METHOD AND SYSTEM FOR CONCENTRATING WASTE SULPHURIC ACIDS FROM NITRATION PROCESSES

Disclosed is a method for recovering diluted waste sulfuric acid containing impurities from nitration processes, a highly concentrated nitric acid required in the nitration process being produced in association with the nitration process by means of extractive rectification with concentrated sulfuric acid which is re-concentrated in order to be reutilized. According to the inventive method, the waste sulfuric acid from the nitration process is fed to the top of a first, indirectly heated stripping column, optionally together with another waste sulfuric acid in the form of a DNT washing acid, and is divided into an overhead product containing nitric acid and nitro-organic compounds as well as a prepurified sulfuric acid in the bottom product. The prepurified sulfuric acid withdrawn from the bottom of the first stripping column is fed to the top of a second, serially connected additional indirectly heated stripping column, into the bottom zone of which another waste sulfuric acid is fed in the form of a diluted sulfuric acid recovered from the nitric acid concentration system such that the prepurified sulfuric acid from the first stripping column is further purified in the second stripping column and is preconcentrated along with the diluted sulfuric acid recovered from the extractive rectification of nitric acid.