Study of adsorption of propane and propylene on CHA zeolite in different Si/Al ratios using molecular dynamics simulation

The separation of propane and propylene mixture is one of the most demanding processes because of the similarity in molecular sizes and chemical properties. In this work, the adsorption of propane and propylene molecules in both pure and mixed forms on Chabazite (CHA) zeolite with different aluminosilicate ratios were investigated using molecular dynamics simulation. The COMPASS force field was used to simulate the adsorption isotherms, and the simulated isotherms were modeled using Langmuir, Toth, and Sips models. Using the Van't Hoff equation, Henry's constant was obtained for different temperatures. Also, the isosteric adsorption heat was acquired using the Clausius-Clapeyron equation and compared with isotherm model results. The adsorption heat at zero loadings for propane and propylene was obtained as -33.28 and - 33.73 kJ/mol. Then, using Si-CHA zeolite, the adsorption isotherm of the propane-propylene mixture was investigated, and the impact of the presence of Na+, K+, and Ca2+ cations with Si-CHA on propylene adsorption was studied. Since the ionic radius of the K+ cation was larger than the ionic radius of Na+ and Ca2+ and caused the blocking of the adsorbed positions, therefore, fewer propylene molecules were adsorbed by K+ in comparison with other two cations Na+ and Ca2+.