| Membrane is an interesting technology for gas separation application due to the facility and cost-effective process. Industrial membranes are usually thin film composites to reduce the cost of membrane preparation, which a selective layer with ∼100 nm thickness provides the gas permeability and selectivity. Membrane materials should exhibit stability, high and durable gas separation performance during the lifetime of the membrane. Herein we study fluorinated polymers as a promising material, which fulfills the criteria for membrane applications.;The first chapter is a terminology of gas transport in polymer films and an introduction to permeability/selectivity tradeoff and physical aging as the most important challenges in polymeric membrane gas separation. The second chapter investigates the effect of physical aging on the gas permeance and selectivity of TFC membranes of perfluoropolymers. The thickness of TFC membranes has a significant effect on the gas permeance stability during the time, which gas permeance decreases faster by decreasing the film thickness. Interestingly, the gas permeance of the perfluoropolymer membranes is much more stable than that in hydrocarbon polymer films with similar thickness. In chapter 3 the effect of physical aging on Tg of the TFC membranes was studied. Tg of the membranes was determined in situ by a new method, Nano-Thermal Analysis (Nano-TA). Physical aging increases the Tg of the TFC membranes during the time. The Tg increasing and decreasing of the gas permeance in the TFC membranes were explained by using a free volume model.;In the 4th chapter in a fundamental study, we investigated the effect of fluorine and chlorine substituents on gas separation performance of PCTFE. PCTFE with a simple structure shows superior He/gas separation performance. Using organic liquids as the markers, we showed fluorine substituents increase He/gas solubility selectivity while the behavior cannot be observed for chlorinated and hydrocarbon organics materials. In addition, the comparison between analogue polyethylenes shows chlorine substituent increases Tg and size-sieving ability of PCTFE.;The last chapter we study gas separation properties of poly(PFMD) and poly(PFMMD) as a new generation of perfluoropolymers for membrane application. The polymers show interesting He/gas, H2/gas, and CO 2/gas separation performance. The comparison between separation of the perfluoropolymers and Teflon AFRTM, Hyflon ADRTM s and CytopRTM which are commercial perfluoropolymers, shows the new perfluoropolymers have superior gas separation performance. For example, while H2 permeability of poly(PFMD) and Cytop RTM are comparable but the H2/CH4 selectivities are 383 and 30, respectively. The new perfluoropolymers show higher size-sieving ability than commercial perfluoropolymers. |
