Method and plant for reprocessing waste sulphuric acids from nitration processes

A process for recovery of concentrated and purified sulfuric acid, and nitric acid from waste acid from processes for preparation of nitroaromatics, the process comprising,

• (a) a first stage comprising
• (i) feeding a waste acid, in preheated form, comprising up to 80% by mass of sulfuric acid, water, nitric acid (HNO3), nitrosylsulfuric acid (as HNO2), and nitroorganics into a first stripping column;
• and
• (ii) separating said waste acid in countercurrent to steam, wherein said stream is obtained by heating the sulfuric acid to at least one vaporous phase, which is recovered from a top portion of the first stripping column, the vaporous phase comprising nitric acid, and accumulating sulfuric acid in a bottom portion of the first stripping column;
• and
• (b) a second stage comprising
• (i) supplying the sulfuric acid obtained from the bottom portion of the first stripping column to a further purification step for removal of nitroorganics and for higher concentrating of the sulfuric acid;
• and
• (ii) working up and recycling back into a nitration process, the nitric acid obtained from the vaporous nitric acid phase and the nitroorganics, including the nitroorganics obtained in the further purification and concentrating of the sulfuric acid,
• wherein,
• the first stage of the process further comprises concentrating the nitric acid present in the at least one vaporous phase in countercurrent to additional purified sulfuric acid having a concentration in the range from 75 to 97% by mass, and the nitric acid vapors obtained from the top portion of the first stripping column of the first stage are condensed to obtain a nitric acid directly in a highly concentrated form suitable for recycling into the nitration process.