Membrane materials in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures—A review

The separation of aromatic/aliphatic hydrocarbon mixtures is a significant process in chemical industry, but challenged in some cases. Compared with conventional separation technologies, pervaporation is quite promising in terms of its economical, energy-saving, and eco-friendly advantages. However, this technique has not been used in industry for separating aromatic/aliphatic mixtures yet. One of the main reasons is that the separation performance of existed pervaporation membranes is unsatisfactory. Membrane material is an important factor that affects the separation performance. This review provides an overview on the advances in studying membrane materials for the pervaporation separation of aromatic/aliphatic mixtures over the past decade. Explored pristine polymers and their hybrid materials(as hybrid membranes) are summarized to highlight their nature and separation performance. We anticipate that this review could provide some guidance in the development of new materials for the aromatic/aliphatic pervaporation separation.

STUDY OF COMPOSITE MEMBRANE OF CELLULOSE ACETATE OR POLYVINYL ALCOHOL BLENDED WITH METHYLMETHACRYLATE-ACRYLIC ACID COPOLYMER FOR PERVAPORATION SEPARATION

In this paper, methylmethacrylate-acrylic acid MMA-AA hydrophilic and hydrophobic copolymers were prepared by copolymerization for preparing membrane materials. The composite membrane of cellulose acetate (CA) blended with MMA-AA hydrophobic copolymer was used for the separation of methanol from pentane-methanol mixture. When the methanol concentration was only 1 wt%, the permeate flux still maintained at 350 g/m(2)h and separation factor was as big as 800. The composite membrane of PVA (polyvinyl alcohol) blended with MMA-AA hydrophilic copolymer was used for the separation of ethanol-water mixture. The permeate flux was increased to 975 g/m(2)h at 74 degrees C and the separation factor reached 3000 at 25 degrees C. The PVA/MMA-AA blended membrane surface modified by ammonia plasma was also investigated for separating ethanol-water mixture. Both permeate flux and separation factor of the membrane was improved. However, there was no obvious difference of plasma treatment time in the interval of 20 similar to 40 min.

Modeling of Pervaporation Separation Benzene from Dilute Aqueous Solutions Through Polydimethylsiloxane Membranes

A modified solution-diffusion model was established based on Flory-Huggins thermodynamic theory and Fujita's free volume theory. This model was used for description of the mass transfer of removal benzene from dilute aqueous solutions through polydimethylsiloxane (PDMS) membranes. The effect of component concentration on the interaction parameter between components, that of the polymer membrane on the selectivity to benzene, and that of feed concentration and temperature on the permeation flux and separation factor of benzene/water through PDMS membranes were investigated. Calculated pervaporation fluxes of benzene and water were compared with the experimental results and were in good agreement with the experimental data.

Studies on Pervaporation Separation of Ethanol/Water Mixtures with Membranes of Polypropylene Sulfonate Salts

Sulfonated polypropylene membranes loaded with different kinds of counter-ions were prepared by heterogeneous chiorosulfonation reaction of polypropylene membrane followed by hydrolysis and ion-exchange reaction. The membranes obtained were used for selective separation of ethanol/water mixtures by pervaporation. The effects of counter-ion species, ion-exchange capacity, solution composition, thickness of membrane and temperature on the separation behavior of the membranes were investigated. Microstructure and morphology of the membranes were examined by X-ray and SEM as well.

Graphene-based membranes for pervaporation processes

Two-dimensional graphene and its derivatives exhibiting distinct physiochemical properties are intriguing building blocks for researchers from a large variety of scientific fields.Assembling graphene-based materials into membrane layers brings great potentials for high-efficiency membrane processes.Particularly,pervaporation by graphene-based membranes has been intensively studied with respect to the membrane design and preparation.This review aims to provide an overview on the graphene-based membranes for pervaporation processes ranged from fabrication to application.Physical or chemical decoration of graphene-based materials is elaborated regarding their effects on the microstructure and performance.The mass transport of pervaporation through graphene-based membranes is introduced,and relevant mechanisms are described.Furthermore,performances of state-of-the-art graphene-based membranes for different pervaporation applications are summarized.Finally,the perspectives of current challenges and future directions are presented.

Process Design of Continuous-Flow Pervaporation Separation for Alcohol Dehydration

The separation characteristics of the PVA-CS (polyvinyl alcohol-chitosan) blended composite membrane for dehydration of ethanol-water mixture are examined. The relationships of flux and separation factor with the feed concentration and operation temperature are established. Using this correlated equation, the continuous-flow pervaporation process about 500 kilolitres/year dehydrated ethanol is designed. The numbers of stage and reheater are calculated by stage-by-stage method for two kinds of cascades: one with equal membrane area and the other with 10℃ of temperature decrement per section. The results show that when the numbers of stage and reheater are the same, the cascade with 10℃ of temperature decrement has more advantages than that with equal membrane area. The influences of feed concentration and flow rate on the numbers of stage and reheater in the cascades are discussed.

ORGANIC PERMSELECTIVE PERVAPORATION CHARACTERISTICS OF POLY(SILYLPROPYNE) AND COPOLYMER DENSE MEMBRANES

An investigation into the organic permselective separation through poly [1-trimethylsilyl-1-propyne] (PTMSP) and (1-trimethylsily 1)-1-(1-penta-methyl-disily 1)-1-propyne copolymer (TMSP-PMDSP) dense membranes was made to gain an insight into the effect of the chemical structure of membrane materials on pervaporation (PV) characteristics. The results show that the copolymer has a higher separation factor alpha(org/water) but with a relatively lower value of flux J(t) (g/m(2).h) than pure PTMSP. This phenomenon may be attributed to the introduction of side chain with large bulk volume in copolymer, which brought about a decrease of excess free volume and the improvement of diffusion selectivity to some extent. With the same molar concentration of organic liquids in feed, THF/water solutions have the highest value of alpha(org/water) as well as J(t) in comparison with ethanol/water, iso-propanol/water and THF/water mixtures.

Concentration of Hydrochloric Acid by Pervaporation Membrane Separation Process

Hydrogen chlorid (HC1) used in chemical industry and laboratory is usually obtainedfrom concentrated hydrochloric acid (approximately 37% of HC1) through distillation,When the hydrogen chloride content in concentrated hydrochloric acid is extracted

PERVAPORATION SEPARATION OF WATER-ACETIC ACID MIXTURES THROUGH AN-co-AA MEMBRANES TREATED WITH RARE EARTH METAL IONS

Pervaporation separation of water-acetic acid mixtures through Poly(AN-co-AA) membranes and rare earth metal ions treated Poly(AN-co-AA)membranes was investigated for the first time. The results showed that the treatment with rare earth metal ions could greatly improve the characteristics of the separation of water-acetic acid mixtures.

Swelling Behaviors and Pervaporation Properties of CA/PAN Composite Membranes for Separation of Caprolactam/Water Mixtures

The composite membranes with cellulose acetate（CA） as the separating layer material and polyacrylonitrile（PAN） as the supporting layer material were prepared for separating caprolactam（CPL） from CPL/water mixtures by pervaporation technique.The swelling experiments were carried out to investigate the effects of swelling time and CPL concentration on the degree of swelling.The results showed that the CA membrane reached swelling equilibrium within 24 h,and the degree of swelling first slightly decreased then increased with the increase of CPL concentration in the feed under the experimental conditions.Respectively comparing flux with permeance,and separation factor with selectivity,we found out that the separation performance of the CA/PAN composite membrane is more strongly dependent on its hydrophilic/hydrophobic nature as well as on the effects of operating parameters,such as feed composition concentration and feed temperature.

SEPARATION OF DIOXANE/WATER MIXTURES BY PERVAPORATION

Pervaporation as a membrane technique of liquid mixtures separation has been rapidly developed recently. The separation process is as follows: the feed is placed in contact with upstream side of membrane, the downstream side of the membrane is kept under vacuum or under a stream of inert gas. If one of the components of the liquid mixture can

Preparation of Different Silane-modified Silicalite-1 Membranes and Their Pervaporation Properties for Aqueous Ethanol Solution

A multi-layer mesoporous silicalite-1 membrane supported on commercially available porous alumina tubes was prepared by firstly dip-coating the tubes in silica colloid sol and then using a hydrothermal synthetic process.The mesoporous silicalite-1 membrane was further modified by grafting organosilane compounds with various alkyl chains length(C_nH_(2n+1)(CH_3)_2SiCl;n = 1,3,8,12 and 18).These hydrophobic silicalite-1 membranes containing silane coupling agents effectively removed ethanol from 3 wt.%,5 wt.%and 10 wt.%aqueous ethanol solutions by pervaporation over a temperature range of 303-323 K.The separation factor(a) of ethanol decreased as the ethanol content in the feed solution increased from 3%to 10%whereas the permeation flux(J) basically remained constant.Ethanol separation factors(a) of 7.90-22.24 with total fluxes(J) of 0.76-2.89 kg/(m^2h) were obtained by pervaporation at 3_3-323 K for ethanol feed composition of 3%-10%.

Catalytically active membranes for esterification:A review

Esterification is an important process in the food industry and can be carried out via homogeneous or heterogeneous catalysis.The homogeneous catalyst,despite providing high conversion,can cause corrosion in reactors,which is not observed with the use of heterogeneous catalysts.However,some of these catalysts require a high process temperature and may lose their catalytic activity with reuse.Thus,catalytic membranes have been proposed as a promising alternative.The combination of catalysis and separation in a single module provides greater conversion,reduction of excess reagents,compact industrial plant,making the process more efficient.Within this context,this work aims to present a literature review on the catalytic membrane for the synthesis of esters,improving the understanding of the production and development.This review examines the materials,catalysts used,and synthetic pathways.A comparison between the methods,as well as limitations and gaps in the literature,are highlighted.

Construction of molecule-selective mixed matrix membranes with confined mass transfer structure

Extraordinary mass transfer phenomenon is usually found when the small molecules pass through a confined structure, whose effective size is commensurate with the mean free path of the molecules. Small changes in the confined mass transfer structure(including size, morphology and properties) will lead to significant fluctuations of the mass transfer coefficient. The mass transfer of the penetrant molecules in the dense membranes for pervaporation, gas separation and so on, is located in the scope of confined mass transfer. Incorporating nanofillers into polymer matrix to construct mixed matrix membranes(MMMs) is an effective approach to tune the confined mass transfer structure and enhance the performance of the widely used polymeric membranes. This review focuses on the construction and manipulation of the confined structure in the polymeric membranes via incorporating one-dimensional(1D), two-dimensional(2D) and three-dimensional(3D) fillers.The comparison of the MMMs for pervaporation is summarized, and the research prospective of the MMMs is provided.

Performance of Catalytically Active Membrane Reactors with Different A/V Ratios

Although the performance of membrane reactors (MR) is highly affected by the ratio of membrane area-to-reaction volume, there are few studies on this effect owing to the difficulties associated with reactor manufacture. In this study, an MR with high A/V ratio, a diameter of 35 m, and a height of 0.8 mm was fabricated. Separation performance of this MR was investigated in an n-butanol/water system. Esterification of acetic acid and n-butanol was used as the model reaction to investigate the performance of catalytically active membrane reactors (CAMR) with different A/V ratios. The reaction conversion was 38.59% in the CAMR with the high A/V ratio of 12,497/m, which was much higher than that in other CAMRs, for reaction time of 60 min and W/Vfratio of 0.093 g/mL. Excellent catalytic stability of the CAMR was confirmed by performing long-term stability experiments. © 2017 Tianjin University and Springer-Verlag GmbH Germany

FAU沸石分子筛膜的制备及渗透汽化研究进展

【目的】faujasite(FAU)沸石分子筛膜作为重要的亲水性、大孔径(0.74 nm)的膜材料,在渗透汽化(pervaporation,PV)液体分离领域具有广阔的应用前景。促进FAU沸石分子筛膜的开发、应用,在PV领域的发展应得到重视。【研究现状】综述近年来FAU沸石分子筛膜的制备方法,包括原位合成法、干凝胶法、二次生长法、微波加热法等,分析各种方法的特点;探讨如何通过制备参数调控实现FAU沸石分子筛膜性能提升的策略;总结FAU沸石分子筛膜的PV分离机制,在PV领域的应用进展和所面临的挑战。【展望】有效制备无缺陷的FAU沸石分子筛膜,提高分离性能,应进一步聚焦于FAU沸石分子筛膜的制备方法创新、制备工艺优化和膜结构精密调控;FAU沸石分子筛膜有望在工业分离过程中发挥更大的作用。

聚酰亚胺渗透汽化膜用于有机溶剂脱水的改性研究进展

聚酰亚胺有机高分子聚合物结构内含有氢键,且具有良好的耐溶剂性、易成膜性、高力学性能等优点。聚酰亚胺膜有望在渗透汽化有机溶剂脱水领域得到广泛应用。然而,聚酰亚胺膜高分子链间作用力强,链段排列紧密,往往造成溶剂分子渗透困难、渗透通量低等问题,限制其发展。对聚酰亚胺膜开展改性研究,以提高其渗透通量,同时保持高分离因子,是近年来的主要研究方向。本文对渗透汽化膜分离技术进行了概述,介绍了其工作原理及常用分离膜种类。详细综述了近年来用于渗透脱水的聚酰亚胺膜的改性研究进展,重点评述了共混、掺杂、交联和共聚改性,并分析了四种改性方法的作用原理,对分离性能的影响及其优缺点。最后,对聚酰亚胺膜在渗透汽化分离领域未来的发展方向进行展望,指出需揭示聚酰亚胺聚合物链与溶剂分子间的作用机制,解决渗透通量与选择性之间“trade-off”的制约关系。

两步干凝胶转化法制备UiO-66膜并用于己烷异构体的高效分离

己烷异构体是石化行业重要的基础原料,对其进行高效低能耗分离具有重要的战略意义。金属-有机骨架(MOF)材料由于其精准可调的孔道结构和表面功能,在解决挑战性的己烷异构体分离方面备受关注。本文报道了一种以两步干凝胶转化策略制备连续致密UiO-66薄膜的方法。对UiO-66膜的形成过程与微结构的表征结果表明,两次引入锆凝胶是形成致密膜的关键,一方面锆凝胶和晶种的混合相作为前躯体层为膜的初步生长提供了均匀且丰富的多尺度成核位点,另一方面锆凝胶的二次自转化可以密封UiO-66膜的晶间缺陷。渗透汽化试验证实了两步干凝胶转化法制备的UiO-66膜能够优先渗透直链和单支链烷烃而排阻双支链烷烃。

基于渗透汽化膜分离技术制备无核白葡萄烈酒原酒的工艺优化及其安全性分析

该文以鲜食无核白葡萄为原料,通过单因素结合响应面试验进行优化,确定无核白葡萄烈酒原酒的最佳发酵工艺,并通过测定甲醇、氨基甲酸乙酯(ethyl carbamate,EC)、赭曲霉毒素A(ochratoxin A,OTA)、生物胺(biogenic amine,BA)、铁离子(Fe^(3+))含量,评价无核白葡萄烈酒的安全性。结果表明,无核白葡萄烈酒原酒最佳发酵工艺为酵母添加量0.4 g/L、发酵温度17℃、初始糖度24°Brix,该发酵工艺下的无核白葡萄原酒酒精度为12.2%vol,经过渗透汽化膜分离技术制备的无核白葡萄烈酒酒精度为53%vol,甲醇含量为190.88 mg/L,EC含量为1.02μg/L,未检出OTA,9种BA检出其中4种(色胺、苯乙胺、章鱼胺、亚精胺),总含量为4.074 mg/L,Fe3+含量为1.30 mg/L,均未超过相关限量标准。

Synthesis and separation performance of silicalite-1 membranes on silica tubes

High-performance silicalite-1 membranes were synthesized on silica tubes by in-situ hydrothermal synthesis. By using the “solution-filling (SF)” method, the average flux of membranes with the SF method was improved by about 25% compared to that of the membranes without using the SF method; the flux and the separation factor of the membranes prepared with the SF method for an ethanol/water mixture at 60°C were 0.99 kg/(m2·h) and 73, respectively. It was found that the membranes synthesized on silica tubes exhibited high thermal stability and high reproducibility, and the relatively standard deviations (R.S.D.) of the average flux and separation factor were only 9.6% and 5.6%, respectively, which suggests that the silica support is more suitable than other kinds of supports for preparing high-performance silicalite-1 membranes.