The product distribution in Fischer–Tropsch synthesis: An extension of the ASF model to describe common deviations

Förtsch, Dieter; Pabst, Kyra; Groß-Hardt, Edwin

doi:10.1016/j.ces.2015.07.005

Cited by 65 publications

(44 citation statements)

References 58 publications

(129 reference statements)

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“…Product termination occurs through either β-dehydrogenation or hydrogenation to a 1-olefin or n-paraffin respectively. This mechanism works well for n-paraffin and 1-olefin formation but it cannot explain the formation of oxygenates (Claeys & van Steen, 2004;Förtsch et al, 2015;Mousavi et al, 2015). From Figure 2.2, it has been proposed that the coupling of a surface hydroxyl (OH) species and an alkyl group may lead to n-alcohol formation.…”

Section: Fischer-tropsch Reaction Mechanismmentioning

confidence: 99%

“…The agreement about the polymerisation character of FT synthesis and that the chain growth steps occur through the addition of a C 1 monomer means that the nature of the product distribution can be estimated using probability theory. This was first developed and applied by Flory for free radical step growth polymerisation (Fogler, 1999;Förtsch et al, 2015). It was extended and applied to FT synthesis by Anderson and Schulz (Davis, 1992;van der Laan, 1999;Puskas & Hurlbut, 2003).…”

Section: Product Selectivitymentioning

confidence: 99%

“…A key assumption of the ASF distribution is that α is independent of carbon number. This allows the entire product distribution to be characterised by a single parameter, α, for values between zero and one (Subiranas, 2009;Förtsch et al, 2015). This is shown in Figure 2.3.…”

Section: Product Selectivitymentioning

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: Fischer-tropsch Reaction Mechanismmentioning

confidence: 99%

Section: Product Selectivitymentioning

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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“…The hydrocarbon chain growth is represented by the chain growth probability factor (α-value) which is the fraction of the rate of propagation, rP,n, to the sum of the rates of propagation and termination of the hydrocarbon chains, rT,n, as described in equation 4 below. The chain length is represented by the carbon number n (Förtsch, Pabst and Groß-Hardt, 2015).…”

Section: Fischer-tropsch Synthesismentioning

confidence: 99%

An Energy Integrated Approach to Design a Supercritical Fischer‐Tropsch Synthesis Products Separation and Solvent Recovery System

Katbeh

Elbashir

El‐Halwagi

2018

Natural Gas Processing From Midstream to Downstream

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“…The Anderson-Schulz-Flory (ASF) model has been used by many researchers to describe the product distribution of hydrocarbons in FTS. [3][4][5][6][7][8] The ASF plot and model predictions are given by equation 1:…”

Section: Introductionmentioning

confidence: 99%

Lu Plot and Yao Plot: Models To Analyze Product Distribution of Long-Term Gas-Phase Fischer–Tropsch Synthesis Experimental Data on an Iron Catalyst

Gorimbo

Muleja

et al. 2017

Energy Fuels

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Fischer-Tropsch synthesis (FTS) is a catalysed chemical reaction in which synthesisgas (H 2 + CO) is converted to clean fuels and chemicals. In addition to the classical ASF model two new models namely Yao and Lu models are presented to show the FTS product distribution using the experimental data obtained in three fixed bed reactors (each loaded with 1 gram of the same iron based catalyst, and reduced with syngas (CO/H 2 ), H 2 and CO, respectively) over a wide range of FTS conditions.In the first approach, we plotted P (n+1) /O (n+1) versus P n /O n with carbon number n = 2-5, which is called Yao's plot. The results showed that although the P/O ratios are strongly dependent on the process conditions, such as reduction agents, flow rate and pressures etc., the plots of P (n+1) /O (n+1) against P (n) /O (n) yielded a nearly linear relationship though with different gradients for all the three reactors; these results indicate that the olefin and paraffin distributions are not independent. The current data, including the effect of the reducing agents on the catalyst performance, widen the range of the application of the Yao plot. Just like the classical Anderson-Schulz-Flory distribution model, this model has some deviations especially for n = 2. The second plot, referred to as the Lu plot, depicts the relationship between normalized mole fractions of O n , O n+1 and P n . These plots show how the equilibrium points migrate with changes in the experimental conditions. These equilibrium point migrations seem to be due to changes in the CO conversion. Using the same normalized mole fraction concept, novel plots of C n H 2n+1 , C n H 2n , and C n+1 H 2(n+1) , that is paraffin n, olefin n and paraffin n+1, when n = 2, 3 and 4, are plotted.

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The product distribution in Fischer–Tropsch synthesis: An extension of the ASF model to describe common deviations

Cited by 65 publications

References 58 publications

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

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

An Energy Integrated Approach to Design a Supercritical Fischer‐Tropsch Synthesis Products Separation and Solvent Recovery System

Lu Plot and Yao Plot: Models To Analyze Product Distribution of Long-Term Gas-Phase Fischer–Tropsch Synthesis Experimental Data on an Iron Catalyst

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