Mechanistic Insight into the Degradation Pathways of P-cresol in Ozonation, Peroxone, and Ozone-persulfate Process

Abstract

ABSTRACT The primary objective of this study is to identify the aromatic intermediate products in p-cresol degradation by ozonation, peroxone, and ozone-persulfate, and elucidate the pathways and mechanisms involved in the processes. The experiments were conducted in semi-batch operating mode, where ozone was bubbled into p-cresol in a 1.0 L cylindrical jacketed glass reactor. In general, the aromatic intermediate products of p-cresol is less toxic compared to p-cresol. All intermediate products degrade to shorter chain of carboxylic acids with further oxidation. The major degradation pathway of p-cresol is benzene ring oxidation through electrophilic aromatic substitution reaction by molecular ozone and hydroxyl radical, and single electron transfer by persulfate radical, evidenced by the presence of methyl group in majority of the detected compounds. Hydroxyl radical also oxidizes p-cresol through hydrogen atom abstraction at methyl group side-chain; evidenced by the detected 4-methylbenzyl alcohol, 4-hydroxy-benzaldehyde, 3,4-dihydroxy-benzaldehyde, and 3,4-dihydroxy-benzoic acid; the simultaneous oxidation pathway in peroxone leads to faster p-cresol degradation as compared to ozonation and ozone-persulfate.