Modeling of Ethylene Absorption from an Ethylene–Ethane Mixture by Silver Nitrate Aqueous Solution in a Hollow-Fiber Membrane Contactor

Convection–diffusion mass transfer in a gas–liquid membrane contactor based on porous polysulfone hollow fiber membranes with a mesoporous (d_pore ~ 2 nm) structure of the separation layer has been studied. The characteristics of the membrane contactor have been investigated in the recovery of ethylene from its mixture with ethane using an aqueous silver nitrate solution as the absorption liquid. A procedure based on the method of lines is proposed for calculating a mass transfer in hollow fiber contactor with a longitudinal laminar flow in an array of parallel fibers. An ethylene flux, depending on the process conditions, has been found by solving numerically a set of convection–diffusion equations with allowance for both the chemical reaction in the liquid stream and transmembrane transport.     

Simulation of the temperature-driven pervaporation of dilute 1-butanol aqueous mixtures through a PTMSP membrane in a cross-flow module

The selective thermal pervaporation (TPV) of dilute aqueous mixtures of 1-butanol through a hydrophobic poly(1-trimethylsilyl-1-propyne) (PTMSP) membrane in plate-and-frame modules with an air gap has been investigated experimentally and theoretically for the first time. The dependences of the composition and the permeate flow on the temperature and initial concentration of the mixture, the liquid coolant temperature, and the membrane thickness have been measured. It has been shown that a permeate flow across the PTMSP membrane can be achieved in the TPV mode that is not inferior to that of vacuum pervaporation at condensation temperatures of 0.5–15.0°C. The permeation and diffusion activation energies have been estimated from the measured temperature dependences of the partial fluxes. Equations for the TPV process have been derived in terms of the one-dimensional resistance model. The temperature dependences of the diffusion coefficients of 1-butanol and water in the membrane have been determined, and the linear temperature and concentration fields of the components in the module for membranes of different thickness have been calculated from the experimental data using these equations.     

磷酸酯化聚乙烯醇渗透汽化复合膜的制备与分离性能研究

制备了以磷酸酯化聚乙烯醇为活性分离层的ＰＰＶＡ／ＰＡＮ渗透汽化复合膜，并用于乙醇－水混合物的分离；比较了分离温度、进料浓度对膜分离性能影响的重要性。结果表明，复合膜活性层的酯化度对其分离性能具有显著影响。     

渗透汽化分离醇-醚及醇-酯物系的研究进展

综述了分离醇-醚、醇-酯物系所使用的膜,主要包括纤维素类、壳聚糖类、聚乙烯醇类、芳香聚合物类膜和聚电解质-表面活性剂复合膜的渗透汽化性能。聚乙烯醇类膜的分离因子大而渗透通量小;聚电解质-表面活性剂复合膜的分离因子和渗透通量都基本复合工业应用的要求,但膜的稳定性较差。对比了交联、共混、小分子无机物填充和表面改性等多种膜制备和改性手段对膜的渗透汽化分离性能的影响,并分析了膜的物理化学结构特性与其渗透汽化分离性能的关系;半互穿网络结构可以增加聚合物膜的自由体积,而使渗透通量显著提高;小分子硅钨酸填充壳聚糖膜的分离因子和渗透通量均基本达到工业应用的要求。     

Permeability of C<Subscript>1</Subscript>–C<Subscript>3</Subscript> hydrocarbons through MDK membranes under nonisothermal conditions at lower temperatures

The presented nonisothermal technique for investigation of membrane gas separation (using MDK-1 membrane as an example) demonstrates possibilities of rapid assessment of the separation power of commercial membranes for both individual components and various mixtures in the temperature range of?20 to +40°C. The efficiency of the membrane process under these conditions (cross-flow membrane module model) for separation of propane–methane mixtures has been evaluated. It has been shown that the permeability of methane decreases with a decrease in temperature in the Arrhenius coordinates and the propane permeability increases. The separation selectivity in the mixture decreases by more than twofold in comparison with the ideal selectivity. Nevertheless, a significant improvement of separation has been observed at lower temperatures, with the recovery of the desired product and its purity being variable in a wide range depending on the practical goal. The nonisothermal technique is supposed to be useful for rapid selection of conditions (temperature, pressure, components to be separated) for efficient application of polymeric membranes for separation of hydrocarbon-containing mixtures that are close in composition to real gas sources.     

A novel hybrid material based on polytrimethylsilylpropyne and hypercrosslinked polystyrene for membrane gas separation and thermopervaporation

To improve the membrane permeability and separation properties in gas separation processes and thermopervaporative (TPV) recovery of butanol from model fermentation mixtures, hybrid membranes based on polymers with an extremely high free fractional volume—polytrimethylsilylpropyne (PTMSP) and hypercrosslinked polystyrene (HCL-PS)—have been first prepared and experimentally studied. The composite membranes have been fabricated using the commercial sorbent Purolite Macronet MN-200 exhibiting high sorption capacity for organic solvents. It has been found that in the hybrid membranes, HCL-PS sorbent particles are nonuniformly distributed throughout the volume: they are located in the surface layer of the membrane. It has been shown that the introduction of a small amount of a modifying component (0.5–1.0 wt %) into the PTMSP matrix improves the time stability of transport properties and increase by a factor of 1.5–2 the permeability coefficients of the material to light gases (N₂, O₂, CO₂, CH₄) and butane vapor. It has been found that hybrid PTMSP/HCL-PS membranes have higher separation factors than those of PTMSP membranes in the TPV separation of a butanol/water binary mixture.     

Concentration history of pervaporation

The permeability and selectivity of the separation of aqueous organic solutions by pervaporation have been studied on semicrystalline poly(ethylene terephthalate) membranes and asymmetric amorphous polyvinyltrimethylsilane membranes in the presence of structural rearrangements initiated by the development of relaxation processes. Attention was focused on the concentration history, which lies in the fact that the permeability and the permeate composition depend on the concentration of the previous solution passed through the membrane at a fixed composition of the feed solution. It has been shown that micropores are formed in both membranes under certain pervaporation conditions and mass transfer occurrs through two competing transport channels. As a result, the oscillatory kinetics of pervaporation and the inversion of separation selectivity in a steady state are observed experimentally.     

Structure and transport properties of pervaporation membranes based on polyphenylene oxide and heteroarm star polymers

Thin-film membranes based on polyphenylene oxide composites with a varying concentration of heteroarm star-shaped polymers (1, 3, and 5 wt %) comprising arms of polystyrene and poly(2-vinylpyridine)- block-poly(tert-butylmethacrylate) diblock copolymer grafted onto a common fullerene C₆₀ core have been developed. The transport properties of the membranes have been studied in the pervaporation separation of a methanol–ethylene glycol mixture. An increase in the star-shaped polymer content in the membrane leads to an increase in the flux and separation factor of the membranes. Sorption studies have revealed that the sorption activity of methanol in the membranes is higher than that of ethylene glycol. The introduction of star-shaped polymer additives into the membrane composition leads to an increase in the degree of equilibrium sorption of the two components of the mixture subjected to separation. The formation of transport channels in pervaporation membranes during sorption in deuterated methanol has been first studied using the small-angle neutron scattering method. Comparative analysis of the data on neutron scattering on the original dry samples, the samples saturated with deuterated methanol, and the samples dried after sorption has shown that the structural uniformity of the composite membranes is higher than that of the matrix polymer. According to scanning electron microscopy, the morphology of the composite membranes is a system of closed cells.     

Downhole Separation of Petroleum Fluids

Abstract

Oil–water separation is one of the oldest practices in the purification of water or oil. Environmentally concerned organizations pay more attention to the purification of water, while oil companies concentrate on the purification of oil. Water management is particularly an important issue in the production of hydrocarbons, because volumes of water steadily increase as a field ages. In fact, increasing costs of water handling such as separation, disposal, treatment, maintenance, and environmental risks make the oil production scheme uneconomic. Recently, several downhole oil/ water separation technologies have been proposed to reduce water volume in the oil production, but they are not yet technically efficient and cost effective. One of the most recent technologies introduced is membrane separation technology. In the past, polymeric membranes have been used for liquid–liquid separation. These membranes induce high pressure drop and are very expensive. This study identifies a novel material that allows oil to pass through it but not water. After in-depth investigations, a surprising capability of Xerox bond paper having different basis weight (24 lb, 32 lb) was discovered. This material was found to permeate oil selectively from an oil/ water mixture. The recovery of oil was more than 85%, which is high in separation efficiency. The oil permeation flux through the paper surface was measured as a function of various operating parameters. The permeation of oil flux was possible only at finite pressure difference. The recovery of oil was increased with the increase of oil concentration in the feed mixture. The permeation of flux was affected with filtering medium thickness, feed flow rate, and pressure, but these parameters did not affect the ultimate oil recovery.     

Transport Rate of Liquid Water and Saturated Water Vapors across Polymer Proton-Exchange Membranes

Dependences of the transport rate of liquid water and saturated water vapor across commercial membranes (Nafion, MF-4SK) and proton-exchange membranes synthesized by the authors (PVDF, PP, UHMWPE, PTFE films modified with sulfonated polystyrene) on the membrane thickness have been studied. It has been found that at room temperature (17–25°C), the transport rate of liquid water and saturated water vapor across the membranes into an air stream hardly depends on the membrane type and thickness (60–240 μm), with the transport rate of saturated vapor being almost an order of magnitude below that of liquid water contacting one of the membrane surfaces. The fact that the flux of water and water vapor across the membrane does not depend on membrane thickness under conditions of maximum moistening suggests that the flow resistance is determined by the resistance at the feed and permeate interfaces. If one of the membrane surfaces is in contact with liquid water, the transport rate is equal to the rate of water removal from the permeate surface of the membrane; in the case of contact with saturated vapor, the transport rate is determined by the rate of water sorption from the vapor phase by the membrane. The results can be used to optimize the operation of fuel cells based on polymer proton-exchange membranes.     

Gas–liquid membrane contactors for carbon dioxide capture from gaseous streams

Membrane technology is characterized by high efficiency, compatibility and flexibility of various membrane processes in integrated systems, low power consumption, high stability and environmental safety of processes, comparative ease and simplicity of controlling and scaling-up, as well as a unique functional flexibility of the membrane processes. This is why the membrane technology is considered as a promising way to reduce anthropogenic emissions of carbon dioxide into the atmosphere. Gas–liquid membrane contactors are a prime example of high-performance hybrid processes using membrane technologies. Integrating several separation methods in one device (membrane contactor) makes it possible to retain benefits of membrane technology, such as small size and flexibility, complementing them with high separation selectivity typical of CO₂ absorption. This review presents the basic principles of operation and design of membrane contactors, and a wide range of materials, membranes, and liquid absorbents for membrane CO₂ absorption/stripping are considered. Particular attention has been paid to current studies on CO₂ removal from thermal power plant flue gas, natural gas, biogas, and syngas. The examples of pilot-scale and semi-commercial implementation of CO₂ absorption/stripping in membrane contactors have been given.     

Structure and properties of poly(4-methylpentene-1) track-etched membranes

The influence of irradiation and the subsequent etching of latent tracks in poly(4-methylpentene-1) (PMP) films on the transport parameters of the resulting membranes has been studied. The films have been irradiated with accelerated Kr and Xe ions of 4.5 and 1.2 MeV/nucleon in energy at a fluence of 10⁶–10⁹ cm^?2. It has been found that the irradiation followed by etching makes it possible to obtain an anisotropic membrane with a nonporous selective layer between two porous layers with tapered pores. The CH₄, CO₂, and He transport characteristics of the membranes have been examined. It has been shown that these modification methods can significantly increase the gas flux through the membrane. It is believed that the ion track etching procedure as applied to PMP can form the basis for fabricating membranes with a highly permeable, nonporous, gas-selective layer.     

Gas permeability of homogeneous and composite membranes based on poly(trimethylsilylpropyne)/poly(vinyltrimethylsilane) blends

Gas transport properties of membranes based on a blend of two silicon-hydrocarbon polymers, poly(trimethylsilylpropyne) (PTMSP) and poly(vinyltrimethylsilane) (PVTMS), have been investigated. The N₂ and CO₂ permeability of the membranes decreases by two orders of magnitude, and CO₂/N₂ selectivity increases about threefold with increasing PVTMS content in the blend from 0 to 100%. The effect of the volume contraction of the membranes has been found. The results of the experiments and calculations showed that the membrane properties throughout all the range of concentrations are in good agreement with the single-phase blend permeability model. The results of the research open the possibility of preparing PTMSP/PVTMS membranes with stable gas separation properties combining a high permeability of PTMSP and a rather high selectivity of PVTMS.     

Elaboration of composite hollow fiber membranes with selective layer from poly[1-(trimethylsylil)1-propyne] for regeneration of aqueous alkanolamine solutions

The results of research on elaboration of the hollow fiber composite membranes for regeneration of aqueous solutions of alkanolamines in membrane gas-liquid contactor are presented in this work. Asymmetric polysulfone (PSF) hollow fiber UF membranes were used as a porous support, poly[1-(trimethylsylil)-1-propyne] (PTMSP) was employed as a diffusion layer. The influence of PSF hollow fiber casting conditions on hydraulic permeability was studied. Samples of composite membranes were obtained with a defectfree layer of PTMSP and carbon dioxide permeance of 0.26 m³ (STP) (m² h bar)^?1. It was revealed by SEM that the thickness of the PTMSP separation layer is 2.5 microns, where in X-ray spectrometry analysis data and calculations according to resistance-in-series model discovered that the selective layer penetration depth to the pores of the support was 1.4 microns. Calculation by resistance-in-series model showed that 98.6% of resistance to the gas transport is attributed to PTMSP, partially intruded in the pores of the support. Chemical stability of materials which comprise composite membrane makes promising their using for regeneration of aqueous solutions of alkanolamines (pH > 11) from carbon dioxide at a temperature of 100°C and a pressure drop of 10 bar in the membrane gas-liquid contactors.     

Preparation and ionic selectivity of carbon-coated alumina nanofiber membranes

A novel type of ion-selective membranes based on Nafen^TM alumina nanofibers coated with carbon is proposed. The membranes are produced by filtration of a Nafen nanofiber suspension through a porous support followed by drying and sintering. A thin carbon layer (up to 2 nm) is deposited on the nanofibers by chemical vapor deposition (CVD). Its formation is confirmed by the results of Raman spectroscopy and visually observed in TEM images. According to low temperature nitrogen adsorption experiments, the formation of carbon layer leads to decreasing pore size (the maximum of pore size distribution shifts from 28 to 16 nm) and the corresponding decrease of porosity (from 75 to 62%) and specific surface area (from 146 to 107 m²g^–1). The measurement of membrane potential in an electrochemical cell has shown that the deposition of carbon on the membrane results in high ionic selectivity. In an aqueous KCl solution, the membranes display high anion selectivity with anion and cation transference numbers of 0.94 and 0.06, respectively. The fixed-charge density of membrane has been determined by fitting the experimental data using the Teorell–Meyer–Sievers model. It has been found that the membrane fixed-charge density increases with increasing electrolyte concentration. Possible applications of the membranes produced include nanofiltration, ultrafiltration, and separation of charged species in mixtures. The formation of a conductive carbon layer on the pore surface can be employed for fabricating membranes with switchable ion-transport selectivity.     

Polydimethylsilalkylene-dimethylsiloxanes as advanced membrane materials for thermopervaporative recovery of oxygenates from aqueous reaction media

Polydimethylsildimethylene-dimethylsiloxane (PSDMS) and polydimethylsiltrimethylenedimethylsiloxane (PSTMS) have been first studied as pervaporation membrane materials for the recovery of butanol from aqueous media. New synthesis procedures that make it possible to obtain the monomers 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane (1) and 2,2,6,6-tetramethyl-1-oxa-2,6-disilacyclohexane (2) in high yields and with high purity required for subsequent polymerization have been developed. The optimum concentration of the crosslinking agent (tetraethoxysilane (TEOS)) of 5% has been found, which provides the maximum degree of crosslinking without sacrificing high values of separation factor and permeate flux. It has been shown that the permselectivity of PSDMS or PSTMS for butanol–water is higher by a factor of 1.5 or- almost 2, respectively, than the selectivity of the industrial membrane polymer, PDMS, at comparable values of the butanol permeability coefficient.     

Percolation of composite poly(vinyltrimethylsilane) membranes with carbon nanotubes

Recent years have seen a flurry of activity in research on the use of nanoparticles to improve the properties of polymeric membranes. It is known that the change in the macroscopic properties of these hybrid materials is associated with the parameters of the cluster of incorporated nanoparticles. The percolation threshold is higher than 15 vol % for the spherical particles and decreases with the increasing aspect ratio of the embedded nanoparticles of another shape. The paper presents the results of study on the permeability of gases (N₂, O₂, CH₄ and C₃H₈) and a test liquid (ethanol) through hybrid membranes based on the glassy polymer poly(vinyltrimethylsilane) (PVTMS) with embedded multiwall carbon nanotubes (MWCNT) with a concentration of 0.3–3 wt %. It has been found that the permeability of gases and liquids alters at MWCNT concentrations above 0.4 wt %, which corresponds to the percolation threshold for the given particles as proved by calculations. In addition, the gas permeability coefficients measured indicate a change in the transport mechanism and selectivity of the membrane.     

The Separation of Aromatic Hydrocarbons Through a Supported Ionic Liquid Membrane

Abstract

Ionic liquids can be considered as environmentally friendly solvents because of their low vapor pressures. Room-temperature ionic liquids are used as a supported liquid membrane for separation of aromatic from aliphatic. Aromatic hydrocarbons, benzene, toluene, ethylbenzene, and p-xylene are successfully transported through the polypropylene supported ionic liquid membrane based on 1-methyl-3-octyl imidazolium chloride. The separation performances, represented by the percentage extraction and separation factor, are analyzed systematically by varying the operating parameters: the contact time, membrane phase composition, and initial feed phase concentration. The mathematical models that have been used to simulate experimental data have been discussed. The scanning electron microscope combined with energy-dispersive X-ray analysis of membranes after continuous operation shows that the membrane phases are still retained within the membrane pores and only small losses of the membrane phase initially located on the surface are observed.     

Preparation of metal-polymer composite membranes with conductance asymmetry

The structure and electrochemical properties of a poly(ethylene terephthalate) track membrane, one side of which was coated with thin aluminum layers by thermal vacuum evaporation, have been investigated. It has been found that the deposition of the aluminum layer on the surface leads to the creation of metal-polymer composite membranes that exhibit in electrolyte solutions conductance asymmetry, the rectification effect similar to the p-n junction in semiconductors. This is due to a change in pore geometry of the composite membranes and to the existence in pores of the interface between the original membrane and the aluminum layer, which bear oppositely charged functional groups on their surface in aqueous solutions. Information on ion transport in the membranes has been obtained by impedance spectroscopy.     

分离有机蒸气/氮气的SiO_2超滤膜的制备

以ZrO2为载体,正硅酸乙酯(TEOS)、乙醇、水为原料,制备了纳米级孔径的SiO2超滤膜,并用液-液排除法和扫描电子显微镜进行表征。考察了溶胶粘度、涂膜时间和支撑体孔径对成膜效果的影响。研究结果表明,合适的制膜参数为:溶胶配比n(TEOS)/n(水)/n(乙醇)=1/8/4,涂膜时间30 s,支撑体孔径35nm左右。四次涂膜可以得到最可几孔半径为1.96nm的S iO2膜;在操作压力0.10MPa下,其对正己烷/氮气的分离因子可达到1.61,进一步改性后用于有机蒸气/氮气的分离。