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AssigneeBayer Aktiengesellschaft
InventorsGunter Lailach, Rudolf Gerken, Karl-Heinz Schultz, Rudolf Hornung, Walter Bockmann, Wolfgang Larbig, Wolfgang Dietz
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In the production of nitrobenzene by subjecting benzene to nitration with a mixture of nitric acid and sulfuric acid, separating off the nitrobenzene formed, concentrating the sulfuric acid by evaporation and returning the concentrated sulfuric acid to the bezene nitration stage, the improvement which comprises concentrating sulfuric acid to a concentration of from 75 to 92% by evaporation in vacuo at temperatures in the range from 130.degree. to 195.degree. C. Thereby the energy per kg of water evaporated is drastically reduced compared to processes wherein the sulfuric acid is concentrated to a higher level, without a corresponding loss in efficiency or capacity.
In the production of nitrobenzene by subjecting an excess of benzene to isothermal nitration with a mixture of nitric acid and sulfuric acid, separating off the nitrobenzene formed, concentrating spent acid consisting essentially of sulfuric acid and a small amount of impurities by evaporation and returning the concentrated sulfuric acid to the benzene nitration stage, the improvement which comprises concentrating sulfuric acid to a concentration of 75 to 92 wt. % by evaporation in vacuo at temperatures in the range from 130.degree. to 195.degree. C. in a plurality of horizontal stages of increasing concentration, the vapors from the evaporation being condensed without rectification, whereby the flow through the horizontal stages results in improved NOx decontamination.
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