JP2002193875A - Method for recovering methacrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably recovering methacrylic acid from a residual liquid of a distillation bottom derived from producing the methacrylic acid, after distilling off the methacrylic acid through purification means such as extraction and distillation, and further the method by which the recovery of the metacrylic acid in a raffinate water derived from recovering the methacrylic acid from an aqueous solution of the methacrylic acid by the extraction operation is simultaneously carried out. SOLUTION: The methacrylic acid is recovered by distilling a mixed liquid obtained by mixing a material containing 5-95 mass% methacrylic acid with an aqueous solution containing 0.01-10 mass% methacrylic acid, and regulated so that the mass of the water included in the mixed liquid becomes 0.1-15 times as much as that of the methacrylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering methacrylic acid, and more particularly, to a method for distilling methacrylic acid together with water from a bottom liquid produced during distillation separation of methacrylic acid (hereinafter referred to as a distillation bottom liquid). The present invention relates to a method for recovering methacrylic acid.

[0002]

2. Description of the Related Art When methacrylic acid is produced industrially,
Purification of methacrylic acid is generally performed by ordinary purification means such as extraction and distillation. After the methacrylic acid is distilled off through such a purification step, the residue in the distillation still is basically discharged as a waste liquid.However, there is a case where a large amount of methacrylic acid is still contained in the residue in the distillation still. Many. This is because the distillation bottoms contain high-boiling components, polymers, tar-like substances, and other components. If the height is increased, the viscosity of the distillation bottom liquid increases, which not only causes blockage of pipes and deterioration of heat efficiency of heat conduction surfaces such as a reboiler of a distillation column, but also causes a risk of causing polymerization of methacrylic acid and the like. .

[0003] Means for recovering methacrylic acid from the distillation bottoms include a method of simply heating the distillation bottoms, a method of performing steam distillation, addition of methanol, and the use of sulfuric acid or a strongly acidic cation exchange resin as a catalyst. Of methacrylic acid and distilling it as methyl methacrylate (JP-B-7-10800, JP-B-7-61881)
Publication), an organic solvent selected from aliphatic hydrocarbons, alicyclic hydrocarbons or aromatic hydrocarbons is added, and the precipitated polymer and some high-boiling components are removed by filtration. Method for recovering methacrylic acid (Japanese Patent Publication No. 7-393)
No. 67) is known.

[0004] However, since the distillation bottom liquid used as a raw material for recovery contains a large amount of high-boiling components and the like, the simple heating method reduces the mass of methacrylic acid in the bottom liquid obtained as a result of the recovery. If the recovery operation is performed in an area of 30% or less with respect to the mass of the liquid, the viscosity of the bottom liquid becomes too high, which not only causes blockage of the pipe and deterioration of the heat efficiency of the heat conducting surface, but also causes polymerization of methacrylic acid and the like. Therefore, there is a problem that it is necessary to frequently stop the apparatus and perform a treatment such as cleaning. Further, the method of performing steam distillation also involves a problem that the concentration of the distilled methacrylic acid aqueous solution is necessarily reduced because excessive steam must be blown. In addition, in the method of esterifying and recovering methacrylic acid, when sulfuric acid is used as a catalyst, sulfuric acid is contained in the bottom liquid obtained as a result of the recovery of methacrylic acid. And increase equipment and utility costs. Similarly, when a strongly acidic cation exchange resin is used as a catalyst, an oxidizing agent that promotes the oxidation of the resin matrix of the ion exchange resin and the decomposition of the exchange group, the active site of the exchange group is made inactive by being adsorbed to the resin matrix. Contaminants and the like contained in the distillation bottoms cause irreversible deterioration of the ion exchange resin, resulting in frequent renewal of the ion exchange resin, which is economical. Is hard to say. Furthermore, in a method of adding an organic solvent, removing a polymer and a high-boiling component precipitated by filtration and recovering methacrylic acid from the organic solvent layer, the organic solvent layer is returned to the methacrylic acid purification step, but distillation is performed. Since the high-boiling components contained in the bottom liquid are easily dissolved in the added organic solvent, a large amount of the high-boiling components is returned to the refining process, which cannot be said to be advantageous.

[0005] As described above, the conventional method of recovering methacrylic acid from the residue of the distillation still has various problems, and further improvements and improvements are desired.

On the other hand, when methacrylic acid is produced industrially, methacrylic acid is generally often recovered from an aqueous methacrylic acid solution by an extraction operation. In this extraction operation, an organic solvent selected from aliphatic hydrocarbons, alicyclic hydrocarbons and aromatic hydrocarbons and having a boiling point lower than that of water is often used as an extractant. However, no matter what kind of extractant is selected, the extraction ability of methacrylic acid is limited, and the extraction residual water after the extraction operation necessarily contains a certain amount of methacrylic acid. In general, this raffinate is treated as wastewater while containing methacrylic acid after separating and recovering the organic solvent as required. Therefore, in order to improve the productivity, it is necessary to increase the extraction efficiency of methacrylic acid or separately recover methacrylic acid from raffinate.

However, even if the number of extraction stages is increased or the amount of extractant is increased in order to increase the extraction efficiency of methacrylic acid, the increase in equipment cost and the separation of methacrylic acid from the extractant are not attributable to the effect of improving the extraction efficiency. The disadvantages of increased utility costs are greater and less efficient. Also, even if methacrylic acid is separately recovered from the raffinate by distillation or the like, the concentration of methacrylic acid contained in the raffinate is considerably small,
Similarly, the increase in equipment cost and utility cost is larger than the effect of recovering methacrylic acid, which is not an effective method. There are several other recovery methods.However, when methacrylic acid is recovered from an aqueous methacrylic acid solution by an extraction operation, the problem that methacrylic acid is discharged together with the raffinate water has not been solved, and further research and development has been carried out. It is necessary.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for recovering methacrylic acid from a residue in a distillation still after removing methacrylic acid through a purification means such as extraction or distillation, which occurs in the production of methacrylic acid. It is an object of the present invention to provide a method for recovering methacrylic acid in raffinate water generated when methacrylic acid is recovered by an extraction operation from an aqueous methacrylic acid solution at the same time.

[0009]

The above object can be solved by the present invention described below. (1) A methacrylic acid-containing material containing 5 to 95% by mass of methacrylic acid is mixed with an aqueous methacrylic acid solution containing 0.01 to 10% by mass of methacrylic acid, and the mass of water contained in the mixture is reduced to the mass of methacrylic acid. A method for recovering methacrylic acid, wherein the methacrylic acid is recovered by distilling the methacrylic acid having a mass of 0.1 to 15 times the mass. (2) A bottom liquid generated when the methacrylic acid-containing substance is obtained by distilling an organic solvent and a low-boiling substance from a mixed liquid of methacrylic acid and an organic solvent by distillation, and then distilling methacrylic acid. (1) The method for recovering methacrylic acid according to (1) above, which is a bottom liquid 2 obtained by separating at least a part of methacrylic acid from the bottom liquid 1. (3) raffinate generated when the aqueous methacrylic acid solution is used to extract methacrylic acid with an organic solvent from a methacrylic acid-absorbed liquid obtained by contacting water with a methacrylic acid-containing gas obtained by a gas phase reaction. 1 or the method for recovering methacrylic acid according to the above (1) or (2), which is raffinate water 2 obtained by separating at least a part of the organic solvent from the raffinate water 1.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to
A methacrylic acid-containing material containing 5% by mass, for example, a methacrylic acid aqueous solution containing 0.01 to 10% by mass of methacrylic acid in a distillation bottom residue after distilling off methacrylic acid through a purification means such as extraction or distillation. And recovering methacrylic acid from the mixture by distillation. In this manner, methacrylic acid can be stably recovered from the bottom of the distillation still containing the high boiling components, the polymer, the tar-like substance, and other components without producing a polymer. Moreover, according to this method, the mass of methacrylic acid in the bottom liquid obtained as a result of the recovery of methacrylic acid is 30% or less of the mass of the bottom liquid, that is, the conventional method in which methacrylic acid is simply recovered by heating. Even if methacrylic acid is recovered within a range that cannot be operated stably by the method of the above, the generation of a polymer in the bottom liquid and an increase in the viscosity of the bottom liquid are suppressed, and as a result, the conventional method of simply heating Higher methacrylic acid recovery can be achieved.

Further, raffinate water 1 generated when methacrylic acid is extracted with an organic solvent from a methacrylic acid-absorbed solution obtained by bringing a methacrylic acid-containing gas obtained by a gas phase reaction into contact with water, or If the raffinate water 2 obtained by separating at least a part of the organic solvent from the raffinate water 1 is used as a methacrylic acid aqueous solution, the methacrylic acid can be recovered from the raffinate water simultaneously with the recovery of methacrylic acid from the distillation bottom liquid. Since it can be performed, there is a great advantage in terms of equipment costs and utility costs as compared with the case where these are collected individually.

Hereinafter, the present invention will be described in detail.

The methacrylic acid-containing substance to which the present invention is to recover methacrylic acid contains 5-95% by mass of methacrylic acid. As the methacrylic acid-containing substance, the bottom liquid 1 generated when the methacrylic acid is distilled off by further distilling the mixture obtained by distilling the organic solvent and low-boiling substances from the mixture of methacrylic acid and the organic solvent, or The bottom liquid 2 obtained by separating at least a part of methacrylic acid from the bottom liquid 1 is preferable. As the liquid mixture of the methacrylic acid and the organic solvent, an extract obtained by extracting methacrylic acid with an organic solvent from a methacrylic acid-absorbed liquid obtained by contacting a methacrylic acid-containing gas obtained by a gas phase reaction with water is preferable. No.

Examples of the methacrylic acid-containing substance include a process for synthesizing methacrolein using a gas phase catalytic oxidation reaction from isobutylene or tert-butyl alcohol or a mixture of both, and a gas phase catalytic oxidation reaction using methacrolein as a raw material. A methacrylic acid produced by cooling an oxidation product obtained through a synthesis step of methacrylic acid using, or a synthesis step of performing both of the two-step synthesis reaction, and absorbing the oxidized product in a liquid containing water as a main component. For aqueous solution, extraction of methacrylic acid with organic solvent,
The distillation bottom 1 produced in the step of recovering the solvent and further purifying methacrylic acid in which the low-boiling components and the high-boiling components are removed by distillation.

In the present invention, it is also preferable to use the bottom liquid 2 obtained by separating at least a part of methacrylic acid from the bottom liquid 1 as a methacrylic acid-containing substance. The present invention is more effective when the content of methacrylic acid is low, and it is more effective to recover the bottom liquid 1 than to recover methacrylic acid from the addition of an aqueous methacrylic acid solution to the bottom liquid 1 having a relatively high methacrylic acid content. It is preferable to recover methacrylic acid from a solution obtained by adding a methacrylic acid aqueous solution to the bottom liquid 2 whose content has been reduced by collecting methacrylic acid by a simple heating method or the like. In addition, the utility cost can be reduced in this manner.

The composition of the distillation bottoms varies depending on the synthesis method and the degree of methacrylic acid distillation in the step of purifying methacrylic acid.
High boiling components, polymers, tar substances, and other components are 95 to 5% by mass. The high-boiling components in the distillation bottoms are polymerization inhibitors used mainly in the purification process of crotonic acid, maleic acid, citraconic acid, paratolualdehyde and methacrylic acid. As this polymerization inhibitor,
Hydroquinone, phenothiazine, methoquinone, cresol, t-butylcatechol, diphenylamine, tetraalkylthiuram disulfide (the alkyl group is any of methyl, ethyl, propyl or butyl;
The same or different ones), methylene blue and the like. The polymer is mainly a polymer of methacrylic acid or methacrolein.

As described above, the present invention is particularly effective when the methacrylic acid content is low, and is particularly preferably used when the methacrylic acid-containing material has a methacrylic acid content of 20% by mass or less.

The aqueous methacrylic acid solution used in the present invention contains 0.01 to 10% by mass of methacrylic acid. As the methacrylic acid aqueous solution, raffinate water 1 generated when methacrylic acid is extracted with an organic solvent from a methacrylic acid-absorbed liquid obtained by contacting a methacrylic acid-containing gas obtained by a gas phase reaction with water, or Preferably, raffinate 2 is obtained by separating at least a part of the organic solvent from raffinate 1.

Examples of the aqueous methacrylic acid solution include a process for synthesizing methacrolein using isobutylene or tert-butyl alcohol or a mixture of both as a raw material and a gas phase catalytic oxidation reaction using methacrolein as a raw material. A methacrylic acid aqueous solution generated by cooling an oxidation product obtained through a synthesis step of methacrylic acid to be used or a synthesis step of performing the two-step synthesis reaction, and absorbing the oxidized product into a liquid containing water as a main component. In contrast, raffinate water 1 generated by extracting methacrylic acid with an organic solvent, or raffinate water 2 from which an organic solvent is further separated and recovered. Examples of the organic solvent used for extraction include ethers such as petroleum ether, unsaturated cyclic compounds such as benzol and toluene, ketones such as methyl ethyl ketone, halogenated hydrocarbons such as chloroform, carbon tetrachloride, and trichloroethylene, isopropyl acetate, and methacrylic acid. Esters such as methyl, and aliphatic hydrocarbons such as heptane. As a method of further separating and recovering the organic solvent from the raffinate 1, distillation and the like are available.

The composition of the raffinate depends on the synthesis method and operating conditions, but is usually 70 to 98% by weight of water, 10 to 0.01% by weight of methacrylic acid, and 20 to 1% of other components.
% By mass. Other components are mainly acetic acid and acrylic acid.

Next, an embodiment of the present invention will be described with reference to the apparatus diagram shown in FIG. However, the present invention is not limited to FIG.

The recovery of methacrylic acid from the methacrylic acid-containing substance, preferably the bottom liquid of the distillation still and the aqueous methacrylic acid solution, preferably the raffinate, is carried out in the evaporator 1. In this description, a can-type evaporator is used, but a distillation tower with a reboiler, a thin-film evaporator, and other general evaporators may be used.

The distillation bottom liquid, which is a raw material for recovering methacrylic acid, is supplied from a distillation bottom liquid supply line 10 to a raw material tank 6. Similarly, raffinate water, which is a raw material for collecting methacrylic acid, is supplied from a raffinate supply line 11 to a raw material tank 6. In the raw material tank 6, the residual liquid of the distillation still and the raffinate are 0.1 to 0.1 mass of the methacrylic acid containing the mass of the contained water.
It is prepared to be 15 times, preferably 5 times or more or 13 times or less. If the water content is smaller than this range, the recovery of methacrylic acid proceeds within a range in which the weight of methacrylic acid in the bottom liquid resulting from the method of the present invention is 30% or less of the weight of the bottom liquid. In this case, it is difficult to keep the concentration of water in the bottom liquid in the range described below, so that the viscosity of the bottom liquid becomes too high, which not only hinders the operation of the apparatus, but also causes methacrylic acid or the like. Polymerization may occur in the equipment. Also, if the water content is larger than this range, the methacrylic acid concentration in the recovered raw material will be very low, so the equipment cost and utility cost required for recovery will be larger than the merit of recovering methacrylic acid. Too much and not economic.

The prepared recovered raw material is supplied to the raw material sending line 1
The liquid is sent to the evaporator 1 through 2 and 13. The raw material supplied to the evaporator 1 is heated by the heating jacket 3. Along with this, mainly methacrylic acid and water evaporate, are cooled by the condenser 5, and are distilled out from the distillation line 14. In this distillate, high-boiling components, polymers and tar-like substances contained in the distillation bottoms are hardly distilled. The concentration of methacrylic acid in the distillate is not constant depending on the composition of the raw material to be recovered and the operating conditions.
% By mass. This distillate may be separately recovered by extraction, distillation, or the like, or may be returned to the step of extracting methacrylic acid from the aqueous methacrylic acid solution with an organic solvent. Further, the bottom liquid generated by the recovery of methacrylic acid is discharged from the bottom line 16, and is usually separately treated as waste liquid. This bottom liquid mainly contains the above-mentioned high boiling components, polymers, tar substances, water and other components.

By the way, the distillation bottom residue supply line 10 and
The raw material sending lines 12, 13 and the canning line 16 may be kept warm as needed. This is because, depending on the composition, the distillation bottoms, the mixture of the distillation bottoms and the raffinate, and the bottoms generated by the collection of methacrylic acid cannot be sent stably without keeping the temperature. This is because the viscosity of the liquid may increase up to.

The operation of recovering methacrylic acid in the present invention may be carried out batchwise or continuously. If it is performed in batch, after supplying the raw materials to the evaporator 1,
The heating may be started after the valves 8 and 9 are closed and the operating pressure is adjusted. If the operation is to be performed continuously, in addition to the adjustment of the operating pressure and the amount of heating, the liquid sending pump 7 and the valves 8 and 9 may be used. The raw material supply speed and the unloading speed may be controlled by adjusting the temperature.

Also, since the recovered raw material contains a large amount of highly polymerizable substances other than methacrylic acid, when exposed to a high temperature, this methacrylic acid or the like may polymerize, which may hinder stable operation of the apparatus. Therefore, the temperature of the liquid in the evaporator 1 is preferably set to 95 ° C. or lower, particularly preferably 90 ° C. or lower.
Therefore, in order to distill and recover methacrylic acid, the operating pressure is adjusted and the boiling point of the liquid in the evaporator 1 is set to 95 ° C. or less,
Particularly, the temperature is preferably set to 90 ° C. or lower. The operating pressure is not constant depending on the composition of the recovered raw material and the liquid in the evaporator 1, but is usually 50 kPa or less if the water concentration in the liquid in the evaporator 1 is 5% by mass or more.

Further, the heating amount, the feed rate of the raw material and the removal speed of the bottom are preferably adjusted by using the water concentration of the bottom liquid extracted from the evaporator 1 as an index. The adjustment range of this water concentration is:
Although it cannot be unconditionally determined by the composition of the raw material to be recovered and other operating conditions, methacrylic acid is recovered within a range where the mass of methacrylic acid in the bottom liquid extracted from the evaporator 1 is 30% or less of the mass of the bottom liquid. Is usually set to preferably 5 to 50% by mass, more preferably 8 to 48% by mass. If the concentration of water is too low, the viscosity of the bottom liquid discharged from the evaporator becomes high, and the operation of the apparatus may not be performed stably. Also, if the concentration of water is too high, the recovery rate of methacrylic acid tends to not increase, and the amount of the residual liquid discharged becomes significantly large, which is not economical in terms of processing costs. There is also.

As described above, if the recovered raw material is prepared and the evaporator is operated, the recovery operation can be performed stably even if the methacrylic acid distillation rate is increased. Furthermore, according to the present invention, methacrylic acid can be recovered from the raffinate simultaneously with the recovery of methacrylic acid from the residual liquid of the distillation still.

[0030]

Next, the reaction method of the present invention will be described in detail with reference to specific examples. These specific examples are examples of the best embodiment of the present invention, but the present invention is not limited to these.

Example 1 In this example, methacrylic acid was recovered by a batch operation using the apparatus shown in FIG.

The raw material for recovery of methacrylic acid was prepared as follows.

The tert-butyl alcohol is vapor-phase oxidized using a molybdenum-bismuth-based oxidation catalyst, and the produced methacrolein is recovered, and contains methacrylic acid produced by vapor-phase catalytic oxidation using a heteropolyacid-based catalyst. The reaction gas was cooled and absorbed in a liquid containing water as a main component. Then, methacrylic acid was extracted from the methacrylic acid absorption liquid with an organic solvent containing toluene and methyl methacrylate as main components. Collect this extract (organic solvent),
The organic solvent and low-boiling substances were distilled off from the extract by distillation, and the methacrylic acid was further distilled off by distillation, and the distillation residue was used as a raw material for recovering methacrylic acid (methacrylic acid-containing substance). .

The extraction water from the methacrylic acid-absorbed solution obtained by extracting methacrylic acid with the above organic solvent is
The organic solvent separated and recovered by distillation was used as an aqueous methacrylic acid solution.

This raw material is supplied to the raw material tank 6 through the distillate bottom liquid supply line 10 and the raffinate water supply line 11, respectively, so that the mass of the raffinate water is 10 times the mass of the distillate bottom liquid. Was done. Then, the raw material sending line 12,
Through 13, the mixture was supplied to the evaporator 1. As the evaporator 1, a separable flask made of glass (volume 3)
L) was used. Table 1 shows the composition and mass of the distillation bottom liquid, the raffinate water, and the mixture thereof.

[0036]

[Table 1]

This mixture was heated at a pressure of 40 kPa and a heating jacket temperature of 120 ° C. to recover methacrylic acid. During the recovery, the liquid temperature in the evaporator 1 was almost constant at about 76 ° C. As a result of this recovery, 928.1 g of distillate was distilled out from the distilling line 14, and 171.
9 g remained. This bottom liquid was drawn out of the system through a discharge line 16. At the time of recovery and withdrawal of residual liquid, evaporator 1
No polymerization in the inside, no scorching of the heating surface of the evaporator 1, no blockage of the piping, etc. occurred. Table 2 shows the composition and mass of the distillate and the bottom liquid.

[0038]

[Table 2]

As a result of the recovery, about 94% of methacrylic acid in the mixed liquid as a raw material for recovery was recovered. In addition, as shown in Table 2, the methacrylic acid concentration in the obtained bottom liquid was 2.
It was 9% by mass. Further, when this recovery rate is applied to methacrylic acid contained in the distillation bottoms, which is a raw material for recovery, 75.2 g of 80.0 g can be recovered. Similarly, when this recovery rate is applied to methacrylic acid contained in the raffinate water, 1.9 g of 2.0 g could be recovered.

(Embodiment 2) In this embodiment, the operating pressure is set to 2
kPa, methacrylic acid was partially recovered by heating in an evaporator, and the bottom liquid (that is, bottom liquid 2) obtained as a raw material to be recovered was used. The methacrylic acid was recovered under substantially the same conditions as in Example 1 except that the amount was 3.5 times the mass of the liquid. Table 3 shows the composition and mass of the distillation bottom liquid, the raffinate water, and the mixture thereof.

[0041]

[Table 3]

This mixture was heated at a pressure of 40 kPa and a heating jacket temperature of 120 ° C. to recover methacrylic acid. During the recovery, the liquid temperature in the evaporator 1 was almost constant at about 78 ° C. As a result of this recovery, 284.4 g of a distillate was distilled off, and 165.6 g of a bottom residue were obtained. At the time of recovery and withdrawal of the bottom liquid, polymerization in the evaporator 1, scorching of the heating surface of the evaporator 1, blockage of the piping, and the like did not occur at all. Table 4 shows the composition and mass of the distillate and the bottom liquid.

[0043]

[Table 4]

As a result of the recovery, about 68% of methacrylic acid in the mixed liquid as the raw material for recovery was recovered. In addition, as shown in Table 4, the methacrylic acid concentration in the obtained bottom liquid was 6.
It was 5% by mass. Further, when this recovery rate is applied to methacrylic acid contained in the distillation bottom liquid, which is a raw material for recovery, 22.4 g of 33.0 g can be recovered. Similarly, when this recovery rate is applied to methacrylic acid contained in the raffinate water, 0.5 g out of 0.7 g could be recovered.

(Embodiment 3) In this embodiment, a mixed solution of distillation bottom and raffinate, which is a raw material to be recovered, is continuously supplied to the evaporator 1 at 180 g / hr. The methacrylic acid was recovered under substantially the same conditions as in Example 2 except that the bottom liquid was extracted. The composition and the supply ratio of the distillation bottom liquid and the raffinate water as the recovered raw materials are substantially the same as those in the second embodiment. Table 5 shows the composition of these liquid mixtures and the mass flow rates of each component.

[0046]

[Table 5]

This mixture was heated at a pressure of 40 kPa and a heating jacket temperature of 120 ° C. to recover methacrylic acid. During the recovery, the liquid temperature in the evaporator 1 was almost constant at about 78 ° C. In this recovery, the distillation speed was 115.7 g /
hr, the unloading speed was 64.3 g / hr. At the time of collection,
No polymerization in the evaporator 1, no scorching of the heating surface of the evaporator 1, no blockage of the piping, etc. occurred. Table 6 shows the compositions of the distillate and the bottom liquid and the mass flow rates of each component.

[0048]

[Table 6]

As a result of the recovery, about 68% of the methacrylic acid in the mixed liquid as the recovered raw material was recovered. Further, as shown in Table 6, the methacrylic acid concentration in the obtained bottom liquid was 6.
It was 7% by mass. Further, when this recovery rate is applied to methacrylic acid contained in the distillation bottoms, which is a raw material for recovery, 9.0 g out of 13.2 g could be recovered per hour. Similarly, when this recovery rate is applied to methacrylic acid contained in raffinate water, 0.3 g per hour is obtained.
In the middle, 0.2 g was collected.

(Embodiment 4) In this embodiment, a thin film evaporator made of glass (heat transfer area: 0.034 m ² ) is used as the evaporator 1.
And recovering methacrylic acid under substantially the same conditions as in Example 3, except that a mixture of the distillation bottom liquid and the raffinate water as the raw material to be recovered is continuously supplied to the evaporator at 100 g / hr. went. The composition and the supply ratio of the distillation bottom liquid and the raffinate water as the recovered raw materials are substantially the same as those in the third embodiment. Table 7 shows the composition of these liquid mixtures and the mass flow rates of each component.

[0051]

[Table 7]

This mixture was heated at a pressure of 40 kPa and a heating jacket temperature of 140 ° C. to recover methacrylic acid. During the recovery, the temperature of the gas phase in the thin film evaporator was almost constant at about 77 ° C. In this recovery, the distillation speed was 73.
6 g / hr, and the unloading speed was 64.3 g / hr. At the time of recovery, polymerization in the thin film evaporator, scorching of the heating surface of the thin film evaporator, and blockage of the piping did not occur at all. Table 8 shows the compositions of the distillate and the bottom liquid and the mass flow rates of each component.

[0053]

[Table 8]

As a result of the recovery, about 73% of the methacrylic acid in the mixed solution as the raw material was recovered. Further, as shown in Table 8, the methacrylic acid concentration in the obtained bottom liquid was 7.
It was 6% by mass. Further, when this recovery rate is applied to methacrylic acid contained in the distillation bottom liquid, which is a recovered raw material, 5.4 g of 7.3 g can be recovered per hour. Similarly, when this recovery rate is applied to methacrylic acid contained in the raffinate water, 0.1 g of 0.2 g can be recovered per hour.

Comparative Example 1 In this comparative example, methacrylic acid was recovered under substantially the same conditions as in Example 1 except that only the distillation residue was used as the raw material to be recovered and the operating pressure was changed. Was. The composition of the distillation bottoms is also substantially the same as in Example 1. In addition, the mass of the distillation bottom liquid to be charged into the evaporator 1 was 1 kg.

This distillation bottom liquid was heated at a pressure of 2 kPa and a heating jacket temperature of 120 ° C. to recover methacrylic acid. At the start of the recovery, the liquid temperature in the evaporator 1 was about 80 ° C. However, as the recovery of methacrylic acid proceeds, the liquid temperature and viscosity in the evaporator 1 increase, and when 737.0 g of distillate distills out from the distillate line 14, the liquid temperature exceeds 95 ° C. The liquid viscosity increased to a range where operation was impossible, and the recovery had to be stopped. After collection is stopped, evaporator 1
When the bottom liquid in the container was examined, formation of a polymer was confirmed. On the other hand, the concentration of methacrylic acid in the distillate was 98.2% by mass. From this, the mass of methacrylic acid in the bottom liquid in the evaporator 1 was calculated to be 76.0 g,
It was 28.9% with respect to the mass of the obtained bottom liquid. The recovery of methacrylic acid was only about 92%.

Comparative Example 2 In this comparative example, methacrylic acid was recovered under substantially the same conditions as in Example 2 except that only the distillation bottom liquid was used as the raw material to be recovered and the operating pressure was changed. Was. The composition of the distillation bottoms is also substantially the same as in Example 2. In addition, the mass of the distillation bottom liquid to be charged into the evaporator 1 was 1 kg.

This distillation bottom liquid was heated at a pressure of 2 kPa and a heating jacket temperature of 120 ° C. to recover methacrylic acid. At the start of the recovery, the liquid temperature in the evaporator 1 was about 80 ° C. However, as the recovery of methacrylic acid proceeds, the liquid temperature and viscosity in the evaporator 1 increase, and when 58.0 g of distillate distills out from the distillate line 14, the liquid temperature exceeds 95 ° C.
The liquid viscosity increased to a range where the recovery operation was impossible, and the recovery had to be stopped. After the collection was stopped, the bottom liquid in the evaporator 1 was examined, and it was confirmed that a polymer was formed. On the other hand, the concentration of methacrylic acid in the distillate was 98.5% by mass. From this, the mass of methacrylic acid in the bottom liquid in the evaporator 1 was calculated to be 273.0 g, which was 29.0% based on the mass of the obtained bottom liquid. Also,
The recovery of methacrylic acid was only about 17%.

As is clear from the examples and comparative examples, it is understood that the use of the method of the present invention can achieve a higher methacrylic acid recovery rate than the conventional method of recovering methacrylic acid by simply heating.

[0060]

According to the recovery method of the present invention, methacrylic acid is further recovered from the residual liquid of the distillation still after the methacrylic acid is distilled off through purification means such as extraction or distillation, which occurs in the production of methacrylic acid. When doing, stable operation of the device,
In addition to the effect of enabling compatibility with a high recovery rate of methacrylic acid, it is also possible to simultaneously recover methacrylic acid in raffinate water generated when methacrylic acid is recovered by an extraction operation from an aqueous methacrylic acid solution. Is also obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the configuration of an evaporator used when carrying out the method for recovering methacrylic acid of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Evaporator 2 Stirrer blade 3 Heating jacket 4 Stirrer 5 Condenser 6 Raw material tank 7 Liquid feed pump 8 Valve 9 Valve 10 Distillation bottom liquid supply line 11 Extraction water supply line 12 Raw material liquid supply line 13 Raw material liquid supply line 14 Distillation Line 15 Vacuum line 16 Can discharge line 17 Heat medium supply line 18 Heat medium withdrawal line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Koizumi 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Inventor Shingo Tanaka 201-1 Miyukicho, Otake City, Hiroshima Prefecture F term in Central Research Laboratory of Mitsubishi Rayon Co., Ltd. (reference) 4D076 AA07 AA16 AA22 BB01 BB13 CD02 CD13 CD22 DA10 DA25 EA04X EA05Z EA20Z EA26X FA02 FA12 HA03 4H006 AA02 AD11 AD16 BB11 BB17 BB31 BD31 BD53 BS10

Claims (6)

[Claims] 1. A method for recovering methacrylic acid by distillation from a methacrylic acid-containing material containing 5 to 95% by mass of methacrylic acid, wherein the methacrylic acid-containing material contains 0.01 to 10% by mass of methacrylic acid. A method for recovering methacrylic acid, comprising mixing an aqueous methacrylic acid solution and distilling the mixture so that the mass of water contained in the mixture is 0.1 to 15 times the mass of methacrylic acid. 2. The methacrylic acid-containing substance is generated when a mixture of methacrylic acid and an organic solvent, from which an organic solvent and a low-boiling substance are distilled off, is further distilled to remove methacrylic acid. 2. The method for recovering methacrylic acid according to claim 1, wherein the liquid is a bottom liquid 1. 3. The methacrylic acid-containing substance is produced when a mixture of methacrylic acid and an organic solvent, from which an organic solvent and a low-boiling substance are distilled off, is further distilled to remove methacrylic acid. The method for recovering methacrylic acid according to claim 1, characterized in that it is a bottom liquid 2 obtained by separating at least a part of methacrylic acid from the bottom liquid 1. 4. A methacrylic acid is extracted with an organic solvent from a methacrylic acid-absorbed liquid obtained by contacting a mixed liquid of methacrylic acid and an organic solvent with a methacrylic acid-containing gas obtained by a gas phase reaction and water. The method for recovering methacrylic acid according to claim 2 or 3, wherein the method is an extract. 5. An extraction method for extracting methacrylic acid with an organic solvent from a methacrylic acid-absorbed liquid obtained by contacting a methacrylic acid-containing gas obtained by a gas phase reaction with water and the methacrylic acid aqueous solution. The method for recovering methacrylic acid according to any one of claims 1 to 4, wherein the residual water is 1. 6. An extraction method for extracting methacrylic acid with an organic solvent from a methacrylic acid absorbing solution obtained by contacting water with a methacrylic acid-containing gas obtained by a gas phase reaction. The method for recovering methacrylic acid according to any one of claims 1 to 4, wherein it is raffinate water 2 obtained by separating at least a part of the organic solvent from the residual water 1.