Pc. Watson et Mp. Harold, RATE ENHANCEMENT AND MULTIPLICITY IN A PARTIALLY WETTED AND FILLED PELLET - EXPERIMENTAL-STUDY, AIChE journal, 40(1), 1994, pp. 97-111
Phase transition during an exothermic multiphase reaction was studied
experimentally using a single catalytic pellet reactor. Cyclohexene hy
drogenation (to cyclohexane) and disproportionation (to benzene and cy
clohexane) on Pd/Al2O3 comprised the test reaction system. The steady-
state behavior of the pellet exposed on part of its surface by a flowi
ng liquid rivulet containing the liquid reactant (cyclohexene) and the
other part by a flowing gas containing the gaseous reactant (hydrogen
) was examined. Measurements included the pellet weight (liquid holdup
), degree of external welting, center and surface temperature and over
all reaction rates. Two regimes observed are: a low-rate regime for al
l hydrogen gas-phase concentrations in which the partially wetted pell
et is filled mostly with liquid and nearly isothermal, a high-rate reg
ime for hydrogen concentrations exceeding a critical value in which th
e pellet is filled only partially with liquid and the pellet temperatu
re rise is considerable. Benzene formation was observed in this state.
The difference in overall cyclohexane formation rates between the two
states was as high as a factor of 20 for the same bulk conditions. Ov
er the range where multiple states were observed, the steady state of
the pellet depended on whether the pellet was prefilled with the react
ive gas mixture or with liquid cyclohexene. The range over which the h
igh-rate state was sustained was the largest for the most active catal
yst and declined as the catalyst slowly deactivated. Data features are
interpreted using the theoretical foundations of the half-wetted cata
lytic slab model (Harold and Watson, 1993).