Permeability of Co2 in Amorphous and Crystalline Teflon Membranes
Ram B. Gupta and Kayoko Ono. Chemical Engineering, Auburn University, 0322 Haley Center, Auburn, AL 36849-5127
Gas and vapor separations using polymer membranes has been brought to focus in the past 20 years. Teflon AF products (DuPont) are amorphous, glassy copolymers consisting of 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (PDD) and tetrafluoroethylene (TFE). Teflon AF 2400 contains 87 mol % of PDD and 13 % of TFE with Tg = 240 C, whereas Teflon AF 1600 contains 65 mol % of PDD and 35 % of TFE with Tg = 160 C. Teflon AFs have high temperature stability and chemical resistance, as well as high free volume compared to the conventional glassy polymers. Permeability coefficients of CO2 in Teflon AF 2400, Teflon AF 1600, and poly(tetrafluoroethylene) (PTFE) are measured, at varying feed pressure and temperature. The permeability increase in the order of PTFE < Teflon AF 1600 < Teflon AF 2400. This can be explained by the fact that PTFE is a semicrystalline polymer and Teflon AFs are high free volume glassy polymers. In addition, the reuse of the membrane for second and third time resulted in enhancement of the permeability, which can be attributed to the CO2 plasticization of the membrane. Further understanding of the transport of CO2 through the membranes is obtained by applying solution-diffusion model.