Non-stop homogeneous catalysis

Reactor enables rhodium to be used as a catalyst without decomposition.

Scientists in the UK have constructed a reactor that allows a rhodium-based catalyst to be used in hydroformylation reactions of alkenes and enables its reuse through the system. David Cole-Hamilton and his colleagues report a reactor system that enables the reaction to occur continuously for several hours with lower pressures and temperatures than was previously possible. This means that the more effective, highly selective rhodium catalyst, which is unstable at high temperatures and pressures, can be used without fear of decomposition.

In the reactor, flow rates are set but can be varied depending on the reaction rate required, and controlled by the gas flow which is regulated by mass controllers. The catalyst and substrate are contained in a fluorous solvent and are fed through high-performance liquid chromatography pumps followed by a heat exchanger before entering the reactor. The reaction mixture is removed through a complex system at the bottom of the reactor, passed through a heat exchanger, and eventually into a gravity separator allowing the release of dissolved gases and the separation of catalyst which is reintroduced into the reactor. Organic phases pass through an overflow tube fitted to the separator, and are collected.

The team illustrates the reactor’s potential by studying the hydroformylation of 1-octene, an important reaction in the production of plasticiser alcohols. Previously, the reaction has been initiated by cobalt-based catalysts although 10 per cent of the substrate has been lost to hydrogenation.

Carolyn Ackers