Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 186-203). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006. / Ching-Hua Huang, Committee Co-Chair ; F. Michael Saunders, Committee Member ; Jae-Hong Kim, Committee Chair.

Centrifugal membrane and density separation (CMS) is a novel technology proposed for treatment of waste water and industrial process streams. This cross flow filtration process combines the energy recovery inherent to centrifugal reverse osmosis (CRO) with the potential alleviation of membrane fouling and concentration polarization due to the favourable effects of centrifugal and Coriolis accelerations. This dissertation presents a computational study of CMS undertaken to understand the basic hydrodynamics and mass transfer of the processes and to provide insight for the design of CMS devices. Two distinct membrane models were developed, the porous wall model (PWM) and the source term model (STM), and incorporated into Computational Fluid Dynamics (CFD) codes which solve the full Navier-Stokes equations coupled to a scalar transport equation which accounts for dissolved species. These models are used to simulate two and three dimensional laminar flows in both non-rotating and rotating reverse osmosis membrane cartridges and to predict permeate fluxes. Plate and frame geometries are first examined and it is determined that CMS benefits most from channels with streamwise directions directed radially. It is also shown that the benefits of CMS can be attributed largely to the secondary flows and mixing associated with Coriolis acceleration, and the PWM and the STM are found to perform similarly in the case of reverse osmosis. Next, the STM is used to perform a parametric study of the flow and mass transfer in rectangular and square rotating channels. It is shown that while normal rotation is preferable to spanwise rotation, relatively small deviations from the spanwise orientation are adequate to achieve most of the normal rotation performance, and that differences between the two orientations are minimal in the case of square channels. Also, the flow characteristics are again shown to correlate well with the magnitude of the Coriolis acceleration. Flows in triangular and circular channels are also considered, and are shown to perform similarly to rectangular channels. These channel orientations have application in hollow fiber membrane modules and potentially in spiral wound membrane modules. Finally, the flow and mass transfer in channels with periodic streamwise obstacles are considered. Such obstacles are related to feed spacers used in spiral wound membrane elements and impact considerably on the flow characteristics and mass transfer performance. Flow obstacles are shown to increase mass transfer performance in all cases, with alternating surface mounted performing best. A preliminary investigation is undertaken into rotating flows with periodic obstacles, and the flow fields are shown to depend strongly on the blockage ratio and on the Rossby number. In most cases, it is found that mass transfer performance does not necessarily correlate with either wall shear stress or the local flow field. Several general conclusions regarding CMS can be drawn from this work. It is preferable to operate a CMS devices at low flow rates, which is contrary to conventional wisdom in membrane separation. Secondly, the mixing induced by channel rotation is both more effective and more efficient than the mixing induced by the feed spacers considered here. Finally, the magnitude of the Coriolis acceleration is the dominant parameter in determining CMS performance. This means that a CMS device can either operate at relatively low rotational speeds with flow in the radial direction, or at higher speeds but lower angles of inclination with respect to the rotational axis. / Graduate

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, Cape Town, 2006 / During recent years, the use of liquid membranes has gained general interest in the treatment of effiuents where solute concentrations are low and large volumes of solutions should be processed, and, if possible, without generating any secondary waste. Liquid membrane processes have been proposed as a clean technology, owing to their characteristics, i.e. high specificity, low energy and utilization. Two liquid membrane processes have been used in metal recovery, which are the liquid surfactant membrane (LSM), which corresponds to double water-in-oil emulsion and solid . supported liquid membranes (SLM), which are made by dispersing or impregnating the extractant within the pores of in.ert solid support. Previously, the recovery of eu (IT) in a SLM system was conducted by other membrane models such as hollow fibre, spiral and flat sheet. Only a small measure of success on scale-up and industrialization of these models has been attained. One of the disadvantages of the hollow fibre system was the small lumen size through which the feed needed to pass. Pores became clogged by suspended particles because the pressure drop over the small diameter augments lower flow rates and therefore, pre-filtering is necessary (Rathore, et al., 2001). In this study the behaviour of a tubular SLM reactor with an inner diameter of the lumen approximately fifty times bigger than that of the hollow fibre are used in order to solve the problem of clogging. This tubular reactor was incorporated in to a bench scale plant and proved successful in copper extraction. By observing transient data, mass transport coefficients were determined and compared to published values.

Thesis (Masters Diploma (Technology)--Cape Technikon, Cape Town,1993 / Various experimental and established membranes were tested on industrial effluents. Ultrafiltration, reverse osmosis and nanofiltration membranes were used in various applications. Research was done on aspects such as the cleaning of fouled membranes, production quality control and process development. Polyvinyl alcohol ultra-thin-film reverse osmosis membranes were manufactured for the desalination of brackish water to a potable standard. The membranes were manufactured in the tubular configuration. Experimental ultrafiltration, reverse osmosis and nanofiltration membranes were tested on cooling water blowdown on a laboratory-scale. On-site testing was done directly on the effluent at a later stage. A s!udy was also conducted to determine the effect of gel-polarization on membrane performance. The gel-layer model was used to predict the limiting flux of specific membranes. Membrane processes were also applied in the fractionation of wine-lees to provide usable by-products such as yeast cells and potassium bitartrate. Ultrafiltration membranes operated in diafiltration mode were used to "wash" the slurry at different solid concentrations. The bitartrate-rich permeate collected from ultrafiltration was then concentrated using reverse osmosis and nanofiltration to allow subsequent precipitation of the product.

Sustainable energy supply and environmental protection are the major global scientific challenges in the 21st century, such as greenhouse gas capture, natural gas production, desalination of seawater for clean water production. Membrane separation technology offers attractive energy-efficient and environmental-friendly solutions to these challenges. This PhD thesis is focused on design and fabrication of membranes from novel molecularly defined polymers and understanding their physical properties, particularly the transport properties of gas molecules in polymer membranes. First, we demonstrate a simple approach of fabricating novel polymer nanocomposite membranes using established colloidal science. Crystalline microporous zeolitic imidazolate frameworks (ZIFs) nanocrystals are incorporated into a polyimide polymer matrix via solution mixing. The resulting nanocomposite membranes show excellent dispersion of nanoparticles, good adhesion at the interface, and enhanced gas permeability while the selectivity remain at high level. We then fabricated membranes from novel microporous polymers, polymers of intrinsic microporosity (PIMs). Using the PIM-1 polymer as a prototype, we discovered that ultraviolet irradiation of PIM-1 membranes in the presence of oxygen induces oxidative chain scission at the surface, resulting in local densification and structural transformation of free volume elements. Consequently, the membrane become asymmetric with a more gas-selective layer formed at the surface, while the overall permeability maintains at high level. Finally, we report a simple thermal oxidative crosslinking method to tailor the architecture of channels and free volume elements in PIM-1 polymer membrane by heat treatment in the presence of trace amounts of oxygen molecules. The resulting covalently crosslinked polymer networks offer superior thermal stability, chemical stability, reasonable mechanical strength, and enhanced rigidity. Most important of all, thermally crosslinked PIM-1 polymer membranes show significantly enhanced molecular sieving functions that yield remarkably high selectivity and high gas permeability, which surpass the upper bound that has been limiting the polymer membranes for decades. We also demonstrate that the thermal crosslinking method is effective for crosslinking of nanocomposite membranes with porous or nonporous fillers. These microporous molecular sieve membranes are promising for a wide range of molecular-level separation applications.

No description available.

Separating mixtures into their components is a ubiquitous feature of industry, and these separations are necessary for every facet of life down to the simple functions of breathing clean air and drinking potable water. These chemical separations account for a large portion of the total energy use both in the United States and globally. Polymer membrane based separations are desirable when applicable due to their lower energy requirements relative to thermal methods such as distillation. This has led to increases in membrane usage to reduce energy costs; however, membrane separations are not without limitations relating to the membrane material and application requirements. Herein I will address membrane separation technologies, their limitations, and the impact of incorporation of high aspect ratio cellulose nanocrystals (CNCs) on the performance of the resulting polymer composite membranes for desalination and gas phase separations. Lack of available drinking water is an increasing problem across the world with much of the world living in water scarce regions. Desalination using reverse osmosis (RO) membranes is one of the most effective methods of producing clean drinking water. Aromatic polyamide based thin film composite membranes (TFCs) are the most commonly used for commercial desalination and have been since the late 1970s. These TFCs suffer from drawbacks including irreversible performance reduction from fully drying the membrane before use and susceptibility to biological fouling. One technique to mitigate issues with TFCs is to utilize the desirable properties of nanoparticles through their incorporation in the TFC selective layer to create thin film nanocomposite membranes (TFNs). CNCs were selected for this work due to their high aspect ratio, potential for surface modification, attractive mechanical properties, sustainable feedstock, and low toxicity. Membranes containing as received CNCs, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs), tertiary amine functionalized cellulose nanocrystals (aCNCs), or zwitterionic functionalized cellulose nanocrystals (zCNCs) were synthesized to investigate the effects of nanoparticle functionality and loading level on the brackish water desalination, drying behavior, and fouling resistance of polyamide based TFNs. Loading level was investigating using TOCN containing TFNs which exhibited an increase in water flux and sodium salt rejection up to a maximum when the m-phenylenediamine monomer to TOCN ratio was 20:1 followed by a decrease in both water flux and salt rejection with more TOCN added to the membrane. At the optimal loading level there was a 25% increase in the water flux and 0.2% increase in salt rejection relative to the unloaded control for the membranes kept hydrated and a 146% increase in water flux and 1.6% increase in salt rejection relative to the unloaded control for membranes that were dried. These increases yielded equivalent water flux and salt rejection for the membranes kept hydrated and those dried prior to use at the optimal loading level. The changes in desalination performance are attributed to the introduction of a new water transport pathway at the interface of the TOCN nanoparticle and the polymer matrix and a structural reinforcement effect preventing the collapse of pores present in the polymer during the drying process. The optimal loading level from the previous investigation was used for all work with the other CNC functionalities. The TFNs containing CNCs yielded a 10% increase in water flux and no change in salt rejection relative to the unloaded control while those containing aCNCs and zCNCs yielded no change in water flux and a 0.6% and 0.3% decrease in salt rejection respectively. These differences in behavior relative to the TOCN loaded TFNs are attributed to the transport pathway and structural reinforcement effects being subject to the interaction between the polymer and functionality of the nanoparticle as well as the size and shape of the functional group leading to the differences for each CNC functionality. There were no changes in the foulant resistance for any of the membranes when exposed to water containing bovine serum albumin and sodium alginate as probe foulants. This is attributed to the synthesis procedure in which the nanoparticles are added to the membrane in the denser aqueous phase of the interfacial polymerization. The CNCs will not diffuse well through the polymer as it begins to form, so they would be likely to be concentrated deeper in the membrane while fouling is a surface sensitive behavior, so if the nanoparticles aren't near the surface they will not affect that behavior. Gas separations are of interest for investigation into the effects of high aspect ratio nanoparticles in composite membranes as it allows for investigating more fundamental information through control of the membrane morphology and mixture composition. The range of molecule sizes in the separation is much smaller for gas separations compared to desalination with kinetic diameter differences on the order of 0.1-1 Å compared to 4.5Å. Additionally, with the lower pressure requirements for gas transport relative to reverse osmosis, simple membrane geometries can be investigated using dense films rather than TFNs. In this investigation, dense film composite membranes were made consisting 0, 0.07, 0.7, 3.6, 7.2% or 15% CNCs by volume in a thermoplastic polyurethane (TPU) matrix. The addition of TPU showed increased structural strength in the film with loading modulus increasing from 10 MPa for the unloaded TPU to 58 MPa for 3.6% CNC loaded TPU and 105 MPa for 7.2% CNC loaded TPU. The gases tested during this investigation are CO2, He, Ar, O2, and N2. As the CNC loading level increased, the gas permeability for each gas decreased. For the gases other than CO2, there 0.07, 0.7, and 3.6% CNC films all had the same permeability with all, but Ar, 47 ± 3 % less than the unloaded film permeability. The 15% CNC permeabilities were all 44 ± 1 % less than that of the 0.07, 0.7, and 3.6% CNC films. For CO2, the permeability decreased with each addition of CNC. None of these decreases are described by simple space filling by an impermeable particle. This indicates that the structural reinforcement providing strength to the membrane may be limiting some of the chain mobility inhibiting the diffusion of gases through the membrane which is seen in the diffusion coefficient of CO2 which decreases with increasing CNC loading. / Doctor of Philosophy / Mixtures often need to be separated into their individual parts. These mixtures are often difficult to separate like salt from water or pollution from air. These are important problems as everyone needs clean air to breath and clean water for drinking, cleaning, and watering crops and there are places all over the world without enough clean air and water. A common way to separate these difficult mixtures involves boiling the liquids to become gases and then cooling the gases back down to form a purified liquid. Unfortunately, these methods take immense amounts of energy at a time in which energy demand is at an all-time high. It is important to improve the performance of the low energy demand methods such as membrane separations, where a thin material acts as a filter on scale small enough to conduct these difficult separations. Membranes come with their own drawbacks that must be addressed such as a tradeoff between the rate of separation and product purity as well as a tendency to be blocked by contaminants that get stuck to the membrane surface. One method people have tried to address these drawbacks is the introduction of incredibly small particles called nanoparticles that have properties the membrane material lacks. This can lead to improved separation performance, but it is important to expand the separation conditions, the form of membranes tested, and the type of mixture separated to better understand how the nanoparticles work within the membrane. A better understanding of how nanoparticles work will allow for more widespread application and increased efficiency lowering energy demands and improving access to needs such as clean air and water. In this work we have included long, thin nanoparticles produced from wood into desalination and gas separation membranes to investigate the changes in the rate and purity of clean water produced, the resistance to contaminates, and rate that gases can cross the membrane.

Submitted in fulfilment of the requirements for the degree of Master of Engineering, Durban University of Technology, Durban, South Africa, 2015. / Fermentation processes are vital for the production of numerous bioproducts. Fermentation being the mass culture of micro – organisms for the production of some desired product, is an extensive field, with immense prospects for study and improvement. Enzyme production is of significance as these proteins are biological catalysts, finding niches in numerous industries, xylanase for example is utilized in the pulp and paper, animal feed, biofuel and food production processes. During enzyme production, a critical step is biomass separation, whereby the valuable product, the enzyme, is removed from the broth or micro – biological culture before it is denatured. This is typically achieved via centrifugation. The aim of this study was to develop and evaluate a submerged membrane fermenter system with the specific outcome of increasing the rate of production of xylanase, from the thermophilic fungal species Thermomyces lanuginous DSM 5826. Preliminary shake flask experiments were performed to determine the optimal production conditions, followed by partial characterization of the enzyme. A bioreactor was then fabricated to include a flat sheet membrane module, with outlets for permeate and broth withdrawal and inlets for feed and sterile air input. Experiments were conducted to determine the optimal dilution rate for maximum volumetric productivity. Results from the shake flask experiments indicated that the best conditions for xylanase production, yielding xylanase activity of 5118.60 ± 42.76 U.mL-1 was using nutrient medium containing beechwood xylan (1.5 % w/v), yeast extract (1.5 % w/v), potassium dihydrogen phosphate (0.5 % w/v), adjusted to a pH of 6.5 and inoculated with 1.0 mL of spore solution, rotating in a shaking incubator set to 150 rpm at 50 °C. Apart from analysis of the effect of the carbon source on xylanase activity, coarse corn cobs were used in the shake flask experiments as a cost saving initiative. The pH optima was determined to be 6.5 while the temperature optima of the enzyme was 70 °C. SDS PAGE analysis revealed that the molecular weight of the enzyme was between 25 and 35 kDa and qualitative analysis via a zymogram revealed clear zones of hydrolysis on a xylan infused agarose gel. During short run membrane fermenter experiments the percentage increase in enzyme activity between the batch operation (610.58 ± 34.54 U.mL-1) and semi – continuous operation (981.73 ± 55.54 U.mL-1) with beechwood xylan nutrient replenishment was 60.78 %. The maximum volumetric productivity achieved with beechwood supplementation after 192 hours in semi – continuous operation (5.32 ± 0.30 U.mL-1.hr-1) was 2.1 times greater than that of batch operation (2.54 ± 0.14 U.mL-1.hr-1) which equates to an increase of 110.28 % in productivity measured at its peak. The increase in total activity between batch (610 576.92 U) and beechwood xylan medium supplemented semi – continuous mode (1 184 937.50 U) resulted in a 94.07 % increase. During long run experimental periods, the increase in production of xylanase between the batch (873.26 ± 61.78 U.mL-1) and the xylan medium membrane system (1522.41 ± 107.65 U.mL-1) was determined to be 74.34 % while an overall average increase in productivity between the batch and xylan fed membrane system was 43.25%. The total enzyme activity with in membrane mode with beechwood xylan nutrient medium feed was 160 % greater than the batch process offering a 2.6 – fold increase. Experiments where de – ionized water was alternated with beechwood xylan nutrient medium had no significant impact on the productivity or enzyme activity. The optimal dilution rate for maximum volumetric productivity as determined to be 0.0033 hr-1. The results are indicative of the potential viability of such a design, yielding the desired outcome of a membrane integrated system to significantly increase the production of enzymes during fermentation.