Packed-bed anodes

Figure 11. Schematic diagram of an anodic packed-bed anode reactor.

Figure 14 Schematic diagram of the packed bed cell and the flow circuit utilized for the treatment of human wastes (1) reservoir (2) pump (3) valve (4) flow meter (5) anode current collector (6) packed bed anode (7) cathode (8) water condenser (9) water inlet (10) water outlet and (11) outlet for gases. (From Ref. 57.)...

Fig. 15.29. Schematic diagram of a packed-bed cell and flow circuit. 1, Reservoir 2, pump 3, valve 4, flowmeter 5, anode current collector 6, packed-bed anode 7, cathode ...

The oxidation of aniline in sulfuric acid was studied by Kirk et al. on a packed-bed anode made up of 1 mm spherical lead pellets in contact with a pure lead anode collector plate [27]. The lead pellets were oxidized to lead dioxide for an hour in sulfuric acid (pH = 2) at 300 A/m. No mention was made of the corrosion resistance of these anodes. The anodic destruction of aniline to CO2 was found to occur through the formation of benzoquinone and maleic acid. At a current of 2 A, the initial rate of aniline (2.7 mM) oxidation was very rapid with more than 90% of the initial aniline being oxidized within one hour. After 5 h of operation, 72.5% of the... 

Fig. 6. An electrochemical reactor used for aniline oxidation on a lead dioxide packed-bed anode (A) lead anode (B) 1 mm lead pellets (C) stainless steel cathode (D) Na-fion 427 membrane (E) stainless steel retaining screen (F) glass beads (G) gasket (H) inlet (I) outlet (J) cathode gas vent. (Adapted from (27]).

Card et al. [108] oxidized dissolved sulfur dioxide gas to sulfuric acid, at room temperature, using packed bed anodes. The corresponding cathodic reaction was oxygen reduction to water. A variety of electrodes and electrode systems were studied,... 

A packed bed graphite reactor has been applied to the direct oxidation of SO2. At the steady state the reactor was able to reduce the concentration of SO2 in the gas phase from 8000 ppm to 200 ppm [48]. The electro-generative oxidation of dissolved sulphur dioxide has also been demonstrated with packed bed anodes [52]. 

A system based on a copper redox system [55] is a combined electrolytic and catalytic process carried out in a three-compartment cell. The cell consists of a central packed bed anode of graphite separated by an ion exchange membrane from a packed cathode bed of copper on one side, and on the other side a packed bed of Cu which acts as an absorber. In the absorption chamber the copper, after first being oxidised to cuprous oxide, is responsible for the oxidation of SO2 to sulphuric acid. 

Card, J. C., Foral, M. J., Langer, S. H. (1988). Electrogenerative oxidation of dissolved sulfur dioxide with packed-bed anodes. Envionmental Science Technology, 22, 1499—1505. http //dx.doi.org/10.1021/es00177a018. 

Sell, D., Kramer, P., Kreysa, G. (1989) Use of an oxygen gas diffusion cathode and a three-dimensional packed bed anode in a bioelectrochemical fuel cell. Applied Microbiology and Biotechnology, 31, 211-213. 

ER cell ElectroCell AB For example, packed bed of carbon particles within a parallel plate and frame Discontinuous via anodic or open circuit leaching Yes V V... 

Figure 8 (Top) Electrochemical flow cell for the oxidation of phenol and aniline (a) Pb anode feeder (b) packed bed of 1-mm lead pellets (c) stainless steel cathode plate (d) Nation membrane (e) stainless steel screen (f) Luggin capillary (g) glass beads (h) gasket (i) reactor inlet (j) reactor outlet. (Bottom) Schematic of apparatus (a) electrochemical reactor (b) peristaltic pump (c) water bath (d) heater (e) anolyte reservoir (t) gas sparging tube (g) C02 adsorbers. (From Ref. 39.)... 

Osasa K, Kawanami H, Tukamoto E, Sakai K. Performance of continuous electroflotation of an oil-in-water (O/W) emulsion using a packed-bed-type sacrificial electrode as an anode. Kagaku Kogaku Ronbunshu 1996 22 1450-1456. 

Kaba and Hitchens (1989) found that electrolysis of a mixture of urine and feces produced C02, N2, and H2. Some HOC1 is generated this eliminates the pathogens and bleaches the contents. The anodic reactions at 90 °C consume the biomass the cathode evolves hydrogen and can be assumed to deposit the small metal content. The residuum is sodium chloride from the urine. Most of the electrochemical studies that establish the basis of a practical process for electrochemical sewage treatment have been carried out on packed-bed electrodes as shown in Fig. 15.29. 

Another way to obtain high degrees of conversion, besides the close positioning of anode and cathode, is through the use of porous and packed bed electrodes. Since these electrodes have great importance in the laboratory as well as at an industrial level, they are described separately. 

Ho et al. used a packed-bed reactor and a series of 316 stainless steel fiber an-ode/cathode pairs to decompose cyanide-containing effluent [41]. The cyanide destruction process was enhanced by the presence of metal ions, which led the authors to treat a copper cyanide effluent. The cyanide concentration was decreased from an initial concentration of 1400ppm to less than 20 ppm within a 4-20 h time period at an energy consumption of 5 -13 kW h/kg CN. At a CN/Cu ratio of 4.6 most of the copper was deposited on the cathode while some was converted to the divalent form and deposited on the anode surface as an oxide. 

To avoid high-pressure drop and clogging problems in randomly packed micro-structured reactors, multichannel reactors with catalytically active walls were proposed. The main problem is how to deposit a uniform catalyst layer in the microchannels. The thickness and porosity of the catalyst layer should also be enough to guarantee an adequate surface area. It is also possible to use methods of in situ growth of an oxide layer (e.g., by anodic oxidation of a metal substrate [169]) to form a washcoat of sufficient thickness to deposit an active component (metal particles). Suzuki et al. [170] have used this method to prepare Pt supported on nanoporous alumina obtained by anodic oxidation and integrate it into a microcatalytic combustor. Zeolite-coated microchannel reactors could be also prepared and they demonstrate higher productivity per mass of catalyst than conventional packed beds [171]. Also, a MSR where the microchannels are coated by a carbon layer, could be prepared [172]. 

This process was developed further with packed-bed techniques. A limitation is that the particle size had to be reduced and this was carried out by the ultrasonic irradiation of the mixture before electrolysis. The average particle size was 25 p.m. A detailed analysis of the material balance was made [37], Ebonex reduced TiC>2 coated with SnC>2 doped with Sb2C>3 was found to be the best anode materials. A 1996 model cell is shown in Figure 1.20 [38]. 

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