Structure effects of imidazolium ionic liquids on integrated CO2 absorption and transformation to dimethyl carbonate

The integration of chemical absorption of CO 2 and in situ transformation to highly valuable chemicals is a promising process as an alternative toward fossil fuels . Here, three imidazolium ionic liquids (ILs), 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium 1,2,4-triazole ([Bmim][Tz]), and 1-butyl-2,3-dimethylimidazolium 1,2,4-triazole were synthesized to absorb and activate CO 2 by the formation of CO 2 -adducts, which can be in situ converted into dialkyl carbonates with alcohols (ROH, R = CH 3 , C 2 H 5 , and C 4 H 9 ) in solvent diiodomethane under ambient temperature and pressure. The results show [Bmim][Tz] exhibits the best CO 2 absorption capacity and dimethyl carbonates (DMC) yield, where CO 2 capacity is up to 0.216 g CO2 /g IL and DMC yield (based on methanol) is as high as 20.2 %. The structures of imidazolium ILs have significant effects on the absorption of CO 2 and subsequent transformation process. Fourier transform infrared and carbon nuclear magnetic resonance spectroscopies demonstrate ILs structures influence binding sites for CO 2 absorption, which can combine with CO 2 to form CO 2 -adducts, zwitterion [Bmim-CO 2 ], and [Tz-CO 2 ] − . Furthermore, density functional theory calculations verify the structure effects (binding sites and steric hindrance) of ILs on the activation of CO 2 and methanol, through the elongated C O bond lengths of CO 2 -adducts and O-H bond lengths of methanol in IL-methanol complexes, respectively, leading to different DMC yields. The integrated process is promising for the energy-efficient capture and utilization of CO 2 under ambient conditions.