Abstract: 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.

Abstract: The invention concerns a process for working up an effluent containing nitro-hydroxy-aromatic compounds which comprises heating said effluent to 150.degree. C. to 500.degree. C. with the exclusion of air and oxygen and under elevated pressure. The process results in a decrease of nitro-hydroxy-aromatic compound concentration in the effluent to below 20 ppm. and the resulting material can then be fed to a microbiological sewage plant for further working up, without the microorganisms therein being killed by the bactericidally active nitro-hydroxy-aromatic compounds.

Abstract: A process for the electrophoretic breaking of electrically conductive emulsions of electrical conductivity greater than 2,000 .mu.Mhos is described which process comprises adjusting the conductivity of the emulsion so that it is in the range of 0.1 to 2,000 .mu.Mhos by increasing the degree of dispersion and thereafter passing through the emulsion a constant-voltage field of 100 to 1,000 volts.