Oxidative coupling of methane in porous Vycor membrane reactors

Porous Vycor membrane tubes were used in shell-and-tube type membrane reactors to study the effect on the oxidative coupling of methane of metering the oxygen into the catalyst bed. Experimental studies showed that under conditions of complete oxygen conversion, Vycor membrane reactors packed with Sm₂O₃ catalyst exhibited enhanced hydrocarbon (C₂) selectivity. C₂ yields were comparable to those of the conventional co-feed packed bed reactors operated under the same conditions. The higher C₂ selectivity in the membrane reactors indicated that, for methane coupling, regulating the supply of oxygen along the length of the packed bed may be beneficial to C₂ formation.     

Fabrication of a thin palladium membrane supported in a porous ceramic substrate by chemical vapor deposition

A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl₂) vapor and H₂ as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al₂O₃ top layer and a coarse-pore -Al₂O₃ substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al₂O₃ top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al₂O₃ top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H₂ permeation flux of these membranes was in the range 0.5–1.0 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 350–450°C. The H₂ permeation data suggest that surface reaction steps are rate-limiting for H₂ transport through such thin membranes in the temperature range studied.     

Inorganic Membranes for Hydrogen Separation

Hydrogen, one of the most promising energy carriers for the future, is currently produced mainly by natural gas reforming or coal gasification, where mixtures containing H₂, CO₂ and contaminants like CO, H₂S and CH₄ are obtained. Among other methods, membrane technology has received special attention due to its potential efficiency for hydrogen separation, simplicity of operation, low energy consumption, and because it is environmentally friendly. For this application, the inorganic membranes can be essentially divided into five main families: metallic and proton conducting (dense phases), and silica, zeolite and carbon molecular sieve (porous solids). Over the past 20 years, palladium-based membranes have been the most studied and implemented at industrial level; however, recent advances in other membrane types have received a great deal of attention. This article critically reviews more than 520 publications, highlighting the latest research developments on inorganic membranes for the recovery and purification of hydrogen, with emphasis on their structural characteristics, synthesis, commercial application, drawbacks and challenges. Furthermore, a large compilation of data is provided in Supplementary Material divided according to membrane type.     

Asymmetric membranes with modified gold films as selective gates for metal ion separations

Thin layers of gold (700 Å) were deposited on manufactured alumina pourous supports to yield nanopores with openings of <7 nm. A self-assembled monolayer (SAM) of alkyl thiols was then attached to provide a hydrophobic support for trialkyl phosphine oxide-based metal ion carriers. The resulting gated membranes provided a barrier to ions including H⁺, and Ca²⁺, NO₃⁻, and CH₃COO⁻. When an aqueous feed solution of 4.2 mM uranyl nitrate and 1 M lithium nitrate pH 4, and a receiving solution of 1 M sodium acetate pH 5.5 were used 100% of the metal was transported across the membrane by facilitated transport via the phosphate or phosphine oxide carrier. The thin gates transported metal ions as neutral nitrate complexes with fluxes high enough to be limited by the alumina support. The flux rates of 200,000 metal ions per pore per second are only a factor of 5 below that observed for the potassium channel. High selectivity of U over Eu is observed until the [U] is <0.84 mM in the feed solution, despite the fact the Eu actually transports faster when U is not present. This work demonstrates that selectivity can be added without impeding transport by using thin selective layers.     

有机-无机杂化分离膜研究进展

有机-无机杂化膜材料结合了有机膜材料和无机膜材料的优良性能,已成为分离膜材料研究的一个热点。本文以有机、无机组分间相互作用类型对其进行分类,着重介绍组分间以化学键相结合的有机-无机杂化膜的优良特性,总结了影响此类杂化膜结构和性能的主要因素,概括了它在膜分离中的应用,提出了目前研究工作中存在的不足,并做出了简要的述评。     

Advances in Biohybridized Planar Polymer Membranes and Membrane-Like Matrices

The past few decades have seen increasing growth in the field of biomimetic membranes and thus also a rapid expansion of their biomedical and technological applications. Versatility, stability and scalability have moved biohybrid polymer membranes into the limelight. This review focuses on planar, soft polymer membranes and polymer-based matrices and their role as a host for different types of biomolecules. Because biomimetic polymer platforms present an extensive, ever-growing field, we limit ourselves mostly to the discussion of producing planar polymer membranes on solid supports that lend themselves to functionalization by biomolecules. We present an overview of the major highlights and challenges associated with the biohybridization of such polymer platforms. In particular, we elaborate on procedures developed to maintain optimal peptide and membrane protein performance in a customized polymer membrane or membrane-like environment. Finally, we discuss a number of applications of such biohybridized polymer platforms and contemplate future developments to further exploit their potential.     

Separation of hydrogen from silane via membranes: A step in the production of ultra-high-purity silicon

Ultra-high-purity silicon (Si) is an important material for the electronics industry. Most of this Si is produced by thermal decomposition of trichlorosilane (SiHCl₃). A second route is through decomposition of silane (SiH₄). Since the conversion per pass in this process is not complete, the hydrogen which is co-produced can be separated from the gaseous SiH₄ and purged so that the SiH₄ can be recovered and reused. Three different separation schemes for accomplishing this separation, including absorption, cold box and membranes, were proposed and the relatives merits of these three were studied. The results of this study show that the separation by membranes is the preferred one because of its simplicity in equipment and its low cost in energy. To define the process for the separation of SiH₄ and H₂ by membranes, three aspects were investigated: (1) permeability measurement, (2) comparison of the mixture performance with the predictions of a design model, and (3) chemical stability of the permeator in the presence of SiH₄. The results of permeation of a mixture of the two gases agree well with predictions by the design model using the pure-component permeabilities. The permeator is stable in the presence of SiH₄. Thus, a solid data base was obtained for design of a full-scale unit.     

Study of a new pervaporation membrane Part I. Preparation and characteristics of the new membrane

A new alcohol dehydration membrane, poly(vinyl alcohol)—chitosan blended composite membrane (PVA-CS) has been prepared. This membrane has high selectivity and promising permeability, especially in separating ethanol—water near the azeotropic region (J_t > 200 g/m² h, _w/e > 500, 70°C). The separating characteristics, which vary with feed composition, operating temperature and the surface structure of the membrane, are determined and the results agree well with the theoretical predictions.

The characteristics of mechanical strength, stability and resistance to water were also determined. The results show that they are considerably enhanced by blending and crosslinking, in comparison with PVA composite membranes.     

Achievements in the field of proton-conductive portion electrolyte membranes

The 2000–2006 achievements in the field of synthesis, property examination, and application of proton-exchange membranes are reviewed on the basis of more than 120 papers.     

Physical aspects of heterogeneities in multi-component lipid membranes

Ever since the raft model for biomembranes has been proposed, the traditional view of biomembranes based on the fluid-mosaic model has been altered. In the raft model, dynamical heterogeneities in multi-component lipid bilayers play an essential role. Focusing on the lateral phase separation of biomembranes and vesicles, we review some of the most relevant research conducted over the last decade. We mainly refer to those experimental works that are based on physical chemistry approach, and to theoretical explanations given in terms of soft matter physics. In the first part, we describe the phase behavior and the conformation of multi-component lipid bilayers. After formulating the hydrodynamics of fluid membranes in the presence of the surrounding solvent, we discuss the domain growth-law and decay rate of concentration fluctuations. Finally, we review several attempts to describe membrane rafts as two-dimensional microemulsion.     

Polymeric Membrane Nanofiltration and Its Application to Separations in the Chemical Industries

The application of membrane technology, particularly water-based nanofiltration, as a separation process in the chemical industries has increased tremendously in recent years. However, the use of membranes capable of molecular separation in non-aqueous systems (e.g. nanofiltration) is a relatively new and growing application of membrane technology. The main challenge in applying polymeric nanofiltration membranes to non-aqueous systems is that the polymers developed for water-based applications are not suitable. Polyimide is a particularly interesting polymer as it has excellent chemical resistance, and membranes produced from it provide desirable separation properties – i.e. economically viable flux and good separation of nanoscale molecules. Various research works have shown that commercial polyimide organic solvent nanofiltration (OSN) membranes, trademark STARMEM™, 1 are robust and suitable for performing molecular separations. This work will discuss in detail the use of STARMEM™ in a pharmaceutical application. The EIC-OSN process was developed for separating the enantiomers of chiral compounds in pharmaceutical applications. High optical purity (94.9%) of (S)-phenylethanol from rac-phenylethanol was achieved through the use of STARMEM™122. Process simulation of the ideal eutomer-distomer system predicted that the highest theoretical resolvability from this process would be 99.2%. Other application areas of OSN are varied, including purification and fractionation in the natural products industry, homogeneous catalyst recovery, monomer separation from oligomers, etc. Currently, OSN is used in a small number of processes including a very large petrochemical application, but it has the potential to be applied to a wide range of separations across the full spectrum of the chemical industries.     

The undulation force; theoretical results versus experimental demonstrations

In 1978 Wolfgang Helfrich published a paper (Helfrich W. Z Naturforsch 1978; 33a:305) where he introduced the notion of an undulation force between bilayers. This is caused by thermal excitations of the bending modes being restricted by the presence of neighboring layers. Although there is now a consensus on the qualitative picture put forward by Helfrich there is still a debate concerning the quantitative aspects. We discuss in particular the distance dependence of the interaction and also the value of the numerical coefficient of the force law derived by Helfrich.     

Study of a new pervaporation membrane Part 2. Performance test and analysis of the new membrane

The compatibility of poly(vinyl alcohol)—chitosan blends was tested and analyzed by their glass transition temperatures with differential scanning calorimetry with a DSC-7 (Epson). Highest selectivity, promising permeability and good mechanical strength for the dehydration of alcohol—water mixtures were obtained at a 4:1 composition of the blend.

The chemical composition, physical structure and morphology of this blended composite membrane were studied by a variety of surface science techniques, including infrared spectrometry (IR), small-angle X-ray diffraction (SAXRD) and scanning electron microscopy (SEM). The surface investigation is needed for the study of the blended composite membrane, and the results confirm well with the characteristics of the new membrane.     

膜片电极支撑自组装双层脂膜中短杆菌肽离子通道的形成

通过一个两步程序在膜片电极尖端形成自组装双层脂膜：（1）膜片电极尖端沾取成膜液；（2）将吸附成膜液的尖端浸入电解液中，排除尖端多余的成膜液，通过电学方法监测双层脂膜的形成。将短杆菌肽通道蛋白分散在成膜液和电解质溶液中，在制备膜片电极支撑双层脂膜过程中，短杆菌肽重组到双层脂膜中形成离子通道，对通道的一般特性进行了研究，并观察到通道开放和关闭的现象。     

Mixed hybrid bilayer lipid membrane incorporating valinomycin: improvements in preparation and functioning

The paper deals with the reconstruction of lipid bilayer membranes on a Au-covered polycarbonate membrane. Such a kind of like-biomembranes (namely mixed hybrid bilayer lipid membrane (MHBLM)) are characterised by appreciable long-term stability. Here we describe changes that have been made in the geometry of the experimental device in order to avoid artefacts and render membrane reproduction easier. Incorporation of valinomycin was performed to check the membrane and its stability: conductance and membrane potential following the changes of ion concentration were recorded. This new approach permits increase of successful trials and renders possible, when it breaks, easily formation of a new MHBLM on the same Au-covered polycarbonate membrane support. Finally, the stability shown by the MHBLM renders this system a promising tool for use under flowing conditions.     

In Situ Growth and Characterization of Metal Oxide Nanoparticles within Polyelectrolyte Membranes

This study describes a novel approach for the in situ synthesis of metal oxide–polyelectrolyte nanocomposites formed via impregnation of hydrated polyelectrolyte films with binary water/alcohol solutions of metal salts and consecutive reactions that convert metal cations into oxide nanoparticles embedded within the polymer matrix. The method is demonstrated drawing on the example of Nafion membranes and a variety of metal oxides with an emphasis placed on zinc oxide. The in situ formation of nanoparticles is controlled by changing the solvent composition and conditions of synthesis that for the first time allows one to tailor not only the size, but also the nanoparticle shape, giving a preference to growth of a particular crystal facet. The high‐resolution TEM, SEM/EDX, UV‐vis and XRD studies confirmed the homogeneous distribution of crystalline nanoparticles of circa 4 nm and their aggregates of 10–20 nm. The produced nanocomposite films are flexible, mechanically robust and have a potential to be employed in sensing, optoelectronics and catalysis.     

Functional properties and electroanalytical selectivity of some anion exchange membranes

Heterogeneous membranes of Fe(III)-Zr(IV), Cr(III)-Zr(IV) mixed hydrous oxides and one doped with Sn(II) ion have been prepared using polystyrene as a binding material. Functional properties like water content, porosity, swelling, electrolyte absorption and conductance of these membranes have been determined in various anionic forms and correlated with their electroanalytical selectivity.     

Anti-trade-off in dehydration of ethanol by novel PVA/APTEOS hybrid membranes

Novel organic–inorganic hybrid membranes were prepared through sol–gel reaction of poly(vinyl alcohol) (PVA) with γ-aminopropyl-triethoxysilane (APTEOS) for pervaporation (PV) separation of ethanol/water mixtures. The membranes were characterized by FTIR, EDX, WXRD and PALS. The amorphous region of the hybrid membranes increased with increasing APTEOS content, and both the free volume and the hydrophilicity of the hybrid membranes increased when APTEOS content was less than 5 wt%. The swelling degree of the hybrid membranes has been restrained in an aqueous solution owing to the formation of hydrogen and covalent bonds in the membrane matrix. Permeation flux increased remarkably with APTEOS content increasing, and water permselectivity increased at the same time, the trade-off between the permeation flux and water permselectivity of the hybrid membranes was broken. The sorption selectivity increased with increasing temperature, and decreased with increasing water content. In addition, the diffusion selectivity and diffusion coefficient of the permeants through the hybrid membranes were investigated. The hybrid membrane containing 5 wt% APTEOS has highest separation factor of 536.7 at 50 °C and permeation flux of 0.0355 kg m⁻² h⁻¹ in PV separation of 5 wt% water in the feed.     

由聚合物结构预测气体的透过性能

本文利用基团加和法,对20多种常见聚合物的自由体积和内聚能进行了计算。发现氧气和氮气在聚合物膜中的透过率与自由体积和内聚能的比值有直接关系。此比值越大,气体的透过率越大,透过率的对数与自由体积和内聚能的比值基本呈线性关系。据此,对未知聚合物可根据其化学结构,从已有的基团数据计算该比值,从而预测它对氧气和氮气的透过性能。