DYNAMIC EFFECTS OF VAPORIZATION WITH EXOTHERMIC REACTION IN A POROUS CATALYTIC PELLET

A single catalytic pellet reactor was used to investigate dynamic multiphase reaction-transport interactions. The experiments permitted the simultaneous measurement of pellet weight (liquid holdup) and center temperature under conditions which mimic the unsteady, local events within a fixed-bed multiphase reactor. In the liquid-prefilled pellet experiments, the pellet (Pd/Al2O3-clay) was prefilled with liquid reactant (AMS or cyclohexene) and then exposed to a flowing gas containing hydrogen. In the gas-prefilled pellet experiments, the pellet was prefilled with hydrogen and then contacted by a liquid reactant pulse of prescribed flow rate and duration. The liquid-prefilled experiments revealed an acceleration in the drying rate due to the exothermic reaction. The pore emptying process was accompanied by a significant increase in the pellet temperature. The considerably slower dynamics observed for the AMS system compared to the cyclohexene system are attributed both to differences in liquid-phase volatility and to self-oligimerization of the AMS. In the gas-prefilled experiments, a pore filling with reaction process precedes the pore emptying step. The degree of catalyst overheating is highest for a liquid pulse of intermediate duration. A phenomenological mechanism of drying with exothermic reaction built on the well-accepted theory of drying of granular media is offered to explain the trends in the data. Implications of the findings with regards to hot spot formation in the catalytic reactor are discussed.