Ozone Initiated Oxidation of Cresol Isomers Using γ-Al2O3 and SiO2 as Adsorbents

Abstract

Ozone initiated oxidation of environmentally unfriendly organic compounds is one of the powerful tools that is utilized to convert and/or completely mineralize these substances. Here we have adopted the adsorption phenomenon in combination with ozonation (0.123 mg/L) of the hazardous cresol isomers mounted in a glass column. An oxide of aluminum (γ-Al2O3) or silicon (SiO2) was used as an adsorbent material. These materials were characterized using XRD, SEM and TEM techniques. Various cresols (m-, o-, p-cresol) were oxidized for different time intervals, viz. 1, 3 and 5 h. The γ-Al2O3 adsorbent was found to have a relatively high catalytic effect towards conversion of m-cresol (52%) into oxidation products, whereas SiO2 promoted the conversion of o-cresol (57%) and p-cresol (62%) the most. The resultant oxidation products that were identified using GC–MS were dominantly isomeric from all three cresols. Oxidation of m-cresol produced m-tolyl acetate (m-TA), 2,3-dihydroxytoluene (2,3-DT) and diethyl maleate (DM) whereas o-cresol produced o-tolyl acetate (o-TA), 2,5-dihydroxytoluene (2,5-DT) and DM. Finally, the oxidation of p-cresol produced p-tolyl acetate (p-TA), 3,4-dihydroxytoluene (3,4-DT) and DM. Amongst all identified oxidation products, tolyl acetates recorded highest percentage selectivities from all adsorbates especially in 1 h reactions. The ozone initiated oxidation of various cresol isomers was explored using various metal oxide (γ-Al2O3 or SiO2) material as adsorbents. The metal oxide adsorbent materials were characterized using XRD, SEM and TEM techniques. The effect of adsorption and ozonation time on percentage conversion and selectivity towards reaction products upon ozonation of various cresols is emphasised. The positively identified oxidation products contains various tolyl acetates, dihydroxytoluenes and diethyl maleates that are isomeric to the cresol isomer used. The ethanol mediated esterification of carboxylic acid to produce tolyl acetate as product is reported.