Separation of Concentrated Binary Gases by Hybrid Pressure-Swing Adsorption/Simulated-Moving Bed Processes

Stripping-type PSA (S-PSA) is a commonly used gas separation process for purification of the light component. Rectifying-type PSA (R-PSA), although not commonly used, is a gas separation process for purifying predominately the heavy component. Because S-PSA and R-PSA each tend to favor the production of a single product, these processes are typically not used for complete binary separation. On the other hand, the gas-phase simulated-moving bed (SMB) is capable of achieving complete binary separation; however, its commercial application has been stymied by the need for carrier gas/desorbent recovery and unfavorable economics. In this work, S-PSA and R-PSA are combined with a two-zone SMB to develop S-PSA/SMB and R-PSA/SMB hybrid processes and these processes are integrated into combination-type C-PSA/SMB processes. Combining PSA and SMB eliminates the carrier gas/desorbent by taking advantage of gas expansion and by using both light and heavy purge streams. Separation of H 2 and CH 4 mixtures with Zeolite 5A was simulated to determine the feasibility of the hybrid processes. The primary products are H 2 and CH 4 plus an impure offgas may be produced. Complete binary separation can be achieved by recycling the entire offgas stream. The best separation was achieved with an eight-bed combination of the S-PSA/SMB and R-PSA/SMB processes, the SRC-PSA/SMB. This process separated a 70% H 2 /30% CH 4 feed into 99.99% H 2 with 99.6% H 2 recovery and 99% CH 4 with 99.9% CH 4 recovery with productivity of 9.37 × 10 −5 mol feed/(kg·s) and an energy requirement of 260.9 kJ/mol feed.