Wet peroxide oxidation of phenol over carbon/zeolite catalysts. Kinetics and diffusion study in batch and flow reactors

Abstract

New composite catalysts were synthesized by pyrolysis of carbon-containing compounds supported of Cu-substituted ZSM-5 zeolite. Three series of the catalysts containing 12 wt% of carbon and 1 wt% of copper were prepared (powder, honeycomb monolith and extruded trefoils) and characterized by TEM, XPS, N2 adsorption. Kinetics of catalytic wet peroxide oxidation (CWPO) of phenol was studied in the presence of the composite catalysts using batch and flow reactors. The substrate conversion in the batch reactor was reached 45% in two minutes over the composite catalyst but no more than 8% in five minutes over the zeolite catalyst. Studies of the granulated composites (monoliths and trefoil) in the flow reactor demonstrated a higher efficiency of the trefoil catalyst. The conversion of phenol at the flow rate 20 mL min−1 was 35% higher over the composite trefoils than over the carbon-free zeolite. The obtained kinetic data allowed the conclusion to be made about different mechanisms of CWPO over zeolite and composite catalysts. The developed kinetic model of phenol CWPO over the composite catalyst described the formation and destruction of intermediate products of phenol oxidation. It was established that inhibiting of phenol oxidation by the substrate was less pronounced in the presence of the composite catalysts than in the presence of the carbon-free catalysts. The flow reactor for phenol oxidation was modeled with account for the external and internal diffusion deceleration of the reaction over real catalyst granules of different geometry to provide adequate description of the experimental results.