JPS6115057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating methacrylic acid. More specifically, the present invention relates to a method for separating methacrylic acid from a liquid mixture containing water, methanol, methacrylic acid, and methyl methacrylate by distillation. The esterification reaction of methacrylic acid with methanol is an equilibrium reaction, and the resulting reaction products are water,
It is a mixture consisting of methanol, methacrylic acid and methyl methacrylate. Many methods such as extraction and distillation are known as methods for separating the desired product, methyl methacrylate, from such reaction products, but these methods are not necessarily satisfactory from an economic standpoint. In such cases, the presence of methacrylic acid in the esterification reaction product often makes the separation operation of methyl methacrylate complicated and economically disadvantageous. For example, when performing liquid phase extraction of the esterification reaction product with an organic solvent and water and separating methyl methacrylate into the organic phase and methanol into the aqueous phase, methacrylic acid is easily dissolved in water, so the aqueous phase However, it is difficult to recover dilute methacrylic acid from this aqueous solution, and even if it is to be disposed of, decomposition and detoxification of methacrylic acid using biological methods is required, making it economically extremely difficult. It is disadvantageous. Furthermore, since methacrylic acid is easily polymerized, when the esterification reaction product is distilled to separate methyl methacrylate, the methacrylic acid may polymerize and cause problems. Therefore, it is desirable to separate and remove methacrylic acid before separating methyl methacrylate from the esterification reaction product. An object of the present invention is to provide a method for efficiently and highly selectively separating methacrylic acid from a mixed liquid containing water, methanol, methacrylic acid, and methyl methacrylate; Therefore, a mixture containing water, methanol, methacrylic acid and methyl methacrylate is distilled while maintaining the distillation system such that methyl methacrylate is present in the distillation system during the period in which water is present in the distillation system. This is achieved by separating methacrylic acid by distilling off substantially all of the water, methanol and methyl methacrylate from the top of the column, and extracting substantially all of the methacrylic acid from the bottom of the column. To explain the present invention in detail, according to the method of the present invention, a mixed liquid containing water, methanol, methacrylic acid, and methyl methacrylate (for example, a reaction product of esterification of methacrylic acid with methanol) is distilled from the top of the column. In order to distill out substantially all of the water, methanol and methyl methacrylate and to extract substantially all of the methacrylic acid from the bottom of the column, the water contained in the above liquid mixture is distilled by azeotropic distillation with methyl methacrylate. It is necessary that a sufficient amount of methyl methacrylate be contained in the mixture so that it can be substantially distilled off from the top of the column. If a sufficient amount of methyl methacrylate is not present for water to be substantially removed from the top by azeotropic distillation with methyl methacrylate, methacrylic acid is removed from the top by azeotropic distillation with water. Since it is distilled off, methacrylic acid is contained in the distillate. The amount of methyl methacrylate that is sufficient to substantially distill off the water contained in the liquid mixture from the top of the column by azeotropic distillation with methyl methacrylate is as follows:
Once the amounts of water and methanol in the mixture are known, calculations can be made based on the composition of the water-methyl methacrylate and methanol-methyl methacrylate azeotropes under operating pressure. In other words, since methyl methacrylate azeotropes with methanol as well as water, the amount of methacrylate necessary to distill substantially all of the water and methanol in the mixture from the top of the column by azeotropic distillation with methyl methacrylate. The presence of methyl acid is sufficient. If methyl methacrylate is insufficient, methyl methacrylate may be replenished by refluxing the oil phase of the distillate. In this case, the reflux amount may be selected as appropriate, but the reflux ratio is usually 0.
Selected from the range ~0.5. The above-mentioned distillation is carried out in a conventional manner using a conventional distillation column. Distillation is usually carried out under normal pressure or reduced pressure, but preferably carried out at reduced pressure and low temperature in order to prevent polymerization of methacrylic acid and methyl methacrylate. By carrying out the distillation as described above, substantially the entire amount of methacrylic acid is obtained from the bottom of the column in a state containing almost no other components. Although methacrylic acid is distilled from the top of the column in an amount corresponding to the vapor pressure, this is negligible in terms of the total amount of methacrylic acid. The methacrylic acid thus obtained from the bottom of the column is recovered and reused as a raw material for purification or esterification reaction, if necessary. Methyl methacrylate can be relatively easily extracted from a mixture of methyl methacrylate, water and methanol, which is a distillate from the top of the tower and which does not substantially contain methacrylic acid, by methods such as solvent extraction and distillation. Can be separated. As described above, according to the method of the present invention, water,
Separation of methacrylic acid from a mixed solution containing methanol, methacrylic acid, and methyl methacrylate can be performed easily and economically. 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. Example A raw material mixture (38
°C), top pressure 115 Torr, bottom temperature 110
Distillation was carried out under conditions of 37°C and a column top temperature of 37°C. The distillate is separated into two liquid phases after cooling, so the oil phase is
It was refluxed at a reflux ratio of 0.1. The compositions of the distillate and bottoms thus obtained are shown in the table below. 【table】

Claims (1)

[Claims] 1. A mixture containing water, methanol, methacrylic acid, and methyl methacrylate is maintained in the distillation system so that methyl methacrylate is present during the period when water is present in the distillation system. 1. A method for separating methacrylic acid, which comprises distilling water, methanol, and methyl methacrylate from the top of the column, and extracting substantially all of the methacrylic acid from the bottom of the column. 2. In the method for separating methacrylic acid as set forth in claim 1, a sufficient amount of methacrylic acid is used to substantially distill off water contained in the liquid mixture from the top of the column by azeotropic distillation with methyl methacrylate. A method characterized in that methyl acid is contained in the mixture.