Preferential Adsorption and Selective Permeation of Alcohol/Hydrocarbon Mixtures in Reverse Osmosis

Abstract

In binary mixtures of alcohols and hydrocarbons there are two types of reverse osmosis performances. These are selective permeation of the alcohol and selective permeation of the hydrocarbon. Liquid chromatography results have been used to predict the selective permeation of reverse osmosis membranes where the membranes may be difficult to fabricate as well as to determine performance limits in terms of separation. These results are of interest for the production of oxygenated fuel blending agents where specifications require the removal of unreacted methanol for further processing and distillation is not viable.     

The Effect of Pulsatile Flows on the Transport Across Membranes: An Analytical and Experimental Study

Abstract

Pulsatile flows have shown to increase the permeation flux in reverse osmosis studies and to reduce fouling that exists in using membranes for separation processes. However, this study demonstrates that permeation from the inside of a hollow fiber with a membrane boundary to the outside decreases once pulsations are added to the inside of the membranes. The increase in the axial flux due to the flow pulsations are the reason for the increased permeation in reverse osmosis and the decrease in transport from inside to outside. An analytical model for a two‐dimensional system is presented along with experimental results in separating oxygen from air using polycarbonate based hollow fiber membranes.     

Concentration and pressure dependence of rate of membrane permeation

The permeation of water and sodium chloride in cellulose acetate membranes has been examined over a wide range of concentration and pressure. The results obtained from reverse osmosis experiments have been used to evaluate relations derived on the assumption that permeation of both solution components takes place by diffusion down a concentration gradient in the membrane. With the aid of equilibrium and raidoactive tracer measurements, most of the deviations could be attributed to nonconstancy of the diffusion, and, especially, the distribution coefficients of water. A comparison of the net flux in reverse osmosis with the rate of tracer permeation in the same membrane provided positive evidence to show that hydrodynamic flow under pressure cannot account for the water flux through the membrane. Differences in the shape of the distribution isotherms for salt and water between solution and membrane provide an explanation for the high selectivity of cellulose acetate membranes in favor of water.     

正渗透过程中汲取质反向渗透研究进展

正渗透(FO)作为一种浓度驱动的膜技术,因其膜污染轻、能耗低和回收率高等优点而逐渐成为膜技术领域的研究热点之一。汲取质的反向渗透是正渗透过程中不可忽视的现象,但其研究相对比较滞后。本文主要介绍了汲取质反渗模型的研究进展,分析了渗透压差、膜表面流速、膜结构与膜材料、温度、汲取质种类、膜取向、离子水力半径等因素对汲取质反向渗透的影响情况,并发现汲取质的反向渗透通量可由其浓度或汲取液渗透压的一元多项式表达。总体而言,FO模式的汲取质反渗模型经过不断发展已相对比较完善,而压力阻尼渗透(PRO)模式的反渗模型则缺陷较大,有待进一步研究;此外,关于汲取质反渗过程影响因素及其影响机制的研究对于汲取质、膜材料的选择与开发,以及正渗透过程的优化均具有重要的指导作用,因此会引起越来越多的关注。     

The mechanism of liquid transport through swollen polymer membranes

The pressure-driven transport of liquids employed in reverse osmosis has been shown to occur by a solution-diffusion mechanism in highly swollen polymer membranes. A theory based on this mechanism was successfully used earlier to correlate permeation fluxes for such membranes. Positive confirmation of this theory is provided here by direct measurement of the proposed concentration gradient. A study of the temperature dependence of the liquid diffusion coefficient in the polymer membrane has provided additional evidence of a hydrodynamic regime of diffusion in highly swollen membranes. It is also shown that the proposed ceiling flux in reverse osmosis is equal to the pervaporation flux.     

反渗透技术在废水处理中应用的研究进展

反渗透技术是一种高效、易操作的液体分离技术,同传统的废水处理方法相比具有处理效果好,可实现废水的循环利用和对有用物质回收等优点。文章简要介绍了反渗透技术的基本原理,重点介绍了反渗透技术在垃圾渗滤液、矿区污水、钢铁工业废水、电厂废水处理中的应用研究进展状况。并讨论了反渗透膜技术的预处理、反渗透膜污染及清洗和反渗透技术的发展前景。     

Pervaporation und Gaspermeation — Grundlagen der Prozeßentwicklung

Pervaporation and gas permeation – fundamentals of process development . Non-porous membranes represent the basis of reverse osmosis, of pervaporation, and also of gas permeation. In each case, economic viability was achieved only when it proved possible to use this kind of membrane in its asymmetric form in each of the processes concerned. Starting from the mass transfer in the membrane, the influence of each of the following points on plant design for pervaporation and gas permeation is discussed: 1. asymmetry of the membranes; 2. concentration polarization; 3. flow in the module; 4. the pressure drop; and 5. the heat transfer problem (exists only for pervaporation). In connection with the flow in the modules, the economics of series of membranes and membrane columns are compared. In conclusion, a number of applications are discussed which demonstrate where economically sound uses of the two processes are to be found.     

Highly permeable reverse osmosis membranes incorporated with hydrophilic polymers of intrinsic microporosity via interfacial polymerization

Enhancing the water permeation while maintaining high salt rejection of existing reverse osmosis (RO) membranes remains a considerable challenge. Herein, we proposed to introduce polymer of intrinsic microporosity, PIM-1, into the selective layer of reverse osmosis membranes to break the trade-off effect between permeability and selectivity. A water-soluble a-LPIM-1 of low-molecular-weight and hydroxyl terminals was synthesized. These designed characteristics endowed it with high solubility and reactivity. Then it was mixed with m-phenylenediamine and together served as aqueous monomer to react with organic monomer of trimesoyl chloride via interfacial polymerization. The characterization results exhibited that more “nodule” rather than “leaf” structure formed on RO membrane surface, which indicated that the introduction of the high free-volume of a-LPIM-1 with three dimensional twisted and folded structure into the selective layer effectively caused the frustrated packing between polymer chains. In virtue of this effect, even with reduced surface roughness and unchanged layer thickness, the water permeability of prepared reverse osmosis membranes increased 2.1 times to 62.8 L·m^-2·h^-1 with acceptable NaCl rejection of 97.6%. This attempt developed a new strategy to break the trade-off effect faced by traditional polyamide reverse osmosis membranes.     

膜法海水淡化系统在华能威海电厂的应用

随着我国水资源的日益匮乏,海水淡化技术不断应用于工业中。华能威海电厂三期海水淡化系统设备为笔者所在公司提供,海水作为该厂锅炉补给水水源,采用了超滤(UF)-海水反渗透(SWRO)-一级反渗透-二级反渗透-电去离子技术(EDI)全膜法制备。其中能量回收作为海水淡化系统的重要部分,本文将介绍几种常用的能量回收装置,并详细介绍膜法海水淡化系统在该厂中的应用。     

Improving permeation flux by pulsed reverse osmosis

Pulsed and nonpulsed reverse osmosis experiments were conducted with a sucrose solution in cylindrical cellulose acetate membranes. For pulsing frequencies up to 1 Hz, permeation increases of more than 70 per cent were observed. A simple quasisteady-state theory for concentration polarization based on a film model of mass transfer describes the increase.     

The use of direct osmosis tests as complementary experiments to determine the water and salt permeabilities of reinforced cellulose acetate membranes

In this article the use of the direct osmosis test as a complementary experiment to the reverse osmosis test is described. The membranes investigated are cellulose acetate membranes reinforced with mineral fillers. In both tests the same influence of the type of fillers on the water permeability coefficients is found. The salt permeability coefficients indicate the presence of pressure sensitive defects in the reinforced membranes. The direct osmosis test is found to be a suitable test to confirm and predict the membrane properties under reverse osmosis conditions.     

Membranverfahren zur Fraktionierung von Gemischen mit organischen Komponenten

Membrane processes for fractionating mixtures with organic components. The maximum demand that can be placed on development of processes for removal of contaminants from waste water and waste gases is that the separated substances can be recovered for use. In this context, membrane processes are attracting steadily increasing interest because the separated substances are changed neither chemically, nor biologically, nor thermally. Two examples, in which solvent mixtures are recovered from waste water and waste gases by means of reverse osmosis, pervaporation, and gas permeation, are cited to demonstrate the potential of the method. The examples, are preceded by a joint consideration of the three above-mentioned membrane processes, which all use socalled pore-free solution-diffusion membranes. The limitations, which result from practical limits of the driving force and the respective resistances to transport are discussed in detail.     

反渗透技术在碳酸钾生产废水处理中的应用

对碳酸钾生产中产生的废水进行了概述,针对目前生产情况和环保要求,经过多方面探讨,确定采用反渗透膜技术处理该废水,介绍了反渗透膜处理技术的工艺流程,详细说明了反渗透处理废水的应用经验及效果。分析了反渗透的优势与不足,提出了今后的改进设想。     

Studies on desalination by reverse osmosis

The structure of cellulose acetate membranes used for desalination in the process of reverse osmosis has been examined. By means of a technique involving aqueous solutions of the stain Biebrich Scarlet, the membranes are shown to consist of two regions, one of which acts as a mechanical support for the much thinner desalinating layer. The phenomenon of asymmetric permeation across these membranes has been studied and shown to be a consequence of the two-layer structure of the membrane.     

Economic comparison of transverse and longitudinal flow hollow fiber membrane modules for reverse osmosis and ultrafiltration

The presently used hollow fiber membrane modules consist of a bundle of fibers in a cylindrical polymer or metal shell parallel to the shell axis. The feed solution flows either through the lumen or at the outside parallel to the fibers. This paper compares the performance of these modules with a new transverse flow module where the hollow fibers are positioned perpendicularly to the flow direction. For both types of modules the product costs are calculated for desalination by reverse osmosis and Dextran concentration by ultrafiltration. These calculations are based on literature data. The main conclusion is that the application of the tr‘ansverse flow module is only attractive if the permeation resistance is mainly determined by the hydrodynamics (ultrafiltration) and not attractive if the membrane permeability is the main resistance (reverse osmosis).     

Formalized poly(vinyl alcohol) membranes for reverse osmosis

The permeation properties of formalized poly(vinyl alcohol) membranes are described. The interest of this work is centered on the properties relevant to desalination by reverse osmosis. These membranes, when properly prepared, showed reasonably high water permeability, high salt rejection, and stability in the presence of acids and alkalies.     

PVA/TEOS crosslinked membranes incorporating zinc oxide nanoparticles and sodium alginate to improve reverse osmosis performance for desalination

Pure water is becoming less available with increases in world population, so seawater desalination is becoming more important. For efficient seawater desalination, this paper proposes a novel mixed matrix membrane (MMM) based on the deposition of a poly(vinyl alcohol) (PVA) nanofibrous active layer on a 3-triethoxysilylpropylamine-functionalized cellulose acetate substrate. The active layer is fabricated by utilizing a tetraethyl orthosilicate–crosslinked PVA incorporating zinc oxide nanoparticles (ZnO-NPs) and sodium alginate (NaAlg). The overall reverse osmosis performance of the MMMs is enhanced by the infusion of ZnO-NPs and NaAlg in PVA; we find the optimum concentration for the best performance to be ZnO-NPs at 0.1 wt % and NaAlg at 0.01 wt %. In terms of permeation flux, salt rejection, salt passage, stability, long-term rejection, membrane antifouling, reusability, and chlorine resistance, the proposed MMMs are examined using a dead-end reverse osmosis filtration setup. The results show that the active layer achieves an optimal permeation flux of 34.6 L/m² h, a natural sea salt rejection of 97%, and a chlorine resistance of 93%, suggesting that the proposed MMMs can be useful for seawater desalination. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47559.     

A study of reverse osmosis separation and permeation rate for sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) membranes in different cationic forms

Thin film composite membranes were prepared by coating a thin layer of sulfonated poly(1,4-dimethyl-2,6-phenylene oxide) polymer on the surface of a polysulfone ultrafiltration membrane. The membrane performance was studied when the sulfonate was either in the hydrogen form or loaded fully with an alkali metal cation. It was found that the permeation rate was greater than the pure water permeation rate, when the sulfonate was in the hydrogen form and the feed solution contained an alkali metal chloride solute. The permeation rate increased with an increase in the ionic radius of the alkali metal cation. With respect to membranes in which the sulfonate was loaded with an alkali metal cation, the pure water permeation rate was found to increase with a decrease in the ionic radius of the alkali metal cation. The permeation rate was the same as the pure water permeation rate when the membranes of the latter form were tested for reverse osmosis of aqueous solutions involving either sodium chloride or an organic solute. © 1994 John Wiley & Sons, Inc.     

Spiral Wound Reverse Osmosis Modules Decomposition into Elementary Units by Analyzing Stimulus Response Experiments: Characterization of the Solute Transfer across the Membrane

A model for spiral wound reverse osmosis modules FT30‐4040 has been developed by analyzing stimulus response experiments. Perfect mixing cells represent edthe flow and dispersed plug flow represented the membrane. The model was based on phenomenological equations describing the permeation. The identification of the Peclet number and the space‐time characterizing each dispersed plug flow led to the estimation of the tracer dispersion coefficient in the membrane. Ones new and two used composite reverse osmosis modules were tested. The decrease of the rejection properties of the used membranes was linked to the apparition of new plug flows with high dispersion coefficients within the membrane.