The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S),... more The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S), and mechanism of sulfur poisoning Fe catalyst were studied using an iron Fischer-Tropsch synthesis (FTS) catalyst (100 Fe/5.1 Si/2.0 Cu/3.0 K). The FTS reaction was carried out at 230-270 o C, 1.3MPa, H 2 /CO = 0.67-0.77 and 30-70% CO conversion using a 1-L slurry phase reactor. The used Fe catalysts were characterized by XRD, Mössbauer spectroscopy and XANES spectroscopy to understand the deactivation mechanism of the Fe based catalyst after adding up to 1 ppm H 2 S in the feed. Co-feeding of 0.1 ppm H 2 S in syngas for 70 h changed very little the activity of the Fe catalyst, but increasing the H 2 S level to 0.2 ppm or above resulted in measurable deactivation of the Fe catalyst over a similar time period. The limit of sulfur level in the syngas feed (sensitivity) was determined to be 50 ppb. Co-feeding of up to 1.0 ppm H 2 S level was found to increase the extents of the secondary reaction of 1-olefins and the water gas shift (WGS) reaction even though the absolute rates were decreased with time. The addition of H 2 S decreased CH 4 selectivity and increased C 5+ selectivities of the Fe catalyst. The Fe/S ratio, which can be used to define the poison ability of sulfur for the iron catalyst, was quantified based on the deactivation data obtained. The Fe/S ratio strongly depended on temperature and decreased
The current investigation was undertaken to identify limits of hydrohalic acid (HX, X = F, Cl, Br... more The current investigation was undertaken to identify limits of hydrohalic acid (HX, X = F, Cl, Br) impurities in syngas and shed light on the mechanism of HX poisoning of a 100 Fe/5.1 Si/2 Cu/3 K FTS catalyst under industrially relevant conditions using a 1-L slurry-phase reactor. Co-feeding <2.0 ppm of HCl or HBr in syngas for 72−170 h did not significantly deactivate the Fe catalyst. On the other hand, cofeeding 3.0−5.0 ppm of HCl or HBr in syngas for a similar time period resulted in slow deactivation. A higher tolerance, that is, 5−10 ppm, was observed for HF, indicating a weaker poisoning effect. In all cases, rapid deactivation was accompanied by decreases in C 5+ and CO 2 selectivities at higher levels of HX (i.e., 20 ppm and above). Mossbauer spectroscopy and XRD were used to study the Fe phases in the catalyst before and after deactivation induced by each of the HX poisons. Results of Mossbauer spectroscopy suggest that an adsorptive mechanism is responsible for the deactivation of Fe catalysts by HX poisoning. Co-feeding HX neither significantly changed the distribution of iron carbides (χ-Fe 5 C 2 and ε′-Fe 2.2 C) and magnetite nor formed Fe−X compounds. In addition, it was found that Hagg carbide (χ-Fe 5 C 2) converted to ε′-Fe 2.2 C during the startup period or under low temperature FTS conditions. In this study, the poisoning strengths of F − , Cl − , and Br − on the Fe catalyst were also quantified by calculating the loss in surface Fe atoms per halide ion (Fe/X −), with the following trend being observed at 260°C: Fe/Br − (1.0) > Fe/Cl − (0.9) > Fe/F − (0.4). This order remained the same at 270°C, but the Fe/X − ratio decreased slightly, as expected for an adsorptive mechanism.
The kinetic experiments of Fischer-Tropsch synthesis (FTS) over an industrial Fe-Cu-K catalyst ar... more The kinetic experiments of Fischer-Tropsch synthesis (FTS) over an industrial Fe-Cu-K catalyst are carried out in a micro-fixed-bed reactor under the conditions as follows: temperature of 493-542 K, pressure of 10.9-30.9 bar, H 2 /CO feed ratio of 0.98-2.99, and space velocity of 4000-10 000 h 21. The effects of secondary reactions of olefins are investigated by co-feeding C 2 H 4 and C 3 H 6. A detailed kinetics model taking into account the increasingly proven evidence of the olefin re-adsorption mechanism is then proposed. In this model, different sites are assumed for FTS reactions and water gas shift (WGS) reaction, respectively. Rate expressions for FTS reactions are based on the carbide polymerisation mechanism, in which olefin re-adsorption is considered to be a reverse step of olefin desorption reaction. Rate expression for WGS reaction is based on the formate mechanism. An integral reactor model considering both FTS and WGS kinetics is used to describe the reaction system, and the simultaneous estimation of kinetic parameters is conducted with non-linear regression procedure. The optimal model shows that the rate determining steps in FTS reactions proceed via the desorption of hydrocarbon products and the adsorption of CO and the slowest step in WGS reaction is the desorption of gaseous carbon dioxide via formate intermediate species. The activation energies of FTS reactions and WGS reaction are in good agreement with literature values.
Iron Fischer-Tropsch (F-T) catalyst particles break-up during reaction in slurry phase reactors b... more Iron Fischer-Tropsch (F-T) catalyst particles break-up during reaction in slurry phase reactors by physical attrition, and due to chemical stresses caused by phase transformations. Although ''chemical'' attrition is known to be important with iron (Fe) F-T catalysts, there have been no studies of attrition properties of precipitated Fe catalysts under reaction conditions. Here we report on attrition properties of three precipitated Fe catalysts (100 Fe/3-5 Cu/4-6 K/16-25 SiO 2) during F-T synthesis in a stirred tank slurry reactor (STSR). Our results show that after 295-497 h of F-T synthesis with these three catalysts in the STSR, the particle size reduction by fracture was moderate, whereas erosion (generation of particles smaller than 10 lm) was small (2.3-2.7%). The attrition strength of these catalysts is adequate for use in Slurry bubble column reactors (SBCRs) for F-T synthesis.
The chain growth probability of Fischer-Tropsch synthesis (El'S) was investigated on the basis of... more The chain growth probability of Fischer-Tropsch synthesis (El'S) was investigated on the basis of data from a set of experiments over an industrial coprecipitated Fe-Cu-K catalyst developed by the Institute of Coal Chemistry (China). The experimental results show that the ASF chain growth probability (a) depends on operation conditions, temperature (T) and I-!2/CO ratio in the feed. a decreases with T or H2/CO feed ratio increasing. The experimental results also show that chain growth probabilities of hydrocarbons are not constant, but a function of carbon number. This deviation from ASF assumption is further discussed.
Caldwell and van Vuuren (1986) [1] were the first to realize the importance of vapor-liquid equil... more Caldwell and van Vuuren (1986) [1] were the first to realize the importance of vapor-liquid equilibrium (VLE) considerations in the Fischer-Tropsch (FT) synthesis modeling. They used Raoult's law to describe VLE. Recently, a variety of VLE thermodynamic models have been used to model FT products. Thus the aim of this study was to conduct an experiment to measure actual vapor and liquid compositions of long chains hydrocarbons under FT reaction conditions to ascertain whether Raoult's law is sufficient or other elaborate VLE models are required. The results obtained show that VLE is attained inside an FT reactor. The measured vapor and liquid compositions (K-values) can be sufficiently described by Raoult's law. Hydrocarbons with carbon number greater than 18 deviates from Raoult's law. The deviations from Raoult's law are due to diffusion limitations. Elaborate thermodynamic models could be used given the pure component parameters with relevant mixing rules for a higher degree of accuracy.
OBJECTIVES The main objective of this project is to develop improved attrition resistant iron cat... more OBJECTIVES The main objective of this project is to develop improved attrition resistant iron catalysts for converting coal-derived synthesis gas to high quality diesel fuels in slurry reactors. Slurry phase catalysts based on iron tend to break down into fine particles leading to severe operational difficulties in separating the hydrocarbon products from the catalyst. Attrition resistant catalysts will be prepared by spray drying in a bench-scale spray drier unit. Attrition behavior will be studied in a stirred tank reactor (STSR) by determining particle size distribution at the start of the test (TOS = 0) and at the end of the run (EOR). This provides a direct measure of changes in particle size distribution in the STSR during F-T synthesis, and accounts for both physical and chemical effects. The attrition resistance and the catalyst performance during F-T synthesis will be determined simultaneously under conditions representative of industrial practice.
The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a Ni... more The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a NiMo/Al catalyst was studied at 380 °C and 3.5 MPa using octacosane (C28). The catalyst physical structure and acidity were characterized by BET, XRD, SEM-EDX and FTIR techniques. The N2 activation generated more active nonsulfided NiMo/Al catalyst relative to the H2 or H2S activation (XC28, 70–80% versus 6–10%). For a comparison, a NiMo/Si-Al catalyst was also tested after normal H2 activation and showed higher activity at the same process conditions (XC28, 81–99%). The high activity of the NiMo/Al (N2 activation) and NiMo/Si-Al catalysts was mainly ascribed to a higher number of Brønsted acid sites (BAS) on the catalysts. The hydrocracking of cobalt wax using Pt/Si-Al and Pt/Al catalysts confirmed the superior activity of the Si-Al support. A double-peak product distribution occurred at C4–C6 and C10–C16 on all catalysts, which illustrates secondary hydrocracking and faster hydrocracking...
This review emphasizes the importance of the catalytic conversion techniques in the production of... more This review emphasizes the importance of the catalytic conversion techniques in the production of clean liquid and hydrogen fuels (XTF) and chemicals (XTC) from the carbonaceous materials including coal, natural gas, biomass, organic wastes, biogas and CO2. Dependence of the performance of Fischer–Tropsch Synthesis (FTS), a key reaction of the XTF/XTC process, on catalyst structure (crystal and size) is comparatively examined and reviewed. The contribution illustrates the very complicated crystal structure effect, which indicates that not only the particle type, but also the particle shape, facets and orientation that have been evidenced recently, strongly influence the catalyst performance. In addition, the particle size effects over iron, cobalt and ruthenium catalysts were carefully compared and analyzed. For all Fe, Co and Ru catalysts, the metal turnover frequency (TOF) for CO hydrogenation increased with increasing metal particle size in the small size region i.e., less than t...
... Tuesday, April 3, 2012: 8:45 AM. 339B (Hilton of the Americas). Branislav S. Todic 1 , Tejas ... more ... Tuesday, April 3, 2012: 8:45 AM. 339B (Hilton of the Americas). Branislav S. Todic 1 , Tejas J. Bhatelia 1 , Wenping Ma 2 , Gary Jacobs 2 ... Experiments were conducted over 25% Co/0.48%Re/Al 2 O 3 catalyst in 1L stirred tank slurry reactor over a range of operating conditions ( ...
During the Fischer-Tropsch synthesis (FTS) reaction, selectivities of hydrocarbons (HCs) includin... more During the Fischer-Tropsch synthesis (FTS) reaction, selectivities of hydrocarbons (HCs) including CH4, and C5+, 1-olefins and 2-olefins exhibit dependencies on the CO conversion (XCO). In order to compare the selectivities over different catalysts, experiments must be conducted at similar conversion levels [1,2]. A majority of FTS investigations available in the open literature over supported Co catalysts were conducted below or at moderate conversion levels – in the range of 40-55%- and do not provide information about the dependencies between catalyst conversion and selectivity. For instance, there are uncertainties about how CO conversion influences the extent of secondary reaction of olefins at high CO conversion levels. In addition, a complete set of fundamental data relating catalyst selectivities (HCs, CO2), H2/CO usage ratios, and catalyst stability as a function of the CO conversion level over a wide range (10 to 90%) on cobalt-based catalysts is lacking. Recently, Borg et...
... Effect Of Mo Loading And Support Type On Hydrocarbons And Oxygenates Produced Over Fe-Mo-Cu-K... more ... Effect Of Mo Loading And Support Type On Hydrocarbons And Oxygenates Produced Over Fe-Mo-Cu-K Catalysts Supported On Activated Carbons Wenping Ma, Edwin L. Kugler, and Dady B. Dadyburjor Department of Chemical Engineering, West ... [11] EL Kugler, L. Feng, X. Li ...
The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S),... more The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S), and mechanism of sulfur poisoning Fe catalyst were studied using an iron Fischer-Tropsch synthesis (FTS) catalyst (100 Fe/5.1 Si/2.0 Cu/3.0 K). The FTS reaction was carried out at 230-270 o C, 1.3MPa, H 2 /CO = 0.67-0.77 and 30-70% CO conversion using a 1-L slurry phase reactor. The used Fe catalysts were characterized by XRD, Mössbauer spectroscopy and XANES spectroscopy to understand the deactivation mechanism of the Fe based catalyst after adding up to 1 ppm H 2 S in the feed. Co-feeding of 0.1 ppm H 2 S in syngas for 70 h changed very little the activity of the Fe catalyst, but increasing the H 2 S level to 0.2 ppm or above resulted in measurable deactivation of the Fe catalyst over a similar time period. The limit of sulfur level in the syngas feed (sensitivity) was determined to be 50 ppb. Co-feeding of up to 1.0 ppm H 2 S level was found to increase the extents of the secondary reaction of 1-olefins and the water gas shift (WGS) reaction even though the absolute rates were decreased with time. The addition of H 2 S decreased CH 4 selectivity and increased C 5+ selectivities of the Fe catalyst. The Fe/S ratio, which can be used to define the poison ability of sulfur for the iron catalyst, was quantified based on the deactivation data obtained. The Fe/S ratio strongly depended on temperature and decreased
The current investigation was undertaken to identify limits of hydrohalic acid (HX, X = F, Cl, Br... more The current investigation was undertaken to identify limits of hydrohalic acid (HX, X = F, Cl, Br) impurities in syngas and shed light on the mechanism of HX poisoning of a 100 Fe/5.1 Si/2 Cu/3 K FTS catalyst under industrially relevant conditions using a 1-L slurry-phase reactor. Co-feeding <2.0 ppm of HCl or HBr in syngas for 72−170 h did not significantly deactivate the Fe catalyst. On the other hand, cofeeding 3.0−5.0 ppm of HCl or HBr in syngas for a similar time period resulted in slow deactivation. A higher tolerance, that is, 5−10 ppm, was observed for HF, indicating a weaker poisoning effect. In all cases, rapid deactivation was accompanied by decreases in C 5+ and CO 2 selectivities at higher levels of HX (i.e., 20 ppm and above). Mossbauer spectroscopy and XRD were used to study the Fe phases in the catalyst before and after deactivation induced by each of the HX poisons. Results of Mossbauer spectroscopy suggest that an adsorptive mechanism is responsible for the deactivation of Fe catalysts by HX poisoning. Co-feeding HX neither significantly changed the distribution of iron carbides (χ-Fe 5 C 2 and ε′-Fe 2.2 C) and magnetite nor formed Fe−X compounds. In addition, it was found that Hagg carbide (χ-Fe 5 C 2) converted to ε′-Fe 2.2 C during the startup period or under low temperature FTS conditions. In this study, the poisoning strengths of F − , Cl − , and Br − on the Fe catalyst were also quantified by calculating the loss in surface Fe atoms per halide ion (Fe/X −), with the following trend being observed at 260°C: Fe/Br − (1.0) > Fe/Cl − (0.9) > Fe/F − (0.4). This order remained the same at 270°C, but the Fe/X − ratio decreased slightly, as expected for an adsorptive mechanism.
The kinetic experiments of Fischer-Tropsch synthesis (FTS) over an industrial Fe-Cu-K catalyst ar... more The kinetic experiments of Fischer-Tropsch synthesis (FTS) over an industrial Fe-Cu-K catalyst are carried out in a micro-fixed-bed reactor under the conditions as follows: temperature of 493-542 K, pressure of 10.9-30.9 bar, H 2 /CO feed ratio of 0.98-2.99, and space velocity of 4000-10 000 h 21. The effects of secondary reactions of olefins are investigated by co-feeding C 2 H 4 and C 3 H 6. A detailed kinetics model taking into account the increasingly proven evidence of the olefin re-adsorption mechanism is then proposed. In this model, different sites are assumed for FTS reactions and water gas shift (WGS) reaction, respectively. Rate expressions for FTS reactions are based on the carbide polymerisation mechanism, in which olefin re-adsorption is considered to be a reverse step of olefin desorption reaction. Rate expression for WGS reaction is based on the formate mechanism. An integral reactor model considering both FTS and WGS kinetics is used to describe the reaction system, and the simultaneous estimation of kinetic parameters is conducted with non-linear regression procedure. The optimal model shows that the rate determining steps in FTS reactions proceed via the desorption of hydrocarbon products and the adsorption of CO and the slowest step in WGS reaction is the desorption of gaseous carbon dioxide via formate intermediate species. The activation energies of FTS reactions and WGS reaction are in good agreement with literature values.
Iron Fischer-Tropsch (F-T) catalyst particles break-up during reaction in slurry phase reactors b... more Iron Fischer-Tropsch (F-T) catalyst particles break-up during reaction in slurry phase reactors by physical attrition, and due to chemical stresses caused by phase transformations. Although ''chemical'' attrition is known to be important with iron (Fe) F-T catalysts, there have been no studies of attrition properties of precipitated Fe catalysts under reaction conditions. Here we report on attrition properties of three precipitated Fe catalysts (100 Fe/3-5 Cu/4-6 K/16-25 SiO 2) during F-T synthesis in a stirred tank slurry reactor (STSR). Our results show that after 295-497 h of F-T synthesis with these three catalysts in the STSR, the particle size reduction by fracture was moderate, whereas erosion (generation of particles smaller than 10 lm) was small (2.3-2.7%). The attrition strength of these catalysts is adequate for use in Slurry bubble column reactors (SBCRs) for F-T synthesis.
The chain growth probability of Fischer-Tropsch synthesis (El'S) was investigated on the basis of... more The chain growth probability of Fischer-Tropsch synthesis (El'S) was investigated on the basis of data from a set of experiments over an industrial coprecipitated Fe-Cu-K catalyst developed by the Institute of Coal Chemistry (China). The experimental results show that the ASF chain growth probability (a) depends on operation conditions, temperature (T) and I-!2/CO ratio in the feed. a decreases with T or H2/CO feed ratio increasing. The experimental results also show that chain growth probabilities of hydrocarbons are not constant, but a function of carbon number. This deviation from ASF assumption is further discussed.
Caldwell and van Vuuren (1986) [1] were the first to realize the importance of vapor-liquid equil... more Caldwell and van Vuuren (1986) [1] were the first to realize the importance of vapor-liquid equilibrium (VLE) considerations in the Fischer-Tropsch (FT) synthesis modeling. They used Raoult's law to describe VLE. Recently, a variety of VLE thermodynamic models have been used to model FT products. Thus the aim of this study was to conduct an experiment to measure actual vapor and liquid compositions of long chains hydrocarbons under FT reaction conditions to ascertain whether Raoult's law is sufficient or other elaborate VLE models are required. The results obtained show that VLE is attained inside an FT reactor. The measured vapor and liquid compositions (K-values) can be sufficiently described by Raoult's law. Hydrocarbons with carbon number greater than 18 deviates from Raoult's law. The deviations from Raoult's law are due to diffusion limitations. Elaborate thermodynamic models could be used given the pure component parameters with relevant mixing rules for a higher degree of accuracy.
OBJECTIVES The main objective of this project is to develop improved attrition resistant iron cat... more OBJECTIVES The main objective of this project is to develop improved attrition resistant iron catalysts for converting coal-derived synthesis gas to high quality diesel fuels in slurry reactors. Slurry phase catalysts based on iron tend to break down into fine particles leading to severe operational difficulties in separating the hydrocarbon products from the catalyst. Attrition resistant catalysts will be prepared by spray drying in a bench-scale spray drier unit. Attrition behavior will be studied in a stirred tank reactor (STSR) by determining particle size distribution at the start of the test (TOS = 0) and at the end of the run (EOR). This provides a direct measure of changes in particle size distribution in the STSR during F-T synthesis, and accounts for both physical and chemical effects. The attrition resistance and the catalyst performance during F-T synthesis will be determined simultaneously under conditions representative of industrial practice.
The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a Ni... more The effect of activation environment (N2, H2 and H2S/H2) on the hydrocracking performance of a NiMo/Al catalyst was studied at 380 °C and 3.5 MPa using octacosane (C28). The catalyst physical structure and acidity were characterized by BET, XRD, SEM-EDX and FTIR techniques. The N2 activation generated more active nonsulfided NiMo/Al catalyst relative to the H2 or H2S activation (XC28, 70–80% versus 6–10%). For a comparison, a NiMo/Si-Al catalyst was also tested after normal H2 activation and showed higher activity at the same process conditions (XC28, 81–99%). The high activity of the NiMo/Al (N2 activation) and NiMo/Si-Al catalysts was mainly ascribed to a higher number of Brønsted acid sites (BAS) on the catalysts. The hydrocracking of cobalt wax using Pt/Si-Al and Pt/Al catalysts confirmed the superior activity of the Si-Al support. A double-peak product distribution occurred at C4–C6 and C10–C16 on all catalysts, which illustrates secondary hydrocracking and faster hydrocracking...
This review emphasizes the importance of the catalytic conversion techniques in the production of... more This review emphasizes the importance of the catalytic conversion techniques in the production of clean liquid and hydrogen fuels (XTF) and chemicals (XTC) from the carbonaceous materials including coal, natural gas, biomass, organic wastes, biogas and CO2. Dependence of the performance of Fischer–Tropsch Synthesis (FTS), a key reaction of the XTF/XTC process, on catalyst structure (crystal and size) is comparatively examined and reviewed. The contribution illustrates the very complicated crystal structure effect, which indicates that not only the particle type, but also the particle shape, facets and orientation that have been evidenced recently, strongly influence the catalyst performance. In addition, the particle size effects over iron, cobalt and ruthenium catalysts were carefully compared and analyzed. For all Fe, Co and Ru catalysts, the metal turnover frequency (TOF) for CO hydrogenation increased with increasing metal particle size in the small size region i.e., less than t...
... Tuesday, April 3, 2012: 8:45 AM. 339B (Hilton of the Americas). Branislav S. Todic 1 , Tejas ... more ... Tuesday, April 3, 2012: 8:45 AM. 339B (Hilton of the Americas). Branislav S. Todic 1 , Tejas J. Bhatelia 1 , Wenping Ma 2 , Gary Jacobs 2 ... Experiments were conducted over 25% Co/0.48%Re/Al 2 O 3 catalyst in 1L stirred tank slurry reactor over a range of operating conditions ( ...
During the Fischer-Tropsch synthesis (FTS) reaction, selectivities of hydrocarbons (HCs) includin... more During the Fischer-Tropsch synthesis (FTS) reaction, selectivities of hydrocarbons (HCs) including CH4, and C5+, 1-olefins and 2-olefins exhibit dependencies on the CO conversion (XCO). In order to compare the selectivities over different catalysts, experiments must be conducted at similar conversion levels [1,2]. A majority of FTS investigations available in the open literature over supported Co catalysts were conducted below or at moderate conversion levels – in the range of 40-55%- and do not provide information about the dependencies between catalyst conversion and selectivity. For instance, there are uncertainties about how CO conversion influences the extent of secondary reaction of olefins at high CO conversion levels. In addition, a complete set of fundamental data relating catalyst selectivities (HCs, CO2), H2/CO usage ratios, and catalyst stability as a function of the CO conversion level over a wide range (10 to 90%) on cobalt-based catalysts is lacking. Recently, Borg et...
... Effect Of Mo Loading And Support Type On Hydrocarbons And Oxygenates Produced Over Fe-Mo-Cu-K... more ... Effect Of Mo Loading And Support Type On Hydrocarbons And Oxygenates Produced Over Fe-Mo-Cu-K Catalysts Supported On Activated Carbons Wenping Ma, Edwin L. Kugler, and Dady B. Dadyburjor Department of Chemical Engineering, West ... [11] EL Kugler, L. Feng, X. Li ...
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