Monopolar diaphragm cells

Fig. 8. Anode for monopolar diaphragm cells a, activated (coated) expanded metal b, expanding spring c, titanium-clad copper bar d, copper thread to fix...

Figure 6 presents a sketch of a modern monopolar diaphragm cell (there are bipolar arrangements as well). 

Control of the flow(s) to each electrolyzer frequently is manual, with the aid of rotameters. This is especially true in monopolar installations with large numbers of electrolyzers. Monopolar diaphragm cells have essentially one chamber each for anolyte and catholyte and only one feed line (for brine). They rely on division of the feed brine... 

OxyTech Systems manufactures and licenses the MDC series of monopolar diaphragm cells (Fig. 39). The MDC cells feature woven steel wire cathode screen tubes open at both ends, which are welded into thick steel tube sheets at each end. The tubes, tube sheets, and the outer steel cathode shell form the catholyte chamber of the cell (Fig. 40). Copper is bonded, rather than welded, to the rectangular cathode shell on the two long sides parallel to the tube sheets. Copper connectors attached at the ends of the bonded copper side plates complete the encompassing of the cathode with copper. Anodes are connected to a copper patented cell base, which is protected from the anolyte by a rubber cover or a titanium base cover (TIBAC) [126], Orientation of the cathode tubes is parallel to the cell circuit, the opposite of a Hooker-type cell. This arrangement accommodates thermal expansion of the cell and circuit without changing the anode-to-cathode alignment. 

In the United States, 76% of the chlorine produced is from diaphragm cells. Production is equally divided between bipolar and monopolar electroly2ers. 

Kazimir, E.S. (1999) Monopolar Cathode Design Improvements and Other Diaphragm Cell Component Advances. ELTECH Systems Corporation, Chlorine/Chlorate Seminar. 

For the membrane cellroom of the same capacity there are two choices of technology type either monopolar or bipolar electrolysers. In the case of monopolar membrane electrolysers (Fig. 15.9), such as the ICI FM1500, one membrane electrolyser can replace one diaphragm cell. Since the membrane electrolyser has smaller dimensions there is an overall space saving. The monopolar membrane electrolysers may use the same pipework galleries and overhead crane from the... 

If the choice is to utilise the full capacity of the existing rectifiers and install more membrane electrolysers then adequate space is available. In the 200 000 tonnes per year example, utilising the voltage saved and adding 16 extra monopolar electrolysers would take less space than the original diaphragm cells. In the case of bipolar electrolysers, the length of the electrolyser could be increased as more anodes and cathodes are added to each electrolyser. The number of electrolysers, however, would stay the same. 

Staged conversions may also be carried out whereby a number of diaphragm cells is replaced with the equivalent number of membrane electrolysers. For example, four diaphragm cells are removed, to be replaced by five monopolar membrane electrolysers. A special switch would be required of, say, 20 V capacity to enable the work to be carried out with minimal loss of production. A special manifold header enables the pipe connections of the five membrane electrolysers to be fed into the original four diaphragm cell flanges on the headers. 

Replacement of diaphragm cells with monopolar membrane cells is straightforward in that it can be a one-for-one replacement, ending up with the same electrical circuit but accomplished in a shorter new length (see Figs 15.15 and 15.16). 

Commercial amalgam cells are strictly monopolar, and diaphragm cells exist in monopolar and bipolar variety. This holds for membrane cells, and having presented a monopolar industrial diaphragm cell as... 

With a monopolar circuit, the usual technique is to employ a mobile switching device that can be brought into position adjacent to the appropriate electrolyzer. With diaphragm cells, this takes the form of a cabinet on wheels, placed in the aisle next to the cell. With membrane cells, the switch may be above, below, or beside the cell. Depending on the arrangement of intercell connectors, it may be necessary to switch two electrolyzers fixim the circuit, but the principle remains the same. 

Figure 12.11 is a schematic of a commercial diaphragm cell, typically operated in the range of 75,000 to 150,000 amperes. Many such cells are connected in series, as shown in Figure 12.12, so that the current leaving at the anode of one cell enters the cathode of the next cell, with the anode terminal cell connected to the positive bus of the rectifier, and the cathode terminal cell connected to the negative bus of the rectifier. Bipolar and monopolar cell circuit layouts are shown in Fig. 12.13. ... 

The most widely used brine electrolytic cells are the Hooker and Diamond Shamrock which are both monopolar, but bipolar designs like that of Figure 19.19(a) also are popular. That figure does not indicate the presence of a diaphragm but one must be used. 

Figure 19.16. Basic designs of electrolytic cells, (a) Basic type of two-compartment cell used when mixing of anolyte and catholyte is to be minimized the partition may be a porous diaphragm or an ion exchange membrane that allows only selected ions to pass, (b) Mercury cell for brine electrolysis. The released Na dissolves in the Hg and is withdrawn to another zone where it forms salt-free NaOH with water, (c) Monopolar electrical connections each cell is connected separately to the power supply so they are in parallel at low voltage, (d) Bipolar electrical connections 50 or more cells may be series and may require supply at several hundred volts, (e) Bipolar-connected cells for the Monsanto adiponitrile process. Spacings between electrodes and membrane are 0.8-3.2 mm. (f) New type of cell for the Monsanto adiponitrile process, without partitions the stack consists of 50-200 steel plates with 0.0-0.2 ram coating of Cd. Electrolyte velocity of l-2 m/sec sweeps out generated Oz.

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