Partial separation of an azeotropic mixture of hydrogen chloride and water and copper (ii) chloride recovery for optimization of the copper-chlorine cycle

Abstract

An atmospheric-pressure distillation system is designed and constructed to partially separate hydrochloric acid and water. The system concentrates HCl(aq) between the electrolyzer and hydrolysis steps of the Copper-Chlorine (Cu-Cl) cycle. Thus, the system partially recycles HCl(aq), thereby decreasing the total operating cost of the cycle. The separation is only partial, as the mixture is unable to cross the azeotrope with only a single pressure. The distillation system consists primarily of one packed distillation column, which employs heating tapes and thermocouples to achieve a desired axial temperature profile. The column can be operated in batch or continuous mode. After performing physical distillation experiments, it is found that feeds less than azeotropic concentration are separated into H2O(l) and highly-concentrated HCl(aq) (albeit at less than azeotropic concentration). Feeds greater than azeotropic concentration are not investigated as they are extremely corrosive (rich in HCl) and would likely destroy the apparatus. Corrosion product is prevalent in the bottoms product; it is a source of error that is partially mitigated by filtration. No correlation is found between feed concentration and output concentration. That is, the distillate is H2O(l) and the bottoms is HCl(aq) near azeotropic concentration; as long as the feed concentration is any value less than azeotropic. In other words, the degree of separation is found to be independent of the feed concentration, for feed concentrations less than azeotropic. The bottoms concentration varies from experiment to experiment, but does so randomly, likely the result of corrosion impurities affecting the calculation of its concentration. A simulation of pressure-swing distillation (PSD) is also performed to help determine the feasibility of HCl-H2O separation and the degree of separation. Furthermore, an investigation into metastability and its effect on the crystallization of CuCl2 from HCl(aq) solutions is presented in Chapter 4.