(234b) Capturing CO2 with Phase-Changing Polyamine/Ethanol Solutions

Sequestration of carbon dioxide has been intensively studied in recent years as the global warming becomes a serious concern among the public. Absorption processes based on aqueous alkanolamines are often used as a benchmark for CO₂ capture technologies. The major drawback of such processes is the large energy consumption required for the regeneration of the absorbent. One of the alternative ways to tackle this challenge is to use a new class of non-aqueous amine solutions called phase-changing solvents, which can form two phases after absorbing CO₂. One phase is rich of CO₂, while the other is lean of CO₂. Significant energy saving can be achieved as only the CO₂ rich phase needs to be treated to obtain regenerated absorbents. In this work, we observed that polyamines dissolved in ethanol can produce solid precipitate after CO₂ absorption which can then be easily separated. The four polyamines investigated here are ethanediamine (EDA), piperazine (PZ), diethylenetriamine (DETA), and triethylenetetramine(TETA). The reaction kinetics of CO₂ and polyamines in ethanol solutions are also examined. Phase changing transition of solutions only occurs when CO₂ is absorbed into polyamine/ethanol solutions, but not monoamine/ethanol solutions. Results show that polyamine/ethanol solutions offer both higher absorption rate and larger absorption capacity for CO₂ than aqueous amine solutions. More than 80% of the absorbed CO₂ was captured in the solid phase. Moreover, solid precipitates can be regenerated at 90°C. The polyamine/ethanol solutions also show a stable performance after multiple absorption/regeneration cycles.