Switchable Ionic Liquids (SWILs) are solvents that can switch between polar (ionic) and non-polar (non-ionic) states by the means of a chemical trigger such as CO2. Modern classes of SWILs, under the trade name CO2-Binding Organic Liquids (CO2BOLs), have shown great promise towards many applications ranging from separations, synthesis, and catalysis. CO2BOLs have been recently suggested as promising water-lean CO2 capture solvents showing potentially more favorable energetics than aqueous solvent systems. Since their inception, nearly all derivatives have been known to exhibit non-linear increases in viscosity with CO2 loading, which possibly limits their applications in industrial processes where circulation of viscous fluids is energetically unfeasible. Our findings suggest the presence of a previously undiscovered glass transition (Tg) around 40 C for multiple formulations. The Tg, was observed to occur through minute changes in mesoscopic ordering within the fluid. Here, we present an integrated theoretical and experimental study to characterize the commonalities and subtle differences in the mesoscopic structure of a “metastable” and “glassy state” of an archetypical alkanolguanidine derivative. Through the use of small angle neutron scattering, diffraction coupled with small and wide-angle X-ray analysis, and advanced molecular theory, we demonstrate that the glass transition occurs via reversible aggregation of small 2-5 nm oblong zwitterionic guanidinium carbonate clusters in solution. We conclude with implications of the newly discovered Tg on CO2 capture applications and CO2 capture performance.

Glass transitions in water-lean CO2 capture solvents: Influence of dynamic changes in mesoscopic structure

2019 Fall National Meeting

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