分子筛型促渗透材料加入膜中后对渗透蒸发过程的影响

研究了沸石分子筛填充醋酸纤维素膜渗透蒸发分离乙醇－水体系，考察了全浓度范围内膜的选择性和渗透通量，含有3A、13X分子筛的醋酸纤维素膜的渗透选择性增加，含有5A分子筛的醋酸纤维素膜在不同浓度范围内的选择性是相反的。     

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.     

Novel Pervaporation Technique Using Permeate Vapor Adsorption for Removal of Chlorinated Organics from Aqueous Media

A novel pervaporation technique has been proposed that makes it possible to selectively remove volatile chlorinated organics (VCO) from contaminated water; to localize them on activated carbon directly in the membrane module; to create a sufficient driving force of the process due to both high sorption capacity of activated carbon and its VCO adsorption selectivity; and to abandon the use of expensive vacuum equipment, thereby minimizing vacuum pump operating costs. The influence of VCO concentration in the solution and the feed flow rate on the efficiency of VCO removal from water has been studied. It has been found that the dominant resistance to VCO flux through the membrane is due to an additional flux resistance associated with diffusion constraints in the boundary liquid layer near the membrane surface. It has been shown that VCO flux values in the case of this pervaporation method (up to 0.47 kg/(m² h) at 30°C) are several times larger than those for conventional pervaporation approaches. The separation factor can be as high as 380–2400 for a chloroform/water mixture or 400–4800 for a trichloroethylene/water mixture.     

α-Al_2O_3中空纤维复合膜的制备及其对甲醇水溶液的分离

采用聚酰胺酸(PA)-N,N-二甲基乙酰胺(DMAC)或PA-SiO2颗粒-DMAC涂膜液涂敷,通过300℃亚胺化或800℃碳化处理,对α-Al2O3中空纤维膜进行改性。在改性α-Al2O3中空纤维膜上浸涂聚乙烯醇(PVA)溶液并用戊二醛(GA)交联剂进行交联,制备α-Al2O3中空纤维渗透汽化复合膜,并对甲醇水溶液进行渗透汽化膜分离,考察了温度、料液浓度、涂膜液组成对复合膜分离性能的影响。实验结果表明,涂敷PA-DMAC涂膜液并经亚胺化的改性方式最佳,在此基础上浸涂12%(w)PVA溶液和6%(w)GA交联剂制备的复合膜分离性能较好;在温度40℃、压差100 kPa的条件下,对96%(w)甲醇水溶液的分离因子为25.0,渗透通量为15.0 g/(m2·h)。     

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.     

电泳沉积预涂晶种制备NaY分子筛膜及其分离性能

通过电泳沉积方法预涂晶种二次生长法制备出Y型分子筛膜。采用Y型分子筛合成的导向剂作为预涂晶种。考察了导向剂的陈化时间,电泳电压和电泳沉积时间对晶种质量以及分子筛膜的影响。结果表明,在电泳的作用下,导向剂作为晶种能够均匀地沉积在载体表面。二次合成后的载体的XRD表征显示,纯的Y型分子筛膜成功地生长在载体表面。SEM电镜表明,经过二次合成后的载体表面被高度孪生的分子筛晶体所覆盖。分子筛膜在不同渗透温度条件的分离性能用CO2/N2混合物进行评价。此外,考察了不同浓度的异丙醇水溶液在分子筛膜上的渗透汽化脱水性能。合成的Y型分子筛膜展现出较好的脱水性能和渗透通量.     

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。     

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。     

Co~(2+)固载PVA促进传递膜渗透汽化分离环己烯/环己烷的研究

针对无载体膜分离烯烃/烷烃选择性差的状况,制备了Co2+固载促进传递膜,研究了固载量、阴离子种类、料液温度及料液中环己烯的质量分数等对膜分离性能的影响。结果表明,膜的较佳固载量([Co2+]/[-OH])是0.75;应优先选用尺寸较大且与Co2+之间的离解能较小的阴离子;料液温度升高,膜的渗透通量增加,分离因子下降,但渗透通量和料液温度之间不符合Arrehenius关系;料液中环己烯的质量分数增大,膜的渗透量增大,分离因子下降。     

苯-环己烷分离渗透蒸发膜的研究进展与展望

由于苯和环己烷的相对挥发度非常接近,利用传统分离方法(如萃取精馏或共沸精馏)分离苯-环己烷混合物的分离效率较低。相比之下,利用膜的溶解和扩散选择性对苯-环己烷混合物进行分离的渗透蒸发技术具有优势。综述了渗透蒸发膜分离苯-环己烷混合物的研究进展,重点介绍了用于渗透蒸发技术的膜材料(特别是高分子膜材料),对渗透蒸发技术分离苯-环己烷混合物的研究前景进行了展望。     

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.     

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.     

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.     

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.     

Investigation of pervaporation membranes based on polycarbamide: Effect of residual solvent

Effect of the amide solvent N-methylpyrrolidone occurring in polymer films after their formation on the physicochemical and transport properties of the membranes during pervaporation of a water-isopropanol mixture has been investigated in detail. The objects of study have been new polycarbamide-based membranes a prepared by solvent evaporation from polymer solutions and containing the residual solvent and the membranes from which the residual solvent was removed by special treatment. It has been shown that the removal of the residual solvent increases the density and decreases hydrophilicity of the membrane; in this case, the permeate flux decreases partly during the process of pervaporation, although the separation factor of the water-isopropanol mixture remains high. A composite membrane comprised of a thin selective layer of polycarbamide (～6 μm) and a porous polyphenylene oxide support designed to enhance the flux has been made and investigated.     

Composite membranes containing metal-organic polymers: Morphology and gas transport properties

Metal-organic framework compounds used in gas separation membranes based on polyimides with different chemical structures have been surveyed. According to analysis of published data, a metal-organic framework compound composed of MIL-101 and two polyimides with different chemical structures has been selected. Samples of gas separation membranes containing the additive in an amount of 2.5–20 wt % have been prepared to analyze the gas transport characteristics. A significant difference in the permeability and selectivity for a wide range of gases has been shown. The morphological structure of the polymer composites with additive different contents has been analyzed, a the differences in the gas transport properties have been explained.     

Asymmetry of ion transport in hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia

Results of studies of the properties of hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia nanoparticles through the thickness prepared by layer-by-layer casting from a polymer solution are described. The effect of the dopant concentration on the properties of the membranes is studied. At a low oxide concentration, the water uptake and ionic conductivity of the resulting samples increase compared to the original MF-4SC membrane. It is found that the diffusion permeability of HCl and NaCl solutions across these membranes exhibits an asymmetric behavior. It is shown that the diffusion permeability is higher in the case of diffusion of the solutions from the unmodified side of the membrane. The maximum asymmetry coefficient is obtained for a membrane containing 10% ZrO₂ in the modified layer for the diffusion of 0.1 M HCl solution (38%). The causes of the diffusion permeability asymmetry are discussed.     

CO2/CH4 separation using prepared and characterized poly (ether-block-amide)/ZIF-8 mixed matrix membranes

In this study, poly (ether-block-amide) (Pebax-2533) based mixed matrix membranes were prepared by incorporating various contents of synthesized zeolitic imidazole framework (ZIF-8) nanoparticles into the polymer matrix. The membranes were fabricated via a solution casting–solvent evaporation technique. The results of gas permeation through the membranes revealed that the addition of the ZIF-8 into the polymer matrix enhances both permeability and CO₂/CH₄ selectivity values. As an example, for the mixed matrix membrane comprising 25 wt% of ZIF-8, CO₂ permeability and ideal CO₂/CH₄ selectivity values are 269.73 Barrer and 9.31, respectively, while the corresponding values are 187.54 Barrer and 7.25 for the neat membrane.     

渗透汽化膜分离技术及其在石油化工中的应用

概述了渗透汽化过程的进展和动向,简述了渗透汽化膜分离技术的基本原理,综述了有机膜、无机膜、有机-无机复合膜3种渗透汽化膜的特点、制备方法及其分离性能和分离特性,介绍了渗透汽化膜组件特别是适用于管状无机膜的圆管式膜组件的研究和开发情况;从有机溶剂脱水、废水中有机物的脱除、有机混合物的分离、酯化反应的强化4个方面着重介绍了渗透汽化膜分离技术在石油化工领域的应用;最后指出了渗透汽化膜分离技术面临的困难和挑战。     

氨基碳点/聚酰亚胺混合基质膜的制备及CO2分离性能研究

将水热合成法制备的氨基碳点与聚酰亚胺复合得到混合基质膜。通过SEM、FT-IR、XRD和DSC考查了氨基碳点掺杂质量分数对混合基质膜形貌和结构的影响。氨基碳点表面的氨基可以提供碱性环境,同时增加了膜内的自由体积,促进CO₂传递。当氨基碳点掺杂质量分数为0.3%时,混合基质膜的CO₂分离性能最佳,其CO₂、CH₄、N₂渗透通量分别为85.87 barrer、1.69 barrer、2.62 barrer,CO₂/CH₄、CO₂/N₂选择性分别为50.81和32.77。 