2,4-dichlorophenoxyacetic acid continuous reaction crystallization particle size control method

Abstract

The invention relates to a method for controlling a continuous reaction crystal size of a herbicide 2,4-dichlorphenoxyacetic acid. The method comprises the following steps: (1) preparing a 80-100 DEG C saturated or nearly saturated solution of a 2,4-dichlorphenoxyacetic acid salt, and 10-38% hydrochloric acid respectively; (2) in a crystallizer, continuously adding the 2,4-dichlorphenoxyacetic acid salt solution and the hydrochloric acid prepared in the step (1), wherein a molar ratio of the 2,4-dichlorphenoxyacetic acid salt to hydrochloric acid is 1 to (1-1.2), controlling the crystallization temperature at 20-60 DEG C, controlling the retention time to 2-10 hours, continuously discharging the material to an after-treatment process to obtain the 2,4-dichlorphenoxyacetic acid product. According to the crystal size control method disclosed by the invention, the 2,4-dichlorphenoxyacetic acid salt is dissolved at a high temperature, the 2,4-dichlorphenoxyacetic acid salt solution and hydrochloric acid are subjected to a continuous reaction crystallization process in the crystallizer at a low temperature, so that the problems that the 2,4-dichlorphenoxyacetic acid product produced by the process of performing acidification reaction at a high temperature and then cooling for crystallizing is low in purity and small in crystal size and easily causes equipment corrosion are solved. The method has the advantages that the prepared produce has a great crystal size and a high purity, energy consumption is low, equipment corrosion is hardly caused, the operation is simplified and the process is easily controlled automatically.

Description

(1) Technical field [0001] The invention relates to a particle size control method of herbicide 2,4-dichlorophenoxyacetic acid. (2) Background technology [0002] 2,4-dichlorophenoxyacetic acid, referred to as 2,4-D, is one of the most widely used herbicides with the longest history in the world. In its synthetic production process, it is usually necessary to first generate 2,4-dichlorophenoxyacetate, that is, 2,4-D sodium salt or 2,4-D potassium salt, and finally acidify to obtain 2,4-D acid. [0003] The preparation method of 2,4-D in the published patent CN1194259A is as follows: the 2,4-dichlorophenoxyacetic acid sodium salt prepared above is purified in the aqueous phase at a pH value of 9-10 to reduce its phenol content . The sodium salt is then acidified in hydrochloric acid to convert it into 2,4-dichlorophenoxyacetic acid. The acid is filtered through suction to make the chloride qualified, then separated, dried, and packaged into a genuine product; the preparati...

AI Technical Summary

Problems solved by technology

It avoids the phenomenon of liquid-liquid stratification during the crystallization process by cooling after the acidification reaction at high temperature, and then overcomes the problem of small particle size and wide distribution caused by explosive nucleation caused by liquid-liquid stratification