Direct air capture and conversion of carbon dioxide into cyclic carbonates with basic ionic liquids



Achieving net zero greenhouse gas emissions (ghg) is a top priority to limit the impacts of global warming. Carbon dioxide is the most abundant ghg and its direct air capture (DAC) is a very attractive strategy to reduce its concentration in the atmosphere. However, the existing capturing processes are technologically challenging due to the costs of the processes and the low concentration of CO2. The efficient valorisation of the CO2 captured could help overcoming many technoeconomic limitations. Sorbants capable to concentrate CO2 from the atmosphere require strong interactions (e.g. carbamate synthesis), which increase the cost of regeneration of the sorbants and introduce thermodynamic barriers to efficiently transform the CO2 into added value products. Here we present a novel methodology for direct air capture and conversion (DACC) able to efficiently convert CO2 from air into cyclic carbonates using epoxides or halohydrins as substrates. The new approach employs commercially available basic ionic liquids (ILs), it works without the need of sophisticated and expensive co-catalysts or sorbants and under mild reaction conditions. The CO2 from atmospheric air was efficiently captured by IL solution (0.98 molCO2/molIL) and subsequently completely converted (> 99%) to cyclic carbonate. A mechanism of conversion was evaluated and proposed, which helped to identify relevant reaction intermediates based on halohydrins, which could be sourced from biomass derivatives. A 100% selectivity towards the desired cyclic carbonates was obtained employing this methodology. Finally, the catalyst was reactivated employing an ion exchange column, and reused for at least 3 cycles.