Exploring zeolite potential for hydrofluorocarbon capture and recycling: Insights from molecular simulations

Abstract

The need for efficient separation of hydrofluorocarbons for recycling and environmental protection is critical due to their substantial impact on global warming. However, conventional methods such as cryogenic distillation face significant limitations due to the azeotropic behavior of many of these hydrofluorocarbons. This study evaluates the adsorption behavior of various hydrofluorocarbons in zeolite structures, specifically Linde Type A (3A, 4A, and 5A) and Faujasite Type X (13X), using molecular dynamics and grand canonical Monte Carlo simulations. The simulations were validated against experimental data, confirming the reliability of the computational models. Adsorption isotherms were fitted using the Langmuir-Freundlich model to describe the adsorption behavior across different pressures. Focusing on fluoromethane derivatives, the study highlighted key interactions and adsorption capacities in various zeolites. The isotherms of various hydrofluorocarbons in zeolite 13X were explored, revealing differential adsorption based on molecular structure. The potential for using zeolite 13X and 5A to separate refrigerant mixtures was also studied, showing distinct selectivity patterns. Additionally, the temperature dependence of adsorption isotherms and isosteric heat was studied to gain insights into the thermodynamics of the adsorption processes. Key results indicate that zeolite 13X demonstrates strong cation-fluorine interactions, particularly effective for the adsorption of large hydrofluorocarbon molecules, which preferentially occupy 12-membered ring windows. In contrast, zeolite 5A exhibited predominant hydrogen bonding interactions at low pressures, with hydrofluorocarbon molecules occupying the smaller 8-membered ring windows. These findings underscore the selective adsorption capabilities of these zeolites, highlighting their potential application in hydrofluorocarbon separation and recycling processes.