Catalytic wet air oxidation of phenol by cordierite honeycomb washcoated with Al/Zr pillared bentonite in a plug flow reactor

Abstract

Cordierite monoliths coated with Al/Zr pillared bentonite clay powder were synthesized and tested for catalytic wet air oxidation (CWAO) of phenol aqueous solutions in a plug flow reactor. The catalysts were characterized by using various techniques (EDS, SEM, BET and XRD), confirming the effective deposition of Al/Zr pillared bentonite clay on the channel walls of cordierite monolith. The composite catalyst showed good mechanical stability after ultrasound treatment. The performance of the composite catalyst was evaluated in a catalytic plug flow reactor for continuous oxidation of phenol in terms of catalytic activity as well as their stability. The composite catalyst achieved high catalytic performance (100 % phenol conversion and 91 % total organic carbon reduction) with high stability after 140 h long experiment. During the CWAO of phenol reaction, aromatic ring intermediates (p-benzoquinone, catechol and hydroquinone) and short-chain carboxylic acids (oxalic acid, maleic acid, formic acid, acetic acid and malonic acid) were identified. Kinetic parameters of the model that describes the formation and oxidation of intermediate aromatic compounds and short-chain carboxylic acids were determined. The obtained experimental data results were described sufficiently with respect to phenol conversion. The proposed CWAO of the phenol kinetic model accounts for internal and external diffusion limitations, assuming the pseudo-first-order reaction. Therefore, synthesized monolithic catalysts have great potential for application in CWAO of phenol, since the materials used in the process are inexpensive, abundant and require minimal modifications.