Continuous flow homogeneous hydroformylation of 1-octene over supported ionic liquid phase rhodium catalysts using supercritical CO₂

Abstract

The hydroformylation of 1-octene with supported ionic liquid phase catalyst was demonstrated when using a system involving the substrate, reacting gases and products in CO₂ and N₂ flow over a fixed bed supported ionic liquid phase catalyst (silica gel and carbon aerogels as solid support respectively) at different system pressures. Yields, reaction rates, selectivities and rhodium leaching were all monitored. A pressure of CO₂ flow just below the critical point of the flowing mixture (106 bar at 100 °C if no 1-octene has been converted) was the best condition for the hydroformylation. It gave the highest acitivity (conversion to aldehyde up to 70 %), fastest reaction (TOF up to 575.3 h⁻¹) and best stable selectivity ( l:b ratio reaching 3.37 ). The utilization of scCO₂ as reaction media leads to remarkable stability of the catalyst. The supercritical or near critical (expanded liquid) system completely overcame the progressive decrease in activity of catalyst at 50, 75 bar with liquid phase transport and also showed much better results than when using other gas flows such as N₂ flow at 100 bar. In the high pressure scCO₂ phase, the concentration of 1-octene at the catalyst bed was reduced so that the conversion to aldehyde was reduced. The pore size and surface groups of the solid support should be suitable for the SILP catalyst consisting of metal complex, excess ligand and ionic liquid. Using microporous carbon aerogels as the supports, whether activated or not, gave disappointing results.