JPH0217150A - Purification of methyl methacrylate - Google Patents

Abstract

PURPOSE:To obtain the title from the bottom of distillation column by feeding a mixture of methyl methacrylate containing impurities to a distillation column, subjecting methyl methacrylate to azeotropic distillation while making a specific azeotropic solvent exist in a concentrating part of distillation column to purify methyl methacrylate and distilling away the impurities as an azeotropic mixture from the top of the column at a stroke. CONSTITUTION:A mixture mainly consisting of water, methanol and methyl methacrylate is fed to a distillation column, a 6C hydrocarbon such as n-hexane is made to exist as an azeotropic solvent in a concentrating part of distillation column, the mixture is subjected to azeotropic distillation to purify methyl methacrylate, water and methanol, main impurities are fractionated as an azeotropic mixture of the 6C hydrocarbon from the top of the column and the aimed methyl methacrylate is obtained from the bottom of the column. The solution distilled way from the top of the column is subjected to phase separation, an upper layer liquid, the 6C hydrocarbon is returned to the top of the column as a reflux solution, a lower layer solution, methanol and water are removed from out the system and optionally are recovered as an esterifying raw material properly.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for purifying methyl methacrylate.

(Prior art) As a method for purifying methyl methacrylate (hereinafter referred to as MMA), an azeotrope-forming agent that forms an azeotrope with methanol is added to a water-containing mixture of MMA and methanol, and azeotropic distillation is performed. A method for separating methanol using
180457) or ■ When purifying a mixed solution consisting of methanol, water, and MMA by distillation, distillation is performed in the presence of a saturated hydrocarbon having 6 to 7 carbon atoms, and the saturated hydrocarbon and methanol are distilled out from the top of the column. A method of separating MMA and water from the lower part using a decanter and extracting them separately is already known (Japanese Patent Laid-Open No. 57-9740). However, these methods have the following problems. In other words, in method (■), since water still exists in the bottom residue, further treatment such as distillation is required to separate this water, and in method (2), when the top distillate is not separated into two liquids, In this case, separate treatment such as extraction is required to separate the azeotropic solvent and methanol.

Furthermore, in method (2), since water and MMA are separated from the bottom of the column by layer separation, water is contained in MMA up to the maximum solubility variation (for example, the solubility of water in MMA is 25
(1.2% at °C) Further operations such as distillation are required to remove this moisture.

(Problem to be solved by the invention) Generally, MMA contains methacrylic acid, methacrylic acid amide,
It is produced by reacting methacrylonitrile or the like with an excess amount of methanol in the presence of an acidic catalyst. MMA produced by these esterification reactions is extracted by Fujihata,
Mainly water, methanol and MMA are separated by layer separation etc.
It is separated from the esterification reaction solution as a mixture consisting of: Since this mixture mutually forms an azeotrope, complicated operations are required to effectively separate the target component MMA from other impurities, and no satisfactory method has yet been found. .

An object of the present invention is to provide a method for more efficiently distilling and separating water and methanol, which are the main impurities when purifying MMA.

(Means for Solving the Problems) According to the present invention, when a mixture mainly consisting of water, methanol and MMA is supplied to a distillation column to purify MMA by distillation, MMA is used as an azeotropic solvent. Hydrocarbons having 6 carbon atoms (hereinafter referred to as C6 hydrocarbons) are present in the concentration section of the distillation column, and water and methanol are removed from the top of the column.
It is distilled out as an azeotropic mixture of 6 hydrocarbons, and M
This is achieved by an MMA purification method characterized by extracting MA.

(Function) According to the present invention, when a mixture of water, methanol and MMA is supplied to a distillation column to purify MMA by distillation, a C6 hydrocarbon is present as an azeotropic solvent in the concentration section of the distillation column.

In addition to these, the mixture of water, methanol, and MMA usually contains impurities with low boiling points and high boiling points relative to MMA. Further, the mixture is supplied to the distillation column in liquid or vapor form. The C6 hydrocarbons used as an azeotropic solvent in the present invention include n-hexane, cyclohexane, benzene, etc., and n-hexane is preferred because it exhibits better effects.

The most distinctive feature of the present invention is that during distillation,
By allowing C6 hydrocarbons that form azeotropic mixtures with water and methanol to exist in the concentration section of the distillation column, water and methanol can be distilled out at once from the top of the column as an azeotropic mixture of 06 hydrocarbons. It is in.

This column overhead distillate is easily separated into layers using a decanter, and the upper layer is refluxed to the top of the distillation column as substantially C6 hydrocarbons. On the other hand, the lower layer liquid is removed from the system as an aqueous methanol solution, but is appropriately recovered as an esterification raw material if necessary.

The reflux amount of C6 hydrocarbon, which is an azeotropic solvent, is the amount of C6 hydrocarbon necessary to form an azeotropic composition of methanol and 06 hydrocarbon and an azeotropic composition of water and 06 hydrocarbon. For example, n-hexane has an azeotropic composition as shown in Table 1.

Table 1 Note that the azeotropic composition is usually controlled in an amount slightly in excess of the theoretical amount of the azeotropic composition.

(Example) The method of the present invention will be explained below with reference to Examples.

As the distillation column, an Oldershaw type distillation column having an inner diameter of 50 nm and 30 plates was used. A raw material supply port is installed at the 15th stage from the top of the column, while the distillate from the top of the column is separated into layers in a decanter, the upper layer liquid is refluxed to the top of the column, and the lower N liquid is removed from the system. Ta. A round flask is connected to the bottom of the tower.
Immersed in an oil bath.

As a raw material mixture, 97.3 shiro of methyl methacrylate,
Methanol 8.0%, Water 12.7%, Fetch Asia 0
．． Atmospheric distillation was carried out by supplying a liquid having a composition of 0.01% at a flow rate of 135 g/hour.

On the other hand, n-hexane and water have been charged in advance in the decanter, and at the same time as the distillation starts, n-hexane and water are poured into the decanter.
-Hexane was refluxed to the top of the column at 350 g/h. During steady operation of the distillation column, the top temperature is 58℃, and the bottom temperature is 105℃.
It was ℃.

Through this distillation operation, water and methanol were distilled off from the top of the column as an azeotropic mixture with n-hexane, and water and methanol could be removed from the system as a decanter bottom liquid. 18ppm of methanol and 130p of water from the bottom of the tower
105 g/h of MMA containing pm was obtained.

(Effects) According to the method of the present invention, water and methanol, which are the main impurities, can be distilled off at once from the top of the column by azeotropic distillation with C6 hydrocarbons, and then separated from C6 hydrocarbons by layer separation. It shows an excellent effect in that it can be removed from the system.

September 1, 1986

Claims (3)

[Claims] (1) When supplying a mixture mainly consisting of water, methanol and methyl methacrylate to a distillation column to purify methyl methacrylate by distillation, a hydrocarbon having 6 carbon atoms is present in the distillation column concentration section as an azeotropic solvent, A method for purifying methyl methacrylate, which comprises distilling water and methanol from the top as an azeotropic mixture of the hydrocarbons, and extracting methyl methacrylate from the bottom of the column. (2) A method for purifying methyl methacrylate according to claim 1, wherein the liquid distilled from the top of the column is separated into layers, the upper layer liquid is returned to the top of the column as a reflux liquid, and the lower layer liquid is removed from the system. . (3) A method for purifying methyl methacrylate according to claims 1 and 2, in which n-hexane is used as the saturated hydrocarbon having 6 carbon atoms.