Exchange Membranes and Electrodialysis

The concentrates of salt solutions made by electrodialysis of seawater are suited as feed to the evaporators of salt manufacturing plants with considerable savings in overall energy requirements. Other applications also are based on the concentrating effects of electrodialysis, for instance, tenfold increases of concentrations of depleted streams from nickel and copper plating plants are made routinely. 

2 m dia are described and mentions that diameters up to 5 m are feasible and may have throughputs of 10,000 metric tons/yr. 

TABLE 15.8. Examples of Chromatographic Separations in a Column 125 mm dia (a) Five Separations 

Case Mixture Charge (mol %) Product (mol %) Temperature (°C)/ Pressure (Torr) Remarks 

Anderson, Adsorption (general), Encycl. Chem. Process. Des. 2, 174-213 (1977). 

Figare 15.26. Continuous and UOP simidated continuous moving bed liquid adsorption processes [Broughton, Sep. Sci. Technol. 19, 723-736 1984-1985)]. (a) Continuous moving bed liquid adsorption process flows and composition profiles, (b) UOP Sorbex simulated moving bed adsorption process. 

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Ion Exchange Membranes and Electrodialysis 517 Chromatographic Equipment 520 References 522... 

Many attempts to prepare ion exchange membranes having permselectivity for specific ions and to find electrodialysis methods to achieve such a purpose have been made. In this chapter, studies on the modification of ion exchange membranes and electrodialysis methods to permeate specific ions through the membrane, mainly in electrodialysis, are explained. 

FIGURE 26.2 Electrodialysis purifying a feed solution. An alfemation of anion-exchange membranes and cafion-exchange membranes is placed between electrodes in a receiving solution outside the last membranes. Only a central section is shown. 

Electrodialysis (ED) is a unit operation for the separation or concentration of ions in solutions based on their selective electromigration through semi-permeable membranes under the influence of a potential gradient (Lacey and Loeb, 1972 Strathmann, 1992). Owing to their selectivity, ion-exchange membranes (IEM) allow transport of only cations (cation-exchange membranes) or anions (anion-exchange membranes) and thus can be used to concentrate, remove, or separate electrolytes. 

Stack design in bipolar membrane electrodialysis The key component is the stack which in general has a sheet-flow spacer arrangement. The main difference between an electrodialysis desalination stack and a stack with bipolar membranes used for the production of acids and bases is the manifold for the distribution of the different flow streams. As indicated in the schematic diagram in Figure 5.10 a repeating cell unit in a stack with bipolar membranes is composed of a bipolar membrane and a cation- and an anion-exchange membrane and three flow streams in between, that is, a salt... 

Josefsson [5] determined soluble carbohydrates in seawater by partition chromatography after desalting by ion exchange membranes. The electrodialysis cell used had a sample volume of 430mL and an effective membrane surface area of 52cm2. Perinaplex A-20 and C-20 ion exchange membranes were used. The water-cooled carbon electrodes were... 

The future for electrodialysis-based wastewater treatment processes appears bright. The dilute concentrations of metals in the waste streams do not degrade or foul the cation or anion exchange membranes. The concentrate streams are recirculated to build up their metal content to a level that is useful for further recovery or direct return to the process stream. Ongoing research in the development of cheaper cation exchange membranes, and stable anion exchange and bipolar membranes will allow electrodialysis-based applications to become more competitive with other treatments. 

To assess the feasibility and to verify if the ED operations of the EDBM2C configuration could be expensive because of the NaOH and energy consumption, the authors recently published a work comparing this method with different methods used for deacidification of clarified passion fmit juice [18]. They compared EDBM with other physicochemical technologies, ion-exchange resins, and electrodialysis with homopolar membranes (Figure 21.25), as well as the conventional chemical method based on the precipitation of calcium citrate obtained by addition of calcium hydroxide or carbonate to the clarified juice. 

FIGURE 26.28 Diagram of an electrodialysis salt separation process. A denotes an anion-exchange membrane and C denotes a cation-exchange membrane. 

Figure 8.1 Membranes affect ionic transport, (a) Electrolytic conduction with inefficient electrolysis, (b) Addition of cation-exchange membrane allows efficient electrolysis of NaCI for Cl2 and NaOH production, (c) Salt depletion occurs between a pair of anion- and cation-exchange membranes, (d) Electrodialysis multiple membrane pairs between a single pair of electrodes efficiently use current to produce dilute and concentrated NaCI solutions.

Table 3.3 Current efficiency in electrodialysis of hydrochloric acid solution and electrical resistance of anion exchange membranes and composite membranesa...

G.A. Gutter and H.K. Bishop, Investigation of inorganic ion exchange membranes for electrodialysis application, Office of Saline Water, Research and Development Progress Report, No. 279. 

K.S. Rajan, D.B. Boies, A.J. Casolo and J.I. Bregman, Inorganic ion-exchange membranes and their application to electrodialysis, Desalination, 1966, 1, 231-246 Electrodialytic demineralization of brackish waters by using inorganic ion-exchange membranes, Desalination, 1968, 5, 371-390. 

R.B. Hodgdon, E. Witt and S.S. Alexander, Macroreticular anion exchange membranes for electrodialysis in the presence of surface water foulants, Desalination, 1973, 13, 105-127. 

Figure 5.19 Change in voltage drop across the cation exchange membrane during electrodialysis with concentration of 18-crown-6 or 15-crown-5. 1 without crown ether 2 with 100gC of 18-crown-6 3 with 300gl ] of 18-crown-6 4 with 300gl l of 15-crown-5. After the cation exchange membrane (NEOSEPTA CM-1, Na+ form) had been immersed in the respective aqueous 20% crown ether solution until equilibration (48 h at 60 °C), a 1 1 mixed solution of 0.250 N potassium chloride and 0.250 N sodium chloride was electrodia-lyzed with 10 mA cm 2 for 60 min in the presence of the respective crown ether at various concentrations in the desalting side solution.

Table 5.5 Transport numbers of sulfate and nitrate ions relative to chloride ions, equivalent ratios of sulfate and nitrate ions to chloride ions during electrodialysis in anion exchange membranes and the ratio of mobility of sulfate ions and nitrate ions to that of chloride ions in the membrane...

Figure 5.25 Distribution of sulfur based on sulfonate groups through a cross-section of an anion exchange membrane before electrodialysis (analyzed by EPMA). A commercial anion exchange membrane (NEOSEPTA AM-1 strongly basic anion exchange) was immersed in an aqueous 200ppm anionic polyelectrolyte (polycondensation product of naphthalene sulfonate and formaldehyde, MW ca. 1000) solution for 17 h at 25.0 °C, washed with pure water, and dried.

Figure 5.29 Effect of ion exchange capacity of anion exchange membranes and composite membranes on Paso4. (H) Commercial anion exchange membrane (NEOSEPTA AM-1, AM-2 and AM-3, strongly basic anion exchange) ( ) Fe-Py membrane (A) Py-Fe membrane. Transport numbers of sulfate ions relative to chloride ions were measured by electrodialysis using a 1 1 mixed salt solution of sodium sulfate and sodium chloride (concentration of sodium ions 0.04 N) at 10 mAcm 2 for 60 min at 25.0 °C under vigorous agitation. The ion exchange capacity on the horizontal axis represents values before preparation of the composite membranes.

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