JPS58183641A - Purification of methyl (meth)acrylate - Google Patents

Abstract

PURPOSE:To obtain methyl (meth)acrylate in high purity and yield, by distilling crude methyl (meth)acrylate in contact with an acidic catalyst, thereby decomposing and regenerating the beta-methoxy-propionaldehyde produced as a by-product during the esterification reaction. CONSTITUTION:The crude methyl (meth)acrylate obtained by the oxidative esterification of (meth)acrolein with an oxygen-containing gas in methanol in the presence of a catalyst, is distilled at 55-130 deg.C, preferably 55-110 deg.C in contact with an acidic catalyst (e.g. benzenesulfonic acid, toluenesulfonic acid, etc.). The beta-methoxypropionaldehyde or beta-methoxyisobutylaldehyde or dimethyl acetal of (meth)acrolein produced as a by-product during the reaction is decomposed and regenerated to (meth)acrolein and methanol by this process, and purified methyl (meth)acrylate can be obtained. The decomposed and regenerated product is separated as a low-boiling fraction, and recycled and reused.

Description

Detailed Description of the Invention The present invention provides crude (meth)acrylate obtained in a method for oxidatively esterifying (meth)acrolein in methanol in the presence of a catalyst to produce methyl (meth)acrylate. This article relates to a method for purifying methyl acrylate, and more specifically, the by-product β-in the methyl (meth)acrylate layer.
Methoxypropionaldehyde or β-methoxyisobutyraldehyde and (meth)acrolein acetal are decomposed and regenerated into (meth)acrolein and methanol in the presence of an acid catalyst to produce methyl (meth)acrylate in high quality and high yield. The present invention relates to a method for purifying methyl (meth)acrylate.

A method for producing industrially useful methyl (meth)acrylate is to oxidize (meth)acrolein in the gas phase, esterify the obtained (meth)acrylic acid, and produce methyl (meth)acrylate. is being actively researched, a method for producing methyl acrylate has already been industrialized, and a method for producing methyl methacrylate is under development.

However, in recent years, an innovative method has been proposed in which (meth)acrolein is oxidatively esterified in methanol in the presence of a catalyst with an acid-containing gas to produce methyl (meth)acrylate. This method uses relatively low temperatures (20°C
~100°C), preferably in a liquid phase, so it is a method with good selectivity and few decomposition products derived from (meth)acrolein, but it also contains a small amount of by-products that are different from conventional methods. do. Therefore, in order to produce high-quality methyl (meth)acrylate, treatment and purification methods suitable for the oxidative esterification method are required.

In the oxidative esterification method, (meth)acrolein and methanol are reacted with oxygen or #1 leaf-containing gas in the liquid phase in the presence of an excess amount (3 to 50 times the mole) of methanol using a catalyst to form an ester. That is. The crude methyl (meth)acrylate obtained by separating unreacted (meth)acrolein from the reaction solution obtained in this way and then separating methanol and water does not substantially contain methanol, although it still contains a trace amount. contains various by-products. or,
Water may have been removed, but the solubility variation, i.e. 7~
It often contains around 3% water. This coarse (meta)
When methyl (meth)acrylate is purified by removing low-boiling and high-boiling substances from methyl acrylate by distillation, the product may contain more impurities such as methanol, (meth)acrolein, and acetal than conventional products. However, there was a problem in that it was difficult to keep these amounts to a sufficiently low level.

As a result of intensive investigation into this problem, the present inventors found that 0.3% of β-methoxypropionaldehyde or β-methoxyisobutyraldehyde was present in crude methyl (meth)acrylate.
2% to 7% of dimethyl acetal of (meth)acrolein is produced as a by-product, and its boiling point is close to that of the main product ester, making it difficult to separate by distillation. Although it is a small amount, it has been found that these substances dissociate and decompose to generate aldehyde and methanol, which are mixed into the product, which may not satisfy quality requirements.

JP-A-14-14-9.22G No. O discloses that an acetal, which is an impurity in a carboxylic acid ester obtained by reacting an olefinically unsaturated compound, carbon oxide, and alcohol, is converted into vinyl ether in the presence of a strong acid. Methods have been disclosed in which acetals and aldehydes are separated as low-boiling substances or removed as high-boiling substances by aldol condensation.
Dimethyl acetal of (meth)acrolein does not have hydrogen at the α-position, so if it is made into a high boiling point by aldol condensation with vinyl ether xypropionaldehyde or β-methoxyisobutyraldehyde, the active ingredients will be lost, and these substances will be mixed with methanol (meth) ) It was necessary to dissociate and decompose into acrolein and recover it. Furthermore, since water coexists, it was necessary to take measures to prevent hydrolysis of methyl (meth)acrylate under acid treatment conditions. Furthermore, acetal and β-methoxypropionaldehyde or β-methoxyisobutyraldehyde have a boiling point close to that of methyl (meth)acrylate, such as methyl methacrylate (b.
p. 1000°C), the boiling point of methacrolein dimethyl acetal is 101°C, and the boiling point of β-11" diisobutyraldehyde is /211"C.These substances are difficult to separate by distillation, and various solvents The distribution ratios were also similar, making it difficult to separate by extraction.

It has also been found that β-methoxypropionaldehyde or β-methoxyisobutyraldehyde and acetal are produced by contact between (meth)acrolein and methanol in the liquid phase, regardless of the catalytic reaction.

Under these circumstances, in order to remove acetal, β-methoxypropionaldehyde, or β-methoxyisobutyraldehyde and to establish a stable purification process, various studies were conducted, and it was found that crude methyl (meth)acrylate was distilled at Jj'C or above. However, when treated with a solid or liquid acid, acetal, β-methoxyprobialdehyde, or β-methoxyisobutyraldehyde can be quickly decomposed and regenerated into methanol and (meth)acrolein without remaining. At the same time, despite the presence of water, hydrolysis of methyl (meth)acrylate does not occur, and when distilled after removing low-boiling substances from the distillate, alcohol and aldehyde are mixed into the product ester. The main purpose of the present invention is to oxidize and esterify (meth)acrolein with a gas containing # in methanol in the presence of a catalyst. hand(
Crude methyl (meth)acrylate obtained in the method for producing methyl meth)acrylate is distilled at 55"C or higher and brought into contact with an acidic catalyst to remove β-methoxypropionaldehyde or β- It is characterized by a process of decomposing and regenerating methoxyisobutyraldehyde and/or dimethyl acecool of (meth)acrolein into (meth)acrolein and methanol (meth)
A method for purifying methyl acrylate is provided.

The above crude methyl (meth)acrylate contains ~3% water, which is close to saturated solubility. If the acetal is simply heated together with an acid catalyst, the acetal is decomposed into aldehyde and methanol, but the decomposition of β-methoxypropionaldehyde or β-methoxyisobutyraldehyde occurs only insufficiently. In addition, many hydrolysis reactions occurred, resulting in the production of (meth)acrylic acid, which was an undesirable result. Furthermore, simply distilling at a temperature higher than jS''C does not decompose acetal or the like, and it is difficult to separate it.

The effect obtained in the present invention is that the acid catalyst has j, t″C0 or more (
This is produced by contacting methyl meth)acrylate while distilling it, and if this distillation is not carried out at the same time, hydrolysis of the ester will occur, which is economically disadvantageous and cannot be carried out industrially. There isn't. Furthermore, the distillate obtained by the treatment of the present invention does not contain acetal and β-methoxypropionaldehyde or β-methoxyisobutyraldehyde, and the decomposition products methanol and (meth)acrolein can be reused in the reaction. to do,
Since it is separated from the distillate as a low boiling point component, (meth)
When purifying methyl acrylate by distillation, methanol and (
No contamination with meta)acrolein, high quality (
Methyl meth)acrylate was obtained.

Furthermore, in addition to simply removing acetal, β-methoxypropionaldehyde, or β-methoxyisobutyraldehyde, the illegal method involves dissociating and decomposing these byproducts into methanol and aldehyde, which are the starting materials for oxidative esterification. Since these can be used again in the reaction, they not only improve quality but also have the great advantage of increasing yield.

The crude methyl (meth)acrylate used in the present invention contains some high-boiling substances, but they are not distilled out under the acid treatment conditions of the present invention and are contained in the reactor residual liquid, and by extracting the residual liquid. taken out of the system. Therefore, the present invention also has the effect of removing a part of high-boiling substances, and when the distillate is further distilled to purify methyl (meth)acrylate, a distillation tower is used for high-boiling substances. Another advantage of the present invention is that the temperature at the bottom of the column tends to rise and the viscosity of the liquid at the bottom increases, making it difficult to operate, and stable operation can be maintained.

Examples of the liquid or solid alcohol used in the present invention include sulfuric acid, benzenesulfonic acid, toluenesulfonic acid, sulfonic group-containing ion exchange resins, and heteropolyacids such as phosphogestic acid, phosphomolybdic acid, and silicotungstic acid. It will be done. When using a liquid or a solid acid that dissolves in the reaction solution, the acid also comes out of the thread at the same time when the residual liquid from the reactor is drawn out, so it is necessary to continuously supply the acid to the reactor.

The acid extracted with the residual liquid can be recovered and used again, and at this time, it can also be subjected to regeneration treatment if necessary. When using an insoluble solid acid, it is possible to extract it together with the residual liquid and perform the same treatment as above, or alternatively, only the residual liquid can be extracted and the solid acid is used continuously without being extracted. You can also do that. The acid cap used in the present invention is preferably used at a ratio of 10% to the feed solution and 1% by weight to o, os-s.

Under the conditions of the present invention, acetal is much easier to decompose than β-methoxypropionaldehyde or β-methoxyisobutyraldehyde, so the conditions for distilling off the reaction solution should be Although it is determined by the content, decomposition behavior, etc., the reaction can be carried out at a temperature above jf'c, and in order to prevent polymerization, it is best to carry out the reaction at a temperature below /30"C, preferably below 770℃, and the pressure is set at a specified temperature. The liquid is set to boil.

Crude methyl (meth)acrylate used in the present invention often does not contain methanol, but if methanol is poorly separated and contains a small amount of methanol, or if there is a large amount of methanol
Even in the case of the present invention, when the acetal, β-methoxypropionaldehyde, or β-methoxyisobutyraldehyde is brought into contact with an acid catalyst before distillation, decomposition of the acetal, β-methoxypropionaldehyde, or β-methoxyisobutyraldehyde occurs without being inhibited. Therefore, crude methyl (meth)acrylate containing methanol can also be applied to the present invention.

The distillate can be sent to the next purification step as a vapor, as a liquid by condensation, or as a gas-liquid mixture. In distilling, it is preferable to distill out at least 70% by weight, more preferably at least 0% by weight, of the supplied liquid. The residual liquid from the reactor is further sent under reduced pressure to a step for extracting active ingredients such as methyl (meth)acrylate.

The crude methyl (meth)acrylate used in the present invention contains polymerization inhibitors such as hydroquinone and phenothiazine, which are added during the reaction and separation stages.
It can be further added if necessary, and can also be added in the step of further purifying the distillate.

Next, the method of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. In addition, % used below,
and solutions are on a weight basis unless otherwise specified.

Example: A 20% methanol solution of methacrolein is oxidized with a palladium-based catalyst to produce methyl methacrylate, and unreacted methacrolein is removed from the reaction solution by distillation along with a portion of the methanol. Next, methanol is removed by azeotropic distillation with hexano, and crude methyl methacrylate and produced water are separated into two layers, and the water is separated to obtain crude methyl methacrylate.

This crude methyl methacrylate contains 06% methacrolein dimethyl acetal and 7% β-methoxyisozotyl aldehyde.
3% water/6%, it% methacrylic acid and 20% other compounds.

In a sowtl flask equipped with a stirrer, a raw material supply port, an acid supply port, a steam distillation port, and a drain port for the liquid inside the kettle,
Hydroquinone 200pp to the above crude methyl methacrylate
, J f O to which phenothiazine 100F was added
Supplied with vAr. For the rice, use para-toluenesulfonic acid and make it a 30% methanol fi liquid. Average:
The pressure in the flask was maintained at 3.27 degrees, and the preparation was set to J'/''C. on average from 32' It/hr (distillation rate 92
%), 2g,! ;? /hr, and the condensate contains 1311% methacrolein, 73% methanol, and water/hr.
It was methyl methacrylate containing 7% methacrylic acid, 06% methacrylic acid, and 0j% other components, and acetal and β-methoxyisobutyraldehyde were not detected. or,
The liquid extracted from the flask contains methacrolein O/%,
Methanol 03%, β-methoxyisobutyraldehyde 0.02%, methacrylic acid/iII%, other ingredients 1
g9%, para-toluenesulfonic acid and 1% methyl methacrylate AI'. Note that, at this time, hydrolysis of methyl methacrylate did not occur.

The condensate was distilled under reduced pressure, and from the top of the column a liquid containing 2% methacrolein, 227% methanol, 2% water comb, 7% methyl methacrylate, and 2% other liquid (this was separated into two layers) ) was supplied to the methacrolein separation process, and after the methanol separation process, methacrolein and methanol were helicycled into an oxidation reactor. Furthermore, the crude methyl methacrylate from which low-boiling substances have been removed is distilled, and methacrolein, methanol, and
A clear, highly pure methyl methacrylate free of acecool and β-methoxyisobutyraldehyde was desired.

Example 2 - An acid treatment reaction was carried out under the same conditions as in Example 2 using the acid shown in Table 1 instead of gparatoluenesulfonic acid, and the decomposition rate of acetal and β-methoxyisobutyraldehyde was measured.

Table / Note that the methyl methacrylate obtained by distillation purification after these treatments was highly pure, containing almost no methacrolein, methanol, etc.

Example j Instead of supplying para-toluenesulfonic acid in Example/, a sulfonic acid type ion exchange resin (Dowex jOJJ) was used!
;Put Of into the flask and carry out the same procedure as in Example/ without otherwise supplying acid, and the decomposition rate of acecool q
r% or more, decomposition rate of β-methoxymemetalolein 96%
received rice allowance.

Comparative Example/Example/crude methyl methacrylate 1001 and sulfonic acid tank ion/exchange resin (Dowex 5OW)/3? was added and heated at to'c for 7 hours. The decomposition rate of Acecool is 9
Ir% or more, the decomposition rate of β-methoxyisobutyraldehyde was 75%, but hydrolysis of methyl methacrylate occurred, and the concentration of methacrylic acid decreased from /r% to 17.1%.
increased to

Example 6 A similar reaction and operation was carried out using acrolein instead of methacrolein in Example 1 to produce acrylic acid containing 10% acrolein dimethyl acetal, 3% β-methoxypropionaldehyde, and 1% water. Methyl was obtained. This was treated in the same manner as in Example/1 and the decomposition rate of acecool and β-methoxypropionaldehyde was measured.
The acetal decomposition rate was 9 Ir% or more, and the β-methoxypropionaldehyde decomposition rate was 97%. Furthermore, the methyl acrylate obtained by distilling and purifying this treated solution was highly pure, containing almost no methanol or acrolein.

Patent applicant: Asahi Kasei Industries, Ltd. Representative patent attorney Hoshi No Toru 771

Claims (3)

[Claims] (1) In a method for producing methyl (meth)acrylate by oxidizing and esterifying (meth)acrolein with an oxygen-containing gas in the presence of a catalyst in methanol, the obtained crude methyl (meth)acrylate is heated to 53°C or above. While distilling the mixture, it is brought into contact with an acidic catalyst to decompose and regenerate the dimethyl acetal of β-methoxypropionaldehyde or β-methoxyisobutyraldehyde and/or (meth)acrolein produced by the reaction into (meth)acrolein and methanol. A method for purifying methyl (meth)acrylate, characterized by carrying out a treatment. (2) The method according to claim 1, wherein (meth)acrolein and methanol, which have been decomposed and regenerated, are separated from the distillate as low-boiling substances and recycled to the oxidative esterification reactor. (3) The method according to claim 1, wherein the acid catalyst is sulfuric acid, benzenesulfonic acid, toluenesulfonic acid, an ion exchange resin containing a sulfonic acid group, or a heteropolyacid.