Fischer-Tropsch Synthesis Of Hydrocarbons Research Articles

Specifics of the mechanism of formation and molecular-mass distribution of hydrocarbons in fischer-tropsch synthesis on Co/SiO2 Mn+ catalysts

It was shown that molecular-mass distributions of hydrocarbons produced over Co/SiO2 · Fe(III), Co/SiO2 · Cr(III), and Co/SiO2 · Zn(II) catalysts are described well by a mathematical model proposed earlier for rationalizing the distribution of products formed in the presence of a Co/SiO2 · Zr(IV) catalyst with a probability α. This model is based on the concept that α1-hydrocarbons are produced from alkyl intermediates and α2-hydrocarbons (α1 < α2) are formed from alternative surface compounds. The primary α1-products are olefins, and ethylene is involved in chain growth with a lower value of α. Reasons for the speculation that the difference in the pattern of molecular-mass distribution of hydrocarbons produced on cobalt and iron catalysts is due to the difference in the mechanism of formation of α1-hydrocarbons are given.

Enhancement in the reducibility of cobalt oxides on a mesoporous silica supported cobalt catalyst

The silylation of SBA-15 enhances the reducibility of cobalt oxides on a SBA-15 supported cobalt catalyst, and consequently increases the catalytic activity for Fischer-Tropsch synthesis of hydrocarbons from syngas and selectivity for longer chain products.

Direct synthesis of middle iso-paraffins from synthesis gas on hybrid catalysts

This paper focuses on the synthesis of iso-paraffin-rich hydrocarbons by Fischer–Tropsch synthesis (FTS) over silica gel supported Co catalyst (Co/SiO 2). The basic concept is to isomerize and/or hydrocrack the primary FTS hydrocarbon products. A physical mixture consisting of a small amount of zeolite or Pd/zeolite mixed with Co/SiO 2 enhanced the formation of C 4–C 10 iso-paraffins while suppressing the formation of higher molecular hydrocarbons, probably because of the selective cracking of these hydrocarbons on them. In separate experiments, a two-reactor system was used. The first reactor contained a physical mixture of Co/SiO 2 and zeolite, and the second reactor contained zeolites or Pd-supported zeolites. The two-reactor system gave sharp C-number distribution within C 3–C 6 and iso-paraffins-rich products. The hydrocracking of n-octane and n-decane (model compound simulating products of the FTS reaction) over mixed catalysts composed of various compositions of Pd/SiO 2 and ZSM-5 in the presence of gaseous hydrogen showed high and stable activity, and produced primarily iso-paraffin-rich hydrocarbons. The isomerization was favored for mixtures rich in Pd/SiO 2. The role of Pd was thought to be the inlet of hydrogen spillover to the zeolite surface.

Direct synthesis of middle iso-paraffins from synthesis gas

This paper focuses on the synthesis of iso-paraffin-rich hydrocarbons by Fischer–Tropsch synthesis (FTS) over Co/SiO 2 catalyst. The basic concept was to secondarily isomerize and/or hydrocrack the primary FTS hydrocarbon products. A physical mixture of a small amount of added H-ZSM-5 in the Co/SiO 2 catalyst enhanced the formation of C 4–C 10 iso-paraffins while suppressing the formation of longer hydrocarbons, probably because of the selective cracking of higher hydrocarbons on ZSM-5. The three-component catalyst (Co/SiO 2–Pd/SiO 2–ZSM-5) promoted the formation of paraffins, whereas the yield of isomerized products was not high enough. For a two-step reaction, the first step catalyst was the Co/SiO 2+ZSM-5 catalyst and the second step catalyst was Pd/SiO 2+ZMS-5 catalyst where additional hydrogen was added. The selectivity of iso-paraffins was markedly promoted and the molecular weight of the product decreased while the syngas conversion was kept constant. The hydrocracking of n-octane (which is the model compound of FTS reaction) over hybrid catalyst composed of Pd/SiO 2–zeolite and showed high and stable activity giving iso-paraffin-rich hydrocarbons. The isomerization was favored for Pd rich catalyst. The role of Pd was thought to be the port hole of hydrogen spillover to zeolite.

Hydrothermal deactivation of silica-supported cobalt catalysts in Fischer–Tropsch synthesis

Hydrothermal conditions created by high conversion in Fischer–Tropsch hydrocarbon synthesis induce cobalt–silica mixed oxide formation causing deactivation of silica-supported cobalt catalysts. The mixed oxide phase displays a distinctive needle-like morphology with a 1-nm lattice spacing and has a Co/Si atomic ratio of 1.2/1. The hydrothermal origin of the mixed oxide is confirmed by the fact that steamed catalyst samples contain the same needle-like phase with identical lattice spacing and Co/Si ratio. Reduction in 1.2 MPa H 2 at ⩾400 °C decomposes the mixed oxide and recovers small metallic cobalt particles.

A review of the occurrence and origin of abiogenic hydrocarbons in igneous rocks

Abstract Reports on the presence of hydrocarbons in igneous rocks have been on the increase and generating greater interest in the scientific community over the last 20 years. Most of the occurrences are due to the incorporation of organic material into the magmatic systems. However, reports on the presence of hydrocarbons formed by abiogenic processes have also increased in recent years, suggesting that these hydrocarbons may not be as rare as previously thought and may have implications for natural gas resources in the future. This paper reviews these occurences and the models proposed for the generation of these hydrocarbons, in particular the nature of the hydrocarbon-bearing fluids in the alkaline complexes Khibina, Lovozero and Ilímaussaq. The origin of these hydrocarbons remains controversial, whether they are (1) derived directly from the mantle, (2) formed during late crystallization stages by respeciation of a C-O-H fluid below 500°C, or (3) formed during postmagmatic alteration processes involving Fisher-Tropsch type reactions catalysed in the presence of Fe-oxides and silicates. The reports suggest that a direct mantle origin for the hydrocarbon fluid is unlikely. A model involving near-solidus reequilibration of a C-O-H fluid to a CH 4 -rich composition is possible, although only for extreme melt compositions that have large crystallization temperature ranges (i.e. hyperagpaitic melts). The Fischer-Tropsch synthesis of hydrocarbons in igneous rocks seems to be a more applicable model for a wide variety of igneous rocks.

Winter diesel fuel production from a Fischer-Tropsch wax

A process for the production of a winter diesel fuel from wax containing hydrocarbons produced by the Fischer-Tropsch hydrocarbon synthesis process. A 300° F.+ Fischer-Tropsch fraction is upgraded first by hydroisomerization followed by catalytic dewaxing resulting in a diesel fuel suitable for use as a winter diesel fuel having excellent cold flow properties and reduced emissions.

Anti-ASF Distribution of Fischer–Tropsch Hydrocarbons in Supercritical-Phase Reactions

Direct wax synthesis from syngas was implemented by supercritical-phase Fischer–Tropsch synthesis (FTS) reaction. By introducing supercritical-phase n-pentane into the reaction, waxy hydrocarbon formation rate was increased significantly while light hydrocarbon formation rate was suppressed effectively. Anti-Anderson–Schultz–Flory distribution of FTS hydrocarbons was realized at lower temperatures, such as 473 K. The intermediate, olefins, readily readsorbed onto the catalyst surface and significantly stimulated the carbon chain-growth process.

Fischer-Tropsch synthesis of hydrocarbons during sub-solidus alteration of the Strange Lake peralkaline granite, Quebec/Labrador, Canada

The composition of the carbonic phase(s) of fluid inclusions in pegmatite quartz from the Strange Lake peralkaline complex has been analysed by gas chromatography using online extraction of inclusion contents and a PoraPLOT® Q capillary column. The measured gas species are, in order of abundance, CH 4, H 2, C 2H 6, CO 2, N 2, CA, n-C 4H 10, n-C 5H 12, C 2H 2, i-C 4H 10 and C 2H 4 Minor amounts of i-C 5H 12, n-C 6H 14, i-C 6H 14, and neo-C 6H 14 were also detected (but not quantified) in some samples. A suite of quartz samples from Ca-metasomatised pegmatites contains fluid inclusions with a similar distribution of hydrocarbons but much higher proportions of C0 2. The carbonic fluid coexisted immiscibly with a brine ( Salvi and Williams-Jones, 1992), which on the basis of field and petrographic evidence, was interpreted to have originated from the magma. However, thermodynamic calculations indicate that the above gas species, specifically the hydrocarbons, could not have coexisted at equilibrium in the proportions measured, at any geologically reasonable conditions either prior to or post entrapment. We propose, instead, that the gas compositions measured in the Strange Lake inclusions, and in inclusions from other alkalic complexes, resulted from the production of H 2 during the alteration of arfvedsonite to aegirine, and the subsequent reaction of this H 2 with orthomagmatic C0 2 and CO to form hydrocarbons in a magnetite-catalysed Fischer-Tropsch synthesis. Locally, influx of an oxidised calcic brine, derived externally from the pluton, altered the original composition of the fluid by converting hydrocarbons to C0 2.

Estimates of rate coefficients for elementary processes occurring during Fischer-Tropsch synthesis over [formula omitted

The dynamics of elementary processes involved in Fischer-Tropsch synthesis of hydrocarbons over Ru TiO 2 have been determined from the analysis of data from both steady-state and transient-response experiments. Both types of experiments were carried out with different feed catalyst bed residence times to assess the effects of olefin readsorption on the dynamics of chain initiation, propagation, and termination. Strong evidence was found for the rapid reentry of ethylene into the chain growth process. The reentry of C 3+ olefins, though, is negligible for the conditions studied. The holdup of hydrocarbons in a weakly physisorbed state was found to be significant for C 6+ products and must be accounted for in the simulation of transient-response experiments. When the effects of ethylene readsorption and C 6+ holdup are properly taken into account, the rate coefficients for chain initiation, propagation, and termination, determined from simulations of the transient-response experiments, are independent of carbon number and catalyst-bed residence time. Rate coefficients for the readsorption of ethylene, the depolymerization of adsorbed ethyl groups, and the dehydrogenation of methyl to methylene groups were also determined from simulations of the transient-response experiments.

Hydrogenation of Carbon Oxides over Perovskite-Type Oxides

Abstract Transition metals, metal oxides and metal-containing mixed oxides have been extensively used for Fischer-Tropsch hydrocarbon synthesis (1–9) and their ability to yield oxygenated compounds. During the last two decades, an extensive search has been carried out in examining the mechanism of catalytic hydrogenation of co and CO, which produced hydrocarbons and oxygenate compounds. The catalytic models for hydrocarbon synthesis have already been reviewed by Vannice (lo), which gives detailed information and discusses the data which were obtained during their development. As a broad product distribution is obtained during the FT synthesis, the mechanisms are extremely complicated and not clearly understood: therefore this topic is beyond the objective of this chapter and hence no further attention will be paid.

Iron oxide pillared clay with large gallery height: Synthesis and properties as a Fischer-Tropsch catalyst

New iron oxide pillared montmorillonites have been prepared by the reaction of Na + montmorillonite with base-hydrolyzed solutions of Fe 3+ salts and subsequent thermal conversion of the intercalated polycations. Depending on the hydrolysis conditions used to generate the pillaring solutions, pillared products with basal spacings in the range 18 to 25 Å were obtained. Under optimum hydrolysis conditions (base/metal = 2.0 meq/mol, aging time = 23–147 hr) the pillared products contained 6.8–9.8 Fe 3+ ions per O 20(OH) 4 unit cell and exhibited basal spacings of 25–29 Å. These latter spacings corresponded to exceptionally large gallery heights of 15–19 Å. Upon calcination at 300°C, the spacings decreased to 23–27 Å. N 2 BET surface areas after outgassing at 350°C were in the range 270 to 350 m 2/g. The pillared products are active catalysts that have undergone Fischer-Tropsch synthesis of hydrocarbons at 275°C and 120-psi (CO: H 2 = 1 : 2). The hydrocarbon distribution in the C 1–C 6 range (1.3% conversion) followed Anderson-Schulz-Flory statistics with a chain propagation probability of α = 0.49. X-ray energy dispersive analysis indicated that substantial amounts of the intercalated iron migrated to the edge sites of the clay particles under reaction conditions. The redistribution of iron resulted in a distribution of gallery heights sufficiently heterogeneous to preclude Bragg X-ray scattering along the 001 direction. Iron migration also occurred upon exposure of the pillared products to the ambient atmosphere for prolonged periods (≥3 months).

Fischer-Tropsch Synthesis of Hydrocarbons Using Iron-Mordenite Catalysts

Fischer-tropsch catalysts with high activity and selectivity for olefins were produced using mordenite type SiO2/Al2O3= 12, 20, 28, 62 zeolite supported iron carbonyl compounds and were characterized by X-ray powder diffraction. The adsorptionof volatile Fe(CO)5 on the support surface was carried out under vacuum at room temperature. Reduction les were monitored by vibrating sample magnetometer (VSM). The magnetic saturation time was observed to increase with increasing the Al2O3 content of catalyst system indicating an increasing interaction between iron and alumina. The activity and selectivity of different iron deposited mordenite sample were investigated during Fischer-Tropsch synthesis of hydrocarbons with H2/CO=3 in the temperature range of 400-500 °C using a microreactor system. The results correlated with the acidic properties of surface and/or with metallic state of active iron particles of the catalyst.

ChemInform Abstract: The Role of Surface Science Studies in Elucidating the Mechanism of the Fischer‐Tropsch Hydrocarbon Synthesis

Abstract The Fischer-Tropsch hydrocarbon synthesis: n CO +(2n+2) H 2 → C n H 2n+2 +n H 2 O was discovered in 1923 and is most effectively catalyzed by iron, cobalt and ruthenium. Nickel is an excellent catalyst for methanation, the special case where n=1. We argue that surface science studies have established the key role of carbon monoxide dissociation in Fischer-Tropsch synthesis and have also been important in identifying majority surface species present during reaction. The relationship between surface and bulk carbide stability is then discussed. The lack of useful surface science evidence on the nature of the polymerization step is considered, relevant information from organometallic chemistry is outlined and a new mechanism tentatively proposed. Finally, the role of promoters such as alkali metals and of electronegative poisons is explored briefly.

Kinetic studies for elucidation of the promoter effect of alkali in Fischer-Tropsch iron catalysts

The kinetics of the formation of hydrocarbons in Fischer-Tropsch synthesis and of consecutive reactions, i.e., hydrogenation and double bond isomerization of primarily formed 1-alkenes, were studied in a slurry-phase reactor using alkalized and nonalkalized precipitated iron catalysts. Both consecutive reactions have an order of about −2 with respect to carbon monoxide and an order of about 1 with respect to 1-alkenes. The order with respect to hydrogen is 1 for the hydrocarbon formation and also 1 for the consecutive hydrogenation, but 0 for the consecutive isomerization. The reaction orders are not changed by addition of K 2CO 3 to the catalyst. The kinetics of consecutive reactions can be interpreted by competitive adsorption of 1-alkene and carbon monoxide. Alkali addition causes an increase in the strength of carbon monoxide adsorption and consequently a decrease in 1-alkene adsorption so that the rates of the consecutive reactions are reduced. This hypothesis could be proved by studies of 1-hexene hydrogenation in the presence and absence of carbon monoxide for alkalized and nonalkalized iron catalysts. The kinetics were studied in the ranges 1.3 < P CO(10 5Pa) < 7, 1.6 < P H2(10 5Pa) < 9, and 490 K < T < 530 K.

Stability of bulk and surface carbide layers and their relation to the Fischer-Tropsch hydrocarbon synthesis

Using a combination of the recently developed selfconsistent layer Koringa-Kohn-Rostoker LKKR) scheme and a non-selfconsistent cluster method, the local densities of states for bulk and surface carbides of iron, nickel and copper have been determined. Ia the bulk carbides, a decrease in carbon-metal bonding is observed, due both to decreased splitting of the carbon p orbitals, and an increase in filling of the antibonding p orbital. This exactly mirrors the observed trend in stability of the carbides, decreasing from iron to nickel, with copper carbide unknown. Similar trends are observed from the LDOS of the surface carbides, and it is concluded that the carbidic carbon species is thermodynamically unstable at copper surfaces. The catalytic implication of these results and those of Feibelman for ruthenium and rhodium carbides is discussed, with particular reference to their implications for the mechanism and selectivity of these metals in Fischer-Tropsch synthesis.

The mechanism of chain growth in the Fischer-Tropsch hydrocarbon synthesis

It is proposed that the slow step in chain growth during the Fischer-Tropsch hydrocarbon synthesis is the formation of an adsorbed ethylidene species from two adsorbed methylenes. Addition of a further methylene species gives a diadsorbed C3H6 entity, which leads to a singly attached carbonium ion. A 1,2 hydrogen shift then forms a methyl substituted ethylidene species, which is available for further polymerisation. Further hydrogen shift may occur, yielding an olefin and terminating the chain growth. The extent of chain branching is dictated by the relative stability of secondary and primary carbonium ions, as previously proposed by McCandlish, (J. Catalysis 83 (1983) 362).

The role of surface science studies in elucidating the mechanism of the Fischer-Tropsch hydrocarbon synthesis

The Fischer-Tropsch hydrocarbon synthesis: n CO+(2n+2) H 2→ C n H 2n+2+n H 2 O was discovered in 1923 and is most effectively catalyzed by iron, cobalt and ruthenium. Nickel is an excellent catalyst for methanation, the special case where n=1. We argue that surface science studies have established the key role of carbon monoxide dissociation in Fischer-Tropsch synthesis and have also been important in identifying majority surface species present during reaction. The relationship between surface and bulk carbide stability is then discussed. The lack of useful surface science evidence on the nature of the polymerization step is considered, relevant information from organometallic chemistry is outlined and a new mechanism tentatively proposed. Finally, the role of promoters such as alkali metals and of electronegative poisons is explored briefly.

Contributions of gas chromatography to the development of heterogeneous catalysis

Examples of the application of gas chromatography in catalysis are presented. In the first example it is demonstrated how in Fischer-Tropsch synthesis of hydrocarbons, alcohols, aldehydes, ethers, esters and acids, the polar and apolar components are separated on a capillary column. The second example discusses the use of gas chromatography for the study of reaction kinetics on single-crystal, model-catalyst surfaces in a high-pressure/low-pressure cell. Thirdly the use of gas chromatography in continuous catalyst testing is discussed.

Catalytic properties of materials derived from iron-containing clays

The catalytic activities of iron-containing fireclays reduced at 1020°C, determined using the Fischer-Tropsch hydrocarbon synthesis reaction in a wax-slurry reactor, are proportional to the intensity of an unusual singlet peak in the Mossbauer spectra of the reduced samples. This singlet peak is attributed to γ-Fe, a metastable high-temperature form which appears to be stabilized by the cubic host lattice resulting from kaolinite decomposition at ca. 980°C. The enhanced activity of γ-Fe is discussed in terms of steric factors related to the structure of this phase. The effects of different thermal pretreatments and additions of alkali promotors on the catalytic activity are also discussed.