Computational fluid dynamics modeling of catalytic wet air oxidation of phenol in a trickle bed reactor

Abstract

In this study, phenol was oxidized in a trickle bed reactor operated in a continuous mode using aluminum/zirconia pillared (Al/Zr-PILCs) catalyst. The reactor was connected to a gas chromatography and a sample was taken every 1 h to analyze carbon dioxide emitted. A commercial software (Ansys Fluent) was used to simulate experimental results obtained. The powder catalyst (Al/Zr-PILCs) was wash-coated on a surface of cordierite monolith and dried using different drying mediums. After wash-coating the catalyst, different drying methods were used and two samples were dried in an oven at 40 °C and 60 °C while others were dried using thermally assisted microwave and room temperature. X-ray diffraction peak of natural bentonite shifted from 8.25° to lower angle of 7° and basal spacing increased from 12.44 to 15.15 A° confirming that natural clay was successfully pillared. However, montmorillonite peak disappeared after wash-coating the catalyst on the surface of a support due to the amorphous phase of SiO2 shielding the peak. The morphology of the catalyst was determined using scanning electron microscopy (SEM) and the results clearly showed that the surface of the catalyst was smooth and no cracks were observed when all drying mediums were used due to hygroscopic nature of glycerol. The sample dried using thermally assisted microwave oven was smoother compared to others due to heat that is homogeneously dispersed inside the microwave. To test catalyst activity and reaction kinetics, phenol was oxidized in a trickle bed reactor operated at 10 bar and temperatures ranging between (120–160 °C) over Al/Zr-pillared clay catalyst using monolith as a support. To understand the kinetics of the process, different variables were studied including reaction temperature and liquid flow rate. It was concluded that an increase in temperature has a positive impact on phenol conversion, whereas an increase in liquid flow rate has a negative effect. A simple power law model was used to model reaction kinetics and the activation energy was found to be 42.289 kJ/mol. To understand the behaviour of the fluid inside the reactor, a computational fluid dynamics (CFD) model was developed from experimental data using an Euler-Euler model. The model indicated that a hot spot was formed near the center of the reactor due to liquid mal-distribution. Moreover, incorporating monolithic structure in a reactor packing material helped to lower pressure drop due to low velocities inside monolith channels. When the reactor was modeled at 160°C and 10 bar phenol was completely oxidized to CO2.