Tropsch Products Research Articles

Hybrid zirconia catalysts for conversion of Fischer–Tropsch waxy products to transportation fuels

Conversion of long-chain normal paraffins found in Fischer–Tropsch products to high-quality transportation fuels, especially middle range products, was investigated using model hydrocarbons ( n-C 24 and n-C 36) and a Fischer–Tropsch wax over modified zirconia catalysts. Most work was carried out using n-C 24 as a representative reactant. With Pt-promoted tungstated zirconia (Pt/WO 3/ZrO 2, 0.5 wt.% Pt and 12.5 wt.% W) used as a base, addition of sulfated zirconia (SO 4/ZrO 2), tungstated zirconia (WO 3/ZrO 2) or certain zeolites increased its reactivity and selectivity at 200 °C to middle range products such as kerosene and diesel fuel. The effect of improving the performance of Pt/WO 3/ZrO 2 by adding the zeolite, mordenite, was studied in detail; an optimal mixing ratio exists for maximum conversion of n-C 24 under certain reaction conditions. The hybrid catalysts are physical mixtures of compounds with different functions. Hybrid catalysts based on Pt/WO 3/ZrO 2 provide a promising way to obtain higher catalytic activity and higher selectivity for desired transportation fuels from Fischer–Tropsch products.

Assessment of internal diffusion limitation on Fischer–Tropsch product distribution

A reactor is modeled for ideal vapor–liquid equilibrium (VLE) conditions and is operated with a single α catalyst. Under steady state conditions, the relative concentration of hydrocarbon product in the catalyst pores decreases with increasing carbon number until about C 20. It is deduced that the two α product distribution in Fischer–Tropsch (FT) reactions is not due to the effect of product diffusion limitations of the heavier products.

Selecting optimum syngas technology and process design for large scale conversion of natural gas into Fischer—Tropsch products (GTL) and methanol

Selecting optimum syngas technology and process design for large scale conversion of natural gas into Fischer—Tropsch products (GTL) and methanol

Improved conversion of syngas from Fischer—Tropsch products via olefin metathesis

Improved conversion of syngas from Fischer—Tropsch products via olefin metathesis

About the impact of olefin reactions of Fischer—Tropsch product distributions for high diesel yield

About the impact of olefin reactions of Fischer—Tropsch product distributions for high diesel yield

Interpretation and kinetic modeling of product distributions of cobalt catalyzed Fischer–Tropsch synthesis

Carbon number distributions of Fischer–Tropsch products on iron and cobalt catalysts show deviations from the ideal Anderson–Schulz–Flory (ASF) distribution. For products obtained on cobalt catalysts these deviations are traced back by many authors to re-adsorption and incorporation of 1-alkenes followed by subsequent chain growth. In the present work, it could be shown by means of model calculations and based on experiments with co-feeding of ethene and 1-alkenes that such subsequent chain growth cannot be regarded as the main reason of observed deviations of the carbon number distribution from the ideal ASF distribution. The co-feeding experiments suggest that these deviations are the consequence of two different mechanisms of chain growth causing a superposition of two ASF distributions. Consequently, the carbon number distributions are represented by this superposition. In order to describe distributions as a function of reaction conditions the model parameter, the growth probabilities α 1 and α 2 as well as μ 1, the fraction of distribution ( α 1) are presented as function of the partial pressures of hydrogen and carbon monoxide. Finally, the typical model parameters of products formed on cobalt and iron are compared.

Transient initial kinetic regimes of Fischer–Tropsch synthesis

Transient kinetic regimes of Fischer–Tropsch (FT) synthesis with a potassium-promoted iron catalyst have been observed and characterized by time-resolved conversion and selectivity studies using H 2/CO and a H 2/CO 2 synthesis gases. Up to six episodes relating to catalyst transformations/reconstructions could be distinguished. Amazingly, with the H 2/CO 2 synthesis gas a Fischer–Tropsch product of nearly the same composition as that with the H 2/CO synthesis gas was finally obtained at the steady state. However, the transient episodes lasted for a long time. Selectivity has been related to steps of elemental reactions by use of a kinetic model. As intrinsic FT feature, the principle of selective inhibition is established from the detailed selectivity results. Spatial constraints at the FT sites appear also to control selectivity. The iron catalyst exhibits fundamental differences in how generating FT sites, as compared with cobalt catalysts. FT sites on iron are stable, whereas FT sites on cobalt are of dynamic nature.

Kinetic modelling of Fischer–Tropsch product distributions

Starting from the idea of Fischer–Tropsch (FT) synthesis as an ideal polymerisation reaction it is easily realised, that product olefins undergo secondary reactions and thereby modify the product distribution. This generally leads to chain length dependencies of certain olefin reaction possibilities, which are again suited to serve as a characteristic feature for the kind of olefin conversion. By extending an existing model and accounting for olefin readsorption, incorporation, hydrogenation and isomerisation via double bond shift and the chain length dependence of product solubilities, typical deviations from ideal distributions can be simulated and experimentally observed data with cobalt and iron catalysts can be satisfactorily described, suggesting the correctness of the assumptions made. Furthermore, other existing models dealing with the same issue are briefly discussed in this paper.

Correlation of synthesis gas solubility in n-paraffin solvents and Fischer—Tropsch waxes

A correlation of the solubility of Fischer—Tropsch synthesis and product gases in heavy n-paraffin waxes is obtained with the Lacombe—Sanchez equation of state (EOS). The EOS parameters for pure n-paraffins are developed and correlated as functions of carbon number. Interaction parameters with the n-paraffins are determined from solubility data and expressed as functions of carbon number of the n-paraffin solvent for the gases hydrogen, carbon monoxide, methane, carbon dioxide, ethylene and ethane.

The effect of time on stream and feed composition on the selectivity of a cobalt fischer—Tropsch catalyst

AbstractThe Taylor–Wojciechowski formulation of Fischer Tropsch product distributions has been used to study the effect of time on stream and of feed composition on the parameters which arise in the T–W treatment. An experimental setup which allows the required evaluation of product yields is also described.The T–W formulation was found to give an excellent fit to data obtained using a cobalt‐on‐kieselguhr catalyst. Since the ratios of the various specific rates of parallel synthesis reactions were found to be different functions of the H2/CO ratio in the reactor, we conclude that propagation, branching and termination reactions are not governed by the same kinetics.

Chain limitation of Fischer–Tropsch products in zeolites

Fischer-Tropsch synthesis on RuY-molecular sieves shows a non-linear Schulz–Flory plot and a drastic decline in chain growth probability after C10; thus, pure dimensions in zeolite-based catalysts are capable of limiting reaction product chain growth.

Fischer—tropsch waxes. VI. Distribution of branches and mechanism of branch formation

AbstractA statistical method for the calculation of the concentrations of normal and mono‐, di‐ and trimethyl paraffins to be expected in Fischer—Tropsch products was derived from first principles. It was tested by means of analytical results that were available for the lighter products, found to be quite adequate and then applied to “hard wax”. An explanation is sought for the extremely high degree of branching of a certain wax fraction reported previously, in the light of the results of the statistical calculations. A comparison is made between the calculated and experimental values for isoparaffin content.The method was also used to predict the variation of isoparaffin content with molecular weight and the theoretical curve thus obtained compared with reported analytical results. The possibility of a variation of the probability of a carbon atom being a branching site with chain length is discussed in the light of results reported by other workers.A mechanism for the formation of branches during Fischer—Tropsch synthesis is proposed. It is based on the single site growth point concept and on the separation of a chain from the catalyst surface as a free radical. Isomerisation of the original primary free radical to a secondary one occurs. If the latter re‐attaches itself to the catalyst surface and grows further, a branched chain product is obtained.