Anderson-Schulz-Flory distribution

A comparative study of the alumina-supported catalysts prepared from [H2FeOs3(CO)i3], [H20s3Rh(acac)(CO)io], and [Rli4(CO)i2] was performed and each catalyst was found to be active in the conversion of CO -I- H2. The major product observed in each experiment was methane and the hydrocarbon products were formed in approximately a Schulz-Flory-Anderson distribution. The heterogeneous [Os3Rh] catalyst was two orders of magnitude more active at 543 K than the [FeOs3] catalyst, but showed a lower selectivity for ether formation. ... 

When determining the product selectivities, all compounds of equal carbon numbers (paraffines, olefins, isomers, and oxygen compounds) were summarized to one product fraction. The chain growth probability was determined by the Anderson-Schulz-Flory (ASF) distribution ... 

The carbon number distribution of Fischer-Tropsch products on both cobalt and iron catalysts can be clearly represented by superposition of two Anderson-Schulz-Flory (ASF) distributions characterized by two chain growth probabilities and the mass or molar fraction of products assigned to one of these distributions.7 10 In particular, this bimodal-type distribution is pronounced for iron catalysts promoted with alkali (e.g., K2C03). Comparing product distributions obtained on alkali-promoted and -unpromoted iron catalysts has shown that the distribution characterized by the lower growth probability a, is not affected by the promoter, while the growth probability a2 and the mass fraction f2 are considerably increased by addition of alkali.9 This is... 

The experimentally obtained Anderson-Schulz-Flory (ASF) distribution (solid line) follows the theoretical values closely and was an early indication that the reaction to form the hydrocarbons was a type of polymerization, and indeed of Ci species. An interesting feature of the ASF plot is that it is not quite smooth but has a kink at A = 2 which comes below the curve (see Figure 15). The reason why substantially less ethane and ethylene than expected is formed has been widely debated it can occur if fewer free C2 species are produced or if the C2 fraction preferentially undergoes further reaction. The former explanation seems to be the more accepted one, in other words the rate at which surface-attached C2 undergoes further polymerization is faster than the rate of liberation of the free C2 hydrocarbons from the surface. 

Concurrent with FTS mechanism studies, product distribution models were developed based on the analysis of product composition. Friedel and Anderson28 29 in the 1950s published the Anderson-Schulz-Flory (ASF) distribution model to predict the wide range of products yielded from FTS. The equation is shown as follows ... 

Overall hydrocarbon distributions on the four carbon supports are shown in Figure 11. The hydrocarbon mole fractions comply with the Anderson-Schulz-Flory (ASF) distribution. Note that hydrocarbons of carbon number up to 34 are detected for all carbon supports. However, the chain-growth probability (a) for catalyst with wood-AC support is 0.65 (at least for carbon numbers of up to 20), smaller than that of the catalysts using the other three AC supports ( 0.71). 

For the production of higher alcohols from syngas, two kinds of perovskites have been reported in the literature. First, perovskites with noble metals, like LaRhOs, have been studied in the past [23,24] for the ethanol synthesis with a CO/H2 mixture. More recently, LaCoi Cu 03 perovskites have been investigated to explore the opportunity of the Ci-C alcohols synthesis following an Anderson-Schulz-Flory (ASF) distribution [25-32] similar to that obtained by the so-called Co-Cu IFP catalyst [33]. 

The FTS mechanism could be considered a simple polymerization reaction, the monomer being a Ci species derived from carbon monoxide. This polymerization follows an Anderson-Schulz-Flory distribution of molecular weights. This distribution gives a linear plot of the logarithm of yield of product (in moles) versus carbon number. Under the assumptions of this model, the entire product distribution is determined by one parameter, a, the probability of the addition of a carbon atom to a chain (Figure 4-7). ... 

The description of the product distribution for an FT reaction can be simplified and described by the use of a single parameter (a value) determined from the Anderson-Schulz-Flory (ASF) plots. The a value (also called the chain growth probability factor) is then used to describe the total product spectrum in terms of carbon number weight fractions during the FT synthesis. In the case... 

The production of hydrocarbons using traditional F-T catalysts is governed by chain growth (polymerization) kinetics. The theoretical equation describing the distribution of hydrocarbon products, commonly referred to as the Anderson-Schulz-Flory (ASF) equation, is... 

The F-T synthesis typically follows polymerization kinetics. The Anderson-Schulz-Flory equation describes the product distribution ... 

FIGURE 5 Anderson-Schulz-Flory distribution of the linear hydrocarbons, linear oxygenates (n-alcohols, n-aldehydes, and linear carboxylic acids), and methyl alkyl ketones formed in the Fischer-Tropsch synthesis on an iron-containing Fischer-Tropsch catalyst operating at a temperature of 498 K (plotted using log(lO)). 

In a recent study, R. Pettit et at. examined the validity of tire Fischer-Tropsch carbide mechanism, the Anderson-Emmett hydroxy carbene mechanism and the Pichlcr-Schulz mediaiiism [174. In a first experiment, the Schulz Flory distribution obtained by CO/H conversion over a cobalt catalyst in the absence and in the presence of CH N] was studied. It was found that addition of CHjN resulted in a signillcant increase of the propagation rate which is in favour of the assumption of methylene as a building block, as predicted by the carbide mechanism. Furthermore, the reaction was carried out using labeled CO (90% CO and 10% CO), H2. and CHjNj in variable ratios. The number of atoms in the propenc fraction was calculated according to the three... 

Krishna and Bell (299) described the results of their steady-state tracing experiments by the model shown in Fig. 31. The scheme is in accord with the Anderson-Schulz-Flory distribution of products, based on chain growth by the successive addition of monomers s to chain fragments C s- is different from Ci,s. ft is assumed that the probability of chain growth a is not a function of n, where... 

Product distributions can be evaluated for reaction probabilities of elemental surface reaction steps with the model of non trivial surface polymerisation [2]. Specific inhibition of desorption of a chemisorbed organic species has been postulated to be the intrinsic principle of the FT-synthesis [5]. A chemisorbed species can react further by linear chain prolongation or chain branching or it can desorb as a paraffin, olefin or an organic oxygen compound. Growth probabilities pg, that contain a similar information as the Anderson-Schulz-Flory parameter a. 

Product distribution from the Fischer-Tropsch unit is generally regarded as being approximated by the Anderson-Schulz-Flory equation ... 

In 1951 Anderson[l] established the production distribution formulation of the Fischer-Tropsch synthesis (FTS), which is called Anderson-Schulz-Flory (ASF) formulation. Since then,for a long time it is almost always possible to describe FTS product distribution by ASF formulation,which has the following mathematical expression ... 

The product distribution of hydrocarbons formed during the Fischer-Tropsch process follows an Anderson-Schulz-Flory distribution (Spath and Dayton, 2003) ... 

Keywords Cobalt catalyst. Kinetics, Modeling, Fischer-Tropsch synthesis. Hydrocarbon Product Distribution, Anderson-Schulz-Flory. 

The Fischer-Tropsch s)mthesis is a process to convert synthesis gas (a mixture of carbon monoxide and hydrogen) to hydrocarbons that can be used as for instance transportation fuels. In the process all (straight chain) hydrocarbons fi om methane to heavy waxes are produced. In general this product distribution can be described by an Anderson-Schulz-Flory distribution based on a constant chain growth probability. As a consequence the selectivity towards diesel production is limited. When the diesel fraction is defined as CIO till C20, the maximum fraction of diesel that can be obtained is 39.4%, reached at a chain growth probability of 0.87. 

Marano and Holder have calculated the VLE of the Fischer-Tropseh system. The pseudo-components were defined with the aid of an analytical molar-mass distribution function (Anderson-Schulz-Flory distribution). The properties of a pseudo-component were based on a hypothetical model component in each carbon-number cut. 

Sasol has built and operated several FT plants in South Africa. The product usually follows the Anderson-Schulz-Flory distribution and typically consists of linear paraffins and waxes in the range of C5-C40. It is emphasized that A/f° values depend on the number of C atoms in the resulting -paraffln. Thus, for = 1,2,3, and 4, A77° values are -206.1, -347.3, -497.5, and -649.9 kJ/mol, respectively. In fact, it can be inferred from these examples that A/7° -148.2 x — 54.8... 

Figure 15.14 (a) Product distribution of the Fischer—Tropsch synthesis predicted by Anderson—Schulz—Flory (ASF) polymerization model, (b) Product distribution obtained in the Fischer—Tropsch synthesis with different catalysts. 

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