Preparation And Research Of Antifouling Composite Membranes For Oil/Water Separations

Oily wastewater is a common pollution in the world which has lot of harm to environments, whereas water is important source of living and production. Thus, separation of oily wastewater is very important. Traditional treatments for oil/water separation had low efficiency or consumed lots of energy. In some case, water had been polluted by chemical additive. In recent years, membrane technologies have been successfully applied for treating oil/ waste emulsion which could supply a gap of those traditional treatments. However, the performances of membrane separation are limited by the membrane fouling and concentration polarization. Therefore, development of antifouling membranes is a most pressing task at present.A novel fouling-resistant polyamide/polyvinyl alcohol (PVA) composite membrane was developed for removal of oil-in-water (O/W) emulsions. The composite membrane was featured with an asymmetric three-layer structure, i.e., a tubular porous ceramic (or polyethylene) membrane, a polyethersulfone (or polyvinylidene fluoride) ultrafiltration substrate, and a polyamide/ PVA composite thin top-layer. The PES (or PVDF) polymer was cast onto the tubular porous ceramic (or PE) membrane with a sol-gel method, and the polyamide/PVA composite thin top-layer was fabricated with an interfacial polymerization method. FT-IR, SEM, XPS, SAXS and AFM were employed to characterize the composite membrane. In this study, investigations were systematically carried out on preparation of composite membrane and substrate of composite membrane. Separation performance of composite membrane had been also investigated, and some exciting results have been gotten.A composite membrane is based on the substrate which should haveappropriate size, density, distributing of its pore and good chemical stability. PES and PVDF had been chosen as substrate of composite membrane in this study. The factors of preparing PES substrate had been investigated. The average pore size of substrate was smaller when PES concentration was increased in casting solution, and the result of experiments shows PES concentration should be higher than 10% for good structure of substrate. Prolonged vacuuming time of casting solution and volatile time of solvent were leading smaller average pore size of substrate. The average pore size of substrate was smaller when sodium chloride concentration was increased or ethanol concentration was decreased in casting solution. The average pore size was of substrate bigger when temperature of coagulation bath was decreased or temperature of heat treatment was increased. Lithium chloride (LiCl) and Polyethylene glycol (PEG) were employed as additives in the casting solution, in order to obtain desired membrane pore size for separation. The average pore size of substrate was smaller when PEG concentration increased, and the result was reverse as LiCl instead of PEG. The fingerlike hole appeared in interior of substrate when LiCl and PEG were employed together in casting solution. And this structure of substrate was availed to flux of composite membrane.Investigations of pure water and oil/water emulsion separation performance in different operation condition of PES (PVDF) substrate of composite membrane and tubular porous ceramic (or PE) membrane were carried out. The increasing of operating temperature would increase flux of tubular porous membrane. The change of pore size of same kind of tubular porous membrane had little effect on flux of composite membrane. The operating pressure which less than 0.4MPa wouldn't destroy the structure of substrate of composite membrane. The average pore size of substrate should be as big as possible when there was no disfigurement in top-layer of composite membrane by using the substrate.A small average pore size, high hydrophilic polyamide/PVA composite membrane based on PVDF substrate was prepared by using the method of interfacial polymerization for separating drastically emulsified oil/water emulsions. TC wasorganic monomer and PA was aqueous monomer. The aqueous solution was also in...