Dual-membrane natural gas pretreatment process as CO2 source for enhanced gas recovery with synergy hydrocarbon recovery

Membrane-based natural gas pretreatment process is able to efficiently recover hydrocarbons and separate low-cost CO2 for enhanced gas recovery (EGR). Dual-membrane module (DMM) is an enhanced module configuration for membrane gas separation, which synchronously recovering CO2 and hydrocarbons by housing CO2-selective and hydrocarbon-selective membranes in the same module. Implementing DMMs in natural gas pretreatment system could significantly improve the separation performance of membranes, and further reduce investment and operational costs; however, the impacts of separation sequence still require intensive investigations. In this work, two DMM-based processes are proposed and compared with conventional single-membrane-based processes, aiming to find the optimal separation sequence and quantify the enhancing effects of DMMs. The results indicate that condensation-DMM is the optimal process design, which is able to provide 90-mol%-purity CO2 for EGR, and reduce 3-12% investment cost and CO2 avoidance cost. The sensitivity analysis of membrane selectivity shows that, the DMM-based processes demands lower investment cost than single-membrane-based processes with elevated membrane selectivities, and the DMM-condensation becomes the best-performance process design. The effect implies that the synergetic enrichment effect inside DMMs could amplify the impacts of membrane selectivity, enabling the DMMs to provide higher separation performance. This work demonstrates the potential applications of DMMs, and indicates that employing DMM to natural gas industry is an effective solution for current-available and advanced membrane materials.