Preparation and characterization of PVDF-PFSA flat sheet ultrafiltration membranes

High performance polyvinylidene fluoride (PVDF) flat sheet ultrafiltration (UF) membranes have been prepared by an immersion precipitation phase inversion method using perfluorosulfonic acid (PFSA) as a pore former and as a hydrophilic component of the membranes and polyethylene glycol (M_w = 400) (PEG400) as a pore forming agent. The effects of the presence of PEG and the concentration of the PFSA on the phase separation of the casting solutions and on the morphologies and performance of UF membranes including their porosity, water flux, rejection of bovine serum albumin (BSA) protein, and anti-fouling property were investigated. Phase diagrams, viscosities and the phase separations upon exposure to water vapor showed that both PEG400 and PFSA promoted demixing of the casting solution. Scanning electron microscopy measurements showed that the PVDF-PFSA blend membranes had more macropores and finger-like structures than the native PVDF membranes. The PVDF-PFSA membrane (5 wt-% PEG400+ 5 wt-% PFSA) had a pure water flux of 141.7 L/m²·h, a BSA rejection of 90.1% and a relative pure water flux reduction (RFR) of 15.28%. These properties were greatly superior to those of the native PVDF membrane (pure water flux of 5.6 L/m²·h, BSA rejection of 96.3% and RFR of 42.86%).     

Plasma polymer membranes from hexafluoroethane/hydrogen mixtures for separation of oxygen and nitrogen

Thin plasma polymer layers were produced employing feed mixtures of hexafluoroethane and hydrogen in an rf parallel-plate reactor. The layers are intended for use in membrane-based separation of oxygen and nitrogen. The hexafluoroethane-to-hydrogen mixture ratio was varied over a wide range, whereas all other process parameters (power, pressure, substrate temperature, and total gas flow) were held constant. The plasma polymers were examined by scanning electron microscopy, X-ray analysis, quantitative elemental analysis, and X-ray photoelectron spectroscopy. Permeability coefficients of oxygen and nitrogen and selectivities of the pure gases were determined. Pinhole-free plasma polymer films containing different amounts of fluorine, carbon, and hydrogen were formed. The distributions of fluorine and hydrogen in the products reflect their distributions in the feed gas. Traces of oxygen in some of the polymers are explained by the reaction of trapped radicals with atmospheric oxygen on the samples' exposure to air. Fluorine-containing carbon moieties such as CF₃, CF₂, and CF, and carbon moieties with fluorine atoms exclusively in secondary positions are present. A method of calculating crosslink density using the analytical data is described. The oxygen permeability coefficient and the selectivity of the plasma polymers increase as the hexafluoroethane content of the feed gas is raised. This behavior is attributed to growing solubility selectivity as a result of the rising fluorine content of the polymers. Maximum selectivity amounts to 3.4 at an oxygen permeability coefficient of 21 Barrer. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1517–1526, 1997     

Pervaporation characteristics of methyl methacrylate–methacrylic acid copolymer membranes ionically crosslinked with metal ions for a benzene/cyclohexane mixture

Methyl methacrylate–methacrylic acid copolymer (MMA–MAA) membranes ionically crosslinked with Fe³⁺ and Co²⁺ ions (MMA–MAA–Fe³⁺ and –Co²⁺) were prepared, and characteristics of permeation and separation for a benzene/cyclohexane mixture of 50 wt % benzene through these membranes in pervaporation (PV) were studied. Although the introduction of the metal ions to the MMA–MAA membrane enhanced both benzene permselectivity and permeability for a benzene/cyclohexane mixture, the PV characteristics between the MMA–MAA–Fe³⁺ and –Co²⁺ membranes were significantly different. The difference in the PV characteristics between these membranes was strongly governed by the difference of these membrane structures based on the glass transition temperature, contact angle to methylene iodide, degree of swelling, and mixture composition absorbed in the membrane, and so on. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 233–241, 1999     

含氟体系中MFI型分子筛膜的制备及其乙醇/水分离性能

以氟化铵为矿化剂、四丙基溴化铵为模板剂,在负载晶种的钇稳定氧化锆(YSZ)中空纤维支撑体表面合成了MFI型分子筛膜,并用于乙醇/水的分离;系统考察了氟硅比(n_NH4F/n_SiO2)、合成时间等条件对膜分离性能的影响,在n_NH4F/n_SiO2为0.8、合成时间为8 h下合成出高性能膜,其通量达8.2 kg·m^-2·h^-1、乙醇/水分离因子为47;同时研究了MFI型分子筛膜在乙醇/水体系中的分离稳定性,揭示出该方法所合成膜表面无Si-OH,从而避免了Si-OH与乙醇反应而带来膜分离性能的下降.