1-Butyl-1-methylpyrrolidinium-based ionic liquids for integrated CO2 absorption and transformation into dimethyl carbonate

The transformation of captured CO 2 into highly-valued dimethyl carbonate (DMC) is a promising approach for CO 2 capture and utilization. However, the direct synthesis of DMC from CO 2 and methanol is limited by high activation barrier derived from inert CO 2 and thermodynamic equilibrium constraints. Herein, three 1-butyl-1-methylpyrrolidinium (BMP)-based ionic liquid (ILs) with polar pyrrole, pyrazole, and 1,2,4-triazole (Tz) azole anions were designed to integrate CO 2 absorption and transformation into DMC. [BMP][Tz] exhibits a relatively high CO 2 uptake capacity of 0.6 mol·mol IL −1 and DMC yield reaches 12.2 % under mild reaction conditions of atmospheric temperature and pressure in 12 h. The reaction equilibrium thermodynamic model reveals that the process involves a combination of 1:1 and 2:1 stoichiometric reaction between [BMP][Tz] and CO 2 . Density functional theory calculations verify that [BMP][Tz] with increased absorption efficiency of azole anions promotes critical bond activation (particular C − O and O − H bonds), thereby enhancing catalytic efficiency. Besides, the reaction mechanism is clarified by the calculation of intermediates and transition state, wherein [BMP][Tz] can efficiently decrease the energy barrier of the rate-controlled step, which involves the insertion of CH 3 O − into CH 3 OCOO − species. Furthermore, polarity-induced phase separation of DMC from the IL phase to solvent phase favors DMC generation by breaking through the reaction equilibrium. The integration of CO 2 absorption-reaction-extraction based on basic and polar ILs, provides a promising approach for CO 2 capture and utilization. • BMP ILs integrated CO 2 absorption, activation, and transformation into DMC • [BMP][Tz] with stronger basicity shows higher CO 2 absorption capacity • The RETM reveals dual 1:1 and 2:1 CO 2 absorption processes of [BMP][Tz] • The polarity of [BMP][Tz] induced phase separation of DMC into solvent phase