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Modelling reaction and diffusion in a wax-filled hollow cylindrical pellet of Fischer Tropsch catalyst

Accepted version
Peer-reviewed

Type

Article

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Authors

Hubble, R 
York, APE 
Dennis, JS 

Abstract

Previous modelling of fixed-bed, Fischer-Tropsch (FT) reactors has demonstrated the advantages relative to spherical pellets of using cylindrical and shaped pellets to provide improved transport attributes under conditions relevant to industrial operation. However, mass transport models have focussed on the investigation of transport within pellets with spherical symmetry, whilst detailed investigations of more complex shapes have not been undertaken. Here, a pseudo-isothermal, steady-state, two-dimensional model was investigated for catalyst pellets of cylindrical form, both solid and hollow. A cobalt-based catalyst was considered at conditions where the rate of condensable hydrocarbon generation is large enough to result in the accumulation of liquid hydrocarbons in the pores of a catalyst. It was found that effectiveness factors were bounded by those of sphere and slab above and below Thiele moduli of ~0.75 and ~1.15, respectively, for the conditions examined, with the effectiveness factors exceeding those of both sphere and slab models between these moduli. Here, comparisons were made on the basis of the characteristic diffusion length, the catalyst particle’s volume divided by its external surface area. However, values of the FT chain growth parameter, α, between these values of Thiele modulus were lower than both those of sphere and slab geometry, and thus under these conditions hollow cylinders gave the greatest methane selectivity.

Description

Keywords

Modelling, Fischer Tropsch catalyst, Cylindrical geometry, Reaction and diffusion

Journal Title

Chemical Engineering Science

Conference Name

Journal ISSN

0009-2509
1873-4405

Volume Title

207

Publisher

Elsevier BV