High purity 2,4-dinitrotoluene from toluene nitration process

摘要

A method for preparing substantially pure 2,4-DNT isomer from its admixture with other DNT isomers which comprises contacting the isomer mixture with aqueous sulfuric acid at an elevated temperature, separating excess DNT isomer mixture from the sulfuric acid phase and cooling the sulfuric acid phase. Also, in a method for producing dinitrotoluenes which comprises:(a) nitrating toluene in a first nitration stage with an aqueous mixture of sulfuric and nitric acids to form an organic phase containing mononitrotoluenes and a first aqueous spent acid Ohase;(b) separating the organic phase from the first aqueous spent acid phase;(c) nitrating the mononitrotoluenes contained in the organic phase in a second nitration stage using a mixture of sulfuric and nitric acids to form an organic phase containing dinitrotoluenes and a second aqueous spent acid phase; and(d) separating the organic phase from the second aqueous spent acid phase for recovery of the dinitrotoluene product from the organic phase; the novel feature comprising:(e) cooling at least a portion of the first or second aqueous spent acid phase to a temperature sufficient to effect crystallization of substantially pure 2,4-DNT;(f) recovering the 2,4-DNT crystals from the cooled aqueous spent acid phase; and(g) returning the portion of the cooled spent acid phase to a nitration stage.