(383i) Multi-Scale Computational Modeling and Simulation of All-Silica Zeolites for Adsorptive Separation of Ternary (H2S/CO2/CH4) Mixtures

Natural gas (NG) consists of H₂S and CO₂, and the presence of these gases are detrimental to the usage of NG for energy generation. Adsorptive separation is a promising avenue to remove H₂S and CO₂ from a mixture NG. Toward this end, identification of high-performing adsorbent materials that could simultaneous remove both H₂S and CO₂ is necessary. In this study, we conducted multicomponent multiscale simulations integrating molecular simulations, process modeling, and optimization to identify the optimal zeolites for the simultaneous removal of acid gases (H₂S and CO₂) from a ternary mixture of H₂S/CO₂/CH₄. GCMC simulations were performed for 16 zeolites from prior-screening study to generate single-component adsorption isotherms for H₂S, CO₂, and CH₄. These data were fitted to the dual-site Langmuir–Freundlich (DSLF) model to obtain isotherm parameters for process simulation. We validated the fitted parameters by comparing the adsorption data obtained from the GCMC simulations under mixture conditions with the predicted mixture adsorption isotherms from the extended DSLF (EDSLF) model. We identified only three zeolites (APC-0, APC-2, and ATV-1) have valid DSLF parameters and process simulations and optimizations were conducted for these three zeolites. We simultaneously maximized CH₄ purity and recovery during the process optimizations and found ATV-1 exhibited the lowest CH₄ purity of approximately 76% at 90% CH₄ recovery for the 20/20/60% H₂S/CO₂/CH₄ mixture condition. In contrast, APC-0 and APC-2 (APC-type zeolites) exhibited excellent separation performance of simultaneous acid gas removal, achieving 90% CH₄ recovery at CH₄ purity 99%. Further investigation of the column internal composition profiles and acid gas removal revealed that, unlike APC-type zeolites, ATV-1 exhibited minimal CO₂ removal owing to the displacement of the CO₂ front by the H₂S front due to lower amount of adsorbed CO₂ in the framework. The process economic optimizations were performed to maximize CH₄ productivity and minimize energy consumption for APC-type zeolites. The results showed that APC-0 required more than 50 kWh/tonne CH₄ of additional energy compared with APC-2 at a productivity of 2 mol CH₄/tonne adsorbent/s or more for the 20/20/60% H₂S/CO₂/CH₄ mixture. Consequently, APC-2 emerged as the optimal energy-efficient zeolite material for simultaneous acid gas removal from ternary mixtures. Finally, molecular simulation snapshots of the adsorbed gases within the zeolites and the adsorption energy distributions were examined to elucidate the lower CO₂ removal performance of ATV-1 compared to APC-type zeolites. We found that the orientation of CO₂ influenced its competitive adsorption behavior within the zeolite for ATV-1. In contrast to APC-type zeolites, ATV-1 favored only H₂S adsorption over CO₂, resulting in significantly lower adsorbed CO₂ in zeolite. This observation emphasized the significant impact of the CO₂ adsorption orientation on its overall behavior in mixtures and, consequently, on the end-use process performance, providing the basis of more efficient adsorbent materials design strategy for simultaneous acid gas removal. The modeling approach demonstrated in this work provides future guidelines for integrated evaluation of materials and adsorption process for realistic gas mixtures with more than three components.