Thesis (M.E.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 121-125). Also available via the World Wide Web.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The aim of this study was to modify the surface of polyethersulfone (PES) ultrafiltration (UF) membranes to produce a more hydrophilic membrane by cross-linking poly(vinyl alcohol) (PVA) with sodium tetraborate (Na2B4O7.10H2O) (SB) on the surface. Key preparation factors were identified as PVA molecular weight, concentrations of the PVA and SB, cross-linking reaction time, number of coatings and the mode of coating. The effect of these factors on the membrane performance (salt retention and permeate flux) is discussed. These PVA-SB membranes typically had 11.46% retention and 413.30 L/m2.h flux for a feed containing 2000 ppm NaCl (0.45 MPa, 20°C, 45 – 50 L/h). The coating was shown to be uniform and stable by Fourier transform infrared spectroscopy (FT-IR) analyses. Coating significantly increased hydrophilicity and a maximum flux increase of 500 L/m2.h was reached. Measurements showed a reduced water contact angle and this confirmed the obvious enhancement of surface hydrophilicity. As a control, the role of the PVA base layer without cross-linking and the effects of its drying and heating on the water permeability of the PES-UF membrane were also studied, in order to ascertain maximum treatment conditions. Retention and permeate flux were determined (feed solution: 2000 ppm NaCl, applied pressure 0.45 MPa, 25°C, 45 – 50 L/h). It was found that the heating had the largest effect on the reduction of water permeability and therefore 50°C was the limit for treatment of this specific PES-UF membrane. Thin-film composite (TFC) membranes were prepared by an interfacial polymerization (IP) reaction between a polyfunctional amine and tri- or di-functional carboxylic chloride and then evaluated for their reverse osmosis (RO) performance. The salt retention of the PVA-SB membranes was improved when covering the cross-linked PVA gel sub-layer with a polyamide (PA) layer. However, the permeate flux decreased to below 30 L/m2.h (2000 ppm NaCl, 1 – 2 MPa, 20°C, 45 – 50 L/h). Two TFC membranes made from trimesoyl chloride (TMC) with m-phenylenediamine (MPD) or 2,6-diaminopyridine (DAP) exhibited retentions of 96.71% to 89.65% and fluxes of 10.93 to 27.91 L/m2.h, depending on the type of diamine used, when tested with a 2000 ppm NaCl solution (2 MPa, 25°C, 45 – 50 L/h). Two TFC membranes made from a n ew 2,5-furanoyl chloride (FC) with MPD or DAP exhibited retentions of 34.22% to 58.54% and fluxes of 49.21 to 25.80 L/m2.h, depending on the type of diamine used, when tested with a 2000 ppm NaCl solution (1 MPa, 25°C, 45 – 50 L/h). Novel PVA-SB-DAP-FC membranes made from the DAP with FC had the highest hydrophilicity value and exhibited >58.54% NaCl retention and 25.80 L/m2.h flux, and 75.08% MgSO4 retention and 34.75 L/m2.h flux, when tested with (2000 ppm feed, 1 MPa, 25°C, 45 – 50 L/h). The effect of the chemical structures of the different amines and carboxylic chlorides used on the RO performances of the TFC membranes prepared by two amines reacting with TMC or FC, on the surfaces of the modified asymmetric PES-UF membranes, was investigated. FT-IR and water contact angle determination were used to characterize the chemical structure, morphology and hydrophilicity of the PA layers of the composite membranes. The response surface methodology (RSM) was used to optimize the preparation conditions that had the largest effects on the RO performance of the PVA-SB-DAP-FC membranes. Good membrane performance could be realized particularly by manipulating three variables: DAP concentration, FC concentration and polymerization time (PT). The regression equation between the preparation variables and the performance of the composite membranes was established. Main effects, quadratic effects and interactions of these variables on the composite membrane performance were investigated. The membranes were characterized in terms of pure water permeation (PWP) rate, molecular weight cut off (MWCO), solute separation and flux. Mean pore size (μp) and standard deviation (σp) of the membranes were determined using solute transport data. The results revealed that PVA-SB membranes have almost the same pure water permeation that PES-UF membranes have. The MWCO of the PES-UF membranes decreased from 19,000 to 13,000 Daltons when the membrane was coated with PVA. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie is die modifikasie van die oppervlakte van poliëtersulfoon ultrafiltrasie (PES-UF) membrane om meer hidrofiliese membrane te berei deur die kruisbinding van polivinielalkohol (PVA) met natriumtetraboraat ((Na2B4O7.10H2O) (NaB) op die membraanoppervlakte. Sleutelfaktore in die bereidingsproses is geïdentifiseer, naamlik: PVA molekulêre massa, PVA en NaB konsentrasies, kruisbindingsreaksietyd, die aantal bestrykingslae, en die manier waarop die bestrykingslae aangewend is. Die invloed van hierdie faktore op die membraanontsouting en vloed is ondersoek, en word hier bespreek. Hierdie PVA-NaB membrane het die volgende tipiese resultate getoon: 11.46% ontsouting en 413.30 L/m2.h vloed (Kondisies: 2000 dpm NaCl oplossing, 0.45 MPa toegepaste druk, 20 °C, vloeitempo 45–50 L/h). Die deklaag was uniform en stabiel, soos bepaal d.m.v. FTIR. Die aanwesigheid van die deklaag het die hidrofilisiteit verhoog en 'n maksimum vloed van 500 L/m2.h is behaal. Die waterkontakhoek is ook gemeet; 'n laer waarde het 'n verbetering in die hidrofilisiteit van die oppervlakte bevestig. Die rol van die PVA basislaag, sonder kruisbinding (kontrole), en die effek van uitdroging en verhitting hiervan, is ook bestudeer, om sodoende optimale behandelingskondisies te bepaal. Membraanontsouting en vloed is bepaal (Kondisies: 2000 dpm NaCl oplossing, 0.45 MPa toegepaste druk, 25 °C, vloeitempo 45–50 L/h). Verhitting het die grootste effek gehad op die afname in vloed. Daar is bevind dat 'n maksimum temperatuur van 50°C geskik is vir die behandeling van hierdie spesifieke PES-UF membraan. Dunfilmsaamgestelde (DFS) membrane is berei d.m.v. 'n tussenvlakpolimerisasiereaksie tussen 'n polifunksionele amien en 'n di- of tri-funksionele karbonielchloried, en daarna is die tru-osmose (TO) gedrag bepaal. Die ontsouting van die PVA-NaB membrane was hoër nadat die kruisgebinde PVA jel sub-laag met 'n poliamied (PA) laag bedek is. Die vloed het egter afgeneem, tot onder 30 L/m2.h (Kondisies: 2000 dpm NaCl oplossing, 1–2 MPa toegepaste druk, 20 °C, vloeitempo 45–50 L/h). Twee DFS membrane is berei met trimesoïelchloried (TMC), naamlik met m-fenieldiamien (MFD) of 2,6-diaminopiridien (DAP). Afhangend van die diamien wat gebruik is, is die volgende ontsoutingsresultate en vloede verkry: 96.71% tot 89.65% en 10.93 to 27.91 L/m2.h (Kondisies: 2 000 dpm NaCl oplossing, 2 MPa toegepaste druk, 25 °C, v loeitempo 45–50 L/h). Twee DFS membrane is ook berei met 'n nuwe verbinding, 2,5-furanoïelchloride (FC), en MFD of DAP. Afhangend van die diamien wat gebruik is is die volgende ontsoutingsresultate en vloede behaal: 34.22% tot 58.54% en 49.21 tot 25.80 L/m2.h (Kondisies: 2000 dpm NaCl oplossing, 1 MPa toegepaste druk, 25 °C, vloeitempo 45–50 L/h). Die PVA-NaB-DAP-FC membrane het die hoogste hidrofilisiteit getoon: 58.54% NaCl ontsouting en 25.80 L/m2.h vloed, en 75.08% MgSO4 ontsouting en 34.75 L/m2.h vloed (2000 ppm NaCl oplossing, 1 MPa toegepaste druk, 25 °C, vloeitempo 5–50 L/h). Die invloed van die chemiese struktuur van die verskillende diamiene en karboksielsuurchloriedes wat gebruik is in die bereiding van die DFC membrane op die oppervlakte van die gewysigde PES-UF membrane is in terme van TO ondersoek. FTIR en kontakhoekbepalings is gebruik om die chemiese struktuur, morfologie en hidrofilisiteit van die PA lae van die saamgestelde membrane te bepaal. Die eksperimentele oppervlakte ontwerp metode is gebruik om die bereidingskondisies vir die TO aanwending van die PVA-NaB-DAP-FC membrane te optimiseer. Goeie resultate is verkry deur die volgende veranderlikes te manipuleer: DAP en FC konsentrasies en die tydsduur van die polimerisasie. 'n Regressie-vergelyking tussen die bereidingsverandelikes en die funksionering van die saamgestelde membrane is bepaal. Die volgende is ook ondersoek vir hul effek op die funksionering van die saamgestelde membrane: hoof-effekte, vierkantseffekte, en interaksie tussen veranderlikes. Die eienskappe van die membrane wat bepaal is, is: deurlatingstempo van suiwer water (DSW), molekulêre massa-afsnypunt (MMAP), skeiding van opgeloste sout en vloed. Deurlating van opgeloste sout data is gebruik om gemiddelde poriegrootte (μp) en standaard afwyking (σp) van die membrane te bepaal. Resultate het getoon dat die PVA-NaB membrane amper dieselfde DSW gehad het as die PES-UF membrane. Die MMAP van die PES-UF membrane het afgeneem van 19,000 tot 13,000 Daltons na behandeling met PVA.

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: William J. Koros; Committee Member: Amyn Teja; Committee Member: Carson Meredith; Committee Member: Sankar Nair; Committee Member: Wallace W. Carr.

The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram]/cm2), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling. / text

Providing an energy efficient recycle for the Teflon® synthesis process is of great interest due to environmental and economic reasons. This recycle step involves separating CO2 from a stream containing scCO2 and valuable monomer (C2F4). Membranes provide economical and environmental friendly separations compared to conventional methods (e.g. distillation, amine absorption). Therefore, I am investigating membrane materials that are well-suited for this important separation. Developing a robust membrane that can withstand the aggressive scCO2 environment (~1070 psi of CO2) is a key challenge. Supercritical CO2 swells traditional polymeric membrane materials, thereby increasing segmental mobility of the polymer chains which leads to a decrease in separation capacity. There have been no polymeric membrane materials identified in the literature which are suitable for this separation. In this work, I have identified an advanced polymer, Torlon® (a polyamide-imide), that solves this problem. After determining the appropriate material, it is important to choose a membrane morphology that is industrially desirable. The asymmetric hollow fiber membrane morphology provides the highest productivity. I have successfully produced defect-free asymmetric hollow fiber membranes using Torlon® that withstand high pressure feeds. These membranes have been shown to provide selective separations under scCO2 conditions without being plasticized. To further improve the separation performance of Torlon® membranes, mixed matrix concept was explored. Zeolite 4A, which is relatively more permeable and selective compared to Torlon®, was chosen as the sieve material. Mixed matrix membranes from Torlon® and zeolite 4A were made and their separation performance was measured. Based on these experimental measurements and Maxwell modeling, challenges in making successful mixed matrix membranes were identified and feasible solutions for these challenges are suggested.