Method for purifying 3,4,5,6-tetrachloro-2-cyanopyridine by sublimation and catching, and catcher and system thereof

Abstract

The invention relates to preparation of a compound 3,4,5,6-tetrachloro-2-cyanopyridine, in particular to a method for catching and purifying 3,4,5,6-tetrachloro-2-cyanopyridine in a gas reaction product in a gas phase chlorination process for producing 3,4,5,6-tetrachloro-2-cyanopyridine. The method comprises the following steps: (1) primary sublimation catching: a reaction gas mixture containing3,4,5,6-tetrachloro-2-cyanopyridine from a reaction bed enters a first catcher, an inert gas is introduced, the gases are thoroughly mixed and quenched to 135-165 DEG C, and sublimated flocculent crystals fall to a material outlet at the bottom of the first catcher by gravity and are discharged; and (2) secondary sublimation catching: the gas which is not sublimated in the primary sublimation catching enters a second catcher, an inert gas is introduced, gases are thoroughly mixed and quenched to 55-110 DEG C, sublimated flocculent crystals fall to a material outlet at the bottom of the secondcatcher by gravity and are discharged, and the gas which is not sublimated enters a bubbling absorber. In the invention, the solid product can be further hydrolyzed to obtain high-purity 3,4,5,6-tetrachloropyridine-2-carboxylic acid; and the invention has the characteristic of simple technique, and is easy to operate and control.

Description

technical field [0001] The present invention relates to the preparation of compound 3,4,5,6-tetrachloro-2-cyanopyridine, in particular to a method for producing 3,4,5,6-tetrachloro-pyridine from 2-cyanopyridine gas phase chlorination A method for trapping and purifying 3,4,5,6-tetrachloro-2-cyanopyridine from gaseous reaction products of 2-cyanopyridine, a desublimation trap and a device system. Background technique [0002] 3,4,5,6-Tetrachloro-2-cyanopyridine is hydrolyzed to produce 3,4,5,6-tetrachloropicolinic acid, which is an important intermediate in pesticides and fine chemicals. It is mainly used in the synthesis of herbicides diquam (3,6-dichloropicolinic acid, biktax), picloram (piclopyr), and citriron (fluroxypyr, fluroxypyr, fluroxypyr) and so on. [0003] At present, there are mainly two methods for synthesizing 3,4,5,6-tetrachloropicolinic acid at home and abroad. One method is to use 2-picoline as the starting material, and synthesize 3,4,5 through liquid pha...

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Problems solved by technology

The main defect of this method is that due to the batch reaction of kettle type, the control of process conditions is complicated, so the reaction selectivity is poor, the separation of products is difficult, resulting in low yield, large amount of three wastes, and it is not easy to realize automatic control.

[0004]Another method is to use 2-cyanopyridine as the starting material to synthesize 3,4,5,6-tetrachloropicolinic acid through gas phase chlorination and hydrolysis , European Patent EP182111 uses 2-cyanopyridine and chlorine in a fluidized bed reactor equipped with activated carbon at 500 ° C to obtain 98% of 3,4,5,6-tetrachloro-2-cyanopyridine and 4% pentachloropyridine; Chinese patent CN 100579964C also uses 2-cyanopyridine as a raw material, and increases the components of zinc chloride and cobalt chloride in activated carbon impregnated with ferric chloride and hydrochloric acid as a catalyst to synthesize 3,4 , 5,6-tetrachloro-2-cyanopyridine, none of these patents mentioned how to trap and purify 3,4,5,6-tetrachloro-2-cyanopyridine solid product from the reaction mixture

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