Process for purification and concentration of sulfuric acid

In a process for the purification and concentration of spent sulfuric acid obtained from a mixed acid nitration of aromatic compounds wherein organic contaminants and nitrogen containing by-products contained in the spent sulfuric acid are removed in a purification system and then the contaminant-free sulfuric acid concentrated in a sulfuric acid concentration system

• the improvement residing in the integration of the purification system with a concentration system which comprises:
• heat exchanging spent sulfuric acid feedstock in indirect heat exchange with heated, concentrated sulfuric acid obtained from the sulfuric acid concentration system prior to introduction to said purification system;
• introducing the preheated hot sulfuric acid feedstock into an upper portion of a purification system comprising a stripping column wherein organic contaminants and nitrogen-containing by-products are removed by countercurrent contact with superheated steam or heated gases;
• removing a contaminant-free sulfuric acid stream from a lower portion of said stripping column and introducing said contaminant-free sulfuric acid to a first stage of a sulfuric acid concentration system comprising a multiple effect vacuum concentration system;
• establishing a pressure differential between the removal point for the contaminant-free sulfuric acid from the stripping column and the entry point to the first stage of said sulfuric acid system comprising a multiple effect evaporator system such that the pressure differential is sufficient to provide flow from said stripping column to the multiple effect evaporator system without external pumps.