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.     

多孔陶瓷分离膜支撑体的制备研究

采用氧化铝为主要原料制备出多孔陶瓷分离膜支撑体,对原料粉体做了TG/DSC曲线分析,研究了支撑体的烧结温度对收缩率的影响及烧结温度、保温时间和原料粉体粒径对孔结构、孔径的影响,造孔剂用量对孔隙率的影响。结果表明：在烧结温度为1200℃,保温时间4h,控制造孔剂用量大于20%时,制备出孔径分布均匀,孔隙率大于50%,符合透水要求的多孔陶瓷分离膜支撑体。     

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.     

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).     

液膜分离在金属离子分离中的应用研究

液膜分离是一种高效、快速、节能的新型分离技术。综述了液膜分离技术在金属离子分离和富集中的应用进展,并指出其发展前景。     

Synthesis of Vertically Aligned Porous Silica Thin Films Functionalized by Silver Ions

In this work, we have developed a chemical procedure enabling the preparation of highly ordered and vertically aligned mesoporous silica films containing selected contents of silver ions bonded inside the mesopore channels via anchoring propyl-carboxyl units. The procedure involves the electrochemically assisted self-assembly co-condensation of tetraethoxysilane and (3-cyanopropyl)triethoxysilane in the presence of cetyltrimethylammonium bromide as a surfactant, the subsequent hydrolysis of cyano groups into carboxylate ones, followed by their complexation with silver ions. The output materials have been electrochemically characterized with regard to the synthesis effectiveness in order to confirm and quantify the presence of the silver ions in the material. The mesostructure has been observed by transmission electron microscopy. We have pointed out that it is possible to finely tune the functionalization level by controlling the co-condensation procedure, notably the concentration of (3-cyanopropyl)triethoxysilane in the synthesis medium.     

Separation of Hydrogen from Carbon Monoxide Using a Hollow Fiber Polyimide Membrane: Experimental and Simulation

The separation of hydrogen from carbon monoxide (syngas ratio adjustment) with polymeric membranes was investigated in this work. A polyimide hollow fiber membrane module was used for hydrogen separation. This polymer has shown large permeability and selectivity for hydrogen separation (selectivity of ca. 30). Permeation tests were carried out at different feed conditions. Feed flow rates were varied between 150–300 mL/min, temperature was varied in the range of 20–80 °C and feed pressure was varied between 5–9 bar. Mixtures containing 0–50 % carbon monoxide were used when carrying out experiments. Measured membrane permeances for hydrogen and carbon monoxide were about 70–100 GPU (gas permeation units) and 3–5.5 GPU, respectively. In addition, a mathematical model for simulation of gas separation in hollow fiber membrane modules with all flow patterns (crossflow, countercurrent and cocurrent) was presented. This model can be used for calculation of membrane performance or its required surface area for a specific separation. Experimental results have shown good correlation with simulation results. Plasticization, competitive sorption and concentration polarization effect of carbon monoxide on membrane performance is shown with experimental results. This effect reduced hydrogen permeances in mixed gas experiments.     

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。     

超声协同PDMS膜渗透汽化分离吡啶和水

对自制聚二甲基硅氧烷(PDMS)膜渗透汽化分离低浓度吡啶-水体系的性能进行了研究.采用扫描电镜(SEM)和X射线能谱仪(EDS)对膜的形貌及化学组成进行了分析和表征,测定了PDMS膜在吡啶-水溶液中的溶胀行为.分别考察了膜厚度、操作温度、下游侧压强、进料浓度以及超声对PDMS膜渗透蒸发分离性能影响.结果表明,随着操作温...