The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Dragomir B. Bukur - One of the best experts on this subject based on the ideXlab platform.
-
effect of process conditions on the product distribution of fischer tropsch synthesis over a re promoted cobalt alumina catalyst using a stirred tank Slurry Reactor
Journal of Catalysis, 2014Co-Authors: Branislav Todic, Dragomir B. Bukur, Gary Jacobs, Burtron H DavisAbstract:Abstract The effects of process conditions on Fischer–Tropsch synthesis (FTS) product distribution were studied using a 1-L stirred tank Slurry Reactor and a 0.48%Re–25%Co/Al 2 O 3 catalyst. It was found that the chain growth probability of C 1 intermediate ( α 1 ) has the most dominant effect on CH 4 and C 5+ selectivity. α 1 was found to be highly dependent on process conditions. Relatively constant values of C 2+ growth probabilities with Reactor residence time, as well as other process variables, suggest that 1-olefin readsorption has a minor effect on product selectivities. A low value of α 1 and its different response to variations in process conditions, compared to higher chain growth probabilities, seems to support a hypothesis that a higher-than-expected yield of methane is caused by at least two separate methane formation pathways. Understanding these pathways and ways to suppress excess methane formation is a key factor in obtaining higher C 5+ selectivity.
-
kinetic model of fischer tropsch synthesis in a Slurry Reactor on co re al2o3 catalyst
Industrial & Engineering Chemistry Research, 2013Co-Authors: Branislav Todic, Tejas Bhatelia, Gilbert F Froment, Gary Jacobs, Burtron H Davis, Dragomir B. BukurAbstract:A kinetic model for Fischer–Tropsch synthesis is derived using a Langmuir–Hinshelwood–Hougen–Watson approach. Experiments were conducted over 25% Co/0.48% Re/Al2O3 catalyst in a 1 L Slurry Reactor over a range of operating conditions (T = 478, 493, 503 K; P = 1.5, 2.5 MPa; H2/CO = 1.4, 2.1; WHSV = 1.0–22.5 NL/(gcat·h)). Rate equations were based on the elementary reactions corresponding to a form of well-known carbide mechanism. The 1-olefin desorption rate constant was assumed to be a function of carbon number due to the effect of weak interaction of the hydrocarbon chain with the catalyst surface. Values of estimated activation energies are in good agreement with those reported previously in the literature. The kinetic model was able to correctly predict all of the major product distribution characteristics, including the increase in chain growth probability and decrease in olefin-to-paraffin ratio with carbon number, as well as formation rates of methane and ethylene.
-
pretreatment effect studies with a precipitated iron fischer tropsch catalyst in a Slurry Reactor
Applied Catalysis A-general, 1999Co-Authors: Dragomir B. Bukur, Xiaosu Lang, Yunjie DingAbstract:Abstract Effects of pretreatment procedures, using H2, CO, and syngas (H2/CO = 2/3) as reductants, on the performance (activity, selectivity and stability with time) of a precipitated iron catalyst (100 Fe/3 Cu/4 K/16 SiO2 on a mass basis) during Fischer–Tropsch (F–T) synthesis were studied in a stirred tank Slurry Reactor. The catalyst reduced with hydrogen to magnetite only reached its steady state activity faster than the catalyst partially reduced to metallic iron (2 h versus 4 h). Activity of the catalyst partially reduced to metallic iron under mild reduction conditions (250°C for 4 h) was about 40% higher than that of the catalyst reduced at 280°C for 8 h. The steady state activities of the catalyst reduced to magnetite only (240°C for 2 h) and of the unreduced catalyst were the same as that of the catalyst partially reduced to metallic iron at 280°C for 8 h. Initial activity of the CO activated catalyst (280°C for 8 h) was relatively low, and increased with time, reaching a steady state level at about 50 h on stream. However, its steady state activity was the highest among all the pretreatment procedures used. Methane and gaseous hydrocarbon selectivities on the hydrogen reduced and the unreduced catalyst increased with time before reaching a steady state, whereas the opposite trend was observed on the CO and the syngas (280°C for 8 h) activated catalysts. The catalyst which was initially in an oxide form (unreduced catalyst and catalyst reduced to magnetite) had lower gaseous hydrocarbon selectivities than the catalyst partially reduced to α-Fe. The unreduced catalyst had the lowest gaseous hydrocarbon selectivity, whereas the syngas activated catalyst had the highest. Total olefin and 1-olefin contents decreased in the following order: CO activated ≈ unreduced > syngas > H2 reduced.
A.y. Khodakov - One of the best experts on this subject based on the ideXlab platform.
-
Deactivation of a Co/Al2O3 Fischer-Tropsch catalyst by water-induced sintering in Slurry Reactor: Modeling and experimental investigations
Catalysis Today, 2013Co-Authors: Majid Sadeqzadeh, P. Fongarland, D. Schweich, Stephane Chambrey, S Piche, Francis Luck, Jacques Bousquet, D. Curulla-ferre, A.y. KhodakovAbstract:The deactivation of cobalt based catalysts in Slurry Fischer-Tropsch Reactor has been modeled assuming a sintering mechanism which involves the intermediate formation of cobalt oxide layer on metallic nanoparticles. The mechanism, correlating the crystallite size growth to the water to hydrogen concentration ratio in the liquid phase, has been used to describe the activity decline with time on stream. The effect of operating conditions on the rate of sintering is considered. It is found that at the same initial conversion, sintering rate is higher for lower H-2/CO ratios, whereas higher ratios could lead to larger crystallites once operated at constant gas flow rate. The presence of water in the inlet syngas stream also accelerates sintering. The sintering model is then used to describe the deactivation in laboratory-scale Slurry Reactor. (C) 2013 Elsevier B.V. All rights reserved.
-
Influence of syngas composition on the transient behavior of a Fischer–Tropsch continuous Slurry Reactor
Catalysis Today, 2005Co-Authors: P. Fongarland, D. Schweich, J. Anfray, S. Jallais, A.y. Khodakov, M. BremaudAbstract:The influence of syngas composition on the initial behaviour of a Co/Al2O3 catalyst in Fischer–Tropsch reaction has been studied in a continuous perfectly mixed Slurry Reactor for an inlet H2/CO ratio between 1.6 and 3.35 keeping other conditions constant (T = 220 °C, P = 2 MPa). Significantly different behaviors of initial deactivation for CO conversion have been observed with different H2/CO ratios. It was observed that the deactivation increases with increase in H2/CO ratio and in carbon monoxide conversion. The computed liquid concentrations of CO, H2 and H2O have shown that water is the most abundant species in the liquid phase of the Reactor during our experiments. The concentration of the water produced by the FT reaction seems to be the key parameter responsible of the initial behavior and then of the initial deactivation. For moderate levels of water (Click to view the MathML source corresponding to PH2O/PH2
Penchi Chiang - One of the best experts on this subject based on the ideXlab platform.
-
Multiple model approach to evaluation of accelerated carbonation for steelmaking slag in a Slurry Reactor.
Chemosphere, 2016Co-Authors: Shu-yuan Pan, E E Chang, Yi Hung Chen, Hsing Lu Liu, Hyunook Kim, Penchi ChiangAbstract:Basic oxygen furnace slag (BOFS) exhibits highly alkaline properties due to its high calcium content, which is beneficial to carbonation reaction. In this study, accelerated carbonation of BOFS was evaluated under different reaction times, temperatures, and liquid-to-solid (L/S) ratios in a Slurry Reactor. CO2 mass balance within the Slurry Reactor was carried out to validate the technical feasibility of fixing gaseous CO2 into solid precipitates. After that, a multiple model approach, i.e., theoretical kinetics and empirical surface model, for carbonation reaction was presented to determine the maximal carbonation conversion of BOFS in a Slurry Reactor. On one hand, the reaction kinetics of BOFS carbonation was evaluated by the shrinking core model (SCM). Calcite (CaCO3) was identified as a reaction product through the scanning electronic microscopy and X-ray diffraction analyses, which provided the rationale of applying the SCM in this study. The rate-limiting step of carbonation was found to be ash-diffusion controlled, and the effective diffusivity for carbonation of BOFS in a Slurry Reactor were determined accordingly. On the other hand, the carbonation conversion of BOFS was predicted by the response surface methodology (RSM) via a nonlinear mathematical programming. According to the experimental data, the highest carbonation conversion of BOFS achieved was 57% under an L/S ratio of 20 mL g(-1), a CO2 flow rate of 0.1 L min(-1), and a pressure of 101.3 kPa at 50 °C for 120 min. Furthermore, the applications and limitations of SCM and RSM were examined and exemplified by the carbonation of steelmaking slags.
-
carbonation of basic oxygen furnace slag with metalworking wastewater in a Slurry Reactor
International Journal of Greenhouse Gas Control, 2013Co-Authors: E E Chang, An Chia Chiu, Yi Hung Chen, Penchi ChiangAbstract:Abstract CO 2 capture by accelerated carbonation of basic oxygen furnace (BOF) slag in a Slurry Reactor containing metalworking wastewater was investigated in this study. Two types of metalworking wastewater provided by China Steel Corp. (Kaohsiung, Taiwan) were used: cold-rolling wastewater (CRW) and effluent from a metalworking wastewater treatment plant (EW). The effect of operational conditions including the type of metalworking wastewater, reaction time, liquid-to-solid (L/S) ratio, CO 2 flow rate, and Slurry volume on the CO 2 fixation process was evaluated. The results indicated that BOF slag in CRW provided the highest degree of carbonation, 89.4%, with a reaction time of 120 min, an L/S ratio of 20:1, and a CO 2 flow rate of 1 L min −1 at ambient temperature and pressure. In addition, the kinetics of the aqueous carbonation was evaluated using the surface coverage model. This study provided a promising alternative for CO 2 capture from the flue gas in steelmaking process by reusing the metalworking wastewater and steelmaking slag as feedstock, which could reduce the use of water resources as well as the total cost. Compared with other studies in the literature, this study showed a higher carbonation conversion with less consumption of energy and resources.
-
co2 capture by using blended hydraulic slag cement via a Slurry Reactor
Aerosol and Air Quality Research, 2012Co-Authors: E E Chang, Ya Chu Wang, Yi Hung Che, Penchi ChiangAbstract:Mitigation and adaptation are viable strategies for resolving climate change issues which may pose significant challenges to both ecosystems and human populations around the world. Aqueous carbonation is a promising process for mitigating CO2, due to the permanent storage of gaseous CO2 into carbonate precipitations (CaCO3 and/or MgCO3). In this study, aqueous carbonation of blended hydraulic slag cement (BHC) for CO2 sequestration was investigated and evaluated under various operating conditions, i.e., different reaction temperatures and CO2 concentrations, in a Slurry Reactor. The suspension BHC Slurry was strongly alkaline (pH ~11.4) before carbonation, whereas the pH of the Slurry dropped rapidly to nearly a weakly acidic solution (i.e., pH ~6.3) after introducing CO2 gas into the Reactor. The results show that the maximum CO2 capture capacity was 181 g CO2 per kg BHC at a reaction time of 120 min, a CO2 concentration of 10%, and a gas flow rate of 2.5 L/min at 65°C. The reaction temperature slightly influenced the carbonation conversion of BHC, with an increasing temperature resulting in relatively higher conversion. In addition, the SEM and XRD results suggest that the BHC should be carbonated with CO2 to form CaCO3 in a Slurry Reactor. It was thus concluded that the CO2 could be successfully captured by the carbonation of BHC in this manner. Furthermore, the experimental data were utilized to determine the rate-limiting mechanism based on the shrinking-core model (SCM), which was validated by the observations of SEM images. The SCM results indicate that the overall carbonation reaction of BHC in a Slurry Reactor was controlled by the ash-layer diffusion mechanism.
-
Performance evaluation for carbonation of steel-making slags in a Slurry Reactor
Journal of hazardous materials, 2010Co-Authors: E E Chang, Yi Hung Chen, Shu-yuan Pan, Chung Hua Chen, Penchi ChiangAbstract:CO(2) sequestration by the aqueous carbonation of steel-making slag under various operational conditions was investigated in this study. The effects of the operational conditions, including type of steel-making slag, reaction time, reaction temperature, and CO(2) flow rate, on the performance of the carbonation process were evaluated. The results indicated that the BOF slag had the highest carbonation conversion, approximately 72%, at a reaction time of 1h, an operating pressure of 101 kPa and a temperature of 60°C due to its higher BET surface area of BOF slag compared to UF, FA, and BHC slags. The major factors affecting the carbonation conversion are reaction time and temperature. The reaction kinetics of the carbonation conversion can be expressed by the shrinking-core model. The measurements of the carbonated material by the SEM and XRD instruments provide evidence indicating the suitability of using the shrinking-core model in this investigation. Comparison of the results with other studies suggests that aqueous carbonation by Slurry Reactor is viable due to its higher mass transfer rate.
Majid Sadeqzadeh - One of the best experts on this subject based on the ideXlab platform.
-
deactivation of a co al2o3 fischer tropsch catalyst by water induced sintering in Slurry Reactor modeling and experimental investigations
Catalysis Today, 2013Co-Authors: Majid Sadeqzadeh, Stephane Chambrey, S Piche, Pascal Fongarland, Francis Luck, Daniel Curullaferre, Daniel Schweich, Jacques Bousquet, Andrei Y KhodakovAbstract:Abstract The deactivation of cobalt based catalysts in Slurry Fischer–Tropsch Reactor has been modeled assuming a sintering mechanism which involves the intermediate formation of cobalt oxide layer on metallic nanoparticles. The mechanism, correlating the crystallite size growth to the water to hydrogen concentration ratio in the liquid phase, has been used to describe the activity decline with time on stream. The effect of operating conditions on the rate of sintering is considered. It is found that at the same initial conversion, sintering rate is higher for lower H 2 /CO ratios, whereas higher ratios could lead to larger crystallites once operated at constant gas flow rate. The presence of water in the inlet syngas stream also accelerates sintering. The sintering model is then used to describe the deactivation in laboratory-scale Slurry Reactor.
-
Deactivation of a Co/Al2O3 Fischer-Tropsch catalyst by water-induced sintering in Slurry Reactor: Modeling and experimental investigations
Catalysis Today, 2013Co-Authors: Majid Sadeqzadeh, P. Fongarland, D. Schweich, Stephane Chambrey, S Piche, Francis Luck, Jacques Bousquet, D. Curulla-ferre, A.y. KhodakovAbstract:The deactivation of cobalt based catalysts in Slurry Fischer-Tropsch Reactor has been modeled assuming a sintering mechanism which involves the intermediate formation of cobalt oxide layer on metallic nanoparticles. The mechanism, correlating the crystallite size growth to the water to hydrogen concentration ratio in the liquid phase, has been used to describe the activity decline with time on stream. The effect of operating conditions on the rate of sintering is considered. It is found that at the same initial conversion, sintering rate is higher for lower H-2/CO ratios, whereas higher ratios could lead to larger crystallites once operated at constant gas flow rate. The presence of water in the inlet syngas stream also accelerates sintering. The sintering model is then used to describe the deactivation in laboratory-scale Slurry Reactor. (C) 2013 Elsevier B.V. All rights reserved.
Burtron H Davis - One of the best experts on this subject based on the ideXlab platform.
-
effect of process conditions on the product distribution of fischer tropsch synthesis over a re promoted cobalt alumina catalyst using a stirred tank Slurry Reactor
Journal of Catalysis, 2014Co-Authors: Branislav Todic, Dragomir B. Bukur, Gary Jacobs, Burtron H DavisAbstract:Abstract The effects of process conditions on Fischer–Tropsch synthesis (FTS) product distribution were studied using a 1-L stirred tank Slurry Reactor and a 0.48%Re–25%Co/Al 2 O 3 catalyst. It was found that the chain growth probability of C 1 intermediate ( α 1 ) has the most dominant effect on CH 4 and C 5+ selectivity. α 1 was found to be highly dependent on process conditions. Relatively constant values of C 2+ growth probabilities with Reactor residence time, as well as other process variables, suggest that 1-olefin readsorption has a minor effect on product selectivities. A low value of α 1 and its different response to variations in process conditions, compared to higher chain growth probabilities, seems to support a hypothesis that a higher-than-expected yield of methane is caused by at least two separate methane formation pathways. Understanding these pathways and ways to suppress excess methane formation is a key factor in obtaining higher C 5+ selectivity.
-
kinetic model of fischer tropsch synthesis in a Slurry Reactor on co re al2o3 catalyst
Industrial & Engineering Chemistry Research, 2013Co-Authors: Branislav Todic, Tejas Bhatelia, Gilbert F Froment, Gary Jacobs, Burtron H Davis, Dragomir B. BukurAbstract:A kinetic model for Fischer–Tropsch synthesis is derived using a Langmuir–Hinshelwood–Hougen–Watson approach. Experiments were conducted over 25% Co/0.48% Re/Al2O3 catalyst in a 1 L Slurry Reactor over a range of operating conditions (T = 478, 493, 503 K; P = 1.5, 2.5 MPa; H2/CO = 1.4, 2.1; WHSV = 1.0–22.5 NL/(gcat·h)). Rate equations were based on the elementary reactions corresponding to a form of well-known carbide mechanism. The 1-olefin desorption rate constant was assumed to be a function of carbon number due to the effect of weak interaction of the hydrocarbon chain with the catalyst surface. Values of estimated activation energies are in good agreement with those reported previously in the literature. The kinetic model was able to correctly predict all of the major product distribution characteristics, including the increase in chain growth probability and decrease in olefin-to-paraffin ratio with carbon number, as well as formation rates of methane and ethylene.
-
fischer tropsch synthesis over iron based catalysts in a Slurry Reactor reaction rates selectivities and implications for improving hydrocarbon productivity
Catalysis Today, 1997Co-Authors: Ajoy Raje, Burtron H DavisAbstract:Abstract A promoted iron Fischer-Tropsch synthesis catalyst is used in a Slurry Reactor to evaluate and compare the selectivity and yields of total hydrocarbons, light alkenes (C2-C3) and intermediate range (C6-C16) linear-α-alkenes for syngas derived from natural gas and coal. The catalyst has a high hydrocarbon yield of 0.6 g (of hydrocarbon)/h-g Fe at high CO conversions (>85%). The syngas derived from coal produces a slightly higher total hydrocarbon yield than natural gas-derived syngas, due to a lower Reactor partial pressure of water which inhibits the Fischer-Tropsch reaction rate. The natural gas-derived syngas produces a lighter and more paraffinic hydrocarbon product than coal-derived syngas. The selectivity and yields of light alkenes as well as the intermediate range linear-α-alkenes decrease considerably with reaction time and CO conversion for syngas derived from both sources. The yields of these valuable products can be considerably improved by a lower single-pass Reactor CO conversion with recycle of unconverted syngas or by using Reactors in series. The syngas derived from coal produces a slightly lower ethylene and propylene yield, but a higher intermediate-range linear-a-alkene yield than that of natural gas-derived syngas.