METHOD FOR COMBINED SYNTHESIS OF ISOCYANATES AND CHLORINE Russian patent published in 2012 - IPC C07C263/10 C07C265/12 C07C265/14 C01B7/04 C01B7/07 C25B1/26 C07C201/08 C07C205/06 

FIELD: chemistry.

SUBSTANCE: method involves a step a) for nitratio of aromatic compounds selected from a group comprising toluene, chlorotoluene, benzene and chlorobenzene, to obtain in a single step or two steps the corresponding one- or two-fold nitrated aromatic compounds, respectively, using nitric acid. Nitration is carried out in the presence of sulphuric acid with concentration of 65.0-98.0 wt % of sulphuric acid per weight parts of sulphuric acid and water as a catalyst. After nitration, sulphuric acid is diluted to concentration which is 0.5-25% lower than that of the sulphuric acid used. At step b), the diluted sulphuric acid obtained at step a) is concentrated, where the total flux of sulphuric acid is first concentrated to concentration required for nitration at step a) and then only a portion of the stream from the total flux of sulphuric acid is concentrated at an additional distillation step. At step c) the one- or two-fold nitrated aromatic compound obtained at step a) reacts with hydrogen in the presence of a catalyst to form the corresponding amine. At step d) the amine obtained at step c) reacts with phosgene to form the corresponding isocyanates. At step e) hydrogen chloride which is dissolved in water or gaseous, formed during reaction of amine with phosgene, is recycled from step d) to step f) to obtain chlorine gas via electrolysis of HCl or catalytic gas-phase oxidation of HCl with oxygen. At step g) reaction water is removed while drying chlorine gas obtained at step f) by treating chlorine gas with sulphuric acid with concentration of 90.0-99.0 wt % of sulphuric acid per weight fraction of sulphuric acid and water until sulphuric acid has concentration of 65.0-90.0 wt % sulphuric acid per weight fraction of sulphuric acid and water. At step h), dry chlorine gas obtained at step g) reacts with carbon monoxide to obtain phosgene. At step i), phosgene obtained at step h) is taken to step d). At step j), diluted sulphuric acid obtained at step g) is directed either for the same concentration of sulphuric acid at step b) or directly to one or more nitration steps according to step a) and diluted sulphuric acid from said step or said nitration steps is then finally directed for the same concentration of sulphuric acid according to step b). Diluted streams of sulphuric acid at step b) obtained at steps a) and g) are merged and concentrated together and through one or more vacuum distillation steps, the merged stream is brought to high concentration or by tapping a portion of the streams after different distillation steps, the merged stream is brought to several high concentration values required, respectively, for one or more nitration steps of aromatic compounds according to step a) or drying chlorine gas according to step g). At step k), concentrated sulphuric acid obtained at step j) undergoes final recirculation either for complete or partial feed to step g) and/or step a). The invention also relates to a method for combined synthesis of aromatic isocyanates and chlorine, in which at step a) the aromatic compound used is benzene.

EFFECT: method enables to cut power consumption and consumption of neutralising agents during combined synthesis of aromatic isocyanates and chlorine owing to treatment of the merged stream of diluted sulphuric acid obtained in each of said processes.

9 cl