Process for purifying and concentrating spent sulfuric acids

Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing


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423523, 423526, 423528, 423529, 423531, C01B 1790




A process is provided for the purification of sulfuric acid contaminated with impurities, such as nitric acid, nitrosylsulfuric acid, dinitrotoluenes and mononitrotoluenes, wherein this contaminated sulfuric acid was obtained from the production of nitrated toluene using toluene and nitric acid. The contaminated sulfuric acid is preheated to a temperature in the range of 50 to C. in a heat exchanger. The heated, contaminated sulfuric acid is freed from steam-volatile impurities, such as dinitrotoluenes and mononitrotoluenes, and the nitrogen-containing compounds within the sulfuric acid are decomposed by counter currently contacting the contaminated sulfuric acid with steam and vapors from a downstream concentration step in a steam stripper, which is operated at a pressure ranging from 300 to 1,000 mbars. The steam-stripped sulfuric acid is fed into a first concentration stage, which is operated at the same pressure used in the steam stripper. The concentrated sulfur acid is then fed into a vacuum concentration process which produces a sulfuric acid having a concentration of 88 to 97 percent by weight. By using the same pressure that the steam stripper operates at in the first concentration stage, the crystallization of nitroaromatic compounds can be avoided in the condensation system of the concentration stages, along with the concomitant blockage of the condensation system that would have been caused by the crystals.

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