Permeation and sorption of organic solvents and separation of their mixtures through an amorphous perfluoropolymer membrane in pervaporation

The permeation and sorption of a few common organic solvents and separation of their mixtures through a polymeric membrane of perfluoro-2,2-dimethyl-1,1,3-dioxole copolymerized with tetrafluoroethylene (PDD-TFE) was investigated by vacuum-based pervaporation. Pure component permeations of common pharmaceutical solvents such as, toluene, methanol, ethyl acetate and tetrahydrofuran (THF), were carried out using a 25μm thick dense polymeric membrane supported by a porous polytetrafluoroethylene (PTFE) sheet. Overall permeability coefficients for these solvents along with those of aprotic solvents dimethylformamide (DMF) and dimethylacetamide (DMAc) determined earlier (Tang and Sirkar, 2012 [1]), plotted against their longest molecular diameters were correlated to yield a relationship between the molecular solvent size and their permeation through the membrane. The sorption of each pure solvent and a few of their mixtures were determined. Separation of a few organic-organic mixtures of these solvents was also implemented. These systems include: toluene-methanol, toluene-ethyl acetate and toluene-tetrahydrofuran. Modest separation factors were achieved using the PDD-TFE membrane unlike the very large values achieved earlier between water and aprotic solvents such as DMF, DMAc and DMSO (Tang and Sirkar, 2012 [1]). The maximum separation factor value for all systems was approximately 7.8 for a 75wt% toluene and 25wt% methanol feed at 30°C. The separation factor obtained using a 50wt% toluene and 50wt% THF feed at 50°C was close to 1. Maximum flux values through a 25μm thick PDD-TFE membrane were approximately 5g/(m²h) for toluene-ethyl acetate systems and 2.2g/(m²h) for toluene-methanol and toluene-THF systems. The membrane was typically selective for the organic solvent with the smaller molecular dimensions. The solubility of the individual components in a mixture provided unique insights into such behavior. The observed separation behavior provides a window into the complex phenomena of organic solvent transport through the PDD-TFE membrane.