Parametric Optimization of Cupric Chloride Crystallization in Copper Chlorine Thermochemical Cycle for Hydrogen Production: A Sustainable Alternative to Spray Drying

The crystallization behavior of CuCl2 from the electrolyzer effluent presents a critical challenge in the Cu–Cl thermochemical cycle for green hydrogen production. In this work, the crystallization behavior of the CuCl2–HCl–H2O system was systematically investigated to define operating boundaries and optimize process parameters on the laboratory scale. The results demonstrated that crystallization occurs within a narrow operational window, with HCl concentration and cooling rate being the most critical factors. Optimal conditions of 6 N HCl and 30% w/w CuCl2 feed concentration yielded a maximum crystallization of 55%. Structural characterization by X-ray diffraction revealed the formation of CuCl2·2H2O crystals that dehydrate to anhydrous CuCl2 upon drying, with distinctive needle-like morphologies that were observed via scanning electron microscopy, with surface fracturing after drying. Extending to process-level evaluation, Aspen Plus simulations on the basis of 1 kg of H2 production showed that crystallization requires 1140.59 kW of energy, nearly 44% lower than spray drying (2021.87 kW). Economic assessment indicated a higher capital cost burden for spray drying (USD 21.8 million) than that of the crystallization system (USD 15.4 million). Furthermore, the operating cost of the spray dryer was found to be 43% higher than that of the crystallization system. The environmental impact analysis highlighted significantly lower gas emissions (32%) for crystallization compared to the spray drying system. By combining experimental insights with process simulation, economic analysis, and environmental evaluation, this study establishes crystallization as an energy-efficient, cost-effective, and sustainable route for solid CuCl2 production in the thermochemical Cu–Cl cycle.