Electrodialysis membranes

The temperature of the feed should be 20 to 40 °C above the feed dew point. 

Configuration, see Section 4.15. Usually use flat or hollow fiber. 

Driving force for the rate of separation concentration of target species. 

Membrane symmetric microporous with 0.1 to 10 nm pore diameter. Hydraulic permeability 10 to 8 g/s m MPa. Membrane-solute permeability 0.05 to 9 m/s depending on the solute and the membrane. Dialysis transfer coefficient 1 to 10 pm/s. Hollow fiber. 

Proteins denature at temperatures 80 °C. Glass temperature for many polymers = 60 °C. Very high flowrates should be avoided since they can generate transmembrane pressure. 

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Membrane Porosity Separation membranes run a gamut of porosity (see Fig. 22-48). Polymeric and metallic gas separation membranes, electrodialysis membranes, pervaporation membranes, and reverse osmosis membranes are nonporous, although there is hnger-ing controversy over the nonporosity of the latter. Porous membranes are used for microfiltration and ultrafiltratiou. Nanofiltration membranes are probably charged porous structures. 

Ion-exchange processes can be driven by concentration gradients or by an electric field applied across the membrane (electrodialysis), the ions not merely being exchanged but actually passing across. 

The process operates at current densities of about 1 kA/m2 and unit cell voltage of 1.5 V. The specific energy consumption is about 2 kWh/kg NaOH. Under the influence of the electric gradient the H + and OH ions emerge on opposite faces of the membrane. Bipolar membrane electrodialysis is being developed by several companies, e.g. WSI Technologies Inc. [270] and Aquatech Systems [129,275,276], Typical product specification ranges for the ICI electrodialysis process is summarized in Table 19. 

Fig. 32. Bipolar membrane electrodialysis of NaA to HA and NaOH ( salt splitting ) [270]...

Paleologou M, Wong P-Y, Berry RM (1992) A solution to the caustic/chlorine imbalance bipolar membrane electrodialysis, J Pulp and Paper Sci, 18(4) J138 Chem Abstr 117 (1991) 253647u... 

Bazinet, L., Lamarche, F., Labrecque, R., Toupin, R., Boulet, M., and Ippersiel, D. 1997. Electroacidification of soybean proteins for the production of isolate. Food Technol. 51(9), 52-56, 58, 60. Bazinet, L., Lamarche, F., and Ippersiel, D. 1998. Bipolar-membrane electrodialysis Applications of electrodialysis in the food industry. Trends in Food Sci. Technol. 9, 107-113. 

Gillery, B., Bailly, M., and Bar, D. 2002. Bipolar membrane electrodialysis The time has finally come. In Proceedings of 16th International Forum on Applied Electrochemistry Cleaner Technology—Challenges and Solutions. Amelia Island Plantation (FL, USA) November 10-14 (online publication htpp //ameridia.con.htmEebc.html). 

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... 

Problems in the practical application of bipolar membrane electrodialysis In addition to the precipitation of multivalent ions in the base containing flow stream and the stability of the ions in strong acids and bases a serious problem is the contamination of the products by salt ions that permeate the bipolar membrane. In particular, when high concentrations of acids and bases are required the salt contamination is generally high [28] as illustrated in Figure 5.13 that illustrates the conversion of... 

Recovery of lactic acid is complicated by the high solubility of its salt. The traditional method of recovering calcium lactate is being replaced by membrane, electrodialysis, or... 

Membranes may be hastily classified according to the driving force at the origin of the transport process (1) a pressure differential leads to micro-, ultra-, nanofiltration, and reverse osmosis (2) a difference of concentration across the membrane leads to diffusion of a species between two solutions (dialysis) and (3) an electric potential difference applied to an ion-exchange membrane (lEM) leads to migration of ions through the membrane (electrodialysis, membrane electrolysis, and... 

Bazinet L, Lamarche E, and Ippersiel D. Bipolar-membrane electrodialysis An application of electrodialysis for the food industry. Trends Food Sci. Tech. 1998 9 107-113. 

Escudier J, Saint-Pierre B, Batlle J, and Moutounet M. Automatically controlled tartaric stabiUsation of wine by membrane electrodialysis which reduces its conductivity to the desired level. 1995. World Patent no 9 506 110-Al. 

Xu TW and Yang WH. Effect of cell conUgurations on the performance of citric acid production by bipolar membrane electrodialysis. 

Concentration of HI over Hix solution by polymer electrolyte membrane electrodialysis was investigated using galvanodynamic and galvanostatic polarisation method. For this purpose, Hix solution with sub-azeotrope composition (HI L HjO = 1.0 0.5 5.8) was prepared. It was noticed that the electrical energy demand for electrodialysis of Hix solution decreases with increasing temperature. From the experimental results, it is concluded that the system resistance crucially affects the electrodialysis cell overpotential and hence the optimisation of cell assembly as well as the selection of low resistance materials should be carried out in order to obtain high performance electrodialysis cell. 

Electrodialysis involves the use of a selectively permeable membrane, but the driving force is an electrical potential across the membrane. Electrodialysis is useful for separating inorganic electrolytes from a solution, and can therefore be used to produce freshwater from brackish water or seawater. Electrodialysis typically consists of many cells arranged side by side, in a stack. Figure 9.12 illustrates a two-cell stack. 

Figure 3.17 Organic fouling of an anion exchange membrane. Electrodialysis was carried out using 0.05 N sodium chloride solution containing sodium dodecylbenzene sulfonate (100ppm) at a current density of 3.5 mA cm 2 at 25.0 °C. (Membrane strongly basic anion exchange electrical resistance measured in 0.05 N sodium chloride solution 3.5 Q cm2).

R. Yamane, T. Sata, Y. Mizutani and Y. Onoue, Concentration polarization phenomena in ion-exchange membrane electrodialysis. II. The effect of the condition of the diffusion-boundary layer on the limiting current density and on the relative transport numbers of ions, Bull. Chem. Soc. Jpn., 1969, 42, 2741. 

Y. Tanaka, Concentration polarization of ion exchange membrane, J. Membr. Sci., 1991, 57 Water dissociation in ion-exchange membrane electrodialysis, J. Membr. Sci., 2002, 203, 227-244. 

Josefsson, B.O., 1970. Determination of soluble carbohydrates in seawater by partition chromatography after desalting by ion-exchange membrane electrodialysis. Anal. Chim. Acta, 52 65—73. 

Bazinet, L., Lamarche, F., and Ippersiel, D. (1998) Bipolar membrane electrodialysis Applications of electrodialysis in the food industry. Trends in Food Science and Technology 9, 107-113. 

Tanaka, Y. (2006) Irreversible thermodynamics and overall mass transport in ion-exchange membrane electrodialysis. Journal of Membrane Science 281, 517-531. 

Y. Tanaka, Ion Exchange Membrane Electrodialysis Fundamentals, Desalination, Separation, Nova, New York, NY, 2010. 

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