Electrochemical reactor model

Fig. 2. Schematic models of a plug flow electrochemical reactor (PFER) and a stirred tank electrochemical reactor (STER).

Scale- Up of Electrochemical Reactors. The intermediate scale of the pilot plant is frequendy used in the scale-up of an electrochemical reactor or process to full scale. Dimensional analysis (qv) has been used in chemical engineering scale-up to simplify and generalize a multivariant system, and may be appHed to electrochemical systems, but has shown limitations. It is best used in conjunction with mathematical models. Scale-up often involves seeking a few critical parameters. Eor electrochemical cells, these parameters are generally current distribution and cell resistance. The characteristics of electrolytic process scale-up have been described (63—65). 

Filtration of Liquids Depending on the specific electrochemical reactor type, the filtration rate of a liqnid electrolyte throngfi tfie separator should be either high (to secure a convective snpply of snbstances) or very low (to prevent mixing of the anolyte and catholyte). The filtration rate that is attained under the effect of an external force Ap depends on porosity. For a separator model with cylindrical pores, the volnme filtration rate can be calcnlated by Poiseuille s law ... 

Ford WPJ, Walsh FC, Whyte I (1992) Simplified batch reactor models for the removal of metal ions from solution Inst Chem Eng Symp Ser, 1992, 127(Electrochem Eng Environ 92)111 Chem Abstr 117 (1992) 197712x... 

Markov chains theory provides a powerful tool for modeling several important processes in electrochemistry and electrochemical engineering, including electrode kinetics, anodic deposit formation and deposit dissolution processes, electrolyzer and electrochemical reactors performance and even reliability of warning devices and repair of failed cells. The way this can be done using the elegant Markov chains theory is described in lucid manner by Professor Thomas Fahidy in a concise chapter which gives to the reader only the absolutely necessary mathematics and is rich in practical examples. 

IV. MARKOVIAN MODELING OF ELECTROLYZER (ELECTROCHEMICAL REACTOR) PERFORMANCE... 

Figure 20. Schematic diagram of the packed-bed electrochemical reactor for 2-D model.

Cheng, C.Y. and Kelsall, G.H. (2007) Models of hypochlorite production in electrochemical reactors with plate and porous electrode. J. Appl. Electrochem. 37, 1203-1217. 

Mathematical Modeling of Cross-Flow, Solid State Electrochemical Reactors... 

In mathematical modeling of cross-flow solid-state electrochemical reactors, the dimension of the mathematical model increases with two additional variables compared to gas-liquid processes, since both the heat balance and the electron balance have to be considered. Introduction of an integral electron conservation balance results in an integro-differential problem. A comprehensive study of this kind was performed by Vayenas et al. [48] and by Debenedetti and Vayenas [49]. 

An overview of dynamic and the stady state analysis for design and modeling of the continuously stirred tank electrochemical reactor has been published [40]. 

Electrochemical reaction engineering deals with modeling, computation, and prediction of production rates of electrochemical processes under real technical conditions in a way that technical processes can reach their optimum performance at the industrial scale. As in chemical engineering, it centers on the appropriate choice of the electrochemical reactor, its size and geometry, mode of operation, and the operation conditions. This includes calculation of performance parameters, such as space-time yield,... 

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. 

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 ... 

Recently, Do and coworkers have extensively studied the electrochemical oxidation of benzyl alcohol in an aqueous-organic emulsion phase in the presence of a PT catalyst (soluble and immobilized) and Cl /QO in batch (Do and Chou, 1989, 1990, 1992) and continuous (Do and Do, 1994a-c) electrochemical reactors. Besides studying the various factors affecting the current efficiency, a detailed mathematical model has been developed for this system in these articles, accounting for the kinetics and mechanism of the reaction. 

Do and Do(1994a-c) have reported a detailed modeling and kinetic study of the electrochemical oxidation of benzyl alcohol to benzaldehyde in a continuous-stirred tank electrochemical reactor. 

The dynamic model for the rotating- anode electrochemical reactor is based upon a differential mass balance for Ag(II) and organics [13]. The rate of accumulation of the i-th reactant in the anolyte, VdC/dt, is equivalent to the difference between generation and loss terms ... 

The modeling of ECR systems involves, as that of any other reaction system, the development of a suitable reaction model for subsequent use in reactor modeling. The reaction model for an ECR is an expression for the dependence of current density on reaction parameters such as reactant concentration, electrode potential, rate constants, pH, temperature, etc. The reactor model relates the reactor parameters to performance criteria. The objective is to evolve suitable expressions for the computation of the electrode area required for a desired conversion, batch time, etc. We devote the next section to developing reaction models for simple electrochemical systems and proceed to reactor modeling in the following section. 

Now we illustrate the application of some of the reactor modeling methods outlined to a typical electroorganic process, the electrochemical production of />-anisidine, using the parameter values given by Goodridge and Scott (1995) (see also Clark et al., 1988). 

Bisang, J.M. (1997), Modelling the startup of a continuous parallel plate electrochemical reactor, Journal of Applied Electrochemistry, 27(4) 379-384. 

A work targeted at chemistry and engineering students at master s degree and PhD level. Covering concepts related to electrochemical engineering, kinetics, two-phase flow elecfrocatalysis and reactor modeling. 

---