Heat utilized pressure swing distillation (PSD) process for the separation of the maximum boiling azeotrope HCl and Water in the Cu-Cl Cycle

Abstract

The four-step copper-chlorine cycle is utilized for hydrogen production from water. Intermediate copper and chlorine compounds facilitate the process, while all other reactants are regenerated and recycled, forming a closed-loop system. Hydrolysis of CuCl2, leading to the formation of Cu2OCl2 and dilute HCl, is a crucial step that uses a large excess of steam to ensure completion of reaction leading to the formation of dilute hydrochloric acid which needs to be recycled for the electrolysis reaction, requiring removal of the azeotrope between HCl and water. This study explores the utilization of pressure swing distillation (PSD) for concentrating HCl above azeotropic composition. Separation of the aqueous mixture of HCl and water using PSD is optimized using a sequential iterative optimization technique, focusing on process intensification. Integration of a simple heat-utilized FE-Process results in a reduction of TAC and energy cost (4.27% TAC and 7.20% energy cost) compared to the process without heat integration. A higher feed composition of HCl (8 mol %) leads to savings of ∼ 38.75% in TAC and a reduction of 53.06% in CO2 emissions compared to a lower feed composition (2.53 mol % HCl). The heat-utilized FE-Process with a higher feed composition is more economically viable for the separation of HCl and water.