Electrochemical batch reactor

Several of these studies were conducted in an electrochemical batch reactor that had a rotating-cylinder anode (RCA). Since the anode was operated below the limiting current for mediator generation, relatively high coulombic efficiencies were achieved. Ion-exchange membranes were used to separate electrodes in Ag(II)-based processes, but were eliminated in processes based upon Co(III) and H2SO4. Rates of CO2 generation were measured and used to... 

ELECTROCHEMICAL GENERATION OF OXIDANTS IN BATCH REACTOR Electrochemical batch reactor... 

Numerous treatability studies have been performed in small electrochemical batch reactors [13-15]. A typical batch reactor has a rotating cylinder anode (RCA) that is operated well below the limiting current for Ag(II) generation (Figure 4). The RCA enables the scientist or engineer to use a small apparatus to mimic mass-transport conditions in a pilot plant, without using massive flow-through electrochemical cells and pumps. 

THEORETICAL MODEL FOR ELECTROCHEMICAL BATCH REACTOR Differential mass balance for Ag(II)... 

Figure 16. Comparison of model predictions and experimental data for MEO of EG by Ag(II) in the electrochemical batch reactor. The cell was maintained at 40% i (673 mA and 33°C). Square ( ) and triangular (A) symbols represent data obtained during experiments with Nafion 117 cation-exchange membrane and Vycor microporous glass, respectively.

A batch reactor is charged with reactant, the required conversion takes place, and the reactor is emptied. One consequence is that the concentration of the reactant and products in the reactor are a function of time. There are two types of electrochemical batch reactors those without electrolyte recirculation (Fig. 4.1a), and those with recirculation (Fig. 4.1b). The former are suitable as laboratory devices for obtaining performance data as a function of electrode potential, reactant concentration, and hence conversion as described in Section 3.2.2.2. The reactor is often run in a potentiostatic... 

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... 

The investment for equipment is somewhat higher than for chemical reactors, but an electrochemical reactor can be applied to many more reaction types than a chemical one. Technical electrolyses are mostly run in continuous flow reactors, sometimes for years without change of the electrodes, which saves personnel, maintenance, and solvent costs as compared to chemical conversions, which are often performed in batch reactors. 

Fig. 15.1. Types of electrochemical reactor (a) Batch reactor (b) Plug flow reactor (c) Backmix flow reactor.

Factors to consider when selecting an electrochemical reactor are listed in Table 26.10 [30]. Batch reactors are chosen for the synthesis of high value-added products in small quantities, whereas continuous reactors are more amenable to large-scale production. When the anolyte and catholyte... 

The simple batch reactor was considered in Chapter 4, A modified version in which the electrolyte is recirculated, however, is the preferred mode of operation in the electrochemical industry because it provides flexible batch volume and also enhances the mass transfer characteristics of the cell due to circulation. Further, with recirculation, the reactor can be operated either in the plug-flow or mixed-flow mode. We consider all three cases here along with a few other common modes of operation. 

The experimental setup of a batch reactor employed by Rastogi et al. [52] to monitor potential changes at the cathode during electrochemical deposition of lead metal at an air-water interface is shown in Fig. 13.23. In this experiment the micro-slide is put in a dish containing an aqueous solution of lead acetate in such a manner that a small volume of the solution is just above the slide. Two platinum electrodes Pj and Pj are inserted in the solution. The anode Pj is inserted below the surface of the solution while the lower end of the cathode is put just at the surface of the solution. Potential changes during electrochemical deposition of lead metal were monitored with the help of platinum electrode P2 coupled with a calomel electrode C. 

Batch and flow reactor experiments were compared. In case of CSTR, fluctuations were periodic whereas in a batch reactor oscillations were more like random noise when the current was 8.0 mA. It has been found that polymer influenced the oscillatory and growth behaviour during electrochemical deposition of lead. Results also indicated a transition from dendritic to DLA/fractal-type structure on the addition of PVA in the solution. 

The tank cell is the classical batch or semi-batch reactor of electrochemical technology. In most tank cells, the electrodes are vertical and made from sheet, gauze or expanded material. The cell is arranged with parallel lines of alternate anodes and cathodes, the electrodes extending across and to the full depth of the tank. The anode-cathode gap is made as small as possible to maximize the space-time yield and to reduce the energy consumption. It is unusual in tank cells to induce convection by mechanical means, but electrolyte stirring is in generally promoted... 

Oxidation and reduction are fundamental processes in the synthesis of organic and inorganic compounds. Some oxidation and reduction reactions are difficult to control in macro-scale batch reactors and in such cases microflow reactors serve as powerful tools for accomplishing the reactions in a highly controlled manner. This is especially true for many oxidation reactions because of their exothermic nature. It should also be noted that the danger of unexpected explosions can be avoided by the use of microflow reactors because of the small volume and highly efficient heat transfer ability of microflow systems. This chapter provides an overview of oxidation and reduction reactions using chemical, electrochemical and biochemical methods in microflow reactors. 

The overall kinetic behaviour of an electrochemical reactor may be illustrated by considering the example of a simple batch reactor. 

Fig. 2.23 Simplified heat balance over electrochemical reactors, (a) Simple batch reactor with electrolyte cooling via an internal heat exchanger, (b) Flow-through reactor with the electrolyte acting as a heat-exchanging medium.

Vasudevan, D. Basha, C. A. A kinetic study on the electrochemical bromination of fluorescein to eosin in a batch reactor. J. Indian Chem. Soc. 1998, 75, 165-166. 

For obtaining meaningful results, the experimental setup needs to enable accurate electrochemical measurement of the current and voltage, and it should also allow highly sensitive product identification and quantity of all possible products. Two main types of reactors have proven efficient (i) batch reactors and (ii) flow reactors, the latter enabling enhanced mass transfer of carbon dioxide, as compared to batch reactors. One can utilise conventional H-cells or one can devise special cells, equipped with parallel electrodes to achieve uniform electric field distribution. Home-designed gas-tight cells were also reported. 

Eig. 3. Configurations for the stirred tank electrochemical reactor (STER). The surge tank contains both reactant and product, (a). Batch (b), semibatch ... 

Product Recovery. Comparison of the electrochemical cell to a chemical reactor shows the electrochemical cell to have two general features that impact product recovery. CeU product is usuaUy Uquid, can be aqueous, and is likely to contain electrolyte. In addition, there is a second product from the counter electrode, even if this is only a gas. Electrolyte conservation and purity are usual requirements. Because product separation from the starting material may be difficult, use of reaction to completion is desirable ceUs would be mn batch or plug flow. The water balance over the whole flow sheet needs to be considered, especiaUy for divided ceUs where membranes transport a number of moles of water per Earaday. At the inception of a proposed electroorganic process, the product recovery and refining should be included in the evaluation to determine tme viabUity. Thus early ceU work needs to be carried out with the preferred electrolyte/solvent and conversion. The economic aspects of product recovery strategies have been discussed (89). Some process flow sheets are also available (61). 

A first application using ferroceneboronic acid as mediator [45] was described for the transformation of p-hydroxy toluene to p-hydroxy benzaldehyde which is catalyzed by the enzyme p-cresolmethyl hydroxylase (PCMH) from Pseudomonas putida. This enzyme is a flavocytochrome containing two FAD and two cytochrome c prosthetic groups. To develop a continuous process using ultrafiltration membranes to retain the enzyme and the mediator, water soluble polymer-bound ferrocenes [50] such as compounds 3-7 have been applied as redox catalysts for the application in batch electrolyses (Fig. 12) or in combination with an electrochemical enzyme membrane reactor (Fig. 13) [46, 50] with excellent results. 

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