PREPARATION METHOD OF DINITROTOLUENE BY TWO-STEP NITRATION OF TOLUENE COMPRISING ADIABATIC REACTION AND ISOTHERMAL REACTION TO USE AT LEAST SOME PART OF REACTION HEAT TO CONCENTRATE WASTE ACID AND TO INHIBIT HIGH TEMPERATURE STRESS OF DINITROTOLUENE OR MEDIUM CONTAINING DINITROTOLUENE

摘要

PURPOSE: A method for preparing dinitrotoluene by two-step nitration of toluene is provided, to allow at least some part of reaction heat to be used to concentrate the waste acid and to inhibit the high temperature stress of dinitrotoluene or a medium containing dinitrotoluene. CONSTITUTION: The method comprises a first step comprising the steps of adiabatic reacting toluene with a nitration acid, wherein 90% or more of toluene is removed by reaction and 70 % or less of the used toluene is reacted to form dinitrotoluene, separating an organic phase containing mononitrotoluene and an aqueous phase containing sulfuric acid, flash evaporating the aqueous phase containing sulfuric acid to concentrate it, and recirculating the concentrated sulfuric acid into a reaction part(A) of a first step, a reaction part(E) of a second part, a vacuum evaporator(F) of a second step or their combination; and a second step comprising the steps of isothermal reacting the organic phase containing mononitrotoluene with a nitration acid completely, separating an organic phase and an aqueous phase containing sulfuric acid, concentrating the aqueous phase containing sulfuric acid in vacuum, and recirculating the concentrated sulfuric acid into a reaction part of a first step, a reaction part of a second part or their combination.