Biogas upgrading to methane: Application of a regenerable polyethyleneimine-impregnated polymeric resin (NKA-9) via CO2 sorption

Biogas upgrading technology is important for increasing the heating value of biogas via separating CH 4 and CO 2 , before biogas can be utilized as a vehicle fuel or for grid injection. In this work, using a porous polymeric resin (NKA-9), we prepared a new sorbent, namely polyethyleneimine (PEI)-impregnated NKA-9, for use in biogas upgrading to methane via CO 2 sorption firstly. The adsorption performance, regeneration behavior, cyclic stability and CH 4 /CO 2 separation performance were then evaluated in detail. The sorbent exhibited high adsorption capacity of up to 151.1 mg/g with negligible CH 4 adsorbed, demonstrating its high selectivity towards CO 2 over CH 4 . In column breakthrough experiments, binary mixtures were separated effectively under each set of reaction condition, where high CH 4 purities of >95% could be obtained as the final product in the outlet gas. As tested, excessive PEI loading, high temperature and low CO 2 concentration in biogas would result in unfavorable effects on biogas upgrading. In addition, we tested the regenerability of the sorbent using the two most common methods-N 2 and CO 2 purging, where the sorbent could be regenerated completely at temperatures above 85 °C and 155 °C, respectively. During the long-term operation, PEI-impregnated NKA-9 exhibited excellent cyclic stability, with 1.4% and 5.2% decreases in adsorption capacity after 30 adsorption-regeneration cycles. Detailed characterization revealed that the sorbent was chemically stable at 155 °C, in contrast to other conventional amine-modified sorbents. Therefore, the regenerable PEI-impregnated NKA-9 sorbent could be a promising choice for biogas upgrading to methane via CO 2 sorption.