JP3238894B2 - Method for producing methyl methacrylate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering methanol by distillation from a reaction mixture containing at least methyl methacrylate and methanol obtained by a direct esterification reaction of methacrolein and methanol, and converting the recovered methanol to the direct ester The present invention relates to a method for producing methyl methacrylate used as a raw material for a chemical reaction.

[0002]

2. Description of the Related Art As a method of recovering methanol from a mixed solution containing methyl methacrylate and methanol by distillation, Japanese Patent Publication No. 47454/1994 discloses a method in which a saturated hydrocarbon having 6 to 8 carbon atoms is fed to a distillation column and methanol is fed. Have been proposed.

A similar method is disclosed in Japanese Patent Application Laid-Open No. 57-9740.
In the publication, a mixed liquid comprising methanol, water and methyl methacrylate is fed to a distillation column to distill and purify methyl methacrylate, and a saturated hydrocarbon having 6 to 7 carbon atoms is substantially converted from a feed stage of the mixed liquid. , The saturated hydrocarbon and substantially the entire amount of methanol are distilled off from the top of the column, and after separating this in a phase separation tank, the methanol phase is fed to a second distillation column and A method for recovering methanol from the bottom has been proposed.

[0004] JP 58 in -180457 discloses methanol, a mixture consisting of water and methyl methacrylate, was added to azeotrope forming agent to form methanol azeotrope in the presence of methyl methacrylate and water It is disclosed that by azeotropic distillation, a mixture of an azeotropic forming agent and methanol is removed from the top of the column, and when the mixture is separated into two phases, methanol can be separated by separating the two phases. . In addition, as a suitable azeotropic forming agent at this time, in addition to hydrocarbon solvents such as n-hexane, n-octane, cyclohexane, benzol, and toluene, solvents such as diisopropyl ether, tetrahydrofuran, and dimethyl carbonate are mentioned.

In Japanese Patent Application Laid-Open No. 7-69948, a hydrocarbon solvent and water are added to a reaction mixture to obtain a mixture, and the mixture is separated into two phases to form an organic phase and a hydrated methanol phase. It is disclosed that the methanol is recovered by separating and separating methanol from the aqueous methanol phase by distillation.

[0006]

However, in these methods, since a large amount of hydrocarbon is added as an azeotropic agent during distillation to carry out azeotropic distillation, a large amount of utility is required for distillation. There is. Furthermore, if it is intended to produce methyl methacrylate by using the recovered methanol in a direct esterification reaction with methacrolein, it is necessary to separate the azeotropic agent contained in the recovered methanol by distillation or extraction, etc. Is complicated. As a method for recovering methanol, besides the above-mentioned method, there is also a method of distilling a reaction mixture without using an azeotropic agent. There is a problem that it is not efficient because it contains a large amount of methyl methacrylate.

Accordingly, an object of the present invention is to recover methanol by distillation from a reaction mixture containing at least methyl methacrylate and methanol obtained by a direct esterification reaction of methacrolein and methanol, and to recover the recovered methanol by the direct esterification. In the method for producing methyl methacrylate used as a raw material for the conversion reaction, in order to simplify the process, hydrocarbons that need to be separated and recovered when methanol is recovered by distillation are not used as an azeotropic agent, It is an object of the present invention to provide a method capable of reducing the amount of methyl methacrylate contained in water.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above problem can be solved by separately adding methacrolein as an azeotropic agent when recovering methanol by distillation. The present invention has been completed.

That is, the present invention provides a method for recovering methanol by distillation from a reaction mixture containing at least methyl methacrylate and methanol obtained by a direct esterification reaction of methacrolein and methanol, and converting the recovered methanol to the direct esterification reaction. In the method for producing methyl methacrylate used as a raw material of the present invention, wherein methacrolein is separately added as an azeotropic agent when methanol is recovered by distillation.

[0010]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the method for producing methyl methacrylate by direct esterification reaction of methacrolein with methanol (hereinafter referred to simply as direct esterification reaction) is not particularly limited. Any of In addition, the type of reaction is not particularly limited, and any type such as a continuous type and a batch type may be used. Specifically, a method of continuously performing a reaction in a liquid phase using a palladium-based catalyst is exemplified.

Usually, the reaction mixture obtained by the direct esterification reaction contains unreacted raw materials and the product methyl methacrylate. It contains methanol as a raw material and methyl methacrylate as a product.

The concentration of methanol or methyl methacrylate contained in the reaction mixture varies depending on the reaction conditions and the like.
For example, when the reaction is carried out in a liquid phase using a palladium catalyst, the concentration of methanol contained in the reaction mixture is usually 25%.
~ 70 wt%, the concentration of methyl methacrylate is usually 20 ~
60% by weight. Usually, the reaction mixture further contains unreacted raw materials such as methacrolein, by-products methyl formate and water.

When it is necessary to remove low-boiling by-products such as methyl formate from the reaction mixture, before the distillation for recovering methanol, for example, the reaction mixture is supplied to a distillation column in advance, and the top of the column is supplied. It is advisable to perform an operation such as distilling off low-boiling by-products together with a part of methacrolein and methanol.

In the present invention, when recovering methanol from the reaction mixture by distillation, methacrolein is separately added as an azeotropic agent. The method for adding methacrolein is not particularly limited, and examples thereof include a method of supplying the reaction mixture and methacrolein to appropriate positions in the distillation column, and a method of adding methacrolein to the reaction mixture and then supplying the same to the distillation column. Is mentioned. By this distillation, methanol is removed from the top of the column together with the azeotropic methacrolein.

The amount of methacrolein added at this time is 20 to 2 parts by weight based on 100 parts by weight of methanol in the reaction mixture.
It is preferably 00 parts by weight, particularly preferably 40 to 80 parts by weight. When the amount of methacrolein is less than 20 parts by weight,
When recovering methanol, a large amount of methyl methacrylate may be distilled off, making recovery of methanol difficult.
If it exceeds 0 parts by weight, excess methacrolein is recycled to the reactor, adversely affecting the reaction such that the ratio of the raw material methanol and methacrolein cannot be controlled to an appropriate range, and may cause methacrolein to polymerize.

In the present invention, the type of distillation column used for recovering methanol is not particularly limited, and a known type such as a plate type or a packed column type can be used. When two liquid phases are formed in the column, a decanter may be provided to separate and take out water. The distillation conditions are not particularly limited, but the distillation pressure is preferably normal pressure or reduced pressure, and the column bottom temperature is preferably 120 ° C. or lower to prevent polymerization.

In the present invention, methanol recovered by distillation contains methacrolein. The concentration of methanol and methacrolein in the recovered methanol varies depending on the reaction mixture to be distilled, the operating conditions for distillation, and the like.
% By weight, and the concentration of methacrolein is usually 20 to 70% by weight.

The methanol thus recovered can be directly used as a raw material for producing methyl methacrylate by a direct esterification reaction. When this is used as a raw material for the direct esterification reaction in the original reactor or another reactor, usually, methanol or methacrolein is appropriately added to adjust the desired raw material concentration or supply amount.

[0019]

The present invention will be specifically described below with reference to examples and comparative examples. The weight composition of the reaction mixture and the like was analyzed by gas chromatography.

Example 1 A catalyst (5% by weight palladium-1% by weight lead-1) was placed in a reactor having a 4 L refluxer and a stirrer.
A reaction solution of 350 g of calcium carbonate catalyst containing 700 wt% iron, 700 g of methacrolein, and 1280 g of methanol was added, and while blowing air at a rate of 4.77 Nl / min and nitrogen at a rate of 5.0 Nl / min, the pressure was increased. 40
The reaction was carried out at 0 kPa · abs at a bath temperature of 80 ° C. for 4 hours to synthesize methyl methacrylate. As a result of collecting and analyzing the reaction product, the conversion of methacrolein was 75.1% and the selectivity of methyl methacrylate was 85.2%.

The reaction mixture thus obtained was collected, supplied to a 50-stage distillation column, and low boiling components such as methyl formate were distilled off from the top of the column. The composition of the reaction mixture after distillation was 32.1% by weight of methyl methacrylate, 51.1% by weight of methanol, 8.8% by weight of methacrolein, and 6.4% by weight of water.

Next, this solution was supplied at 394.7 g / h to the 25th stage of an 50-stage Oldershaw distillation column, and methacrolein was supplied to the 24th stage at 105.3 g / h. Distillation was carried out at a ratio of 2.0 and an overhead pressure of 80 kPa · abs. As a result, 53.9% by weight of methanol, 37.4% by weight of methacrolein, 7.4% by weight of methyl methacrylate from the top of the distillation column.
% Of a distillate was obtained at 374.1 g / h, and 78.8% by weight of methyl methacrylate and 16.4% by weight of water were obtained from the bottom of the column.
As a result, a liquid substantially free of methacrolein and methanol was obtained at 125.8 g / h. The distribution ratio of methyl methacrylate in the distillate to methyl methacrylate in the bottom liquid was 0.28. The distillate obtained from the top of the tower
Although it contained a small amount of methyl methacrylate, it could be used as a raw material for the direct esterification reaction without any problem by adding methanol and methacrolein.

Comparative Example 1 Example 1 was repeated except that methacrolein was not supplied to the distillation column.
Distillation for recovering methanol was performed in the same manner as described above. As a result, a liquid containing 72.0% by weight of methanol, 12.3% by weight of methacrolein, and 14.7% by weight of methyl methacrylate was obtained at 280.0 g / h from the top of the distillation column, and methacrylic acid was obtained from the bottom of the column. Methyl 74.7% by weight, water 20.
At 1% by weight, a liquid substantially free of methacrolein and methanol was obtained at 114.7 g / h. However, the distribution ratio of methyl methacrylate in the distillate to methyl methacrylate in the bottom liquid was 0.48, which was higher than that in Example 1.

[0024]

According to the method of the present invention, there is provided a method for producing methyl methacrylate by a direct esterification reaction of methacrolein with methanol, wherein at least methyl methacrylate and methanol obtained by the direct esterification reaction are produced. In a method in which methanol is recovered from a reaction mixture containing the same by distillation and used as a raw material for the direct esterification reaction, the steps are simplified, and the amount of methyl methacrylate contained in the recovered methanol can be reduced.

Continuation of the front page (56) References JP-A-58-157740 (JP, A) JP-A-57-9739 (JP, A) JP-A-58-180457 (JP, A) JP-A-8-268938 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C07C 69/54 C07C 67/54 C07C 67/39

Claims (1)

(57) [Claims] 1. A method for recovering methanol by distillation from a reaction mixture containing at least methyl methacrylate and methanol obtained by direct esterification of methacrolein and methanol, and using the recovered methanol as a raw material for the direct esterification reaction. A method for producing methyl methacrylate, wherein methacrolein is separately added as an azeotropic agent when methanol is recovered by distillation.