Batch Electrolysis Research Articles

Properties and applications of electrodes covered with a porous diaphragm— 1. Mass transfer investigation

The use of porous coverings on counter electrodes is proposed for controlling the mass transfer rates to the electrode and therefore the extent of possible loss reactions. An experimental study was undertaken to determine the mass transfer rates to electrodes with and without coverings of porous materials (porous PVC, porous-polyethylene, non-woven polypropylene). Additionally the effect of simultaneous gas evolution was investigated. The electrochemical method, based on the measurement of the limiting current for ferricyanide reduction, was employed for most experiments with the exception of those in which gassing at the covered electrode occurred. In the latter case the mass transfer rates were calculated from the concentration change observed during the batch electrolysis with recirculation of Ce(IV) (reduction to Ce(III)). The results have been correlated for the case of the non-woven material type E 1583 with no simultaneous gassing according to ▪ where Sh, Sc and Re are the Sherwood and Schmidt and Reynolds numbers, respectively and l, d p and ϵ are the covering thickness, pore diameter and porosity, respectively. Reductions by a factor of 100 in mass transfer rate at the mass transfer surface are easily attainable through the use of porous coverings. Interestingly, the results obtained at covered gassing electrodes, showed that the mass transfer rate decreases with increasing gassing rate. This is the inverse behaviour to that obtained at uncovered gassing electrodes. The implications on the current efficiency for operation of a differential diaphragm-less electrolysis cell in which loss reactions can occur at the counter electrode are discussed. The use of porous electrode coverings on the counter electrode in diaphragm-less cells is a technique which opens up new applications for these simpler cells.

Electrical control and optimisation of the electrochemical batch reactor

AbstractFor galvanostatic, potentiostatic and constant cell voltage control, parameters such as conversion degree, energy efficiency, space‐time yield, specific energy consumption and their time‐dependencies have been calculated for a diffusion‐controlled reaction in an electrochemical batch reactor. Comparison of the results showed that potentiostatic control is the most efficient operation mode, but that constant cell voltage control is more useful and provides a similar efficiency. Some results from model calculations were compared with those from laboratory experiments. A numerical optimisation procedure was applied to an electrochemical batch reactor with constant cell voltage control. The resulting optimum batch electrolysis time, the optimum conversion degree, and the minimum costs were calculated as functions of the initial reactant concentration, specific electrode surface area, costs of raw materials and investment costs.