SU639858A1 - Method of purifying acrylic or methacrylic acid - Google Patents

Description

the temperature in the external crystallizer before the crystals form in it, then the mixers of the crystallizer and the column are turned on, while the suspension of crystals is fed from the external crystallizer to the column, cooling the liquid there due to partial melting of the crystals. After the column is filled with a suspension of crystals, the melter is turned on. The crystals move downward and melt, the liquid displaced by the crystals moves upward to the countercurrent of the crystals.

Due to the mass exchange between the crystals and the liquid, and also because of the repeated inversion of the phases, impurities accumulate in the upper part of the column. Purified acid is taken from the bottom of the column, and from above the mother liquor, part of which is returned to the external crystallizer.

Example 1. The proposed method is purified acrylic acid, obtained nz ethylene cyanohydrin and containing impurities: acrylic aldehyde, propyl alcohol, butyl alcohol, acetic and propionic acid. Cleaning parameters: temperature in the crystallizer from -5 to -2 ° С, temperature in the mass-exchange part of the column is 10-13 ° С. Solids phase

55%. The flow of the solid phase 0,00005.

CM

The analysis for the content of impurities is carried out by gas-liquid chromatography, which has a sensitivity for individual impurities mol%. The relative analysis error is ± 10%. Conditions for gas chromatographic analysis: liquid phase - polyethylene glycol adipate, applied in an amount of 15% per W chromosorb with a grain size of 60-80 mesh, a column of 0.8 m glass with a diameter of 3 mm, carrier gas (nitrogen) 50 at a column temperature of 100 ° C.

The results of purification of acrylic acid are given in table. one

Table 1

Note. Acrylic aldehyde and -propnlovy alcohol within the range of 10 - 10 mol. % is not detected. The water content is determined by Fisher titration.

Example 2. The methacrylic acid obtained from acetone cyanohydrin and containing impurities is purified using the proposed method: acetone, methyl methacrylate, acetic acid, and isobutyric acid. Cleaning parameters: the temperature in the crystallizer is 2–4 ° C, the temperature in the mass transfer part of the column is 13–15 ° C. The fraction of the solid phase is 45%. Solid Phase 0.000034

45%. Solid phase flow 0.000034 -.

The content of impurities is determined by gas-liquid chromatography, which has a sensitivity for individual impurities of 10 -lO-- mol. %, relative analysis error ± 10%. The results of cleaning samples of methacrylic acid containing different amounts of impurities are given in table. 2 and 3.

The proposed method allows to obtain a purified product with a basic substance content of 99.9% and with almost no loss.

Claims (1)

Table 2 Claims of the invention The method of purification of acrylic or methacrylic acid by crystallization of the technical specified acid differs by 5 times and in order to increase Table 3 stages of purification of the target product, crystallization is carried out from the melt of technical acrylic acid using countercurrent liquid phase and crystals and the process is carried out at a temperature of from -5 to + 8 ° C.