Perflourinated Membranes for Pervaporation Separation of Organic Solvent Mixtures In Pharmaceutical Processing

Perfluoro-2,2-dimethyl-1,3-dioxole-tetrafluoroethylene (PDD-TFE) is an amorphous, glassy, perfluorinated copolymer with a very high fractional free volume and a high glass transition temperature. As with similar materials, it exhibits considerable thermal and chemical stability. Previous studies show this copolymer having a very high oxygen permeance and a significant selectivity of oxygen over nitrogen. Due to its ability to separate gaseous mixtures, coupled with its chemical stability, separating organic solvent mixtures through pervaporation (PV) seems highly favorable. Furthermore, the pharmaceutical industry would greatly benefit from a lower temperature-based and economic means to separate common solvents used in processing. Reported maximum free volume dimensions of perfluorinated copolymers are on the order of 5.9-6.4 Å. Solvents whose molecular dimensions are larger are typically rejected. This study is an attempt to utilize such free volume dimensions of this particular PDD-TFE formulation as we determine its performance as a membrane in PV. Common pharmaceutically relevant solvents of varying sizes and boiling points have been selected: toluene, ethyl acetate, tetrahydrofuran, methanol, n-dimethylsulfoxide, n-dimethylformamide, and n-dimethylacetamide. Testing for pure component permeation of all organic solvents was implemented to create a baseline of performance. The effects of temperature and composition in mixtures were explored to properly gauge the behavior of the membrane. By analyzing separation/permeation data and molecular dimensions of each solvent, a permeance profile can be generated for a variety of solvents that are expected to permeate through the membrane. In addition, extensive studies of removal of water from some of the high-boiling organic solvents identified earlier have been carried out.