JP2582127B2 - Purification method of methyl methacrylate - Google Patents

Description

Description: TECHNICAL 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 azeotropic agent that forms an azeotropic mixture with methanol is added to a water-containing mixture of MMA and methanol, and azeotropic distillation is performed. (JP-A-58-180457)
When distilling and purifying a mixed solution consisting of methanol, water, and MMA, distillation is performed in the presence of a saturated hydrocarbon having 6 to 7 carbon atoms to distill the saturated hydrocarbon and methanol from the top of the column, and from the bottom of the column There is already known a method of separating MMA and water by a decanter and extracting them separately (Japanese Patent Application Laid-Open No. 57-9740). However, these methods have the following problems. That is, in the method (2), since water still exists in the bottom residue, further treatment such as distillation is required for this separation. In such a case, the top distillate may not be separated into two liquids. In such a case, a separate treatment such as extraction is required to separate the azeotropic solvent and methanol.

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

(Problems to be Solved by the Invention) Generally, MMA is methacrylic acid, methacrylamide,
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 separated from the esterification reaction liquid as a mixture mainly composed of water, methanol and MMA by a method such as evaporation, extraction, and phase separation. Since this mixture forms an azeotropic composition with each other, complicated operations are required to effectively separate the target component MMA from other impurities, and a satisfactory method has not 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 main impurities when MMA is purified.

(Means for Solving the Problems) According to the present invention, such a purpose is achieved by supplying a mixture mainly consisting of water, methanol and MMA to a distillation column by feeding the mixture to a distillation column.
In purifying MA by distillation, a hydrocarbon having 6 carbon atoms (hereinafter referred to as C6 hydrocarbon) is used as an azeotropic solvent in an amount required to form an azeotropic composition with water and methanol in the enrichment section of the distillation column. This is achieved by a method for purifying MMA, comprising distilling water and methanol from the top of the column as an azeotrope of C6 hydrocarbons and extracting MMA from the bottom of the column.

The present invention provides water, a mixture of methanol and MMA to a distillation column to distill and purify MMA, C6 as an azeotropic solvent
The hydrocarbon is caused to exist in the enrichment section of the distillation column. Here, a mixture of water, methanol and MMA usually contains impurities having a low boiling point and a high boiling point relative to MMA. The mixture is supplied to the distillation column in a liquid or vapor state. The C6 hydrocarbon used as the azeotropic solvent in the present invention is n-hexane, cyclohexane, benzene, etc., and n-hexane is preferable because it shows a better action.

The most characteristic feature of the present invention is that C6 forms an azeotrope with water and methanol upon distillation.
By making the hydrocarbons present in the enrichment section of the distillation column, water and methanol can be distilled off at once from the top of the column as an azeotropic mixture of C6 hydrocarbons.

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

The amount of reflux of C6 hydrocarbon, which is an azeotropic solvent, is
It is the amount of C6 hydrocarbon required to form an azeotropic composition with C6 hydrocarbons and an azeotropic composition with water and C6 hydrocarbons. For example, n-hexane shows an azeotropic composition as shown in Table 1.

Normally, the azeotropic composition is controlled in a slightly excessive amount than the theoretical amount.

(Examples) Hereinafter, the method of the present invention will be described with reference to examples.

An old-shaw distillation column having an inner diameter of 50 mm and 30 stages was used as the distillation column. A feed port was provided at the 15th stage from the top of the tower. On the other hand, the distillate from the top was separated into layers by a decanter, the upper liquid was refluxed to the top, and the lower liquid was removed outside the system. A round flask is connected to the bottom of the column and is immersed in an oil bath.

As a raw material mixture, a liquid having a composition of 79.3% of methyl methacrylate, 8.0% of methanol, 12.69% of water, and 0.01% of phenothiazine was supplied at a flow rate of 135 g / hour, and atmospheric distillation was performed.

On the other hand, n-hexane and water were previously charged in the decanter, and n-hexane was refluxed from the decanter to the top of the tower at a rate of 350 g / hour simultaneously with the start of distillation. During steady state operation of the distillation column, the top temperature was 58 ° C, and the bottom temperature was 105 ° C.

By this distillation operation, water and methanol were distilled off from the top of the column as an azeotrope with n-hexane, and water and methanol could be removed outside the system as a decanter lower layer liquid. MMA containing 18 ppm of methanol and 130 ppm of water was obtained at a rate of 105 g / h from the bottom of the column.

(Effect) According to the method of the present invention, water and methanol as main impurities can be distilled off at once from the top of the column by azeotropic distillation with C6 hydrocarbon, and then separated from C6 hydrocarbon by layer separation, It has an excellent effect that it can be removed outside the system.

Continuation of front page (56) References JP-A-57-9740 (JP, A) JP-A-57-9739 (JP, A) JP-A-58-203940 (JP, A) JP-A-58-180457 (JP) JP-A-49-5916 (JP, A) JP-A-48-14617 (JP, A)

Claims (1)

(57) [Claims] 1. When a mixture mainly composed of water, methanol and methyl methacrylate is supplied to a distillation column to purify methyl methacrylate by distillation, a hydrocarbon having 6 carbon atoms is added as an azeotropic solvent to the enrichment section of the distillation column. And methacrylic acid, which is present in an amount required to form an azeotropic composition with methanol and methanol, distills water and methanol as an azeotropic mixture of the hydrocarbon from the top of the column, and extracts methyl methacrylate from the bottom of the column. Method for purifying methyl acid.