SE8206251L - PREPARATION OF CHLORIDE Dioxide - Google Patents

Abstract

HCl and H2SO4 are prepd. by (a) separately feeding Cl2, SO2 and water vapour reaction zone and intimately contacting in the presence of air, excess Cl2 and water according to SO2+Cl2+2H2O=2HCl+H2SO4, forming an aq. mixt. of HCl and H2SO4; (b) venting unreacted Cl2 and air, with partial press. vented Cl2 controlled within 150-550 Mmm Hg to provide sufficient excess Cl2 in the zone to form an aq. mixt. of HCl and H2SO4 having total acid normality 6-14N which is free from dissolved SO2; and (c) removing the SO2-free acid mixt. from the reaction zone. ClO2 is prepd. by (d) reacting NaClO3 with Cl-ions provided by HCl and opt. NaCl, and H+ ions, provided by HCl and H2SO4, in aq. acid reaction medium having total acid 2-4.8N; (e) maintaining at b.pt., ClO2 decomposition temp., under subatmospheric pressure, to form steam with a steam:ClO2 vol. ratio 4-10:1; (f) depositing anhydrous neutral Na2SO4 and removing from the medium; (g) removing a gas mixt. of ClO2, Cl2 and steam from the zone and forming an aq. soln. of ClO2 contg. some Cl2; (h) forwarding remaining Cl2 admixed with air at atmos. pressure for reaction as (a), (b) in a second reaction zone; and (i) forwarding the prod. from (c) to (d) with additional H+, Cl- and SO4=to maintain stoichiometry. The acid prod. is suitable for ClO2 prodn., where even 1 g/l SO2 decreases efficiency. The relationship between excess Cl2 and acid normality for prod. contg. O g/l SO2 is linear, pressure decreasing with normality, e.g. from 150 mm Hg excess Cl2 for 6.5N to 550 mm Hg for 14N, so control of gas outlet pressure provides simple control of dissolved gas in the prod.