Add time:09/08/2019         Source:sciencedirect.com

Naphthenic acids (NAs) are refractory carboxylic acids that are believed to be one of the main causes of the oil sands process water (OSPW) toxicity. Understanding the kinetics, selectivity and structure-reactivity relation is a key factor to evaluate any process proposed for NAs degradation. Anodic oxidation (AO) using graphite anode was investigated for model NA compounds degradation. The degradation of cyclohexane carboxylic acid (CHA) increased with increasing the applied current density from 0.25 to 20 mA/cm2 and followed pseudo first-order degradation kinetics with rates increased from 0.00091 to 0.01 min−1, respectively. Carbonate species in the electrolyte medium had a scavenging effect on the degradation rate. The main oxidation mechanism for CHA during AO using graphite was through oxygenated species generated on the surface of graphite anode. Direct electron transfer (DET) mechanism had no contribution in the degradation of CHA. Structure-reactivity analysis by using different model NA compounds showed that NAs with higher carbon number were preferentially degraded by AO. Branched NAs were more reactive than non-branched NAs only if the branch existed far enough from the carboxylate group. Monocyclic NAs were more reactive than linear NAs but any increase in the cyclicity beyond one ring resulted in reduced reactivity. Aliphatic compounds were found to be more reactive than aromatic compounds and the existence of more than one carboxylate group in the structure hindered the reactivity. The kinetics and structure-reactivity of anodic oxidation for NAs shown that AO using graphite electrodes can be an attractive option for OSPW treatment.

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