The
influence of physical
properties and the resulting limitations of heat and mass transport
for the ethoxylation of octanol in a microstructured reactor were
investigated by CFD simulations. The reaction was performed under
supercritical conditions in a one-phase system at pressures between
90 and 100 bar and temperatures between 180 and 240 °C. A 2D
CFD model was applied to determine the kinetic parameters by fitting
the model to experimental data. Furthermore, the sensitivity of the
simulations regarding different physical properties was determined.
The influence of diffusion was studied in detail, and it was found
that a low diffusion coefficient results in a radial gradient in viscosity
which leads to segregated streamlines and a bending of the streamlines
toward the center. This “bottleneck” effect causes a
large increase of the velocity in the center of the pipe, with the
risk of the breakthrough of ethylene oxide. This effect occurs only
in the case of higher ethoxylation degrees.
A two-dimensional
computational fluid dynamics model was utilized
to test different kinetic models for the description of the anionic
polymerization of octanol with ethylene oxide in a microreactor. The
reaction was performed as a continuous reaction under elevated pressure
and temperatures in a one-phase system. The kinetic parameters were
determined with numerical methods by reducing the deviation to experimental
data based on the Nelder–Mead method. Four different reaction
models with one, two, three, and four different rates for the first
propagation steps were tested. The best agreement with the experimental
data was found for the four rate model, with a prediction accuracy
close to the experimental error. The gathered data suggests an increasing
reaction rate for the first four propagation steps, which is in agreement
with the Weibull–Törnquist effect [Berichte
vom VI. Internationalen Kongress für Grenzflächenaktive
Stoffe, Zürich, vom 11. bis 15. September 1972Carl Hanser VerlagMunich1972125; Tenside Deterg.198017298].
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