Selective electrochemical reactions of an alumina hydrate crystallization inhibitor

Abstract

Selective reactions of catechol have been studied in regard to its inhibition properties towards alumina hydrate crystallization. Electrochemical reactions of the inhibitor leading to products without inhibition behaviour have been obtained using different conditions. First, a pure sodium hydroxide solution (1.0 M NaOH) was used to electrochemically react the catechol. The inhibitor reactions were then carried out in both saturated and supersaturated sodium aluminate solutions (NaAl(OH)4). Electrocatalytic hydrogenation (ECH) of the aromatic ring over rhodium-based catalysts leads to the saturated non-inhibiting molecule, 1,2-cyclohexanediol. Temperature shows no significant influence on the ECH process within the temperature range where the alumina hydrate crystallization is normally carried out. The presence of aluminate ions in solution has, however, a detrimental effect on the current efficiency. Electro-oxidation of the catechol produces muconic acid by cleavage of the carbon-carbon bound. It also produces other oxidation products and, eventually, may lead to total mineralization of catechol into carbonate, which is a less inhibiting molecule. A detrimental effect of the presence of aluminate on the electro-oxidation is also observed. Electrochemical techniques are proposed as new pathways for organic control in caustic medium.