Process and installation for concentrating waste sulphuric acids from nitration processes

Abstract

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 The prepurified sulfuric acid withdrawn from the bottom of the first stripping column is fed to the top of a second, serially connected additional indirectly heated stripping column, into the bottom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.

Description

technical field [0001] The present invention relates to a method and a device for purifying and concentrating spent and water-diluted sulfuric acid from a nitration process in which nitric acid is used as a nitration medium in the presence of sulfuric acid. Such water-diluted sulfuric acid is generally referred to hereinafter as "nitration spent acid". Background technique [0002] The nitration process plays an important role in the chemical industry for the preparation of nitro compounds and is carried out on an industrial scale. The nitro compounds produced are in most cases used as valuable intermediates due to the numerous reactivity possibilities of the nitro group and the secondary products which can be generated thereby. [0003] Of particular importance is the nitration of aromatic compounds (e.g. toluene) to produce nitroaromatics, especially dinitrotoluene (2,4-dinitrotoluene; DNT), because aromatic nitro groups can be Easily converted to amino groups, which in ...

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Problems solved by technology

[0038] The main disadvantage of this solution is that the production of the large quantities of water vapor required for DNT stripping from the spent nitrification acid used cannot be successfully achieved by a self-evaporation process, even if the steam is operated under optimal negative pressure conditions for this purpose. Extractor and its evaporator, where the dew point or boiling point of water is still higher than the temperature at which DNT starts to precipitate

Stripping of DNT with the desired efficiency therefore requires the use of significant amounts of additional stripping steam, which greatly increases the steam consumption of the overall process and also implies a significant increase in the amount of waste water

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