Electrochemical reduction of 2-ethyl-9,10-anthraquinone (EAQ) and mediated formation of hydrogen peroxide in a two-phase medium - Part II: Production of alkaline hydrogen peroxide by the intermediate electroreduction of EAQ in a flow-by porous electrode in two-phase liquid-liquid flow

Hydrogen peroxide production by the intermediate electroreduction of the 2-ethyl-9,10-anthraquinone (EAQ) was carried out in a flow-by cell and a two-phase electrolyte formed by a mixture of tributylphosphate (TBP) and diethylbenzene (DEB) as the organic phase, and a solution of NaOH as the aqueous phase. The cathode used was a reticulated vitreous carbon (RVC) foam. We have examined the following process variables: electrolysis current (0.3-3.1A), catholyte flow rate (470-1630 ml min(-1)), EAQ concentration in the organic phase (0.21-0.42 M), organic/aqueous phase volume ratio (1/9-4/6) and grade of porosity of the RVC (30-45 ppi). The electrolyses can be carried out in the presence or absence of oxygen gas. The first method is the so-called 'one-step electrolysis' and the second method is the 'two-step electrolysis'. In the second method, the disodium salt of the hydroquinone (EAQNa(2)) is electrochemically formed in the absence of oxygen. The second step consists of the chemical reaction of this salt with oxygen to form hydrogen peroxide. We obtained a hydrogen peroxide concentration of 0.8 M after 10 A h with an electrolysis current of 1.55 A and a current efficiency of 70%.