The Research On The Separation Of 2,4-dinitrotoluene By Crystallization And Sweating Process

Dinitrotoluene(DNT)is a kind of important organic intermediate,especially 2,4-DNT is an important organic chemical raw material which can be used for producing polyurethane materials,dye and pharmaceutical intermediates.Currently the high purity of industrial made DNT was chosen to prepare the 2,4-DNT.This paper adopts the method of crystallization sweating to separate 2,4-DNT from industrial DNT,and the influence of temperature,equipment structure on the purity and yield of 2,4-DNT was studied.The used equipment structure is simple and easy to be operated,no waste water producing,the obtained waste and intermediates during the separation procedure can be recycled in DNT production line.Using the method of crystallization sweating,experimental studies on the separation of2,4-DNT was done in a small vertical separator,and the optimized conditions in the process of crystallization sweating was determined as cooling rate 0.12 ~ 0.12 ? / min,the terminal temperature of crystallization controlled as 25 ~ 30 ?,heating rate less than0.1 ? / min,ending temperature of sweating as 66 ~ 68 ?.Finally,the purity of 2,4-DNT is achieved to be more than 98.5% with freezing point above 68.0 ? and the yield around 25 ~ 35%.The pilot scale experiment was carried out on the basis of the pilot test.From the study of vertical separator with horizontal separator,it can be concluded that the equipment structure of separation has an influence on the result of crystallization separation.In pilot vertical separator test,separation time is in 16 ~ 18 hours,purity of 2,4-DNT can be obtained around 98.5 ~ 98.8%,freezing point is 67.0 ~ 69.0 ?,and the yield is approximate 16 ~ 22%.In pilot test of horizontal separator,separation time is 12 ~ 15 hours,purity of 2,4-DNT is 98.5 ~ 99.3%,freezing point is 67.0 ~ 69.0 ?,and the yield is 10 ~15%.The result of pilot test is slightly smaller than that of vertical separation test.Comprehensive analysis of the pros and cons of vertical separator and horizontal separator for preparation of 2,4-DNT,vertical separator is advisable to adopt at industrialized production.