High-temperature Fischer Tropsch Research Articles

Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2

Oil has long been the dominant feedstock for producing fuels and chemicals, but coal, natural gas and biomass are increasingly explored alternatives1–3. Their conversion first generates syngas, a mixture of CO and H2, which is then processed further using Fischer–Tropsch (FT) chemistry. However, although commercial FT technology for fuel production is established, using it to access valuable chemicals remains challenging. A case in point is linear α-olefins (LAOs), which are important chemical intermediates obtained by ethylene oligomerization at present4–8. The commercial high-temperature FT process and the FT-to-olefin process under development at present both convert syngas directly to LAOs, but also generate much CO2 waste that leads to a low carbon utilization efficiency9–14. The efficiency is further compromised by substantially fewer of the converted carbon atoms ending up as valuable C5–C10 LAOs than are found in the C2–C4 olefins that dominate the product mixtures9–14. Here we show that the use of the original phase-pure χ-iron carbide can minimize these syngas conversion problems: tailored and optimized for the process of FT to LAOs, this catalyst exhibits an activity at 290 °C that is 1–2 orders higher than dedicated FT-to-olefin catalysts can achieve above 320 °C (refs. 12–15), is stable for 200 h, and produces desired C2–C10 LAOs and unwanted CO2 with carbon-based selectivities of 51% and 9% under industrially relevant conditions. This higher catalytic performance, persisting over a wide temperature range (250–320 °C), demonstrates the potential of the system for developing a practically relevant technology.

Experimental modeling to design a heat exchanger control strategy for a Fischer–Tropsch fluidized bed

Fluidized beds are ideal contactors for high temperature Fischer–Tropsch (FT) synthesis because of their superior heat transfer and low pressure drop compared to fixed bed reactors. However, as the reaction is extremely exothermic, even in these systems, runaway reactions sinter catalyst when the heat removal is insufficient or the control strategy is deficient. Although FT technology has been well established for decades, new catalysts, process intensification, and modular designs require a cooling strategy and control system a priori to ensure the process operates safely through the development stages. Here, we designed a safe mode experiment for a pilot fluidized bed reactor (200mm in diameter) charged with 36kg of alumina powder with a vertical cooling coil bundle. We measured the heat transfer rate between hot water in the coils and the fluidized bed operating up to 300°C, 0.5-1MPa, and superficial gas velocities from 5 × to 10 × the minimum fluidization velocity (umf=2.4mms−1). The dynamics of the cooling was 35% faster at higher gas velocities and the preliminary estimates concluded two tube bundles with 4 vertical runs each with 3/4 in. Schedule 10 pipe was sufficient to remove the heat generated. The calculated convective heat transfer coefficients were comparable to several published models but they were lower than expectation. We compared heat transfer rates of a single bundle and a set of two bundles and designed a PI and a PID controller plus filter (PIDf) separately using the internal mode control approach. Based on the results, the performance of the PIDf controller is better than the PI, as it minimizes oscillations and responds faster.

Coupling the high-temperature Fischer–Tropsch synthesis and the skeletal isomerization reaction at optimal operation conditions in the Power-to-Fuels process route for the production of sustainable aviation gasoline

Power-to-Fuels route for the production of aviation gasoline: stable operation of the coupled high-temperature Fischer–Tropsch synthesis and the skeletal isomerization reaction, at optimal operating conditions respectively.

Optimization of coal-to-liquid processes; A way forward towards carbon neutrality, high economic returns and effective resource utilization. Evidences from China

As the world's largest consumer of coal, China is committed to developing a carbon–neutral coal industry. For this purpose, upgrading the carbon emission-intensive coal-chemical industries, such as coal-to-liquids (CTL) is imperative. This study develops a technical–economic framework to model and test four promising CTL upgrading processes. First and second processes involve low-temperature Fischer-Tropsch (FT) synthesis practices with larger gasifiers and air-separating units than the current level. Third, the process combines olefin and fuel co-production practices that utilize low- and high-temperature FT synthesis processes. Finally, the process produces both electricity and fuel by sending the tail gas of the synthesis process to an integrated cycle. Aspen Plus® is used to simulate the chemical processes, and the financial cost accounting model of the American Association of Cost Engineers is utilized to estimate the financial costs accurately. The results show that the upgraded processes can achieve an energy efficiency of more than 48 %, which is 6 % higher than the existing coal-to-oil process. Additionally, the break-even point is 2 %–14.45 % lower than the actual process, reducing carbon emissions by 2.78 %–10.34 %. According to these findings, the upgrade can help China reach its carbon neutrality targets and significantly contribute to global climate change and sustainable development goals.

Effect of Preparation Conditions on Precipitated Iron-Based Catalysts for High-Temperature Fischer–Tropsch Synthesis of Light Olefins

Effect of Preparation Conditions on Precipitated Iron-Based Catalysts for High-Temperature Fischer–Tropsch Synthesis of Light Olefins

High-temperature Fischer–Tropsch synthesis over the Li-promoted FeMnMgOx catalysts

Fischer–Tropsch-to-Olefins (FTO) over iron-based catalysts is a promising process for the production of light olefins from a non-petroleum source. However, the catalytic mechanism is unclear because of the variation in the iron phase during the reduction and activation processes and the complex iron phase composition under the reaction conditions. A series of Li-promoted FeMnMgOx catalysts is synthesized using co-precipitation and impregnation methods, after which the effect of promoters on the evolution of the iron phase, chemisorption, and FTO performance are analyzed. The results demonstrate that Mg enhances dissociative CO adsorption and hydrogen adsorption, improving the FTO activity. Mg facilitates the dispersion of α-Fe2O3 and suppresses the carbonization, which weakens the chain propagation, encourages the formation of short-chain hydrocarbons, and increases the selectivity of light olefins. Li also enhances dissociative CO adsorption and increases CO conversion. Moreover, Li facilitates the formation of the ε'-Fe2.2C phase, which reveals a higher FTS activity and better C–C coupling ability than the χ-Fe5C2 phase. This results in a decrease in CO2 and increase in light olefins. At the optimal Li loading, the FeMnMg-0.75Li sample displays the highest space time yield of light olefins at 355 g/(kgcat·h).

Effect of the Zr promoter on precipitated iron-based catalysts for high-temperature Fischer–Tropsch synthesis of light olefins

FeMnxZr and FeMnxZr2Na catalysts prepared by coprecipitation and impregnation methods were applied to investigate the promoting effects of Zr on iron-based catalysts for high-temperature Fischer–Tropsch synthesis (HTFT).

Direct Conversion of Syngas to Light Olefins through Fischer-Tropsch Synthesis over Fe-Zr Catalysts Modified with Sodium.

Fe–Zr–Na catalysts synthesized by coprecipitation and impregnation methods were implemented to investigate the promoting effects of Na and Zr on the iron-based catalyst for high-temperature Fischer–Tropsch synthesis (HTFT). The catalysts were characterized by Ar adsorption–desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, CO temperature-programmed desorption, H2 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy (MES). The results indicated that Na changed the active sites on the catalyst surface for the CO and hydrogen adsorption, owing to the electron migration from Na to Fe atoms, which resulted in an enhanced CO dissociative adsorption and a decrease in hydrogen adsorption on the metallic Fe surface. The decreased H/C ratio on the catalyst surface accounted for the increased chain propagation and weakened hydrogenation of light olefins. Besides, Na could also facilitate the carbonization of catalysts and protect the iron carbide against oxidation, which provides more active sites for HTFT reaction and is beneficial to the C–C coupling. Zr could decrease the hematite crystallite size and stabilize the active phase to improve the HTFT activity. At an optimal Na loading of 1.0 wt %, the Fe–Zr–1.0Na catalyst exhibited the highest light olefin selectivity of 35.8% in the hydrocarbon distribution at a CO conversion of 95.2%.

Mn-Decorated CeO2 nanorod supported iron-based catalyst for high-temperature Fischer–Tropsch synthesis of light olefins

The synergistic effect between Mn and Ce can improve electrons transfer from Ce to Fe and the oxygen migration. The remarkable properties promote the dissociation of CO, suppress the hydrogenation, and improve the selectivity of light olefins.

High-Temperature Fischer–Tropsch Synthesis of Light Olefins over Nano-Fe3O4@MnO2 Core–Shell Catalysts

A one-pot hydrothermal process was adopted to synthesize nano-Fe3O4@MnO2 core–shell catalysts with diverse thicknesses of MnO2 for the high-temperature Fischer–Tropsch (HTFT) synthesis of light ole...

Li-decorated Fe-Mn nanocatalyst for high-temperature Fischer–Tropsch synthesis of light olefins

Fe-Mn-Li nanocomposite particles were prepared using the combined urea hydrolysis and incipient wetness impregnation method. No surfactant or capping agents were involved in the preparation process, which ensured that this was low-cost and environmentally friendly method. In this study, the effects of urea hydrolysis temperature and Li amount on the catalyst structure, morphology, and particle size were analyzed combining various characterization techniques, including N2 adsorption–desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction, CO2 temperature programmed desorption, CO temperature programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and Mössbauer spectroscopy. The nanocatalyst synthesized at 140 °C (Fe-Mn-140) presented the largest specific surface area and highest selectivity for light olefins and the lowest selectivity for CO2 and CH4 of all Fe-Mn-x samples in this study. These findings were consistent with the results of the Mössbauer spectroscopy and XRD testing, where Fe-Mn-140 was determined to contain the maximum amount of χ-Fe5C2 and minimum amount of Fe3O4 after reaction of all Fe-Mn-x samples in this study. It was also determined that Li slightly restrained the reduction of iron oxides. In addition, Li increased the surface basicity of the catalysts, which reduced their selectivity for CH4 and light alkanes while increases those for light olefins and heavier hydrocarbons. Therefore, this study could lead to developing a facile and environmentally-friendly method for synthesizing iron-based nanocatalysts that present high activity and selectivity for light olefins for high-temperature Fischer–Tropsch synthesis processes.

Preparation of Iron Carbides Formed by Iron Oxalate Carburization for Fischer–Tropsch Synthesis

Different iron carbides were synthesized from the iron oxalate precursor by varying the CO carburization temperature between 320 and 450 °C. These iron carbides were applied to the high-temperature Fischer–Tropsch synthesis (FTS) without in situ activation treatment directly. The iron oxalate as a precursor was prepared using a solid-state reaction treatment at room temperature. Pure Fe5C2 was formed at a carburization temperature of 320 °C, whereas pure Fe3C was formed at 450 °C. Interestingly, at intermediate carburization temperatures (350–375 °C), these two phases coexisted at the same time although in different proportions, and 360 °C was the transition temperature at which the iron carbide phase transformed from the Fe5C2 phase to the Fe3C phase. The results showed that CO conversions and products selectivity were affected by both the iron carbide phases and the surface carbon layer. CO conversion was higher (75–96%) when Fe5C2 was the dominant iron carbide. The selectivity to C5+ products was higher when Fe3C was alone, while the light olefins selectivity was higher when the two components (Fe5C2 and Fe3C phases) co-existed, but the quantity of Fe3C was small.

Light hydrocarbons to BTEX aromatics over hierarchical HZSM-5: Effects of alkali treatment on catalytic performance

Abstract Three HZSM-5 zeolites with initial Si/Al ratios of 15, 25, and 40 were treated using an alkali solution to establish a hierarchical micropore-mesopore interconnected structure in alkali-treated zeolite samples Z15-AT, Z25-AT, and Z40-AT, respectively. The aim of the present work is to improve the catalytic stability in the aromatization of ethylene, a model compound representing the light hydrocarbons produced by the high-temperature Fischer‒Tropsch synthesis. By using characterization techniques, such as XRD, ICP, N2 adsorption/desorption, TEM, 27Al and 29Si MAS/NMR, NH3-TPD, Pyridine-IR, and TGA, we analyzed the textural property and acidity of the fresh catalysts, as well as the coke formation rate of the spent catalysts. The catalytic stability was shown to be successfully enhanced in the light hydrocarbon aromatization and the initial Si/Al ratio is a crucial factor for the mesopore formation and the catalytic performance. Among the prepared zeolite samples, the Z25-AT sample seemed to be the most suitable catalyst owing to its significant enhancement in the catalytic stability. The main reason for the improved stability by alkali treatment seems to be that the hierarchical pore structure facilitates the mass transfer and provides the additional space for carbon deposition as well, thus weakening the pore blocking and prolongs the lifetime of the catalyst.

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.

Controlled formation of iron carbides and their performance in Fischer-Tropsch synthesis

Iron carbides are unmistakably associated with the active phase for Fischer-Tropsch synthesis (FTS). The formation of these carbides is highly dependent on the catalyst formulation, the activation method and the operational conditions. Because of this highly dynamic behavior, studies on active phase performance often lack the direct correlation between catalyst performance and iron carbide phase. For the above reasons, an extensive in situ Mössbauer spectroscopy study on highly dispersed Fe on carbon catalysts (Fe@C) produced through pyrolysis of a Metal Organic Framework was coupled to their FTS performance testing. The preparation of Fe@C catalysts via this MOF mediated synthesis allows control over the active phase formation and therefore provides an ideal model system to study the performance of different iron carbides. Reduction of fresh Fe@C followed by low-temperature Fischer-Tropsch (LTFT) conditions resulted in the formation of the ε′-Fe2.2C, whereas carburization of the fresh catalysts under high-temperature Fischer-Tropsch (HTFT) resulted in the formation of χ-Fe5C2. Furthermore, the different activation methods did not alter other important catalyst properties, as pre- and post-reaction transmission electron microscopy (TEM) characterization confirmed that the iron nanoparticle dispersion was preserved. The weight normalized activities (FTY) of χ-Fe5C2 and ε′-Fe2.2C are virtually identical, whilst it is found that ε′-Fe2.2C is a better hydrogenation catalyst than χ-Fe5C2. The absence of differences under subsequent HTFT experiments, where χ-Fe5C2 is the dominating phase, is a strong indication that the iron carbide phase is responsible for the differences in selectivity.

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.

System development of integrated high temperature and low temperature Fischer–Tropsch synthesis for high value chemicals

The conventional indirect coal-to-liquid process suffers from improperly utilization of Fischer–Tropsch (FT) syncrude and poor economic performance. In consideration of the potential synergies in the process and product integration from the high temperature Fischer–Tropsch (HTFT) and the low temperature Fischer–Tropsch technology (LTFT), the novel HTFT–LTFT system integrated HTFT and LTFT synthesis is proposed based on the advanced coal gasification and FT techniques to improve efficiency and add products value. The HTFT–LTFT system is firstly modelled in Aspen Plus platform and then evaluated by the energy, exergy, and detailed economic analysis. The synergies of the integrated system are discussed by comparing with the separate HTFT or LTFT system. Results show that the integrated HTFT–LTFT system is efficiently and economically superior to the separate HTFT or LTFT system, which reduces the capital investment by 18.2% and increases the annual income by more than 10%. The integrated HTFT–LTFT system with the coproduction of olefins and base oil simultaneously presents the IRR of 15.2% and has high ability against product prices fluctuation.

Development of Integrated High Temperature and Low Temperature Fischer-Tropsch System for High Value Chemicals Coproduction

The conventional indirect coal-to-liquids process for transportation fuel production suffers from inefficiency in syncrude utilization and poor economic performance. This is largely because the FT syncrude are not properly used. In consideration of the potential synergies in fuel quality improvement and chemicals coproduction, for further high value utilization of the hydrocarbon products, the novel HTFT-LTFT system integrated high temperature Fischer-Tropsch process and low temperature Fischer-Tropsch process together is proposed based on the advanced coal gasification and FT techniques and modelled in Aspen Plus. Energy, exergy analysis and a detailed economic analysis are performed. The synergies of the integrated system is also discussed by comparing with the separated HTFT/LTFT system. Results show that the integrated HTFT-LTFT systems can increase the annual income by more than 10% by high utilization of FT syncrude and reduce the capital investment by 18.2% by sharing infrastructure. Higher energy and exergy efficiencies as well as internal rate of return (IRR) are achieved by the integrated systems. The integrated HTFT-LTFT system is more efficiently and economically than the separated HTFT/LTFT system. Therein the integrated HTFT-LTFT system coproduce both olefins and base oils simultaneously presents an excellent economic performance with IRR of 18%, much higher than the 4.7% of the separated HTFT/LTFT system.

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.

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.