Studies of the fischer‐tropsch synthesis on a cobalt catalyst i. evaluation of product distribution parameters from experimental data

Abstract

Two models describing the distribution of linear and monomethyl alkanes in Fischer‐Tropsch products from a cobalt catalyst are formulated. Distribution parameters for monomethyl isomers are derived by assuming either a post‐branching effect on linear chain growth or a decreasing reactivity toward branching with increasing chain length. Distribution parameters for each of the models have been extracted from an extensive experimental data set. We find that the experimental results are well represented by both the models. A “break” in the distribution of linear paraffins has also been observed and is modelled as a sum of the yields of two Anderson‐Schulz‐Flory distributions. We postulate that the two chain growth processes which produce the distributions are governed by two kinds of termination.

Fischer–Tropsch Synthesis: Deuterium Kinetic Isotope Study for Hydrogenation of Carbon Oxides Over Cobalt and Iron Catalysts

“…Contrary to other hydrocarbons, methane does not follow the trend and this shows that the mechanism for methane and other hydrocarbon formation may follow different pathways for hydrogenation of CO 2 over Pt promoted cobalt catalyst or there are two pathways for the formation of methane. The mechanism of methane formation and its high yield observed during cobalt or iron Scheme 2 Plausible mechanism for hydrogenation of CO 2 using conventional Fe and Co catalysts (K i -rate constant for initiation; K prate constant for propagation; K t -rate constant for termination) Fischer-Tropsch synthesis is a subject under debate [42][43][44]. The high methane formation has been explained by an increased surface mobility of the methane precursor [42,43] and by different reaction mechanisms and/or active sites for methanation (dissociation of CO) and chain growth (CO insertion) [44].…”

“…The mechanism of methane formation and its high yield observed during cobalt or iron Scheme 2 Plausible mechanism for hydrogenation of CO 2 using conventional Fe and Co catalysts (K i -rate constant for initiation; K prate constant for propagation; K t -rate constant for termination) Fischer-Tropsch synthesis is a subject under debate [42][43][44]. The high methane formation has been explained by an increased surface mobility of the methane precursor [42,43] and by different reaction mechanisms and/or active sites for methanation (dissociation of CO) and chain growth (CO insertion) [44]. Many argued that it is difficult to point out one process or one type of site responsible for the increased methane production under all circumstances [45].…”

A comprehensive mathematical model for the Fischer–Tropsch synthesis in well-mixed slurry reactors

“…Reaction rate expressions for the FT and the WGS reactions are taken from Sarup and Wojciechowski (1988) and Singh and Saraf (1977), respectively, for a given Co catalyst. However, in order to allow their usage at high pressures, they were expressed in terms of the fugacity coefficients:…”

“…Reviews of the kinetic equations for iron and cobalt catalysts can be found in the works of Huff and Satterfield (1984), Zimmerman and Bukur (1990), Van der Laan and Beenackers (1999), Sarup and Wojciechowski (1988) and Keyser et al (2000) among others. A common characteristic of these works is the use of lumped kinetic models, i.e., the hydrocarbons are lumped according to the number of carbon atoms in their molecules and, sometimes, all the hydrocarbons are treated as one lump or split into a paraffin lump and an olefin lump (Wang et al, 2003).…”

“…Regarding the selectivity modeling, two effects are usually pointed out as the causes for non-ASF product distributions in FT synthesis: 1-olefin readsorption with secondary chain propagation (Iglesia et al, 1991;Van der Laan and Beenackers, 1999;Schulz and Claeys, 1999) and the existence of two chain propagation mechanisms or sites (Madon and Taylor, 1981;Sarup and Wojciechowski, 1988;Donnelly et al, 1988;Patzlaff et al, 1999Patzlaff et al, , 2002. Although 1-olefin readsorption with secondary chain propagation is regarded as the correct explanation of non-ASF product distributions for ruthenium catalysts (Iglesia et al, 1991;Patzlaff et al, 1999), the existence of two different mechanisms or active sites for chain propagation seems to be the major effect for iron and cobalt catalysts (Patzlaff et al, 1999(Patzlaff et al, , 2002.…”