Patent EP-1876142-B1 (EP)
Inventor: WALTER ULRICH
IPC: C01B17/80
Filed: 2006-06-21
Granted: 2008-09-17
Abstract: Recovery of diluted and contaminated sulfuric acid wastes from nitration processes comprises subjecting the nitrating acid waste mixture containing 80 wt.% of sulfuric acid and water, nitric acid, nitrous acid and nitro organic compounds, preferably dinitrotoluene and mononitro toluene as further components, to at least partial purification process in a stripping column for the isolation of the further components; and supplying the obtained mixture into one or more downstream evaporator under vacuum for further saturation process. Recovery of diluted and contaminated sulfuric acid wastes from nitration processes comprises subjecting the nitrating acid waste mixture containing 80 wt.% of sulfuric acid and water, nitric acid, nitrous acid and nitro organic compounds, preferably dinitrotoluene and mononitro toluene as further components, to at least partial purification process in a stripping column for the isolation of the further components; and supplying the obtained mixture into one or more downstream evaporator under vacuum for further saturation process, where: the nitration processes is associated with the manufacture of a highly concentrated nitric acid, which is required for the nitration processes, from a more diluted nitric acid by extractive rectification using concentrated sulfuric acid as extracting solvent; the sulfuric acid is diluted during the extractive rectification process and re-concentrated for reuse; the nitrating acid waste mixture (F1) is supplied at the top of a first stripping column (K1), which is indirectly heated and isolated into an overhead product containing nitroorganic compounds and nitric acid, and pre-purified sulfuric acid as the bottom product, which is then led at the top of a second, sequentially-connected further stripping column (K2), which is also indirectly heated, in whose bottom region or an evaporator, dilute sulfuric acid (F3) from the plant for the saturation of nitric acid by means of extractive rectification process is fed, such that the partially purified sulfuric acid from the first stripping column is further purified in the second stripping column and is pre-concentrated together with the diluted sulfuric acid from the extractive rectification process of nitric acid, after which the partially concentrated sulfuric acid withdrawing from the evaporator of the second stripping column is further concentrated in one or more known evaporator under vacuum. An independent claim is included for a plant for the implementation of the process comprising a first and a second stripping column, each of which is provided with bottom-heaters and condensators, pipelines for the supply of two feed streams from a nitration plant to the top of the first stripping column, and pipelines for feeding an additional feed stream from a plant for higher concentration of nitric acid by extractive distillation, into the evaporator or bottom part of the second stripping column, pipelines for refluxing at least a portion of the condensate from the condensators of the first and second stripping columns, into the nitration plant, at least an evaporator, which is connected with the bottom region of the second stripping column by a pipeline and which works under vacuum, and pipelines for the reflux of a part of the more concentrated sulfuric acid from the evaporator(s) as extracting solvent into the plant for the manufacture of highly concentrated nitric acid by extractive rectification process.