Synergistic effects of structured and powdered Calcium Chloride-Activated Carbon composites on Ammonia adsorption: the role of salt distribution and pH-controlled crosslinking

Abstract

The porous powdered composites, containing metal halide salts are being used to enhance the storage of cold thermal energy storage (CTES) medium such as ammonia for efficient cooling systems. However, due to the low mass transfer attributable to agglomeration, reduction in pore accessibility, and sample loss, the powdered samples face challenges translating from lab to pilot scale. Conversely, the structuring of composites in beads and pallets can modify the surface chemistry and adsorption mechanism. To investigate the impact of structuring, a comparative analysis of pure, calcium chloride (CaCl2)-impregnated activated carbon (AC) powder and CaCl2-crosslinked AC beads was conducted in this work, to observe the ramification of surface chemistry due to salt distribution, porosity, surface area and pH-controlled crosslinking, on ammonia adsorption. The role of pH in bead formation introduced a new dimension in tailoring ammonia adsorption efficiency. The bead sample containing 20% CaCl2 (AC-B (20%)), with pH-8 crosslinking solution, has shown the two times more ammonia adsorption due to optimum crosslinking, physicochemical interactions and the presence of tuned amount of calcium chloride (CaCl2) on the surface and pores. SEM, XRD, FTIR, BET, DFT, and XPS are used to analyse the fabricated samples before and after the adsorption to thoroughly investigate the adsorption mechanism. The kinetic analysis of experimental results was conducted by applying nonlinear Pseudo 1st order (PFO), Pseudo 2nd order (PSO), and Elovich models, with best fit with N-PSO model confirming the highest mass transfer by the bead sample (AC-B (20%)). Lastly, the economic feasibility analysis as well as the impact of thermal treatment on recovery and sample regeneration was studied by desorbing the best samples at four different temperatures (120 °C, 140 °C, 160 °C, and 180 °C).