JPS62126151A - Production of methacrylic acid ester - Google Patents

Abstract

PURPOSE:To obtain the titled compound in high yield, by esterifying methacrylic acid with a lower alcohol in the presence of an acidic solid catalyst, distilling the resultant reaction product, treating the bottom containing unreacted methacrylic acid, etc., with activated carbon and reusing the treated material. CONSTITUTION:Methacrylic acid and a lower alcohol are esterified in the pres ence of an acidic solid catalyst and the obtained reaction product is distilled under atmospheric pressure or reduced pressure to obtain a bottom containing unreacted methacrylic acid and a column top distillate containing water, alcohol and a methacrylic acid ester. The bottom containing methacrylic acid is treated with granular activated carbon having particle diameter of preferably 0.5- 3.3mm at 20-60 deg.C to effect the ready adsorption and removal of methacrylic acid, which is reused for the esterification reaction to obtain the objective compound. The activated carbon can be easily regenerated and reused by pass ing an aqueous solution of sodium hydroxide of about 3-10% concentration through the activated carbon at normal temperature and a space velocity of 0.2-3l/l-Hr for 0.5-2hr, washing the treated carbon with water and substituting water with methanol.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing methacrylic acid ester, and more specifically to a method for producing methacrylic acid ester, which is obtained in a reaction of esterifying methacrylic acid and a lower alcohol in the presence of an acidic solid catalyst. The present invention relates to a method for recovering unreacted acrylic acid from a product produced by the present invention.

[Conventional technology]

Since the esterification reaction of methacrylic acid with a lower alcohol is an equilibrium reaction, even if the reaction is sufficient, the raw materials methacrylic acid and alcohol are present at a certain concentration in the reaction product. Therefore, an improvement in yield cannot be expected unless the above-mentioned raw materials in the reaction product are recovered and reused.

Various methods have already been proposed for separating residual methacrylic acid and/or alcohol from the esterification reaction product. That is, in Japanese Patent Publication No. 48-1389, the esterification reaction product is taken out from the esterification reactor, distilled or flashed, unreacted alcohol is separated, and methacrylic acid is recovered by rectification. , in JP-A No. 55-82047, the reaction product is sent directly to an alcohol extraction column to separate the alcohol, then low-purity substances are removed, and then unreacted methacrylic acid is separated in a methacrylic acid ester rectification column. JP-A-49-124018 discloses a method in which esterification is performed in the presence of a solvent, unreacted methacrylic acid is separated, and esterification is performed in a second stage esterification reactor. has been done.

However, the methacrylic acid recovered by these methods contains high-boiling impurities and polymers from the methacrylic acid manufacturing process and/or polymers generated during the esterification reaction process and the distillation process of the reaction product. That is inevitable. If methacrylic acid containing such high-boiling point impurities and polymers is esterified again in the presence of an acidic solid catalyst, it will cause clogging in the catalyst layer, deterioration of the catalyst, and decrease in catalyst activity, making long-term continuous operation impossible. make it impossible. As a result, it is necessary to stop the operation for replacing and replacing the catalyst, or to install a spare device, which is not economically advantageous.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for recovering methacrylic acid that does not have the various problems mentioned above in the prior art.

[Means for Solving the Problems] As a result of intensive research to solve these problems, the inventors of the present invention have conducted active carbon treatment of methacrylic acid containing high-boiling substances and polymers that have a negative effect on the catalyst. It can be easily removed by adsorption.

Furthermore, they discovered that activated carbon can be easily regenerated by washing it with an alkaline aqueous solution, leading to the completion of the present invention.

That is, in the present invention, when methacrylic acid and lower alcohol are esterified in the presence of an acidic solid catalyst, the obtained reaction product is distilled at normal pressure or reduced pressure to produce bottoms containing unreacted methacrylic acid, A method of producing methacrylic acid, which comprises obtaining an overhead distillate containing water, alcohol and methacrylic acid ester, treating the bottoms containing methacrylic acid with activated carbon, and then reusing the bottoms according to the degree of esterification. This is a method for producing acid esters.

In the present invention, the activated carbon for treating the methacrylic acid-containing cans is not particularly limited, and any commercially available wood-based, coal-based, etc. can be used, and molded products (granular products) are preferably used. 5m+a~3.3am, preferably 0
．． 9a+a+~2. It is Omm.

The treatment process with activated carbon may be either a batch contact method or a continuous liquid flow method, but a continuous liquid flow method is usually advantageous industrially. of methacrylic acid-containing bottoms is passed through at a predetermined flow rate. The temperature at that time is 20 to 80°C, especially 2
0-50°C is preferred.

If the temperature is too low, the methacrylic acid will solidify, and if the temperature is too high, the methacrylic acid will easily polymerize, which is not preferred. In addition, the processing speed (space velocity) is 1 to 2017 hours, especially 2 to 10 hours of methacrylic acid-containing bottoms per liter of activated carbon.
If the space velocity is too small, it has the advantage of being able to sufficiently adsorb the high-boiling point impurities and polymers, but the required amount of activated carbon for the bottoms to be processed per unit time is If the space velocity is too high, the removal rate of high-boiling impurities and polymers will decrease, and the activation frequency of activated carbon will increase, resulting in an increase in the amount of chemicals used, This is not desirable because it increases the amount of washing water used and the amount of waste water.

The adsorption capacity of activated carbon gradually deteriorates as the bottoms are treated, but a 3-10% aqueous solution of caustic soda can be passed through it at room temperature for 0.5-2 hours at a space velocity of 0.2-3 fL/1Hr. By doing so, it can be easily reproduced. After alkaline washing, wash with water and replace the water with methanol before use.

〔Example〕

Examples of the present invention are shown below.

Example 1 Strongly acidic cation exchange resin Evati) SPo 108 (
Methacrylic acid (17.2 g/Hr (0,2
mol/Hr) and methanol9. f1g/Hr (0
, 3 mol/Hr), reaction temperature: 90°C, contact time: 1
．． Esterification was carried out for 5 hours, and 70% of the methacrylic acid was esterified to obtain a product having the following composition.

Methyl methacrylate 52.0%, methacrylic m19.2
%, methanol 19.1%, water 9.4%, other products 0.3%.

This product was fed at a rate of 348 g/Hr from the top to the 20th stage of a perforated plate distillation column with a column diameter of 50 mm and 30 plates.
Distillation was carried out at a C1 pressure of 50 mmHg, and from the top of the column 64.7% of methyl methacrylate, 23.6% of methanol, and 11% of water were collected.
．． 280g/Hr of distillate consisting of 6%, and 88g/Hr of bottoms consisting of 0.3% methyl methacrylate, 98.2% methacrylic acid, 1.5% high boilers and polymers from the bottom of the column.
Obtained at the rate of Hr. The thus obtained canned product was placed in a treatment tower in which a column with an inner diameter of 20 mm was filled with 150 g of activated carbon CAL (trade name, manufactured by Carbon Co., Ltd.) with an apparent ratio i of 0.45 and an average particle size of 12 to 40 mesh, at a temperature of 40 mm. ℃
1 liquid flow rate 700g/Hr, (space velocity 2.11/1H
The liquid was passed in a countercurrent manner under the treatment conditions of r). The composition of the obtained liquid was 0.3% methyl methacrylate and 88.0% methacrylic acid.
%, and others 0.7%. The recovered methacrylic acid was subjected to esterification using another esterification reactor under the same conditions as the ester described above, and the esterification rate was 89.5%.

Comparative Example 1 The bottoms obtained in Example 1, consisting of 0.3% methyl methacrylate, 98.2% methacrylic acid, and 1.5% high boilers and polymers, were not treated with activated carbon. As a result of carrying out the esterification reaction under the same conditions, the esterification rate was 8.
It was 2.7%.

Example 2 Activated carbon whose adsorption capacity deteriorated after being used for 8 hours in Example 1 was replaced with methanol, then washed with water, and a 5% aqueous solution of caustic soda was passed through it at 150 cc/Hr at room temperature for 1.5) It. . The regeneration was completed by washing with water after alkaline washing and exchanging the head with methanol, and the activated carbon that had recovered its adsorption capacity could be used repeatedly.

Claims (1)

[Claims] When methacrylic acid and lower alcohol are esterified in the presence of an acidic solid catalyst, the resulting reaction product is distilled at normal pressure or reduced pressure to extract bottoms containing unreacted methacrylic acid, water, alcohol, and methacrylic acid. A method for producing a methacrylic ester, which comprises obtaining an overhead distillate containing an acid ester, treating the bottoms containing methacrylic acid with activated carbon, and then reusing the bottoms in an esterification reaction.