The liquid-phase hydrogenation kinetics of benzene and three
monosubstituted alkylbenzenes,
toluene, ethylbenzene, and cumene, was determined in a semibatch
reactor operating at hydrogen
pressures of 20−40 atm and at temperatures of 95−125 °C.
Commercial preactivated catalyst
particles of nickel−alumina were used in all experiments. The
hydrogenation activity of the
compounds decreased in the order benzene ≫ toluene > ethylbenzene >
cumene. The main
reaction product was always the completely hydrogenated cycloalkane,
whereas only trace
amounts of cycloalkenes were detected. The hydrogenation rates had
a slow initial period
followed by a period of a virtually constant rate, which decreased at
the end of the reaction.
The analysis of the data with a reaction−diffusion model
revealed that the kinetics was influenced
by pore diffusion. Rate equations based on a sequential addition
mechanism of adsorbed
hydrogen to the aromatic nucleus were derived, and the kinetic
parameters were estimated
from the reaction−diffusion model with nonlinear regression analysis.
The rate equations were
able to describe all the features of the experimental
data.
The liquid phase hydrogenation kinetics of five di- and
trisubstituted alkylbenzenes, xylenes,
mesitylene, and p-cymene were determined in a semibatch
reactor operating at hydrogen
pressures of 20−40 atm and at temperatures of 95−125 °C.
Commercial preactivated catalyst
particles of nickel−alumina were used in all experiments. The
hydrogenation activity of the
aromatic compound was affected by both the number of substituents and
their relative positions
in the benzene ring. The trisubstituted benzene (mesitylene) had a
lower reaction rate than
the disubstituted compounds (xylenes). The activity of the
different substituent positions
decreased in the order para > meta > ortho. The main reaction
product was always the
completely hydrogenated cycloalkane; no cycloalkenes were detected.
The hydrogenation rates
were virtually constant at low and intermediate conversions of the
aromatics, but at high
conversions the rates decreased. Rate equations based on the
formation of partially hydrogenated
surface complexes were derived, and the kinetic parameters were
estimated from a heterogeneous
reactor model with nonlinear regression analysis. The rate
equations were able to describe the
features of the experimental data.
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