Title:
Synergetic effects on the capture and release of CO2 using guanidine and amidine superbases
Abstract:
The capture of CO2 from air is of utmost importance, not only to reduce its impact on climate change but also for its utilisation as a tremendous, renewable source of C1 building blocks for sustainable chemical synthesis. Novel and known superbase structures are compared in a new selection of solvents for CO2 capture and release. Bicyclic amidine and guanidine superbases with 6–5, 6–6 and 6–7 configurations and many methylated analogues are investigated. As reported here, identified superbase/solvent combinations offer a highly efficient, reversible, and kinetically favourable CO2 capture process from air. The two most beneficial superbase/solvent synergic combinations identified are 1,5,7-triazabicyclo[4.3.0]non-6-ene (TBN) in butyl acetate and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) in acetonitrile. They reach saturation after 15 min with pure CO2 and after 24 hours under open-air conditions and release CO2 with a CO2/superbase molar ratio of 0.41 and 0.25, respectively. Due to the favourable thermodynamics of the systems, quantitative CO2 release for TBN and DBN occurs under mild conditions at 90 °C and 60 °C within 20 minutes. The required time for a complete absorption–desorption cycle for both TBN-butyl acetate and DBN-acetonitrile was only 48.5 and 38.5 minutes respectively. Superbase–solvent mixtures are recyclable and the system retains its initial CO2 capturing capability after 5 cycles. As this apparently easy emerging system design allows the direct capture of CO2 from air, it has potential for positive utilization on the global scale.
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