Liquid Phase Epoxidation of Propylene to Propylene Oxide with Hydrogen Peroxide on Titanium Silicalite-1: Spatially Resolved Measurements and Numerical Simulations

The
spatial profile measurement technique was applied for the first
time to a liquid phase reaction to study the selective oxidation of
propylene to propylene oxide with hydrogen peroxide on titanium silicalite-1
catalyst, also known as the HPPO process. A spatial profiling reactor
based on minimal invasive capillary sampling measurements was used
to obtain the experimental data. The reactor is able to measure spatially
resolved concentration and temperature profiles at industrially relevant
conditions, that is, 40 °C and 20–35 bar pressure, with
propylene in the liquid phase. The reaction was carried out at different
contact times of LHSV 3.0, 6.0, and 12.0 h–1, respectively,
achieving high conversion and selectivity. The experimental data show
that the concentration profiles of the main epoxidation reaction follows
a pseudo-zeroth-order behavior. In contrast, the side product concentration
profiles exhibit a nonlinear trend. The primary side products of the
reaction 1-methoxy-2-propanol, 2-methoxy-1-propanol, and propylene
glycol were quantified. Furthermore, hydroxacetone and methoxyacetone
from the consecutive reaction of 1-methoxy-2-propanol, 2-methoxy-1-propanol,
and propylene glycol with hydrogen peroxide were detected as secondary
side products. Formic acid, methylformate, dipropylene glycol methyl
ether isomers, and dipropylene glycol isomers were detected in trace
amounts. Quantitative data for the formation of hydroxyacetone is
provided for the first time. The experimental concentration profiles
were simulated using an axial 1D-pseudo-homogeneous dispersion model
with two kinetic models reported in the literature. Additionally,
a kinetic model based on the Eley–Rideal mechanism is proposed.
Upon linearization, the derived model shows a correlation of R2 = 0.99 and R2 =
0.98 with the linearized form of the experimental differential rate.
Statistical analysis of the models in this work shows that the derived
Eley–Rideal mechanism has the highest correlation with the
concentration gradients measured within the catalyst bed.