An improved vacuum pressure swing adsorption process with the simulated moving bed operation mode for CH4/N2 separation to produce high-purity methane

• Conventional VPSA process improved by introduction of SMB mode for CH4/N2 separation. • Separation of CH 4 /N 2 mixture using an eight-column improved VPSA process. • High-purity CH 4 /N 2 product gases obtained by improved VPSA process from 30% CH 4 feed. • Comparison of CH 4 /N 2 separation performance among several VPSA processes. Methane is a clean fossil fuel and an important greenhouse gas, so it is more significant to recover methane from massive resources of unconventional gas. Because of the similar physicochemical properties of methane and nitrogen, it is difficult to obtain the high-purity methane from the low-grade methane gas with nitrogen mixture by the conventional vacuum pressure swing adsorption (VPSA) process. In this work, this process was improved, where multicolumn in series operation was adopted at both adsorption and displacement steps to enhance the CH 4 /N 2 separation, and one column went on blowdown, purge, and pressurization steps for the effective regeneration of the adsorbent. In order to run the improved VPSA process automaticly, the SMB operation mode was introduced, synchronously shifting the inlet and outlet stream ports from one column to other column along the gas flow direction, and a countercurrent contact between the gas phase and adsorbent phase in the multicolumn system was formed to enhance the CH 4 /N 2 separation. To verify the feasibility of the improved VPSA process, the experimental device with eight-column unit had been set up in laboratory, and 30% ~ 50% CH 4 gases were denitrified by the improved VPSA process using activated carbon beads. The experimental results demonstrated that the improved VPSA process was capable of producing a high-purity CH 4 product gas (99.99% CH 4 ) meeting pipeline grid specification and a high-concentration N 2 by-product gas meeting emission standards from 30% ~ 50% CH 4 feed gases. In the end, we compared the CH 4 /N 2 separation performance among the conventional VPSA process, dual reflux-pressure swing adsorption process, improved VPSA process with SMB operation mode, CO 2 displacement VPSA process and concentration temperature swing adsorption process.