(655c) Carbon Dioxide Conversion into Polycarbonate Diols: A Parametric Study

Conversion of carbon dioxide into valuable chemicals is an attractive approach to achieve sustainability and carbon neutrality goals for chemical processes. In the nonreductive CO₂ conversion route, polycarbonate diols production is a lucrative option as they can be used in the synthesis of high-performance polyurethanes. Traditionally, polycarbonate diols have been produced using hazardous phosgene and dichloromethane. However, recently, an atmospheric flow-based system using only CO₂ and 1,6-hexanediol was demonstrated with high polycarbonate diol yields using a cerium oxide-based catalyst by Gu and coworkers. Given this three-phase system, multiple parameters need to be considered and optimized to enhance yield and selectivity to diol products.

For the current work, CO₂ conversion into polyhexamethylene carbonate diols was investigated in a similar atmospheric flow system. Our studies evaluated parameters such as type of cerium oxide catalysts, shape of the flask, type of condenser, and addition of a dehydrating agent for the thermal system. The different CeO₂ catalysts were characterized using BET, Raman spectroscopy, and XRD. BET analysis was used to identify if the amount of conversion was influenced by the surface area, Raman spectroscopy was used to identify the defect (active) sites and XRD was used to identify different phases of the catalyst. The reaction products were qualitatively analyzed using FTIR and quantitatively by using GC and GPC.

It was found that the shape of the flask influenced the mixing behavior of the fluid, and thus improved water removal and consequently increased the yield of polycarbonate diol. Whereas length of the condenser influenced the overall mass balance (evaporation loss) of the reaction system and the tightly packed condenser resulted in lowering evaporation losses. Addition of a dehydrating agent helped further improve the yield of the polycarbonate diol indicating that water was not completely removed and further optimization might be necessary.