Anderson-Schulz-Flory Distribution Research Articles

Insights into Fischer–Tropsch catalysis: current perspectives, mechanisms, and emerging trends in energy research

Fischer–Tropsch (FT) synthesis is an important module for the production of clean and sustainable fuels and chemicals, making it a topic of considerable interest in energy research. This mini-review covers the current literature on FT catalysis and offers insights into the primary products, the nuances of the FT reaction, and the product distribution, with particular attention to the Anderson–Schulz–Flory distribution (ASFD) and known deviations from this fundamental concept. Conventional FT catalysts, particularly Fe- and Co-based catalysis systems, are reviewed, highlighting their central role and the influence of water and water–gas shift (WGS) activity on their catalytic behavior. Various mechanisms of catalyst deactivation are also investigated, and the high methanation activity of Co-based catalysts is illustrated. To make this complex field accessible to a broader audience, we explain conjectured reaction mechanisms, namely, the carbide mechanism and CO insertion. We discuss the complex formation of a wide range of products, including olefins, kerosenes, branched hydrocarbons, and by-products such as alcohols and oxygenates. The article goes beyond the traditional scope of FT catalysis by addressing topics of current interest, including the direct hydrogenation of CO2 for power-to-X applications and the use of bifunctional catalysts to produce tailored FT products, most notably for the production of sustainable aviation fuel (SAF). This mini-review provides a holistic overview of the evolving landscape of FT catalysts and is aimed at both experienced researchers and those new to the field while covering current and emerging trends in this important area of energy research.

A New Cure Rate Model Based on Flory–Schulz Distribution: Application to the Cancer Data

In this article a new flexible survival cure rate model is introduced by assuming that the number of competing causes of the event of interest follows the Flory–Schulz distribution and the competing causes follow the generalized truncated Nadarajah–Haghighi distribution. Parameter estimation for the proposed model is derived based on the maximum likelihood estimation method. A simulation study is performed to show the performance of the ML estimators. We discuss three real data applications related to real cancer data sets to assess the usefulness of the proposed model compared with some existing cure rate models for the sake of comparison.

The Molecular Weight Distribution of Occluded Hydrocarbon Gases in the Khibiny Nepheline–Syenite Massif (Kola Peninsula, NW Russia) in Relation to the Problem of Their Origin

The origin of hydrogen–hydrocarbon gases present in the rocks of the Khibiny massif in unusually high concentrations has been the subject of many years of discussion. To assess the role of potential mechanisms and relative time of formation of gases occluded in inclusions in minerals, the molecular weight distribution of C1–C5 alkanes in the main rock types of the Khibiny massif was studied. For this purpose, the occluded gases were extracted from rocks by mechanical grinding and their composition was analyzed on a gas chromatograph. It is established that the molecular weight distribution of occluded hydrocarbon gases in the Khibiny massif corresponds to the classical Anderson–Schulz–Flory distribution. In addition, the slopes of the linear relationships are relatively steep. This indicates a predominantly abiogenic origin of the occluded gases of the Khibiny massif. At the same time, a small proportion of biogenic hydrocarbons is present and is associated with the influence of meteoric waters. It was also found that in the Khibiny massif, the proportion of relatively high-temperature gases decreases towards the Main foidolite Ring in the following sequence: foyaite and khibinite–trachytoid khibinite–rischorrite and lyavochorrite–foidolites and apatite–nepheline ores. In the same sequence, an increase in the proportion of heavy hydrocarbons and the increasing role of oxidation and condensation reactions in the transformation of hydrocarbons occurs.

Reaction chemistry of ethanol oligomerization to distillate-range molecules using low loading Cu/MgxAlOy catalysts

We study ethanol oligomerization to higher alcohols and other oxygenates with a 0.3 wt. %Cu/Mg2.9AlO catalyst. This reaction involves more than 130 products in a complicated reaction network. The selectivity towards diesel fuel precursor compounds (hereafter ‘DFPC’) increased with conversion until reaching a plateau at an ethanol conversion of ~70 %. Alcohol selectivity was found to follow Schultz-Flory distribution at all studied conversions. Larger sized alcohols then are formed mostly by chain-growth mechanisms via surface reactions of adsorbed oligomers with ethanol-based monomers. Higher esters are formed from alcohols and aldehydes in a series reaction mechanism. Moreover, C6+ ester and C4+ ketones selectivities increase as conversion increases. We also found that C4+ alcohols most likely undergo Guerbet coupling with the studied catalyst to form even higher alcohols once, and that the oxygen of these alcohols is active as a nucleophile, resulting in the selective formation of esters if the starting alcohol is branched. Finally, we performed several cofeed studies varying ethanol-to-H2 inlet partial pressures, and adding acetaldehyde and ethyl acetate as cofeeds to ethanol at different concentrations. We conclude from these experiments that acetaldehyde concentration controls reaction chemistry, with conditions favoring larger concentrations of the molecule promoting both alcohol coupling and ester formation, and conditions leading to lower concentrations of acetaldehyde resulting in higher alcohol selectivity at the expense of esters and higher aldehydes.

Ethanol to distillate-range molecules using Cu/MgxAlOy catalysts with low Cu loadings

A series of calcined MgAl mixed metal oxide catalysts with low Cu loadings (0.1–1.5 wt%) were tested for ethanol oligomerization to distillate-range molecules. The low Cu loading catalysts (0.1–0.6 wt%) had high selectivity to linear chain C4+ alcohols (49–63% selectivity) and C6+ esters (45–66% of total esters). More specifically, the diesel fuel precursor selectivities were over 75% for low Cu loading catalysts (0.1–0.6 wt%), with a decrease to 49% for a higher Cu loading catalyst (>1.2 wt% Cu) due to increased ethyl acetate and acetone formation. Alcohol and ester product selectivities follow a Schultz-Flory distribution. Alcohol selectivity was found to vary inversely with BET surface areas of the catalysts, whereas ester selectivity was found to increase with higher base site counts. However, Cu wt% loading was found to have a stronger impact in overall catalyst activity. The catalysts deactivated proportionally to the number of turnovers mainly due to coking, but could be regenerated by calcination.

Catalytic performance of porous Yb2O3 sesquioxide

ABSTRACT Porous Yb2O3 ceramic (55%) was pressureless sintered at 900°C for four hours in air. The crystal structure of Yb2O3 was confirmed to be cubic () with c = 10.43731 Å by neutron diffraction. The spectral vibrational signature of Yb2O3 was also confirmed by micro-Raman spectroscopy. Yb2O3 is an amphoteric oxide with both acid and base character, which presents the potential for producing different hydrocarbons when used as a Fischer–Tropsch (FT) catalyst. It was found that Yb2O3 is indeed catalytically active and can be used to convert syngas (CO + H2) into useful hydrocarbons. Production of methane, ethene, and ethane was detected in the catalytic experiment performed at 500°C, but propane, propene, butane, and methanol were also detected in the experiment performed at 250°C. Hydrocarbons heavier than C4 were not observed. The limited data show deviation from a Flory–Schulz distribution suggesting additional surface processes are occurring beyond chain growth and termination.

Chromium(III) complexes based on phenoxy-imine ligands with pendant N- and O-donor groups as precatalysts for ethylene oligomerization: synthesis, characterization, and DFT studies

Chromium complexes of general formula [Cr{ZNO}(THF)Cl2] [2a, ZNO = C9H6N-8-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2b, ZNO = Ph(NH)-C2H4-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2c, ZNO = 2-MeO-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2d, ZNO = 2-PhO-Ph-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2e, ZNO = PhO-C2H4-(N=CH)-2,4-tert-butyl-2-(OC6H2)] and the bis(ligand) complex [Cr{C9H6N-8-NH2}2Cl2]Cl (4) were synthetized and characterized by elemental analysis, IR spectroscopy, and by X-ray crystallography for 4. In the solid state, 4 is monomeric with two 8-amino-quinoline acting as bidentate ligands and two chloride ligands in cis position. The DFT calculations showed slightly higher HOMO energy for 2d. In addition, the energy levels of the LUMO are slightly influenced by pendant O- and N-donor group. Particularly, the LUMOs for complexes 2a and 2d show a small contribution from Cr and Cl atoms as compared to other chromium complexes (2b, 2c and 2e), and the orbitals are almost entirely delocalized over the phenoxy-imine unit. Upon activation with methylaluminoxane (MAO), chromium precatalysts 2a-2e showed good activity in ethylene oligomerization (TOF = 22.0 – 52.7 × 103 (mol ethylene)(mol Cr)−1⋅h−1 at 80°C) with Schultz-Flory distribution of oligomers (KC4-C10 ≈ 0.92), and production of polymer varying from 2.9 to 22.3 wt.%. The catalytic performance is mainly controlled by electronic effects at the phenoxy-imine ligands. The bis(ligand) chromium complex 4 showed good activity in ethylene oligomerization (TOF = 39,400 (mol ethylene)(mol Cr)−1 h−1), producing mostly oligomers (95.2 wt% of total products) with high selectivity for α-olefins. The highest activity among the six precatalysts screened was reached with 2c (TOF = 52,700 mol(ethylene)•mol(Cr)−1•h−1).

Relay catalysis in the conversion of syngas

China’s energy resource structure is rich in coal but poor in crude oil. For a long time, China has to rely on importing crude oil to meet the domestic demand for liquid fuels (including gasoline, aviation fuel and diesel fuel) and basic chemicals (such as C2–C4 lower olefins, aromatics, and C2+ oxygenates). In 2019, China’s dependence on oil imports has exceeded 70%, which has a negative impact on the social-economic development and national security. Thus, it is very urgent and important to produce liquid fuels and bulk chemicals based on coal resource. Syngas (a mixture of CO and H2) can be largely produced from the non-oil resources, such as coal, gas (natural gas, shale gas, and coal-bed methane), and biomass. From syngas, various hydrocarbon products can be produced as supplement of oil-derived products. The conversion of syngas to target products with high selectivity is the core of C1 chemistry. However, by the classical Fischer-Tropsch synthesis (FTS) route, the product selectivity is limited by the Anderson-Schulz-Flory (ASF) distribution, which results in the low selectivity of target products. In practice, the yields of liquid fuels and bulk chemicals are increased by a secondary process such as (hydro)cracking, isomerization and aromatization. The direct conversion of syngas to target products with high selectivity is attractive but challenging. Recently, the concept of relay catalysis has been successfully applied to the one-step transformation of syngas to liquid fuels and bulk chemicals with ultrahigh selectivity over bifunctional or multifunctional catalysts. The selectivity of target hydrocarbon products can break the limitation of the ASF distribution. In the conversion of syngas to liquid fuels, the used bifunctional catalysts are composed of FT catalysts and zeolites. FT catalysts, such as Fe (Fe x C y ), Co and Ru, are responsible for the activation of CO and the growth of carbon chain. Zeolites are in charge of the hydrocracking and isomerization. High selectivity of middle-distillates, such as gasoline (C5–C11 hydrocarbons), jet fuel (C8–C16 hydrocarbons) and diesel fuel (C10–C20 hydrocarbons), have been obtained via relay catalysis. It was found that the catalytic performances were strongly influenced by the topology, acidity and mesoporosity of zeolites as well as the metal sizes and promoters. The importance of hydrocracking on acid sites and hydrogenolysis on the metal nanoparticles for the selective C–C cleavage has also been analyzed. The selective synthesis of basic chemicals can also be achieved by relay catalysis, where the bifunctional catalysts consist of metal oxides (such as the solution solid ZnO-ZrO2, and the spinel structure of ZnCr2O4, ZnAl2O4) and zeolites (such as SAPO-34, ZSM-5, MOR). The activation of CO to intermediates (CH3OH/DME or ketene) proceeds on the metal oxides and the selective C–C bond formation proceeds on the zeolites. The reaction mechanism of such kind of bifunctional catalysts differs from that of the conventional FT catalysts, where the CO activation and C–C coupling are conducted over different sites. The selectivity of lower olefins and aromatics could reach up to 85% without the formation of undesired methane. Besides, multifunctional catalysts can offer an 80% selectivity towards C2+ oxygenates such as methyl acetate, acetic acid, and ethanol by coupling CO activation and carbonylation. The product selectivity of oxygenates was significantly impacted by the zeolite acidity and the proximity between the two functional components. The present review not only summarizes the major advantages and disadvantages of the relay catalysis in syngas conversion but also offers prospects for future development of relay catalysis in syngas conversion.

A Polyaddition Model for the Prebiotic Polymerization of RNA and RNA-Like Polymers.

Implicit in the RNA world hypothesis is that prebiotic RNA synthesis, despite occurring in an environment without biochemical catalysts, produced the long RNA polymers which are essential to the formation of life. In order to investigate the prebiotic formation of long RNA polymers, we consider a general solution of functionally identical monomer units that are capable of bonding to form linear polymers by a step-growth process. Under the assumptions that (1) the solution is well-mixed and (2) bonding/unbonding rates are independent of polymerization state, the concentration of each length of polymer follows the geometric Flory-Schulz distribution. We consider the rate dynamics that produce this equilibrium; connect the rate dynamics, Gibbs free energy of bond formation, and the bonding probability; solve the dynamics in closed form for the representative special case of a Flory-Schulz initial condition; and demonstrate the effects of imposing a maximum polymer length. Afterwards, we derive a lower bound on the error introduced by truncation and compare this lower bound to the actual error found in our simulation. Finally, we suggest methods to connect these theoretical predictions to experimental results.

Core–Shell Metal Zeolite Composite Catalysts for In Situ Processing of Fischer–Tropsch Hydrocarbons to Gasoline Type Fuels

Fischer–Tropsch synthesis has two main challenges related to direct production of gasoline fuels. First, the chain length distribution of the products follows a broad and unselective Anderson–Schulz–Flory distribution. Second, mostly linear hydrocarbons are formed in the Fischer–Tropsch reaction, thus requiring isomerization while manufacturing gasoline fuels. The present paper addresses a synthetic strategy for the preparation of hierarchical metal and zeolite nanocomposite catalysts for direct synthesis of iso-paraffins from syngas. The nanocomposites are synthesized in three steps. In the first step, the parent (core) zeolite is etched with an ammonium fluoride solution. The etching creates small mesopores inside the zeolite crystals. In the second step, the Ru nanoparticles prepared using water-in-oil microemulsion are deposited in the mesopores of the zeolite. In the third step, a zeolite shell of MFI-type zeolites (silicalite-1 or ZSM-5) is grown on the parent zeolite crystals coating both the etched surface and metallic nanoparticles. Thus, the metal nanoparticles become entirely encapsulated inside the zeolite matrix. Most important parameters such as ruthenium content, zeolite mesoporosity, and more particularly, the acidity of the catalyst shell, which affect the catalytic performance of the synthesized nanocomposite materials in low-temperature Fischer–Tropsch synthesis were identified in this work. The higher relative amount of iso-paraffins was observed on the catalysts containing a shell of ZSM-5. The proximity between metal and acid sites in the zeolite shell of the nanocomposite catalysts is a crucial parameter for the design of efficient metal zeolite bifunctional catalysts for selective synthesis of gasoline-type fuels via Fischer–Tropsch synthesis, while the acidity of the catalyst core has only a limited impact on the catalytic performance.

Design of a core-shell catalyst: an effective strategy for suppressing side reactions in syngas for direct selective conversion to light olefins.

An elegant catalyst is designed via the encapsulation of metallic oxide Zn–Cr inside of zeolite SAPO34 as a core–shell structure (Zn–Cr@SAPO) to realize the coupling of methanol-synthesis and methanol-to-olefin reactions. It can not only break through the limitation of the Anderson–Schulz–Flory distribution but can also overcome the disadvantages of physical mixture catalysts, such as excessive CO2 formation. The confinement effect, hierarchical structure and extremely short distance between the two active components result in the Zn–Cr@SAPO capsule catalyst having better mass transfer and diffusion with a boosted synergistic effect. Due to the difference between the adsorption energies of the Zn–Cr metallic oxide/SAPO zeolite physical mixture and capsule catalysts, the produced water and light olefins are easily removed from the Zn–Cr@SAPO capsule catalyst after formation, suppressing the side reactions. The light olefin space time yield (STY) of the capsule catalyst is more than twice that of the typical physical mixture catalyst. The designed capsule catalyst has superior potential for scale-up in industrial applications while simultaneously extending the capabilities of hybrid catalysts for other tandem catalysis reactions through this strategy.

Role of the activation process on catalytic properties of iron supported catalyst in Fischer-Tropsch synthesis

Monometallic Fe and bimetallic Ru–Fe supported catalysts were prepared by impregnation method and tested in Fischer-Tropsch synthesis (F-T). Their physicochemical properties were characterized by BET, SEM-EDS, FTIR, XRD, H2-TPR, TPD-NH3 techniques. The catalytic activity tests showed that the activation process has a huge impact on the reactivity properties in the studied process. The most active system in F-T reaction was 40%Fe/Al2O3–Cr2O3 catalyst which exhibited CO conversion equal 89.9% and the selectivity towards liquid product of 66.6%. The liquid products obtained in F-T process on 40%Fe/Al2O3–Cr2O3 consisted mainly of linear (76.8%), branched (17.7%) and unsaturated (5.5%) hydrocarbons. The chain growth probability in F-T process was estimated using an Anderson-Schulz–Flory distribution of obtained liquid product for all tested catalysts. The calculated α value for the most active catalyst was 0.76. The activity results indicate that iron carbides formed during activation process affects on the catalytic activity and selectivity of the iron catalyst during F-T synthesis. The activity measurements showed that the activity of the iron supported catalysts depends strongly on the catalyst phase composition and their acidic properties. XRD results confirmed that the most active catalyst in the investigated process exhibited the highest concentration of iron carbides phases on its surface.

Methanol-to-Hydrocarbons Product Distribution over SAPO-34 and ZSM-5 Catalysts: The applicability of Thermodynamic Equilibrium and Anderson-Schulz-Flory Distribution

The product distribution of methanol to hydrocarbons conversion over SAPO-34 and ZSM-5 catalysts was studied using thermodynamic equilibrium and Anderson-Schulz-Flory (ASF) distributions. The equilibrium compositions were calculated using constrained Gibbs free energy minimization. The effect of catalyst type was considered by setting upper limits to product carbon number due to shape selectivity according to zeotype catalyst channel size; that is, n£5 for SAPO-34 but n£6 for aliphatic and n£10 for aromatic compounds over H-ZSM-5 catalyst. The equilibrium selectivity of kinds of paraffin is negligible over SAPO-34 system while that of olefins is very small over H-ZSM-5, both in agreement with experimental results for methanol to olefins and to gasoline, respectively. The methanol to olefins hydrocarbon product distributions over SAPO-34 and H-ZSM-5 showed fair agreements with thermodynamic equilibrium and ASF distributions, respectively. It was found that propylene is the only product the selectivity of which can be maximized among hydrocarbon products over both SAPO-34 and ZSM-5 catalysts, and therefore, it can be an easier target molecule in methanol to hydrocarbon conversions.

Carbon–Silica Composite as an Effective Support for Iron Fischer–Tropsch Synthesis Catalysts

Carbon–silica composite is prepared by the impregnation of silica with aqueous glucose solution followed by drying and calcination in an inert atmosphere. This material is proposed as a support for the potassium‐promoted iron catalysts for Fischer–Tropsch synthesis (FTS). The catalysts are prepared by incipient wetness impregnation. The reducibility of CQ‐supported iron is increased and Hägg carbide is formed in the course of activation in CO/H2 flow at 400 °C for 2 h. Subsequent exposure in FTS conditions results in the significant increase of iron carbide particles, from 3–4 to 20–30 nm, while no such increase is detected for the pure silica as support. The carbon–silica composite support provides a beneficial effect on the catalytic activity of iron in CO hydrogenation as well as the suppression of methane formation and increasing Anderson–Schulz–Flory distribution (ASF) chain growth parameter. The catalysts are characterized by nitrogen adsorption, X‐ray absorption spectroscopy (XPS), transmission electron microscopy (TEM), and in situ magnetic measurements in the course of temperature‐programmed reduction by H2 and synthesis gas.

Synthesis of mixed alcohols with enhanced C3+ alcohol production by CO hydrogenation over potassium promoted molybdenum sulfide

Alcohol mixtures with high C3+ alcohols content can enhance the performance of alcohol mixtures as a blend component in gasoline. Sulfur-resistant potassium promoted molybdenum sulfide (K-MoS2) catalysts enabled synthesizing mixed alcohols through CO hydrogenation. However, the liquid oxygenate selectivity and yield of K-MoS2 catalysts are usually low, and the alcohols follow the Anderson-Schulz-Flory (ASF) distribution, which means methanol and ethanol present the main liquid oxygenates. To achieve high liquid oxygenate selectivity and yield enhancing C3+ alcohol production, we designed multilayer K-MoS2 catalysts possessing a well-contacted MoS2 and KMoS2 phase, respectively. The reduced rim site exposure and the well-contacted MoS2-KMoS2 dual site induced by the multilayer structure enhance the chain growth through CHx β-addition and CO insertion. Accordingly, the observed higher alcohol formation deviates from the ASF distribution. By tailoring the K/Mo ratio, catalysts with varying composition of MoS2 and KMoS2 phases were obtained for suppressing the formation of hydrocarbons and CO2 effectively. An optimized production of liquid oxygenates with enhanced C3+ alcohol production under appropriate reaction temperature became possible. The optimized catalysts have liquid oxygenate selectivity and yield of 29.1–32.7% and 7.9–10.6%, respectively, yet with good stability. C3+ alcohols take up more than 46% (carbon atom fraction) in the liquid oxygenate. The C3+ alcohol yield reaches 3.6–5.1%.

Fischer–Tropsch Synthesis: Analysis of Products by Anderson–Schulz–Flory Distribution Using Promoted Cobalt Catalyst

This work aims to evaluate formed products according to the Anderson-Schulz- Flory (ASF) distribution in Fischer-Tropsch synthesis. The crystalline phases of cerium and cobalt were confirmed in the mesoporous structure of the SBA-15 molecular sieve. The ASF distribution model showed a distribution of products with two chain growth probabilities, α1 and α2 for Co/Ce/SBA-15 catalyst. The maximum production of hydrocarbons was in the range of light olefins, followed by gasoline.

Promoted cobalt metal catalysts suitable for the production of lower olefins from natural gas

Due to the surge of natural gas production, feedstocks for chemicals shift towards lighter hydrocarbons, particularly methane. The success of a Gas-to-Chemicals process via synthesis gas (CO and H2) depends on the ability of catalysts to suppress methane and carbon dioxide formation. We designed a Co/Mn/Na/S catalyst, which gives rise to negligible Water-Gas-Shift activity and a hydrocarbon product spectrum deviating from the Anderson–Schulz–Flory distribution. At 240 °C and 1 bar, it shows a C2-C4 olefins selectivity of 54%. At 10 bar, it displays 30% and 59% selectivities towards lower olefins and fuels, respectively. The spent catalyst consists of 10 nm Co nanoparticles with hcp Co metal phase. We propose a synergistic effect of Na plus S, which act as electronic promoters on the Co surface, thus improving selectivities towards lower olefins and fuels while largely reducing methane and carbon dioxide formation.

The role of intermediate CoxMn1-xO (x = 0.6-0.85) nanocrystals in the formation of active species for the direct production of lower olefins from syngas.

Cobalt-manganese (CoMn) oxides obtained through a one-pot synthesis can be controllably reduced to CoxMn1-xO nanocrystals for the direct production of C2-C4 olefins with high selectivity (50.9 mol%) from syngas at high CO conversion (92.4%), higher than predicted by the Anderson-Schulz-Flory distribution. The formed CoxMn1-xO is the key to generating an active Co2C quadrangular nanoprism phase with (101) and (020) exposed facets in-situ during the reaction, which plays a pivotal role in the high lower-olefin yield. No deactivation was observed after 100 hours under harsh high-conversion reaction conditions, and the activity is one order of magnitude higher than that of the traditional cobalt catalyst.

Equation-Oriented Framework for Optimal Synthesis of Integrated Reactive Distillation Systems for Fischer–Tropsch Processes

To explore reactive distillation (RD) for Fischer–Tropsch synthesis (FTS), we develop a steady-state adiabatic RD model for this system. Here, the calculation of the vapor–liquid equilibrium (VLE) through cubic equation of state is used to describe the phase behavior. Rate expressions for the FT and the water–gas shift reactions are expressed in terms of fugacities and product selectivity of catalysts are based on Anderson–Schulz–Flory distribution and experimental data. Next, a mass, equilibrium, summation, and heat model is extended by considering bypass streams for nonreactive trays and is used to integrate column structure blocks. A step-by-step initialization procedure is proposed to accommodate the complexity of the RD column and the high nonlinearity. This includes case studies of operating variables in a reactive flash model prepared for performance optimization of RD. Finally, a typical low-temperature FT process, which favors diesel production is implemented in the RD model. Comparing the RD for...

Fischer-Tropsch synthesis: Effect of CO conversion on CH4 and oxygenate selectivities over precipitated Fe-K catalysts

The explanation for CH4 selectivity for iron based Fischer-Tropsch catalysts in the low conversion region (i.e., <50%) remains elusive. In this contribution, the CO conversion effect was carefully examined over four K promoted Fe catalysts (100 Fe/5.1Si/2Cu/ x K, where x = 1–5) over a wide range of CO conversion (i.e., 4–85%). Moreover, the effect of CO conversion on oxygenate selectivity of the Fe-K catalysts was carefully studied as well. The change in CH4 selectivity with CO conversion was found to resemble asymmetric “V” shaped curves, with the minimum values occurring at approximately 50% CO conversion. Adding greater than x = 2 K significantly alleviated the CO conversion effect which was attributed to the high K loading greatly decreasing the surface H coverage while improving CO adsorption. The unique CH4 selectivity trend suggests a complicated CH4 formation process that results from different aspects of the catalyst (i.e., chain growth and hydrogenation rates), and process conditions. Oxygenate selectivity was in the range of 0.7–2.8% and varied with the CO conversion and K loading. The addition of K up to x = 3 was found to promote oxygenate formation and chain growth. The overall oxygenate distribution up to C17 follows an Anderson-Schulz Flory (ASF) distribution, with ethanol being the dominant oxygenate. Mechanisms of oxygenate formation different from that of hydrocarbon formation (e.g., CO insertion versus CO dissociation) were proposed to explain the experimental results.