Bipolar trickle-bed reactors

After discussing characterisation and scale-up methods of electrochemical reactors, a literature review is given on design and applications of bipolar cells in organic electrosynthesis and effluent treatment.The bipolar trickle-bed reactor is essentially a column packed with carbon Raschig rings in layers separated by insulating mesh. The electrolyte trickles down the stack of rings as a thin film, while reactant gas flows cocurrently with the electrolyte with no flooding problems. Constant voltage applied between the top and bottom feed electrodes renders the carbon rings bipolar. A theoretical model for this reactor is discussed extensively; measurements of solution potential and reaction distribution profiles in a model cell have shown good agreement with the prediction of the theory.A parametric study of hypobromite generation in bench scale reactors is described, showing how operational variables affect the reactor's performance. High current efficiencies were observed for few recycles of fairly concentrated electrolyte (0.114 NaBr), showing that the nonFaradaic current by-passing the rings is minimal. It was also shown that the reactor behaves similarly during hypochlorite generation, demonstrating the possibility of the reactor's use in electrolytic water treatment.The scale-up of the bench scale reactor to a semi-pilot size reactor is described. By dimensional analysis, an equation was formed giving the polarisation parameter as a function of Reynolds and Galileo numbers.Production of propylene oxide via the oxidation of propylene by the electrochemically formed hypobromite was carried out at high current efficiencies and good energy yields. The variables affecting the process and the possibility for further development are discussed.