How Much Fuel Does the Fischer Troph Process Produce

Fischer-Tropsch Process

Even today, the FT process produces a broad range of hydrocarbons that are refined to gasoline, jet fuel, and diesel, in contrast to the MTG process that uniquely produces gasoline from methanol.

From: Future Energy (Third Edition) , 2020

Stabilization of intermittent renewable energy using power-to-X

Yu Luo , ... Ningsheng Cai , in Hybrid Systems and Multi-energy Networks for the Future Energy Internet, 2021

5.3.2 Power-to-F-T liquid fuels

Fischer-Tropsch process (F-T) has been industrialized as a mature chemical engineering technology to produce liquid hydrocarbon fuels from syngas. H ₂O/CO₂ co-electrolysis using SOEC can produce syngas with adjustable H₂/CO ratio, revealing a good compatibility with the conventional F-T synthesis.

Becker et al. [5] from Colorado School of Mines, USA carried out a comprehensive analysis on a hybrid system integrating H₂O/CO₂ co-electrolysis and F-T synthesis. Fig. 5.11A and B demonstrates the H₂O/CO₂ co-electrolysis subsystem and F-T synthesis subsystem In the H₂O/CO₂ co-electrolysis subsystem, CO₂ is first fed into a LO-CAT reactor and ZnO bed for removing the sulfur below 1 ppm. Then CO₂ mixes with steam and H₂, and exchanges heat with the outlet gas from the light fuel gas (LFG, C₄₋ hydrocarbons from the F-T synthesis) burner to 800°C. After heating the cathode gas, the outlet gas from the LFG burner further heats the air that has been preheated by the anode outlet gas. Therefore, the inlet gas from both anode and cathode are preheated to 800°C before fed into the SOEC stack. A part of the inlet H₂O feeding to the SOEC cathode comes from the steam produced from F-T synthesis and the water separated from the condenser. The inlet H₂O is preheated by the cathode outlet gas, and the remaining heat containing in the cathode outlet gas is used to generate electricity by using steam Rankine cycle (SRC). After condensation, the produced syngas is compressed to 40 bar and preheated 240°C for the sequent F-T synthesis. After preheating the SOEC subsystem and the produced syngas, the outlet gas from LFG burner can still keep at 781°C. This gas stream is further used to support heat for the sequent F-T synthesis, and then produce electricity through another SRC.

Figure 5.11. System layouts of the SOEC subsystem and F-T synthesis subsystem.

From Ref. [5]. Copyright 2012 Elsevier Ltd.

In the F-T synthesis subsystem, there are two main modules, that is, F-T synthesis reactor and the sequent F-T upgrading module. Becker et al. [5] uses the Anderson-Schulz-Flory (ASF) model to describe the complicated products from the F-T reactor operating at 240°C and 38–40 bar. The main products and their composition from the F-T reactor is shown in Fig. 5.12. The gaseous LFG with shorter carbon chains accounts for 5% in weight, which is mainly used for supplying heat or generating power. The C₅/C₆ hydrocarbons have a mass fraction of 7%, which can be blended into the gasoline after isomerization. Naphtha, denoting the C_7–10 hydrocarbons, accounts for 16% of all the products in weight, which are the major components of the gasoline stock. The middle distillates, the C_11–10 hydrocarbons, account for 34% of all the products in weight, which can be blended with the diesels. As the carbon number rises to higher than 20 (C₂₀₊), the products belong to the wax, accounting for 37% of all the products in weight. The wax can be used to produce gasoline or diesel through the selective catalytic cracking. Typically, the conversion efficiency of the F-T reactor is 60%–90%, which is selected to 80% in Becker's study [5]. In other words, 80% of CO is converted into the hydrocarbon products in the F-T reactor. In the F-T synthesis subsystem, the gasoline and diesel are the target products. Thus, the products from the F-T reactor are further upgraded through naphtha hydrotreating, distillate hydrotreating, wax hydrocracking, C₅/C₆ isomerization, and catalytic reforming. The upgrading products from these processes are summarized in Table 5.1.

Figure 5.12. Products and their composition of F-T synthesis.

From Ref. [5]. Copyright 2012 Elsevier Ltd.

Table 5.1. Product composition in molar fraction [5].

Process	LFG	C5/C6	C7–10	C11–19	Isomerate	Reformate
C5/C6 isomerization	2.0%	0	0	0	98.0%	0
Naphtha hydrotreater	7.9%	14.2%	77.9%	0	0	0
Distillate hydrotreater	2.5%	0	0	97.5%	0	0
Wax hydrotreater	6.0%	5.0%	25.0%	65.0%	0	0
Catalytic reformer	14.2%	0	0	0	0	85.8%

Becker et al. [5] analyzed the system efficiency using their built simulation platform. In the reference condition, the SOEC operates at 800°C and 1.6 bar, and the F-T reactor has a CO conversion of 80%. The SCR efficiency is set to 25%. The whole system (including the H₂O/CO₂ co-electrolysis subsystem and F-T synthesis subsystem) requires an electricity input of 54.5 MW_e, a CO₂ feedstock of 3.88 kg s⁻¹ and a water supply of 181 gpm for generating 6.8 kgal gasoline and 12.7 kgal diesel per day. To evaluate the effectiveness of each part in this system, they defined a series of efficiency. The electricity-to-syngas efficiency represents the ratio of the energy stored in syngas (in higher heat value, HHV) to the total energy inputs to the SOEC subsystem (including the AC power input, energy in the cathode inlet gas and energy in the consumed LPG). The syngas-to-F-T liquids efficiency represents the ratio of the energy stored in the produced gasoline and diesel in HHV to the total energy inputs to the F-T synthesis subsystem (including the AC power input to the F-T subsystem and energy in the inlet syngas in HHV). Overall, the electricity-to-F-T liquids efficiency represents the ratio of the energy stored in the produced gasoline and diesel in HHV to the AC power input (to the whole system). The SOEC subsystem shows an electricity-to-syngas efficiency of 84.5%, the F-T subsystem reveals an syngas-to-F-T liquids efficiency of 49.4%. The whole system reveals the electricity-to-F-T liquids efficiency of 51.0% in lower heat value (LHV) and 54.8% in HHV. Table 5.2 shows these efficiencies at various CO conversion in the F-T reactor. As CO conversion drops to 70%, the syngas-to-F-T liquids efficiency reduces remarkably by 6.4 points of percentage, and the electricity-to-syngas efficiency also decreases by 3.6 points of percentage because of the reduction in the LFG. As a result, the electricity-to-F-T liquids efficiency (HHV) reduces by 4.7 points of percentage. On the contrary, a CO conversion of 90% significantly enhances these efficiency. The syngas-to-F-T liquids efficiency rises by 6.5 points of percentage, the electricity-to-syngas efficiency by 3.2 points of percentage, and the electricity-to-F-T liquids efficiency (HHV) by 4.9 points of percentage.

Table 5.2. System efficiency with CO conversion in the F-T reactor [5].

Efficiency (%)	CO conversion in F-T reactor
	70%	80%	90%
Electricity-to-syngas (HHV)	80.9	84.5	88.7
Syngas-to-F-T liquids (HHV)	43.0	49.4	55.9
Electricity-to-F-T liquids (LHV)	46.6	51.0	55.5
Electricity-to-F-T liquids (HHV)	50.1	54.8	59.7

Fig. 5.13 shows the economics of the PtL system including the cost breakdown and cost sensitivity to the system parameters. The total investment cost for the PtL system is estimated to be 56.07 million dollars. Considering extra buildings and service facilities, the total direct cost needs an extra 12% cost, that is, 6.73 million dollars [5]. When it comes to the liquid fuels cost, the cost breakdown is shown in Fig. 5.13A. The liquid fuels including gasoline and diesel are converted into equivalent gasoline for comparability. The operating capacity factor (OCF) denotes the ratio of the time the PtL system operates at the maximum capacity to the lifetime. The intermittence of renewable power can significantly affect this factor. At a high OCF, the PtL system is utilized better, hence, the ratio of the capital cost to the total liquid fuels cost is much lower than that at a lower OCF. The ratio of the capital cost is only 29% at an OCF of 90%, and increases to 45% at an OCF of 40%. On the contrary, the costs for electricity consumption and CO₂ feedstock play a more important role in the total liquid fuels cost at a higher OCF. The electricity cost accounts for 54% at an OCF of 90%, and this ratio drops to 38% at an OCF of 40%. The costs for operation and maintenance (O&M) accounts for 13% of the total liquid fuels cost. O&M cost slightly drops at lower OCF due to the assumption that the SOEC replacement cost decreases linearly with OCF. The cost for CO₂ feedstock is only 4% of the total liquid fuels cost.

Figure 5.13. (A) Distribution of the liquid fuels cost; (B–D) sensitivity of the liquid fuels cost to electricity price (B,D), operating capacity factor (B,C), SOEC performance (C) and CO conversion in F-T reactor (D).

From Ref. [5]. Copyright 2012 Elsevier Ltd.

The sensitivities of the total liquid fuels cost to the electricity price, OCF, SOEC performance, and CO conversion in F-T reactor are estimated. Fig. 5.13B indicates that the liquid fuels cost can reduce down to $4.4 per gallon gasoline equivalent (GGE) with a low electricity price of $0.02 per kWh and an OCF of 90%, while soars up to $7.35 per GGE with an electricity price of $0.08 per kWh and an OCF of 40%. As the electricity price rises by $0.01 per kWh, the liquid fuels cost increases by ∼$0.64 per GGE, that is, 15%–26%. Fig. 5.13C shows the effect of the SOEC performance on the liquid fuels cost. At a low OCF, the effect of the SOEC performance becomes more significant. As the ASR of the SOEC reduces from 1.5 to 0.25 Ω cm², the total liquid fuels cost reduces from $7.6 by 9% to $6.9 per GGE at OCF = 90%, while from $11.3 by 14% to $9.7 per GGE at OCF = 40%. When the PtL system is powered by a highly intermittent renewable power, a high-performance SOEC stack is more significant for the cost reduction. Fig. 5.13D shows the effect of the CO conversion in the F-T reactor on the total liquid fuels cost. At low electricity price, the syngas can be obtained with a lower cost, hence, the sensitivity of the total liquid fuels cost to the CO conversion in the F-T reactor is relatively low. As the electricity price rises, the cost for the syngas production also increases dramatically. Therefore, CO conversion in the F-T reactor has a more apparent influence on the total cost. At an electricity price of $0.10 per kWh, the liquid fuels cost rises by $1.7 per GGE (17%) to $8.6 per GGE with the CO conversion improving by 20%.

To sum up, it is vital for the economics of the PtL system to operate the PtL at its maximum capacity as much as possible (higher OCF). This is current challenge for the application of the PtL system driven by renewable power. Furthermore, Becker et al. [5] suggested that more incentives should be implemented to make the PtL technology more economically feasible.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128191842000055

Biomass and Biofuel Production

G. Evans , C. Smith , in Comprehensive Renewable Energy, 2012

5.11.4.5.1(i) FT reaction

FT processes convert synthesis gas with a given hydrogen to carbon monoxide ratio into hydrocarbon liquids and waxy solids with water as a coproduct via a stepwise polymerization process. As noted above, the process is carried out in the presence of an iron or cobalt catalyst at moderate temperature (200–350   °C) and pressure (c. 20–50   bar).

The FT chemistry involves a series of complex reactions, which can be summarized as follows:

[2] $\begin{array}{l}\text{Fischer-Tropsch reaction:}\\ n\text{CO}+2n{\text{H}}_2+\text{heat}=n\left({\text{CH}}_2\right)+n{\text{H}}_2\text{O}\end{array}$

The first step of the FT process involves adsorption of carbon monoxide onto the catalyst surface, followed by cleavage of the C–O bond to form carbides and oxides, followed by ligand hydrogenation to form a hydrocarbon with water as a by-product. The sequential addition of carbon, followed by hydrogen to form hydrocarbon groups, allows the nascent hydrocarbon chain to grow. Selective production by the FT process is dependent on the ability of the catalyst to promote chain elongation and to prevent termination reactions.

In addition to the hydrocarbon products, very small quantities of oxygen-containing hydrocarbons and some light gases (methane, ethane, etc.) are formed. The choice of catalyst and operating conditions influences the physical nature of the hydrocarbon product, that is, either a liquid or wax product is formed or some combination of both.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780080878720005151

11th International Symposium on Process Systems Engineering

Li Sun , Robin Smith , in Computer Aided Chemical Engineering, 2012

2.2 FT process tail gas treatment

FT process tail gas contains CO, H₂, C1-C4 light alkanes, and a small amount of heavy alkanes. There are three ways to treat this tail gas.

1)

The tail gas is fully burnt as fuel in gas turbines for power generation or in boilers for very high pressure (VHP) steam generation in the utility plant.

2)

The components CO and H₂ in the tail gas are recovered and recycled to the FT synthesis by separation units. H₂ recovery is carried out by membrane separation, and CO by pressure swing adsorption (PSA) [3]. This recycle can be achieved because there are no components in the tail gas to poison FT catalysis reaction. It is beneficial for FT production profit with the recourse of supplying extra fuel in the utility plant.

3)

The tail gas is fed to the reforming process to regenerate more CO and H₂ from C1- C4 alkanes in the tail gas, and recycle these CO and H₂ to the FT synthesis.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444595065500754

Biojet fuel production pathways

Cheng Tung Chong , Jo-Han Ng , in Biojet Fuel in Aviation Applications, 2021

2.4.1 Fischer–Tropsch

FT process is the process of converting a mixture of carbon monoxide and hydrogen (synthesis gas) into transportation fuels and other liquid products of higher molecular weight hydrocarbons. The process was developed by German researchers Franz Fischer and Hans Tropsch in 1922 as a method for making liquid fuels from coal with alkalized iron chips at 400°C and pressures above 100   bar (Liu et al., 2013). The industrial use of natural gas as FT feedstock is also economically attractive especially in the context of stranded natural gas and shale gas (Eschemann and de Jong, 2015), with minimal contaminants being produced (Luque et al., 2012). Biomass has received considerable attention as potential feedstock for gasification to produce synthesis gas via the FT process to produce hydrocarbon fuels, as shown in the process flow in Fig. 2.9. The FT process can be thought of as a catalytic polymerization of carbon monoxide accompanied by reaction with hydrogen to make the methylene (CH₂) units of paraffins, which comprises two general reactions (Santos and Alencar, 2020),

Figure 2.9. Process flow of converting lignocellulosic biomass into biojet fuel through gasification and Fischer–Tropsch synthesis.

(3.1) $\text{Alkane formation}:n\text{CO}+\left(2n+1\right){\text{H}}_2\leftrightarrow {\text{C}}_n{\text{H}}_{2n+2}+n{\text{H}}_2\text{O}$

(3.2) $\text{Alkene formation}:n\text{CO}+2n{\text{H}}_2\leftrightarrow {\text{C}}_n{\text{H}}_{2n}+n{\text{H}}_2\text{O}$

The product composition from the FT process varies depending on the hydrocarbon to carbon monoxide ratio, catalyst, and process conditions. The FT synthesis generally requires H₂ and CO at a ratio near 2.1:1, depending on the selectivity, and operates at pressure ranging from 20 to 40   bar and 180–250°C. The selectivity of the FT product is also influenced by the catalyst, types of catalyst support, and reactor used (Tijmensen et al., 2002). Additional processing of the raw product of FT synthesis is usually needed to further process into acceptable fuel. Such processes include the cracking the long chains into smaller units before rearranging some of the atoms via isomerization to obtain the desired fuel properties. The upgrading process typically produces liquid hydrocarbon product with a wide boiling range that consists of naphtha, kerosene, and diesel, which are subsequently distilled to obtain the final products. The European aviation industry predicts that approximately 140 kilotons of FT fuel could be produced annually based on the pilot plants planned (Kousoulidou and Lonza, 2016).

The products derived from FT process are usually free from sulfur or nitrogen compounds, which is advantageous from the combustion perspective as no contaminants such as sulfur dioxide or sulfuric acids are produced. FT fuels have been shown to emit 2.4% less CO₂, 50%–90% less PM, and no sulfur compared with fossil jet fuels (Zhang et al., 2016). Besides, the lack of aromatic results in cleaner burning with low level of soot produced. FT fuels were reported to display decreased contrail formation and lesser soot emissions, which decreases the potential of the fuel to act as a cloud condensation nuclei (Jürgens et al., 2019). However, FT fuels with low aromatic content have caused fuel leakage problems in the engine due to shrinkage of elastomer and have lower energy efficiency (Kandaramath Hari et al., 2015; Wei et al., 2019). These issues can be solved by blending the FT fuel with conventional jet fuel to maintain a certain level of aromatics in the jet fuel. The ASTM D7566 standard has specified that a minimum of 8% aromatics have to be maintained in aviation turbine fuel, regardless of any type of synthetic jet fuel used as blend (ASTM D7566-19b, 2019). Other significant drawbacks of the FT process include the high gasification costs and relative higher CO₂ emissions compared with crude oil refining (Marsh, 2008). The chain growth mechanism also produces approximately 25–45   wt% of FT wax, which has a boiling point above 360°C and reduces the cost-effectiveness of the process (Tomasek et al., 2020).

The advantage of the FT process is the versatility of the feedstock that can be used, including coal, natural gas, and biomass. Commercial-scale application of FT products has been shown feasible by Sasol and Shell (Tijmensen et al., 2002). Sasol has produced three types of SPK fuels, namely the Sasol IPK derived from coal, while Sasol GTL-1 and GTL 2 are derived from natural gas. The Sasol GTL-1 is a distillate cut from the GTL fuel produced at the Oryx plant in Qatar, while the Sasol GTL-2 is an upgrade from GTL-1 with reduced paraffinic fraction with wider boiling range. Shell GTL is produced from natural gas in Bintulu, Malaysia, and is used by the US Air Force. The S-8 FT fuel produced by Syntroleum is derived from natural gas and is used by the US Air Force for test flights by blending with JP-8. Comparison of the compositional analysis of the synthetic paraffinic fuels is shown in Table 2.12. The FT SPKs consists primarily of isoparaffins and normal paraffins with a small fraction of cycloparaffins. The S-8 has slightly higher mass fraction of cycloparaffins compared with other SPKs. There is virtually no aromatics in the FT fuels. In spite of the similar carbon-to-hydrogen ratio for all the FT fuels, the distribution of hydrocarbon by carbon number can be quite different, as shown in Fig. 2.10.

Table 2.12. Comparison of the compositional analysis of different FT-SPK (Moses, 2008).

Property	Test method	Limit (ASTM D7566)	Sasol IPK	S-8	Shell GTL	Sasol GTL-1	Sasol GTL-2
Hydrocarbon composition, mass %
Aromatics	D2425	≤0.5	0	0	0	0	0.3
Cycloparaffins	D2425	≤15	2.6	9.0	4.0	2.6	7.7
Iso   +   n-paraffins	D2425	Report	97.4	91.0	96.0	97.4	92.0
Carbon and hydrogen content, mass %
Hydrogen	D5291	–	84.33	83.99	85.00	84.45	84.69
Carbon	D5291	–	15.38	15.58	15.71	15.40	15.50

Figure 2.10. Distribution of hydrocarbons for different SPK fuels (Moses, 2008). SPK, synthesized paraffinic kerosene.

Variation in the hydrocarbon chain length and the ratio of normal paraffins to isoparaffins can be attributed to the processing differences. Sasol IPK has a narrow range of hydrocarbon chain between C8 and C15 consisting of isoparaffins with practically no normal paraffins. Although the Sasol GTL-1 contains similar carbon numbers as Sasol IPK, the majority of the composition is normal paraffins and a small fraction of isoparaffins. The Sasol IPK has about 7–13% of cycloparaffins, but other FT fuels have less than 1% cycloparaffins. The S-8 and Sasol GTL-2 contain a wider range of 8–9 carbon numbers dominated by isoparaffins, but the Sasol GTL-2 contains normal paraffins with longer hydrocarbon chain. The difference in the hydrocarbon groups and chain length leads to the slight variation in physicochemical properties as shown in Table 2.13. The boiling point distribution curve is noticeably different among the fuels. Shell GTL has narrower range of boiling point. The S-8 and Sasol GTL-2 fuels are distilled to have boiling point slopes that are typical of conventional jet fuel, while the rest are relatively flat. The relatively high final boiling point and viscosity for Sasol-2 imply its less volatile characteristic; thus the flash point can be seen to be higher. All the FT fuels have excellent freeze point characteristics and conform to the batch requirement of ASTM D7566. The heat of combustion for all FT fuels are almost similar, but the sooting tendencies are considerably higher for Sasol 1 and Sasol 2. Corporan et al. (2011) reported that the FT-SPK fuels produced by Sasol, Shell, and Rentech possess superior thermal stability and produced less pollutant emissions when fueled in a T63 engine.

Table 2.13. Properties of different FT fuels (Moses, 2008).

Property	Limits ASTM D7566	Sasol IPK	S-8	Shell GTL	Sasol GTL-1	Sasol GTL-2
Total acid number (mg KOH/g)	≤0.015	0.004	0.004	0.003	0.002	0.003
Initial boiling point (°C)	Report	174	144	154.1	144	179
Final boiling point (°C)	≤300	232	275	195.2	208	266
Freezing point (°C)	≤−40	<−65	−51	−53.8	−52.5	−62
Existent gum (mg/100   mL)	≤7	0.6	0.6	4.2	0.9	0.6
Viscosity at −20°C (cSt)	≤8	3.23	4.9	2.49	2.43	6.09
Density @ 15°C, kg/m3	730–770	765	756	736	735	762
Smoke point (mm)	≥25	42	42	>50	29	28
Flash point (°C)	≥38	53	45	43	48	70
Heat of combustion (MJ/kg)	≥42.8	44.0	43.9	44.2	44.3	44.2
Water, mg/kg	≤75	25	22	28	40	32
Sulfur, mg/kg	≤15	0.7	0.6	0.6	0.6	0.6

FT, Fischer–Tropsch.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128228548000032

Biomass

Mariano Martín Martín , in Industrial Chemical Process Analysis and Design, 2016

8.3.2 Hydrocarbon and Alcohol Mixture Separation

FT processes and mixed alcohol synthesis require the use of distillation to separate the products. FT liquid fuels are separated using petrochemical-based technologies (see also chapters: Chemical processes and Syngas chapter: Chemical processes chapter: Syngas ). In the case of mixed alcohols, a sequence of distillation columns is required; see Chapter 2, Chemical processes for the heuristics behind the technique, and Fig. 2.1 for a block flowsheet of the process. The separation of butanol mixtures is more complex due to the inmiscibility between water and ethanol. Recently a hybrid extraction–distillation scheme was proposed that uses mesitylene in an extraction column that processes the fermentation broth. This setup is followed by a sequence of three distillation columns operating at 1, 2, and 0.5   bar, respectively, to separate the solvent, mesitylene, butanol, acetone, and ethanol (Kramer et al., 2011). Ibutene purification is the simplest in the sense that it is a gas produced in the fermentation. Therefore, it exits the reactor together with CO₂ and oxygen. PSA and membrane systems can be used for its purification.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780081010938000227

Cluster Beam Deposition of Functional Nanomaterials and Devices

Avik Halder , Stefan Vajda , in Frontiers of Nanoscience, 2020

1.4.4 Fischer-Tropsch synthesis on small oxidized cobalt clusters

Fischer-Tropsch (FT) process is one of the most applied techniques for gas-to-liquid (GTL) conversion which is based on the catalytic conversion of CO and H₂ to long-chain hydrocarbons. Alumina-supported cobalt nanoparticles are well-known for their high catalytic activity and selectivity in the FT reaction. There has been considerable interest in recent years to understand the effect of particle size and support in order to develop more active FT catalysts. Here we summarize results of in situ investigation of Co_4±1 and Co_27±5 clusters supported on metal oxide (Al₂O₃, MgO) and carbon (ultrananocrystalline diamond, UNCD) supports under low-pressure CO conversion conditions, with focus on the XANES results measured at the Co K-edge [18].

The XANES of as prepared Co cluster samples on different supports (measured under a continuous flow of 30 sccm gas mixture of H₂:CO:He   =   1:0.5:98.5, p_total  =   1.07   bar, p _H2  =   0.01   bar, p_CO  =   0.005   bar) along with the spectra of bulk Co standards are shown in Fig. 1.6A. The comparison of the spectra indicates the presence of a CoO phase in the as made samples. Fig. 1.6B shows in situ XANES results obtained for Co_4±1 clusters supported on alumina. XANES from a set of three samples of Co_27±5 clusters supported on alumina, magnesia, and UNCD are shown in Fig. 1.6C,D and F, respectively, as a function of temperature during reaction. The different extent of changes in the spectra of the individual samples with increasing reaction temperature is illustrated in Fig. 1.6F. It is worth noting, from Fig. 1.6B–E, that the evolution of the spectra of the individual samples are quite distinct, reflecting cluster size as well as support dependency.

Figure 1.6. Fischer-Tropsch Synthesis using Co cluster catalysts.

(A) XANES of the as-made Co_4±1 and Co_27±5 cluster samples collected under vacuum at 25°C. Reference spectra of bulk Co standards (Co, CoO, and Co₃O₄) are also shown for comparison. In situ XANES spectra of (B) Co_4±1/Al₂O₃ and (C) Co_27±5/Al₂O₃, (D) Co_27±5/MgO, and (E) Co_27±5/UNCD with temperature ramp (from bottom to top: 25°C, start, 75°C, 125°C, 175°C, 225°C, and 25°C, after reaction) (F) Summary plot of spectra obtained at 25°C and 225°C. (G) Cospecific activity of Co_4±1/Al₂O₃, Co_27±5/Al₂O₃, Co_27±5/MgO, and Co_27±5/UNCD at 225°C. (H) Selectivity ratio of C1 and C4−8. The reactivity was compared on the basis of C1 (methane) formation rate of Co_4±1. The reactivity of various cluster catalysts were normalized by the number of total deposited Co atoms. (I) Probability of chain growth derived based on ASF distribution model at 225°C as the function of cluster size and supports at 225°C.

Figures reproduced with permission from Lee et al., J. Phys. Chem. C 119 (2015) 11210. Copyright 2015, American Chemical Society.

Fig. 1.6B shows that XANES of Co_4±1/Al₂O₃ recorded at 175°C and 225°C show a significant decrease in white line intensity as well as a slight white line shift to lower energies indicating partial reduction. The changes are quite identical to Co_27±5/Al₂O₃. On the other hand the spectra of the MgO-supported Co_27±5 clusters remain practically unchanged under the applied reaction conditions indicating a stable oxidation state. Co_27±5 clusters, supported on UNCD exhibited the most pronounced shift toward lower energy and the biggest drop in white line intensity during the reaction, thus indicating the highest degree of reduction. The degree of oxidation among the clusters investigated at 225°C can be ranked as Co_27±5/UNCD   <   Co_4±1/Al₂O₃  ∼   Co_27±5/Al₂O₃  <   Co_27±5/MgO.

The mass spectrometer signal of methane from Co₄ was used as a reference (Fig. 1.6F) in comparing catalytic activity and selectivity of the studied catalysts, revealing a significant increase in the catalytic activity for 27 atom Co clusters. Co_27±5/UNCD is the most active and also the most selective toward the formation of longer-chain hydrocarbons as seen from Fig. 1.6G and H. The comparison of the activity and selectivity at 225°C shows that the cumulative activity of the observed products increases in the order Co_4±1/Al₂O₃  <   Co_27±5/Al₂O₃  <   Co_27±5/MgO   <   Co_27±5/UNCD. The selectivity toward longer-chain hydrocarbons is best for Co_27±5/UNCD catalysts, which produce the highest fraction of C4+ hydrocarbons (35%) followed by Co_4±1/Al₂O₃ (20%), Co_27±5/Al₂O₃, and Co_27±5/MgO catalysts (12%). It is important to note that in this study low pressure and short contact time compared to real FT conditions were applied, which results in higher selectivity toward low molecular weight hydrocarbons. Mass fragment pattern analysis based on the Anderson−Schulz−Flory (ASF) [19] distribution model showed that under these conditions the probability of chain growth (α) on subnanometer cobalt clusters was α   =   0.3–0.45 (see Fig. 1.6I), which is lower than those reported for conventional high-pressure FT catalyst (α   =   0.85–0.95) [20].

In situ XANES cobalt clusters deposited on oxide and carbon supports revealed significant differences in the oxidation state of the clusters affected by the size of the clusters and the nature of the support, which could have implications for the use of such cluster-support combinations in a range of reactions as discussed in this case for FT processes.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780081025154000015

Wood Bioenergy

William G. Hubbard , in Bioenergy, 2015

Fischer–Tropsch process

The Fischer–Tropsch process was first demonstrated in Germany in the 1920s. It converts carbon monoxide and hydrogen into oils or fuels that can be substituted for petroleum products. The reaction uses a catalyst based on iron or cobalt and is fueled by the partial oxidation of coal or wood-based fuels such as ethanol, methanol, or syngas, typically coming from an adjacent gasifier. This process can produce "green diesel" or syngas, depending on the temperature and level of oxygen involved in the process (Hubbard et al., 2007).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124079090000043

The Indirect and Direct Conversion of CO2 into Higher Carbon Fuels

Liam J. France , ... Hamid Almegren , in Carbon Dioxide Utilisation, 2015

10.3.2.3 Fischer–Tropsch synthesis and process

The Fischer–Tropsch process now represents a relatively mature technology developed by Franz Fischer and Hans Tropsch in 1926 at the Kaiser Wilhelm Institute for Coal Research. Since its development, different nations, at different times, have turned to its application of synthetic hydrocarbon fuels. ⁵⁴ There are four critical factors dictating the development of such processes ⁵⁵ :

1.

A shift in dominant fuel source from solid (coal) to liquid (gasoline/diesel).

2.

The development of novel processes for the transformation of solid hydrocarbons into liquid hydrocarbons.

3.

Limitations associated with quantity of available petroleum reserves in comparison to the (local) availability of coal.

4.

Energy independence.

Perhaps a fifth factor should now be considered; Environmental Impact. Thus, in contrast to their fossil fuel counterparts, the synthetic fuels produced from such a process contain no sulphur or nitrogen containing compounds. Additionally, syngas produced from CO₂ allows for fuel (primarily diesel and lube oils) to be produced that can be, in effect, carbon-neutral: provided, of course, that any energy input emanates from a truly sustainable energy source. Even without the synthesised fuels being carbon neutral, Fischer–Tropsch is predicted to play a big role in the future of liquid fuels. ⁵⁶

The Fischer–Tropsch process is in actuality, extremely flexible in what it can produce and is strongly dependent upon reaction or process conditions (temperature, pressure, syngas ratio, reactor technology and catalyst deactivation) and invariably upon catalyst choice. Figure 10.6 is an abbreviated form of five primary reactions, which each yield a different product type. ⁵⁷ While the Fischer–Tropsch process results in a broad range of hydrocarbons, it can also be optimised to be selective, given the correct conditions are optimised.

FIGURE 10.6. Routes to different products via the Fischer–Tropsch process.

From the perspective of generating fuel-based hydrocarbons, Fischer–Tropsch may be operated in two distinctly different high and low temperature regimes. High-temperature processes (300–350   °C) using an Fe catalyst can be used to generate gasoline range hydrocarbons (approximately 40   wt%) with low-molecular weight olefins. However, the gasoline tends to be of a low octane value due to the low isomer and aromatic contents. ⁵⁸ As such, secondary reactions such as hydrogenation and isomerisation need to be undertaken on the so-called light cut (C₅–C₆), with more severe processing on the mid-range cut (C₇–C₁₀). ⁵⁹

The low temperature regime is operated between 200 and 240   °C with either Fe or Co catalysts. Under these operation conditions linear waxes are generally produced in large quantities ⁶⁰ and from these diesel-range hydrocarbons can be produced via secondary reactions such as hydrocracking. ⁶¹ Under both of these conditions, the product distribution follows a typical Anderson–Schulz–Flory distribution (Eqn (10.2)):

(10.2) ${\text{W}}_{\text{n}}/\text{n}=\left({(1-\mathrm{\alpha })}^2{\mathrm{\alpha }}^{\text{n}-1}\right)$

Where W_n is the weight fraction of hydrocarbons containing n carbon atoms and α is the chain growth probability (determined by catalyst choice and specific process conditions).

Some deviation may occur from these idealised conditions, but these can be sufficiently accounted for by incorporating correction factors; determined from assumptions of secondary reactions in conjunction with their kinetic information into the equation. ⁶²

In many respects, the reaction mechanism for Fischer–Tropsch can be considered akin to that observed for surface-catalysed polymerisation, where an initiation step occurs, giving rise to active species, followed by propagation step(s) which is, of course, a chain growth mechanism and, finally, termination steps, which determine the maximum hydrocarbon chain length. ⁶³

In the first step, the activation of CO may proceed by two proposed routes for the production of hydrocarbons. The first is the (unassisted) activation of CO that gives rise to CO₂ (Scheme 10.7) and the second is a H₂-assisted method giving rise to H₂O (Scheme 10.8). While both may occur, it has been determined that over an Fe catalyst the assisted mechanism dominates. However, CO₂ is observed as a by-product. Over fine Co metal catalysts, the unassisted mechanism is not competitive enough, leading to activation routes via H₂O generation only. A summary of the potential reaction steps is given for both unassisted and then assisted reaction of CO activation. ⁶⁴

SCHEME 10.7. Fischer–Tropsch initiation step.

Unassisted activation of CO.

SCHEME 10.8. Fischer–Tropsch initiation step.

Hydrogen assisted activation of CO.

From these elementary steps the process subsequently proceeds via insertion of CH₂ monomer units between the metal-alkyl bonds, to generate the higher analogous alkyl group. Subsequent termination steps occur via a number of means. For alkanes the end groups are capped as CH₃ inhibiting further insertion (Scheme 10.9). Additionally, alkenes may be eliminated from the process, but may still react via alkylation- or cyclisation-type reactions to produce secondary products (higher alkanes, alkenes or aromatics). ³⁷

SCHEME 10.9. Fischer–Tropsch propagation and termination steps for alkane and alkene products. ³⁷

However, the above reaction schemes must not be taken as definitive mechanistic schemes. Such Schemes must be used as a generic means of expressing potential initiation routes in conjunction with chain growth. Even now, the actual reaction mechanism is still a subject of much debate, with varying ideas regarding intermediates, such as a number of functional oxygen-containing species, ⁶⁵ in conjunction with a more direct approach as that outlined above.

In broad terms, active catalysts can be characterised by the nature of the products that they produce, in conjunction with their deactivation characteristics. A number of metals possess sufficient activity for consideration in commercial applications, these being Fe, Co, Ni and the noble metal Ru. However, Ni generates an excessive amount of methane in relation to higher carbon products, and Ru is extremely expensive compared to either Fe or Co (50,000 and 50 times more so, respectively), in addition to being significantly less abundant than either. ^37,66,67

While the use of noble metals is well documented, they are primarily used as promoters in an attempt to enhance the activity of the group VIII transition metal. ^68,69 Interestingly, the use of novel catalytic phases has also been explored in the form of Mo₂C, ⁷⁰ which is often described as having a hybridised electron configuration akin to noble metals and possessing some similar catalytic properties to these materials as a result. ⁷¹ Hence it would be of interest to explore the use of bimetallic- or cobalt-supported catalysts doped with molybdenum carbide and compared to those doped with platinum or rhodium. In addition to this, the widespread application of bimetallic carbides will also be of interest.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444627469000104

Feedstock and pathways for alternative aviation fuels

Chenxing Ling , ... Bhupendra Khandelwal , in Aviation Fuels, 2021

5.2 Fischer–Tropsch

The FT process was developed more than a century ago by Germans Franz Fischer and Hans Tropsch. Hydrocarbons are produced from low boiling gases to high-boiling wax [22]. Studies have shown that the FT pathways can have a GHG emission reduction as high as 86%–104% as compared with the fossil fuel pathway counterparts [8]. The feedstocks of FT pathways are dominated by coal, natural gas, and biomass. In general, synthetic paraffinic kerosene (SPK) is generated through gasification and catalytic cracking process. The resultant SPK fuel could be used directly in the jet engine, and no significant problems have been reported in the past few years.

At present, FT fuels derived from coal and natural gas have been used in the commercial flights with 50% blends of conventional jet fuel [26]. Depending on the producer, the basic feedstock for FT process varies (coal for Sasol, natural gas for Shell). However, all processes required to produce synthesis gas must first go through gasification. FT jet fuel produced by Sasol is the first approved Alternative Jet Fuel(s) (AJF) to be used with the blending of Commercial Jet Fuel(s) (CJF). The resultant FT fuel produced by Shell is a narrow-cut kerosene compared with JP8.

As compared with coal and natural gas, biomass has a much shorter history of the development regarding FT processes. The main drawback of using biomass is the cleaning of the syngas and finding sustainable resources. The cost of the biomass also significantly affects the process of large-scale production. It should be noted that approximately 75% of the price of biomass FT fuel is used on the purchase of the feedstock itself. Some scale-up testing has been done, and since 2009, up to 50% blending with petroleum has been used commercially.

In addition, some recent research has indicated the possibility of using coal and biomass as feedstock, sometimes referred to as CBTL. Liquid fuel is generated though the newer and more efficient single-step hydrolysis process. The by-product is a high-purity carbon dioxide, which could be reused and repurposed. The detailed information of this novel pathway is limited as it still needs further development.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128183144000042

Coal gasification processes for synthetic liquid fuel production

J.G. Speight , in Gasification for Synthetic Fuel Production, 2015

9.5.2.1 Fischer-Tropsch process

In the Fischer-Tropsch process, coal is converted to gaseous products at temperatures in excess of 800  °C (1470   °F), and at moderate pressures, to produce synthesis gas.

$\mathrm{C}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{CO}+{\mathrm{H}}_2$

In practice, the FT reaction is generally carried out at temperatures in the range 200-350   °C (390-660   °F) and at pressures of 75-4000   psi; the hydrogen/carbon monoxide ratio is usually at ca. 2.2:1 or 2.5:1. Because up to three volumes of hydrogen may be required to achieve the next stage of the liquids production, the synthesis gas must then be converted by means of the water-gas shift reaction to the desired level of hydrogen after which the gaseous mix is purified (acid gas removal, etc.) and converted to a wide variety of hydrocarbons.

$\mathrm{CO}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{CO}}_2+{\mathrm{H}}_2$

$\mathrm{CO}+\left(2\mathit{n}+1\right){\mathrm{H}}_2\to {\mathrm{C}}_{\mathit{n}}{\mathrm{H}}_{2\mathit{n}+2}+{\mathrm{H}}_2\mathrm{O}$

These reactions result primarily in low- and medium-boiling aliphatic compounds; present commercial objectives are focused on the conditions that result in the production of n-hydrocarbons as well as olefins and oxygenated materials (Speight, 2013a).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780857098023000096

How Much Fuel Does the Fischer Troph Process Produce

Source: https://www.sciencedirect.com/topics/engineering/fischer-tropsch-process

Share this post