Temperature excursions in packed bed reactors with an axial variation of catalyst activity

Research appears to be growing on a type of structured reactor in which cat alyst activity varies or in which different catalysts are arranged in the r eactant flow direction. These reactors offer improved selectivity for some classes of complex reactions under non-isothermal conditions or when compos ition modulation is employed. Our examination of the rather extreme case of alternating layers of inert and active catalyst indicate that this reactor structure accentuates wrong-way temperature excursions after a step-change in temperature and amplifies periodic input temperature disturbances. Expe riments used a near adiabatic 2.5 cm diameter reactor packed with 3 mm part icles of 0.2 wt.% Pt/Al2O3. Inert layers were just the 3 mm alumina particl es. Step and triangular wave inputs of constant amplitude were used. Temper ature response in the bed was measured by an axial array of computer-monito red thermocouples. Measurements were compared to those made on a homogeneou s mixture of catalyst and support under identical input conditions. Simulat ion studies show that accentuation of the temperature excursions depends on layer thickness. Even first-order reaction kinetics show accentuated tempe rature excursions when layered beds are used. (C) 2001 Published by Elsevie r Science B.V.