Membranes anion exchange

Stannous Sulfate. Stannous sulfate (tin(Il) sulfate), mol wt 214.75, SnSO, is a white crystalline powder which decomposes above 360°C. Because of internal redox reactions and a residue of acid moisture, the commercial product tends to discolor and degrade at ca 60°C. It is soluble in concentrated sulfuric acid and in water (330 g/L at 25°C). The solubihty in sulfuric acid solutions decreases as the concentration of free sulfuric acid increases. Stannous sulfate can be prepared from the reaction of excess sulfuric acid (specific gravity 1.53) and granulated tin for several days at 100°C until the reaction has ceased. Stannous sulfate is extracted with water and the aqueous solution evaporates in vacuo. Methanol is used to remove excess acid. It is also prepared by reaction of stannous oxide and sulfuric acid and by the direct electrolysis of high grade tin metal in sulfuric acid solutions of moderate strength in cells with anion-exchange membranes (36). 

The feed solution containing ions enters a compartment whose walls are a cation-exchange and an anion-exchange membrane. If the anion-exchange membrane is in the direction of the anode, as shown for the middle feed compartment, anions may pass through that membrane in response to an electrical potential. Tne cations can likewise... 

Dijfusion Dialy The propensity of and OH" to penetrate membranes is useful in diffusion dialysis. An anion-exchange membrane will block the passage of metal cations while passing hydrogen ions. This process uses special ion-exchange membranes, but does not employ an applied electric current. 

The liquid membrane (thickness 0.2 cm) was separated from the aqueous solutions by two vertical cellophane films.The electrode compartments were filled with 0.05 M sulfuric acid solutions and were separated by the solid anion-exchange membranes MA-40. Binary mixtures contained, as a mle, 0.04 M Cu(II) and 0.018 M Pt(IV) in 0.01 M HCl. 0.1 M HCl was used usually as the strip solution. 

Fluoride F Few major industrial water problems Reduces dental decay Alum coagulation Magnesium Hydroxide reaction Anion exchange Membrane separation... 

Among electrochemical methods of water purification, one can also list the various electromembrane technologies, electrodialysis in particular. The simplest elec-trodialyzer consists of three compartments separated by semipermeable membranes (usually, cation- and anion-exchange membranes). The water to be purified is supplied to the central (desalination) compartment. In the outer (concentration) compartments, electrodes are set up between which a certain potential difference is applied. Under the effect of the electric field, ions pass througfi the membranes so that the concentration of ionic contaminants in the central compartment decreases. 

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. 

The feed solution containing ions enters a compartment whose walls are a cation-exchange and an anion-exchange membrane. If the... 

Varcoe JR, Slade RCT. 2005. Prospects for alkaline anion-exchange membranes in low temperature fuel cells. Fuel Cells 5 187-200. 

Matsuoka K, Iriyama Y, Abe T, Matsuoka M, Ogumi Z. 2005. Alkaline direct alcohol fuel cells using an anion exchange membrane. J Power Sources 150 27-31. 

Varcoe JR, Slade RCT. 2006. An electron-beam-grafted ETFE alkaline anion-exchange membrane in metal-cation-fiee solid-state alkaline fuel cells. Electrochem Commun 8 839-843. 

Yu EH, Scott K. 2004. Development of direct methanol alkahne fuel cells using anion exchange membranes. J Power Sources 137 248-256. 

In ED, cation-exchange membranes are alternated with anion-exchange membranes in a parallel manner to form compartments 0.5 to 1.0 mm thick. The entire membrane assembly is held between two electrodes. When an electrical potential is applied to the electrodes, all positive ions tend to travel towards the negative electrode, and all negative anions tend to move toward the positive electrode. 

This type of cell is limited by the performance of the anion-exchange membrane. The membrane can tolerate only a limited concentration of acid in the anolyte before backdiffusion of protons through the anion membrane becomes rather significant, causing a decrease in the cell s current efficiency, and acid gets into the salt stream. Unconverted salt in the product solutions can be eliminated by the use of the three compartment device, but this option substantially adds to the capital costs and operating complexity of the plant. 

A bipolar membrane is a sandwich of a cation and an anion exchange membrane which splits H20 to H+ and OH- under a potential of about 0.9 V. The reactor consists of a stack, of bipolar membranes, cation exchange membranes and anion exchange membranes arranged between a single anode and a single cathode with parallel hydraulytic circuits for the salt, acid product and alkali product, Fig. 32. 

The laboratory unit was based on a ElectroCell MP cell with an elec-trode/membrane area of 0.01 m2. A DSA (Dimensionally Stable Anode) anode served as oxygen electrode, Ni as cathode. Anion exchange membranes = Neosepta ACM (Tokuyama Soda) AMH cation ex-change membranes = Nafion 324 Nation 902. 

Animal uptake, of herbicides, 23 310 Animal viruses, 3 135-136 Animal waxes, 26 203, 206 Anion binding, in supramolecular chemistry, 24 43-47 Anion-exchange membranes, 15 836 Anion exchangers, organic fouling of, 24 416... 

The need to develop alternative electrocatalysts with low or, even better, without noble metals (platinum), to decrease the costs due to Pt shortage. New nano-structured electrocatalysts (HYPERMEC by ACTA SpA for example, http // www.acta-nanotech.com) [51, 52] have been developed, which are based on non-noble metals, preferentially mixtures of Fe, Co, Ni at the anode, and Ni, Fe or Co alone at the cathode. With ethanol, power densities as high as 140 mW cm-2 at 0.5 V have been obtained at 25 °C with self-breathing cells containing commercial anion-exchange membranes. 

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