Method for separating 4-cyanopyridine by cooling solvent crystallization

Abstract

The invention provides a method for separating 4-cyanopyridine through solvent cooling crystallization. The method comprises the following steps: S1, preparing a 4-cyanopyridine saturated solution; S2, cooling the saturated solution to obtain a mixed slurry; S3, carrying out centrifugal filtration on the mixed slurry, washing with pure water, and carrying out centrifugal filtration and drying to obtain highly-pure 4-cyanopyridine; S4, performing reduced pressure distillation on the obtained filtrate to obtain a solute, heating and decolorizing the solute, and repeating step S1 and step S2 to obtain highly-pure 4-cyanopyridine; and S5, collecting the highly-pure 4-cyanopyridine obtained in step S3 and step S4 to obtain the finished 4-cyanopyridine product. The purity of the 4-cyanopyridineseparated through cooling crystallization is high, and reaches up to 99.54%; the primary filtrate and the washing filtrate are distilled and then purified, so the yield of 4-cyanopyridine is increased, and can reach up to 97.2%; and a separation and purification device for 4-cyanopyridine can complete a series of steps of crystallization, centrifugation, washing, drying and the like in separationand purification of 4-cyanopyridine.

Description

technical field [0001] The invention relates to the technical field of chemical production separation and purification, in particular to a method for separating 4-cyanopyridine by solvent cooling and crystallization. Background technique [0002] 4-cyanopyridine, the molecular formula is C 6 h 4 N 2 , with a molecular weight of 104.11, is a white to pale yellow needle-like crystal with a characteristic odor. Soluble in ethanol, ether and benzene. The main purpose is to be used as intermediate products of medicine and pesticide. [0003] 4-cyanopyridine is mainly derived from the ammoxidative synthesis of alkylpyridine, but the synthesis of 4-cyanopyridine using alkylpyridine is usually accompanied by the formation of 3-cyanopyridine. In order to obtain the required high-purity intermediate raw materials, it is necessary to Separation and purification of crude 4-cyanopyridine, but since 3-cyanopyridine is an isomer of 4-cyanopyridine, the boiling point difference between...

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Problems solved by technology

[0003]4-cyanopyridine is mainly derived from the ammoxidative synthesis of alkylpyridine, but the synthesis of 4-cyanopyridine using alkylpyridine is usually accompanied by 3-cyano Pyridine is generated, in order to obtain the required high-purity intermediate raw material, the crude product of 4-cyanopyridine must be separated and purified, but since 3-cyanopyridine is an isomer of 4-cyanopyridine, 3-cyanopyridine The boiling point difference from 4-cyanopyridine is only 5°C, so it is difficult to separate

[0004] At present, most industrial separations use vacuum distillation to separate and purify 4-cyanopyridine, both 3-cyanopyridine and 4-cyanopyridine are easily sublimable substances , and there is a small amount of fumaronitrile as a by-product in the mixture, fumaronitrile is prone to polymerization during the rectification and separation process, and it is easy to block the equipment of the rectification device and affect its normal operation, resulting in 4-cyanide in industrial production. Unsatisfactory separation of base pyridines and high operating and running costs

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