Adding Value to Power Station Captured CO2: Tolerant Zn and Mg Homogeneous Catalysts for Polycarbonate Polyol Production

Using captured waste carbon dioxide (CCU) as a chemical reagent is an attractive means to add value to carbon capture and storage (CCS) and is a high-priority target for manufacturing. One promising route is to copolymerize carbon dioxide and epoxides, to prepare aliphatic polycarbonates. In this study, three homogeneous dinuclear Zn and Mg catalysts, previously reported by our group (see Kember, M. R.; Knight, P. D.; Reung, P. T. R.; Williams, C. K Angew. Chem., Int. Ed. 2009, 48, 931-933 and Kember, M. R.; Williams, C. K. J. Am. Chem. Soc. 2012, 134, 15676-15679) have been investigated using captured and contaminated carbon dioxide, with cyclohexene oxide, to produce polymers. Carbon dioxide captured from the carbon capture demonstrator plant at Ferrybridge Power Station, U.K., is applied for the efficient production of poly(cyclohexylene carbonate). Remarkably, the dinuclear Zn and Mg catalysts display nearly equivalent turnover numbers (TON) and turnover frequencies (TOF) using captured CO2 versus those using purified CO2. The tolerance of the catalysts to reactions contaminated with known quantities of exogenous water, nitrogen, SO2, amine, and octadecanethiol are reported. The catalyst activities, productivities, and selectivities are presented, together with the polymers number-average molecular weights (M-n), dispersities (D), and end-group analyses. The catalysts show high tolerance to protic impurities, including the addition of amine, thiol, and water. In particular, under certain conditions, efficient polymerization can be conducted in the presence of up to 400 equiv of water without compromising catalytic activity/productivity or selectivity. Furthermore, the catalysts can selectively produce polycarbonate polyols with molecular weights in the range of 600-9000 g/mol and disperities <1.10.