Fischer-Tropsch synthesis over monolithic honeycomb catalysts in the
Taylor flow regime
J. Knochen, R. Güttel, U. Kunz, T. Turek
Institute of Chemical Process Engineering, Clausthal University of Technology
Leibnizstrasse 17, 38678 Clausthal-Zellerfeld, Germany
The Fischer-Tropsch synthesis (FTS) is a highly exothermic, heterogeneously catalyzed reaction to
produce hydrocarbons from synthesis gas obtainable from different carbon sources. While fluidizedbed reactors are employed for high-temperature FTS processes, multi-tubular fixed-bed reactors and
slurry bubble column reactors are used on industrial scale in the modern low-temperature FTS, where
gaseous reactants and liquid products are present under reaction conditions. Main drawbacks of these
commercial low-temperature FTS reactors are the development of hot spots in multi-tubular reactors
and the highly elaborate catalyst separation in slurry bubble column reactors. For theses reasons, novel
structured catalysts and reactors aiming at the intensification of heat and mass transfer characteristics
are presently under investigation [1].
One example for these new concepts is the application of wall coated monolithic honeycomb catalysts
in a loop reactor alignment as suggested by Kapteijn and Moulijn [2]. Theoretical comparison of
monolithic FTS reactors with other reactor types revealed a high potential for process intensification,
especially for future more active FTS catalysts [3]. Monolith honeycomb FTS catalysts have been
used in earlier investigations. Kapteijn et al. [4] carried out experiments with single-pass operation of
synthesis gas. Hilmen et al. studied monolith catalysts during recirculation of the liquid phase [5].
These authors found that liquid recirculation improves temperature control in the reactor, while the
observed reaction rate decreased. The latter effect might be explained by the presence of the film flow
regime inside the monolith capillaries, which limits the external mass transfer rate.
In the present contribution experiments with monolith catalysts for low-temperature FTS carried out in
the Taylor flow regime are presented. The catalyst used in this study consists of 20 wt% Co and 1 wt%
Re on γ-Al2O3 and was prepared as described elsewhere [6]. The honeycombs were investigated in an
experimental setup with independent recycle of gas and liquid. By using different gas and liquid
velocities various flow regimes can be adjusted and for the first time, the especially advantageous
Taylor flow regime was realized. For comparison, powder catalysts were also employed in a stirredtank reactor. The obtained results reveal that monolith catalysts allow for an improvement of the
synthesis gas conversion due to their superior gas-liquid mass transfer properties. In additional
simulation studies, the heat management for the adiabatic monolith loop reactor was investigated. It
can be concluded that monolith loop reactors offer the possibility to intensify mass transfer
phenomena and thereby allow for increased reactor productivity, while temperature control is
maintained by recycling the liquid products. Using a monolithic fixed-bed catalyst arrangement with
highly effective mass transfer, these novel structures offer an interesting alternative to established
multi-tubular and slurry bubble column FTS reactors.
[1]
R. Guettel, U. Kunz and T. Turek, Chem. Eng. Technol., 31 (2008) 746.
[2]
R.M. de Deugd, R.B. Chougule, M.T. Kreutzer, F.M. Meeuse, J. Grievink, F. Kapteijn and
J.A. Moulijn, Chem. Eng. Sci., 58 (2003) 583.
[3]
R. Guettel and T. Turek, Chem. Eng. Sci., (2008) in press.
[4]
F. Kapteijn, R.M. de Deugd and J.A. Moulijn, Catal. Today, 105 (2005) 350.
[5]
A.-M. Hilmen, E. Bergene, O.A. Lindvag, D. Schanke, S. Eri and A. Holmen, Catal. Today,
105 (2005) 357.
[6]
R. Guettel, J. Knochen, U. Kunz, M. Kassing and T. Turek, Ind. Eng. Chem. Res., 47 (2008)
6589.