Captured CO₂ Could Work As A Green Industrial Solvent

The few impurities in carbon dioxide captured from burning coal and natural gas should not preclude using the gas to generate supercritical CO₂ for use as an industrial solvent, according to a team of European chemists (Green Chem., DOI: 10.1039/c1gc15503b). Although successfully used to replace organic solvents in a variety of lab-scale reactions, only a few supercritical CO₂ processes have been commercialized because of the high cost of pressurizing CO₂. Carbon capture and storage, which is being implemented to cut CO₂ emissions, now provides a continuous, cost-effective source of pressurized CO₂. But how impurities in captured CO₂ might affect chemical processes presented a question. Martyn Poliakoff, Michael W. George, and Trevor C. Drage of the University of Nottingham, in England, and coworkers have answered it by testing a discontinued commercial process—hydrogenation of isophorone to make trimethylcyclohexanone—in supercritical CO₂ laced with N₂, CO, or H₂O to simulate probable contaminants. They found that N₂ introduces modest phase changes and that CO and H₂O reduce catalyst activity, but that activity can be maintained by increasing the reaction temperature. None of the impurities cause insuperable problems, the researchers note, and they believe their findings could help reboot industrial supercritical CO₂ reactions.