CO2 removal from biogas by using green amino acid salts: Performance evaluation

•Five amino acid salts are evaluated for CO2 removal from biogas.•Potassium l-ornithinate and potassium glycinate have overwhelming advantages.•l-arginine has a special reaction mechanism with CO2.•Cyclic CO2 uptake and molecular weight should be considered in absorbent screening.

Five natural amino acid salts (AASs) as green absorbents for CO2 removal from biogas are evaluated using the typical absorption–regeneration screening method in the present study. CO2 absorption performance and reaction mechanism of l-arginine are also investigated. Experimental results show that the initial CO2 absorption rate increases but the regeneration efficiency decreases with the rise in the basicity of AASs. Potassium l-ornithinate and potassium glycinate have some overwhelming advantages such as negligible absorbent loss, high absorption kinetics, relatively low absorption enthalpy, and high regeneration efficiency, making them suitable and favorable candidates for CO2 absorption from biogas. l-arginine may be superior to monoethanolamine in terms of the saturated CO2 absorption loading, absorption enthalpy and regeneration efficiency, but it suffers from slow reaction kinetics. The results of FTIR analysis suggest that l-arginine is more likely to act as a base in catalyzing the hydration of CO2. Both the cyclic CO2 uptake and the molecular weight of the absorbent should be considered in absorbent screening. Adopting AASs with high cyclic CO2 uptakes may not be effective in minimizing the absorber/desorber size due to their high molecular weights.