Separation Of The 2, 4-/2, 6-dinitrotoluene

Dinitrotoluenes(DNT) are extremely useful compounds as intermediates in the manufactureof the fuel, the pigment, the medicine, the plant protecting agent and the cosmetics. Especially,2,6-DNT is an important raw material in polyurethane industry. Since it is difficult to designgood routes of chemical synthesis of 2,6-DNT, pure 2,6-DNT is obtained by separation fromtechnical mixtures of DNT in recent years.In this paper, the methods of crystallization separation and the chemical reduction werecarries on the separation of industrial DNT. The high purity 2,4-DNT was isolated bycrystallization separation from industrial DNT. The optimum operating condition forcrystallization separation was determined by solubility curve of 2,4-DNT to ethanol.2,6-DNT was obtained in high purity by selective reduction by ammonium sulfide in place ofhydrogen sulfide as reduction agent. The best technological condition was determined bystudying influence of various factors on the results such as 2,4-/2,6-DNT proportion,reduction time and reduction temperature.On the base of the above methods, pure 2,4- and 2,6-DNT were isolated from industrialDNT by the method of combining crystallization separation and chemical reduction. Firstly,high purity 2,4-DNT was isolated by crystallization separation from the industrial DNT, then2,6-DNT was obtained in high purity by selective reduction of the rest. In reduction process,2,4-DNT was removed to 3-nitro-p-toluidine by ammonium sulfide in dioxane solvent. Thereduction product that is an important intermediate employed in medicine and dye industrywas isolated by the filtrate as its hydrochloride salt by passing dry hydrogen chloride.In the crystallization separation, the crystallization cost was reduced through 95wt%ethanol in place of the absolute ethanol. The purity of 2,4-DNT was more than 95%, and theratio of 2,4- DNT to 2,6-DNT in the rest reached 1:1, which is favorable to the furtherseparation. In this paper, hydrogen sulfide was replaced with firstly ammonium sulfide toreduce crude DNT, the best process condition was obtained, when the reaction proceeded at30~40℃ for 4h, the yield of 2,6-DNT reached 75% and the purity was more than 98%(GC).