Bipolar filterpress cell

Filtcrpress cells are structurally more complex and require electrolyte circulation and gas-electrolyte separators external to the cell but they give enhanced space-time 3rields. Typically, bipolar filterpress units with various sizes give hydrogen delivery rates between 3 and S0m h. The important components are the anodes and cathodes based on perforated steel (perforated... 

The old design of cell is based on a lead-lined tank filled with aqueous sulphuric acid, and the spent chromic acid solution in porous ceramic pots was placed in the tank. The anodes were lead rods dipped into the ceramic pots and the cathode was the lining to the tank. The plant was obviously operated totally as a batch process. More modern and economic cells are now available they are often based on a bipolar filterpress concept with lead alloy anodes, steel cathodes and a Nafion proton-conducting membrane. The energy consumption and space-time yields with such cells are clearly likely to be superior. Moreover, such cells can be operated as continuous or semi-continuous processes. 

Expansion of such a laboratory pilot cell to several plates in a filterpress arrangement may be used to check bipolar operation or the use of internal manifolds,... 

More than a dozen companies throughout the world oficr membrane cell technology and only two types of cell will be used to illustrate here the important features of the designs. Most membrane cells are based on a filterpress containing a series of plate and frame cells. Both monopolar and bipolar electrical connection is used. The basic structure of this type of cell is illustrated in Fig. 3.12 (note that the relative dimensions are not correct - membrane areas may be up to 2 x 2 m, although more normally I x I m, while the thickness of the electrolyte chambers is usually much less than 1 cm). The electrodes are vertical and constructed with louvres or from expanded metal so that the gases formed at the electrodes are directed to the back of the electrodes and do not stay in the... 

The electrolyte inlets and outlets must be designed to give a low pressure drop over the reactor and the required flow characteristics (for mixing or mass transport reasons) with due regard for the nature of the reactants and products. In the case of a filterpress, parallel-plate reactor, internal manifolding provides a neat, compact method of distributing the catholyte and anolyte flows but it requires precise sealing and offers little control over bypass currents in bipolar cells. 

Fig. 2.28 Plate-and-frame cells. Typically, these cells are mounted in a filterpress with suitable gasket materials between components to seal the assembly. Compression may be applied via a screwpress, a hydraulic press or tiebars. A = anolyte C = catholyte. (a) Monopolar electrodes external manifolding, (b) Bipolar electrodes internal manifolding. Only the anolyte flow is shown, for clarity. The cells are shown in the divided mode.

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