Homogeneous catalyst separation and re-use through nanofiltration of organic solvents

Abstract

The separation of reaction products from catalysts is a major problem existing in many forms of homogeneous catalysis, including phase transfer catalysis and transition metal catalysed reactions. This study describes a new and generic approach to solving this separation problem using solvent resistant nanofiltration (SRNF) membranes. Data for SRNF separation of a phase-transfer catalyst (PTC), and a Heck reaction transition metal catalyst (TMC), from their respective reaction media is presented. SRNF was used to retain each catalyst from the reaction solvent and, when applied in a coupled reaction-separation system, allowed several subsequent catalyst recycles and re-uses. PTC rejection was high (99+%) whether SRNF was applied to pre- or post-reaction mixtures, and no reaction rate decline was observed for two consecutive catalyst recycles. TMC rejection, while 96% for pre-reaction mixtures, dropped to 90% for post-reaction mixtures and reaction rate decline was observed for four consecutive catalyst recycles. The clear difference between the two systems is the much higher stability of the PTC due to a less demanding catalytic cycle. The need for stable catalytic systems for effective generic use of this technology in homogeneous catalysis is highlighted.