PVA膜渗透汽化分离低浓度丙酮/水溶液的实验研究

采用聚乙烯醇（PVA）膜渗透汽化分离浓缩低浓度丙酮/水溶液,考察了原料液浓度、温度、膜后真空度等对PVA膜渗透通量和分离因子的影响。结果表明,随着原料液浓度的增加、温度和膜后真空度的升高,渗透通量和分离因子均呈增加的趋势,温度对渗透通量的影响基本符合Arrhenius方程。     

Analysis of oxygen permeation through dense ceramic membranes with chemical reactions of finite rate

The oxygen permeation through oxygen ionic or mixed-conducting ceramic membranes under reaction conditions was examined with a model taking into account of different electrical transport mechanisms (p-type and n-type transports) and finite reaction rate. It was demonstrated that with a reaction consuming oxygen in one side of the membrane, the oxygen partial pressure in the reaction side decreases and the oxygen permeation flux increases with the increase in the reaction rate for both the p-type and the n-type transport dominated mechanism. The increase in reaction rate causes a transition of the transport mechanism from p-type to n-type. This transition leads to an increase in the permeation flux by up to 30 times. This effect offers one explanation for the large discrepancies in published permeation data for membrane reactors of partial oxidation reaction employing an oxygen permeable dense ceramic membrane. For a membrane with a specific transport mechanism, the increase in the reactant partial pressure causes an increase in the reaction rate and oxygen permeation flux. However, the increase in the inlet inert gas amount has a complicated effect on the oxygen permeation flux because it lowers both oxygen partial pressure and the reaction rate at the same time.     

Permeation behaviour in cellulose triacetate dense membrane during pervaporation separation of methanol/methyl tert-butyl ether mixture

The pervaporation separation of methanol/methyl tert-butyl ether through cellulose triacetate dense membranes has been carried out under different feed compositions, permeation temperatures and temperature cycles to investigate the permeation behaviour of the membrane during pervaporation process. The experimental data indicate that the plasticization effect has a decisive influence on pervaporation flux, permselectivity and permeation activation energy. The results show that the penetrants of different feeds are transported through the membrane by different pathways with the influence of plasticization effect at different temperatures. It has also been observed that plasticization had great effect on the membrane swelling and sorption selectivity. Furthermore, DSC results show that the membranes retain the influence of the plasticization effect after pervaporation separations are tested. © 2000 Society of Chemical Industry     

高通量二氧化硅复合膜的制备及其渗透汽化性能研究

二氧化硅复合膜展现出的耐酸性和稳定性在渗透汽化领域有着广阔的应用前景。本文采用真空抽吸浸渍法制备二氧化硅复合膜的支撑层,得到高通量二氧化硅复合膜。本文对支撑层真空抽吸的最优条件进行探究,并采用扫描电镜对膜层的表面、截面形貌结构进行表征。结果表明,当支撑层溶胶质量浓度为2%,真空抽吸时间为10 s,真空抽吸压力为0.10 MPa时制备出致密的二氧化硅复合膜,其膜层厚度为6~7 μm。将本文制备的二氧化硅复合膜应用于异丙醇水溶液渗透汽化中,该膜显示出优异的分离性能,其中异丙醇的渗透通量为6.42 kg/(m²·h)。     

Effect of Film Aging on the Pervaporation Properties of Latex Membranes

Abstract

Latex membranes have recently been investigated for their application in pervaporation separation processes. Acrylonitrile-butyl acrylate copolymer latex membrane showed selective permeation to water in pervaporation with water-ethanol mixtures. Different from solvent-cast membranes, the pervaporation properties of latex membranes were found to change with the membrane aging time or under different aging conditions. It is shown that aging leads to better membrane fusion, thus decreasing the permeation rate and increasing the separation factor. Aging the membrane in a medium which keeps the latex particle from good fusion would cause a high permeation rate but a low separation factor. Based on our observations, a comprehensive transport mechanism of the permeant through latex membranes during pervaporation is proposed.     

A characterization of pdms pervaporation membranes for the removal of trace organic from water

A new silicone pervaporation membrane for the removal of one of trace organies, 1,2-dichloroethane from water has been developed using polydimethylsiloxane (PDMS) and oligomeric silylstyrene as a crosslinking agent of PDMS. Optimal conditions for fabricating the best membrane were determined from swelling measurements ard pervaporation experiments and then the membrane was characterized at different membrane thickness and operating conditions. In the pervaporation separation of 55–70 ppm of l,2-dichlorocthanc aqueous mixtures, the developed membrane has flux of 2.5–330 g/(m².h) and selectivity of 230–1750 depending on membrane thickness, permeate pressure and operating Temperature. Water permeation through thin membrane was found to be subjected to significant desorption resistance, while the desorption resistance and thermodynamic factors as well as the concentration polarization of the organic at the boundary layer in feed can affect the organic permeation, depending on membrane thickness. Selectivity change with permcaic pressure depends on membrane thickness: at small membrane thickness range, selectivity increases with permeate pressure and at large thickness region it decreases. From the Arrhenius plots of each component fluxes, the permeation activation energies were determined. Through an analysis of the permeation activation energies of each components, the desorption resistance as well as the effects of the thermodynamic factors on permeation was qualitatively characterized.     

Pervaporation of Methanol/Methyl‐t‐Butyl Ether Mixtures Through Poly(Vinyl Alcohol)/Poly(Acrylic Acid) Blend Membranes

Abstract

Membranes obtained by blending poly(vinyl alcohol) (PVOH) and poly(acrylic acid) (PAA) have been investigated for the separation of methanol and methyl‐t‐butyl ether (MTBE) liquid mixtures through a pervaporation process. Experiments were performed by contacting one side of a polymer dense film with the liquid mixture and removing the vapor on the other side with an inert gas flux, a setup for a process with sweeping gas. The blend membranes, with a COOH/OH ratio in the 0.5–2.5 range, are permeated by methanol preferentially. Higher values of flux and lower values of selectivity are observed when the methanol content in the feed increases. The ratio PAA/PVOH of the membrane influences both flux and selectivity in the same way. A maximum of both flux and selectivity is observed at a COOH/OH ratio of about 2. The swelling of membranes of different composition in the presence of different liquid composition explains the flux behavior in the pervaporation experiments. The observed membrane swelling has been explained on the basis of the solubility parameters of the components of the system.     

渗透汽化膜的制备及其应用进展

渗透汽化（pervaportion, PV）作为一种新颖的分离技术在工业范围内得以应用,至关重要的是它在恒沸混合物、近沸混合物分离方面的显著优势。相比分馏、精馏、萃取等传统分离方法,渗透汽化技术具有经济、高效、便于管理的优点,但目前缺少优质的渗透汽化膜材料和先进的膜制备方法。本文综述了近年来渗透汽化技术以及渗透汽化膜的研究现状,首先介绍了PV技术的分离机理、PV膜的制备方法、PV技术在工业上的应用领域等,并重点讨论了料液温度、料液浓度、料液流速、膜上下游蒸汽压差、膜材料等关键因素对渗透汽化分离性能的影响。文中提出未来渗透汽化技术应在膜材料方面积极探索,选用聚合物为材料,并结合先进的膜制备方法来进一步降低膜的厚度,从而明显地提高膜渗透通量。     

高分子致密膜内渗透现象的同一性研究

在渗透汽化（PV）和蒸汽渗透（VP）膜分离过程,利用高分子膜材料对原料中不同组分的溶解度与扩散系数不同实现混合物分离.由于两种过程原料状态分别呈现液态和蒸汽形式,长期以来作为两种膜分离过程展开研究,其传质推动力都是组分在膜中的化学位梯度.为了从热力学和传质角度研究PV和VP膜分离过程,本文设计了特殊的渗透池,可以在同一渗透池中同时进行渗透汽化和蒸汽渗透膜分离过程,保持气液界面为热力学平衡状态.使用PVA/PAN复合膜进行水/乙醇混合物以及水/异丙醇混合物的PV和VP渗透实验,对两个过程中渗透通量随浓度变化情况进行了分析和比较.实验结果和理论分析表明：溶液的PV过程和与之呈相平衡的蒸汽相的VP过程在一定温度范围内,当原料中水含量较低的情况下具有相同的渗透通量,其传质遵从溶解扩散机理;当原料溶液中水含量较高时,PV过程中膜溶胀现象较为严重,渗透通量存在一定差别.     

Modeling of U-shaped Ba0.5Sr0.5Co0.8Fe0.2O3-δ hollow-fiber membrane for oxygen permeation

A mathematic model is developed for the perovskite-type mixed ionic-electronic conducting (MIEC) membrane,which makes it possible to simulate the process of oxygen separation in the U-shaped Ba0.5Sr0.5Co0.8Fe0.2O3-δ hollow-fiber membrane.The model correlates the oxygen permeation flux to the measurable variables.The trends of calculated results for purge operation coincide well with the experimental data,therefore the model is considerable for flux prediction under vacuum operation.Higher oxygen separation efficiency can be achieved with vacuum operation than purge operation.Parameter study with vacuum operation reveals that oxygen permeation flux increases with higher vacuum levels,and vacuum pressure of around 1.013 × 103 Pa is the optimal.Also,vacuum operation on the lumen side is much more efficient to achieve higher oxygen permeation flux compared with compression mode on the shell side.     

Using pervaporation technique to separate water from organics

This paper is focused on how water may be separated from dioxan, butanone and butyric acid under constant operating conditions. The analysis is presented in terms of variations in the permeation flux, individual partial fluxes and separation factors. As in a membrane process, in order to separate a liquid mixture, pervaporation relies on differences in membrane permeability as well as the vapour pressures of the components in the mixture. It is found that the separation factors reach infinity as the total permeate pressure is reduced to the vapour pressure of the organic permeant. The permeation flux increases with increasing water concentration in the feed. A drop in the flux has been observed on addition of an extra component. The PVA membrane confirmed its hydrophilic characteristics by not allowing butyric acid and butanone to permeate. Values of the activity coefficients and diffusion coefficients are reported versus the vapour composition for binary, ternary and multi-component systems. The diffusion coefficient increases with a decrease in mole fraction of the component in the membrane.     

Effect of transfer in the vapour phase on the extraction by pervaporation through organophilic membranes: experimental analysis on model solutions and theoretical extrapolation

Mass transfer in pervaporation is usually regarded as limited by the solution-diffusion step inside the dense selective polymer layer. In the case of pervaporation for the extraction of volatile organic compounds through organophilic membranes, especially at low feed temperature (about 300 K), the influence of the downstream pressure cannot be neglected. A contribution to the study of the operating parameters on the vapour side in a pilot plant — from the membrane to the condenser — to the overall mass transfer is presented.

A “convection-diffusion” model has been established to calculate the partial pressure gradients in the vapour phase up to the downstream face of the membrane. This equation has been combined with a relation for the mass transfer inside the membrane with a driving force expressed as a difference in fugacities.

The partial permeate pressures and the pervaporate fluxes obtained first with a pure compound (water) and secondly with binary mixtures (water-ethanol) pervaporated through membranes of polydimethylsiloxane (PDMS) on a pilot plant scale are well predicted by the model. Moreover, on the permeate side, the effects of unavoidable non-condensable gases, of the condenser temperature and of the distance between the module and the condenser on the flux and on the selectivity have been established for different total permeate pressures (300–3000 Pa). At high pressure, the pervaporation selectivity towards ethanol exhibits a minimum value as a function of the permeate circuit design.     

Zeolite filled P84 co-polyimide membranes for dehydration of isopropanol through pervaporation process

We have developed zeolite 5A and 13X embedded P84 co-polyimide membranes with enhanced permeability and selectivity for the pervaporation dehydration of isopropanol (IPA). It is found that a higher annealing temperature, i.e., is more favorable to improve adhesion between zeolite and polymer phase, and to enhance charge transfer complexes (CTCs) formation. FESEM, DSC and gas permeation results show that zeolite 13X has better compatibility with the matrix polymer than zeolite 5A because of stronger interactions between Na cations in zeolite 13X framework and electron acceptor groups of P84 polyimide. The addition of zeolite into the P84 dense membrane improves water sorption capacity and pervaporation separation performance significantly. Owing to the bigger pore size, larger pore volume, higher sorption capacity and better adhesion, the zeolite 13X incorporated P84 membranes has a much higher permeability than zeolite 5A filled membranes. Interestingly, both have comparably high selectivity possibly because of the effects of chain rigidification and partial pore blockage. The addition of zeolite 13X reduces activation energy for water permeation through the membrane but increases that for IPA permeation. However, the addition of zeolite 5A increases activation energy for both water and IPA permeation. Pervaporation permeability increases with zeolite 13X loading, while the selectivity achieves the maximum at 30 wt% zeolite 13X loading. When the zeolite 13X loading approaches 40 wt%, the adhesion between zeolite and polymer becomes poor and the membrane selectivity declines. A comparison between pervaporation and gas separation results reveals that pervaporation membranes can tolerate a higher degree of interstitial defects than gas separation membranes because of stronger molecular interactions between the feed and the polymer, and the larger molecular size difference between penetrants in the former.     

A study on permeation behavior of a liquid mixture through PVA membranes having a crosslinking gradient structure in pervaporation

Two types of dense poly(vinyl alcohol) (PVA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique: membranes with uniform crosslinking structure and with crosslinking gradient structure. From the permeation of pure water through a membrane having a uniform crosslinking structure, the effect of crosslinking density in the membrane on the permeation activation energy, plasticizing coefficient, and diffusivity of the permeant was investigated. The concentration and activity profiles of the permeant in the membrane in the pervaporation process were determined using the diffusion equation and Flory–Huggins thermodynamics. PVA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while the other side was blocked by a polyester film to prevent the reaction solution from contacting it. The extent of the gradient was controlled by the exposing time. The pervaporation separation of the water–acetic acid mixture was carried out on the membrane having a crosslinking gradient structure, and the pervaporation performance with different membrane loading in the membrane cell was discussed using a schematic concentration and activity profiles of the permeant which was made based on the results from the permeation of a pure component through the membrane with a uniform crosslinking structure. © 1996 John Wiley & Sons, Inc.     

Pervaporation separation of meOH/MTBE through CTA membrane

In the present work, the pervaporation (PV) separation of a MeOH/MTBE mixture system was studied using a CTA dense membrane. The PV performances were characterized by changing the operating conditions, such as the feed composition and permeation temperature. The results show that the CTA membrane favors MeOH permeation and exhibits specificity during the PV separation process for the MeOH/MTBE system due to the existence of the plasticization effect from the MeOH component. Furthermore, the swelling sorption measurements reaffirm that the plasticization effect has a dominant effect on the transport of the penetrants through the membrane and substantially determines the PV permeation properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 377–386, 1999     

催化-分离脱氢膜反应器的透氢性能研究

1 前言在化学化工领域中利用膜材料的选择性渗透和催化作用来改善反应性能正越来越受到人们的重视。与传统的颗粒状催化剂-固定床反应器体系相比较,膜催化反应器在质量传递、热量传递和活化反应物方面有较大的差异。例如,用传统的固定床反应器由于受热力     

改性复膜对微水异丙醇的渗透汽化脱水

介绍了用缩甲醛改性的PVA/PAN复合膜的制备方法,并用于质量分数低于5%的微水异丙醇体系的渗透汽化(PV)深度脱水研究,考察了操作温度、料液浓度与操作压力等因素对分离性能的影响。渗透通量J与分离系数α均随温度的升高而增大,而随料液异丙醇浓度的升高J减小而α增大,在72℃、1.6 kPa膜后压力下,该膜对含异丙醇质量分数为98%的体系,仍有α=316,J=262 g/(m.h)的分离效能,显示了较好的工业应用前景。     

中空纤维渗透汽化复合膜及组件研究进展

中空纤维渗透汽化膜组件具有器件小型化及成本较低等方面的优势,其工业应用潜力巨大。本文介绍了中空纤维渗透汽化复合膜及组件的研究进展,阐述了膜材料、成膜方法以及组件结构参数等对组件渗透汽化性能的影响,并对中空纤维渗透汽化膜组件的中试研究进行了总结。通过组件放大及中试研究发现,中空纤维渗透汽化膜组件的装填密度、长度以及抽吸方式均会影响其下游侧的真空度,从而影响其渗透汽化性能。膜材料的分子设计、组件的结构参数优化以及耐溶剂耐高温封装将是中空纤维渗透汽化膜组件未来工业放大过程中的关键环节。     

Carbon molecular sieve membranes derived from Matrimid® polyimide for nitrogen/methane separation

A commercial polyimide, Matrimid® 5218, was pyrolyzed under an inert argon atmosphere to produce carbon molecular sieve (CMS) dense film membranes for nitrogen/methane separation. The resulting CMS dense film separation performance was evaluated using both pure and mixed N₂/CH₄ permeation tests. The effects of final pyrolysis temperature on N₂/CH₄ separation are reported. The separation performance of all CMS dense films significantly exceeds the polymer precursor dense film. The CMS dense film pyrolyzed at 800 °C shows very attractive separation performance that surpasses the polymer membrane upper bound line, with N₂ permeability of 6.8 Barrers and N₂/CH₄ permselectivity of 7.7 from pure gas permeation, and N₂ permeability of 5.2 Barrers and N₂/CH₄ permselectivity of 6.0 from mixed gas permeation. The temperature dependences of permeabilities, sorption coefficients, and diffusion coefficients of the membrane were studied, and the activation energy for permeation and diffusion, as well as the apparent heats of sorption are reported. The high permselectivity of this dense film is shown to arise from a significant entropic contribution in the diffusion selectivity. The study shows that the rigid ‘slit-shaped’ CMS pore structure can enable a strong molecular sieving effect to effectively distinguish the size and shape difference between N₂ and CH₄.     

Modeling investigation of geometric size effect on pervaporation dehydration through scaled-up hollow fiber NaA zeolite membranes

A mass transfer model in consideration of multi-layer resistances through NaA zeolite membrane and lumen pressure drop in the permeate sidewas developed to describe pervaporation dehydration through scaled-up hollowfiber supported NaA zeolitemembrane. Itwas found that the transfer resistance in the lumen of the permeate side is strongly related with geometric size of hollow fiber zeolite membrane,which could not be neglected. The effect of geometric size on pervaporation dehydration could bemore significant under higher vacuumpressure in the permeate side. The transfer resistance in the lumen increaseswith the hollowfiber length but decreaseswith lumen diameter. The geometric structure could be optimized in terms of the ratio of lumen diameter to membrane length. A critical value of dI/L (Rc) to achieve high permeation flux was empirically correlated with extraction pressure in the permeate side. Typically, for a hollow fiber supported NaA zeolite membrane with length of 0.40 m, the lumen diameter should be larger than 2.0 mm under the extraction pressure of 1500 Pa.