Process electrochemical conversion

The metallic or semi-metallic character of many common sulfides implies the significance of electrochemical factors in the study of their oxidation, which is relevant to environmental, energy, and metallurgical issues, e.g., in connection with the direct electrochemical conversion of sulfide ores to metals, the pressure leaching of ore materials, or flotation processes. 

The electrolysis in aqueous sulfuric acid with methanol as a cosolvent was perfomed in a filterpress membrane cell stack developed at Reilly and Tar Chemicals. Because of the low current density of the process, a cathode based on a bed of lead shot was used. A planar PbOa anode was used. The organic yield was 93% with approximately 1% of a dimer. The costs of the electrochemical conversion were estimated as one-half of the catalytic hydrogenation on a similar scale. 

Cathodic addition involves either the reduction of a 7T-system in an ECEC process (electrochemical, chemical, electrochemical, chemical) and the chemical reaction (C) of the intermediates with a carbon or heteroatom electrophile or the cathodic conversion of a C—X bond in an ECE process into an anion that adds to an electrophilic jr-system. The electrochemical Birch reduction of arenes... 

Fuel cell operation entails (1) coupled proton migration and water fluxes in the PEM, (2) circulation and electrochemical conversion of electrons, protons, reactant gases, and water in CLs, and (3) gaseous diffusion and water exchange via vaporization/condensation in pores and channels of CLs, GDLs, and EEs. All components of an operating cell have to cooperate well in order to optimize the highly nonlinear interplay of these processes. It can be estimated that this optimization involves several 10s of parameters. 

Development of the industrial process for electrochemical conversion of acrylonitrile to adiponitrile led to extensive investigation into the mechanism of the dimerization process. Reactions of acrylonitrile radical-anion are too fast for investigation but the dimerization step, for a number of more amenable substrates, has been investigated in aprotic solvents by electrochemical techniques. Pulse-radiolysis methods have also been used to study reactions in aqueous media. 

The pyridinium salt NAD 19a and its reduced form NADH 20a are important co-factors for many enzymes, fhe reduced form is involved in enzyme mediated reductions where it is converted to NAD. In natural systems, NAD is converted back to NADH by another enzyme-controlled process. Attempts to effect the direct electrochemical conversion of NAD to NADH are not very successful. Reduction on a mercury cathode at -1.1 V see on the first one-electron reduction wave leads to the radical-zwitterion, which reacts further to give dimers. Three stereoisomers of the 4,4 -dimer account for 90 % of the mixture and three 4,6 -dimers form the remainder [78]. Reduction at -1.8 V on the second reduction wave produces only 50 % of enzymatically active 1,4-NADH. The NAD analogue 19b shows related behaviour and one-electron reduction affords two diastereoisomers... 

The vast majority of small-amplitude methods are based on small-amplitude potential excitations with potential control of the surface concentrations. In earlier chapters, the relationship between surface concentration and electrode potential was explored and the concept of concentration profiles was presented. Whenever there is a flux of electrons at the electrode surface, the concentration profiles of at least two species will exhibit nonzero slopes at the electrode surface, as the electrochemical conversion of one member of a couple into another takes place and mass transport processes act to reestablish a uniform concentration distribution. These processes occur irrespective of whether the current flux arises from a potential or current excitation of the cell. In either case, they result in a perturbation from the previously existing concentration profile. The initial surface concentrations (which existed prior to the application of the new perturbation) are often termed the dc surface concentrations. It is useful to note that at any time, the distance integral of the concentration excess or defect is directly proportional to the charge passed due to that per-... 

For high values of k°r, very sharp decays of the current-time transients are observed, indicating the almost immediate electrochemical conversion of oxidized species (see solid lines corresponding to k°r = 100). Indeed, for k°t > 100, the faradaic conversion is so fast that the oxidized species disappears at the very first instants of the experiment and under these conditions 0p = 0. When k°r decreases, the observed currents also decrease, since the rate constant modulates the whole faradaic current. For k°t < 1, the current transients appear as quasi-linear, with current-time profile being shifted toward more negative potentials. Under these conditions, general equation (6.130) becomes identical to Eq. (6.134), corresponding to irreversible processes. 

In most corrosion processes passivity is desirable because the rate of electrode dissolution is significantly reduced. The rate of aluminum corrosion in fresh water is relatively low because of the adherent oxide film that forms on the metal surface. A thicker film can be formed on the surface by subjecting it to an anodic current in a process known as anodizing. In most electrochemical conversion processes passive films reduce the reaction rate and are, therefore, undesirable. 

Comninellis C. Electrocatalysis in the electrochemical conversion/combustion of organic pollutants for waste water treatment. Proceedings of the Symposium on Water Purification by Photocatalytic, Photoelectrochemical and Electrochemical Processes. Vol. 94-19. Pennington, NJ The Electrochemical Society, 1994 75-86. 

An electrochemical process for treating low-level nuclear wastes is in the laboratory stage and not yet engineered. It must be understood less as a solution to the hazards of the low-level nuclear products contained in nitrate solution than as a solution for the remediation of the huge quantities of nitrate stored at nuclear waste depositories. The economic viability of the electrochemical process for conversion of nitrates to NH3 and N2 depends on the commercial development of its by-products, NaOH and HN03. 

It has a global capacity of 1.3 million tonnes per year. In the United States, production of ADN is based on the hydrocyanation of butadiene or electrochemical conversion from acrylonitrile. In Western Europe, companies produce ADN from adipic acid, butadiene and acrylonitrile. In Japan, the sole producer makes ADN from the electrodimerization of acrylonitrile. Demand for ADN is expected to be around 2% per year through at least 201 (f A comparison of the costs associated with two of the ADN processes are shown in Table 22.1275. 

Abstract. The paper presents results of theoretical and experimental investigations of the process of electrochemical conversion of organic dielectrics into nanosized carbon structures. A new low-temperature method for the synthesis of fractal carbon materials with micro- and nanoparticles having a fibrous, spheroidal, dendritic, and other structure has been briefly characterized. 

For technical purposes a partial conversion with an easy to perform workup is feasible. Therefore, a series of electrolyses were performed to a specific conversion (Fig. 5.11). During electrochemical conversion the amount of 13 increases in a linear fashion up to 0.3 F mol-1 1. Subsequently, side reactions appear and limit the amount of isolated 13. For an efficient process and high-quality product, a partial conversion of about 30% is reasonable. Since excess of 12 is easily recovered, virtually no loss of material occurs, creating a good basis for a continuous preparation of 13. 

PUtter, H., Weiper-Idelmann, A., Merk, C., Fryda, M., Klages, C.-P., Schafer, L. and Hampel, A. (2003) Process for the electrochemical conversion of organic compounds on diamond coated electrodes. European patent EP 1 036 861 Bl. BASF Aktiengesellschaft, Fraunhofer Gesellschaft, Germany. 

The DMFC operates, as its name suggests, by direct, complete electrooxidation of methanol to CO2 at the cell anode. The methanol anode is coupled in the DMFC with an air cathode, completing a cell schematically shown in Fig. 50. In the majority of recent development efforts, the DMFC has been based on a protonconducting polymeric membrane. The uniqueness of this type of fuel cell is the direct anodic oxidation of a carbonaceous fuel. Such a direct electrochemical conversion process of liquid fuel and air to electric power at low temperatures can provide a basis for a very simple fuel-cell system. 

In Chapter 3, by Shaigan, electrodeposition for electrochemical conversion and storage devices is presented. This chapter discusses the latest developments on metal, metal oxide, and conductive polymer electrodeposition processes developed and studied for the applications in the fields of fuel cells, batteries, and capacitors. The importance of electrodeposited materials, which are used or may have the future potential applications in the energy conversion or storage, is clearly shown. 

---