Document Type: Research Article
Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, South Africa
Advanced Materials Division, Mintek, Randburg, South Africa
1. Advanced Materials Division, Mintek, Private Bag X3015, Randburg 2125; RSA 2. Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, South Africa
Single and mixed oxide Al/Zr-pillared clay (Al/Zr-PILC) catalysts were synthesized and tested for catalytic wet air oxidation (CWAO) of aqueous phenol solution under milder conditions, in a semi-batch reactor. The catalysts were synthesized from natural bentonite clay using ultrasonic treatment during the aging and intercalation steps and were characterized by means of high resolution scanning electron microscopy-energy dispersive angle X-ray spectrometry (HRSEM-EDX), powder X-ray diffraction (p-XRD), nitrogen adsorption/desorption, Fourier Transforms Infrared Spectroscopy (FTIR) and zeta potential. Successful pillaring of aluminium and zirconium oxides into the clay was confirmed by p-XRD with increased basal spacing (1.92 nm) and higher specific surface area (230 m2/g). The influence of stirrer speed (200-1000 rpm), catalyst dosage (1-3 g/L), initial pH (1-3), initial phenol concentration (500-1500 mg/L), effect of temperature (80-150 °C) and oxygen pressure (5-15 bar) was evaluated on phenol conversion and their reaction kinetics. At the optimum conditions of initial pH of 3, catalyst dosage of 2 g/L, initial phenol concentration of 1000 mg/L, reaction temperature of 100 °C and oxygen pressure of 10 bar , the complete removal of phenol was achieved by Al/Zr-PILC within 120 min. The CWAO process was well-described by first-order power rate law kinetics model. The apparent activation energy of the reaction calculated by Arrhenius equation was 21.306 kJ mol−1.