COMPARISON OF UPFLOW AND DOWNFLOW 2-PHASE FLOW PACKED-BED REACTORS WITH AND WITHOUT FINES - EXPERIMENTAL-OBSERVATIONS

This study compares the performance of laboratory trickle-bed and upfl ow reactors over a range of operating conditions, using the hydrogenat ion of a-methylstyrene to cumene in hexane solvent over 2.5% Pd on alu mina extrudate catalyst as a test reaction. It is shown that the trick le bed performs better than the upflow reactor at low pressures when t he reaction is gas limited, due to ready access of the gas to the inco mpletely externally wetted catalyst, while the upflow reactor performs better at high pressures when the liquid reactant limitation controls the rate, due to the completely wetted catalyst. Comparison of the tw o reactors at different pressures, liquid reactant feed concentrations , and gas flow rates is presented, and differences in performance are explained based on the observed shift from gas limitation to liquid li mitation. Experiments in beds diluted with fines yield identical perfo rmances in both upflow and downflow modes of operation under both gas- and liquid-limited conditions, corroborating the fact that hydrodynam ics and kinetics can be decoupled by using fines. It is also shown tha t the advantage of upflow or downflow depends on whether liquid or gas reactant is rate limiting and that a single criterion for identifying the limiting reactant can explain most of the data reported in the li terature on these two modes of operation.