Theoretical and experimental studies on the gas transport properties of mixed matrix membranes based on polyvinylidene fluoride



The effects of the impregnation of three types of inorganic fillers into polyvinylidene fluoride (PVDF) polymer membranes on the gas permeability and selectivity of these membranes were studied theoretically and experimentally. Permeabilities of He, CO2, O2, and N2 through three types of mixed matrix membranes (MMMs) based on PVDF, that is, PVDF/SiO2, PVDF/MCM-41, and PVDF/4A MMMs, were experimentally measured and theoretically predicted using Maxwell, Higuchi, Bruggeman, and Bottcher-Landauer models. Theoretical permeabilities of the PVDF/SiO2 MMMs using the above four models predicted the results in the following order: Maxwell model>Bruggeman model>Bottcher model>Higuchi model. However, this sequence was reversed for PVDF/MCM-41 MMMs. The nonporous SiO2, mesoporous MCM-41 and zeolite 4A inorganic fillers had effects on the permeabilities of the challenge gases for the PVDF/SiO2, PVDF/MCM-41, and PVDF/4A MMMs but had no effects on the selectivities of the MMMs. The experimental permeabilities of the MMMs showed that there were no significant differences among the three types of MMMs despite that the inorganic fillers, that is, SiO2, MCM-41, and zeolite 4A, had distinct dissimilar properties such as pore structures and particle sizes. Density measurements indicated that some voids were present in the polymer/particle interfaces. Based on the density measurement results, the void volume fractions of the resulting MMMs were calculated. An equation is derived to determine the void thickness of the MMM in terms of its physical properties and hence this proposed equation can substitute the difficult task of measuring such void thickness through any microscopy techniques. The Maxwell, Higuchi, Bruggeman, and Bottcher-Landauer models could not predict the actual gas permeabilities of the PVDF MMMs. By taking the effects of crystallinity and immobilization factor on gas permeability into consideration, the extended modified Maxwell model showed good agreement with the experimental gas permeabilities of the resulting MMMs, indicating that the model did capture the essence of the gas transport behaviors through the MMMs. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4715–4726, 2013