Conversion of KCl into KHSO4 in a membrane reactor: long-term experiments

The studies of a conversion of KCl with H2SO4 into KHSO4 were performed using a reactor associated with direct contact membrane distillation (DCMD). Polypropylene (PP) capillary membranes were used in the experiments. The feed comprised of solutions containing 1 mol of KCl with various initial concentrations of H2SO4, equal to 1, 1.25 and 2 moles. The feed temperature at the inlet of the module amounted to 343 K and permeate 293 K. The reaction mixture was concentrated close to the saturated state, when crystals of KHSO4 were precipitated from the solution after cooling. The mother liquor after separation of the precipitate was again concentrated by membrane distillation (MD). At DCMD operation conditions the transfer of water vapour and hydrogen chloride from the reaction mixture through the pores of hydrophobic membranes took place, whereas the non-volatile components were totally retained and continuously concentrated in the feed. It was found that amounts of hydrochloric acid in the permeate as well as amounts of KHSO4 salt precipitated from the reaction mixture increased with a rise in the sulphuric acid concentration in the feed.

The membrane reactor associated with DCMD was successfully applied to conversion of KCl with H2SO4 into KHSO4. The presence of salt and H2SO4 in the feed influenced an increase of the molar flux of HCl through the hydrophobic membrane during MD. The excess of H2SO4 was profitable for productivity of KHSO4. The precipitate comprises practically pure KHSO4. Acknowledgment This work was financed by the Polish Government in the framework of a grant (2005-2008).