Higher temperature (~ 200°C) operation for proton exchange membrane (PEM) fuel cells would have several advantages including enhanced electrochemical kinetics, useful heat recovery, and improved catalyst tolerance for contaminants. Conventional perfluorosulfonic acid membranes (PFSA), such as Nafion show a dramatic decrease in proton conductivity at temperatures above 80°C. For this reason, there has been an increasing effort toward the development of stable, higher temperature membranes with acceptable proton conductivity. This work is directed toward the development of Nafion free membranes for direct hydrocarbon PEM fuel cells containing zirconium phosphate as the proton conductor component. Hence, composite membranes composed of zirconium-phosphate (ZrP), a solid proton conductor, which was precipitated within the voids of a porous polytetraflouroethylene (PTFE) support were synthesized. Amorphous-like zirconium phosphate (ZrP) powder was synthesized in this work. ZrP was prepared by precipitation at room temperature via reaction of ZrOCl2 with H3PO4 aqueous solutions. The proton conduction properties of ZrP powder were studied under the processing conditions found in direct hydrocarbon fuel cell. Our experimental results showed that the ZrP powder processed at 200°C possess a proton conductivity that is greater by one order of magnitude than the oven-dried samples at 70°C. Thereby, it was possible to avoid the normal decrease in conductivity with increasing temperature by having sufficient water in the vapor phase. This thesis reports the first synthesis of composite ZrP/PTFE/Glycerol (GLY) membranes. Glycerol (GLY) was introduced into the pores of PTFE with the ZrP proton conductive material using the successive wetting/drying technique. These membranes had reasonable values of proton conductivities (0.045 S cm-1), approaching that of Nafion (0.1 S cm-1) at room temperature. Samples of these composite membranes were processed at the inlet conditions of a propane fuel cell, at 200°C. Experimental results showed that the proton conductivity remained almost unchanged. This thesis also describes and reports the first synthesis of sulphur “S” or silicon, Si–modified zirconium phosphate (ZrP), porous polytetrafluoethylene (PTFE) and, glycerol (GLY) composite membranes. It was aimed at the substitution of a minor amount of phosphorus “P” in the ZrP by (S or Si) in the ZrP to modify the proton conduction properties. The modification was performed by adding a certain amount of silicic acid or sulphuric acid into phosphoric acid then proceeding with the precipitation in situ. A high proton conductivity, of 0.073 S cm-1,i.e. 73% of that of Nafion, was observed for the Si–ZrP/PTFE/GLY composite membrane.

This study deals with polyvinylamine (PVAm)-poly(vinyl alcohol) (PVA) based composite membranes incorporated with carbon nanotubes (CNTs) and molecular amines (e.g., piperazine (PZ), triethanolamine (TEA), N-methyldiethanolamine (MDEA), PZ/TEA and PZ/MDEA blends, diethylenetriamine (DETA) and triethylenetetramine (TETA)) for CO2 separation, solvent dehydration by pervaporation, and hydrogen purification. The effects of the parameters involved in the procedure of membrane formation and operating conditions on the membrane performance were investigated. Composite membranes comprising of a skin layer of PVAm-PVA incorporated with CNTs and a microporous polysulfone substrate were developed for CO2 separation from flue gas and dehydration of ethylene glycol by pervaporation. The membranes were characterized with Fourier transform infrared (FTIR), Raman spectroscopy, X-ray diffraction (XRD), contact angle measurement and water sorption uptake, using dense films of PVAm-PVA/CNTs, to determine the effects of CNTs on the intermolecular interactions, degree of crystallinity, surface hydrophilicity, and degrees of swelling of the membranes. For CO2/N2 separation, adding CNTs in the membrane was shown to enhance CO2 permeance while retaining a similar CO2/N2 selectivity; a CO2 permeance of 18.5 GPU and a CO2/N2 ideal selectivity of 64 were obtained at 0.6 MPa feed pressure. For pervaporative dehydration of ethylene glycol, the incorporation of CNTs into the membrane was shown to increase both the permeation flux and separation factor, and at 70??? a permeation flux of 146 g/(m2.h) and a separation factor of 1160 were achieved at 1 wt% water in feed using a PVAm-PVA/CNT composite membrane containing 2 wt% MWNTs. Novel facilitated transport membranes containing both PVAm as fixed carriers and various molecular amines as mobile carriers were fabricated and used for CO2 separation from N2 and H2, as well as CO2 separation from ethanol fermentation off gas. For membranes containing a single amine (i.e., PZ, DETA or TETA), the CO2 permeance increased with an increase in the amine content in the membrane until the amine content is sufficiently high, beyond which a further increase in the amine content would decrease the membrane performance. The facilitation in CO2 transport was more significant with membranes containing mixed amines (e.g., PZ/TEA and PZ/MDEA). Among all the molecular amines tested, TETA was shown to be most effective in facilitating CO2 transport in terms of CO2/N2 permselectivity. Using a PVAm-PVA/TETA composite membrane with a TETA to polymer (i.e., PVAm plus PVA) mass ratio of 150/100, a CO2 permeance of 22.6 GPU and a CO2/N2 selectivity of 86.5 were obtained at 0.6 MPa feed pressure for the removal of CO2 from flue gas, a CO2 permeance of 23.3 GPU and a CO2/H2 selectivity of 28.5 were obtained at 0.6 MPa feed pressure for CO2 separation from H2, a water vapor permeance of 16700 GPU was obtained at 25??? and 2.5 mol% water vapor concentration in the feed for dehydration of ethanol fermentation off gas.

Higher temperature (~ 200°C) operation for proton exchange membrane (PEM) fuel cells would have several advantages including enhanced electrochemical kinetics, useful heat recovery, and improved catalyst tolerance for contaminants. Conventional perfluorosulfonic acid membranes (PFSA), such as Nafion show a dramatic decrease in proton conductivity at temperatures above 80°C. For this reason, there has been an increasing effort toward the development of stable, higher temperature membranes with acceptable proton conductivity. This work is directed toward the development of Nafion free membranes for direct hydrocarbon PEM fuel cells containing zirconium phosphate as the proton conductor component. Hence, composite membranes composed of zirconium-phosphate (ZrP), a solid proton conductor, which was precipitated within the voids of a porous polytetraflouroethylene (PTFE) support were synthesized. Amorphous-like zirconium phosphate (ZrP) powder was synthesized in this work. ZrP was prepared by precipitation at room temperature via reaction of ZrOCl2 with H3PO4 aqueous solutions. The proton conduction properties of ZrP powder were studied under the processing conditions found in direct hydrocarbon fuel cell. Our experimental results showed that the ZrP powder processed at 200°C possess a proton conductivity that is greater by one order of magnitude than the oven-dried samples at 70°C. Thereby, it was possible to avoid the normal decrease in conductivity with increasing temperature by having sufficient water in the vapor phase. This thesis reports the first synthesis of composite ZrP/PTFE/Glycerol (GLY) membranes. Glycerol (GLY) was introduced into the pores of PTFE with the ZrP proton conductive material using the successive wetting/drying technique. These membranes had reasonable values of proton conductivities (0.045 S cm-1), approaching that of Nafion (0.1 S cm-1) at room temperature. Samples of these composite membranes were processed at the inlet conditions of a propane fuel cell, at 200°C. Experimental results showed that the proton conductivity remained almost unchanged. This thesis also describes and reports the first synthesis of sulphur “S” or silicon, Si–modified zirconium phosphate (ZrP), porous polytetrafluoethylene (PTFE) and, glycerol (GLY) composite membranes. It was aimed at the substitution of a minor amount of phosphorus “P” in the ZrP by (S or Si) in the ZrP to modify the proton conduction properties. The modification was performed by adding a certain amount of silicic acid or sulphuric acid into phosphoric acid then proceeding with the precipitation in situ. A high proton conductivity, of 0.073 S cm-1,i.e. 73% of that of Nafion, was observed for the Si–ZrP/PTFE/GLY composite membrane.

Higher temperature (~ 200°C) operation for proton exchange membrane (PEM) fuel cells would have several advantages including enhanced electrochemical kinetics, useful heat recovery, and improved catalyst tolerance for contaminants. Conventional perfluorosulfonic acid membranes (PFSA), such as Nafion show a dramatic decrease in proton conductivity at temperatures above 80°C. For this reason, there has been an increasing effort toward the development of stable, higher temperature membranes with acceptable proton conductivity. This work is directed toward the development of Nafion free membranes for direct hydrocarbon PEM fuel cells containing zirconium phosphate as the proton conductor component. Hence, composite membranes composed of zirconium-phosphate (ZrP), a solid proton conductor, which was precipitated within the voids of a porous polytetraflouroethylene (PTFE) support were synthesized. Amorphous-like zirconium phosphate (ZrP) powder was synthesized in this work. ZrP was prepared by precipitation at room temperature via reaction of ZrOCl2 with H3PO4 aqueous solutions. The proton conduction properties of ZrP powder were studied under the processing conditions found in direct hydrocarbon fuel cell. Our experimental results showed that the ZrP powder processed at 200°C possess a proton conductivity that is greater by one order of magnitude than the oven-dried samples at 70°C. Thereby, it was possible to avoid the normal decrease in conductivity with increasing temperature by having sufficient water in the vapor phase. This thesis reports the first synthesis of composite ZrP/PTFE/Glycerol (GLY) membranes. Glycerol (GLY) was introduced into the pores of PTFE with the ZrP proton conductive material using the successive wetting/drying technique. These membranes had reasonable values of proton conductivities (0.045 S cm-1), approaching that of Nafion (0.1 S cm-1) at room temperature. Samples of these composite membranes were processed at the inlet conditions of a propane fuel cell, at 200°C. Experimental results showed that the proton conductivity remained almost unchanged. This thesis also describes and reports the first synthesis of sulphur “S” or silicon, Si–modified zirconium phosphate (ZrP), porous polytetrafluoethylene (PTFE) and, glycerol (GLY) composite membranes. It was aimed at the substitution of a minor amount of phosphorus “P” in the ZrP by (S or Si) in the ZrP to modify the proton conduction properties. The modification was performed by adding a certain amount of silicic acid or sulphuric acid into phosphoric acid then proceeding with the precipitation in situ. A high proton conductivity, of 0.073 S cm-1,i.e. 73% of that of Nafion, was observed for the Si–ZrP/PTFE/GLY composite membrane.

Many industrial processes handling organic solvents produce volatile organic compounds (VOCs). These VOCs not only cause environmental pollution, but also represent an economic loss. VOC removal and recovery have become a big issue that needs to be addressed. Traditional techniques for VOCs removal include carbon adsorption, condensation, and absorption, and none is efficient enough to meet every need. Membrane separation has emerged as an excellent alternative or complementary technology for VOC separation. Separation of VOCs from nitrogen by composite hollow fiber membranes is studied in this thesis. Microporous hollow fiber membranes were spun from polyvinylidene fluoride (PVDF) using the phase inversion method, and the hollow fibers were coated with a thin layer of poly(ether block amide) (PEBA), thereby forming composite membranes. PVDF was chosen as the substrate material because of its excellent thermal and chemical stabilities and good mechanical strength, and PEBA was selected as the active separating layer because of its good permselectivity and film forming properties. In PEBA polymer, the hard polyamide blocks provide high mechanical strength, and the soft polyether blocks provide flexibility and elasticity. This study is focused on the preparation and characterization of PEBA/PVDF composite hollow fiber membranes. The membranes were tested for the removal of representative VOCs including hexane, heptane and cyclohexane, which are the main components of gasoline, and dimethyl carbonate (DMC), ethanol, methanol, and methyl t-butyl ether (MTBE) that are the oxygenates and octane number enhancers of gasoline. The separation of gasoline vapor from nitrogen was also investigated. It was found that the PEBA/PVDF composite hollow fiber membranes are effective for the separation of hydrocarbon vapors from nitrogen. The effects of hollow fiber membrane preparation conditions on the membrane performance were studied, and the separation performance of the composite hollow fiber membranes at various operating conditions (e. g. feed concentration, operating temperature) was evaluated.

Many industrial processes handling organic solvents produce volatile organic compounds (VOCs). These VOCs not only cause environmental pollution, but also represent an economic loss. VOC removal and recovery have become a big issue that needs to be addressed. Traditional techniques for VOCs removal include carbon adsorption, condensation, and absorption, and none is efficient enough to meet every need. Membrane separation has emerged as an excellent alternative or complementary technology for VOC separation. Separation of VOCs from nitrogen by composite hollow fiber membranes is studied in this thesis. Microporous hollow fiber membranes were spun from polyvinylidene fluoride (PVDF) using the phase inversion method, and the hollow fibers were coated with a thin layer of poly(ether block amide) (PEBA), thereby forming composite membranes. PVDF was chosen as the substrate material because of its excellent thermal and chemical stabilities and good mechanical strength, and PEBA was selected as the active separating layer because of its good permselectivity and film forming properties. In PEBA polymer, the hard polyamide blocks provide high mechanical strength, and the soft polyether blocks provide flexibility and elasticity. This study is focused on the preparation and characterization of PEBA/PVDF composite hollow fiber membranes. The membranes were tested for the removal of representative VOCs including hexane, heptane and cyclohexane, which are the main components of gasoline, and dimethyl carbonate (DMC), ethanol, methanol, and methyl t-butyl ether (MTBE) that are the oxygenates and octane number enhancers of gasoline. The separation of gasoline vapor from nitrogen was also investigated. It was found that the PEBA/PVDF composite hollow fiber membranes are effective for the separation of hydrocarbon vapors from nitrogen. The effects of hollow fiber membrane preparation conditions on the membrane performance were studied, and the separation performance of the composite hollow fiber membranes at various operating conditions (e. g. feed concentration, operating temperature) was evaluated.

No description available.

The objective of this study was to examine the effects of annealing polyimide-organosilicate hybrid membranes on gas transport. In addition, the effects of carbon dioxide pressure on the gas transport of unannealed polyimide-organosilicate hybrid membranes were evaluated. The membranes in both studies consisted of sol-gel derived organosilicate domains covalently bonded to a 6FDA-6FpDA-DABA polyimide using partially hydrolyzed tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS) or phenyltrimethoxysilane (PTMOS). The first study subjected the hybrid membranes to a 400°C annealing process to enhance gas separation performance by altering the organosilicate structures. The hybrid membranes were evaluated before and after annealing using pure gases (He, O₂, N₂, CH₄, CO₂) at 35°C and a feed pressure of 4 atm. The permeability for most of the membranes increased 200-500% after the annealing process while the permselectivity dropped anywhere from 0 to 50%. The exceptions were the 6FDA-6FpDA-DABA-25 22.5 wt% TMOS and MTMOS hybrid membranes, both of which exhibited increases in the CO₂ permeability and CO₂-CH₄ permselectivity. The increase in permeation was attributed to increases in the free volume and enhanced segmental mobility of the chain ends resulting from the removal of sol-gel condensation and polymer degradation byproducts. For the second study, the transport properties of four membranes, 6FDA-6FpDA polyimide, 6FDA-6FpDA-DABA polyimide, MTMOS and PTMOS-based hybrid materials, were characterized as a function of feed pressure to evaluate how the hybrid materials reacted to CO₂ plasticization. Steady-state gas permeation experiments were performed at 35°C using pure CO₂ and CH₄ gases at feed pressures ranging from 4 to 30 atm. All four materials exhibited dual mode sorption up to feed pressures of 17 atm, at which point the effects of CO₂ plasticization were observed. / Master of Science

Proton-Exchange Membrane (PEM) fuel cells are extremely attractive for replacing internal combustion engines in the next generation of automobiles. However, two major technical challenges remain to be resolved before PEM fuel cells become commercially successful. The first issue is that CO, produced in trace amounts in fuel reformer, severely limits the performance of the conventional platinum-based PEM fuel cell. A possible solution to the CO poisoning is higher temperature operation, as the CO adsorption and oxidation overpotential decrease considerably with increasing temperature. However, the process temperature is limited in atmospheric fuel cells because water is critical for high conductivity in the standard PEM. An increase in operating pressure allows higher temperature operation, although at the expense of parasitic power for the compressor. Further the conventional PEM, Nafion? is limited to 120°C due to it's low glass transition temperature. Thus, the design of higher temperature PEMs with stable performance under low relative humidity (RH) conditions is considered based on a proton transport model for the PEM and a fuel cell model that have been developed. These predictive models capture the significant aspects of the experimental results with a minimum number of fitted parameters and provides insight into the design of higher temperature PEMs operating at low RH. The design of an efficacious high temperature, low RH, PEM was based on enhancing the acidity and water sorption properties of a conventional PEM by impregnating it with a solid superacid. A systematic investigation of the composite Nafion?inorganic PEMs comprising experiments involving water uptake, ion-exchange capacity (IEC), conductivity and fuel cell polarization is presented in the work. The most promising composite is the nano-structured ZrO2/Nafion?PEM which exhibits an increase in the IEC, a 40% increase in water sorbed and a resulting 24% conductivity enhancement vs. unmodified Nafion?112 at 120°C and at RH < 40%.

This study deals with poly(ether block amide) (PEBA) (type 2533) membranes for gas separation. A new method was developed to prepare flat thin film PEBA membranes by spontaneous spreading of a solution of the block copolymer on water surface. The membrane formation is featured with simultaneous solvent evaporation and solvent exchange with the support liquid, i.e. water. The formation of a uniform and defect-free membrane was affected by the solvent system, polymer concentration in the casting solution and temperature. Propylene separation from nitrogen, which is relevant to the recovery of propylene from the de-gassing off-gas during polypropylene manufacturing, was carried out using flat PEBA composite membranes formed by laminating the aforementioned PEBA on a microporous substrate. The propylene permeance was affected by the presence of nitrogen, and vice versa, due to interactions between the permeating components. Semi-empirical correlations were developed to relate the permeance of a component in the mixture to the pressures and compositions of the gas on both sides of the membrane, and the separation performance at different operating conditions was analyzed in terms of product purity, recovery and productivity on the basis of a cross flow model. To further understand gas permeation behavior and transport mechanism in the membranes, sorption, diffusion, and permeation of three olefins (i.e., C2H4, C3H6, and C4H8) in dense PEBA membranes were investigated. The relative contribution of solubility and diffusivity to the preferential permeability of olefins over nitrogen was elucidated. It was revealed that the favorable olefin/nitrogen permselectivity was primarily attributed to the solubility selectivity, whereas the diffusivity selectivity may affect the permselectivity negatively or positively, depending on the operating temperature and pressure. At a given temperature, the pressure dependence of solubility and permeability could be described empirically by an exponential function. The limiting solubility at infinite dilution was correlated with the reduced temperature of the permeant. The separation of volatile organic compounds (VOCs), which are more condensable than olefin gases, from nitrogen stream by the thin film PEBA composite membranes for potential use in gasoline or other organic vapour emission control was also studied. The membranes exhibited good separation performance for both binary VOC/N2 and multi-component VOCs/N2 gas mixtures. The permeance of N2 in the VOC/N2 mixtures was shown to be higher than pure N2 permeance due to membrane swelling induced by the VOCs dissolved in the membrane. The effects of feed VOC concentration, temperature, stage cut, and permeate pressure on the separation performance were investigated. Additionally, hollow fiber PEBA/polysulfone composite membranes were prepared by the dip coating technique. The effects of parameters involved in the procedure of polysulfone hollow fiber spinning and PEBA layer deposition on the permselectivity of the resulting composite membranes were investigated. Lab scale PEBA hollow fiber membrane modules were assembled and tested for CO2/N2 separation with various flow configurations using a simulated flue gas (15.3% carbon dioxide, balance N2) as the feed. The shell side feed with counter-current flow was shown to perform better than other configurations over a wide range of stage cuts in terms of product purity, recovery and productivity.