High-temperature Fischer Tropsch Synthesis Research Articles

A durable nanocatalyst of potassium-doped iron-carbide/alumina for significant production of linear alpha olefins via Fischer-Tropsch synthesis

Improvement of activity, selectivity, and stability of the catalyst used in Fischer-Tropsch synthesis (FTS) to produce targeted hydrocarbon products has been a major challenge. In this work, the potassium-doped iron-carbide/alumina (K-Fe5C2/Al2O3), as a durable nanocatalyst containing small iron-carbide particles (∼ 10 nm), was applied to high-temperature Fischer-Tropsch synthesis (HT-FTS) to optimize the production of linear alpha olefins. The catalyst, suitable under high space velocity reaction conditions (14–36 N L gcat−1 h−1) based on the well-dispersed potassium as an efficient base promoter on the active iron-carbide surface, shows very high CO conversion (up to ∼90%) with extremely high activity (1.41 mmolCO gFe−1 s−1) and selectivity for C5–C13 linear alpha olefins.

Energy use, greenhouse gases emission and cost effectiveness of an integrated high– and low–temperature Fisher–Tropsch synthesis plant from a lifecycle viewpoint

The lifecycle assessment of energy–greenhouse gases emission–economic performance for single low–temperature Fischer–Tropsch synthesis (LTFTS), high–temperature Fischer–Tropsch synthesis (HTFTS) and HTFTS–LTFTS co-production from coal are investigated and compared to the oil refining process. This covers feedstock supply chain and oil production at the oil refinery and Fischer–Tropsch synthesis (FTS) plants. Results show that the energy input and CO2 emission are mostly from coal mining and washing and oil production at the plant for FTS plants or oil refinery. Cost input is largely from feedstock cost and capital cost for FTS plants, crude oil cost, and transport cost for oil refining process. Compared to oil refinery pathway, FTS to oil currently presents no advantages in the aspect of lifecycle of energy use and greenhouse gases emission. However, the HTFTS-LTFTS demonstrates a favorable economic feasibility especially at a low oil price, indicating that the combined system presents high flexibility and strong market adaptability compared to traditional stand–alone HTFTS, LTFTS and oil refinery plant. Furthermore, in comparison with single HTFTS and LTFTS plants, HTFTS–LTFTS makes a big progress in CO2 emission per unit profit due to its excellent economic benefits. Such an alternative way of coal to oil has an enormous potential to simultaneously satisfy requirements of oil safety and standard of CO2 emission reduction in China.

Formulation and catalytic performance of MOF-derived Fe@C/Al composites for high temperature Fischer–Tropsch synthesis

The synthesis of MOF/AlOOH derived composites enhances the selectivity towards light olefins in HTFTS and the mechanical stability of the catalysts.

Soldering of Iron Catalysts for Direct Synthesis of Light Olefins from Syngas under Mild Reaction Conditions

High-temperature Fischer–Tropsch synthesis represents a sustainable alternative for direct light olefin synthesis from syngas derived from fossil and renewable feedstocks. It is found that the promotion of iron catalysts with metals used for soldering (Bi and Pb) results in a remarkable increase in the light olefin production rate with a possibility to conduct Fischer–Tropsch synthesis at low reaction pressure. A combination of characterization techniques uncovered notable migration of the promoting elements during the reaction and decoration of iron carbide nanoparticles with the promoters. The promoters seem to facilitate CO dissociation by removing O atoms from iron carbide.

High-performance Fe5C2@CMK-3 nanocatalyst for selective and high-yield production of gasoline-range hydrocarbons

Highly-loaded and well-dispersed Fe5C2 nanoparticles within ordered mesoporous carbon CMK-3 (Fe5C2@CMK-3) were prepared via a simple melt infiltration method. They were successfully applied to high-temperature Fischer-Tropsch synthesis, and showed high CO conversion (91%) and activity (5.1×10−4molcogFe−1s−1) as well as good selectivity (38wt%) for gasoline-range hydrocarbons (C5–C12). The catalytic property of Fe5C2@CMK-3 was newly interpreted, based on theoretical data obtained by computational simulations.

High-temperature Fischer-Tropsch synthesis over FeTi mixed oxide model catalysts: Tailoring activity and stability by varying the Ti/Fe ratio

A series of Fe-Ti mixed oxide model catalysts containing different Ti/Fe ratios were synthesized and applied as catalysts for the High Temperature Fischer-Tropsch reaction (HTFTS). XRD, H2-TPR and in situ Mössbauer and XAFS spectroscopy were applied to evaluate the role of Ti on the physical and chemical properties of Fe within the mixed metal oxide. It was observed that the Ti/Fe ratio determines the relative amounts of hematite, pseudobrookite, and anatase in the starting materials. The interplay between these phases is responsible for the HTFTS catalytic performance.Our results demonstrate that the presence of pseudobrookite: i) enhances the dispersion of iron; ii) mediates and controls the reduction and carburization degree during the transformation of Fe (III) species to carbides upon activation, and iii) increases the stability under HTFTS conditions by minimizing the re-oxidation of iron carbides. Highest catalytic activity and stability is achieved for the material with Ti/Fe ratio of 1/2.1.

Fischer–Tropsch synthesis in the presence of ultrafine iron-containing catalysts derived from reverse microemulsions

It is shown that active catalysts for Fischer–Tropsch synthesis with a controlled size of the particles of the dispersed phase may be formed on the basis of reverse microemulsions in a slurry reactor. After optimization of the composition of the reverse microemulsion (iron nitrate nonahydrate as a precursor of the active metal and SPAN-80 as a surfactant, 5 wt %), the size of the microemulsion droplets decreases to 130 nm. The chosen method for the synthesis of catalytic systems makes it possible to introduce promoters without any marked enlargement of the dispersed phase (130–160 nm). High-temperature Fischer–Tropsch synthesis is performed in a slurry reactor using catalysts prepared from reverse iron-containing microemulsions. The tested iron-containing catalytic systems feature high selectivity (up 73 wt %) in the formation of gasoline fractions (the C5–C10 fraction) that contain an abnormally high (up to 77 wt %) level of unsaturated hydrocarbons.

Elucidating the Nature of Fe Species during Pyrolysis of the Fe-BTC MOF into Highly Active and Stable Fischer–Tropsch Catalysts

In this combined in situ XAFS, DRIFTS, and Mossbauer study, we elucidate the changes in structural, electronic, and local environments of Fe during pyrolysis of the metal organic framework Fe-BTC toward highly active and stable Fischer–Tropsch synthesis (FTS) catalysts (Fe@C). Fe-BTC framework decomposition is characterized by decarboxylation of its trimesic acid linker, generating a carbon matrix around Fe nanoparticles. Pyrolysis of Fe-BTC at 400 °C (Fe@C-400) favors the formation of highly dispersed epsilon carbides (e′-Fe2.2C, dp = 2.5 nm), while at temperatures of 600 °C (Fe@C-600), mainly Hagg carbides are formed (χ-Fe5C2, dp = 6.0 nm). Extensive carburization and sintering occur above these temperatures, as at 900 °C the predominant phase is cementite (θ-Fe3C, dp = 28.4 nm). Thus, the loading, average particle size, and degree of carburization of Fe@C catalysts can be tuned by varying the pyrolysis temperature. Performance testing in high-temperature FTS (HT-FTS) showed that the initial turnover fr...

Effects of co-feeding with nitrogen-containing compounds on the performance of supported cobalt and iron catalysts in Fischer–Tropsch synthesis

The performance of supported cobalt and iron catalysts in low and high temperature Fischer–Tropsch synthesis was investigated in the presence of small amounts of ammonia in syngas. Ammonia was co-fed to the reactor either by in-situ hydrolysis of acetonitrile or by addition of aqueous ammonia.The addition of acetonitrile and ammonia resulted in significant irreversible deactivation of alumina supported cobalt catalysts. Lower methane and higher C5+ hydrocarbon selectivities were observed. Iron based catalysts did not show any noticeable deactivation in the presence of acetonitrile or ammonia. Moreover, Fischer–Tropsch reaction rate slightly increased after addition of the nitrogen-containing compounds to silica and alumina supported samples. Lower methane selectivity and higher C2–C4 olefin to paraffin ratio were observed in the presence of ammonia when the catalysts were reduced in hydrogen. Iron catalysts activated in carbon monoxide did not demonstrate any significant effect of ammonia on the selectivity. The catalytic data were explained by irreversible formation of inactive cobalt nitrides in cobalt catalysts and transformation of metallic iron and iron oxides in the presence of acetonitrile and ammonia into iron nitrides and iron carbides active in Fischer–Tropsch synthesis.

Design of iron catalysts supported on carbon–silica composites with enhanced catalytic performance in high-temperature Fischer–Tropsch synthesis

Iron catalysts supported by carbon–silica composites prepared via hydrothermal treatment of silica by fructose showed enhanced catalytic performance in Fischer–Tropsch synthesis.

On the role of the stability of functional groups in multi-walled carbon nanotubes applied as support in iron-based high-temperature Fischer–Tropsch synthesis

The role of the stability of surface functional groups in oxygen- and nitrogen-functionalized multi-walled carbon nanotubes (CNTs) applied as support for iron catalysts in high-temperature Fischer–Tropsch synthesis was studied in a fixed-bed U-tube reactor at 340°C and 25bar with a H2:CO ratio of 1. Iron oxide nanoparticles supported on untreated oxygen-functionalized CNTs (OCNTs) and nitrogen-functionalized CNTs (NCNTs) as well as thermally treated OCNTs were synthesized by the dry impregnation method using ammonium ferric citrate as iron precursor. The properties of all catalysts were examined using X-ray diffraction, temperature-programmed reduction in H2, X-ray photoelectron spectroscopy and temperature-programmed oxidation in O2. The activity loss for iron nanoparticles supported on untreated OCNTs was found to originate from severe sintering and carbon encapsulation of the iron carbide nanoparticles under reaction conditions. Conversely, the sintering of the iron carbide nanoparticles on thermally treated OCNTs and untreated NCNTs during reaction was far less pronounced. The presence of more stable surface functional groups in both thermally treated OCNTs and untreated NCNTs is assumed to be responsible for the less severe sintering of the iron carbide nanoparticles during reaction. As a result, no activity loss for iron nanoparticles supported on thermally treated OCNTs and untreated NCNTs was observed, which even became gradually more active under reaction conditions.

Sodium-promoted iron catalysts prepared on different supports for high temperature Fischer–Tropsch synthesis

The paper addresses the effect of sodium promotion on the structure and catalytic performance of iron catalysts supported on alumina, silica, CMK-3 and carbon nanotubes in high temperature Fischer-Tropsch synthesis giving general rules for the selection of supports for selective synthesis of olefins in the presence of promoter.Our results show that the effect of sodium promotion strongly depends on the support. In silica and CMK-3 carbon support, iron species interact with sodium with formation of inactive sodium-iron mixed oxides or carbides which results in higher olefin selectivity and chain growth probability but lower Fischer-Tropsch reaction rate. In alumina supported catalysts, sodium promotion preferentially leads to formation of sodium aluminate with a relatively small effect in Fischer–Tropsch synthesis. The effect of promotion with sodium is more pronounced on carbon nanotubes which contain iron carbide species stabilized by encapsulation in the carbon matrix. The sodium promoted catalysts supported on carbon nanotubes exhibit higher selectivity to both light and long-chain olefins.

Pore size effects in high-temperature Fischer–Tropsch synthesis over supported iron catalysts

This paper addresses the effect of support pore sizes on the structure and performance of iron catalysts supported by mesoporous silicas in high-temperature Fischer–Tropsch synthesis. A combination of characterization techniques showed that the size of supported iron particles was controlled by catalyst pore sizes. The larger iron particles were localized in large-pore supports.Iron carbidization with carbon monoxide resulted in preferential formation of Hägg iron carbide (χ-Fe5C2). Larger iron oxide crystallites in large-pore supports were much easier to carbidize than smaller iron oxide counterparts in small-pore supports. The catalytic performance in Fischer–Tropsch synthesis was attributed to iron carbide. Higher Fischer–Tropsch reaction rates, higher olefin, and C5+ selectivity were observed over larger pore iron catalysts. High dispersion of iron oxide in small-pore silicas was not favorable for carbon monoxide hydrogenation because of poor iron carbidization.

Inorganic complex precursor route for preparation of high-temperature Fischer–Tropsch synthesis Ni–Co nanocatalysts

The effect of the preparation method on the structural properties and activity of Ni–Co catalysts in the Fischer–Tropsch synthesis has been explored. Impregnation, co-precipitation and a novel method, thermal decompositions of inorganic precursor complex, procedures were applied for the generation of the Ni-promoted alumina- or silica-supported cobalt catalysts. The precursors and the catalysts that were obtained from their calcination were characterized by powder X-ray diffraction, thermal gravimetric analysis, Brunauer–Emmett–Teller specific surface area measurements, scanning electron microscopy and Fourier transform infrared spectroscopy. The catalytic performance in Fischer–Tropsch synthesis was investigated for all calcined catalysts in the temperature interval from 280 to 360 °C. The Ni–Co/Al2O3 catalyst prepared by thermal decomposition of [Ni(H2O)6][Co(dipic)2]·2H2O/Al2O3 as a precursor performed optimally for the conversion of synthesis gas to light olefins. The outcomes revealed that this novel procedure is more advantageous than impregnation and co-precipitation methods for the preparation of effective and durable cobalt catalysts for Fischer–Tropsch synthesis.

Support effects in high temperature Fischer-Tropsch synthesis on iron catalysts

The paper addresses the effects of silica and carbon supports on the structure and catalytic performance of iron catalysts for high temperature Fischer-Tropsch synthesis. Iron phase composition and dispersion in both calcined and activated catalysts were strongly affected by the support. Hematite was the major iron phase in calcined silica supported catalysts, while carbon supported counterparts contain magnetite. Catalyst activation in carbon monoxide leads to carbidisation of iron oxides to principally Haag iron carbide. Higher Fischer-Tropsch reaction rates were observed on carbon supported iron catalysts compared to silica supported counterparts. The catalytic performance principally depended on iron phase composition rather than on iron dispersion. Iron catalysts supported on carbon nanotubes and activated carbon showed highest activity in Fischer-Tropsch, which could be attributed to the formation of composites of iron carbide and residual magnetite.

Direct production of light olefins from syngas over potassium modified Fe–Mn catalyst

A series of potassium promoted Fe–Mn catalysts for light olefin synthesis from CO hydrogenation were prepared by the co-precipitation-calcination-impregnation method. The impact of potassium promoter on the textural properties, reduction behavior, adsorption of hydrogen, bulk phase composition and their correlation with Fischer–Tropsch synthesis (FTS) performances were emphatically studied. As revealed by N2 physisorption, the increasing of potassium had no distinct effect on the size of α-Fe2O3 and surface area. H2 temperature-programmed reduction/desorption showed that potassium inhibited the reduction and hydrogen adsorbability of catalysts. CO temperature-programmed desorption showed that potassium enhanced the CO adsorption of catalysts. X-ray photoelectron spectroscopy indicated the enrichment of promoter atoms on the surface of catalysts. The X-ray diffraction and Mossbauer effect spectroscopy results revealed that potassium made carburization easy. After reduction with syngas (H2/CO = 20) for 48 h, FTS test was performed with the syngas (H2/CO = 3.5) in the high temperature Fischer–Tropsch synthesis process. The maximum of CO conversion and selectivity to light olefins was noted on increasing K content (2.8 mol% K/Fe), followed by a significant decline at the excessive potassium level. At the point, the selectivity of light olefins and olefin/paraffin (C2–C4) was 27.75 mol% and 8.54. The results indicated that potassium promoter could inhibit the water gas shift reaction, suppress hydrogenation ability, which promoted the production of light olefins via suppressing the secondary hydrogenation reaction.

Combinations of CO/CO2 reactions with Fischer–Tropsch synthesis

The combination of CO/CO2 shift reactions with Fischer–Tropsch synthesis offers the possibility to produce hydrocarbons from CO-rich syngas (from biomass or coal gasification) and from H2/CO2 mixtures. In the case of CO-rich synthesis gas, the H2/CO ratio needs to meet stoichiometric requirements for the low-temperature Fischer–Tropsch synthesis and therefore the CO is shifted to CO2 to form additional H2. Mixtures of H2/CO2 require the shift of CO2 into CO, which acts as intermediate in the production of short-chain hydrocarbons via high-temperature Fischer–Tropsch synthesis. The present work analyzes based on validated kinetic models how the shift reaction affects the FT reaction under operation conditions of interest and how both FT and shift reactions can be optimized to maximize hydrocarbon production.

Low CO2 selective iron based Fischer–Tropsch catalysts for coal based polygeneration

Integration of electricity generation with liquid fuel production is a viable strategy towards maximising coal utilisation and hydrocarbon supply. Herein we report on catalyst design for process intensification and optimisation of electricity and hydrocarbon production from coal. Low temperature Fischer–Tropsch synthesis with Fe–Zn (Zn/Fe ratio 0.25) based catalysts using H2-deficient syngas feed displayed unprecedented low CO2 selectivity. Promotion of the Fe–Zn with Cu and Ca afforded Fischer–Tropsch product distributions that are typical of high temperature Fischer–Tropsch synthesis. The present report provides foundation for design of iron based catalyst that can compete with cobalt based once in terms of low CO2 selectivity.

Mechanism of oxygenates formation in high temperature Fischer-Tropsch synthesis over the precipitated iron-based catalysts

In-situ DRIFTS and chemical trapping techniques were employed to investigate the adsorbed species over the surface of precipitated iron-based catalysts and the mechanism of oxygenates formation in high temperature Fischer-Tropsch synthesis. The results showed that both linear and bridged CO molecules are present on the catalyst surface, which leads the formation of numerous oxygenated precursors. Some crucial surface intermediates are detected by the in-situ DRIFTS, such as acetate, acetyl and methoxide. The surface of precipitated iron-based catalysts is characterized by following facts: alcohols are able to react with free surface hydroxyls to form alkoxy species; surface adsorbed molecules exhibit certain oxidizing ability; basic sites such as OH− and lattice oxygen may react with CH3OH or CH3CHO molecules. By chemical trapping of the CH3OH + CO and CH3I + CO + H2 reactions, it was found that acetyl is an important intermediate for oxygenates and the hydrogenation of acetyl is a crucial step for the formation of oxygenates. On the basis of these observations, the mechanism of oxygenates formation in high temperature Fischer-Tropsch synthesis over the precipitated iron-based catalysts was then proposed.

High temperature Fischer–Tropsch synthesis in commercial practice

The commercial application of high temperature Fischer–Tropsch (HTFT) technology is described. The types of reactor used are discussed with emphasis on the advantages of using the Sasol Advanced Synthol (SAS) reactor. A reactor replacement project at Secunda, South Africa will result in a total installed capacity of 124 000 barrel per day of products from the new SAS reactors. The preparation of the catalyst used in these reactors is described. The changes to the catalyst structure during synthesis are illustrated, making it clear that the actual catalyst consists of small carbide/magnetite particles embedded in a continuous carbon phase. The changes in catalyst morphology which occur during synthesis are discussed with reference to the effect on the observed post sulphur poisoning behaviour. The SAS process can be considered to be a mature technology which has been applied in large-scale commercial plants. Future applications should take advantage of the considerable potential to recover chemical feedstocks from the primary Synthol products. The potential amounts of these chemical feedstocks are quantified.