Co-Ni/Al2O3catalyst was prepared by the fusion method and used in Fischer-Tropsch synthesis(FTS).The catalysts were characterized by means of nitrogen sorption and scanning electron microscopy.The effect of some react...Co-Ni/Al2O3catalyst was prepared by the fusion method and used in Fischer-Tropsch synthesis(FTS).The catalysts were characterized by means of nitrogen sorption and scanning electron microscopy.The effect of some reaction conditions such as temperature,pressure and H2/CO feed ratio on the catalytic performance of Co-Ni/Al2O3in CO hydrogenation was investigated in a fixed-bed reactor.The results indicate that the optimum reaction conditions are 250℃,0.3 MPa,H2/CO feed ratio of 2.0,and GHSV of 3 000 h-1.Kinetically,the reaction rate was correlated with the Langmuir-Hinshelwood-Hougen-Watson type models.The activation energy for the best fitted model is 88.41 kJ/mol,suggesting that the intra-particle mass transport is not significant.展开更多
Based on formate and direct oxidation mechanisms,three Langmuir-Hinshelwood-Hougen-Watson （LHHW） kinetic models of the water-gasshift （WGS） reaction over a nano-structured iron catalyst under Fischer-Tropsch synth...Based on formate and direct oxidation mechanisms,three Langmuir-Hinshelwood-Hougen-Watson （LHHW） kinetic models of the water-gasshift （WGS） reaction over a nano-structured iron catalyst under Fischer-Tropsch synthesis （FTS） reaction conditions were derived and compared with those over the conventional catalyst.The conventional and nanostructured Fe/Cu/La/Si catalysts were prepared by co-precipitation of Fe and Cu nitrates in aqueous media and water-oil micro-emulsion,respectively.The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons were also made for various rate equations.WGS rate expressions based on the formate mechanism with the assumption that the formation of formate is rate determining step were found to be the best.展开更多
Catalytic co-cracking of Fischer–Tropsch(FT) light distillate and methanol combines highly endothermic olefin cracking reaction with exothermic methanol conversion over ZSM-5 catalyst to produce light olefins through...Catalytic co-cracking of Fischer–Tropsch(FT) light distillate and methanol combines highly endothermic olefin cracking reaction with exothermic methanol conversion over ZSM-5 catalyst to produce light olefins through a nearly thermoneutral process. The kinetic behavior of co-cracking reactions was investigated by different feed conditions: methanol feed only, olefin feed only and co-feed of methanol with olefins or F–T distillate. The results showed that methanol converted to C2–C6 olefins in first-order parallel reaction at low space time, methylation and oligomerization–cracking prevailed for the co-feed of methanol and C2–C5 olefins, while for C6–C8 olefins,monomolecular cracking was the dominant reaction whether fed alone or co-fed with methanol. For FT distillate and methanol co-feed, alkanes were almost un-reactive, C3–C5 olefins were obtained as main products, accounting for 71 wt% for all products. A comprehensive co-cracking reaction scheme was proposed and the model parameters were estimated by the nonlinear least square method. It was verified by experimental data that the kinetic model was reliable to predict major product distribution for co-cracking of FT distillate with methanol and could be used for further reactor development and process design.展开更多
Hydrocarbon production rates and distributions on ruthenium promoted alumina supported cobalt Fischer-Tropsch synthesis （FTS） catalyst were studied by the concept of two superimposed Anderson-Schulz-Flory （ASF） di...Hydrocarbon production rates and distributions on ruthenium promoted alumina supported cobalt Fischer-Tropsch synthesis （FTS） catalyst were studied by the concept of two superimposed Anderson-Schulz-Flory （ASF） distributions.The results indicated that the characterizing growth probabilities α1 and α2 were strongly dependent on reaction conditions.By increasing the H2 /CO partial pressure ratios and reaction temperatures,deviation from normal ASF distribution decreases and the double-α-ASF distribution changes into a straight line.Based on the concept of double-α-ASF distribution,a useful rate equation for the production of hydrocarbons under industrial reaction conditions is obtained.展开更多
The surface species of CO hydrogenation on CeO2-Co/SiO2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H2O...The surface species of CO hydrogenation on CeO2-Co/SiO2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H2O and CO2 was the competitive reaction for the surface oxygen species, CH4 was produced via the hydrogenation of carbon species step by step, and C2 products were formed by the polymerization of surface-active carbon species （-CH2-）. Hydrogen assisted the dissociation of CO. The hydrogenation of surface carbon species was the rate-limiting step in the hydrogenation of CO over CeO2-Co/SiO2 catalyst. The investigation of total pressure, gas hourly space velocity （GHSV）, and product distribution using nitrogen-rich synthesis gas as feedstock over a laboratory scale fixed-bed reactor indicated that total pressure and GHSV had a significant effect on the catalytic performance of CeO2-Co/SiO2 catalyst. The removal of heat and control of the reaction temperature were extremely critical steps, which required lower GHSV and appropriate CO conversion to avoid the deactivation of the catalyst. The feedstock of nitrogen-rich synthesis gas was favorable to increase the conversion of CO, but there was a shift of product distribution toward the light hydrocarbon. The nitrogen-rich synthesis gas was feasible for F-T synthesis for the utilization of remote natural gas.展开更多
Using the highly accurate G4 method, we computed the thermodynamic data of 1287 possible reaction products under a wide range of reaction conditions in the Fischer-Tropcsh synthesis (FTS) process. These accurate therm...Using the highly accurate G4 method, we computed the thermodynamic data of 1287 possible reaction products under a wide range of reaction conditions in the Fischer-Tropcsh synthesis (FTS) process. These accurate thermodynamic data provide basic thermodynamic quantities for the actual chemical engineering process and are useful in analyzing product distribution because FTS demonstrates many features of an equilibrium-controlled system. Our results show that the number of thermodynamically allowed products to increase when lowering temperature, raising pressure, and raising H2/CO ratio. At low temperature, high pressure and high H2/CO ratio, many products are thermodynamically allowed and the selectivity of product has to be controlled by kinetic factors. On the other hand, high selectivity of lighter products can be realized in thermodynamics by raising temperature and lowering pressure. We found that the equilibrium product yield will reach a maximum and remain unchanged when lowering temperature, raising pressure, and raising H2/CO ratio to some limits, implying that optimizing reaction conditions has no effect on equilibrium product yields beyond these limits. The thermodynamic analysis is also useful in designing and evaluating FTS reaction mechanisms. We found that reaction pathways through formaldehyde should be discarded because of its extremely low equilibrium yield. Recently, in the FTS process using metal-oxide-zeolite catalysts for the highly selective production of C2-C4 olefins and aromatic hydrocarbons, there are several guesses on the possible reaction intermediates entering the zeolite channel. Our results show that ketene, methanol, and dimethyl ether are three possible reaction intermediates.展开更多
The effects of Mg,La and Ca promoters on primary and secondary CO2 and H2O formation pathways during Fischer-Tropsch synthesis on precipitated Fe/Cu/SiO2 catalysts are investigated.The chemisorbed oxygen atoms in the ...The effects of Mg,La and Ca promoters on primary and secondary CO2 and H2O formation pathways during Fischer-Tropsch synthesis on precipitated Fe/Cu/SiO2 catalysts are investigated.The chemisorbed oxygen atoms in the primary pathway formed in the CO dissociation steps reacted with co-adsorbed hydrogen or carbon monoxide to produce H2O and CO2,respectively.The secondary pathway was the water-gas shift reaction.The results indicated that the CO2 production led to an increase in both primary and secondary pathways,and H2O production decreased when surface basicity of the catalyst increased in the order Ca 〉 Mg 〉 La.展开更多
文摘Co-Ni/Al2O3catalyst was prepared by the fusion method and used in Fischer-Tropsch synthesis(FTS).The catalysts were characterized by means of nitrogen sorption and scanning electron microscopy.The effect of some reaction conditions such as temperature,pressure and H2/CO feed ratio on the catalytic performance of Co-Ni/Al2O3in CO hydrogenation was investigated in a fixed-bed reactor.The results indicate that the optimum reaction conditions are 250℃,0.3 MPa,H2/CO feed ratio of 2.0,and GHSV of 3 000 h-1.Kinetically,the reaction rate was correlated with the Langmuir-Hinshelwood-Hougen-Watson type models.The activation energy for the best fitted model is 88.41 kJ/mol,suggesting that the intra-particle mass transport is not significant.
文摘Based on formate and direct oxidation mechanisms,three Langmuir-Hinshelwood-Hougen-Watson （LHHW） kinetic models of the water-gasshift （WGS） reaction over a nano-structured iron catalyst under Fischer-Tropsch synthesis （FTS） reaction conditions were derived and compared with those over the conventional catalyst.The conventional and nanostructured Fe/Cu/La/Si catalysts were prepared by co-precipitation of Fe and Cu nitrates in aqueous media and water-oil micro-emulsion,respectively.The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons were also made for various rate equations.WGS rate expressions based on the formate mechanism with the assumption that the formation of formate is rate determining step were found to be the best.
文摘Catalytic co-cracking of Fischer–Tropsch(FT) light distillate and methanol combines highly endothermic olefin cracking reaction with exothermic methanol conversion over ZSM-5 catalyst to produce light olefins through a nearly thermoneutral process. The kinetic behavior of co-cracking reactions was investigated by different feed conditions: methanol feed only, olefin feed only and co-feed of methanol with olefins or F–T distillate. The results showed that methanol converted to C2–C6 olefins in first-order parallel reaction at low space time, methylation and oligomerization–cracking prevailed for the co-feed of methanol and C2–C5 olefins, while for C6–C8 olefins,monomolecular cracking was the dominant reaction whether fed alone or co-fed with methanol. For FT distillate and methanol co-feed, alkanes were almost un-reactive, C3–C5 olefins were obtained as main products, accounting for 71 wt% for all products. A comprehensive co-cracking reaction scheme was proposed and the model parameters were estimated by the nonlinear least square method. It was verified by experimental data that the kinetic model was reliable to predict major product distribution for co-cracking of FT distillate with methanol and could be used for further reactor development and process design.
文摘Hydrocarbon production rates and distributions on ruthenium promoted alumina supported cobalt Fischer-Tropsch synthesis （FTS） catalyst were studied by the concept of two superimposed Anderson-Schulz-Flory （ASF） distributions.The results indicated that the characterizing growth probabilities α1 and α2 were strongly dependent on reaction conditions.By increasing the H2 /CO partial pressure ratios and reaction temperatures,deviation from normal ASF distribution decreases and the double-α-ASF distribution changes into a straight line.Based on the concept of double-α-ASF distribution,a useful rate equation for the production of hydrocarbons under industrial reaction conditions is obtained.
基金the National Key Project for Basic Research of China(973 Project)(No.2005CB221402)the China National Petroleum Corporation.
文摘The surface species of CO hydrogenation on CeO2-Co/SiO2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H2O and CO2 was the competitive reaction for the surface oxygen species, CH4 was produced via the hydrogenation of carbon species step by step, and C2 products were formed by the polymerization of surface-active carbon species （-CH2-）. Hydrogen assisted the dissociation of CO. The hydrogenation of surface carbon species was the rate-limiting step in the hydrogenation of CO over CeO2-Co/SiO2 catalyst. The investigation of total pressure, gas hourly space velocity （GHSV）, and product distribution using nitrogen-rich synthesis gas as feedstock over a laboratory scale fixed-bed reactor indicated that total pressure and GHSV had a significant effect on the catalytic performance of CeO2-Co/SiO2 catalyst. The removal of heat and control of the reaction temperature were extremely critical steps, which required lower GHSV and appropriate CO conversion to avoid the deactivation of the catalyst. The feedstock of nitrogen-rich synthesis gas was favorable to increase the conversion of CO, but there was a shift of product distribution toward the light hydrocarbon. The nitrogen-rich synthesis gas was feasible for F-T synthesis for the utilization of remote natural gas.
基金the National Natural Science Foundation of China (No.91645201, No.21873019 and No.21573044).
文摘Using the highly accurate G4 method, we computed the thermodynamic data of 1287 possible reaction products under a wide range of reaction conditions in the Fischer-Tropcsh synthesis (FTS) process. These accurate thermodynamic data provide basic thermodynamic quantities for the actual chemical engineering process and are useful in analyzing product distribution because FTS demonstrates many features of an equilibrium-controlled system. Our results show that the number of thermodynamically allowed products to increase when lowering temperature, raising pressure, and raising H2/CO ratio. At low temperature, high pressure and high H2/CO ratio, many products are thermodynamically allowed and the selectivity of product has to be controlled by kinetic factors. On the other hand, high selectivity of lighter products can be realized in thermodynamics by raising temperature and lowering pressure. We found that the equilibrium product yield will reach a maximum and remain unchanged when lowering temperature, raising pressure, and raising H2/CO ratio to some limits, implying that optimizing reaction conditions has no effect on equilibrium product yields beyond these limits. The thermodynamic analysis is also useful in designing and evaluating FTS reaction mechanisms. We found that reaction pathways through formaldehyde should be discarded because of its extremely low equilibrium yield. Recently, in the FTS process using metal-oxide-zeolite catalysts for the highly selective production of C2-C4 olefins and aromatic hydrocarbons, there are several guesses on the possible reaction intermediates entering the zeolite channel. Our results show that ketene, methanol, and dimethyl ether are three possible reaction intermediates.
文摘The effects of Mg,La and Ca promoters on primary and secondary CO2 and H2O formation pathways during Fischer-Tropsch synthesis on precipitated Fe/Cu/SiO2 catalysts are investigated.The chemisorbed oxygen atoms in the primary pathway formed in the CO dissociation steps reacted with co-adsorbed hydrogen or carbon monoxide to produce H2O and CO2,respectively.The secondary pathway was the water-gas shift reaction.The results indicated that the CO2 production led to an increase in both primary and secondary pathways,and H2O production decreased when surface basicity of the catalyst increased in the order Ca 〉 Mg 〉 La.
