Low viscosity alkanolguanidine and alkanolamidine liquids for CO2 capture

Abstract

Global carbon dioxide (CO₂) emission is expected to increase tremendously with the shift to coal-powered plants for energy generation. Capture and sequestration of CO₂ are needed to mitigate environmental effects. Solvents currently used for this are the energy-intensive aqueous amines. Here we present 10 advanced solvents called alkanolguanidines and alkanolamidines that are potentially energy-efficient CO₂-capture solvents. These solvents were synthesized in 1–3 steps from commercially available materials. One alkanolamidine derived from a 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) base core has a low vapor pressure and a high viscosity, resulting in low CO₂ uptake capacity at standard temperature and pressure (STP). Three imidazoline base derived alkanolamidines were non-viscous but do not bind CO₂ at STP, however, under mild pressure they effectively capture 7–10 wt%, making them suitable for high-pressure CO₂ capture. Six novel alkanolguanidine molecules have low vapor pressure and low viscosity (<10 cP) which enable high CO₂ uptake at STP. These compounds bind CO₂ chemically via the alcohol moiety forming zwitterionic guanidinium and amidinium alkylcarbonate ionic liquids. These materials can be regenerated thermally by heating the alkylcarbonate to 75 °C. CO₂ binding capacities of up to 12 wt% were achieved using several of these compounds at STP. Through this study we found that alkanolguanidines have low viscosity, are non-volatile, have high CO₂ uptake at STP and are tolerant to water; thus we selected one compound for physical property testing.