Abstract
The second part of the work concerned with mediated electrosynthesis of H2O2 in acidic solutions (pH 3) deals with investigations using divided flow-by fixed bed electrochemical cells operated with co-current three-phase flow (aqueous/organic emulsion and O2 gas at 0.1 MPa). Graphite felt (GF) and reticulated vitreous carbon (RVC) were evaluated as cathodes at superficial current densities up to 3000 A m−2. Typically, at current densities above 600 A m−2 graphite felt yielded higher peroxide concentrations per pass and current efficiencies, most likely due to the almost an order of magnitude higher organic liquid to solid mass transfer capacity for 2-ethyl-9,10-anthraquinone (EtAQ) mediator, that is, 0.13 s−1 in the case of GF vs 0.015 s−1 for RVC with 39 ppc (pores per cm). Factorial experiments revealed a positive interaction effect between superficial current density and emulsion load with respect to the current efficiency for H2O2 electrosynthesis. Thus, at the highest investigated superficial current density of 3000 A m−2, the current efficiency was 84% when the emulsion load was at the highest explored level of 11.7 kg m−2 s−1, whilest for the lowest level of emulsion load, 2.8 kg m−2 s−1, the current efficiency for H2O2 was 18%. Furthermore, the presence of 1 mM cationic surfactant, tricaprylmethylammonium chloride (CH3(C8H17)3N+Cl−, A336), had a positive main effect of about 12% on H2O2 current efficiency and there was also a positive synergistic effect between surfactant and emulsion load, estimated at about 7%. The aqueous to organic phase volume ratio, in the range of 0.9/1 and 3/1, had a statistically insignificant effect on the current efficiency for H2O2 generation. A decrease of the aqueous to organic phase volume ratio from 3 to 0.9 increased the cell voltage from about 6.5 to 7.3 V.
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Gyenge, E., Oloman, C. Electrosynthesis of hydrogen peroxide in acidic solutions by mediated oxygen reduction in a three-phase (aqueous/organic/gaseous) system Part II: Experiments in flow-by fixed-bed electrochemical cells with three-phase flow. Journal of Applied Electrochemistry 33, 665–674 (2003). https://doi.org/10.1023/A:1025094826791
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DOI: https://doi.org/10.1023/A:1025094826791