Browsing by Subject "Surface modification"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Polyamide desalination membrane characterization and surface modification to enhance fouling resistance(2010-05) Van Wagner, Elizabeth Marie; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R.; Bonnecaze, Roger T.; Lawler, Desmond F.; Mickols, William E.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.Item Surface modification of water purification membranes to improve fouling resistance in oily water filtration(2015-12) Kasemset, Sirirat; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R; Sanchez, Isaac C; Ellison, Christopher J; Emrick, Todd SOne of the biggest challenges in using water purification membranes is fouling. Surface modification using hydrophilic materials can reduce hydrophobic interactions between membrane surface and hydrophobic foulants, thereby alleviating fouling. In this Ph.D. research, polydopamine (PDA), a highly hydrophilic and universal coating agent, was used to surface-modified reverse osmosis (RO) and ultrafiltration (UF) membranes. PDA modification conditions (e.g., dopamine coating solution concentration, coating time, and pH of coating solution) control PDA deposition and can directly influence the modified membrane properties. Thus, the influence of PDA modification conditions on membrane physical, permeation, selective, and fouling properties were investigated systematically. A fundamental understanding relating the physical and permeation properties and the fouling characteristics of PDA-modified membranes was established. The RO membranes were modified with PDA at various modification conditions. Permeate fluxes during pure water and oil/water emulsion filtrations were studied. The PDA modification increased the permeate fluxes during oil/water emulsion filtration (thus, improved membrane fouling resistance) relative to unmodified membranes regardless of the initial dopamine concentration or deposition time used. However, these changes were only observed for the membranes coated under alkaline conditions, suggesting that the PDA did not deposit well under acidic condition. For UF membranes, molecular weight cutoff (MWCO) and pure water permeance decreased with increasing initial dopamine concentration or deposition time. A permeability and selectivity tradeoff was also observed. Membrane mean pore size and pore size distribution (modeled using log-normal pore size distribution) were investigated via modelling using a hindered solute transport model, Hagen-Poiseuille equation, and a stagnant film model. The PDA modification increased UF membrane surface hydrophilicity regardless of the coating conditions used, but it did not clearly change surface roughness or zeta potential (i.e., surface charge). Membrane fouling propensity was characterized using threshold flux. Compared to unmodified membranes, the threshold flux increased at minimal PDA coatings, but decreased at excessive PDA coatings. These threshold flux changes were likely governed by a tradeoff between surface hydrophilicity increase and pure water permeance decrease. Excessive PDA coatings resulted in decreased pure water permeance and possibly, pore blockage and pore size reduction, leading to higher local permeate flux causing severe fouling and decreased threshold flux.