Study On The Behaviors Of Solution And Diffusion For Small Molecules In The Polymers By Inverse Gas Chromatography

Pervaporation has broad prospects for application in many fields, such as chemical separation and new energy, with high separation efficiency and low energy consumption. It is critical for pervaporation to the selection and production of membrane materials. According to solution-diffusion model, the separation capacity of pervaporation membranes arises from the difference in solution properties and/or diffusion properties between membrane materials and the components to be separated. Thorough study on the behaviors of solution and diffusion of small molecules in polymer, would further facilitate the mechanism of pervaporation process, which is also effective means to the selection of membrane materials. Inverse gas chromatography(IGC) is a fast and reliable technique to measure the solvent-polymer interplay. The infinite dilute activity coefficients and infinite dilute diffusion coefficients of organic sulfur/polyphosphazenes(POPs) mixture and alcohols/polyether block amide(PEBA) mixture were determined by IGC technique in this paper. The obtained data was used to guide the selection and production of membrane materials and to explain the pervaporation performance.Firstly, the infinite dilute activity coefficients and infinite dilute diffusion coefficients of n-heptane, thiophene, 2-methylthiophene, 2,5-dimethylthiophene, ethyl sulfide, n-butyl mercaptan in poly[bis(trifluoroethoxy)phosphazene](PTFEP) and poly[bis(phenoxy)phosphazene](PBPP) were measured in the temperature ranging from 353.15 K to 373.15 K by IGC technique. The influence of pendant groups on the behaviors of solution and diffusion, and the relation between solution-diffusion properties and pervaporation performance were also studied. The high sulfur enrichment of PTFEP membrane was due to the distinct difference of infinite dilute activity coefficients and infinite dilute diffusion coefficients between organic sulfur and n-heptane. Infinite dilute diffusion coefficients increased with phenoxy group attached to the side chain of POPs, which enhancing the permeability for organic sulfur in PBPP. In addition, the solution and diffusion behaviors of methanol, ethanol, n-propanol, nbutanol in PEBA2533 and PEBA4033 were studied. And PEBA2533 was believed to be an appropriate membrane materials for pervaporation separation of n-butanol/water mixture according to IGC study. PEBA/PVDF composite membranes were prepared, which separation factor and flux were 19.5 and 808.5 g.m-2.h-1, respectively, for the separation of 1.0wt% n-butanol/water(500C). In order to further improve the separation performance, ZIF-8/PEBA hybrid composite membranes were prepared. When ZIF-8 loading was 20% and feed temperature was 500 C, the separation factor and flux could reach 24.8 and 360.5 g.m-2.h-1, respectively, for the separation of 1.0wt% nbutanol/water.