Non-aqueous integrated CO2 capture and conversion system using an ether-containing diamine (EtherDA) for efficient propylene carbonate synthesis

The integration of CO2 capture and conversion to valuable materials (IC3M) provides a practical strategy to improve the energy efficiency and applicability of carbon utilization technologies. In this study, a non-aqueous IC3M system was developed using an ether-containing diamine, 1,1′-[(1-methyl-1,2-ethanediyl)bis(oxy)]bis[2-propanamine] (EtherDA), dissolved in glyme for CO2 capture and subsequent conversion to propylene carbonate (PC). EtherDA showed a high CO2 absorption capacity (0.81 molCO₂/molamine), good chemical stability, and limited side-product formation in the presence of epoxides such as propylene oxide (PO). The cycloaddition of CO2 with PO in the CO2-loaded EtherDA system proceeded efficiently under mild conditions (80 °C), yielding up to 100% PC.Catalyst screening indicated that tetraalkylammonium bromides, particularly tetrabutylammonium bromide (TBAB) and tetraethylammonium bromide (TEAB), were effective and could be reused over multiple cycles. A phase-switching strategy based on CO2-induced polarity changes enabled straightforward decantation-based separation of PC from the absorbent and catalyst. In addition, direct air capture followed by conversion to PC was successfully demonstrated, with yields corresponding to the total amount of CO2 absorbed from air. Overall, this work presents a practical IC³M approach with potential for sustainable CO2 valorization and direct air utilization.