Effects of hydroxyethyl group on monoethanolamine (MEA) derivatives for biomethane from biogas upgrading

Abstract

Upgrading of biogas to produce biomethane is an essential way to increase the calorific value of biogas by separating CH4 and CO2 to satisfy the global renewable energy demand. In this study, the efficiency of carbon dioxide (CO2) trapping in aqueous monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), and triethanolamine (TEA) solution during biogas upgrading for biomethane was determined. Effects of hydroxyethyl groups on MEA derivatives were investigated in terms of biogas upgrading and regeneration, CO2 desorption heat, initial CO2 absorption rate and CO2/CH4 selectivity. The duration of upgraded biogas meeting certain European Union (EU) application standards for methane purity during upgrading was reduced by 70, 78 and 200 mins for DGA, DEA and TEA respectively compared to MEA due to the partial substitution of H-bonds by hydroxyethyl groups, and the absorption rate was also reduced, whereas TEA was not suitable for biogas upgrading as it was inefficient for biogas upgrading effect and absorption rate. The calculated results from the Gibbs-Helmholtz equation showed that MEA had the largest CO2 desorption heat (82.47 kJ/mol CO2) and the other MEA derivatives had lower desorption heat than MEA, indicating that MEA consumes more energy in the desorption process. As for the equilibrium partial pressure, all amine solutions absorbed less than 0.4% of the total volume of CH4 and had a high CO2/CH4 selectivity.