Dialkyl Carbonates as Green Solvents for Polyvinylidene Difluoride Membrane Preparation

Membrane processes are employed in a wide variety of industrial applications such as separation of complex mixtures, hydrogen isolation, CO2 removal, wastewater treatment, etc. Their use allows energy savings on the production cost compared to other traditional separation technologies. Nevertheless, the preparation of membranes not always fulfills sustainability obligations, especially when considering the commonly employed solvents, i.e., N-methyl-2-pyrrolidone and N,N-dimethylformamide, to mention just a few. Dialkyl carbonates (DACs) are well-known green solvents and reagents that have been extensively investigated as safe alternatives to chlorine-based compounds and media such as alkyl halides, phosgene, and chlorinated solvents. Following our recent study on a scale-up procedure to non-commercially available or expensive DACs, herein we report for the first time the application of organic carbonates as green media for membrane preparation. Theoretical thermodynamic studies were first carried out to predict the solubilities in DACs of different polymers commonly employed for membranes preparation. As a result, the use of selected organic carbonates as media for polyvinylidene difluoride membrane preparation was investigated by nonsolvent-induced phase separation (NIPS) and a combination of vapor-induced phase separation (VIPS)-NIPS techniques. Membranes obtained with custom-made DACs displayed greater structural resistances and smaller pore sizes compared to the ones achieved using commercially available cyclic organic carbonates. Data collected showed that it was possible to achieve a wide variety of dense and porous membranes by using a single family of compounds, highlighting once again the great versatility of DACs as green solvents.