Abstract
The hydrodynamics of a three-phase micro-packed bed reactor and its effect on catalysed benzyl alcohol oxidation with pure oxygen were studied in a silicon-glass microstructured reactor. The microreactor was operated at 120 °C and 1 barg and contained a channel with a 300 μm ×600 μm cross section, packed with 1 wt% Au-Pd/TiO2 catalyst 65 μm in average diameter. Improvements in the conversion of benzyl alcohol and selectivity to benzaldehyde were observed with increasing gas-to-liquid ratio, which coincided with a change in the flow pattern from a liquid-dominated slug to a gas-continuous regime. The observed enhancement is attributed to improved external mass transfer, associated with an increase in the gas-liquid interfacial area and reduction in the liquid film thickness that occur with gradual changes in the flow pattern. A maximum selectivity of 93% to benzaldehyde was obtained under partial wetting - which introduced the added benefit of direct gas-solid mass transfer - outperforming the selectivity in a conventional glass stirred reactor. However, this was at the expense of a reduction in the conversion. A response surface model was developed and then used to predict optimal operating conditions, which were in the gas-continuous flow regime. This corresponded to relatively high gas flow rate in conjunction with moderate liquid flow rate ensuring sufficient catalyst wetting with a thin film to reduce transport resistances.