PREDICTION OF MEMBRANE SEPARATION CHARACTERISTICS BY PORE DISTRIBUTION MEASUREMENTS AND SURFACE FORCE-PORE FLOW MODEL

Pore size distribution of polyamide thin film composite reverse osmosis membranes and a cellulosic ultrafiltration membrane were obtained from vapor adsorption data of CO₂ and N₂ gases. The surface: force-pore flow model previously reported in the literature was utilized in this work. The pore distribution data were further used with solutes separation data at a particular pressure to obtain the values of solute-solvent-membrane wall forces involved. The interaction parameters were obtained by the simultaneous solution of the ordinary differential equations describing the model using the software package COLSYS. From the knowledge of the pore distribution data and the interactions forces, the solutes separation data (for nonionized organics and sodium chloride) were predicted over a wide range of pressures and showed excellent agreement with experimental separation data.     

MODELLING OF TEMPERATURE EFFECTS ON THE PERFORMANCE OF REVERSE OSMOSIS MEMBRANES

This paper investigates the modeling of temperature effects on the performance of reverse osmosis membranes at the level of brackish-water concentrations. A new approach in modeling is employed in which the temperature dependencies of the physical properties of the system (such as diffusivity and viscosity) are taken into account and incorporated into the recently developed modified surface force-pore flow (MD-SF-PF) model. The dimensionless potential function in the model, which describes the solute-membrane interactions, is assumed to be temperature independent, which is justified based on an analogy to the interaction energy for the case of parallel flat plates. The three parameters in the model are determined at 25°C and 2000 ppm NaCI-water solution. Based on these parameters, the temperature-extended model predicts the performance of four thin-film composite, aromatic polyamide, FilmTec FT30 commercial membranes, in a temperature range of 5-60°C and a pressure range of 350-7000 kPa. The extended model truly predicts the performance of the membranes well. The compaction effect has no effect on the prediction of membrane separation and the ratio of solution flux to pure water flux. The compaction effect is modelled empirically which then allows the calculation of the absolute solution flux and pure water flux.     

Surface Force-Pore Flow Model in Predicting Separation and Concentration of Polyhydric Alcohols in Aqueous Solutions Using Cellulose Acetate Membranes

Abstract

The reverse osmosis separation and concentration of polyhydric alcohols were experimentally tested by using cellulose acetate membranes of different average pore sizes. An attempt was made to predict membrane performance data, such as the solute separation and the product permeation rate, on the basis of the surface force-pore flow model, and the results were tested by experimental values. The processing capacities of the membranes were also calculated.     

RADIAL FLOW HOLLOW FIBERREVERSE OSMOSIS: EXPERIMENTS AND THEORY

The performance of a hollow fiber reverse osmosis system is studied both theoretically and experimentally. Experiments were carried out for applied pressure ranging from 200 to 400 psig, feed rates varying from 75 to 380 cc/sec and for feed concentrations up to 34,000 ppm of sodium chloride.

A mathematical model is proposed to predict productivity, ϕ, and product concentration, θ_p. The model involves solving membrane transport equations simultaneously with the hydrodynamic equations. The solubility-diffusion-imperfection, or pore diffusion model, is used to describe solute and solvent transport across the membrane. The axial gradients of shell side concentration, neglected in previous investigations, are taken into account. The differential equations are solved numerically by the 4th Order Runge-Kutta method.

Predicted values of ϕ and θ_p agree within 8% and 17% respectively, with experimental data over the entire range of operating conditions. However, membrane transport coefficients were found to be concentration dependent.

An approximate analysis shows that the concentration polarization is negligible in present day hollow fiber systems.     

A method for the determination of the optimal reverse osmosis membrane for two-solute separation

A model has been proposed to determine the optimal membrane for the separation of two dissolved substances employing the reverse osmosis technique. The model is based on certain idealized assumptions, but is nevertheless useful in giving an approximation of separation effectiveness for different membranes from flux and retention data.Experimentally, the separation properties of four different types of cellulose acetate membranes have been investigated with respect to the system: sodium chloride, gluconic-acid and water.In addition to the proposed model, the example illustrates, how the membrane type, as determined by the annealing temperature, and pressure influence the separation efficiency.     

Treatment of Prehydrolysis Liquor from Pulp Mill using a Biological Route Followed by Reverse Osmosis

A new method, comprised of a biological treatment followed by membrane separation, has been suggested for the treatment of spent prehydrolysis liquor (PHL) from a rayon grade pulp mill. First, the PHL was treated biologically using the torula utilis strain for the conversion of sugar into yeast. Reductions of 57 % in the amount of total reducing sugar (TRS) and about 46 % in COD were achieved in the biological treatment step. A “shifting order type” rate equation, where the order shifts from (m–n) at high concentrations to m at lower concentrations, was found to predict the total reducing sugar with high accuracy. An ultracentrifuge was used to separate out the yeast formed during the biological treatment. The clarified biologically treated liquor was subjected to reverse osmosis (RO) to remove all the remaining solutes. The permeate obtained was observed to be of disposable/reusable grade (negligible COD and less than 0.9 mg/L sugar). An attempt was made to predict the permeate flux during reverse osmosis (RO) using an osmotic pressure model. Modified osmotic pressure and concentration polarization models were utilized for the estimation of the osmotic pressure of different concentrations of the PHL's solute constituents. Three different concentration parameters (TRS, COD, and Brix) were chosen to estimate the osmotic pressures. The prediction of the permeate flux by the combination of these models was found to be in good agreement with experimental flux values.     

氧化石墨烯掺杂反渗透混合基质膜制备及性能

由于芳香族聚酰胺反渗透膜在抗污染性以及耐氯性方面存在不足,限制了其在海水淡化等方面的应用。采用往油相中添加氧化石墨烯（GO）的二次界面聚合法改性了商业反渗透膜,评价了GO掺杂反渗透混合基质膜的分离性能和耐氯性能,并用接触角仪、Zeta电位仪、扫描电镜和原子力显微镜等仪器表征了膜的亲水性能、荷电性能以及膜表面形貌。结果表明,GO的添加提高了膜的分离性能、耐氯性能和亲水性能;当GO添加量为30 mg·L^-1时,膜的通量为（77.7±0.9） L·m^-2·h^-1,膜的截留率为97.6%±0.5%,相比商业膜分别提高了38.4%和4.5%。当氯化强度低于4800 mg·L^-1·h时,膜的水通量和盐截留率变化不明显。     

A viscoelastic model for initial flux decline through reverse osmosis membrane

The flux decline through a reverse osmosis membrane is described by assuming that the membrane behaves as a viscoelastic body composed of three elements. This model can be used to predict the flux decline with time for the RO membrane.     

Reverse osmosis separation of inorganic solutes in aqueous solutions using porous cellulose acetate membranes

Using a modified form of the Born expression for the free energy of ion-solvent interaction, to both the bulk solution phase and the membrane–solution interface, a parameter is obtained to express the repulsion of the ion at the interface. This parameter, called the free energy parameter for ions, is then related to solute transport parameter obtained from reverse osmosis experiments. Numerical values of this free energy parameter have been obtained for six monovalent and four divalent cations and for 12 monovalent anions. Using the experimental data for the reverse osmosis separation of sodium chloride as reference, the utility of the above parameter for predicting solute separation in reverse osmosis is illustrated for 32 other inorganic salts.     

Reverse osmosis separations of polyethylene glycols in dilute aqueous solutions using porous cellulose acetate membranes

Reverse osmosis separations of eight polyethylene glycol (PEG) solutes in the average molecular weight range of 200 to 6750 in single-solute dilute aqueous solutions have been studied using porous cellulose acetate membranes at the operating pressures of 50, 75, and 100 psig. Diffusivity data for the above PEG solutes have also been obtained from experimental data on intrinsic viscosities. From an analysis of all experimental data, numerical values for the parameters representing the polar (?ΔΔG/RT), steric (δ^*ΣE_s), and nonpolar (ω^*Σs^*) forces governing reverse osmosis separations of PEG solutes have been generated. These numerical values are useful for precise characterization of cellulose acetate membranes for whose specifications sodium chloride is not the appropriate reference solute because of its low or practically negligible separation under reverse osmosis operating conditions. This work also illustrates that solute separation in reverse osmosis can predictably increase or decrease with increase in operating pressure depending on experimental conditions.     

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.     

Composite melamine-formaldehyde-furfuralcohol copolymerization membrane for reverse osmosis

The preparation and performance of the new composite reverse osmosis membrane were investigated. The ultrathin semipermeable barrier of the composite melamine-formaldehyde-furfuralcohol copolymerization membrane for reverse osmosis is formed on the porous surface of polysulfone support membrane by copolymerization between melamine-formaldehyde prepolymer and furfuralcohol under sulfuric acid catalyst. In the condition of operation pressure 20 kg/cm² and concentrated water flux 20 L/h, the membrane has 95% rejection and 0.3 m³/m².d flux for 1500 ppm aqueous sodium chloride. The factors affecting the reverse osmosis performance of the composite membrane, such as amount of the prepolymer and catalyst, the temperature of the polymerization and the properties of additives etc, were investigated.     

正渗透膜生物反应器膜过滤特性研究

以氯化钠为驱动溶质,采用正渗透膜生物反应器处理模拟生活污水,系统地考察了各因素对正渗透膜过滤性能的影响。结果表明,随着驱动液浓度增加,水通量和反向盐通量也随之增加;正渗透膜活性层朝向驱动液时(AL-DS)的水通量和反向盐通量较活性层朝向原料液(AL-FS)时大;水通量和反向盐通量与错流速率正相关,在错流速率较低时增加不明显;随着活性污泥浓度增加,水通量呈下降趋势,而反向盐通量呈上升趋势。     

High performance forward osmosis cellulose acetate (CA) membrane modified by polyvinyl alcohol and polydopamine

Cellulose acetate (CA) is a low cost and readily available material widely used in forward osmosis (FO) membranes. However, the performance of pure CA membranes is not good enough in salt separation and the traditional modification methods are generally multistep and difficult to control. In this paper, we reported high performance cellulose acetate (CA) composite forward osmosis (FO) membranes modified with polyvinyl alcohol (PVA) and polydopamine (PDA). PVA was first cross-linked onto the surface of CA membranes, and then PDA was coated with a rapid deposition method. The membranes were characterized with respect to membrane chemistry (FTIR and XPS), surface properties comprising wettability (by water contact angle), and osmosis performance. The modified membrane coated by PVA and PDA shown better hydrophilicity and exhibited 16.72 LMH osmotic water flux and 0.14 mMH reverse solute flux with DI water as feed solution and 2.0 M NaCl as draw solution and active layer facing the feed solution. This simple and highly effective modification method makes it as an excellent candidate for further exploration for FO.     

醋酸纤维素衍生物反渗透膜对低分子量有机物分离特性研究

研究用醋酸纤维素衍生物氰乙基醋酸纤维素、羟丙基醋酸纤维素和醋酸纤维素反渗透膜对有机醇、有机酸及有机胺类水溶液的分离特性,考察操作压力对反渗透分离特性的影响,并应用不可逆热力学过程得出的Spiegler—Kedem膜输送方程解析实验数据,获得了反射系数σ、溶质渗透系数ω和溶剂水渗透系L_p等膜参数。     

Specification of commercial reverse osmosis modules and predictability of their performance for water treatment applications

Techniques for specifying membranes in commercial modules and reverse osmosis systems involving such modules, and for predicting data on performance of the modules so specified are illustrated with particular reference to water treatment applications. Four commercial modules (Roga-4000, Westinghouse, Raypak and Du Pont-B9) were studied in. this work for such specification and prediction. Experimental reverse osmosis data using NaCl-H₂O feed solutions were used for obtaining data on membrane specifications. Equations of system analysis were used for prediction of data on module performance. Three sets of calculated data are reported for the operating pressure of 2758 kPa gauge (400 psig). The first set of data shows good agreement between calculated and experimental results on the performance of the modules with aqueous sucrose feed solutions. The second set of data shows the variations in solute separation and membrane productivity for each of the four- modules studied as functions of volumetric fraction product water recovery and membrane compaction for a 3000 ppm NaCl-H₂O feed solution. The third set of data shows the variations in solute separation as a function of solute transport parameter at different levels of mass transfer coefficient on the high pressure side of the membrane for very dilute aqueous feed solutions.     

聚丙烯酸钠汲取液的正渗透性能

研究了聚丙烯酸钠溶液作为汲取液的渗透压特性,并考察了影响水通量和溶质反向渗透量的因素和机制. 结果表明,聚丙烯酸钠浓度与渗透压的关系符合维里方程,第二维里系数对渗透压有较大贡献,聚丙烯酸钠溶液浓度为0.2 g/mL时的渗透压达1.3 Osmol/kg以上,水通量为14.5 L/(m2×h),略高于相同渗透压的氯化钠汲取液[14.0 L/(m2×h)];聚丙烯酸钠汲取液的溶质反向渗透量为1.6 g/(m2×h),低于常规氯化钠汲取液的16.5 g/(m2×h). 升高温度能迅速提高水通量,反向溶质渗透量维持在较低水平,聚丙烯酸钠汲取液适合比常规小分子汲取液更高的操作温度. 聚丙烯酸钠汲取液较高的水通量和较低的溶质反向渗透量表明正渗透性能良好.     

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.     

Cellulose triacetate membranes for seawater desalination

Experimental data on reverse osmosis using a sodium chloride solution by cellulose triacetate membranes are presented. The investigation involved studies on the composition of membrane casting solutions and their effects on the performance. A higher polymer concentration (11–13%) is found suitable for production of a uniform and highly salt rejecting membrane. Salt rejection of 99.0% and 4–5 GFD product water flux were obtained at 1000 psi operating pressure using 30,000 ppm TDS seawater in the initial experiments.