Separation Of Pyridine Compounds In The Pesticide Industry

Separation process has important position in chemical industry. The revised design of the separation process can not only improve the quality of the product but also obtain favorable economic and environmental benefit. The paper studied the separation of two systems: 2-chloro-3-methylpyridine and 2-chloro-5-methylpyridine; 3-methypyridine and 4-methypyridine.A crystalized mother liquor including 2-chloro-3-methylpyridine and 2-chloro-5-methylpyridine is treated by applying extractive distillation. 1,4-butanediol is selected as an appropriate extractant, which enhance a AB of this system from 1.16 to over 1.50. Based on this, vacuum distillation columns are established. By applying semi-continuous extractive distillation method, using the packed column with 43 NTP(number of theoretical plates), both products with purity of over 95%(w.t.) can be obtained in the conditions that the vacuum of the whole column is 0.097-0.093MPa, the temperature of the column top and of its bottom are about 86 C and 112~122C individually and the reflux ratio is 10. These operation conditions are duplicative. Extractant can be recovered and reused. The result shows that extractive distillation can be applied to separate 2-chloro-3-methylpyridine and 2-chloro-5-methylpyridine and can obtain high purity and high yield of the products at the same time. This process has commercial value.Futher more, we have discussed the separation of 3-methylpiridine and 4-methylpiridine and from the molecular structures, we have explained the reason why 1,4- butanediol is useless to separate this system.