Rotating Cylinder Electrode Cells

A rotating cylinder electrode (RCE) with a cylindrical or pseudo-cylindrical counterelectrode around it essentially has the geometry of a parallel plate cell. The RCE was developed as a specialty tool for uniform fast electrodeposition in turbulent flow, and for the removal of metal ions from effluents with recovery of the metal in the form of a foil, flake, or powder [61-63]. In the first application, RCE cathodes became the major tool for silver removal from photographic fixer solutions in compact, high-rate units [64], and enabled the recycling of fixer and resale of more than 98 wt% of the silver. Typically, such cells had a stainless steel RCE cathodes of 10-20 cm diameter rotating at speeds up to 1400 rpm, stationary graphite anodes, and were operated at 50 A. 

RCE cells find continuing use in controlled metal reclamation in a recent study, attention was focused on the recovery of precious metals from spent automobile exhaust catalysts [67]. 

Developments in both design and materials have greatly improved the performance of parallel plate cells, including the incorporation of features such as 3D electrodes from academic studies. Unfortunately, Electrochemical Engineering has not matured as an academic subject in the way that Martin Fleischmann would have wished, and it remains poorly 

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A typical 5 kA Eco cell has a cathode drum with a radius of 0.37 m, a height of 0.74 m and a cathode-membrane gap of about 1 cm. The cathode is rotated at 100-200 rev.min-1. In rotating-cylinder electrode cells, high fractional conversion can be obtained by employing an Eco cascade cell. 

Rotating cylinder electrode cell High High Small... 

Orhan G, Hapci G (2010) Effect of electrolysis parameters on the morphologies of copper powder obtained in a rotating cylinder electrode cell. Powder Technol 201 57-63... 

While a membrane-divided rotating cylinder electrode cell facilitates automatic scraping, provides the convenience of a single cathode and gives a uniform silver product, there are several possible disadvantages which must be cofisidered in cell design ... 

Fig. 4.14 A rotating-cylinder electrode cell for electrorefining of silver, (a) Sectional view. The metal grows as flake, is dislodged continuously by a wiper blade and may be withdrawn at the cell bottom, (b) Plan view. (Compare the metal-extraction cell shown in Fig. 7.7.)...

Fig. 7.8 Treatment of a 100 mg dm " Cu solution by four 2 kA Eco cells in series and operating under identical conditions. In rotating-cylinder electrode cells, high fractional conversion may be obtained by (a) employing a number of separate reactors in hydraulic series or more practically (b) by the Eco Cascade cell.

Robinson and Walsh have reviewed earlier cell designs. The performance of a 500 A pilot plant reactor for copper ion removal is described. Simplified expressions were derived for mass transport both in single pass [243] and batch recirculation [244]. For a detailed discussion of the principle and the role of the rotating cylinder electrode reactor in metal ion removal the reader is referred to Refs. [13] and [241] (46 references). 

Using a rotating cylinder electrode is a good way to achieve high rates of mass transport. This is very different, however, from the RDE in that the flow is turbulent rather than laminar. As a result, it is not possible to derive theoretical equations that relate the rate of mass transport to the various parameters in the reaction, and one must resort to empirical correlations. These tend to be critically dependent on dimensions and on the specific configuration of the cell, hence are less reproducible. A typical equation for mass transport to a rotating inner cylinder of radius r is ... 

High mass-transport coefficients are obtained in cells with a rotating cylinder electrode (RCE) and a small gap between the anode and the cathode, Fig. 4(a). High rates of mass transport are experienced in the turbulent flow regime, so that RCE reactors allow metal deposition at high speed, even from dilute solutions. RCE reactors have been operated at a scale involving diameters from 5 to 100 cm, with rotation speeds from 100 to 1500 rpm and currents from 1 A to 10 kA [79], It... 

Electrode shown is Pt with Teflon (PTFE)-treated glass frit. [Reprinted from B. Bittins-Cattaneo, E. Cattaneo, P. Konigshoven, and W. Vielstich, Electroanal. Chem., 17, 181 (1991), by courtesy of Marcel Dekker, Inc.] Bottom left (c) Electrochemical cell with a rotating cylinder electrode and sampling with separate inlet to MS. [Reprinted from S. Wasmus, E. Cattaneo, and W. Vielstich, Electrochim. Acta., 35, 111 (1990), with permission from Elsevier Science.]... 

The Landolt cell (Figure 5.27) provides controlled convection conditions by the rotating cylinder electrode. A cylindrical shield surrounds a rotating cylinder, preventing direct current flux between rotating cylinder and counter electrode. The enforced longer way of the current lines simulates the variation of current density in a conventional Hull cell. 

Figure 11.4 The Eco-Cell cascade configuration of rotating cylinder electrodes.

Fig. 4.2 — Convective diffusion regimes commonly found in industrial cells, (a) flow through channel formed by two parallel electrode (or by one electrode and a membrane), (b) flow through such a channel but containing a turbulence promoter (e.g. a set of non-conducting bars or a net), (c) fluidised bed electrode, (d) packed bed electrode, (e) rotating cylinder electrode within a concentric tube.

Concerning to the movement of the electrode can be cited the rotating cylinder electrode [5-8], the electrochemical pump cell in monopolar [9] and bipolar [10] electrical connection, and the multiplate bipolar stack [11]. 

Tank Cells. A direct extension of laboratory beaker cells is represented in the use of plate electrodes immersed into a lined, rectangular tank, which may be fitted with a cover for gas collection or vapor control. The tank cell, which is usually undivided, is used in batch or semibatch operations. The tank cell has the attraction of being both simple to design and usually inexpensive. However, it is not the most suitable for large-scale operation or where forced convection is needed. Rotating cylinders or rotating disks have been used to overcome mass-transfer problems in tank cells. An example for electroorganic synthesis is available (46). 

Each of these techniques may be used with numerous cell designs. The design of cell will depend upon the characteristics of the system to be simulated. Commonly, the flow of electrolyte is important and must be known and in such cases, rotating-disc or ring-disc, flow-in-duct, or rotating-cylinder [36, 37] electrodes would be used. 

A very simple method to rotate an electrode is the rotation of an electrode rod or of an electrode cylinder. The calculation of the thickness of the diffusion layer is complicated but, in a first approximation, is proportional to an exponential dependence on rotation speed. An application of this method is the cell developed by Landolt for testing plating electrolytes. The standard equipment for such tests is the Hull cell (Figure 5.26). ... 

Figure 2.2 Elementary cell geometries (a) parallel-plate cell, (b) rotating cylinder in tube cell, (c) two plates in reactor cell, and (d) plate cell with non-parallel electrodes.

Similar cells based on cylindrical geometry have been proposed. In the stationary version, the electrolyte is pumped through a thin gap between two electrodes formed by the inside of a pipe and a concentric central cylinder. When the central electrode is rotated the cell is again self-pumping and the rotating cylinder cell has many of the attractions of the pump cell. It has been manufactured commercially for the removal of metal ions from dilute solutions. The cylinder cells have a poor space time yield compared with their disc counterparts but have the advantage that they may be modified to include a separator. 

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