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.

A review of the determination of organic compounds in Bayer process liquors

“…As such, it is a very flexible technique for the determination of a wide variety of types and sizes of organic compounds in a range of 488 matrices. HPLC can also be used to investigate the fundamentals of adsorption as 489shown by the work of Bouchard et al[58] who used it to determine dynamic adsorption isotherms of organic compounds with the potential to inhibit the precipitation step of the Bayer process.The first reported use of HPLC for analysing Bayer liquors was by Salomon who was able to identify a range of degradation products from the digestion of bauxite in alkaline liquors[29]. Roumeliotis and co-workers[59] used it for the separation, 496 identification and quantification of carboxylic acids.…”

Electrocatalytic hydrogenation of catechol on Rh–Al2O3 in different media — pH-Dependent reduction mechanism for intermediate formation

“…The columns (15 cm) were filled with the sieved Al 2 O 3 , whose average particle size was between 25 and 35 µm. The parameters used to determine the dynamic adsorption isotherms were collected from the HPLC elution chromatograph and the Henry constants were calculated from the well-known equation, Q e = k H C e , according to previous works (23,24).…”

“…Catechol is known to inhibit gibbsite precipitation (1)(2)(3)(4). The scope of this work was to investigate the use of electrocatalytic hydrogenation (ECH) (Fig.…”

“…To understand the influence of the solution medium on reactivity, a newly improved method developed by our group (23,24) was used to determine the adsorption strength by evaluating Henry constants. …”

Coordination-Promoted Bio-Catechol Electro-Reforming toward Sustainable Polymer Production

“…With this electro-reforming technology, we can potentially cleave the bio-derived catechol into pure H 2 and cis , cis -MA, both with high values for the sustainable chemical industry. To date, the electrocatalytic transformation of catechol to cis , cis -MA has been very limited with unsatisfactory cis , cis -MA yields, − and therefore developing new strategies toward high yield and selectivity, as well as revealing the intrinsic mechanism of the electrocatalytic mechanism, are highly desired.…”