Acetophenone hydrogenation on Rh/Al2O3 catalyst: Flow regime effect and trickle bed reactor modeling

Flow regime effect and reactor modeling studies in a gas-liquid downward flow fixed bed reactor were conducted for acetophenone hydrogenation on 1% Rh/Al2O3 catalyst, a relatively complex reaction scheme typical of pharmaceutical applications, using a 7.1 mm ID stainless steel reactor with 0.5 mm catalyst spheres at elevated pressures. A flow regime transition map for trickle and bubbly flows was determined visually in a transparent reactor surrogate and confirmed by monitoring pressure drop fluctuations for different gas/liquid systems, tube/particle materials, and operating pressure and temperature. The flow regime at each operating condition for the opaque stainless steel reactor was identified solely using pressure drop fluctuations. The beneficial effect of bubbly flow on reaction rate was confirmed experimentally at gas and liquid superficial velocity ranges of 0.02-0.19 m/s and 2.5-12 mm/s, respectively, under 80-100 °C, 11-26 bar and 0.04-0.6 M initial substrate concentration. Gas flow rate, temperature, and pressure variations were used to study the effects on reaction performance of partial wetting of the catalyst and of liquid-solid diffusion limited reaction. A reactor model including external/internal mass transfer and flow regime effects was developed using an adjustable parameter to account for partial wetting and flow regime effects. The parameter was fitted using a subset of the experiments, and the model provided good prediction (R2 > 95%) of all remaining experiments.