Parameters for prediction of reverse osmosis performance of cellulose acetate propionate membranes

Data on reverse osmosis separations have been obtained for 12 alkali metal halide solutes and 24 organic solutes (including eight alcohols, four aldehydes, seven ketones, and five ethers) with cellulose acetate propionate (CAP) membranes using single-solute dilute aqueous feed solutions at 250 psig. From the analysis of these data, the parameters and correlations needed to calculate the values of solute transport parameter D_AM/Kδ for the above classes of inorganic and organic solutes for a CAP membrane of any surface porosity from data on D_AM/Kδ for NaCl only have been generated. These parameters and correlations enable one to predict reverse osmosis separations of different solutes included in the classes of compounds studied in this work, from a single set of experimental data on membrane specifications given in terms of pure water permeability constant and D_AM/Kδ for NaCl. The reverse osmosis characteristics of CAP material lie intermediate between those of cellulose acetate and aromatic polyamide materials reported in the literature.     

运用醋酸纤维素丁酯和芳香聚酰胺膜的二元有机液体混合物的反渗透法分离

本文运用实验室制备的醋酸纤维素丁酯膜和芳香聚酰胺膜系统研究并证实了反渗透技术用于分离液体有机混合物的适用性,并用液相色谱法则量了上述二种膜材料的优先吸附性能。研究发现:反渗透枝术能够应用于液体有机混合物的分离。通过考虑进料液中每一个组分的优先吸附特性和斯托克斯半径,能够预测出二元混合物中哪一组分会在膜透过液中得到浓缩。     

Preparation and characterization of thermally crosslinked chlorine resistant thin film composite polyamide membranes for reverse osmosis

Currently, polyamide reverse osmosis membranes are highly effective for desalination, industrial process water, and home drinking water. However, they have poor resistance to strong oxidants especially chlorine due to chain cleavage of aromatic polyamide. In general, aromatic polyamide RO membranes are essentially random copolymers consisting of the linear and crosslinked structures. The amide ring is sensitive to attack by chlorine because it is an electron-rich region. Therefore, the activated carbon or sulfite addition processes are essential to remove the chlorine in the separation processes. Many research groups have studied to improve the chlorine-resistance RO membrane having hydrophilic groups (− SO₃H and − COOH) or nitro groups (− NO₂) such as electron acceptors. In this study, thin film composite polyamide RO membranes were prepared by interfacial polymerization method including cross-linking agents having hydroxyl groups to improve the chlorine-resistance. The chlorine-resistance of polyamide RO membrane was influenced by the thermal cross-linking conditions (temperature and time) and cross-linking density of polyamide membranes.     

Studies on syntheses and permeabilities of special polymer membranes.: 15. Permeation characteristics of nylon-12 cellulose acetate blends

The permeation characteristics of nylon-12-cellulose acetate polymer blend membranes in the separation of polymers, poly(vinyl alcohols), from their aqueous solutions were investigated under various conditions. The permeation characteristics were influenced markedly by the ratio of nylon-12-cellulose acetate, the feed concentration, the operating pressure and temperature. It was found that the changes of polymer ratio and the concentration of blended polymer were related to the change of microporous structure of the resulting membranes. When the cellulose acetate content was higher a significant compaction of the membrane occurred under pressure. It was found that there was a concentration polarization of poly(vinyl alcohol) molecules on the membrane surface, whose thickness increased with increase in molecular weight of poly(vinyl alcohol) and in feed concentration. The bursting strength of the polymer blend membranes swollen with water increased considerably as the cellulose acetate content in the blended polymer increased.     

The effect of low molecular weight additives on the properties of aromatic polyamide membranes

Salts contained in aromatic polyamide solutions were found to have a considerable effect on the performance and structure of reverse osmosis membrannes cast from these solutions. As in cellulose acetate membranes, certain salts greatly increase membrane fluxes without a detrimental effect on rejection. Highly dissociated salts such as LiClO₄ or Mg(ClO₄)₂ exert a stronger influence than the commonly used LiCl. With mixtures of different salts, stronger effects may be obtained than with a single additive. Many experimental facts indicate that the “salt effect” in aromatic polyamide membranes is due to a general effect on solvent activity and thus on the kinetics and equilibria associated with evaporation and coagulation process.     

Permselectivities of 2,2′‐dimethyl‐4,4′‐bis(aminophenoxyl)biphenyl diphenyl methane–based aromatic polyamide membranes for aqueous alcohol mixtures in pervaporation and evapomeation

The separation of aqueous alcohol mixtures was carried out by use of a series of novel aromatic polyamide membranes. The aromatic polyamides were prepared by the direct polycondensation of 2,2′‐dimethyl‐4,4′‐bis(aminophenoxyl)biphenyl (DBAPB) with various aromatic diacids, such as terephthalic acid (TPAc), 5‐tert‐butylisophthalic acid (TBPAc), and 4,4′‐hexafluoroisopropylidenedibenzoic acid (FDAc). The pervaporation and evapomeation performance of these novel aromatic polyamide membranes for dehydrating aqueous alcohol solution were investigated. The solubility of ethanol in the aromatic polyamide membranes is higher than that of water, but the diffusivity of water through the membrane is higher than that of ethanol. The effect of diffusion selectivity on the membrane separation performances plays an important role in the evapomeation process. Compared with pervaporation, evapomeation effectively increases the permselectivity of water. Moreover, the effect of aromatic diacids on the polymer chain packing density, pervaporation, and evapomeation performance were investigated. It was found that the permeation rate could be increased by introduction of a bulky group into the polymer backbone. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2688–2697, 2003     

Cellulose acetate–poly(ether sulfone) blend ultrafiltration membranes. II. Application studies

Ultrafiltration membranes are largely applied as macromolecular solutes and heavy‐metal‐ion separation from aqueous streams. Cellulose acetate and poly(ether sulfone) blend ultrafiltration membranes were prepared by the precipitation phase‐inversion technique in 100/0, 95/5, 85/15, and 75/25% polymer blend compositions in the absence and presence of a polymeric additive, poly(ethylene glycol) 600, at different additive concentrations and were used for the rejection of proteins trypsin, pepsin, egg albumin, and bovine serum albumin; a maximum of 94% rejection was achieved. The toxic heavy metal ions copper, nickel, and cadmium from dilute aqueous solutions were subjected to rejection by the blend membranes by complexation of the ions with the water‐soluble polymeric ligand, polyethyleneimine (PEI). Permeate flux studies of proteins and metal ions were performed simultaneously with the rejection experiments. The atomic absorption spectra results reveal maximum rejection for copper complex and a minimum rejection of about 60% for the cadmium complex. The rejection and permeate flux of the blend membranes were compared with those of pure cellulose acetate membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3659–3665, 2004     

Study of the surface of the water treated cellulose acetate membrane by atomic force microscopy

Water treated cellulose acetate (CA) membrane's surface was studied by atomic force microscopy (AFM). It was observed that when CA membrane (water untouched) was treated with water, the morphology of the surface change was detected by AFM. The roughness parameter of the surface was increased. No significant change was observed on the surface on drying the water treated membrane at room temperature for four days. The results were discussed on the basis that CA membrane contains continuous channels (network pores), which were formed in water-swollen polymer matrix. These water channels are responsible for the rejection of salt in reverse osmosis (RO) phenomenon.     

Adsorption properties of cyclic compounds on cellulose acetate

The interaction between solutes and semipermeable membranes is an important factor for the membrane‐separation process. As an extension to previous works, we studied the adsorption properties of cyclic compounds on cellulose acetate, a material commonly used for semipermeable membranes, in aqueous solution systems by high‐performance liquid chromatography (HPLC). Cycloalcohols, cycloethers, amino acids, heterocyclic aromatic compounds, and nucleosides were used in this study. The logarithm of the capacity factor (log k′) for these compounds was linearly correlated with the logarithm of 1‐octanol/water partition coefficients (log K_o/w) as well as noncyclic compounds. Cyclic compounds were relatively retained more than were noncyclic compounds in spite of their hydrophilic properties, which indicates the structural effects of the solute molecule on the adsorption. Although noncyclic compounds were retained mainly by hydrophobic interaction, the retention of cyclic compounds was suggested to be controlled by their inclusion within the micropore in cellulose acetate. The adsorption of heterocyclic aromatic compounds was not influenced only by ionic dissociation but also by tautomerism. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1657–1663, 1999     

Studies on syntheses and permeabilities of special polymer membranes. XVI. Permeation and separation characteristics of aqueous polymer solutions for acrylonitrile-styrene copolymer membranes

The permeation and separation characteristics of aqueous polymer solutions using acrylonitrile-styrene copolymer membranes were investigated under various conditions. The membranes obtained from dimethyl sulfoxide solution of acrylonitrile-styrene copolymer have not a sufficient reproducibility and stability of permeation. These lacks were improved by adding ethylene glycol or glycerol to the casting solution and treating the membranes with pressure. The permeation and separation characteristics were influenced significantly by the additional amount of above additives, the heat treatment temperature, and the operating pressure. It was found that the concentration polarization of poly(vinyl alcohol) molecules onto the surface of the acrylonitrile-styrene copolymer membranes is smaller than that onto hydrophilic polymer membranes such as membranes of cellulose acetate, cellulose nitrate, and nylon 12, etc. Moreover, the acrylonitrile-styrene copolymer membranes show better performance for separation and concentrating of aqueous polymer solutions than hydrophilic membranes.     

Separation of Lindane from Its Aqueous Solutions by Reverse Osmosis System

Abstract

The separation characteristics of cellulose acetate/reverse osmosis (RO) membranes toward trace levels of lindane in water were investigated. A large fraction of this pesticide readily traversed the membrane; another portion, although tenaciously sorbed in or on the membrane, was slowly released into the product water. The implications of these observations on RO systems for municipal, domestic, and hospital use are discussed.     

Development and characterization of cellulose acetate benzoate flat osmotic membranes

Different parameters of casting solutions and casting conditions were studied for the development of cellulose acetate benzoate flat osmotic membranes. Casting solutions were prepared with different concentrations of the polymer, the additive, and the solvent; viscosity of the casting solution; and the thickness of the membrane developed. The membranes were given different evaporation periods and annealing temperatures under different RH. Different annealing baths were also used. Based on these, conditions were optimized for the development of cellulose acetate benzoate flat osmotic membranes. These membranes were characterized with respect to bound water content, specific water content, transport properties by direct osmosis, salt intake by direct immersion, water permeability coefficient of the dense membrane, diffusion coefficient, salt permeability, and salt distribution by electrical conductivity. Also, cellulose acetate benzoate membranes were compared with conventionally used cellulose acetate membranes. © 1994 John Wiley & Sons, Inc.     

Application of reverse osmosis to automotive electrocoat paint wastewater recycling

Field and bench-scale reverse osmosis experiments on wastewater derived from automotive electrocoat paint operations are reported. Field experiments were performed continuously over a six-month interval using a reverse osmosis unit equipped with cellulose acetate membranes. An operating pressure of 3100 kPa (450 psi) and a temperature of 24–27°C was maintained. These RO experiments were unusual for two reasons. First, certain solutes in the feedwater were allowed to permeate through the membrane along with water. This was done to permit solute recycling and reuse. Since these solutes (ethyl, butyl and hexyl glycol ethers) were present in a 3% total concentration in the feedstream, their permeation through the membrane eliminated a flux reduction mechanism. This would arise from the increased upstream osmotic pressure if these solutes were concentrated. Second, the experiments were performed under conditions where colloidal lead was present. This caused limited membrane fouling which was controlled via weekly cleaning with dilute lactic acid. Some supporting bench-scale RO experiments were carried out to probe factors influencing this RO application.     

压力驱动薄层复合膜中微孔基底的研究进展

压力驱动薄层复合膜（TFC）因其高分离效率和低能耗等优点,在水处理领域得到广泛应用。TFC膜的开发及性能提升可针对聚酰胺（PA）分离层和微孔基底两方面进行优化。其中,微孔基底对其上通过界面聚合（IP）形成的PA层的结构和分离性能具有重要影响。本文对NF/RO TFC膜中微孔基底的研究工作进行了评述。首先对两类微孔基底（相转化微孔基底和静电纺丝微孔基底）进行了概述,进而介绍了传统相转化微孔基底对IP过程的影响机理,并对相转化微孔基底的改性方法（聚合物共混、纳米材料掺杂、表面改性等）进行了总结,最后展望了共价有机框架（COFs）中间层表面改性微孔基底在构建高选择性、高渗透通量压力驱动TFC膜中的发展方向及面临的挑战。     

Permeable domains of segmented polyurethanes studied with paramagnetic spin probe

Studies on the permeable regions of the dense polyurethane-based membranes were performed by electron spin resonance spectroscopy (ESR) using TEMPO spin probe incorporated into the membrane via diffusion from the vapour phase. The ESR spectra were measured as a function of temperature and microwave power for polyurethanes (PU) varying in the molecular structure and morphology. It was found that the TEMPO spin probe exhibited anisotropic rotation whose anisotropy increased as temperature decreased and was more pronounced for PU with shorter soft segments. The simplified method was used to obtain apparent correlation time τ_c enabling the comparison of the polyurethanes studied. This approach was based on the Arrhenius relation of τ_c vs. 1/T determined from motionally narrowed ESR spectra and on the assumption that this behaviour prevails over a broader temperature range at temperatures generally greater than T_g of a given polymer.     

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     

Reverse osmosis membrane sensitivity to ozone and halogen disinfectants

The sensitivity of commercial reverse osmosis (RO) membranes toward halogen and ozone disinfectants has been measured at carefully controlled concentration and pH levels. Membrane sensitivity varies with polymer type, disinfectant chemical, and solution pH. Aromatic polyamide membranes are damaged by halogen addition to aromatic rings within the polymer. This process follows predictable reaction kinetics. Polymer viscosity changes with increasing membrane damage have also been followed. Results of this study will be useful in planning disinfection strategies for RO units in the field.     

Reverse osmosis separation of binary organic mixtures using cellulose acetate butyrate and aromatic polyamide membranes

A systematic investigation has been conducted to demonstrate applicability of reverse osmosis (RO) fractionation of organic liquid mixtures by laboratory-prepared cellulose acetate butyrate (CAB) and aromatic polyamid (PA) membranes. The determination of preferential sorption was also conducted by using liquid chromatography technique. It was found that reverse osmosis was applicable to the fractionation of organic liquid mixtures. It was also found that the component of the binary mixture that is enriched in the membrane permeate can be predicted by considering the preferential sorption and Stokes' radius for each constituent of the feed mixtre.     

Identification,Modelling, and Control of Continuous Reverse Osmosis Desalination System: A Review

Desalination is a separation process used to reduce the amount of dissolved salts in seawater or brackish water to a usable or potable level by distillation, multiple effect vapor compression, evaporation, or by membrane processes such as electro-dialysis reversal, nano-filtration, and reverse osmosis (RO). RO is the most widely used desalination process. Recent advances in RO technology have led to more efficient separation and now is the most cost-effective process to operate. The performance of the Reverse Osmosis process is dependent on the concentration of dissolved solids in the feed-water, feed-water pressure, and the membrane strength to withstand system pressure, membrane solute rejection, membrane fouling characteristics, and the required permeate solute concentration. RO is a promising tool that uses cellulose acetate (or) polyamide membrane and is widely chosen as the cost of production is reduced by the use of energy-efficient and process-control techniques. This article presents a review of literature survey of identification of parameters, dynamic modelling, and control of desalination system in the past twenty years by collecting more than 65 literatures.     

REVERSE OSMOSIS SEPARATION OF GLUCOSE-ETHANOL-WATER SYSTEM BY CELLULOSE ACETATE MEMBRANES

The separation of glucose-ethanol mixed solutes from aqueous solutions was attempted by cellulose acetate membranes of different average pore sizes and pore size distributions at the operating pressure of 6895 kPag (=1000 psig) and at the feed glucose concentration ranging from 2000 to 75000 ppm while maintaining ethanol concentrations at 1/5 to 1/2 of the glucose concentration. Using chosen reference solutes the pore size distribution on the membrane surface was characterized by two normal distributions. It was found that ethanol is attracted to the cellulose acetate membrane material more strongly at the higher glucose concentration in the feed solution, and consequently the separation of ethanol solute is brought down at higher glucose concentrations. These results are attributed to lowering of solubility of ethanol in the solvent when a greater amount of glucose is in the solvent.