Patent EP-2295375-A1 (EP)
Inventor: DICHTL GOTTFRIED
IPC: C01B21/46
Filed: 2009-09-15
Abstract: Processing waste acid obtained from nitroaromatics production, preferably dinitrotoluene- or trinitrotoluene production, comprises: adding a pre-heated waste acid comprising sulfuric acid, water, nitric acid, nitrosylsulfuric acid and nitro-organics, into a stripping column in a counter-flow to the steam obtained from the bottom of the stripping column by heating a pre-concentrated sulfuric acid; separating nitric acid, optionally nitro-organics and the pre-concentrated sulfuric acid into at least one vapor phase; and processing the obtained nitric acid and the nitro-organics. Processing waste acid obtained from nitroaromatics production, preferably dinitrotoluene- or trinitrotoluene production, under recovery of concentrated and purified sulfuric acid and nitric acid, comprises: (i) adding a pre-heated waste acid comprising sulfuric acid and water (up to 80 wt.%), nitric acid, nitrosylsulfuric acid and nitro-organics, preferably dinitrotoluene and mononitrotoluene, into a stripping column in a counter-flow to the steam, which is obtained from the bottom of the stripping column by heating a pre-concentrated sulfuric acid in a first phase; (ii) separating nitric acid, optionally nitro-organics and the pre-concentrated sulfuric acid into at least one vapor phase; and (iii) supplying the obtained pre-concentrated sulfuric acid from the bottom of the stripping column for further purification to separate the highly concentrated nitro-organics in a first downstream stage, and processing nitric acid obtained from the nitric acid vapor phase, and the nitro-organics including the nitro-organics obtained during the further purification and concentration of the pre-concentrated sulfuric acid, and returning back to the nitration process in a second downstream stage. The step (i) comprises: adding the pre-heated waste acid into the stripping column for stripping in the counter-flow to the steam obtained from the pre-concentrated sulfuric acid in concentrating the stripping steam containing nitric acid in the counter-flow to the purified and optionally fresh concentrated sulfuric acid (75-97 wt.%, preferably 80-96 wt.%); and condensing the nitric acid vapors obtained from the top of the column of the first stage, and thus directly obtaining a highly concentrated form of nitric acid for returning back to the nitration process. An independent claim is also included for a device for performing the above method comprising: a first stripping column (K1) with a feeding line for the processed waste acid, an associated evaporator for obtaining the pre-concentrated sulfuric acid and a discharging for the nitric acid containing vapor phase; an additional stripping column (K2) with an associated evaporator for producing a purified sulfuric acid and at least one additional evaporator for highly concentrating the purified sulfuric acid; heat exchanger condensers for vapor phases, which are obtained as top products from the stripping columns and the evaporators; optionally a washing column for washing of nitrogen-containing gases; required piping for feeding the starting materials, transporting, distributing and discharging vapor phase, liquid phase, processing products and waste gases obtained as processing streams; and required heating-, cooling- and pressure control equipments. The first stripping column is provided with a feeding line for a highly concentrated purified sulfuric acid, which is produced during the processing of the waste acid.