Electrochemical reactor optimization

The design optimization of an electrolytic cell aims at a high throughput with a low energy consumption at the lowest feasible cost. The throughput of an electrochemical reactor is measured in terms of the space time yield, Yt, defined as the volumetric quantity of the metal produced per unit time per unit volume of the process reactor. This quantity is expressed as ... 

The concentration of any of these species depends on the total concentration of dissolved aluminum and on the pH, and this makes the system complex from the mathematical point of view and consequently, difficult to solve. To simplify the calculations, mass balances were applied only to a unique aluminum species (the total dissolved aluminum, TDA, instead of the several species considered) and to hydroxyl and protons. For each time step (of the differential equations-solving method), the different aluminum species and the resulting proton and hydroxyl concentration in each zone were recalculated using a pseudoequilibrium approach. To do this, the equilibrium equations (4.64)-(4.71), and the charge (4.72), the aluminum (4.73), and inorganic carbon (IC) balances (4.74) were considered in each zone (anodic, cathodic, and chemical), and a nonlinear iterative procedure (based on an optimization method) was applied to satisfy simultaneously all the equilibrium constants. In these equations (4.64)-(4.74), subindex z stands for the three zones in which the electrochemical reactor is divided (anodic, cathodic, and chemical). 

Furan was also the starting material in the indirect electrochemical preparation of 2,5-dimethoxyfuran in a packed bed electrochemical reactor <2001MI185>. This process had a current efficiency of >9000 %, a product yield >90 %, and the electrical energy consumption was <3 kW h kg of product under the optimized operating conditions. These conditions required a reaction temperature between 0 and 5°C, 4.0. 6 V of electrolysis voltage, and >2000 Am operating current density (c.d.). 

The above analysis is, of course, based on the assumption of simple order reactions under Tafel operation and on the availability of sufficiently accurate data ( 5-10%). With complex reaction kinetics, for example, those involving surface adsorption terms (Eq. 16), a nonlinear regression analysis would yield the best estimate of a, Uj, and for a possible kinetic model. In all cases, use of these parameters for predicting the performance of an electrochemical reactor or the selectivity of a reaction scheme should be restricted within the potential, concentration, and temperature range that they were determined. We should stress here that kinetic information is presently scanty for complex, multiple electrochemical reactions, yet it is essential for the design, optimization, and control of electrochemical processes. 

For a given pair of electrode reactions of known thermodynamic and kinetic characteristics, electrochemical engineering procedures must provide a reactor design in which these reactions can occur with high material and energy efficiencies. Simultaneously, appropriate provisions have to be made for the input of reactants and outflow of products and for the addition (or removal) of electric and thermal energy. The emphasis here is on the complete system and the inter-related surface reactions and transport processes. System analysis and design of electrochemical reactors require elaborate computer-implemented process simulation, synthesis, and optimization. 

The optimization of an electrochemical reactor calls for a full description of the process to accomplish the specific objective of the mass and the energy balances together with heat transfer considerations and thermodynamic and enthalpy changes that are related to the unit cell and the whole stack [1,2]. A full description of the kinetics of both processes, the electric properties of the cell components, and the hydrodynamic aspects of the entire cell is also required. 

Accordingly, the concentration profile of the processes changes with respect to the type of mechanism and to the rate determining specific constant, k (from 10 5 to 1010 s-1). In the case of industrial electrochemistry, the optimized conditions of work imply the minimization of loss, according to the side reactions. This is a consequence of the selectivity condition needed in the case of an electrochemical reactor. In a general treatment the theoretical model of the reactor is based on mass conservation laws with the corresponding electrochemical kinetics (coupled or not to side reactions). For example, the EC mechanism can be treated as follows ... 

This book on "Environmental Oriented Electrochemistry" concentrates on the Electrochemistry/Environment relationship including, among others, chapters on design and operation of electrochemical reactors and separators, process simulation, development and scale-up, optimization and control of electrochemical processes applied to environmental problems, also including economic analysis, description of unique current and future applications, in addition to basic research into developing new technologies. 

EnFACE is an electrochemical method that consists of specialized electrochemical reactor for transfer of micropattem on metal substrates. EnFACE is an acronym for Electrochemical Nano and micro-Fabrication by optimizing Chemistry and Engineering. This is a disruptive electrochemical deposition and dissolution process with the potential to create alternative to many existing micropatteming techniques. 

Fig. 2.3 Cost components for an electrochemical reactor as a function of current density, showing optimization of the current density according to minimum product cost.

Electrochemical reactions proceed, in principle, heterogeneously at the electrode surfaces. Hence, the mass transfer has a major influence, especially on the selectivity of the electrode reactions. Therefore, the mixing conditions in the cell have to be optimized, considering also the operation mode as batch or as flow-through reactor. 

L.L. Raja, R.J. Kee, R. Serban, and L.R. Petzold. A Computational Algorithm for Dynamic Optimization of Chemical Vapor Deposition Processes in Stagnation Flow Reactors. J. Electrochem. Soc., 147 2718-2726,2000. 

Besides these conventional reactors with spherical immobilizates, urease has also been immobilized inside nylon tubing and pipette tips ( enzyme pipette , Sundaram and Jayonne, 1979), on nylon fibers ( enzyme brush , Raghavan et al., 1986), and on the surface of a magnetic stirrer (Guilbault and Starklov, 1975). The urease reaction was in each case carried out at optimal pH after removal of the immobilized enzyme NH3 was assayed electrochemically or photometrically according to Berthelot s method. 

One of the most intensively studied interfaces is the electronic conductor/ionic conductor where the interest is motivated by attempts to prevent corrosion and to improve the catalytic properties of metallic deposition. Both corrosion prevention and catalysis development can be described using an electrochemical and engineering approach, including film formation and growth and its optimization in the cell reactor. 

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