Effect of an AC perturbation on a desalination electrodialysis process

The influence of an alternating (AC) sinusoidal perturbation, of known frequency and small amplitude, superimposed to the usual applied continuous (DC) signal in a desalination electrodialysis process has been studied. The experiments were carried out with two types of ion-exchange membranes and sodium chloride aqueous solutions of two initial concentrations and at different frequencies of the AC signal. The results show that the presence of the AC perturbation favours the desalination process, mainly at the lowest frequencies. This fact is considered as a consequence of that the electroosmotic transport accompanying ion transfer during the process is affected by the AC perturbation. This behaviour suggests that the presence of an AC perturbation may influence on the efficacy of the desalination process.     

膜技术在我国冶金工业中的应用

通过一些实例介绍了扩散渗析、电渗析、膜电解、反渗透等几种膜分离技术在我国冶金工业中的应用情况,并对膜技术在冶金工业中的应用前景作了扼要的评述。     

Process simulation of desalination by electrodialysis of an aqueous solution containing a neutral solute

A model was developed to describe the desalination process of an aqueous solution consisting of a salt and a neutral solute using electrodialysis (ED). Under the assumption of plug flow in compartments, the ED process was analyzed in two-dimensional directions of the electric field and flow to get the differential equations of mass balance in the flow length. Then the transport equations of solutes and water through the membrane were deduced by the irreversible thermodynamics approach. Under the limited condition of uniform current density, the model composed of a first-order differential equation set was developed. While the model parameters such as transport coefficients, dimensions of ED equipment, operation conditions and characteristics of solutes are given, the model was solved by the numerical method. The variations of current density, concentrations of solutes and velocities in dilute and concentrated compartments vs. flow length can be simulated by the model. While there was no neutral solute, the model was used to simulate the desalination process of a salt solution. By comparing the ED experiments to the simulations, it is shown that the model is well suited to describe the actual desalination process. The effects of the initial values of variables in the model on the desalination process were simulated to attempt to construct the actual ED process; and the general simulation of desalination process can be realized by the model. While the effect of concentration polarization on the desalination process is reflected by the variation of membrane conductivity, the model was verified to describe the ED process successfully under low velocity.     

Relation between mass transfer and operation parameters in the electrodialysis recovery of acetic acid

The recovery of acetic acid from dilute wastewater by means of bipolar membrane electrodialysis is studied in more detail. The current efficiency of the electrodialysis recovery of acetic acid from dilute wastewater is related to the current density and other operation parameters. There exists a highest value of current efficiency at optimal current density. The highest concentration of recovered acid is also related to current efficiency. The experimental data are analyzed on a theoretical basis.     

Synthesis and optimisation of an integrated water and membrane network framework with multiple electrodialysis regenerators

The shrinking supplies of freshwater globally, coupled with strict environmental regulations, have driven the manufacturing industry towards sustainable water management for the minimisation of freshwater intake and wastewater generation. By using process integration and its enabling tools, this work considers the synthesis of an optimal water network with multiple regeneration capabilities. Development of the proposed framework is achieved by embedding a subnetwork of detailed electrodialysis models within a water network. Based on a superstructure and fixed flowrate, the optimisation problem is formulated as an MINLP model and solved in GAMS/DICOPT. To demonstrate the applicability of the proposed mathematical model a literature case study on a pulp and paper plant is presented and the results indicate a potential of 12% savings in freshwater intake, 16% reduction in wastewater generated and a 14% saving in the total annualised cost for the entire network.     

Surface-functionalized cation exchange membrane by covalent immobilization of polyelectrolyte multilayer for effective separation of mono- and multivalent cations

The existence of numerous non-conductive regions retards the further functionalization of heterogeneous membrane surface. In this report, a modification scheme for covalent immobilization of polyethyleneimine (PEI) multilayer on heterogeneous cation exchange membrane (CEM) was developed by means of diazonium-induced carboxyl group grafting. Of particular note are the influences of some important modification conditions, including the molecular weight of PEI and its deposition times, which were explored and understood. Series of electrodialysis experiments confirmed the achievement of the monovalent cation permselectivity. Furthermore, the results also indicated that the PEI coating can also effectively improve surface homogeneity and then alleviate concentration polarization behaviour during the electrodialysis process.     

电渗析法研究硝酸中铌胶体

在0.5mol/l HNO_3中,铌量于示踪量到2×10~(-4)mol/l的范围内,进行了18种铌浓度的电渗析实验。铌的表观渗析率与浓度关系曲线中出现两个“坪”,反映了铌胶体形成情况。实验结果表明,0.5mol/l HNO_3中。就电荷而言,可渗析和不可渗析的铌均以带正电荷和中性两种状态存在。     

Characterization of anion exchange membranes with natural organic matter (NOM) during electrodialysis

Natural organic matter (NOM) is thought to be a major source of fouling during membrane filtration of natural waters. The organic matter present in surface waters was characterized in terms of its molecular weight distribution, acidity and electrokinetic properties. The fouling potentials of anion exchange membranes were predicted by the characterization. Changes in the physicochemical properties of anion exchange membranes were also examined during electrodialysis (ED) process of solutions containing NOM. The ED performances were evaluated for the three anion exchange membranes (AMX, AM-1 and ACM) in the presence of NOM. Fouling phenomena in terms of current efficiency and NaCl flux were in good agreement with the fouling potentials predicted by the characterization results. Observations of the molecular weight distribution and the constituents of NOM revealed that the hydrophobic NOM fraction with high molecular weights deposited mainly on the membrane surface, providing fouling effects on the anion exchange membrane.     

INNOVATIVE APPROACHES TO SYNTHESIS OF GT 267-004, A SEQUESTRANT FOR C. DIFFICILE TOXIN

GT 267-004 is a nonabsorbed, nonantibiotic, high molecular weight anionic polymer that is undergoing clinical evaluation as a Clostridium difficile toxin sequestrant. The active pharmaceutical ingredient (API) is a mixed salt form that consists of approximately 30 to 50% potassium and 70 to 50% sodium as the counterions on the polymer. The initial polymerization process results in an aqueous polymer solution with the polymer in the 100% sodium form. This article describes the use of two innovative approaches, electrodialysis (ED) and ion exchange using ion exchange resins (IXR), to convert the single-salt polymer to the mixed-salt form. Electrodialysis experiments were conducted using a stack of five cells, each of which contained two cation and one anion exchange membranes. The electrodialysis was run in batch mode with a sodium chloride solution as the concentrate stream and a potassium chloride solution as the diluate stream. The ED process was monitored on-line by measuring the conductivity of the streams. Yield loss of the API through the ED membranes was minimal. The ED process was found to be fast, efficient, and reproducible. The ion exchange experiments were conducted using a strong acid cation resin in the potassium form. By using a fixed bed column mode, an appropriate amount of ion exchange was carried out to produce the mixed-salt API in the effluent stream. The resin bed could be regenerated using KCl solution and reused for subsequent batches of polymer solution. The recovery of the API in the product solution was excellent. The ion exchange route was used to synthesize radio-labeled API for clinical trials.     

Separation of copper ions by electrodialysis using Taguchi experimental design

With the aid of atomic absorption, a systematical and analytical evaluation method called Taguchi's quality engineering has been applied for the separation of copper ions from a solution using a laboratory electrodialysis set-up to evaluate the optimal experimental conditions and hence to achieve the highest removal percentage and the best robustness of the quantitation from the least number ofexperimental runs. Fourparameters at three levels were studied: concentration (100, 500, 1000 ppm), temperature (25, 40, 60°C), flow rate (0.07, 0.7, 1.2 mL/s) and voltage (10, 20, 30 V). Two types of different membranes with different ion-exchange capacities were used. The optimal levels thus determined for the four influential factors were: concentration 1000 ppm, temperature 60°C, flow rate 0.07 mL/s and voltage 30 V. It has also been found that using a membrane pair with higher ion-exchange capacity improves performance. The highest removal percentage was found to be 94.94% and 97.33% for the two types of membranes.