The Improvement of CO₂ Biphasic Absorption with Spatially Resistive Ionic Liquids

High regeneration energy is a critical barrier to the large-scale implementation of CO2 capture technologies. To address this challenge, we present a novel energy-efficient biphasic absorbent system, designed by incorporating sterically hindered amine ionic liquids (AMP-TZ) with N,N,N′,N′-tetramethyl-1,6-hexanediamine (TMHDA). The innovative design focuses on enhancing the spatial site resistivity of ionic liquids, which plays a key role in optimizing the CO2 absorption and minimizing regeneration energy. This system demonstrates superior performance, achieving a CO2 absorption capacity of 2.72 mol/kg at 313.2 K and 150 kPa, with a low regeneration energy of 2.31 GJ/t of CO2. Molecular dynamics simulations and quantum chemical calculations reveal that AMP-TZ promotes proton transfer during absorption and stabilizes bicarbonate (HCO3–) in the CO2-rich phase via weak hydrogen bonding. The unique role of AMP-TZ as a bifunctional hydrogen bond donor/acceptor and its ability to suppress the self-aggregation of HCO3– enhance both the absorption efficiency and regeneration performance. This study provides insights into the design of low-hydration CO2 capture systems and offers a theoretical framework for developing highly efficient, energy-saving biphasic absorbents.