Effects of Alkyl Groups on Monoethanolamine Derivatives for Biomethane from Biogas Upgrading

Abstract

Amine scrubbing is one of the key technologies for biogas upgrading to biomethane, which can be used to increase the calorific value of biomethane by separating out CO2 to meet the global demand for renewable energy. In this paper, several monoethanolamine (MEA) derivatives with alkyl groups as variables are screened as sorbents for the biogas upgrading process. The effect of alkyl groups on the efficiency of biogas upgrading, the effectiveness of sorbent regeneration, and the selectivity of CO2/CH4 during biogas upgrading are investigated. The analysis of biogas upgrading experiments with different MEA derivatives shows that methyl and butyl are more favorable for improving CO2 absorption and meeting the biogas upgrading effect of methane purity for a long period of time applicable in some countries, and ethyl is more conducive to the regeneration efficiency of amines. The results of the CO2 desorption heat calculations show that the CO2 desorption heat of ethyl monoethanolamine (EMEA) (66.67 kJ/mol CO2), formed by replacing a hydrogen near the nitrogen with an ethyl group, is significantly lower than those of methyl monoethanolamine (MMEA) (73.04 kJ/mol CO2) and butyl monoethanolamine (BMEA) (73.27 kJ/mol CO2), formed by replacing a hydrogen near the nitrogen with a methyl group and a butyl group, respectively. The CO2 desorption heats were significantly lower than those of MEA (82.12 kJ/mol CO2), suggesting that ethyl can significantly reduce the CO2 desorption heat of the amine compared to other alkyl groups. In the CO2/CH4 selectivity experiments, BMEA showed the fastest initial CO2 absorption rate of 0.83%/s, while dimethyl monoethanolamine (DMMEA) showed the lowest initial CO2 absorption rate of 0.16%/s. All amine solutions showed less than 1% absorption of CH4 and had high CO2/CH4 selectivity.