(225a) High Pressure Heterogeneous Catalysis with Continuous Flow Microreactors

Microreactors enable precise control of
reaction parameters (e.g. temperature, pressure).

The improved heat and mass transfer aspects
provide kinetics to be probed at isothermal conditions in the absence of mass
transfer effects. Due to the small footprint of these devices it is possible to
access to high temperatures and high pressure operations, especially for
hydrogenation reactions.

We developed a high pressure and high
temperature microreactor platform to investigate heterogeneous catalysis at
industrially relevant conditions. The system is operable up to 100 bar from 25
ºC to 300 ºC. A packed-bed microreactor which can stand for high pressures has
been microfabricated from silicon and Pyrex as shown in figure 1a. The system
has inline analysis tools as well as a sampling unit for off line liquid
analysis with gas or liquid chromatography. A microfluidic device was
fabricated, which enabled to sample reactor effluents at elevated pressures of up
to 100 bar. With this unit it became possible to couple the high pressure microreactor
with a quadrupole mass spectrometer. The system also involves a microfluidic cell
with attenuated total reflection section for inline Fourier transform infrared
spectroscopy (FTIR) analysis at pressures of up to 100 bar. A pulse
chemisorption microfluidic device has been developed to characterize surface
area of a catalyst in a few mg scales. Carbon monoxide (CO) chemisorption
curves for the fresh (red) and spent (blue) Pt/silica catalysts are given in
figure 1b. The areal difference between the red and the blue curves represents
the active area loss of the catalyst.

Using the microreactor platform with the
inline characterization tools, several catalytic systems have been explored.
Conversion of syngas to methanol has been studied with homemade catalyst.
Effect of several process parameters such as temperature, pressure, residence
time and feed composition on reaction rates has been determined. Apparent
activation energy has been found. Hydrogenation reactions of bio-oil model compounds
(furan derivatives) were also studied. For this system, mass transfer effects
were delineated and operation conditions under which intrinsic kinetics can be
measured were identified. Apparent activation energies have been found as well.

Figure 1. A) Silicon-Pyrex high pressure
microreactor for heterogeneous catalysis. B) CO pulsed chemisorption curves for
fresh and spent 5wt% Pt/silica catalysts. The catalyst amount was 2 mg.