PROCESS FOR THE COUPLED PRODUCTION OF CHLORINE AND ISOCYANATES

A process for coupled production of chlorine and isocyanate is provided to treat the sulfuric acid used in two processes by a process for saving neutralizing agents without high energy costs and investment costs, and to return the treated sulfuric acid both to chlorine production and to nitration reaction. A process for coupled production of chlorine and isocyanate comprises the steps of: (1) nitrating an aromatic compound with nitric acid in the presence of 65.0-98.0 mass% of sulfuric acid until the concentration of the sulfuric acid reachs 0.5-25 mass% to prepare a nitrated aromatic compound; (2) transferring the obtained sulfuric acid to a sulfuric acid concentration plant; (3) reacting the nitrated aromatic compound with hydrogen to obtain an amine or diamine; (4) if the prepared amine is aniline, further reacting the aniline with formaldehyde; (5) reacting the produced amine with phosgene to prepare an isocyanate; (6) transferring hydrogen chloride obtained in step (5) to a chlorine gas production device; (7) producing chlorine gas in the chlorine gas production device; (8) removing moisture from the chlorine gas by treating the chlorine gas with 90.0-99.0 mass % of sulfuric acid until ; (9) reacting the chlorine gas with carbon monoxide to produce phosgene; (10) feeding the obtained phosgene to the reaction in step (5); (11) transferring the sulfuric acid from step (8) either to (i) the sulfuric acid concentration plant or (ii) to at least one nitration reaction; (12) increasing concentration of the sulfuric acid streams added in the sulfuric acid concentration plant by vacuum distillation stages or by removing split streams after different distillation stages; and (13) returning the concentrated sulfuric acid to step (8) and/or step (1).