Product as additive for facilitating CO2 conversion into cyclic carbonate

A meaningful and practical phenomenon was observed and investigated, about which a synthesized (2-hydroxyethyl) triethylammonium bromide (NEt3(HE)Br) was used for catalytic cycloaddition of PO (propylene oxide) and CO2 (carbon dioxide) in a homogeneous state, and then separated from the reaction system in a heterogeneous state. The target products were first reported as additives to regulate the distribution of reactants and carbon dioxide (CO2) in the gas-liquid phase, as well as to facilitate the dissolution of NEt3(HE)Br. Under the optimal conditions of 0.2 mol% NEt3(HE)Br dosage, the PC yield (98.71 %) and TOF value (22.54 h−1) reached are significantly higher than the case of without PC addition. Besides, NEt3(HE)Br exhibited impressive stability after five catalytic cycles. The catalytic performances of different additives (i.e., alcohols, cyclic carbonate, amides, sulfones, petroleum ether, straight-chain carbonate and oxalate) were investigated, and their promotional effects and mechanisms were systematically elucidated. The transition behavior of dissolution-catalysis-precipitation process and intrinsic promoting mechanism of NEt3(HE)Br gave an efficient idea for a homogeneous catalytic reaction and heterogeneous separation of the catalyst. Meanwhile, this work provides an important theoretical and practical basis for efficient and facile catalyst synthesis and the corresponding reaction system design. [Display omitted] •Product-derived additives improve the cycloaddition efficiency between PO and CO2 without introducing impurities.•Adding a PC additive can regulate the distribution of reactants in the gas-liquid phase and efficiently dissolve NEt3(HE)Br.•The solubility variation of NEt3(HE)Br in PC enable both homogeneous reaction and heterogeneous separation of catalyst.