Absorption degree analysis on biogas separation with ionic liquid systems

For biogas upgrading, present work mainly focuses on either thermodynamics or mass transfer properties. A systematical study on these two aspects is important for developing a new biogas separation process. In this work, a new criterion “absorption degree”, which combines both thermodynamics and mass transfer properties, was proposed for the first time to comprehensively evaluate the absorption performance. Henry’s law constants of CO 2 and CH 4 in ionic liquids–polyethylene glycol dimethyl ethers mixtures were investigated. The liquid-side mass transfer coefficients ( k L ) were determined. The results indicate that IL–NHD mixtures exhibit not only a high CO 2 /CH 4 selectivity, but also a fast k L for CO 2 absorption. The [bmim][NO 3 ]   +   NHD mixtures present a high absorption degree value for CO 2 but a low value for CH 4 . For presenting a highest relative absorption degree value, the 50   wt% [bmim][NO 3 ]   +   50   wt% NHD mixture is recommended for biogas upgrading.