Notes on the issues of equilibrium in the Fischer–Tropsch synthesis

Norval, Graeme W.

doi:10.1002/cjce.20110

Cited by 13 publications

(26 citation statements)

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“…Their formation is dependent on process conditions e.g. n-alcohol formation becomes more favourable with increasing pressure (van der Laan, 1999;Norval, 2008). This is shown by the 30-40 bar(a) pressure conditions of the Qian et al (2013) experiments.…”

Section: Literature Reviewmentioning

confidence: 93%

“…The work of Norval & Phillips (1990) and Norval (2008) has shown that the products of FT synthesis are distributed according to thermodynamics, with the yield of hydrocarbons controlled kinetically. This arises because the rates of chain growth are much faster than the rate of monomer formation from CO (Norval, 2008;Allie & Nyathi, 2019;Hensen et al, 2020). If FT synthesis could be modelled as equilibrium-controlled process, the kinetic model could consist of simpler rate…”

Section: 1mentioning

confidence: 99%

“…expressions. An example of a hydrocarbon system in which this strategy has successfully been applied is 1-olefin oligomerisation (Sealy, 1996;Norval, 2008).…”

Section: 1mentioning

confidence: 99%

“…By assuming partial chemical equilibrium exists in the n-paraffin and 1-olefin homologous series, ideal gas behaviour and applying the Gibbs free energy minimisation technique 8 of Smith & Missen (1988), Equations 2.15 and 2.16 were derived for n-paraffins and 1-olefins respectively (Norval & Phillips, 1990;Norval, 2008).…”

Section: Chemical Equilibrium Considerationsmentioning

confidence: 99%

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Development of a kinetic model for low temperature Fischer-Tropsch synthesis

Davies

Möller

2021

Chemical Engineering Science

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Globally, there is a need to replace our dependence on fossil fuels as the main source of energy.This requires a shift towards renewable and sustainable alternatives. The well-established Fischer-Tropsch (FT) synthesis is a potential process route to produce liquid fuels and speciality chemicals and address this challenge. FT synthesis is a polymerisation reaction in which syngas, a mixture of CO and H 2 , is converted to hydrocarbon products ranging from methane to wax when low temperature conditions are used. Subsequent product upgrading steps allow high quality liquid fuels to be obtained which are clean burning. This will help to mitigate the impact of human activity on the environment.The versatility of this process route is attributed to the ability of syngas to be generated from any carbon-containing feed such as coal, natural gas or biomass. The latter is attractive to enable a shift to a more sustainable way of living. Particularly for biomass-to-liquid plants, the high cost of syngas generation means that FT synthesis should use syngas as efficiently as possible. This requires an effective description of the FT reaction kinetics. This study therefore focuses on the development of a kinetic model for low temperature FT (LTFT) synthesis to improve understanding of the reaction behaviour and aid in the development of a biomass-to-liquid process route.Although the kinetics of the FT reactions under the low temperature conditions of 180-260 • C and 20-30 bar(a) have been extensively studied, the challenge to kinetic model development is the large number of possible reaction products. A common simplification is to consider the formation of the main products only, which are linear n-paraffins and 1-olefins. The polymerisation character of FT synthesis means that its product distribution could ideally be described using models based on probability theory. Deviations from probability theory distribution, however, occur especially at the conditions of LTFT synthesis. These deviations are a high methane yield, low ethene yield and the change from mainly 1-olefins at low carbon number to mainly n-paraffins at high carbon number. Comprehensive kinetic models in literature focus on finding a kinetic explanation for these deviations. These kinetic models, however, cannot easily be used with few being extended to include the formation of products of higher carbon number.An aspect ignored in current kinetic model development is that FT synthesis shares many aspects of an equilibrium-controlled process. This is since CO hydrogenation which leads to monomer formation is the rate-determining step for the FT reactions. Consequently, the rate of chain growth is rapid in comparison. This leads to the distribution of n-paraffins and 1-olefins being controlled by equilibrium. By modelling FT synthesis as an equilibrium-controlled process, the kinetic model formulation could be simplified, consist of fewer rate expressions and contain the minimum number of model parameters without compromising on prediction quality. At the condi...

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Section: Literature Reviewmentioning

confidence: 93%

Section: 1mentioning

confidence: 99%

“…expressions. An example of a hydrocarbon system in which this strategy has successfully been applied is 1-olefin oligomerisation (Sealy, 1996;Norval, 2008).…”

Section: 1mentioning

confidence: 99%

Section: Chemical Equilibrium Considerationsmentioning

confidence: 99%

See 2 more Smart Citations

Development of a kinetic model for low temperature Fischer-Tropsch synthesis

Davies

Möller

2021

Chemical Engineering Science

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show abstract

“…Although the Flory distribution is usually derived from kinetics, modifications to this model, such as chain-length dependent termination probabilities, have been necessary to explain experimental results. Based on previous publications and some examples, Norval (132) argued that a one-parameter equilibrium model based on a pseudo-element (CH 2 , H 2 , CO) approach could be used to describe the product distribution for olefins, paraffins and alcohols. In Fig.…”

Section: Theoretical Workmentioning

confidence: 99%