Homogeneous phase transfer catalyst recovery and re-use using solvent resistant membranes

This paper explores the use of nanofiltration (NF) membranes in phase transfer catalysis for separating the catalyst and product present in the post-reaction mixture and recycling the catalyst. The conversion of bromoheptane into iodoheptane with toluene as solvent, using an aqueous solution of potassium iodide, and catalysed by tetraoctylammonium bromide as the phase transfer catalyst, was employed as a model reaction. A range of NF membranes from commercial manufacturers were evaluated in terms of membrane stability, solvent and product permeation rates, and catalyst rejection. The best performance resulted in a catalyst rejection of >99% and a solvent flux of >10 l m−2 h−1, with negligible product rejection. The catalyst was 100% recycled and re-used in subsequent reactions. No loss in catalyst activity was observed over a cycle of three consecutive reactions.