Purification of sulphuric acid used for nitration of aromatics

摘要

Contaminated H2SO4 which has been used for the nitration of aromatic hydrocarbons is purified and concentrated by a process that completely removes steam volatile compounds produced by the decomposition of nitrogen containing impurities and then concentrates the H2SO4. The impure H2SO4 is preheated in a heat exchanger before being passed in counterflow to steam together with vapour from the first concentration stage at a pressure of from 200-1000 (especially 300 to 500) and in a ratio of 10:90-90:10 mbar. The acid is then concentrated in a 1st stage, at similar pressure using indirect heating. This acid is then further concentrated at a lower pressure in a single or multi-stage vacuum concentration process to 88-97 (especially 92 to 96) wt.%.