Methane recovery from low-grade unconventional natural gas by the integrated mode of the conventional/improved vacuum pressure swing adsorption processes

Abstract

There is a strong challenge for the CH4 recovery from nitrogen-rich low-grade unconventional natural gas by the existing adsorption separation technologies to obtain the high-purity methane because of the similar properties between CH4 and N2. Therefore, the developments of both novel sorbents and advanced adsorption processes for the high-efficient separation of CH4/N2 are greatly significant. In this article, the integrated mode of the conventional/improved vacuum pressure swing adsorption (VPSA) processes was developed to capture and upgrade the low-concentration CH4 from N2-rich streams for high-purity CH4 production. The improved VPSA process represented the conventional adsorption process run with the simulated moving bed (SMB) mode to enhance the separation of CH4/N2. To evaluate the feasibility and effectiveness of the integrated VPSA processes, the commercial coconut shell activated carbons (ACs) were used as the tested sorbents for experimental demonstrations, since the ACs were microporous materials widely used in industry. Experiments with one-column and eight-column unit were performed for CH4 recovery from 10% to 50% CH4/N2 feed gas, and the experimental results of the improved VPSA process were compared with the conventional adsorption process. The experimental results confirmed that 10% CH4/N2 feed gas could be enriched and upgraded successfully to 99.0% CH4 product gas by the integrated VPSA processes even if the commercial activated carbons were used as sorbents.