Kinetic Modeling and Trickle-Bed CFD Studies in the Catalytic Wet Oxidation of Vanillic Acid

Abstract

Aiming to examine the catalytic wet air oxidation process in three-phase reactors, we investigated a slurry reactor for kinetic studies and a pilot-unit trickle-bed reactor, considering reaction aspects as well as the transport mechanisms involved in the treatment of an aqueous vanillic acid solution, which is a compound typically found in olive mill wastewater. Kinetic studies were performed to bring up the lumped kinetic parameters in terms of total organic carbon (TOC) over a Mn−Ce−O laboratory-made catalyst. A hydrodynamic model for the prediction of pressure drop and liquid holdup for a trickle-bed reactor has been developed by means of computational fluid dynamics (CFD) according to data taken from the open literature. First, single-phase flow pressure drop was studied in a region of flow rates that is of particular interest to trickle-bed reactors (10 < ReG < 400), and it was demonstrated that the Eulerian model is able to predict reasonably the pressure drop of single-phase flow over spherical particles when the Ergun equation adjusts pressure drop measurements within 10% on average. The two-phase flow operating regime is then investigated, and the CFD Eulerian model predicts very well liquid holdup in the range of gas flows studied (G = 0.10−0.70 kg/(m2 s)). Finally, CFD runs were performed in unsteady state for the catalytic wet air oxidation of the aqueous vanillic acid solution. TOC profiles indicated that complete reduction of organic matter was achieved at space times up to 1.5 h. Moreover, CFD demonstrated the considerable effect of temperature, whereas the air partial pressure only has a minor influence.