Product recovery from ionic liquids by solvent-resistant nanofiltration: application to ozonation of acetals and methyl oleate

In this work we tackle the problematic separation of reaction products from ionic liquid media. Solvent-resistant nanofiltration proves to be an attractive technique for the separation of non-volatile polar products from ionic liquids. In view of the high compatibility between ozone and ionic liquids, two ozone-mediated model reactions were chosen: firstly the oxidation of acetals to esters in the presence of ozone and secondly the ozonation of methyl oleate to monomethyl azelate and pelargonic acid. The objective was to retain the ionic liquid phase by means of a solvent-resistant nanofiltration membrane, while the organic reaction products permeate through the polymeric membrane. First, the ozonations were studied in order to know the characteristic product compositions. Next, a screening of membranes was performed on synthetic product mixtures. The second generation polyimide-based DuraMem™ membranes showed the highest rejection, up to 96%, for the evaluated ionic liquids. These DuraMem™ membranes also proved suitable for the separation of the products on real reaction mixtures, even in a single filtration step. The products of ozonations in ionic liquids permeate through commercial nanofiltration membranes, while the ionic liquids themselves are efficiently withheld.