Ultrafiltration membranes

Ultrafiltration membranes

RESEARCH TRENDS Mass-transfer dynamics of evaporation in membrane formation A ternary diffusion model was developed for the evaporation step of the ph...

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RESEARCH TRENDS Mass-transfer dynamics of evaporation in membrane formation A ternary diffusion model was developed for the evaporation step of the phase inversion process, and it was applied to the analysis of mass-transfer dynamics of the evaporation step for a methanol– acetone–cellulose acetate (CA) ternary casting system. The combined analysis of quantitatively computational results from the ternary evaporation model and qualitative dynamic results during the quench process has shown that the evaporation step is essentially necessary to prepare the defectfree, ultra-thin skinned asymmetric CA membrane for the separation of CO2/CH4. The skin layer of high CA concentration obtained by evaporation has an ability to suppress liquid–liquid phase separation. Furthermore, the skin layer with high tensile strength can resist the interfacial tension caused by spinodal decomposition from the substructure. Although the CA concentration in the skin layer increases considerably because of the evaporation step and the following delay time during the quench process, the substructure can still induce the spinodal decomposition because the strong coagulant, methanol, can diffuse rapidly across the ultra-thin skin layer. Hence the defect-free, ultrathin skinned asymmetric membrane for gas separation can be prepared from methanol–acetone– CA casting system by evaporation step and the wet phase inversion. J.H. Hao and S. Wang: J. of Applied Polymer Science 86(7) 1564–1571 (14 November 2002).

Dehydration of light oil by pervaporation A new blended membrane was prepared and tested by pervaporation of light oil, a mixture of five alcohols and water. The blended membrane was synthesized by blending poly(vinyl alcohol) and poly(acrylic acid-co-maleic acid) sodium salt in the presence of sulphuric acid to dope the reaction. The authors tested several membranes in order to choose the adequate composition to have the best permselectivity. The PVA(60)-PAA-co-maleic acid(40) membrane was selected because it was found to be highly selective. Sorption experiments were per-

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formed using binary and ternary water–alcohol solutions. The influence of temperature and feed composition on the selectivity and flux in pervaporation was investigated for two different binary mixtures (water/ethanol, water/isobutanol) and one ternary system (water/ ethanol/isobutanol). This membrane presents good permselective properties, high water flux and good selectivity, and it can even be used for high-water activities. The performance parameters of this new membrane were compared with those obtained from the PVA(90)PAA(10) synthesized membrane. The fluxes observed for the water– ethanol separation were of the same order of magnitude but the selectivity was found to be much higher. C. Vauclair, P. Schaetzel, R. Nobrega and C. Habert: J. of Applied Polymer Science 86(7) 1709–1716 (14 November 2002).

Ultrafiltration membranes Modification of polymeric membrane materials through the incorporation of hydrophilic properties results in membranes with low fouling behaviour and high flux. For this reason, polysulphone was functionalized by sulphonation, and ultrafiltration (UF) membranes were prepared based on sulphonated polysulphone and cellulose acetate in various blend compositions. Polyethyleneglycol 600 was employed as a non-solvent additive in various concentrations in the casting solution to improve the UF performance of the resulting membranes. The total polymer concentration, cellulose acetate and sulphonated polysulphone polymer blend composition, additive concentration and its compatibility with polymer blends were optimized. The membranes prepared were characterized in terms of compaction, pure water flux, membrane resistance and water content. The compaction takes place within 3–4 hours for all the membranes. The pure water flux is determined largely by the composition of sulphonated polysulphone and concentration of additive. It was found that membrane resistance is inversely proportional to pure water flux, while water content is proportional to pure water flux for all the membranes. D. Mohan, M. Rajendran and V. Mohan: J. of Applied Polymer

Science 86(7) 1749–1761 (14 November 2002).

Novel membranes for CO2 separation A new membrane material having two kinds of CO2 carriers has been developed. Composite membranes were prepared using the material, together with support membranes. The facilitated transport of CO2 through these membranes was performed with pure CH4 and CO2 as well as CH4/CO2 mixtures containing 50 vol% CO2. The results show that the membranes possess better CO2 permeance than that of other fixed carrier membranes reported in the literature. In measurements with pure gases (at 26°C and 0.013 atm of CO2 pressure) the membrane with polysulphone support displayed a CO2 permeance of 7.93×10–4 cm3/cm2 s cmHg, and CH4/CO2 ideal selectivity of 212.1. In the measurements with mixed gases (at 26°C and 0.016 atm of CO2 partial pressure) the membrane displayed a CO2 permeance of 1.69×10–4 cm3/cm2 s cmHg and CH4/CO2 selectivity of 48.1. Y. Zhang, Z. Wang and S. Wang: J. of Applied Polymer Science 86(9) 2222–2226 (28 November 2002).

220 g/m2h) was obtained by the bromination of SPSM (SPSMBr) membrane with a 90 wt% aqueous ethanol solution. C.-L. Li, Y.-C. Wang, S.-T. Kao, S.C. Fan, K.-R. Lee and J.-Y. Lai: J. of Applied Polymer Science 86(9) 2247–2254 (28 November 2002).

Selection of NF membrane Six nanofiltration membranes (NF70, NF255, NTR-7450, NTR7410, Desal-5 and TFC-S) were evaluated in improving the quality of chemically pre-treated surface water in a pilot-scale process. The results indicate that the membrane with high organics removal and slightly reduced ion removal characteristics (NF255) performed best in terms of product water quality as well as membrane productivity and fouling. The most permeable membrane (NTR-7410) suffered intensive fouling and insufficient product water quality. An interesting finding was that the permeates of all the tested membranes possessed a significant potential for microbial growth, despite the low nutrient contents. R. Liikanen, I. Miettinen and R. Laukkanen: Water Research 37(4) 864–872 (February 2003).

Selective separation using pervaporation membranes The pervaporation performances of a series of functionalized syndiotactic poly(styrene-co-4-methylstyrene) (SPSM) membranes for various alcohol mixtures were investigated. The syndiotactic polystyrene copolymers, poly(styrene-co-4-methylstyrene), were prepared by styrene with 4-methylstyrene using a Cp*Ti(OCH3) 3/methyl aluminoxane (metallocene/MAO) catalyst. The effect of functionalization on the thermal properties and polymer structure of the SPSM membranes were also investigated. The crystallinity of the functionalized SPSM membrane is lower than that of the unfunctionalized SPSM membranes. The water molecules preferentially permeate through the SPSM membranes. Compared with unfunctionalized SPSM membranes, the functionalized SPSM membrane effectively increases both the membrane formation performances and the pervaporation performances. The optimum pervaporation performance (a separation factor of 510 and permeation rate of

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Membrane Technology February 2003