| In many trickle-bed reactors, thorough wetting of the external catalyst surface is important for successful operation. Since the transport of a non-volatile liquid phase reactant to the catalyst surface occurs by liquid-solid contact only, incomplete catalyst external wetting could reduce reactor performance. Incomplete catalyst external wetting, documented in the literature, can occur in trickle-bed reactors as liquid flow rate is decreased. A possible remedy for incomplete catalyst external wetting is the introduction of large liquid flow pulses to the bed. This pulsing technique constitutes on-off liquid flow or periodic operation. This approach was studied for the hydrogenation of crotonaldehyde in water in a trickle-bed reactor packed with Pd/gammaAl 2O3 catalyst;Steady operation of the trickle-bed experiments provided data from which a reaction rate law was developed along with an estimate of the kinetic parameters. The activation energy estimate suggested that the kinetic parameters were obtained under conditions of minimal mass transfer resistance. Further analysis revealed that the rate of hydrogenation was largely controlled by surface kinetics.;Periodic operation of the trickle-bed reactor consisted of periodic interruption of liquid flow, while maintaining a constant hydrogen flow rate. This method was applied to the trickle-bed reactor operating at different combinations of temperature, pressure, period duration and split (fraction of the period with liquid flow). Periodic operation, under some conditions, enhanced conversion compared with steady liquid flow (i.e. steady state), while under other conditions, it did not.;Tracer experiments established the response of catalyst external wetting with liquid flow rate. These experiments show a reduction in catalyst external wetting with decreased liquid flow rate, consistent with the literature.;The improvement was based on more complete catalyst external wetting under periodic operation. The observed poor performance was due to depletion of the liquid phase reactant during the no-liquid-flow portion of the period, suggesting that an optimum period duration and split exist.;A model for both steady-state and periodic operation were proposed and tested against the experimental data. |
