Biogas Upgrading by Capturing CO₂ in Non-aqueous Phase-Changing Diamine Solutions

Ethanol solutions of diamine, ethylenediamine (EDA) or piperazine (PZ), were found to be able to produce a solid precipitate after the absorption of CO₂. The precipitate was identified to be a mixture of monocarbamate and dicarbamate. The details of the reactions between CO₂ and diamine were examined. Results show that EDA-ethanol solutions exhibit higher capacity and faster rate for CO₂ absorption than PZ-ethanol solutions. As a comparison, the kinetics of CO₂ absorption with diamine-water solutions were also tested. It was found that the overall average absorption rate of CO₂ in EDA-ethanol solutions is almost double that in EDA-water solutions. Moreover, results show that EDA-carbamate has a decomposition temperature of ∼90°C and requires a regeneration energy of 25.6% less than traditional monoethanolamine (MEA) solutions, which suggests that EDA-ethanol solutions are promising to be used as cost-effective absorbents for CO₂ capture.