Performance of a Recirculating Fixed Bed Reactor for the Oxidation of Phenol and Trisubstituted Phenols by Heterogeneous Photocatalytic Process-mechanistic, Kinetic and Substituents Approach

A recirculating fixed bed reactor was adopted to study the mineralization efficiency of phenol and trisubstituted phenols like 2,4,6- trichlorophenol (TCP), 2,4,6-trinitrophenol (TNP) and 2,4,6-trimethylphenol (TMP) using granular ferric hydroxide (GFH) as a heterogeneous catalyst in the presence of solar light. The effect of operating parameters for the fixed bed reactor namely column bed height and recirculating flow rate were optimized for 2.12 mM of phenol as a model compound at pH 3.0 and 18.3 mM of hydrogen peroxide. Maximum mineralization efficiency of around 96% was attained within 2h of the reaction time at the optimum condition of 5cm bed height and at a recirculating rate of 210 mL/h. The mineralization rate of the trisubstitued phenols follows the following order of TNP > Phenol > TMP > TCP. Higher mineralization efficiency was observed due to the synergetic effect of both photocatalysis and photo-Fenton reaction. The electron withdrawing group in TNP facilitates the higher mineralization efficiency and its rate constant is increased by a factor of 2 compared to electron donating group in TMP .The electronegativity of chlorine together with the scavenging effects of chloride ions decreases the efficiency of TCP by a factor of 2.7 as compared to TNP.