渗透汽化芳烃/烷烃分离膜材料

芳烃/烷烃混合物的分离在石油化工及环保领域都具有重大意义.与传统的萃取精馏等技术相比,渗透汽化膜技术以其清洁、节能和高效的优点,应用于芳烃/烷烃混合物的分离并受到重视.本文综述了渗透汽化芳烃/烷烃分离膜的研究进展,概述了渗透汽化技术的基本原理和应用,重点介绍了用于渗透汽化芳烃/烷烃分离的聚酰亚胺、聚氨酯等高分子膜材料的结构特点和分离性能.总结了膜材料的接枝、共聚和共混,添加传质促进剂的改性方法.分析了渗透汽化芳烃,烷烃分离膜材料的研究思路,在此基础上对渗透汽化芳烃/烷烃分离膜材料的研究方向和发展前景进行了展望.     

渗透汽化优先透醇分离膜

20世纪70年代的能源危机促使了人们对可再生能源-发酵法制备乙醇与节能分离工艺的探求。渗透汽化膜分离技术作为一种新兴的膜分离技术,具有分离效率高、低能耗、易于和发酵装置耦合、易于与其它分离方法联用等显著优点,特别适用于乙醇/水等恒沸混合物体系的分离。本文简要介绍了渗透汽化优先透醇膜的研究背景,总结并分析了用于指导膜材料选择的理论,详细介绍了用于制备优先透醇膜的含硅聚合物、含氟聚合物、有机/无机复合膜材料以及其他聚合物等膜材料的的结构特点、改性方法及膜材料分子结构与渗透汽化性能间的关系,并对不同膜材料对乙醇/水的渗透汽化分离性能进行了总结比较,在此基础上总结了目前渗透汽化乙醇/水分离膜存在的问题,并对其未来的研究方向和发展前景进行了展望。     

渗透汽化复合膜*

渗透汽化是膜科学研究中最活跃的领域之一,在分离液体混合物,尤其是痕量、微量物质的移除,近、共沸物质的分离等方面有独特优势。介绍了渗透汽化膜的种类和复合膜的制备方法。按渗透汽化三大分离体系,即从水相中分离有机物、有机液脱水和有机混合液的分离,综述了近几年渗透汽化复合膜的研究进展。最后,指出了制约其发展的问题和未来发展方向,并对渗透汽化复合膜的应用前景进行了展望。     

MOF-聚合物混合基质膜的制备、改性及其在渗透汽化中的应用

渗透汽化是一种具有能耗低、操作简便等优点的膜分离技术,目前传统聚合物渗透汽化膜在分离性能和稳定性等方面还有欠缺。金属有机框架(MOF)是由金属离子与有机配体以自组装形式组建而成的晶态多孔材料,具有独特的性质,如对目标分子的选择性吸附和分子筛分效应,近年来许多研究表明将MOF作为填料引入聚合物基质中构筑混合基质膜(MMMs)对其渗透汽化性能有很好的促进作用。本文从MOF的不同系列出发,讨论了适用于渗透汽化混合基质膜的MOF种类,分析了MOF-聚合物混合基质膜的制备方法与改性策略,综述了该类混合基质膜在渗透汽化方面(有机溶剂脱水、从稀溶液中回收有机物、有机混合物的分离)的应用进展,总结了用于渗透汽化的MOF-聚合物混合基质膜研究面临的挑战,并对其未来发展提出展望。     

有机液体优先透过渗透汽化膜及其过程

本文回顾了近０年来有机液体优先透过渗透汽化膜的研究与发展状况。包括各种欲分离体系及膜材料的选择、膜的渗透汽化特征表征、影响膜分离性能的各种因素，以及近年来有机液体优先透过ＰＶ膜的一些研究成果。     

渗透汽化膜分离研究的新进展

渗透汽化膜分离技术是当前分离膜研究领域的前沿课题之一.作为化学分离中的重要组成部分,近年来受到高度重视.本文按渗透汽化膜分离的三大类混合液体系有机液脱水、从水相中分离有机物和有机混合液的分离,综述了近几年渗透汽化膜分离技术研究的新进展.其中,又重点报道了有机混合液分离的最新研究成果,将其分为:极性/非极性化合物、芳香烃/脂肪烃体系、芳香烃/脂环烃体系、同分异构体、多元体系和汽油脱硫等六部分进行了详细叙述.文章最后还对渗透汽化膜分离研究进行了展望.     

渗透汽化在化工基础实验中的教学探索

介绍渗透汽化作为化工基础教学实验的开设方式。渗透汽化实验分成课外开放实验(渗透汽化膜制备与表征)和课堂实验(渗透汽化操作)两个阶段进行。学生可在有限的教学时间里,通过考察渗透膜的分离能力和渗透通量随操作条件的变化情况,对渗透汽化实验有较深入的认识。     

聚酰亚胺中空纤维膜用于甲醇/甲基叔丁基醚的分离

甲醇／甲基叔丁基醚混合物的膜法分离，大多采用渗透汽化方法，少有采用蒸汽渗透法。用聚酰亚胺中空纤维膜，对以蒸汽渗透和渗透汽化两种方式分离甲醇／甲基叔丁基醚混合物（甲醇质量分数为0．01－0．30）的效果进行了对比。结果显示，在甲醇质量分数低于0．05时，蒸汽渗透较渗透汽化法的分离性能优越。     

渗透汽化膜表面化学结构设计研究

综述了近年来渗透汽化膜表面结构设计调控的研究进展。膜表面结构的设计与优化是提高其分离性能的重要方法。然而高分子表面具有环境响应性,这往往导致高分子材料在使用环境中失去在表面设计时所期待的性能。因此,高分子膜表面的环境响应性是在对膜表面进行设计和调控过程中必须考虑的因素。本文介绍了渗透汽化膜表面结构设计的方法,重点阐述了高分子膜表面环境响应特性对膜表面性质以及渗透汽化性能的影响。指出了利用高分子膜的表面重构行为可以对其表面结构进行优化,从而有效地提高膜的分离选择性。     

丙烯酸交联壳聚糖渗透汽化膜研究（Ⅱ）──乙醇／水混合液的渗透汽化分离性能

丙烯酸交联壳聚糖渗透汽化膜研究（Ⅱ）──乙醇／水混合液的渗透汽化分离性能钟伟，李文俊，葛昌杰，陈新（复旦大学高分子科学系，上海，２００４３３）关键词交联壳聚糖，渗透汽化，丙烯酸，乙醇／水混合液混合液体的渗透汽化（简称ＰＶ）膜分离自８０年代实现工业化以...     

Composite hybrid membrane of chitosan-silica in pervaporation separation of MeOH/DMC mixtures

Chitosan-silica hybrid membranes (CSHMs) were prepared by cross-linking chitosan (CS) with 3-aminopropyl-triethoxysilane (APTEOS). The dynamic behaviors of the CS membrane and the CSHM were investigated in pervaporation (PV) of methanol/dimethyl carbonate (MeOH/DMC) mixtures. The membranes were characterized by X-ray diffraction (XRD), contact angle meter, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The transition state of PV processes were studied. During the PV processes, the amorphous region of the membranes increases and the contact angle between MeOH and the membrane decreases within a range of operating time and then remains almost constant implying a reconstruction occurred on the membrane surface. The silica is well distributed in the CSHM matrix and the thermal stability of the CSHM is enhanced. The time for a PV process to reach a steady state decreases with increasing MeOH concentration or feed temperature, and it is longer for the CSHM than the CS membrane under the same operating condition. Swelling experiments show that the degree of swelling (DS) is greatly depressed by cross-linking CS with APTEOS. Sorption data indicate that the selectivity of solubility and diffusion of the CSHM are greatly improved over the CS membrane. The CSHM presents superior separation behaviors over other membranes with a flux of 1265 g/(hm(2)) and separation factor of 30.1 in PV separation of 70 wt% MeOH in feed at 50 degrees C.     

PEBA/PVDF blend pervaporation membranes: preparation and performance

In the present research, novel polyether block amide (PEBA)/polyvinyldene fluoride (PVDF) blend pervaporation (PV) membranes were prepared for the removal of isopropyl alcohol (IPA) from the aqueous solution. The membranes obtained at PEBA/PVDF ratios of 100/0, 95/5, and 90/10 were characterized using scanning electron microscopy, thermogravimetric analysis, water contact angle measurement, and tensile test. Moreover, the PV performance of the membranes was assessed via separation of IPA from the aqueous solution. The blended membranes exhibited higher hydrophobicity and separation factor as well as lower permeability in comparison with the pure PEBA membrane. The blended membrane that was prepared at PEBA/PVDF ratio of 95/5 was found as the optimum membrane providing PV separation index of 3171 that appeared to be the maximum value. Copyright © 2016 John Wiley & Sons, Ltd.     

Polyelectrolyte complex membranes – surface and permeability properties

In order to study, how the membrane hydrophilicity influences the pervaporation (PV) separation properties in dehydration of alcohols, two polyelectrolyte complex (PELC) membranes, based on interfacial reaction of polyanionic sodium salt of sulfoethyl cellulose (SEC) with polycationic poly[dimethyl(diallyl)ammonium chloride] (pDMDAAC), or cationic surfactant benzyl(dodecyl)dimethylammonium chloride (BDDDMAC), were prepared and tested. Contact angle measurements on membrane surfaces made in various media showed that the membrane hydrophilicity, in the sense of water wettability, had not influence neither to flux nor selectivity in the PV dehydration process. On the contrary, the membrane wettability determined by contact angle measurements in the real water/alcohol separation mixture, correlated very well with the PV experiments. These findings are confronted with the solution-diffusion PV model.     

Water-alcohol Separation by Pervaporation through Zeolite Modified Poly(amidesulfonamide)s (PASAs)

A series of poly(amidesulfonamide)s (PASAs) which have been synthesized in our laboratory possess good membrane fabrication properties^[1]. The potential use of these membrane materials in RO, UF and PV were demonstrated^[2,3]. Reminiscent to the PV performance of other glassy polymers, most of these materials exhibit a fairly high separation factor albeit a permeation flux below 35 g m^-2 h^-1 in the PV separation of aqueous alcohol mixtures. To have a real application prospect in PV, the permeation flux through the membranes has to e further improved. The present work represents our effort to upgrade the separation characteristics of PASAs by blending with inert hydrophilic zeolites. Three types of PASAs (structure shown in Figure 1) were selected to be fabricated by blending different amount of zeolite NaA or NaX. The zeolite filled membranes were characterized by SEM, IR spectroscopy, sorption measurements and wide-angle X-ray diffraction. By adding proper amount of NaA into the polymer casting solutions, the resultant zeolite filled membranes exhibited improvement in both selectivity and permeability in the separation of 10% aqueous solutions of ethanol, propan-l-ol and propan-2-ol, as compared to the zeolite free membrane (Table 1).     

Preparation of polyphenylsulfone/graphene nanocomposite membrane for the pervaporation separation of cumene from water

Polyphenylsulfone (PPSU) was applied for the first time in the hydrophobic PV process. Nanocomposite membranes of PPSU/graphene (Gr) nanosheets were prepared and used to separate isopropyl benzene (cumene) from water via pervaporation (PV). Analysis of the mechanical properties of the membranes showed that the tensile strength and Young's modulus had an increasing trend with the incorporation of Gr into PPSU. The water contact angle of the membranes had a rising trend with the addition of Gr, confirming the improved hydrophobicity of membranes. In the PV experiments, the membrane containing 3.5 wt% Gr provided the highest separation factor, which was 4.5-fold as much as that of the neat PPSU membrane. Cumene separation from water by the PPSU/3.5 wt% Gr membrane was associated with the total flux of 132.73 gMH, the separation factor of 1566.36, and the PSI of 208,124.8 gMH.     

Dehydration of aqueous acetonitrile solution by pervaporation using PVA–iron oxide nanocomposite membrane

Pervaporative performances were investigated for dehydration of water–acetonitrile using nanocomposite metal oxide and Pervap^® 2202 membranes. Poly (vinyl alcohol) based nanocomposite metal oxide membranes were prepared through co-precipitation of different amounts of Fe (II) and Fe (III). The freestanding nanocomposite metal oxide membranes were characterized by Transmission electron microscopy and X-ray diffraction. Sorption studies evaluated the extent of interaction and degree of swelling of the membranes. Fe containing PVA polymer matrix showed improved flux and selectivity. In order to observe simultaneous effect of flux and selectivity, pervaporation separation index showed 10 wt.% iron oxide containing membrane is the most amongst all tested. The diffusion coefficients were calculated using pervaporation results and sorption kinetics data. An attempt was made to predict sorption selectivity thermodynamically. PV separation factor was observed to be governed by sorption and/or diffusion phenomena and sorption selectivity was found to be higher than PV separation factor. Prediction of concentration profile in the membrane was also attempted and the results showed that water concentration in the membrane drops down with increase in membrane thickness.     

Different viscosity grade sodium alginate and modified sodium alginate membranes in pervaporation separation of water + acetic acid and water + isopropanol mixtures

Different viscosity grade sodium alginate (NaAlg) membranes and modified sodium alginate membranes prepared by solution casting method and crosslinked with glutaraldehyde in methanol:water (75:25) mixture were used in pervaporation (PV) separation of water+acetic acid (HAc) and water+isopropanol mixtures at 30 °C for feed mixtures containing 10–50 mass% of water. Equilibrium swelling experiments were performed at 30 °C in order to study the stability of membrane in the fluid environment. Membranes prepared from low viscosity grade sodium alginate showed the highest separation selectivity of 15.7 for 10 mass% of water in the feed mixture, whereas membranes prepared with high viscosity grade sodium alginate exhibited a selectivity of 14.4 with a slightly higher flux than that observed for the low viscosity grade sodium alginate membrane. In an effort to increase the PV performance, low viscosity grade sodium alginate was modified by adding 10 mass% of polyethylene glycol (PEG) with varying amounts of poly(vinyl alcohol) (PVA) from 5 to 20 mass%. The modified membranes containing 10 mass% PEG and 5 mass% PVA showed an increase in selectivity up to 40.3 with almost no change in flux. By increasing the amount of PVA from 10 to 20 mass% and keeping 10 mass% of PEG, separation selectivity decreased systematically, but flux increased with increasing PVA content. The modified sodium alginate membrane with 5% PVA was further studied for the PV separation of water+isopropanol mixture for which highest selectivity of 3591 was observed. Temperature effect on pervaporation separation was studied for all the membranes; with increasing temperature, flux increased while selectivity decreased. Calculated Arrhenius parameters for permeation and diffusion processes varied depending upon the nature of the membrane.     

Comparative study of the separation of methanol–methyl acetate mixtures by pervaporation and vapor permeation using a commercial membrane

In the present study, the permeation behavior of methanol and methyl acetate in the pervaporation (PV) experiments are compared with those in vapor permeation (VP) experiments using a PVA-based composite membrane. Experiments have been carried out to study the selectivity and mass transport flux of the systems under varying operations conditions of feed temperature (40–60 °C) and feed methanol concentrations (2–34 wt%). The selected membrane was found to be methanol selective. Results show higher permeation flux but a similar separation factor for methanol in PV than in VP. For PV operation, the resulting separation factor at 60 °C shows a monotonous decrease (6.4–4.1) as the alcohol concentration in the feed mixture increases (2.3–34 wt%), whereas the total flux increases from 0.97 to 7.9 kg m⁻² h⁻¹. Based on the solution-diffusion theory, a mathematical model that describes satisfactorily the permeation fluxes of methanol and methyl acetate in both the PV and VP processes has been applied. The fluxes of both permeants can be explained by the solution-diffusion model with variable diffusion coefficients dependent on MeOH concentration in the membrane. Both PV and VP processes can be described with the same model but using different fitting parameters.