Liquid-solid phase-change absorption of acidic gas by polyamine in nonaqueous organic solvent

- Liquid-solid phase-change absorption of acidic gas such as CO2 and SO2 is achieved.
- Primary and secondary polyamines would react with CO2 to form zwitterion product.
- Primary and secondary polyamines would absorb SO2 and water to produce sulfite.

Acidic gas capture by traditional aqueous amine solution requires a plenty of energy for solvent regeneration. A phase-change capture system was considered to be a promising alternative because only the CO2-rich phase needs to be recovered and the CO2-lean phase can be reused directly without disposal, improving the energy utilization efficiency. Based on this principle, the phase-change absorption behavior of linear polyamines including ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine, tetraethylenepentamine, and cyclic diamines including piperazine (PZ) and triethylene diamine (DABCO) in organic solvents was investigated in the present work. The result indicated that polyamines could react with CO2 to form carbamate precipitates except DABCO, which had no absorption effect. For the absorption of SO2, polyamines could react with SO2 and water from air to form rare organic sulfites except DABCO, which merely absorbed two SO2 molecules to form the electron transfer complex DABCO·(SO2)2. The peculiar absorption behavior of DABCO for CO2 and SO2 implied that it is a highly selective phase-change desulfurizer for flue gas. The sequence of decomposition temperature for the CO2 capture product was DETA-carbamate > EDA-carbamate > PZ-carbamate, while for the SO2 capture product was [EDAH2][SO3] > [PZH2][SO3]·H2O > DABCO·(SO2)2.

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