Anderson-Schulz-Flory product distribution

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... 

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 ... 

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 ... 

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. 

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. 

Tavakoli, A., Sohrabi, M., Kargari, A., 2008. Application of Anderson—Schulz—Flory (ASF) equation in the product distribution of slurry phase FT synthesis with nanosized iron catalysts. Chemical Engineering Journal 136 (2—3), 358—363. 

Flory polymerization kinetics (4). Henrici-Olive and Olivd (5) proposed the use of the related equation of Schulz (6). Over the last decade the Flory equation has been used frequently to describe product distributions in FT synthesis. The Friedel-Anderson (i) or Flory (4) approaches apply when the rates of propagation and termination are independent of carbon number. We do not attempt here to discuss all previous research on FT product distributions except to say that the literature contains many examples of product distributions that obey Flory kinetics within relative narrow carbon number ranges and many that do not. 

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. ... 

We studied hydrocarbon synthesis from CO2 using Cu-Zn-Cr (3 3 1)/HY and Fe-ZnO /HY composite catalysts[2 6]. In this case, first CO2 converted to methanol, and then methanol converted to hydrocarbon over zeolite. The main products formed among hydrocarbons was ethane, propane and butane, and hydrocarbon distribution was different from Schulz-Anderson-Flory rule. In MTG reaction, methanol converted to dimethyl ether, then to ethene, and ethene converted to higher hydrocarbons or ethane. In order to obtain higher hydrocarbons, it is important to find active catalysts which have no hydrogenation activity of olefin. 

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