Porous glass desalination membranes: phenomenological transport coefficients and fixed charge salt exclusion

The independent phenomenological transport coefficients for two porous glasses of different average pore diameter and surface charge densities were measured and compared with similar parameters of the asymmetric cellulose acetate membrane.The bound water model is used to explain the variation of the specific hydraulic permeability with pressure. Viscous and diffusive flow are discussed and the fixed charge model tested for one of the porous glasses.The results indicate that these porous glasses have inherently good potential practical desalination properties, their main limitation being imperfections or large cavities which are responsible for viscous flow, membrane degradation and solute leakage.     

New porous perfluoropolyether membranes

A new family of porous fluorinated membranes was developed from perfluoropolyethers (PFPEs). The PFFE–dimethacrylate (3) was dispersed in isopropanol to form a clear homogeneous solution, which after UV curing in polypropylene molds formed a porous polymer disk. A series of 10 polymers was prepared with ratios of isopropanol to PFPE ranging from 1.3:1 to 0.2:1. The water content of the membranes after hydration varied from 56 to 7% (w/w) and was directly proportional to the percentage of isopropanol used in the polymerization. However, the tensile elastic modulus, which ranged from 0.17 to 15 MPa, was inversely proportional to the water content. The high water content membranes [52 and 46% (w/w)] had a similar permeability to glucose, inulin, and albumin, while the membranes with lower water contents of 37 and 25% displayed progressively lower permeability. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1756–1763, 2001     

Studies with thin membranes. II. Measurement of membrane potentials and evaluation of membrane fixed charge density

Membranes prepared from 5% Parlodion solution have been characterized. These and other membranes prepared from 0.38, 0.5, 1.0, 2.0, and 3.0% Parlodion solutions and already characterized, have been used severally to estimate the number of anionic sites present in them by two different methods. The potentiometric method, which is indirect, gave values of X?_P which were higher than X?_T, the values obtained by a direct isotopic method. The order was reversed for well-characterized ion-exchange membranes. These discrepancies were attributed to the shortcomings of the Teorell, Meyer, and Sievers theory of membrane potentials from which the potentiometric method was derived.     

Studies with inorganic precipitate membranes—XI: Evaluation of the thermodynamically effective fixed charge density by various methods

Thermodynamically effective fixed charge densities of parchment supported membranes were estimated by methods of (a) Teorell—Meyer—Sievers, (b) Altug and Hair, and (c) the most recent one of Kobatake based on the thermodynamics of irreversible processes. The two limiting forms of Kobatake's equation for dilute and concentrated ranges gave identical values of charge densities. It is interesting to note that these two values of limiting cases are closer to the Teorell—Meyer—Sievers and Altug and Hair values. The theoretical prediction for membrane potential by the Kobatake's equation were borne out quite satisfactorily by experimental results obtained with both the membranes.     

Electrokinetic measurements on porous polysulfone membranes

The surface properties of porous ultrafiltration membranes were determined by means of the streaming potential. The membranes were prepared from chemically modified polysulfone through a phase inversion process. The chemical reactions were carried out in such a way that the resulting polysulfone either was fitted out with chloromethyl substituents or with quaternary ammonia groups. Due to this, the surface of the membranes cast from these materials were either neutral or positively charged. In aqueous solution, ion adsorption as well as dissociation can occur at the surface of the membranes. This can be demonstrated by streaming potential measurements at different pH values, but constant ionic strength. From the calculated zeta potential using a recently developed model, evidence can be given on the dissociation constants of acidic and basic functional groups on the surface of the membranes and on the amount of charges within the shear plane adjacent to the membrane. Using solutions which contained surfactants, qualitative information on the amount of charges within the capillaries of the membrane can be obtained. In the range from 20 to 70°C no temperature dependency of the zeta potential could be observed.     

Regeneration of deactivated porous ceramic membranes

Because of the pore structure change and blocking of the ceramic membrane pores, deactivation of ceramic membranes occurred after repeated use. A pore blocking mechanism has been observed from the SEM study that in the first stage of deactivation, the membrane pore sizes became smaller due to the accumulation of the unremoved chemicals, and the pore neck parts were closed and/or blocked. Finally, the pore structures changed to the broken piece of long and thin elliptical shapes. Two regeneration methods were explored and tested in attempts to recover useful activity for the deactivated membranes. Relatively fresh membranes, including intermediately used membranes, can recover fluxes as much as 70 percent of fresh membrane flux by chemical treatments such as acetone-acid treatment, while the severely deactivated membranes were partially regenerated by an oxidation method followed by the acetone and acid treatment.     

Temperature-responsive permeability of porous PNIPAAm-g-PE membranes

Grafting a temperature-responsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), onto porous polyethylene (PE) membranes by UV irradiation was investigated. A wide range of graft yields (5–449%) was achieved by varying irradiation time (20–240 min) and monomer concentration (1.2–3.6 wt %). Characterization by XPS and SEM shows that the graft polymers are located both on the external surfaces as well as inside the pores of the membranes. Diffusional permeation experiments show that two distinct types of temperature responses were observed, depending on the graft yield; permeability increases with temperature in low graft yield membranes, while permeability decreases with temperature in high graft yield membranes. A mechanism explaining the dual valve functions of the graft membrane is proposed based on the location of the graft polymers on the membrane. It was also observed the permeability response exhibits a maximum with permeant molecular weight. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2133–2142, 1998     

Multifunctional porous membranes with antibacterial properties

Abstract

The paper describes the results of research on obtaining porous membranes produced from polylactide fibers (PLA) by electrospinning, additionally modified with gentamicin antibiotic (GM) at the stage of preparing a spinning solution to provide bactericidal properties. Both solid (1^oPNF) and porous (2^oPNF 3^oPNF) polymer fibers were obtained, and the control of fiber porosity was achieved using various solvent systems: dichloromethane (DCM), dimethylformamide (DMF), chloroform (CHL) and dimethyl sulfoxide (DMSO). Three types of fibers differing in morphology (fiber diameter) and mean pore size were obtained. Physicochemical properties of porous and solid drug-containing fibers were examined, determining their surface free energy (SFE) and wetting angle (CA), and the effectiveness of modification with the drug was confirmed in spectroscopic studies (FTIR-ATR). Antibacterial activity of the prepared drug-modified nonwovens was confirmed by the disk diffusion method against Gram-negative Escherichia coli bacteria strain. The results of tests have shown that depending on the type of solvents used at the electrospinning stage, porous fibers can be obtained from polylactide. The addition of gentamicin affected antibacterial properties, and the pore size determined the rate of drug release monitored by the ion coupled plasma method (ICP).     

Correlations between water uptake and effective fixed charge concentration at high univalent electrolyte concentrations in sulfonated polymer cation-exchange membranes with different morphology

Water uptakes properties and effective fixed charge concentration have been determined in aqueous electrolyte solutions (LiCl, NaCl and KCl) for different commercial sulfonated polymer cation-exchange membranes with different morphology. Differences in the water uptake properties and in the membrane effective fixed charge concentration has been found, which have been analyzed on the basis of the different membrane structures. The experimental results show correlations between the water uptake and the loss of the membrane selectivity at high electrolyte concentrations which are dependent on the membrane morphology. Relationships are found which permit to estimate the membrane effective fixed charge concentration from equilibrium and morphological properties with the advantage of avoiding the need for membrane potential measurements.     

多孔陶瓷膜制备技术研究进展

多孔陶瓷膜具有化学稳定性好、机械强度大、耐酸碱、耐高温等优点,在石油和化学工业等苛刻环境中有着广泛的应用,多孔陶瓷膜的制备技术是推动多孔陶瓷膜产业发展的核心部分。多孔陶瓷膜制备技术的核心和关键是以提高陶瓷膜整体性能为导向,通过对陶瓷膜微结构的调控,实现陶瓷膜制备技术的突破。针对近十年来陶瓷膜领域的研究,概述了当前陶瓷膜领域在制备具有高渗透性、高渗透选择性的陶瓷膜以及陶瓷膜低成本化方面的研究进展,并对未来陶瓷膜领域的发展趋势及瓶颈性问题进行了讨论。     

Catalytic reactors based on porous ceramic membranes

This overview discusses some of the developments and outstanding opportunities in the field of catalytic reactors based on porous ceramic membranes, both inert and catalytic. This is an emerging area, where inputs from heterogeneous catalysis, material science and reactor engineering are playing the key roles. Rather than attempting a thorough review of the relevant literature, this work deals with some general concepts and then concentrates on a few selected examples that illustrate the application of membrane reactors.     

Graded porous TiO2 membranes for microfiltration

Membrane technology can be integrated into many advanced system concepts for the production of liquid energy carriers and chemicals, for microfiltration, oxygen generation, low-CO₂-emission power generation, hydrogen technology and carbon dioxide capture. Forschungszentrum Jülich has developed a composite membrane consisting of a ceramic TiO₂ membrane with pores in the range of 100 nm deposited on a thin planar metallic substrate made of 316L stainless steel powder. Fabrication of substrate and membrane is described in this paper and the composite structure is characterized. The stainless steel substrate is produced by tape casting, the TiO₂ membrane by wet powder spraying or screen printing. Light microscopy, scanning electron microscopy, EDX and XRD are used to characterize the starting materials and layers. The measurement of air flow rates as a function of the pressure drop is given.     

Hydrophobic polyethersulfone porous membranes for membrane distillation

Membrane distillation (MD) is a thermal, vapor-driven transportation process through micro porous hydrophobic membranes that is increasingly being applied to seawater and brine desalination processes. Two types of hydrophobic microporous polyethersulfone flat sheet membranes, namely, annealed polyethersulfone and a polyethersulfone/tetraethoxysilane (PES/TEOS) blend were prepared by a phase inversion process. The membranes were characterized and their performances were investigated using the vacuum membrane distillation of an aqueous NaCl solution. The performances of the prepared membranes were also compared with two commercially available hydrophobic membranes, polytetrafluorethylene and polyvinylidene fluoride. The influence of operational parameters such as feed temperature (25–65 °C), permeate vacuum pressure (200–800 mbar), feed flow rate (8–22 mL/s) and feed salt concentration (3000 to 35000 mg/L) on the MD permeation flux were investigated for the four membranes. The hydrophobic PES/TEOS membrane had the highest salt rejection (99.7%) and permeate flux (86 kg/m²·h) at 65 °C, with a feed of 7000 ppm and a pressure of 200 mbar.     

多孔离子传导电池隔膜研究进展

具有高离子选择性和高电导率的离子传导膜对于以新能源为主体的新型电力系统（如液流电池、燃料电池、锂电池等）至关重要。近年来,研究者们提出了构建多孔离子传导膜以应对传统隔膜普遍存在的离子选择性和电导率之间的权衡效应。本综述从无机多孔离子传导膜、有机多孔离子传导膜以及多孔离子传导复合膜三个方面简要概述了近年来多孔离子传导膜作为电池隔膜的最新研究进展,总结了多孔离子传导膜在液流电池、燃料电池、锂电池等新能源电池中的前沿性工作,并指出未来多孔离子传导电池隔膜的研究将重点关注多孔膜结构的调控、高性能多孔膜材料的开发以及多孔膜在新型电池中的应用。     

Embedded space charge in porous alumina films formed in phosphoric acid

The embedded charge in the barrier layers of porous alumina, formed potentiostatically in phosphoric acid was studied as a function of anodizing voltage (30-57 V) and bath temperature (18 and 21 °C). For that, the polarization measurements of as-grown and annealed alumina/Al samples were conducted in the same anodizing bath by anodic potential sweep at a scan rate of 2.6 V/min. The plane capacitor model was used for the assessment of the charge density in the barrier layers of as-grown porous alumina. For the barrier layers of films formed at 18 °C this value equals to 0.747 μC cm⁻² and does not depend on the anodizing voltage. Increase in electrolyte temperature rises the embedded charge density. Polarization measurements carried out in this paper clearly present that the barriers of phosphoric acid films grown at the anodizing voltages lower than 39 V contain a layer of virtual cathode while at higher voltages this layer disappers. The obtained results allow speaking about promising opportunities of potentiodynamic polarization measurements of alumina films in the same anodizing solution before and after annealing for the studies of charges embedded within the alumina barriers and for the regularities of ion transport.     

超滤系统在三聚氰胺生产应用中的优化处理

以常压渣油为原料，富产丙烯及高辛烷值汽油。为进一步提高丙烯收率及降低汽油中烯烃含量，采用了北京石油化工科学研究院的MGD技术，经过工业运转结果标明，装置加工量保持在原有水平时，丙烯收率提高了近1．7个百分点，液态烃＋柴油＋汽油产率达到了85．12％，汽油中烯烃含量下降了10个百分点，辛烷值略得到提高。     

多孔陶瓷载体上Y型分子筛膜的气体渗透性能

以一定的晶化液组成、晶化温度及晶化时间 ,经多次涂层 ,制备了较理想的 Y型沸石分子筛膜 ,研究 Y型分子筛膜的气体渗透性能。考察了 H2 、N2 、CO2 、C3 H8等气体的单组分及二元组分的气体渗透性能。结果表明 ,H2 / C3 H8理想分离因数达 5.0 9,CO2 / N2 实际分离因数达 1 0 .87。     

Brackish water salt rejection by porous hyperfiltration membranes

A theory is developed for the rejection of multiple salts by a macroporous hyperfiltration membrane, modelled by cylindrical pores, whose interior surfaces acquire a constant potential when in contact with the salt ions. With three ion types and two valences the ion rejections are shown to depend on the ratio of Debye length to pore radius, a dimensionless wall potential, a filtration Peclet number, and the ratios of concentrations and charge numbers of two of the ions of different valence. Numerical solutions for the rejections are given for large Peclet number and analytic solutions when the Debye length is also large.     

Characteristics of ammonia permeation through porous silica membranes

A sol–gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH₃) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50–400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H₂ > NH₃ > N₂. These results suggest that, for permeation through silica membranes, the molecular size of NH₃ is larger than that of H₂, despite previous reports that the kinetic diameter of NH₃ is smaller than that of H₂. At high temperatures, there was no effect of NH₃ adsorption on H₂ permeation characteristics, and silica membranes were highly stable in NH₃ at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH₃ molecules adsorbed on the silica improved NH₃‐permselectivity by blocking permeation of H₂ molecules without decreasing NH₃ permeance. The maximal NH₃/H₂ permeance ratio obtained during binary component separation was ～30 with an NH₃ permeance of ～10^?7 mol m^?2 s^?1 Pa^?1 at an H₂ permeation activation energy of ～6 kJ mol^?1. © 2009 American Institute of Chemical Engineers AIChE J, 2010