of thermal decomposition of the oligomer of acrylic acid, the concentration of water as a component with a low boiling point is low, as a result of which this equilibrium is shifted essentially to the side maleic anhydride.

- When water is added to such a liquid, part of maleic anhydride is converted to maleic acid in accordance with the amount of added water.

- In the liquid (or gas) of the upper part of the column of the thermal decomposition reactor, there is water formed by thermal decomposition of 3-hydroxypropionic acid, etc., and part of maleic anhydride will interact with this water to form maleic acid.

- The equilibrium reaction takes some time and the equilibrium will be accelerated by heating.

- The solubility of maleic acid in acrylic acid is low compared to maleic anhydride and probably maleic acid should be precipitated.

- The degree of precipitation depends on the concentration of maleic acid or water in a given liquid and on the temperature of the operation, and precipitation will be accelerated by the addition of a water-insoluble solvent.

- Precipitation and separation can be facilitated by reducing solubility by converting maleic anhydride to maleic acid in a liquid that must be fed to the reactor for thermal decomposition of acrylic acid, or in a liquid recovered from the thermal decomposition reactor.

Using this method, circulation in the maleic acid purification system involved in the thermal decomposition and recovery of the acrylic acid oligomer formed during the distillation and purification of the acrylic acid-containing liquid can be easily reduced by precipitation and separation of the solid from the liquid using the chemical equilibrium of maleic acid and maleic anhydride, whereby acrylic acid can be recovered without the problem of clogging by polymerization.

Option e will now be described in detail with respect to each of the objects “Thermal decomposition reactor”, “Preparation of acrylic acid solution”, “Maleic acid reaction”, “Precipitation operation” and “Sludge separation”.

Thermal decomposition reactor

The liquid of the lower part of the acrylic acid purification column (product) or liquid obtained by concentrating and heating the lower part of the column with a film evaporator or the like is used as the liquid to be supplied, and the thermal decomposition of the acrylic acid oligomer is carried out in the temperature range 120- 220 ° C. This thermal decomposition step and the decomposition step of the decomposed products can be carried out in the same equipment, such as a reactive distillation column, or in separate equipment, such as a combination of a heating tank and an evaporator. A catalyst may be used for this thermal decomposition reaction. As the type of catalyst, for example, a compound having a secondary or tertiary amino group or tertiary phosphine may be mentioned. However, the catalyst is not limited to them. Alternatively, the decomposition reaction may be carried out in the absence of any catalyst.

Obtaining a solution of acrylic acid

The liquid to be fed to the thermal decomposition reactor or the liquid recovered from the thermal decomposition reactor (distillate) must be processed.

The concentration of maleic acid and / or maleic anhydride in the recovered liquid is in the range of 1.6-28 wt.%, Preferably 2.5-25 wt.%. If the concentration of maleic acid is low, precipitation tends to be difficult, and if this concentration is too high, the loss of acrylic acid increases during separation of precipitated maleic acid.

The concentration of water is in a molar ratio, shown as follows:

Water

------------------------- less than or equal to 1.0

maleic acid

+ maleic anhydride x 2.

Particularly preferably, it is in the range of [maleic anhydride] x 0.8 ≤ [water] ≤ [maleic acid] x 0.5 + [maleic anhydride]. If the water concentration is too high, the amount of precipitated maleic acid is reduced and the time required for precipitation will be long.

The concentration of acrylic acid is at least 70 wt.%. If it is lower than this, the nature of this liquid will be different and there will be a case where the effect of the present invention may not be obtained.

Maleic acid reaction

Maleic acid and maleic anhydride are present in the solution. Compared to maleic anhydride, maleic acid has a low solubility in acrylic acid. Thus, the larger the maleic acid / maleic anhydride ratio in this solution, the more effective the removal by precipitation.

To accelerate the formation of maleic acid by the interaction of maleic anhydride with water, the temperature of the liquid can be increased to 50-70 ° C. If the temperature rises above this range, the rate of formation of the acrylic acid oligomer will increase, whereby not only the heating, decomposition and recovery of the oligomer will decrease, but also the polymerization of acrylic acid will probably occur, which is undesirable.

The reaction tank is not particularly limited. However, it is preferably provided with a system for mixing the solution, such as stirring blades, or with external circulation using a pump to prevent polymerization in the tank.

In the case where the amount of maleic acid (without anhydride) in the solution exceeds 2 wt.%, The above operation may be omitted.

Deposition operation

Maleic acid is precipitated from the above solution. The reservoir used for such deposition may be the reservoir used for the operation described above, or it may be a separate reservoir. The time required for precipitation is preferably in the range of 0.5-5 hours along with the time of the above operation. If this time is too short, the deposition efficiency is usually poor. In terms of efficiency, the longer the required time, the better. However, the equipment necessary for this must be large, which is uneconomical.

The temperature of this step is in the range 20-70 ^C, preferably 20-40 ° C. If the temperature of this operation is too low, the cooling load will increase, which is uneconomical. Further, the melting point of acrylic acid is 13 ° C and freezing of acrylic acid may occur. The higher the temperature, the more polymerizable is acrylic acid and the solubility of maleic acid will increase, which is undesirable.

A solvent capable of forming double layers of a liquid with water can be added, whereby the amount of precipitation and the rate of precipitation of maleic acid can be increased. A solvent that can be used for this purpose may be, for example, an aliphatic hydrocarbon such as heptene or octene, an aromatic hydrocarbon such as toluene, xylene or ethylbenzene, an ether such as isopropyl acetate, or a ketone such as methyl isobutyl ketone, but not only they. More preferred is a solvent with a low polarity, such as an aromatic or aliphatic hydrocarbon. The amount is preferably 0.5-4 times by volume relative to the volume of the solution of extracted acrylic acid. If this amount is too small, then usually no adequate action is taken regarding the amount of precipitation. On the other hand, an excessive amount of addition aggravates this process in terms of installation size and efficiency, which is uneconomical. In exactly the same way, the azeotropic agent used for the dehydration distillation step can be used, in which case the thermal load to remove the added solvent will not substantially increase.

Stirring can be carried out to prevent the deposition of crystals deposited in the tank on the wall of the reactor. In addition, crystals having a uniform particle size will be precipitated by stirring, which facilitates the subsequent separation step.

Sediment separation

Separation of precipitated maleic acid may be carried out in a reservoir used for precipitation. However, it is convenient to carry out this separation in relation to the liquid withdrawn from the sedimentation tank, so that this operation can be carried out continuously.

As a means for removing precipitated maleic acid in the discharge liquid, a replaceable strainer, for example, may be convenient. However, such a tool is not limited to it and a conventional separator can be used to separate solid and liquid. A thickener (concentrator), a deposition tank, a cyclone separator, a strainer, a centrifugal separator (centrifuge) or the like can be used. Separated liquid may be removed through the opening of such an installation. However, it may dissolve in a small amount of warm water and may be disposed of as waste water. Depending on the installation, the separated solid can be continuously discharged. After removal of the precipitate, the acrylic acid solution contains water and an organic solvent added for the precipitation operation, and therefore is preferably recycled to the purification step before the acrylic acid purification column.

As a result of the above operation, the concentration of maleic acid in the extracted acrylic acid will decrease to a level of 1.4-3 wt.%. The content of this level will not adversely affect the purity of this product, even when recycled to the purification stage.

Option f

The invention of embodiment f relates to a method for establishing a liquid level meter used for this equipment to produce an easily polymerizable compound. More specifically, it relates to a method of establishing a detecting part (detecting part) of a high pressure side of a liquid level meter and relates to a method of installing a liquid level meter, whereby this equipment can be continuously operated without clogging the detecting part of the liquid level meter.

FIG. 12 is a view showing an entire installation in which the method of installing a liquid level meter of the invention of embodiment f is applied to a decomposition reaction column (high boiling material) and to a gas-cooled liquid reservoir of the upper part in the production of acrylic acid, FIG. 13 is a partial enlarged view, showing a liquid level meter mounted on a decomposition reaction column (high boiling material) of FIG. 12, and FIG. 14 is a partial enlarged view showing a liquid level meter, setting enny cooled gas to the tank top of the liquid 12.

First, with reference to FIG. 12, an apparatus for producing acrylic acid will be described in general terms. 6A is a column of a decomposition reaction (high boiling material) and a supply line 61 is connected to a column of a decomposition reaction (high boiling material) 6A. 6B ₁ is a lower part pump, and the inlet side _{of the} lower part pump 6B _{1 is} connected to a lower part liquid discharge line 62 connected to the lower part of the decomposition reaction column 6A (high boiling material), and its discharge side is connected to the decomposition residue discharge line 64.

6C is a heat exchanger for heating, and the inlet side of the heat exchanger for heating is connected to a supply line 63 for a heat exchanger for branching off from the decomposition residue discharge line 64, and its exhaust side is connected to the bottom wall of the decomposition reaction column 6A (high boiling material) .

6D is a heat exchanger for cooling the gas of the upper part of the column, and the inlet side of the heat exchanger 6D for cooling gas of the upper part of the column is connected to a decomposition gas recovery line 66 connected to the upper part of the decomposition reaction column 6A (high boiling material), and its discharge side is connected to the inlet side reservoir 6E gas-cooled liquid top of the column through the pipeline.

Further, the outlet side of the tank 6E of the gas-cooled liquid of the upper part of the column is connected to the line 68 for discharging the gas-cooled liquid of the upper part of the column through the line 65 of the liquid discharge of the lower part of the tank and the pump 6B ₂ , and the gas-cooled liquid of the upper part of the column is transferred via this line 68 to next installation.

A chilled liquid return line 69 branching off from the gas-cooled liquid discharge line 68 of the upper part of the column is connected to the inlet side of the heat exchanger 6D to cool the gas of the upper part of the column.

6F is a heat exchanger for cooling the exhaust gas through the vent, and the inlet side of the heat exchanger 6F for cooling this exhaust gas is connected to the tank 6E of the gas-cooled liquid of the upper part of the column via a pipe. The flue gas passing to the heat exchanger 6F for cooling the flue gas will be cooled and after the extraction of the valuable substance contained in this gas will be led off to the flue gas discharge line 67.

H ₁ and H ₂ are liquid level meters such as a differential pressure meter, and the installation method of such liquid level meters H ₁ and H ₂ is a very important feature of the present invention.

Namely, the high pressure side of the liquid level meter H _{1 of} the differential pressure type meter is connected to the lower part liquid discharge line 62 through the high pressure side detection line 11, and the low pressure side of the liquid level meter H _{1 of} the differential pressure type meter is connected to the wall of the bottom side of the column 6A of the decomposition reaction (high boiling material) through the low pressure side detection line 12.

The high pressure side of the liquid level meter H _{2 of} the type differential pressure meter is connected to the lower part liquid discharge line 65 through the high pressure side detection line 13, and the low pressure side of the liquid level meter H _{2 of} the type differential pressure meter is connected to the lower side of the gas-cooled liquid tank 6E the top of the column through the low pressure side detection line 14.

Now will be explained in detail specific examples of the method of establishing the above-described liquid level meters such as differential pressure meters H ₁ and H ₂ with reference to figures 13 and 14.

13 (1) and (2), 6A is a decomposition reaction column (high boiling material) and liquid accumulated in the lower part of the decomposition reaction (high boiling material) column 6A is discharged from this column through a liquid discharge line 62 of the lower part of the column, from the short liquid discharge pipe 62a of the lower portion attached to the lower part of the column, and the liquid discharge pipe 62b of the bottom of the column.

H ₁ is a liquid level meter such as a differential pressure meter, and the high pressure side of a H ₁ liquid level meter such as a differential pressure meter is connected either to a short conduit 62a or to a conduit 62b consisting of a lower portion liquid discharge line 62 via a side detection line 11 high pressure line consisting of a short high pressure side detection conduit 11a and a high pressure side detection conduit 11b.

The angle of attachment α between the high pressure side detection line 11 and the bottom liquid discharge line 62 is 5-90 °, preferably 10-90 °.

If this attachment angle is less than 5 °, then the attachment is practically impossible, and if this attachment angle exceeds 90 °, then the solid in this fluid is likely to flow into the high pressure side detection line 11, which is undesirable.

The size ratio of D ₂ / D ₁ is 1-20, preferably 1.3-10, where D ₁ is the diameter of the pipe of the high pressure side detection line and D ₂ is the diameter of the pipe of the liquid discharge line.

If the D ₂ / D ₁ ratio is less than 1, the solid in this liquid is likely to flow into the high pressure side detection line 11, which is undesirable, and if D ₂ / D ₁ exceeds 20, the liquid level detection is likely to be difficult.

The low pressure side of the liquid level meter H _{1 of} the type differential pressure meter is connected to the wall of the lower side of the decomposition reaction column 6A (high boiling material) via the low pressure side detection line 12, consisting of the low pressure side detection line 12b and the low pressure side detection short line 12a.

13 (1) is an example in which the high pressure side detection line 11 is connected to the vertical part of the lower part liquid discharge line 62, while FIG. 13 (2) is an example in which the high pressure side detection line 11 is connected to the horizontal part of the line 62 of the discharge of the liquid bottom.

14 (1) and (2), 6E is a reservoir of gas-cooled liquid from the top of the column, and liquid accumulated in the reservoir 6E of gas-cooled liquid from the top of the column is discharged from this tank through a liquid discharge line 65 of the bottom of the tank, consisting of a short liquid discharge pipe 65a of the lower part of the tank connected to the lower part of the tank, and a liquid discharge line 65b of the lower part of the tank.

H ₂ is a liquid level meter such as a differential pressure meter, and the high pressure side of a H ₂ liquid level meter such as a differential pressure meter is connected either to a short conduit 65a or to a conduit 65b consisting of a liquid discharge line 65 of the lower part of the tank through the detection line 13 a high pressure side, consisting of a short high pressure side detection conduit 13a and a high pressure side detection conduit 13b.

Further, the low pressure side of the liquid level meter H ₂ , such as a differential pressure meter, is connected to the lower side of the gas cooled liquid tank E of the top of the column via the low pressure side detection line 14, which consists of the low pressure side detection line 14b and the low pressure side short detection line 14a .

The angle of attachment α between the high pressure side detection line 13 and the bottom of the tank liquid discharge line 65 and the size ratio D ₂ / D ₁ , where D ₁ is the diameter of the pipe of the high pressure side detection line 13 and D ₂ is the pipe diameter of the liquid discharge line 65 the bottom of the tank are acceptable if they satisfy the relationship between the high pressure side detection line 11 and the liquid discharge line 62, as described in detail with reference to the above example of FIG. 13.

Here, FIG. 14 (1) is an example in which the high pressure side detection line 13 is connected to the vertical part of the liquid discharge line 65 of the lower part of the tank, and FIG. 14 (2) is an example in which the high pressure side detection line 13 is connected to the horizontal part of the liquid discharge line 65 of the lower part of the tank.

The liquid discharge line described above is connected to a place where liquid containing an easily polymerizable compound is accumulated, such as a distillation column, a reflux tank for a distillation column, a decomposition reaction column, a film evaporator, a gas-cooled liquid tank at the top of the column, a vertical storage tank, a horizontal tank for storage or a tank, and the detection line of the high pressure side of the liquid level meter is connected to this place so that m The fluid level can be measured.

Further, the liquid level meter used in the present invention may be, for example, a liquid level meter such as a differential pressure meter, a liquid level meter such as a glass instrument or direct observation tube type meter or a displacement type indicator.

Preferably, the gas and / or liquid inlet is connected to a high pressure side detection line and / or a low pressure side detection line of such a liquid level meter.

In the case when, through some operational change, a solid in this liquid flows into such a detection line, it is possible to quickly discharge this solid with gas and / or liquid. Such a gas or such liquid may be supplied continuously or intermittently.

The gas used for this purpose is preferably air nitrogen, carbon dioxide or the like, and as such a liquid, it is preferable to use the same liquid that flows in the liquid discharge line, such as acrylic acid or acrylic acid ester.

Further, preferably, such a part is heated or heated to prevent the deposition of solids in this liquid in the detection line of the high pressure side and / or the detection line of the low pressure side of the liquid level meter.

Measurement of the easily polymerizable compound by the method of establishing a liquid level meter of the present invention is effective in the production of (meth) acrylic acid or (meth) acrylic acid ester.

Further, as a liquid measured by a liquid level meter, a liquid containing at least one type selected from a dimer of acrylic acid, β- (meth) acryloxypropionic acid esters, β-alkoxypropionic acid esters, β-hydroxypropionic acid is particularly effective and β-hydroxypropionic acid esters formed as by-products during the preparation of (meth) acrylic acid or its esters.

EXAMPLES

Now the invention will be described in more detail with reference to examples and comparative examples, but the invention is not limited to these examples. Here, the composition of the high boiling material is analyzed in accordance with a conventional method using a gas chromatograph equipped with a flame ionization detector (FID).

EXAMPLE A1

The decomposition reaction of the high-boiling material was carried out using the apparatus shown in FIG. A column type reactor made of Hastelloy C and having an outer diameter of 600 mm and a length of 1800 mm was used as a decomposition reactor. As a starting material, a high boiling material having the following composition was continuously fed from line 1 at a speed of 580 kg / h.

The composition of the high boiling material (source material) Butyl acrylate: 22 wt.% Butyl-β-butoxypropionate: 67 wt.% Butyl acryloxy propionate: 4 wt.% Butyl-β-hydroxypropionate: 2 wt.% Hydroquinone: 3 wt.% Methoxyquinone: 2 wt.%

Further, as a catalyst for the decomposition reaction, a 1 wt.% Aqueous solution of sulfuric acid was fed at a rate of 58 kg / h (10 wt.% Relative to the feed liquid of the starting material) and the decomposition reaction was carried out at a reaction pressure of 100 kPa at a decomposition temperature of 190 ° C. during a retention time of 1 hour.

From line 6 in the upper part, a valuable substance consisting mainly of acrylic acid and butanol was recovered at a rate of 438 kg / h, while the remainder of the reaction, having the following composition, was discharged from the system through line 4 at a speed of 200 kg / h.

The composition of the reaction residue Butyl acrylate: 11.0 wt.% Butyl-β-butoxypropionate: 68.5 wt.% Butyl acryloxy propionate: 2.0 wt.% Butyl-β-hydroxypropionate: 0.3 wt.% Hydroquinone: 8.7 wt.% Methoxyquinone: 5.8 wt.% Butanol: 0.8 wt.% Sulphuric acid: 2.9 wt.%

From the line 2 of the reactor A, the liquid of the lower part was diverted at a speed of 35350 kg / h and from the line 5 (see Fig. 4) installed in the tangential direction relative to the reactor A, 350 kg / h of the liquid of the lower part was returned to the reactor A by means of a valve a current (not shown in FIG. 1) installed on line 5. The remainder of 34800 kg / h was returned to reactor A through heat exchanger C for heating and a return line 3-2 for heating. At this moment, a spiral flow formed in the lower part of reactor A with the liquid returned from line 5. Next, the pipeline for line 3 was 4B, and the pipeline for line 5 was 1 (1.5) B.

After continuous operation for 6 months, this operation was stopped and the interior of the decomposition reaction column was examined. No accumulation was observed at the bottom of the decomposition reaction column. In addition, during this operation, there was no clogging in the transport line for the remainder of the reaction.

COMPARATIVE EXAMPLE a1

The operation was carried out using the same apparatus (Fig. 1) as in Example A1, except that the connection of line 5 to the decomposition reaction reactor was set in the direction of the center of the column, i.e. not in a tangential direction. After operating for 2 months in the pump B, cavitation unexpectedly occurred. The operation of this decomposition reaction column was discontinued and the interior of the column was examined, whereby an accumulation of solids in the lower part of the decomposition reaction column was observed. The state of the solid accumulated in the lower part of the decomposition reaction column is shown in FIG.

EXAMPLE A2

Using the same setup (FIG. 1) as in Example A1, a high boiling material having the following composition was continuously fed from line 1 at a speed of 580 kg / h.

The composition of the high boiling material (source material) Acrylic Acid: 45.3 wt.% Maleic acid: 10.0 wt.% Acrylic Acid Dimer
(acryloxypropionic acid): 42.4 wt.% Hydroquinone: 1.3 wt.% Phenothiazine: 1.0 wt.%

The decomposition reaction was carried out at a reaction pressure of 72 kPa at a decomposition temperature of 190 ° C. for a retention time of 1 hour. From line 6 at the top, a valuable substance, consisting mainly of acrylic acid, was recovered at a rate of 449 kg / h, while the remainder of the reaction, having the following composition, was withdrawn from the system through line 4 at a rate of 131 kg / h.

The composition of the reaction residue Acrylic Acid: 8.0 wt.% Maleic acid: 14.0 wt.% Acrylic Acid Dimer
(acryloxypropionic acid): 67.2 wt.% Hydroxyquinone: 5.8 wt.% Phenothiazine: 4.4 wt.% Oligomer and polymer: 0.6 wt.%

The liquid of the lower part of the decomposition reaction column was withdrawn from the 3 / 4B tip (line 2) installed in the lowest position of the lower part, and was pumped to B. By pump B, it was withdrawn from line 4 at a speed of 131 kg / h, while it was fed into line 3 at a speed of 32,000 kg / h in the form of a return liquid to the decomposition reaction column through heat exchanger C for heating using a pipeline having a diameter of 4B.

On the other hand, the liquid of the lower part of the decomposition reaction column was supplied as a return liquid by pump B from line 5 to form a peripheral flow in the decomposition reaction column. The diameter of the pipeline of line 5 was 1 and 1/2 (1.5) V, and the flow rate was 400 kg / h, and such regulation was carried out using a current velocity control valve (not shown in Fig.) Installed on line 5.

After continuous operation for 6 months, this operation was stopped and the interior of the decomposition reaction column was examined. No accumulation was observed at the bottom of the decomposition reaction column. In addition, during this operation, there was no clogging in the transport line for the remainder of the reaction.

COMPARATIVE EXAMPLE a2

The work was carried out using the same setup as in example a2, except that the connection of line 5 to the decomposition reaction reactor was set in the direction of the center of the column, and not in the tangential direction.

After operating for 70 days in pump B, cavitation unexpectedly occurred. The operation of this decomposition reaction column was discontinued and the interior of the column was examined, whereby an accumulation of solids in the lower part of the decomposition reaction column was observed. The state of the solid accumulated in the lower part of the decomposition reaction column is shown in FIG.

EXAMPLE a3

The decomposition reaction of the same high-boiling material as in example a2 was carried out using the decomposition reaction column (without septum) shown in FIG. 3, having anchor blades mounted as mixing blades. This decomposition reaction column has a jacket and has a diameter of 600 mm and a height of 1000 mm, the diameter of the anchor blades was 540 mm. The work was carried out under the same operating conditions as in Example A2, with the rotation speed of the anchor blades adjusted to 20 rpm. Six months later, this work was stopped and the interior of the column was examined, as a result of which no accumulation of solids in the column was observed. In addition, clogging was not observed in the discharge line installed at the very bottom of the bottom of the column during the same period.

EXAMPLE b1

The decomposition reaction of high-boiling material was carried out using the apparatus shown in Fig.6. A column type reactor made of Hastelloy C and having an outer diameter of 600 mm and a length of 1800 mm was used as a decomposition reactor. As a starting material, a high boiling material having the following composition was continuously fed from line 1 at a speed of 580 kg / h.

The composition of the high boiling material (source material) Butyl acrylate: 22 wt.% Butyl-β-butoxypropionate: 69 wt.% Butyl acryloxy propionate: 4 wt.% Butyl-β-hydroxypropionate: 2 wt.% Hydroquinone: 2 wt.% Methoxyquinone: 1 wt.%

Further, as a catalyst for the decomposition reaction, a 1 wt.% Aqueous solution of sulfuric acid was fed at a rate of 58 kg / h (10 wt.% Relative to the feed liquid of the starting material) and the decomposition reaction was carried out at a reaction pressure of 100 kPa at a decomposition temperature of 190 ° C. during a retention time of 1 hour.

From the upper part of the column, a valuable substance, consisting mainly of acrylic acid and butanol, was extracted at a speed of 449.5 kg / h and, on the other hand, from the lower part of the column, the reaction residue of the following composition was periodically recovered at a speed of 188.5 kg / h. That is, the periodic discharge control valve D shown in FIG. 6 worked for a closed state time of 75 seconds and an open state time of 5 seconds (open state coefficient: 6.3%).

The discharged liquid was sent to a tank for storing the remainder of the reaction, installed at a distance of 800 m, using a pipeline having a diameter of 3/4 V (inner diameter: 22.2 mm). Continuous work was carried out for 3 months, but clogging in the transport pipeline was not observed for the remainder of the reaction. The results are shown in table 1.

The composition of the reaction residue Butyl acrylate: 11.7 wt.% Butyl-β-butoxypropionate: 72.7 wt.% Butyl acryloxy propionate: 2.1 wt.% Butyl-β-hydroxypropionate: 0.4 wt.% Hydroquinone: 6.2 wt.% Methoxyquinone: 3.1 wt.% Butanol: 0.8 wt.% Sulphuric acid: 3.1 wt.%

In addition, the degrees of decomposition of the respective components in the high boiling material were as follows:

Butyl-β-butoxypropionate: about 67 wt.% Butyl acryloxy propionate: about 83 wt.% Butyl-β-hydroxypropionate: about 74 wt.%

Here, for each component in the high-boiling material, the degree of decomposition was determined as [1- (unloaded amount from the decomposition reactor) / (fed amount to the decomposition reactor)] x 100 (%).

EXAMPLES b2 - b4

The residual reaction liquid obtained using the same installation and operation as in example b1 was sent to the tank for storing the reaction residue in the same manner as in example b1, except that the time of periodic discharge (open state coefficient) was changed regarding this condition, as shown in table 1. Under any condition, clogging in the transport pipeline was not observed as a result of continuous operation of the installation for 3 months. In addition, the decomposition rate of the high boiling material was essentially the same as in Example b1 with respect to each component. These results are shown in table 1.

COMPARATIVE EXAMPLE b1

The residual reaction liquid obtained using the same installation and operation as in example b1 was sent continuously to the tank for storing the reaction residue in the same manner as in example b1. From about the fifth day after the start of work, a gradual decrease in the transported amount of the residual reaction liquid was observed. The pipeline was mechanically shaken from the outside, whereby clogging was partially and temporarily eliminated, but complete restoration of the transported amount was impossible. After this, the amount of discharge was continuously reduced and, accordingly, the retention time in the decomposition reactor gradually increased. As a result, the state of the liquid in the remainder of the reaction became very viscous, and on the 25th day the decomposition reactor should have been stopped. In addition, the degree of decomposition of high-boiling material during stationary operation before shutdown was essentially the same as in example b1, with respect to each component. These results are shown in table 1.

EXAMPLES b5-b8

Using the same apparatus as in Example b1, the decomposition reaction was carried out by supplying a high boiling material having the following composition as starting material at a speed of 580 kg / h.

The composition of the high boiling material (source material) Acrylic Acid: 46.0 wt.% Maleic acid: 10.0 wt.% Acrylic Acid Dimer
(acryloxypropionic acid): 42.4 wt.% Hydroquinone: 0.9 wt.% Phenothiazine: 0.7 wt.%

Decomposition reaction conditions were a reaction pressure of 72 kPa, the decomposition temperature of 190 ^C and a retention time of 1 hour, there was no catalyst feed.

From the top of the column, a valuable substance, consisting mainly of acrylic acid and butanol, was recovered at a rate of 449.5 kg / h, while from the bottom of the column, the reaction residue of the following composition was periodically recovered at a rate of 130.5 kg / h. That is, the closed state time and the open state time of the periodic discharge control valve D shown in FIG. 6 were set as shown in Table 2, and this operation was performed.

The discharged liquid was sent to a tank for storing the remainder of the reaction, installed at a distance of 800 m, using a pipeline having a diameter of 3/4 V (inner diameter: 22.2 mm). Continuous work was carried out for 3 months, but clogging in the transport pipeline was not observed for the remainder of the reaction. In addition, the degree of decomposition of the acrylic acid dimer was approximately 72%. These results are shown in table 2.

The composition of the reaction residue Acrylic Acid: 9.0 wt.% Maleic acid: 14.0 wt.% Acrylic Acid Dimer
(acryloxypropionic acid): 69.5 wt.% Hydroquinone: 4.0 wt.% Phenothiazine: 3.1 wt.% Oligomer and polymer: 0.4 wt.%

COMPARATIVE EXAMPLE b2

The residual reaction liquid obtained using the same installation and operation as in examples b5-b8, was sent continuously to the tank for storing the reaction residue in the same manner as in example b5-b8. Approximately from the fifth day after the start of work, a gradual decrease in the amount of residual reaction liquid transported to the storage tank was observed. The pipeline was mechanically shaken from the outside, whereby clogging was partially and temporarily eliminated, but complete restoration of the transported amount was impossible. After this, the amount of discharge was continuously reduced and, accordingly, the retention time in the decomposition reactor gradually increased. As a result, the state of the liquid in the remainder of the reaction became very viscous and on the 18th day the decomposition reactor should have been stopped. These results are shown in table 2.

Table 1 Examples Comparative example b1 b2 b3 b4 b1 Periodic discharge control valve Open time (sec) 5 3 10 twenty Continuously open Closed Time (sec) 75 60 120 180 0 Open state coefficient 6.3 4.8 7.7 10 one hundred The condition of the transport pipeline in relation to the residual reaction liquid No clogging in flow. 3 months No clogging in flow. 3 months No clogging in flow. 3 months No clogging in flow. 3 months The transported amount gradually decreased by the 25th
day the decomposition reactor was supposed to
to be stopped table 2 Examples Comparative example b5 b6 B7 b8 b2 Periodic discharge control valve Open time (sec) 5 3 10 twenty Continuously open Closed Time (sec) 60 40 90 120 0 Open state coefficient 7.7 7 10 14.3 one hundred The condition of the transport pipeline in relation to the residual reaction liquid No clogging in flow. 3 months No clogging in flow. 3 months No clogging in flow. 3 months No clogging in flow. 3 months The transported amount gradually decreased by the 18th
day the decomposition reactor was supposed to
to be stopped

EXAMPLE c1

The decomposition reaction was carried out in accordance with this invention using as the starting material a liquid of the lower part of the column separating a high boiling fraction in the method for producing methyl acrylate, the starting material having the following composition:

Lower fluid composition Acrylic Acid: 20 wt.% β-hydroxypropionic acid: 1 wt.% Methyl β-hydroxypropionate: 8 wt.% β-acryloxypropionic acid: 8 wt.% Methyl-β-acryloxypropionate: 7 wt.% β-methoxypropionic acid: 41 wt.% Methyl β-methoxypropionate: 12 wt.% Other high boiling components, etc .: 3 wt.%

A stirred tank made of Hastelloy C having an inner diameter of 1000 mm and a height of 2000 mm was used as the reactor part in the lower part of the decomposition reaction column, and the coolant was supplied to the outer jacket to control the temperature at 200 ° C, and the reaction pressure was maintained at 130 kPa . Further, at the top of this stirred reactor vessel, a distillation column having an inner diameter of 400 mm and a height of 4000 mm and, furthermore, a condenser were connected, whereby the decomposition reaction was carried out using a reactive distillation system.

In the inner space of the distillation column shown in Figure 7, were installed 2A dish-shaped discs having a diameter D ₁₂₈₀ mm in five steps with a distance of 600 mm from the uppermost part to the lowermost part and plates were set therebetween 2B in the form of toroids with an opening having an inner diameter D ₂ 260 mm, in the form of four steps with the same distance.

The liquid feed position of the starting material was above the disk of the uppermost stage and the aforementioned liquid of the lower part was supplied at a speed of 150 kg / h. The retention time of the liquid was controlled by the liquid level in the decomposition reactor and adjusted so that the retention time based on the discharged liquid was 10 hours. The operation of the reactor was continued for 1 month at a decomposition reaction temperature of 200 ° C, as a result of which an increase in the pressure drop was not observed and work could be carried out under stabilized conditions.

After this operation of the reactor, the interior of the distillation column was subjected to a visual inspection in which no accumulation of solids was observed. The discharge amount of the decomposition residue during this period averaged 76 kg / h and the composition was analyzed by gas chromatography to obtain the following results:

The composition of the remainder Water: 0.2 wt.% Methanol: 0.2 wt.% Methyl Acrylate: 0.3 wt.% Acrylic Acid: 39 wt.% β-hydroxypropionic acid: 0.3 wt.% Methyl β-hydroxypropionate: 7 wt.% β-acryloxypropionic acid: 4 wt.% Methyl-β-acryloxypropionate: 4 wt.% β-methoxypropionic acid: 31 wt.% Methyl β-methoxypropionate: 8 wt.% Other high boiling components, etc .: 6 wt.%

COMPARATIVE EXAMPLE c1

The decomposition reaction was carried out using the same apparatus, the same starting material and the same reaction conditions as in Example c1, except that as part of the distillation column, a distillation column equipped with a 2000 mm coil (coil) was used as a packing material, instead of plates in the form of disks and toroids. There was no obvious difference compared to Example C1 with respect to the amount discharged or the composition of the residue, but during this period the pressure drop between the upper and lower parts of the distillation column gradually increased and after 1 month an increase in pressure drop of 2.6 kPa was observed. Further, after 1 month, the reactor was stopped and the packing material was removed and examined visually, as a result of which it was found that a significant amount of solid was deposited.

As can be seen from the results of the above examples and comparative examples, using the method of the present invention, it is possible to carry out continuous operation in stable conditions without disruption, for example, due to clogging or increasing pressure drop and to prevent the deposition or accumulation of solids.

EXAMPLE d1

The decomposition reaction of the high boiling liquid was carried out using the apparatus shown in FIG. 11. The decomposition reactor has a column diameter of 1000 mm and a column length of 2800 mm and is made of Hastelloy C. The high boiling liquid had the following composition: 22 wt.% Butyl acrylate, 67 wt.% Butyl-β-butoxy propionate, 4 wt.% Butyl acryloxy propionate, 2 wt. % butyl-β-hydroxypropionate, 3 wt.% hydroquinone and 2 wt.% methoxyquinone and this liquid was supplied at a speed of 580 kg / h.

As the catalyst, decomposition 1 wt.% Aqueous sulfuric acid solution was fed in a weight ratio of 10% relative to the liquid medium and decomposition reaction was carried out under a reaction pressure of 100 kPa at a decomposition temperature of 190 ^{° C} for a retention time of 1 hour whereby the decomposed gas containing 45 , 8 wt.% Butyl acrylate, 23 wt.% Acrylic acid, 16 wt.% Butanol, 11.9 wt.% Water, 2.9 wt.% Butyl-β-butoxypropionate, 0.003 wt.% Hydroquinone, 0.007 wt.% methoxyquinone and 0.39 wt.% other components were obtained from the top of the reaction column p investments at a speed of 437.9 kg / h. To the heat exchanger for cooling the decomposition gas, the liquid obtained by cooling the decomposition gas was returned at a rate of 800 kg / h.

As oxygen or the like. air was supplied at a speed of 3 Nm ³ / h and nitrogen as a diluting inert gas at a speed of 3 Nm ³ / h into the gas pipe 44a of the upper part of the column, as shown in FIG. 11.

After continuous operation for 3 months, the reactor was stopped and the interior of the decomposition reaction column was examined. No polymer was observed in the interior of the decomposition reaction column or in a heat exchanger to cool the gas of the top of this column.

COMPARATIVE EXAMPLE d1

The work was carried out using the same setup as in example d1, except that oxygen or the like. air at a speed of 6 Nm ³ / h and nitrogen as a diluting inert gas at a speed of 6 Nm ³ / h were supplied to the recirculation line 43a before the heat exchanger 43 for heating, i.e. not into the gas pipe 44a of the top of the column.

After continuous operation for 3 months, the reactor was stopped and the interior of the decomposition reaction column was examined. The polymer was observed in the interior of the decomposition reaction column. No polymer was observed in heat exchanger 44 to cool the gas of the top of this column.

COMPARATIVE EXAMPLE d2

The operation of the reactor was carried out in the same manner as in comparative example d1, except that air was supplied at a speed of 3 Nm ³ / h and nitrogen was supplied as a diluting inert gas at a speed of 3 Nm ³ / h.

After continuous operation for 3 months, the reactor was stopped and the interior of the decomposition reaction column was examined. The polymer was observed in the interior of the decomposition reaction column, but its amount was approximately 1/3 of this amount in comparative example d1. In addition, the polymer was also observed in a heat exchanger for cooling the gas of the upper part of this column.

EXAMPLE d2

The decomposition of the high boiling liquid was carried out using the same apparatus as in example d1. The high boiling liquid had the following composition: 5.3 wt.% Acrylic acid, 10 wt.% Maleic acid, 42.4 wt.% Dimer of acrylic acid (acryloxy propionic acid), 1.3 wt.% Hydroquinone and 1 wt.% Phenothiazine and this liquid was supplied at a rate of 580 kg / h.

The decomposition reaction was carried out at a reaction pressure of 72 kPa at a decomposition temperature of 190 ° C. for a retention time of 1 hour, whereby a decomposition gas containing 85.1 wt.% Acrylic acid, 8.7 wt.% Maleic acid, 2.1 wt. % acrylic acid dimer (acryloxypropionic acid), 0.03 wt.% hydroquinone and 4.07 wt.% other components, from the top of the decomposition reaction column at a rate of 449.5 kg / h. To the heat exchanger for cooling the decomposition gas, the liquid obtained by cooling the decomposition gas was returned at a rate of 500 kg / h.

As oxygen or the like. air was supplied at a speed of 2 Nm ³ / h into the gas pipe 44a of the upper part of the column, as shown in FIG. 11.

After continuous operation for 3 months, the reactor was stopped and the interior of the decomposition reaction column was examined. No polymer was observed in the interior of the decomposition reaction column or in a heat exchanger to cool the gas of the top of this column.

COMPARATIVE EXAMPLE d3

The operation of the reactor was carried out using the same installation as in example d1, except that as oxygen or the like. air was supplied at a speed of 3 Nm ³ / h to the recirculation line 3a.

After continuous operation for 3 months, the reactor was stopped and the interior of the decomposition reaction column was examined. The polymer was observed in the interior of the decomposition reaction column. In addition, the polymer was also observed in a heat exchanger for cooling the gas of the upper part of this column.

EXAMPLE e1

Liquid recovered from the thermal decomposition reactor Acrylic Acid: 88 wt.% Acrylic Acid Dimer: 1.1 wt.% Acrylic Acid Trimer: 100 wt. million d Maleic acid: 1.5 wt.% Maleic anhydride: 5.7 wt.%

Water:

Water

------------------------------ (molar ratio) = 0.34

maleic acid +

maleic anhydride x 2

Operation

20 ml of the liquid of the above composition was placed in a test tube with a stopper and subjected to horizontal shaking in an oil bath at 70 ° C for 2 hours with an amplitude of 3 cm at a cycle of 1 sec. Then, toluene was added in an amount of two volumes by volume ratio and this mixture was left to stand at 35 ° C for 1 hour, after which the precipitated solid was separated. The solids were separated at room temperature using vacuum filtration using filter paper with 1 μ holes. The separated solid contained mixed crystals of 96% maleic acid and maleic anhydride and acrylic acid and very small amounts of impurities impregnated therein. The concentration of maleic acid together with maleic anhydride after removal of the solid was 2.6 wt.%, As was calculated by excluding the added toluene.

EXAMPLE e2

The separation of the solid was carried out under the same conditions as in Example e1, except that no toluene was added. The concentration of maleic acid together with maleic anhydride after removal of the solid was 3.2 wt.%.

EXAMPLE e3

The operation was carried out under the same conditions as in example e1, adding 0.08 wt.% Water when heated at 70 ^about C. The amount of water this time was:

Water

------------------------------ (molar ratio) = 0.38

maleic acid +

maleic anhydride x 2

The concentration of maleic acid together with maleic anhydride after removal of the solid was 2.4 wt.%.

COMPARATIVE EXAMPLE e1

The operation was conducted under the same conditions as in Example E2, except that 3 wt% added water while heating at 70 ^C. The amount of water at this time was.:

Water

------------------------------- (molar ratio) = 1.63

maleic acid +

maleic anhydride x 2

No precipitation of the solid was observed, and the concentration of maleic acid together with maleic anhydride was unchanged at 7.2% by weight.

EXAMPLE f1

The decomposition reaction of the high boiling liquid was carried out using the apparatus shown in FIGS. 12 and 13.

The high boiling liquid had the following composition: 22 wt.% Butyl acrylate, 67 wt.% Butyl β-butoxypropionate, 4 wt.% Butyl acryloxy propionate, 2 wt.% Butyl β-hydroxypropionate, 3 wt.% Hydroquinone and 2 wt.% Methoxyquinone and this liquid was supplied at a rate of 580 kg / h.

. The catalyst decomposition of 1 wt% - of the aqueous sulfuric acid solution was fed in a weight ratio of 10% relative to the liquid medium and decomposition reaction was carried out under a reaction pressure of 100 kPa at a decomposition temperature of 190 ^{° C} for a retention time of 1 hour whereby the residue of the reaction, containing 11.7 wt.% butyl acrylate, 68.5 wt.% butyl-β-butoxypropionate, 2 wt.% butyl acryloxy propionate, 0.3 wt.% butyl-β-hydroxypropionate, 8.7 wt.% hydroquinone, 5.8 wt.% methoxyquinone, 0.8 wt.% butanol and 2.9 wt.% sulfuric acid, obtained with co awn 200.1 kg / hr and discharged from the lower part.

The liquid of the lower part of the decomposition reaction column was discharged from the liquid discharge line 62 of the lower part connected in the lowest position of this lower part. The liquid level meter H ₁ at the bottom was a liquid level meter such as a differential pressure meter and was installed as shown in FIG. 13 (1). The angle of attachment α between the high-pressure side detection line 11 and the bottom liquid discharge line was set as an angle of 45 °.

After continuous operation for 6 months, the reactor was stopped and the short high pressure side detection pipe 11a and the high pressure side detection pipe 11b of the high pressure side detection line 11 of the liquid level meter H _{1 were} examined. As a result of such an examination, no deposits were observed in any of them.

COMPARATIVE EXAMPLE f1

The work was carried out under the same conditions as in example f1, except that the high pressure side detection line 11 of the liquid level meter H ₁ , such as the differential pressure meter H _{1, was} connected horizontally to the wall of the lower side of the decomposition reaction column 6A. After 2 months of operation, cavitation unexpectedly occurred in the lower B ₁ pump. The operation of the decomposition reaction column 6A was immediately stopped and the interior was inspected, whereby it was found that no liquid was present in the lower part of the decomposition reaction column 6A and the reading _of the liquid level meter H ₁ was erroneous.

The short high pressure side detection conduit 11a and the high pressure side detection conduit 11b of the high pressure side detection line 11 of the liquid level meter H _{1 were} examined, whereby it was found that the short conduit 11a and conduit 11b were plugged.

COMPARATIVE EXAMPLE f2

The work was carried out under the same conditions as in example f1, except that the high pressure side detection line 11 of the liquid level meter H _{1 of} the type differential pressure meter H _{1 was} connected at an angle of attachment α 45 ° to the wall of the lower side of the reaction column 6A decomposition.

After 3 months of operation, cavitation unexpectedly occurred in the lower part B ₁ pump. The operation of the decomposition reaction column 6A was immediately stopped and the interior was inspected. As a result, it was found that the liquid was not present in the lower part of the decomposition reaction column A, and the reading _of the liquid level meter H ₁ was erroneous.

The short high pressure side detection conduit 11a and the high pressure side detection conduit 11b of the high pressure side detection line 11 of the liquid level meter H _{1 were} examined, whereby it was found that the short conduit 11a and conduit 11b were plugged.

EXAMPLE f3

The evaporation operation satisfying the following conditions was carried out using a film evaporator.

As a composition of the starting material (crude acrylic monomer), a mixture containing 66.6 wt.% Acrylic acid, 8.0 wt.% Maleic acid, 25.0 wt.% Acrylic acid oligomer, 0.5 wt.% Hydroquinone and 0 , 5 wt.% Phenothiazine, was fed at 85 ° C at a speed of 3000 kg / h.

This operation was carried out at a pressure of the upper part of the column of 9 kPa and at a pressure of the lower part of 10 kPa at a temperature of the upper part of the column 95 ° С and a temperature of the lower part 98 ° С, whereby 53% of the added amount was unloaded from the upper part of the column to obtain acrylic acid with purity of at least 88 wt.%.

A mixture containing 41.1 wt.% Acrylic acid, 10.9 wt.% Maleic acid, 46.16 wt.% Acrylic acid oligomer, 0.92 wt.% Hydroquinone and 0.92 wt.% Phenothiazine was unloaded .

The liquid of the lower part of the film evaporator was discharged using the liquid discharge line of the lower part connected to the lowest position of the lower part. The liquid level meter at the bottom was a liquid level meter such as a differential pressure meter and was installed as shown in FIG. 13 (1). The angle of attachment α between the high-pressure side detection line 11 and the bottom liquid discharge line was set as an angle of 45 °.

After conducting a continuous operation for 6 months, the operation was stopped and the short high pressure side detection conduit 11a and the high pressure side detection conduit 11b of the liquid level meter detection line 11 were examined. As a result, it was found that in none of them there was a deposit.

COMPARATIVE EXAMPLE f3

The evaporation operation was carried out under the same conditions as the conditions in example f2, except that the high pressure side detection line 11 of a liquid level meter such as a differential pressure meter was connected to the wall of the lower side of the film evaporator.

After operating for 1 month, cavitation unexpectedly occurred in the lower pump. The operation of the film evaporator was stopped and the internal space was examined. It was found that liquid was not present in the film evaporator and the reading of the liquid level meter was erroneous.

The short high pressure side detection conduit 11a and the high pressure side detection conduit 11b of the high pressure side detection line 11 of the liquid level meter were examined, whereby it was found that the short conduit 11a and conduit 11b were plugged.

INDUSTRIAL APPLICABILITY

but. According to this invention, in the process of extracting a valuable substance by heating and decomposing a high boiling material containing a Michael addition product of (meth) acrylic acids, the remainder of the decomposition reaction can be transported without clogging from the decomposition reactor to a storage tank, whereby continuous operation for a long time will be possible time.

b. Further, according to a method for decomposing a by-product formed during the preparation of the (meth) acrylic acids of the present invention, during the recovery of a valuable substance such as (meth) acrylic acid, (meth) acrylic acid ester and alcohol, thermal decomposition using reactive distillation a by-product system formed during the production of (meth) acrylic acid and / or a by-product formed during the production of (meth) acrylic acid ester, it becomes possible to continuously work in stable conditions with the prevention of adhesion, deposition or accumulation of solid matter and maintaining the extraction rate of this valuable substance at a high level without the occurrence of such problems as clogging (clogging) or an increase in the pressure drop of the distillation column due to a violation of the gas-liquid contact state. In addition, a distillation column having a very simple structure can be used in the present invention, which would be advantageous in that the cost of this structure will be very low compared to other distillation columns using plates or packing material.

from. Further, according to the present invention, it is possible to carry out the decomposition treatment of the Michael addition product formed by-products in the step of producing (meth) acrylic acid and / or (meth) acrylic acid ester under stable conditions, whereby (meth) acrylic acid, ether (meth ) acrylic acid and alcohol, etc. can be extracted at high extraction rates.

d. Further, according to this invention, a gas containing acrylic acid obtained by catalytic oxidation of propane or propylene is reacted with a solvent for collecting acrylic acid in the form of a solution containing acrylic acid, the resulting solution containing acrylic acid is distilled to purify acrylic acid, while the acrylic acid oligomer is liquid the bottom of the acrylic acid oligomer obtained from the purification column is thermally decomposed and acrylic acid having low maleic acid content.

e. Further, if a method for establishing a liquid level meter is used in the apparatus for producing an easily polymerizable compound, it is possible to prevent the flow of solid matter present in the liquid of the easily polymerizable compound into the detection line of the high pressure side of the liquid level meter. Thus, this part of the detection of the liquid level meter will not become clogged with the measured liquid, as a result of which it will be possible to accurately measure the liquid level meter, whereby this unit can operate for an extended period of time.

Claims (43)

1. The method of producing (meth) acrylic acids by catalytic oxidation of propane, propylene or isobutylene in the vapor phase with the separation of the final product and the formation of a high-boiling mixture directed to decomposition as a by-product, characterized in that the high-boiling mixture, which contains the Michael addition product containing water, alcohol or (meth) acrylic acid attached to the (meth) acryloyl group is decomposed in a thermal decomposition reactor while distilling the decomposition products into distillation llyatsionnoy tower from which is taken as a distillate (meth) acrylic acid, and a liquid stream comprising the resulting residue decomposition forcibly attach peripheral direction before discharging it from the reactor. 2. The method according to claim 1, characterized in that the peripheral direction is imparted to the fluid flow by mixing blades mounted in the decomposition reactor. 3. The method according to claim 1, characterized in that the liquid stream is provided with a peripheral direction with the liquid supplied from the outside of the decomposition reactor. 4. The method according to claim 3, characterized in that the liquid supplied from the outside of the decomposition reactor is a high boiling material supplied as a starting material, or the liquid returned by the liquid stream discharged from the decomposition reactor. 5. The method according to any one of claims 1 to 4, characterized in that the liquid stream is periodically discharged from the decomposition reactor. 6. The method according to any one of claims 1 to 4, characterized in that during the extraction of a valuable substance by distillation, as well as thermal decomposition of the high-boiling mixture, the distillation is carried out using a distillation column, which inside is equipped with disk-and-toroid plates. 7. The method according to any one of claims 1 to 4, characterized in that oxygen-containing gas is added to the distillate from the decomposition reactor. 8. The method according to any one of claims 1 to 4, characterized in that from the liquid to be added to the thermal decomposition reactor, or from the liquid extracted from the thermal decomposition reactor, maleic acid contained in said liquid is precipitated and separated. 9. The method according to any one of claims 1 to 4, characterized in that a liquid level meter is installed on the thermal decomposition reactor and a line for detecting the high pressure side of the liquid level meter is connected to the liquid discharge line of the decomposition reactor. 10. A method for producing (meth) acrylic acids by catalytic oxidation of propane, propylene or isobutylene in the vapor phase and, if necessary, carrying out an esterification step to produce an (meth) acrylic acid ester by reaction with alcohol, with the formation of high-boiling by-products subjected to thermal decomposition and distillation characterized in that at the time when the high boiling mixture (hereinafter referred to as high boiling material) containing the Michael addition product is decomposed in the decomposition reactor for the attraction of (meth) acrylic acids, the liquid reaction residue is discharged by forcing a liquid stream in the peripheral direction to give this liquid reaction residue in the decomposition reactor. 11. The method according to claim 10, characterized in that the peripheral direction is imparted to this liquid stream by means of mixing blades installed in the decomposition reactor. 12. The method according to claim 10 or 11, characterized in that these mixing blades are anchor blades, multi-stage bladed blades, multi-stage inclined bladed blades or trellised blades. 13. The method according to claim 10 or 11, characterized in that the design of the mixing blades is such that on the rotational shaft mounted vertically in the central part of the reactor, the flow type radial blades are attached in two or more steps in the direction of the rotation axis, so that the blades adjacent to the direction of the axis of rotation are located relative to the direction of the axis of rotation so that their phases are offset from each other by no more than 90 °, and the lower part of one of the blades of the upper stage adjacent to the axis rotation, located below the highest part of the lower stage blade. 14. The method according to claim 10, characterized in that the peripheral direction is given to the liquid stream by the liquid supplied from the outside of the decomposition reactor. 15. The method according to claim 10 or 14, characterized in that the liquid supplied from the outside of the decomposition reactor is a high boiling material supplied as a starting material, or the liquid returned from the liquid reaction residue discharged from the decomposition reactor. 16. A method for producing (meth) acrylic acid, which is a method for producing acrylic acid, methacrylic acid or ester of (meth) acrylic acid by means of a reaction step comprising catalytic vapor phase oxidation of propylene, propane or isobutylene and then, if necessary, a reaction step, comprising an esterification step, characterized in that while the high boiling mixture (hereinafter referred to as high boiling material) containing the Michael addition product is decomposed in the decomposition reactor for I extract (meth) acrylic acids, the liquid reaction residue is periodically discharged from the decomposition reactor. 17. The method according to clause 16, wherein the unloading stop time is 5 s - 5 min and the unloading time is 2 s - 5 min. 18. The method according to p. 16 or 17, characterized in that the liquid high-boiling material is continuously fed into the decomposition reactor and (meth) acrylic acids are continuously discharged from the vapor phase. 19. The method of decomposition of a by-product formed by the production of (meth) acrylic acid by oxidation of propylene or isobutylene or by the production of an (meth) acrylic acid ester by reaction of an acid with alcohol, by introducing a by-product into a thermal decomposition reactor equipped with a distillation column, while decomposition and distillation with the extraction of a valuable product, characterized in that as the specified distillation column using a distillation column, which is equipped with dishes such as disk-and-donut. 20. The method according to claim 19, characterized in that the by-product formed during the production of (meth) acrylic acid is the liquid of the lower part of the fractionation column of the final stage of the production of (meth) acrylic acid, and the by-product formed during the production of ether ( meth) acrylic acid is the liquid of the lower part of the fractionation column for separating the high boiling fraction in the purification stage of the (meth) acrylic acid ester. 21. The method according to claim 19 or 20, characterized in that the by-product formed during the production of (meth) acrylic acid, and / or the by-product formed during the preparation of the (meth) acrylic acid ester, contains a Michael addition product, containing water, alcohol or (meth) acrylic acid attached to a (meth) acryloyl group. 22. The method according to claim 19 or 20, characterized in that the temperature of the thermal decomposition reaction is 120-280 ° C, and the thermal decomposition reaction time is 0.5-50 hours. 23. The method of decomposition of a by-product formed by the production of (meth) acrylic acids by oxidation of propylene or isobutylene or by the production of an (meth) acrylic acid ester by reaction with alcohol in a decomposition reactor with distillation of the decomposition product, characterized in that to the distillate from the decomposition reactor add oxygen or oxygen-containing gas. 24. The method according to item 23, wherein the by-product formed during the production of (meth) acrylic acid is the liquid of the lower part of the fractionation column of the final stage of the production of (meth) acrylic acid, and the by-product formed during the production of ether ( meth) acrylic acid, is the liquid of the lower part of the fractionating column of the final stage of the production of ester of (meth) acrylic acid or precipitation of the separation column of (meth) acrylic acid. 25. The method according to item 23 or 24, characterized in that the by-product to be decomposed contains a Michael addition product. 26. The method according to item 23 or 24, characterized in that the gas containing oxygen is air or oxygen diluted with an inert gas. 27. The method according to any one of claims 1, 10, 16, 19 or 23, characterized in that the gas containing oxygen is added to the discharge line for the distillate from the decomposition reactor or to the top of the decomposition reactor. 28. A method of producing acrylic acid by catalytic oxidation of propane or propylene by contacting the gaseous reaction products with a solvent to extract acrylic acid in the form of a solution containing acrylic acid, and then purifying the acid by distillation of the solution, characterized in that the residues obtained from the bottom of the fractionation column for acrylic acid, or a liquid obtained by heating and concentrating such residues, is fed to a thermal decomposition reactor to decompose the oligomer acrylic acid in the liquid and the resultant acrylic acid is recovered in a purification step in which from the liquid to be supplied to the thermal decomposition reaction vessel, or a liquid extracted from the reactor for thermal decomposition, and separating the precipitated maleic acid contained in the liquid. 29. The method according to p. 28, characterized in that the composition of the liquid to be supplied to the thermal decomposition reactor, or the liquid extracted from the thermal decomposition reactor, is regulated to obtain a solution containing at least 70 wt.% Acrylic acid, 1.6 -28 wt.% Maleic acid and / or maleic anhydride and water having a molar ratio

and maleic acid is precipitated at 20-70 ° C in the range of 0.5-5 hours, followed by filtration and separation. 30. The method according to p. 28 or 29, characterized in that during the separation operation of maleic acid add an aliphatic or aromatic hydrocarbon in a 1 / 2-4-fold volume ratio based on the volume of the solution of extracted acrylic acid. 31. The method according to p. 30, wherein the added hydrocarbon is a solvent used to collect acrylic acid-containing gas, or an azeotropic agent used for dehydration distillation purification of acrylic acid. 32. Installation for producing (meth) acrylic acid by extracting it from high-boiling by-products formed during the oxidation of propylene, including a thermal decomposition reactor and a distillation column, level meters and discharge lines for liquids containing easily polymerizable compounds, characterized in that where the liquid accumulates, a liquid level meter is installed that records the pressure drop, and the detection line of the high pressure side of this liquid level meter is connected to discharge for the accumulated liquid. 33. The apparatus of Claim 32, wherein the angle of attachment α between the detection line of the high pressure side and the liquid discharge line is 5-90 °. 34. The apparatus of claim 32, wherein the aspect ratio D ₂ / D ₁ is 1-20, where D ₁ is the diameter of the pipeline of the high pressure side detection line, and D ₂ is the diameter of the pipeline of the liquid discharge line. 35. Installation according to p. 32, characterized in that the liquid discharge line is connected to the distillation column, the reflux tank of the distillation column, a decomposition reaction column, a film evaporator, a condensed gas liquid tank of the upper part of the column, a vertical storage tank, a horizontal tank for storage or tank. 36. Installation according to any one of paragraphs.32-35, characterized in that the detection line of the high pressure side and / or the detection line of the low pressure side of the liquid level meter is heated or heated. 37. Installation according to claim 32 or 35, characterized in that the detection line of the high pressure side and / or the detection line of the low pressure side of the liquid level meter are connected to the gas and / or liquid inlet. 38. The apparatus of claim 32 or 35, wherein the easily polymerizable compound is (meth) acrylic acid or its ester, and the liquid to be measured by a liquid level meter contains at least one compound selected from an acrylic acid dimer, β esters - (meth) acryloxypropionic acid, β-alkoxypropionic acid esters, β-hydroxypropionic acid and β-hydroxypropionic acid esters formed as by-products from the production of (meth) acrylic acid or its ester. Priority on points: May 16, 2002 according to claims 1-4, 10-15, 16-18; 12/04/2001 according to claims 5-9, 32-38; 12/25/2001 according to claims 19-22; 12/05/2001 according to claims 23-27; 12/18/2001 according to claims 28-31.

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