Pressure Swing Absorption and Desorption of Ammonia in Calcium Halide Solid Mixtures

The absorption and desorption behaviors of NH₃ in solid CaCl₂-CaBr₂ were investigated using the pressure-swing method at 473 K. Various compositions of CaCl₂-CaBr₂ solid mixture particles were formed by the impregnation method, and the solid-mixture effect on the NH₃ absorption behavior was evaluated. The compositional changes in the lattice sizes followed Vegard's law. For the solid mixture, the absorption rate of NH₃ increased because NH₃ was absorbed into CaCl₂-CaBr₂ at a lower energy and higher rate than CaCl₂ single salt. For x = 1.67 in CaCl Br_2- , the highest storage capacity was obtained; however, NH₃ desorption was not observed until x ≤ 1.00 in CaCl Br_2- , similar to the findings of CaBr₂ single salt. Two absorption energy curves were observed for CaCl₂-CaBr₂ with different compositions, indicating the formation of solid mixtures with different solvent lattices, namely, a CaCl₂-CaBr₂ solid mixture in the CaCl₂ and CaBr₂ lattices, respectively. After five cycles of NH₃ absorption/desorption, degradations such as capacity fade and phase segregation in the CaCl₂-CaBr₂ particles were not observed, confirming their stability toward these processes at 473 K.