Molecular Simulation of the Adsorption Separation of Acidic Natural Gas Contaminants with Zeolites

From an energetic, economic and environmental perspective, the selective removal of carbon dioxide and hydrogen sulfide from industrial natural gas streams is crucial. For this purpose, adsorption separation using nanoporous zeolites composed solely of silicon and oxygen atoms is a promising and environmentally friendly alternative to conventional adsorption and absorption processes. In this study, the adsorption of binary and ternary gas mixtures containing carbon dioxide, methane and/or hydrogen sulfide was examined with more than 100 different pure silica zeolites using atomic-resolution grand canonical Monte Carlo simulations. The IZA database was searched primarily for zeolites that could potentially be used to separate carbon dioxide from methane. However, many of the frameworks found were also suitable for the selective separation of hydrogen sulfide. The dependence of the calculated selectivities on pressure, temperature and gas composition was investigated, and a multi-step adsorption test was also performed with the zeolites showing the best performance. An empirical relationship was observed between certain structural parameters and the preference for binding carbon dioxide. This equation was then used to systematically screen a large database of theoretical zeolites. As a result, not only some IZA zeolites but also several theoretical zeolite structures were identified that strongly favor the adsorption of carbon dioxide over methane.