Green Hydrogen Recovery from Natural Gas Grids by Vacuum Pressure Swing Adsorption

This study focuses on the development of a conceptual vacuum pressure swing adsorption process (VPSA) for green hydrogen (GH) recovery from natural gas grids (NGGs). Accordingly, the kinetics-based separation of H-2 from NGG was achieved by using a commercial carbon molecular sieve (CMS-3K-172) adsorbent. To develop the VPSA cycle, the CMS-3K-172 was characterized, single- and multicomponent breakthrough curves for H-2 and CH4 were performed, and adsorption isotherms were collected between 195 and 273 K and pressures up to 18 bar. To separate H-2 (20%) from CH4 (80%), three different VPSA cycle configurations were designed and simulated by using Aspen Adsorption. The operational variables, such as step times, intermediate-to-high-pressure ratio, purge-to-feed ratio, and H-2 initial concentration, were evaluated for maximum values of purity, recovery, and adsorbent productivity. The results show that the VPSA processes can enrich H-2 in the product stream by up to 68% with a recovery of 92%.