FISCHER-TROPSCH SYNTHESIS IN MICRO FIXED-BED
REACTORS: EXPERIMENTAL STUDY AND SCALE-UP
CONSIDERATIONS
Jens KNOCHEN, Robert GUETTEL, Carsten KNOBLOCH, Thomas TUREK
Institute of Chemical Process Engineering, Clausthal University of Technology
Leibnizstrasse 17, 38678 Clausthal-Zellerfeld, Germany
turek@icvt.tu-clausthal.de
Abstract
The Fischer-Tropsch Synthesis (FTS) is a strongly exothermic, heterogeneously catalysed
reaction to produce hydrocarbons from synthesis gas. Currently, multi-tubular fixed-bed and
slurry bubble column reactors are used industrially for the modern low-temperature FTS
where liquid products are present under reaction conditions. Main drawbacks of commercial
FTS reactors are the development of hot spots in multi-tubular reactors and the highly
elaborate catalyst separation in bubble column reactors. Novel reactor concepts with fixed bed
FTS catalyst arrangements targeted at the improvement of heat removal and mass transfer
properties are thus highly desirable [1]. One option is the use of structured FTS catalysts for
enhancement of gas-liquid mass transfer [2], another possibility could be the employment of
micro-structured reactors which allow for isothermal operation [3].
In the majority of applications for heterogeneously catalyzed reactions, micro-structured
reactors contain a thin catalyst layer directly attached to the reactor walls [4]. Main challenges
in large-scale applications for this configuration are the relatively low catalyst content in the
reactor volume and the development of strategies for the replacement of spent catalysts.
Another approach is the use of micro-structured fixed-bed reactors [5]. Here, a sufficiently
small sieve fraction of industrially proven catalysts can be used allowing for easy catalyst
replacement. On the other hand, the pressure drop over the catalyst bed may become high.
Velocys Inc. have already tested a micro-structured fixed-bed reactor for FTS and obtained
promising results [3].
In this contribution we present results of an extensive experimental and modelling study of
micro-structured fixed-bed reactors for FTS. Measurements were conducted with sieve
fractions of a Re promoted Co/Al2O3 catalyst at pressures of 10-25 bar and temperatures of
200-240 °C in a 1.75 mm capillary reactor along with pressure drop measurements. Based on
the experimental results, a mathematical model for a micro-structured fixed-bed reactor was
developed. The potential of micro-structured fixed-bed FTS reactors was evaluated in a scaleup study. It will be shown that the catalyst and reactor volume specific productivity of microstructured fixed-bed reactors is significantly higher than of conventional fixed-bed reactors
without the danger of excessive pressure drop.
[1]
[2]
[3]
[4]
[5]
R. Güttel, U. Kunz, T. Turek, Chem. Eng. Technol. 31 (2008) 746
R. Güttel, J. Knochen, U. Kunz, M. Kassing, T. Turek, Ind. Eng. Chem. Res. 47 (2008)
6589
K.T. Jarosch, A.L. Tonkovich, S.T. Perry, D. Kuhlmann, Y. Wang, ACS Symp.Ser. 914
(2005) 258
E. Klemm, H. Döring, A. Geisselmann, S. Schirrmeister, Chem. Eng. Technol. 30
(2007) 1615
T. Inoue, M.A. Schmidt, K.V. Jensen, Ind. Eng. Chem. Res. 46 (2007) 1153