(305e) Potential Fouling Resistant Coating Materials Synthesized By UV Induced Polymerization

The lack of sufficient amounts of pure water is one of the world's most serious concerns. Consequently, water reuse and management is becoming more and more important. Produced water is the single largest waste stream in oil and gas production, often containing salts, heavy metals, emulsified oil and other organics. If the organic content and salinity of produced water could be reduced to acceptable limits, produced water could represent a potential new water source with a wide variety of uses. Membranes may be an effective tool for treating water produced during oil and gas production. However, membrane fouling is a serious problem and limits the efficiency of water purification in this application.

The initial objective of this research was to examine potential fouling-reducing coating materials and determined fundamental structure/property relationships governing water transport, rejection of model foulants such as emulsified oil droplets or protein aggregates, and fouling characteristics. A systematic series of hydrogel-based polymers was prepared, and their permeation and fouling properties were studied and correlated with their structure. In a future study, composite membranes prepared via coating of commercial UF membranes will be performed.

In this presentation, the effects of UV intensity, water content in the prepolymer solution, and crosslinker content on film morphology, water transport and rejection properties are presented. Crosslinked free-standing films were prepared by UV-induced free radical polymerization at different UV intensities, using N,N'-methylene bisacrylamide (MBAA) as the crosslinker and N-vinyl-2-pyrrolidone (NVP) as the monomer. The water content in the prepolymer solution was varied from 30 wt% to 70 wt%, and the MBAA content of total solids was varied from 15 wt% to 30 wt%. The crosslinked NVP films show polymerization induced phase separation (PIPS). These PIPS films contain pores that scatter visible light and render them opaque. The films exhibited a porous morphology in CryoSEM studies. Liquid water uptake increased from 100 to 350 g water/100 g dry polymer as water content in the prepolymer solution increased. Dead end filtration of deionized water, oil/water solutions (1500 ppm), and bovine serum albumin (BSA) solutions (1g/l), was performed to explore the fundamental transport and fouling properties of these materials. Different internal structures of crosslinked NVP films at the same composition were made by polymerization at different UV intensities and characterized by molecular weight cutoff (MWCO) measurements. Polymerization under high intensity UV light (~3000 mW/cm2) leads to high water permeability, up to ~3000 L mm/(hr m2 bar) in film containing 70 wt% water and 30 wt% solids (NVP/MBAA: 85/15) and high MWCO, ~10,000 kDa. At the same composition with polymerization at low intensity (~1100 mW/cm2), the water permeability was ~1300 L mm/(hr m2 bar) and the MWCO was also lower, ~650 kDa. The total permeate flux of pure water was almost equal to that of the BSA containing solution and oil/water emulsion containing solution, indicating that crosslinked NVP films resist fouling by oil droplets and BSA under the conditions studied. The oil rejection was ~97% in all samples, while the protein rejection depended on the prepolymer water content, crosslinker concentration, and UV intensity.