Separation of Ions Using Countercurrent Electrolysis in a Thin,Porous Membrane

Abstract

Separation of ions in a thin, porous membrane using countercurrent electrolysis has been studied both theoretically and experimentally. A set of differential equations which describes the separation process is presented. These equations are solved numerically. The separation has been verified in the ternary systems NaCl-HCl-H₂O and NaBr-KBr-H₂O.     

Trace Ions in Countercurrent Electrolysis in a Thin,Porous Membrane

Abstract

The transport of trace ions added to a binary electrolyte system through a porous membrane during countercurrent electrolysis has been studied both theoretically and experimentally. Theoretical models based both on the general transport equations and on the Nernst-Planck equations are presented. Experiments and calculations for the binary system NaCl-H₂O with trace ions Li⁺ and K⁺ were performed. The theoretical model was able to predict the transport phenomena fairly well.     

The Effect of Membrane Thickness on Countercurrent Electrolysis in a Thin,Porous Membrane

Abstract

The effect of membrane thickness on countercurrent electrolysis in a porous membrane is studied and compared with the increase of convection. It was verified both theoretically and experimentally that the separation efficiency increases considerably when the membrane is made thicker. When the fluxes of ions to be separated deviate from zero, no simple relationship between the logarithm of selectivity ratio and convection could be found. Both computed and measured results showed that IgS =f(v^c ) is strictly nonlinear. Results show that in the light of separation efficiency it is more useful to use higher convections than thicker membrane. This is, of course, done at the cost of increased power consumption. Therefore, in practice the most reasonable approach is a compromise between increased convection and making the membrane thicker.     

Ion Exchange in Countercurrent Electrolysis in a Porous Membrane

Abstract

In many sepration processes for electrolytes the economy of the process could be improved if ion exchange could be carried out simultaneously with the separation without additional stages; i.e., when, for instance, separating potassium chloride from a mixture of sodium and potassium chlorides, the anion could be replaced by the hydroxyl ion, thus producing, instead of potassium chloride, more valuable potassium hydroxide. In fact, in the separation of cations an often desired ion-exchange reaction is the abovbe-mentioned replacement of some anion by the hydroxyl inon.     

Countercurrent Electrolysis in a Cell Where Porous Membranes Have Been Connected in Series with Ion-Exchange Membranes. Part 2. Experimental Verification

Abstract

Countercurrent electrolysis in a cell wehre porous membranes have been connected in series with ion-exchange membranes has been studied experimentally for the ternary system NaCl-KC1-H₂O. The number of porous membranes was varied from one to four, and the effect of cationic fluxes on separation was also studied. A comparison between three different kinds of cell arrangements was made, and the present method was found to be the most attractive for practical purposes.     

Preparation of Silica/γ-Alumina Membrane with Bimodal Porous Layer for Improved Permeation in Ions Separation

Creating secondary pores in the intermediate layer of hierarchical ceramic membranes successfully increases the permeability of bi-layered membranes by reducing the density of the separating layer. With the optimum secondary pore volume, the permeability of the silica/γ-alumina membrane with low secondary volume is enhanced with a satisfactory retention of organic ions and inorganic ions. However, the silica layer is not well formed when excessive secondary pores were generated in the intermediate layer. This is likely because the bimodal porous structure of γ-alumina with high secondary pore volume is inadequate to prevent the penetration of silica sol into the α-alumina support during dip coating. Thus, the bi-layered membrane with high secondary pore volume shows insufficient retention of Reactive Orange 16 dye and NaCl at low pH.     

Countercurrent Electrolysis in a Cell Where Porous Membranes Have Been Connected in Series with Ion-Exchange Membranes. Part 1. Method

Abstract

A new cell arrangement for countercurrent electrolysis in a porous membrane is presented. In this cell, where porous membranes are connected in series with ion-exchange membranes, much better separations are obtained compared to the procedure where the membrane is made thicker. However, separation is less than if convection is increased, but power consumption is also less. An iterative method is presented for solving convection as well as the concentrations in different compartments, when electric current, outflow rate, and concentrations of the product stream are specified.     

Effect of a Drying Pretreatment on Morphology of Porous Poly(Ether-Imide) Membrane Prepared Using Vapor-Induced Phase Separation

Symmetric porous membranes were prepared from concentrated poly(ether-imide) (PEI) solutions using vapor-induced phase separation (VIPS) coupled with a drying pretreatment. Moderately concentrated solutions of PEI in N-methylpyrrolidinone (NMP) (14-16 wt%) were first cast on glass plates and the solvent was then allowed to evaporate under a dry air flow up to the desired concentration (16-38 wt%) before forming the membrane structure by VIPS. The polymer concentration profiles (confocal Raman microscopy) and model predictions were in good agreement to show that the evaporation stage did not induce a polymer gradient concentration with PEI/NMP systems. These results were confirmed by examination of the final membrane morphology (SEM).     

Effect of a Drying Pretreatment on Morphology of Porous Poly(Ether-Imide) Membrane Prepared Using Vapor-Induced Phase Separation

Symmetric porous membranes were prepared from concentrated poly(ether-imide) (PEI) solutions using vapor-induced phase separation (VIPS) coupled with a drying pretreatment. Moderately concentrated solutions of PEI in N-methylpyrrolidinone (NMP) (14–16 wt%) were first cast on glass plates and the solvent was then allowed to evaporate under a dry air flow up to the desired concentration (16–38 wt%) before forming the membrane structure by VIPS. The polymer concentration profiles (confocal Raman microscopy) and model predictions were in good agreement to show that the evaporation stage did not induce a polymer gradient concentration with PEI/NMP systems. These results were confirmed by examination of the final membrane morphology (SEM).     

Soluble Polychelatogenes for Separation of Actinide Ions by Membrane Filtration

Separation of metal ions by functionalized soluble polymers using membrane filtration has been investigated. Actinide elements and members from the transition groups and rare earth elements have been bound to polymeric chelatogenes as a function of pH. Sixteen different polymers and derivatives based on poly(ethylenimine), poly(vinylalcohol), poly(urethane), and poly(acrylic acid) have been studied in terms of their capacity and selectivity. Binding studies and cleavage experiments have been carried out by application of membrane filtration for several metals and polychetatogenes. Finally, the stability of polymers and membranes has been studied and found to be sufficient for selective separation of actinide ions.     

Separation of Cupric and Ferric Ions with a Cation-Exchange Membrane in the Presence of Complexing Agents

Abstract

The separation of cupric and ferric ions in chloride solution has been studied with a cation-exchange membrane in a batch dialyzer. Citric acid, oxalic acid, malonic acid, succinic acid, ethylenedinitrilotetraacetic acid, and glycine have been employed as complexing agents used in the feed phase in order to increase the separation effect. The experimental results show that citric acid, compared to the others, is an effective complexing agent to increase the separation coefficient, T _Fe ^Cu, from 0.5 to 50. The separation behavior depends on the pH of the complex solution, the stoichiometric ratios of complexing agents to metal ions, and the kinds of complexing agents, but is independent of counterion concentration in the stripping phase. The integral interdiffusion coefficients of cupric and ferric ions in Selemion CMV have also been evaluated and found to be D _Fe-Na > D _Cu-Na at concentrations ranging from 0.0015 to 0.0085 M. In the absence of complexing agents, T _Fe ^Cu falls in the neighborhood of the D _Cu-Na/ D _Fe-Na value when the pH is less than 2.0.     

Technology for the Purification of Electroplating Washwater from Cadmium Ions by Membrane and Membraneless Electrolysis

Theoretical Foundations of Chemical Engineering - A technology for removing toxic Cd2+ from electroplating process electrolytes and washwater containing $${text{SO}}_{4}^{{2 - }}$$ or Cl– is...     

Gas Separation in a Membrane Unit: Experimental Results and Theoretical Predictions

Abstract

A laboratory membrane separation unit was assembled by using composite hollow fibers. It was tested in an automated apparatus for gas separation measurements. The performances of the system were measured for CH4/CO2 mixtures as functions of temperature, pressure, stage cut, feed gas composition, and flow regime. The results were analyzed on the basis of a predictive mathematical model of the process. A good fitting of the data was obtained in most cases except at high pressure, probably as a consequence of structural changes of the active layer of the fibers under pressurization.     

膜分离技术在重金属废水处理中的应用

综述了电渗析、液膜、纳滤、超低压反渗透、胶束增强超滤和水溶性聚合物络合超滤等膜技术在废水处理中的研究和应用概况，分析了膜技术在处理重金属废水中存在的主要问题，并对膜技术处理重金属废水的发展前景作了展望。     

国内外膜分离法天然气脱水研究现状

分析阐述了国内外膜分离法天然气脱水的现状。与传统的天然气脱水方法相比,膜分离法天然气脱水在工作性能、经济效益等方面具有优势和竞争力。同时对发展中的膜分离天然气脱水法所面临的挑战和策略对策与措施等也进行了讨论。     

利用膜分离技术回收正丁醇/水混合液的工艺研究

研究了聚乙烯醇（PVA）／聚丙烯腈（PAN）、海藻酸钠（SA）／PAN复合膜及海藻酸钠／醋酸纤维素（CA）共混膜等五种膜的渗透汽化特性,发现它们对正丁醇／水的混合液均表现为水优先透过,其渗透通量与选择分离系数都很高。并初步确定了正丁醇／水混合液渗透汽化分离的工业生产操作条件。     

逆流色谱在外消旋体分离中的应用

本文全面深入地综述了逆流色谱拆分消旋体的原理和特点,阐述了手性选择剂和溶剂系统选择在逆流色谱分离消旋体中的重要性,详细总结了手性选择剂和溶剂系统具有发展潜力的研究新进展。     

Mixing and Work of Separation in Countercurrent Recycle Cascades

Abstract

The increased work of separation due to remixing oartially separated streams within countercurrent recycle cascades, W _unmix, was calculated and compared with the absolute minimum thermodynamic work, W _min, required to effect a given separation. Remixing can occur in all countercurrent constant recycle cascades regardless of whether a separation process is potentially reversible, partially reversible, or irreversible in nature, or whether the cascade is composed of double entry or single entry stages. In an ideal cascade (IC), the remixing of materials with different compositions is eliminated and the sum of the stagewise separative work, W _sep, is identically equal to W _min based on the overall separation occurring across the cascade, or W _sep = W _min. However, in the constant recycle cascade (CRC) the work of separation is greater than the thermodynamic minimum by an amount equal to W _mix due to remixing of partially separated streams, or W _sep = W _min + W _unmix. By comparison, the separative work due to remixing is lost or wasted in the CRC. The lost work, W _unmix, can be a significant contribution to the energy requirements of countercurrent recycle cascades since it becomes infinite at both extremes of reflux; the minimum recycle ratio, RR_min, and total recycle, RR_total. Consequently, W _unmix goes through a minimum at some point in between the two limiting extremes of recycle ratio in a constant recycle cascade. For the examples considered in this analysis, W _unmix in the CRCs goes through a minimum at recycle ratios of 1.32, 1.35, and 1.53 times the minimum recycle (RR_min) for separation factors of α = 1.027, 1.067, and 1.20, respectively. At these “optimal” recycle ratios (i.e., minimum W _unmix), the work of separation is increased by about 28 to 31% over the thermodynamic minimum. Finally, many of the perceived differences in the analysis of separation cascades for the partially reversible, potentially reversible, and irreversible processes disappear when mixing within the CRC is taken into account.     

Development of Spiral-Type Supported Liquid Membrane Module for Separation and Concentration of Metal Ions

Abstract

Experiments on the single permeation of cobalt, nickel, and zinc, and the simultaneous permeation of cobalt and nickel were performed using newly developed spiral-type supported liquid membrane modules. These metal ions were successfully separated and concentrated. EHPNA (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) was used as the carrier of cobalt and nickel, and D2EHPA (di-(2-ethylhexyl)phosphoric acid) for the recovery of zinc. In these modules the flow pattern of both feed and stripping solutions is plug flow, which led to very high recovery of metal ions. For example, 99.97% of cobalt in the feed was recovered in a once-through operation, and cobalt could be pumped against its concentration gradient even if the ratio of the metal concentration in the strip phase to that in the feed phase was as high as 70,000. It was confirmed by a life test of the module that the membrane was stable for more than one month without appreciable decrease in metal flux, and that the degraded membrane could be easily and rapidly regenerated without interrupting the permeation of metal ions by re-impregnating the module with the organic membrane solution. The degree of removal for both single and simultaneous permeation of cobalt and nickel was satisfactorily simulated by design equations of the module and the flux equations in which the formation of aggregates of metal-carrier complexes was taken into account.