Membrane Polymers for the Pervaporative Separation of Polar Organics: Methanol and Acetonitrile

ABSTRACT Methanol (MeOH) and acetonitrile (MeCN) are highly polar organic compounds occurring in HPLC waste eluates. Neither of them is evidently more hydrophilic, which renders their pervaporative separation unusual. To identify suitable membrane materials, the pervaporation of MeOH‐MeCN mixtures having composition near the azeotrope (68.3 mol % MeOH at 35.0°C) was studied. For this purpose, homogeneous membranes from well‐established polymers were investigated, namely cellulose triacetate (CTA), polysulfone (PSU), poly(1‐trimethylsilyl‐1‐propyne) (PTMSP), Matrimid (MIM), poly(dimethyl siloxane) rubber (PDMS), polylactic acid (PLA), and chloroprene rubber (CR). Materials with discernible MeCN selectivity, namely CR, MIM, and PDMS, were further examined at 35.0°C, 45.0°C, and 52.9°C with feeds of varying composition. Plasticization and swelling effects were analyzed using Broadband Dielectric Spectroscopy (BDS) and liquid sorption measurements. Permeability decreased with increasing content of the less sorbing MeOH (except for MIM); BDS measurements indicated plasticization by both components; MeCN sorbed more and appears more organophilic.