MXPA00011705A - Dewatering process - Google Patents

Abstract

A process for separating a formaldehyde-containing product from a formalin solution comprising formaldehyde, water and methanol, wherein said formaldehyde-containing product contains substantially less water than said formalin solution, comprising distilling said formalin solution in the presence of a water entraining compound, especially methyl propionate or methyl methacrylate. The formaldehyde-containing product is suitable for use in a further process which requires a source of formaldehyde containing a relatively low level of water. One example of such a process is the reaction of methyl propionate with formaldehyde and methanol over a catalyst to produce methyl methacrylate.

Description

WATER EXTRACTION PROCESS DESCRIPTION OF THE INVENTION The present invention relates to a process for the removal of water from formaldehyde-containing solutions for the production of de-branched form. Formaldehyde is a commercial chemical that is conveniently produced and transported in the form of formalin solutions. Formalin solutions typically contain between 30% and 60% formaldehyde, the balance of the solution is mostly water, usually with some methanol present. Formaldehyde is present predominantly as complexes with water or methanol in the form of glycols or hemi f or rma 1 e s. There are a number of methods described in the patent literature for the dehydration of formaldehyde solutions in order to produce a dry monomer formaldehyde stream. For example, U.S. Patent 4,962,335 describes the purification of a methanol / water / formaldehyde mixture, by distillation in the presence of a polyalkylene oxide so that the formaldehyde vapor is produced in the upper part of the column and the polyalkylene oxide, acfua and methanol are removed from the bottom of the column. NL-A-6814946 describes a process for recovering formaldehyde from aqueous formaldehyde streams by contacting the stream with a Cg-Cio aliphatic alcohol that reacts with formaldehyde to form a hemiformal which can be separated from water and subsequently dissociated from water. "that to the alcohol and formaldehyde components US-A-3174912 describes a process for the removal of water and colored organic impurities from a mixture of aqueous formaldehyde diluted by distillation in the presence of acetone A mixed stream containing acetone and formaldehyde and a small amount of water are removed from the top of the column and separated by partial condensation of a stream containing a relatively small amount of formaldehyde in acetone and a stream containing a large proportion of formaldehyde in acetone. However, it is desired to avoid the introduction of additional chemical compounds into a A process that requires purified formaldehyde because the additional compound may need to be removed from the process in a subsequent step. A process in which formaldehyde is used is that for the production of methyl methacrylate by the reaction of methyl propionate with formaldehyde in the presence of methanol. The use of formaldehyde according to a readily available formalin solution introduces water into the reaction which may have a deleterious effect on the catalyst used and is likely to promote the hydrolysis reactions of the methyl propionate reagent and the methyl methacrylate product. Water is produced as a byproduct of the methacrylate synthesis reaction and therefore it is desired to reduce to a minimum the amount of water that is introduced into the reaction zone with the flow rates so that the water level in the reactor Keep yourself as low as possible. The processes for the production of methyl methacrylate are described in US-3535371, US-4336403, GB-A-1107234, JP-A-63002951, in which propionic acid or its methyl ester is reacted with formaldehyde or methylal in the presence of methanol. However, there is no description in these references of how to prepare the supply materials, particularly the formaldehyde for the required reaction. US 4,040,913 discloses the use of water entraining compounds such as benzene, toluene, or -me ti 1 is obu ti 1 ce tone and FR-A-2409 975 describes the use of saturated hydrocarbons of C 4 -C 6 GB-A 1301533 describes the use of alkanols that are C3-C6 compounds although the alkanols are not used as water entraining compounds. It is therefore an object of the invention to provide a process for the preparation of a formaldehyde supply product from a solution having formaldehyde. It is a further object of the invention to provide a process for the treatment of a solution containing formaldehyde to produce a flow rate of formaldehyde suitable for use in a methyl methacrylate production process which contains a reduced amount of water compared to the solution that It contains original formaldehyde. According to the invention, a process for preparing a formaldehyde-containing product from a formaldehyde solution comprising formaldehyde, water and optionally methanol, wherein The product containing formaldehyde contains substantially less water than the formalin solution, which comprises distilling the formalin solution in the presence of a water entraining compound. The water entraining compound is selected so that it is capable of di. Solve water, formaldehyde, methanol and hemiformal compounds formed by the reaction of formaldehyde with methanol. The water entraining compound preferably is a saturated or unsaturated carboxylic acid or ester or a carbonyl compound that is substantially not reactive to formaldehyde under the conditions of distillation and is also capable of entraining water, preferably forming a boiling azeotropic mixture. minimum with water. Preferably, the water entraining compound forms a heterogeneous minimum boiling azeotrope with water. Suitable compounds include C 4 -C alkanoic acids and their alkyl esters are lower than Ci-Cß, and ketones having at least 4 carbon atoms such as di t i i ce t ona. Particularly preferred compounds are esters and methyl propionate and methyl methacrylate have been found to be especially useful in certain processes. It is more preferred to use a compound that intends to be introduced in a process in which the dehydrated formaldehyde product is intended to be used. A particularly preferred compound for use in extracting water in a formaldehyde solution to produce formaldehyde suitable for use in a process that reacts formaldehyde with methyl propionate in the presence of methanol which is methyl propionate. In a preferred embodiment of the invention there is thus provided a process for separating a formaldehyde-containing product from a solution of formaldehyde comprising formaldehyde or, water and optionally methanol, wherein the product containing formaldehyde contains substantially less water than the formalin solution, which comprises distilling the formaldehyde solution in the presence of methyl propionate. According to a second aspect of the invention, a process for the production of methyl methacrylate is provided by the reaction of formaldehyde with methyl propionate in the presence of methanol and a suitable catalyst, where formaldehyde is produced in a solution of formaldehyde by distillation of the formaldehyde solution in the presence of methyl propionate. Suitable catalysts are known in the art and include silica catalysts having alkali metal sites. The process of this aspect of the invention is beneficial, in that the formaldehyde flow rate is recovered as a complex with methanol in a stream rich in methyl propionate and the water is removed from the substantially organic-free process. The integration of the process to produce formaldehyde of the present invention with a process that produces methyl methacrylate as described, has the additional advantage that all the energy requirement for the combined process can be reduced compared to other formaldehyde water extraction methods. . Although it has been found that the process of the present invention is particularly suitable for providing formaldehyde supply material for the subsequent reaction for the production of methyl methacrylate, the invention is not limited to the production of formaldehyde for such a process and can be Suitable for producing dehydrated formaldehyde for other applications.

The formaldehyde solution is preferably standard formalin which usually contains water and formaldehyde in approximately equal proportions, usually with a small amount of methanol. At least part of the formaldehyde is normally present as various adducts of water-formaldehyde or methanol-formaldehyde. Normally the term "formaldehyde" will be used herein to refer to total formaldehyde, either present or free of formaldehyde or in the form of such adducts. The composition of formalin solutions can vary and the process of the invention can be operated by a variety of different formalin compositions. It is preferred that the formaldehyde solution be premixed with methanol prior to the distillation process. The mixture of metal 1 / fo rma 1 i na is preferably left to equilibrate so that the formation of adducts species of fo rma 1 dehí do-me t ano 1 are promoted, for example allowing the mixture to equilibrate long enough or, by stirring or adjusting the temperature of the mixture. Preferably, an adequate amount of methanol is used to provide a molar ratio of methanol to formaldehyde of 0.3-1.5: 1, more preferably 0.5-1.2: 1, especially 8.0-1.1: 1. The methanol may be provided in the form of a mixture with methyl propionate, for example to allow the methanol recirculated to be used from the distillation or from an associated process or preparation step. The amount of the water entraining compound introduced into the distillation is an excess of the amount required to form an azeotropic mixture with the water preferably also with any methanol present so that the water in the mixture is more volatile than the formaldehyde adducts . Methyl propionate forms an azeotropic mixture with water comprising 92% methyl propionate and 8% water. The water methacrylate contains about 14% water (by mass) and the diethyl ketone / water azeotrope contains about 84% diethylacetone per mass. Preferably, the relative proportion of the water entrainment compound for the formaldehyde and the base of the column is in the range of 5: 1-20: 1, for example about 10: 1 by mass. However, when the water entraining compound is promoted, the amount that supplies the column can be adjusted as necessary. Most of the water is removed as a mixture with the water drag compound. A stream containing most of the water can be removed from the distillation process as a liquid stream, for example using a chimney pan or a similar device in an appropriate position in the column. A suitable position for extracting such a current can be determined by considering the composition of the liquid phase through the column by methods known in the art. Methyl propionate and water form a heterogeneous azeotrope comprising 92% methyl propionate w / w. This azeotropic mixture can be separated in a carafe and the organic phase thus produced, comprising primary methyl propionate can be promoted in the distillation process. The aqueous phase produced from the decanter which can be further treated in a second distillation unit, preferably at elevated pressure, to give an aqueous stream which is largely free of methanol, formaldehyde and methyl propionate. The vapors from the second distillation unit can be recycled back to SÉ? I - fc --_ dtaüÉMua-. the main column or the decanter or pretreatment formaldehyde solution if present. Most formaldehyde is carried as an inferior product as a mixture with the water entraining compound. This mixture can be used directly if it is required for an additional reaction in which both compounds are used together, for example in the synthesis of methyl methacrylate. The formaldehyde-containing mixture contains substantially less water than the formaldehyde solution supplied to the process. For example, in a typical process according to the invention that methyl propionate is used as the entrainment of water, a solution of formaldehyde containing formaldehyde and water at a weight ratio of about 1: 1 can produce a dehydrated formaldehyde stream that It contains formaldehyde and water in a weight ratio of approximately 10: 1. The process of the present invention is preferably carried out in such a way that the purified formaldehyde product can be used in an additional process for which it is required. Preferably, the process of the present invention This is integrated with such an additional process so that formaldehyde is supplied directly to that additional process. When the formaldehyde product of the present invention is intended to be used as a supply material together with the water entraining compound in an additional process, for example for the production of methyl methacrylate of formaldehyde and methyl propionate when the propionate of Methyl is used as the water entraining compound, then the process of the present invention and the manufacture of methyl propionate can be advantageously operated in proximity to or integrated with the additional process. In a preferred arrangement, methyl propionate is produced by a process that provides a source of methyl propionate mixed with methanol and optionally water. This mixture can be supplied to the distillation of the present invention to extract the formaldehyde from a formalin solution. In this way, the separation of methyl propionate from the process in which it occurs can be avoided. When the supply materials used contain methanol as described, an azeotropic mixture of propionate Methyl and methanol not mixed with formaldehyde can be removed from the top of the distillation column. The mixture can be recycled or removed for storage or for an additional process. When the formaldehyde of the process of the invention is intended to be reacted with methyl propionate and methanol to produce methyl methacrylate, then the process of the present invention is especially convenient, if it is used particularly together with a process that produces methyl propionate as describes in the above. Thus, in a second preferred embodiment, the mixture of dehydrated formaldehyde with methyl propionate is used, directly or after an intermediate treatment, in the methyl methacrylate process. Similarly, a stream of methyl propionate 1 o -meta no 1, which can be derived from a process for producing methyl propionate, and used in the present invention, can also be used to make methyl methacrylate in a process integrated. A further embodiment of the invention will be described by way of example only with reference to the accompanying drawings which is a schematic process diagram. The formalin solution is mixed with methanol and introduced into distillation column 10 as flow 22. Distillation unit 10 includes a chimney pan attachment to extract little or all of the liquid at a location above flow 22. Above the tray of chimney is admitted an additional flow 21 that includes methanol, water, and methyl propionate that it could be derived from a previous process. A side stream 40 is removed from the chimney pan which can represent the total liquid flow in the column and separate phase in the canister 12. The organic phase is returned to the column below the chimney pan as stream 43 while the aqueous phase is passed to column 11 for further processing as stream 41. Column 10 is typically operated so that most of the formaldehyde leaves the bottom as stream 31 mixed with methanol, the free methanol is removed the vapors as its azeotrope with methyl propionate as stream 30 while the water is removed via side stream and the carafe system.

Column 11 is operated to drive the vapors of formaldehyde, methanol and methyl propionate in stream 42 with a little water. This is best achieved at high pressures typically between 3 and 20 bar. The bottom product is a clear water stream 31 that can be reused in the process or removed. The stream 42 is shown as being returned to the canister 12 although it can be returned directly to the column 11 or mixed with the stream 22 and thereby recirculated to the column 10.

EXAMPLE 1 Formalin consisting of 28.5% of hydrolytic acid, 30.7% of methanol and 40.8% of water per mass was mixed with methyl propionate so that methyl propionate represents 43.5% by mass of the mixture. This is allowed to remain for several hours for the mixture to equilibrate and then is supplied to the plate 15 of a laminated Oldersha column which lists the ascending bottom, at a range of 150 ml / h. The column is equipped with a cooled water condenser and a decanter. The pure methyl propionate is added to the decanter in a range of 360 ml / h. The organic phase of the carafe is made to ascend to the column while the aqueous phase is collected and analyzed. 90% of the formaldehyde supplied is recovered in the stream taken from the bottom of the column and 95% of the water supplied is recovered in the aqueous smoke stream. The bottom stream contains formaldehyde: water in the ratio of 1: 0.076 while the original formalin contains formaldehyde to water in the ratio of 1: 1.4.

Example 2 In one example to operate the process of the invention on a continuous basis, the formalin solution consists of 55% water, 35% formaldehyde and 10% methanol mixed with an azeotropic mixture of methane propionate and methanol resulting in a mixture containing 20% methyl propionate, 23% methanol, 35% water and 22% formaldehyde the mixture is allowed to remain at least 12 hours to allow the formaldehyde adducts to equilibrate. The mixture is then allowed to supply to stage 30 (counting with the lower stage) of an Oldersha column of stage 100 at a range of 18 ml per hour. A second flow that MMÚautaMUa ^^ i ^.

It contains 83% of methyl propionate, 95 of methanol, 3% of water and 2% of formaldehyde is supplied to stage 80 of the column at a range of 162 ml per hour. A lateral stream containing the total liquid flow of the column in this way from step 60 and supplied to a carafe of ice water where it is left in a separate phase. The organic phase is returned to the column as a reflux and the aqueous phase is removed. After operating the column continuously for 12 hours, the total product collected from the upper and lower streams of the column were analyzed. The product from the top of the column was an azeotropic mixture of methanol and methyl propionate. The product from the bottom of the column obtained approximately 0.3% water, 4.75% formaldehyde with the balance being methyl propionate. Therefore, the water mass ratio for formaldehyde has been reduced from 1.57: 1 in the formalin solution to 3.06: 1 in the lower column product stream. '' ri? "« 'my ... «** -. ^^ - A -....,.» ...

Claims (13)

1. Process for separating a formaldehyde-containing product from a solution of formaldehyde comprising 1-methyl, water and methanol, wherein the formaldehyde-containing product contains substantially less water than the formaldehyde solution, the solution comprising distilling of formaldehyde in the presence of a water entraining compound.

2. Process as claimed in rei indication 1, wherein the formaldehyde solution contains methanol in a molar ratio of methanol to formaldehyde of 0.3-1.5: 1.

3. Process as claimed in claim 2, wherein the formaldehyde solution is premixed with an amount of methanol before the distillation process so that the molar ratio of methanol to formaldehyde is in the range of 0.1-0.5: 1.

4. Process as claimed in any one of the preceding claims, wherein the water entraining compound comprises a saturated or unsaturated carboxylic acid or ester or carbonyl compound.

5. Process as claimed in rei indication 4, wherein the water entraining compound comprises methyl propionate or methyl methacrylate.

6. Process as claimed in any of the preceding claims, wherein the ratio of the water entraining compound to formaldehyde at the base of the column is in the range of 5: 1-20: 1 per mass.

7. Process as claimed in any of the preceding claims, wherein a lateral stream of the liquid containing most of the water contained in the formaldehyde solution is extracted from the distillation process.

8. Process as claimed in any of the claims, wherein the process is integrated with an additional process so that the ^ * ^^^. product containing formaldehyde is supplied directly to the additional process.

9. Process as claimed in rei indication 8, wherein the additional process is a process for the production of methyl methacrylate.

10. Process for the production of methyl methacrylate by the reaction of formaldehyde with methyl propionate in the presence of methanol and a suitable catalyst, where formaldehyde contains a product containing formaldehyde produced from a solution of formaldehyde by means of distilling the solution of formaldehyde in the presence of methyl propionate.

11. Product containing formaldehyde produced from a supply material of aqueous formaldehyde solution containing the product, by distilling the aqueous formaldehyde solution with a water entraining compound.

12. A formaldehyde-containing product as claimed in claim 11, wherein the water-entraining compound comprises a saturated or unsaturated carboxylic acid or ester or carbonyl compound.

13. Product containing formaldehyde as claimed in claim 12, wherein the water entraining compound comprises or 10 methyl methacrylate. rii ^^ dh