Reverse osmosis performance of organosilica membranes and comparison with the pervaporation and gas permeation properties

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300^°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90^°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013     

Experimental study and modeling of organic solvent reverse osmosis separations through organosilica membranes

Exceptionally stable, mechanically robust, and highly methanol-selective organosilica membranes, including Bis(triethoxysiyl)acetylene (BTESA), fluorine-doped bis(triethoxysiyl) methane (F-BTESM), and Cetyltrimethylammonium chloride-etched bis(trimethoxysiyl)hexane (CTAC-BTMSH), were prepared and utilized for organic solvent reverse osmosis (OSRO) separations. The BTESA membrane showed optimal separation performance regarding methanol/toluene and possessed the highest levels of both permeation flux and rejection. Continuous measurements were performed to highlight the molecule size/shape discrimination of BTESA membranes using compounds such as methanol/methyl acetate, methanol/dimethyl carbonate (DMC) and methanol/methyl tert-butyl ether (MTBE). Also, a generalized solution-diffusion model was successful in predicting the permeation behaviors through organosilica membranes when used in an OSRO modality, and proved to be capable of accurate predictions on pressure-dependent permeation flux and rejection for a wide range of feed concentrations (0–55 wt%) and pressures (2–14 MPa). This study lends important insight for the development of organosilica membranes and process design for the energy-efficient OSRO separation of organic liquids.     

乙烯基桥联有机硅膜的羧基化改性及反渗透性能研究

利用1,2-二(三乙氧基硅基)乙烯(BTESEthy)和硫代苹果酸(MSA)的巯基-烯点击反应对桥联有机硅进行羧基化改性,以管式α-Al₂O₃微滤膜为支撑体制备羧基官能化的桥联有机硅膜。通过傅里叶变换红外光谱(FT-IR)、激光粒度仪(DLS)、智能重量分析仪(IGA)和扫描电镜(SEM)等对膜结构和表面性质进行了表征。量子化学计算表明羧基化改性的有机硅网络拥有更加致密的孔结构和更高的水亲和力。将改性的BTESEthy-MSA膜用于反渗透脱盐,系统考察了BTESEthy-MSA膜反渗透脱盐性能。实验结果表明,与BTESEthy膜相比,羧基化改性的BTESEthy-MSA膜的水渗透率和盐截留率均有所提高。同时,BTESEthy-MSA膜表现出优异的水热稳定性和耐氯性能。在250 h的长期反渗透测试中,BTESEthy-MSA膜的水渗透率高达3.2×10^-13 m³/(m²·s·Pa),NaCl截留率始终保持在94.7%以上。     

优先透过有机物渗透汽化膜研究进展

近年来膜分离技术被广泛应用于有机物的分离回收。渗透汽化能有效地分离共沸混合物、近沸混合物、异构体和热敏性化合物等有机物。渗透汽化以成本低、条件温和、设备简单、无污染等优点在有机物分离回收领域有着巨大优势，可广泛的应用于工业生产。该文以优先透过有机物为主旨，首先分析了材料对膜结构和特点的影响。其次综述了制备方法和改性方法对膜性能的影响。重点讨论了膜在有机混合物分离回收领域的应用。最后，对目前渗透汽化技术所存在的问题做出了总结，对未来的研究方向和研究思路进行了展望。未来优先透过有机物渗透汽化膜的研究应借助新的计算工具，侧重于材料选择、制备方法和改性方法的改进，如探索具有多功能化学基团和具有明确层次结构的多孔填料的聚合物材料等，使优先透过有机物渗透汽化膜具有更加广阔的应用前景。     

用于渗透汽化的有机—无机杂化膜研究进展

近年来,有机-无机杂化膜的研究受到学术界广泛关注,随着有机-无机杂化膜制备方法的多样化和分离性能的提高,其研究前景也越来越广阔。该文首先分析了有机-无机杂化膜相比于普通无机膜和有机膜在结构和性能上存在的优势,其次综述了有机-无机杂化膜的制备方法以及其在醇类、有机酸等有机溶剂或有机混合物中的分离提纯应用,重点讨论了其在渗透汽化中的应用。最后,对有机-无机杂化膜的研究前景进行展望。未来有机-无机杂化膜的研究应借助于新的计算工具,侧重于材料的选择或制备方法的改进,如探索具有多功能化学基团和具有明确层次结构的多孔填料的聚合物材料等,使有机-无机杂化膜具有更加广阔的应用前景。     

Separation of organic solvent from dilute aqueous solutions and from organic solvent mixtures through crosslinked acrylate copolymer membranes by pervaporation

The composite membranes of acrylate polymers and porous substrate were prepared. The separation of the organic solvent–water mixtures and the organic solvent–organic solvent mixtures through these membranes by pervaporation was investigated. The acrylate copolymer membrane showed the organic solvent permselectivity for the separation of the organic solvent–water mixture, especially for the chlorinated hydrocarbon–water mixture separation. The high organic solvent permselectivity should be governed by solubility selectivity. The influence of the ester residue of acrylate on the phenol–water mixture separation was observed. The copolymerization of the macromonomers containing the polystyrene, poly(methyl methacrylate), and polydimethylsiloxane chain had a small effect on the separation of the chlorinated hydrocarbon–water mixture. High flux and low selectivity of organic solvent were observed in the case of the organic solvent mixture separation through the n-butylacrylate membrane. The difference of permeability of organic solvent was observed for the acrylate copolymer which has various structures of ester residue. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1483–1494, 1998     

二元水溶液在渗透蒸发膜中的传质模型

对二元水溶液在渗透蒸发膜中的传质过程进行了研究,基于Flory Huggins高分子热力学理论和Fujita自由体积理论建立了改进的溶解 扩散模型。在该模型中考虑了组分间相互作用,组分体积分数、温度、膜材料和渗透物特性对传质过程的影响,考察了组分体积分数对相互作用参数的影响,膜材料对水的溶解选择性的影响,原料液组分体积分数、操作温度以及膜厚对渗透通量和分离因子的影响。     

Polymer membranes for separating organic mixtures

Polyvinyl alcohol (PVA), polyacrylonitrile (PAN), and cellulose ester were respectively chosen as the separation layer and the support in the composite membranes based on the concept of the solubility parameter and the permselectivities for separating ethanol/water mixture, isopropanol/water mixture, and caprolactam/water mixture. The effects of the membrane materials and the construction of the composite membrane on the separation performance were preliminary discussed. The separation performance of the membranes prepared by several making‐membrane techniques, i.e., the polymer solution making‐membrane technique, and the membrane treatment technique (heat treatment, organic solvent modification) were presented. The composite membranes of PVA/PAN and PVA/cellulose acetate, and cellulose triacetate hollow fiber membrane modified, which possess good performance in separating the organic systems, were developed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1160–1164, 2006     

Oxidative degradation of polyamide reverse osmosis membranes: Studies of molecular model compounds and selected membranes

Selected aromatic amides were used to model the chemical reactivity of aromatic polyamides found in thin‐film composite reverse osmosis (RO) membranes. Chlorination and possible amide bond cleavage of aromatic amides upon exposure to aqueous chlorine, which can lead to membrane failure, were investigated. Correlations are made of the available chlorine concentration, pH, and exposure time with chemical changes in the model compounds. From the observed reactivity trends, insights are obtained into the mechanism of RO membrane performance loss upon chlorine exposure. Two chemical pathways for degradation are shown, one at constant pH and another that is pH‐history dependent. An alternative strategy is presented for the design of chlorine‐resistant RO membranes, and an initial performance study of RO membranes incorporating this strategy is reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1173–1184, 2003     

Preparation and characterization of high-performance dehydrating pervaporation alginate membranes

In a previous work, sodium alginate dense membranes demonstrated a good combination of selectivity and permeation flux for dehydrating organic solvents by pervaporation. In this article, the pervaporation performances of alginate composite membranes has been investigated to find out the best condition of membrane formation and the optimum operating conditions. Some ultrafiltration membranes made of poly-(vinylidene fluoride), polyacrylonitrile, and hydrolyzed polyacrylonitrile—either commercially available or prepared in our laboratories—were used as supports for the composite membranes. Sodium alginate dense membranes, modified through ion exchange of sodium with multivalent metal ions (such as Al³⁺, Cr³⁺, Fe³⁺, and Mg²⁺) have also been prepared, and their permselectivities have been tested for the water–ethanol mixture. An interesting stability of the modified membranes in long-term operation is expected. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 959–968, 1998     

有机物优先透过渗透汽化膜的改性方法研究进展

有机物优先透过渗透汽化是一种能耗低、投资少、操作简便的分离技术,综述了其发展现状,重点介绍了其渗透膜的改性方法研究进展,包括填充法、共聚/共混法和接枝法,并对其发展前景进行了展望。     

纳滤/反渗透膜处理重金属废水的性能

The performance of different nanofiltration （NF） and reverse osmosis （RO） membranes was studied in treating the toxic metal effluent from metallurgical industry. The characteristics and filtration behavior of the processes including the wastewater flux, salt rejection and ion rejection versus operating pressure were evaluated. Then the wastewater flux of RO membrane was compared with theoretical calculation using mass transfer models, and good consistency was observed. It was found that a high rejection rate more than 95% of metal ions and a low Chemical Oxygen Demand （COD） value of 10 mg·L^-1 in permeate could be achieved using the RO composite membrane, while the NF rejection of the salt could be up to 78.9% and the COD value in the permeate was 35 mg·L^-1. The results showed that the product water by both NF and RO desalination satisfied the State Reutilization Qualification, but NF would be more suitable for large-scale industrial practice, which offered significantly higher permeate flux at low operating pressure.     

Pervaporation via silicon-based membranes: Correlation and prediction of performance in pervaporation and gas permeation

Pervaporation (PV) is a membrane technology that holds great promise for industrial applications. To better understand the PV mechanism, PV dehydrations of various types of organic solvents (methanol, ethanol, iso-propanol, tert-butanol, and acetone) were performed on five types of organosilica and two types of silicon carbide-based membranes, all with different pore sizes. Water permeance was dependent on the types of organic aqueous solutions, which suggested that organic solvents penetrated the pores and hindered the permeation of water. In addition, water permeance of various types of membranes in PV was well correlated with hydrogen permeance in single-gas permeation. Furthermore, a clear correlation was obtained between the permeance ratio in PV and that in single-gas permeation, which was confirmed via the modified-gas translation model. These correlations make it possible to use single-gas permeation properties to predict PV performance.     

Study of the structure and transport of asymmetric polyamide membranes for reverse osmosis using the electron spin resonance (ESR) method

The electron spin resonance technique (ESR) was used to study the structure and transport of asymmetric aromatic polyamide membranes. TEMPO (2,2,6,6-tetramethyl-1-piperridinyloxy free radical) was used as a spin probe that was brought into the membrane either by (a) immersion ofthe membranes in aqueous TEMPO solutions, (b) reverse osmosis (RO) experiments with feed solutions involving TEMPO or (c) blending TEMPO in casting solutions. The membranes were further tested for the separation of sodium chloride and TEMPO from water by RO. It was concluded that aromatic polyamide membranes contain water channels in the polymer matrix like cellulose acetate membranes. The presence of such water channels allows aromatic polyamide membranes to be used as RO membranes. The diffusion of organic solutes through the water channels seems much slower in aromatic polyamide membranes than in cellular acetate membranes, which probably causes a higher separation of organic solutes by aromatic polyamide membranes than cellulose acetate membranes. A comparison was made with other RO membranes (cellulose acetate, CA) and ultrafiltration membranes (polyethersulphone, PES). It was observed that the ESR technique can be used to study the structure of OF and RO membranes. The presence of water channels in the polymer matrix seems indispensable for the RO membrane.     

反渗透膜的污染及其化学清洗

反渗透膜的污染是反渗透系统应用中最大的问题之一,及时的化学清洗可有效地恢复反渗透膜的性能、延长其使用寿命。对反渗透膜的污染及其化学清洗方法进行了综述,主要内容包括反渗透膜污染物的种类,污染物形成的原因,以及清洗时机的选取,清洗药品的选择,影响清洗效果的主要因素、清洗系统的构成,化学清洗的方法和清洗效果的评价指标。     

PA/PEG交联共聚反渗透膜的制备及耐污染性能

以聚丙烯腈（PAN）超滤膜为基底,在均苯三甲酰氯（TMC）和间苯二胺（MPD）界面聚合反应过程中引入聚乙二醇（PEG）,制备聚酰胺（PA）/PEG反渗透复合膜。利用傅里叶红外光谱（FTIR）、X射线光电子能谱（XPS）、场发射扫描电镜（FE-SEM）和原子力显微镜（AFM）等对膜的结构和物化性质进行了表征。考察了PEG分子量、PEG加入量、热处理温度及时间对膜反渗透性能的影响,并系统考察了膜对十二烷基硫酸钠（SDS）、十二烷基三甲基溴化铵（DTAB）以及牛血清蛋白（BSA）三种不同荷电性典型污染物的耐受性能。实验结果表明,相比于未改性的PA反渗透膜,PEG交联共聚反渗透膜的盐截留率和通量恢复率均有所提高。其中PA/PEG1000-0.1膜渗透通量为3.96kg/(m²?h),NaCl表观截留率为97.5%,并且对于SDS、DTAB和BSA都表现出较高的耐污染性,其中,SDS污染清洗后膜的通量恢复率可达89.4%。     

Removal of organic substances from aqueous solutions by reagent enhanced reverse osmosis

The reagent enhanced reverse osmosis treatment of aqueous solutions containing phenol and its derivatives has been studied. A combination of the reverse osmosis with the oxidation of organic substances by hydrogen peroxide in the presence of FeCl₂ salt as a catalyst was shown to lead to the effective removal of phenol and its derivatives from aqueous solutions. The phenol catalytic decomposition was believed to occur not only in the bulk solution but also on the membrane surface. This phenomenon is of particular interest, but additional studies are necessary. In the case of solutions containing lignosulphonates (LS), a combination of the reverse osmosis treatment with the LS oxidation by hydrogen peroxide was found to provide the high degree of solution purification from both organic substances and inorganic salts. Furthermore, it shows a possibility for the recirculation of water.     

Dehydration of glycerin/water mixtures by pervaporation using homo and copolymer membranes

Separation characteristics of glycerol/water mixtures were studied using hydrophilic poly(acrylonitrile-comethacrylic acid) (PANMAC), poly(acrylonitrile-co-hydroxyethyl methacrylate) (PANHEMA), Poly(vinyl alcohol) GFT-1001, and poly(vinyl alcohol) (PVA) crosslinked with maleic anhydride (PVAManh) membranes. All membranes were found to be highly water selective. PVAManh membrane yielded the highest permeation flux for water over the entire range of water concentration studied. Homopolymers (PVAManh and GFT-1001) gave better permeation rates than copolymer membranes (PANHEMA and PANMAC). But the swelling of homopolymers is nuch greater than that of copolymers, which is why PVA membranes have poor longevity. No effect on selectivity of the membrane was observed with a change in operating parameters. No decomposition/polymerization of glycerin was observed, as there was no involvement of high temperatures as there is with distillation. A comparison of pervaporation with vapor-liquid equilibrium data showed that pervaporation of glycerin/water mixtures yielded better selectivity than vapor-liquid equilibrium, particularly for glycerol concentrations above 90 wt%.     

反渗透膜有机污染的研究进展

介绍了反渗透进水中一些主要有机污染物质的污染机理以及操作条件、膜自身特性、溶液化学性质对于污染过程的影响,还综述了预处理技术、清洗方法以及通过膜的表面改性等措施来控制反渗透膜的有机污染,最后指出了目前研究中需关注的一些问题。     

反渗透膜的背压损坏分析及相关安全性研究

背压损坏是反渗透膜元件使用中常见的故障之一,一旦发生则会对反渗透膜造成永久性损坏,无法修复。对反渗透膜元件背压损伤的位置以及背压对膜片造成的损伤进行深入分析,同时归纳了导致反渗透系统背压产生的设计和运行因素,提出现场判别背压损伤的方法。依托工业示范装置对带背压运行的反渗透系统开关机过程进行了模拟,并通过实时数据采集对全过程进行监控分析,对其安全性进行论证。