Global ETD Search

1	Poly(vinylidene fluoride) membranes: Preparation, modification, characterization and applications Sun, Chenggui January 2009 (has links) Hydrophobic microporous membranes have been widely used in water and wastewater treatment by microfiltration, ultrafiltration and membrane distillation. Poly(vinylidene fluoride) (PVDF) materials are one of the most popular polymeric membrane materials because of their high mechanical strength, excellent thermal and chemical stabilities, and ease of fabrication into asymmetric hollow fiber membranes. In this work, specialty PVDF materials (Kynar 741, 761, 461, 2851, RC-10186 and RC10214) newly developed by Arkema Inc. were used to develop hollow fiber membranes via the dry/wet phase inversion. These materials were evaluated from thermodynamic and kinetic perspectives. The thermodynamic analysis was performed by measuring the cloud points of the PVDF solution systems. The experimental results showed that the thermodynamic stability of the PVDF solution system was affected by the type of polymer and the addition of additive (LiCl); and the effects of the additive (LiCl) depended on the type of polymer. The kinetic experiments were carried out by determining the solvent evaporation rate in the “dry” step and the small molecules (solvent, additive) diffusion rate in the “wet step”. Solvent evaporation in the early stage could be expressed quantitatively. In the “wet” step, the concentrations of solvent and additive had a linear relationship with respect to the square root of time (t1/2) at the early stage of polymer precipitation, indicating that the mass-transfer for solvent-nonsolvent exchange and additive LiCl leaching was diffusion controlled. The kinetic analysis also showed that the slope of this linear relationship could be used as an index to evaluate the polymer precipitation rate (solvent-nonsolvent exchange rate and LiCl leaching rate). The extrusion of hollow fiber membranes was explored, and the effects of various fabrication parameters (such as dope extrusion rate, internal coagulant flow velocity and take-up speed) on the structure and morphology of the hollow fiber membranes were also investigated. The properties of the hollow fiber membranes were characterized by gas permeation method and gas-liquid displacement method. The morphology of the hollow fibers was examined by scanning electron microscope (SEM). It was found that Kynar 741 and 2851 were the best among the PVDF polymers studied here for the fabrication of hollow fiber membranes. In order to reduce the problems associated with the hydrophobicity of PVDF on hollow fiber module assembly, such as tubesheet leaking through problem and fouling problem, amine treatment was used to modify PVDF membranes. Contact angle measurements and filtration experiments were performed. Fourier-transform infrared (FT-IR) spectroscopy and energy dispersive x-ray analysis (EDAX) were used to analyze the modified polymer. It was revealed that the hydrophilicity of the modified membrane was improved by amine treatment and conjugated C=C and C=O double bonds appeared along the polymer backbone of modified PVDF. Hollow fiber membranes fabricated from Kynar 741 were tested for water desalination by vacuum membrane distillation (VMD). An increase in temperature would increase the water productivity remarkably. Concentration polarization occurred in desalination, and its effect on VMD could be reduced by increasing the feed flowrate. The permeate pressure build-up was also investigated by experiments and parametric analysis, and the results will be important to the design of hollow fiber modules for VMD in water desalination. PVDF membrane membrane distillation Chemical Engineering
2	Poly(vinylidene fluoride) membranes: Preparation, modification, characterization and applications Sun, Chenggui January 2009 (has links) Hydrophobic microporous membranes have been widely used in water and wastewater treatment by microfiltration, ultrafiltration and membrane distillation. Poly(vinylidene fluoride) (PVDF) materials are one of the most popular polymeric membrane materials because of their high mechanical strength, excellent thermal and chemical stabilities, and ease of fabrication into asymmetric hollow fiber membranes. In this work, specialty PVDF materials (Kynar 741, 761, 461, 2851, RC-10186 and RC10214) newly developed by Arkema Inc. were used to develop hollow fiber membranes via the dry/wet phase inversion. These materials were evaluated from thermodynamic and kinetic perspectives. The thermodynamic analysis was performed by measuring the cloud points of the PVDF solution systems. The experimental results showed that the thermodynamic stability of the PVDF solution system was affected by the type of polymer and the addition of additive (LiCl); and the effects of the additive (LiCl) depended on the type of polymer. The kinetic experiments were carried out by determining the solvent evaporation rate in the “dry” step and the small molecules (solvent, additive) diffusion rate in the “wet step”. Solvent evaporation in the early stage could be expressed quantitatively. In the “wet” step, the concentrations of solvent and additive had a linear relationship with respect to the square root of time (t1/2) at the early stage of polymer precipitation, indicating that the mass-transfer for solvent-nonsolvent exchange and additive LiCl leaching was diffusion controlled. The kinetic analysis also showed that the slope of this linear relationship could be used as an index to evaluate the polymer precipitation rate (solvent-nonsolvent exchange rate and LiCl leaching rate). The extrusion of hollow fiber membranes was explored, and the effects of various fabrication parameters (such as dope extrusion rate, internal coagulant flow velocity and take-up speed) on the structure and morphology of the hollow fiber membranes were also investigated. The properties of the hollow fiber membranes were characterized by gas permeation method and gas-liquid displacement method. The morphology of the hollow fibers was examined by scanning electron microscope (SEM). It was found that Kynar 741 and 2851 were the best among the PVDF polymers studied here for the fabrication of hollow fiber membranes. In order to reduce the problems associated with the hydrophobicity of PVDF on hollow fiber module assembly, such as tubesheet leaking through problem and fouling problem, amine treatment was used to modify PVDF membranes. Contact angle measurements and filtration experiments were performed. Fourier-transform infrared (FT-IR) spectroscopy and energy dispersive x-ray analysis (EDAX) were used to analyze the modified polymer. It was revealed that the hydrophilicity of the modified membrane was improved by amine treatment and conjugated C=C and C=O double bonds appeared along the polymer backbone of modified PVDF. Hollow fiber membranes fabricated from Kynar 741 were tested for water desalination by vacuum membrane distillation (VMD). An increase in temperature would increase the water productivity remarkably. Concentration polarization occurred in desalination, and its effect on VMD could be reduced by increasing the feed flowrate. The permeate pressure build-up was also investigated by experiments and parametric analysis, and the results will be important to the design of hollow fiber modules for VMD in water desalination. PVDF membrane membrane distillation Chemical Engineering
3	Effects of Multi-walled Carbon Nanotubes (MWCNTs) and Integrated MWCNTs/SiO2 Additives on Polymeric PVDF Membrane for Membrane Distillation Zhou, Rufan 30 November 2018 (has links) Multi-walled carbon nanotubes (MWCNTs) and integrated MWCNTs/ SiO2 nanoparticles (NPs) were loaded as additives into nanocomposite polyvinylidene fluoride (PVDF) membranes fabricated via phase inversion methods, and the effects of these additives on the structure and vacuum membrane distillation (VMD) performance of the membranes have been studied. With an appropriate amount of MWCNTs (2 wt.% to PVDF) blended into the membrane, VMD performance of membrane was improved significantly due to higher membrane porosity, contact angle and surface roughness without extreme compromise of liquid entry pressure of water (LEPw), which could reach up to 72 psi. Further integration of MWCNTs with a small amount of SiO2 nanoparticles (NPs) showed a synergic effect resulting in further improvement of VMD flux due primarily to the increase in surface pore size. When the amount of SiO2 NPs additive was large, the effects of NPs dominates the VMD performance. However, the asymmetric structure of PVDF membrane disappears, which exercises an unfavourable effect on VMD performance. All fabricated membranes exhibited a great desalination potential with extremely high salt rejection (>99.98%). The incorporation of MWCNTs did not improve the tensile properties of the membrane. Multi-walled Carbon Nanotubes Polymeric PVDF Membrane integrated MWCNTs/ SiO2 nanoparticles
4	Transfer of small molecules across membrane-mimetic interfaces Velicky, Matej January 2011 (has links) The presented thesis investigates the transfer of drug molecules across interfaces that mimic biological membrane barriers. The permeability of drug molecules across biological membrane mimics has been investigated in a novel artificial membrane permeation assay configuration using an in situ time-dependent approach and reproducible rotation of the membrane. A method to determine the membrane permeability from the knowledge of measured permeability and the applied stirring rate is presented. The initial transient of the permeation response, previously not observed in situ, is investigated and its importance in data evaluation is discussed. The permeability coefficients of 31 drugs are optimised for the conditions found in vivo and a correlation with the fraction absorbed in humans is presented. The evidence for ionic and/or ion-pair flux across the artificial membrane obtained from measurement of permeability at different pH is supported by the investigation of the permeation assay with external membrane polarisation. The permeability coefficient of the solute's anionic form is determined. Liquid/liquid electrochemistry has been used to study the transfer of ionized species across the interface between water and 1,2-dichloroethane. An alternative method to study the transfer of partially ionised drug molecules employing a rotating liquid/liquid interface is presented. In addition, a bipolar electrochemical cell with a rotating-disc electrode is developed and its properties investigated in order to verify the hydrodynamics of the rotating artificial membrane configuration. Finally, in support of the electrochemical techniques used is this thesis, a detailed preparation and evaluation of the silver/silver sulphate reference electrode is presented. 571.64
5	Development of High-throughput Membrane Filtration Techniques for Biological and Environmental Applications / Development of High-throughput Membrane Filtration Techniques Kazemi, Amir Sadegh 11 1900 (has links) Membrane filtration processes are widely utilized across different industrial sectors for biological and environmental separations. Examples of the former are sterile filtration and protein fractionation via microfiltration (MF) and ultrafiltration (UF) while drinking water treatment, tertiary treatment of wastewater, water reuse and desalination via MF, UF, nanofiltration (NF) and reverse-osmosis (RO) are examples of the latter. A common misconception is that the performance of membrane separation is solely dependent on the membrane pore size, whereas a multitude of parameters including solution conditions, solute concentration, presence of specific ions, hydrodynamic conditions, membrane structure and surface properties can significantly influence the separation performance and the membrane’s fouling propensity. The conventional approach for studying filtration performance is to use a single lab- or pilot-scale module and perform numerous experiments in a sequential manner which is both time-consuming and requires large amounts of material. Alternatively, high-throughput (HT) techniques, defined as the miniaturized version of conventional unit operations which allow for multiple experiments to be run in parallel and require a small amount of sample, can be employed. There is a growing interest in the use of HT techniques to speed up the testing and optimization of membrane-based separations. In this work, different HT screening approaches are developed and utilized for the evaluation and optimization of filtration performance using flat-sheet and hollow-fiber (HF) membranes used in biological and environmental separations. The effects of various process factors were evaluated on the separation of different biomolecules by combining a HT filtration method using flat-sheet UF membranes and design-of-experiments methods. Additionally, a novel HT platform was introduced for multi-modal (constant transmembrane pressure vs. constant flux) testing of flat-sheet membranes used in bio-separations. Furthermore, the first-ever HT modules for parallel testing of HF membranes were developed for rapid fouling tests as well as extended filtration evaluation experiments. The usefulness of the modules was demonstrated by evaluating the filtration performance of different foulants under various operating conditions as well as running surface modification experiments. The techniques described herein can be employed for rapid determination of the optimal combination of conditions that result in the best filtration performance for different membrane separation applications and thus eliminate the need to perform numerous conventional lab-scale tests. Overall, more than 250 filtration tests and 350 hydraulic permeability measurements were performed and analyzed using the HT platforms developed in this thesis. / Thesis / Doctor of Philosophy (PhD) / Membrane filtration is widely used as a key separation process in different industries. For example, microfiltration (MF) and ultrafiltration (UF) are used for sterilization and purification of bio-products. Furthermore, MF, UF and reverse-osmosis (RO) are used for drinking water and wastewater treatment. A common misconception is that membrane filtration is a process solely based on the pore size of the membrane whereas numerous factors can significantly affect the performance. Conventionally, a large number of lab- or full-scale experiments are performed to find the optimum operating conditions for each filtration process. High-throughput (HT) techniques are powerful methods to accelerate the pace of process optimization—they allow for multiple experiments to be run in parallel and require smaller amounts of sample. This thesis focuses on the development of different HT techniques that require a minimal amount of sample for parallel testing and optimization of membrane filtration processes with applications in environmental and biological separations. The introduced techniques can reduce the amount of sample used in each test between 10-50 times and accelerate process development and optimization by running parallel tests. Membrane filtration Ultrafiltration Downstream bio-processing High-throughput (HT) testing Wastewater treatment Hollow-fiber membranes Humic acids High-throughput filtration Design-of-experiments (DOE) Process optimization Microscale filtration Microfluidic flow control system Stirred well filtration SWF High-throughput hollow-fiber module HT-HF Constant TMP Constant flux Multi-modal filtration Bioseparation MMFC MS-PS-CFF PEG Dextran FITC-Dextran BSA DNA IgG α-lactalbumin Biomolecule separation Module hydrodynamics Concentration polarization Membrane fouling Micromixing Omega™ membrane Microscale processing Fouling test PVDF membrane Surface modification Polydopamine Membrane cleaning Membrane backwashing Sodium alginate Polyethersulfone PES Hydraulic permeability Membrane permeability ZeeWeed® membrane Filtration ionic strength Filtration pH Solution conditions Water treatment Environmental separations Biological separations

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