Simulation of the direct reduction conditions was performed in a laboratory furnace. Lump samples from natural hematite iron ore were reduced by a gas mixture of H2 and CO (H2/CO =1.5) at temperatures of 700°...Simulation of the direct reduction conditions was performed in a laboratory furnace. Lump samples from natural hematite iron ore were reduced by a gas mixture of H2 and CO (H2/CO =1.5) at temperatures of 700°C, 800°C and 900°C. The effect of reduction temperature on the reduction degree, reduction rate of samples and carbon deposition were investigated and discussed in this study. The thermo-gravimetric data obtained from the reduction experiments was run in a programme that calculates the solid conversion rate. Also, three models: 1) Grain Model (GM), 2) Volumetric Model (VM), and 3) the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. It was found that the RPM model result agreed best with the obtained experimental results. Furthermore, it gave better predictions of the natural iron oxide conversion and thereby the reduction kinetics.展开更多
The kinetics of H<sub>2</sub>S removal by zinc oxide desulfurizer was studied through thermogravimetricanalysis.The experimental results show that desulfurization rate was controlled,at high temperatureand...The kinetics of H<sub>2</sub>S removal by zinc oxide desulfurizer was studied through thermogravimetricanalysis.The experimental results show that desulfurization rate was controlled,at high temperatureand low conversion,by the chemical reaction rate,and at low temperature and high conversion by thegrain diffusion rate.The reaction is first order with respect to H<sub>2</sub>S concentration in the differentcontrolled stages.The kinetic behavior can be modeled through the employment of the shrinking coremodel.The values of the model parameters were determined.The variation tendencies with temperatureand concentration of H<sub>2</sub>S at the controlled stages were discussed.展开更多
Reduction of hematite pellets using H2-CO mixtures with a wide range of H2/CO by molar （1：0, 3：1, 1：1, 1：3, and 0：1） at different reducing temperatures （1073, 1173, and 1273 K） was conducted in a program redu...Reduction of hematite pellets using H2-CO mixtures with a wide range of H2/CO by molar （1：0, 3：1, 1：1, 1：3, and 0：1） at different reducing temperatures （1073, 1173, and 1273 K） was conducted in a program reducing furnace. Based on an unreacted core model, the effective diffusion coefficient and reaction rate constant in several cases were determined, and then the rate-control step and transition were analyzed. In the results, the effective diffusion coefficient and reaction rate constant increase with the rise in temperature or hydrogen content. Reduction of iron oxide pellets using an H2-CO mixture is a compound control system; the reaction rate is dominated by chemical reaction at the very beginning, competition during the reduction process subsequently, and internal gas diffusion at the end. At low hydrogen content, increasing temperature takes the transition point of the rate-control step to a high reduction degree, but at high hydrogen content, the effect of temperature on the transition point weakens.展开更多
Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was con...Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.展开更多
The kinetics of asymmetric production of R-（-）-mandelic acid （R-MA） from phenylglyoxylic acid （PGA） catalyzed by Saccharomyces cerevisiae sp. strain FD11b was studied by fed-batch cultures. The concentrations of...The kinetics of asymmetric production of R-（-）-mandelic acid （R-MA） from phenylglyoxylic acid （PGA） catalyzed by Saccharomyces cerevisiae sp. strain FD11b was studied by fed-batch cultures. The concentrations of glucose and PGA were controlled respectively with a dual feeding system. When the electron donor glucose was supplied at the rate of 0.0833mmol·gdw^-1·h^-1, the specific production rate （qp） and the enantiomeric excess of R-MA reached the maximum 0.353mmol·gdw^-1·h^-1 and 97.1%, respectively. The apparent reduction activity of yeast FD 11 b was obviously affected by both substrate PGA and product MA. The qp value reached the maximum 0.36-0.38mmol·gdw^-1·h^-1 when the PGA concentration was controlled between 25 and 35mmol·L^-1. The obvious substrate inhibition of bioconversion was observed at the PGA concentrations higher than 40mmol·L^-1. The accumulation of product MA also caused a severe feed-back inhibition for its production when the product concentration was above 60mmol·L^-1. The kinetic model with the inhibition effect of both substrate and product was simulated by a computer-based least-square arithrnatic. The established kinetic model was in good agreement with the experimental data.展开更多
An experimental study of thermal de-NOx using NH3 as reductant in 02/C02 atmosphere with the effect of S02 and different additives was performed in a drop tube furnace. Results show that the optimum temperature win- d...An experimental study of thermal de-NOx using NH3 as reductant in 02/C02 atmosphere with the effect of S02 and different additives was performed in a drop tube furnace. Results show that the optimum temperature win- dow is 841-1184 ℃, and the optimum reaction temperature is about 900 ℃ with a de-NOx efficiency of 95.4%. A certain amount of S02 has an inhibiting effect on NO reduction. The effect of additives, including Na2C03, C2H5OH and FeCI3, on NO reduction by NH3 is also explored. The addition of Na2CO3 and FeCI3 is useful to widen the tem- perature window and shift the reaction to lower temperature for the efficiency is increased from 30.5% to 74.0% and 67.4% respectively at 800 ℃. Qualitatively, the modeling results using a detailed kinetic modeling mecha- nism represent well most of the process features. The effect of Na2CO3, C2H5OH and FeCI3 addition can be reproduced well by the Na2C03, C2H5OH and Fe（CO）5 sub-mechanism respectively. The reaction mechanism analysis shows that the effects of these additives on NO reduction are achieved mainly by promoting the produc- tion of OH radicals at lower temperature.展开更多
In this letter, we report a quantitative analysis of how a Pt（II） precursor is reduced to atoms at different temperatures for the formation of Pt nanocrystals with different morphologies and sizes. Our results sugge...In this letter, we report a quantitative analysis of how a Pt（II） precursor is reduced to atoms at different temperatures for the formation of Pt nanocrystals with different morphologies and sizes. Our results suggest that in the early stage of a synthesis, the Pt（II） precursor is reduced to atoms exclusively in the solution phase, followed by homogeneous nucleation to generate nuclei and then seeds. At a relatively low reaction temperature such as 22℃, the growth of the seeds is dominated by autocatalytic surface reduction that involves the adsorption and then reduction of the Pt（II） precursor on the surface of the just-formed seeds. This particular growth pathway results in relatively large assemblies of Pt nanocrystals. When the reaction temperature is increased to 100 ℃, the dominant reduction pathway will be switched from surface to solution phase, producing much smaller asselnblies of Pt nanocrystals. Our results also demonstrate that a similar trend applies to the seed-rnediated growth of Pt nanocrystals in the presence of Pd nanocubes.展开更多
Using high temperature carbon tube furnace, reduction of manganese ore pellets containing carbon was investigated. The reaction was divided into two stages at five minutes after reaction, and the kinetics model of red...Using high temperature carbon tube furnace, reduction of manganese ore pellets containing carbon was investigated. The reaction was divided into two stages at five minutes after reaction, and the kinetics model of reduction process was established. The experimental results showed that, the reaction rate in the earlier stage was controlled by the chemical reactions between FeO, MnO and carbon reductant, and the activation energy was 28.85 KJ/mol. In the later stage, as the carbon reductant replaced by CO, the reaction rate was controlled by CO-diffusing in solid products, and the cor- responding activation energy was 86.56 KJ/mol. Reaction rate of the later stage was less than the earlier one.展开更多
In metallurgical processes, more and more usage of hydrocarbons is encouraged to bring down the carbon emissions. In this regard, numerous investigations on reduction of oxides by C-O-H-N gas mixture have been reporte...In metallurgical processes, more and more usage of hydrocarbons is encouraged to bring down the carbon emissions. In this regard, numerous investigations on reduction of oxides by C-O-H-N gas mixture have been reported. Attempts to simulate these reduction processes using shrinking core model, one of the common models used for such studies, have under predicted the reduction rates. This may be owing to the fact that the homogeneous reaction in the gas phase is not being considered. If the reaction temperatures are above 1,000 K, generally so for many reduction processes, the homogeneous gas reaction rates are expected to be high enough that local equilibrium in the gas phase can be assumed. In the present study, reduction of wustite in a C-O-H-N gas mixture has been modeled using shrinking core model considering the water gas shift equilibrium in the gas while it diffuses through the product layer.展开更多
Phosphogypsum(PG) desulfurization slag is a calcium-rich residue from reductive decomposition of PG using sulfur as the reductant. We proposed a technology of preparation light calcium carbonate with PG desulfurizatio...Phosphogypsum(PG) desulfurization slag is a calcium-rich residue from reductive decomposition of PG using sulfur as the reductant. We proposed a technology of preparation light calcium carbonate with PG desulfurization slag, which mainly contains two steps: leaching and carbonizing. In this work, we concentrated on the former, in which ammonium chloride aqueous solution was utilized as leaching agent to extract calcium from the slag, and conducted thermodynamics and kinetics study on it. Fact Sage software was employed to do thermodynamic and phase equilibrium diagram calculations. The influence of leaching conditions including agitation speed, initial concentration of leaching solution, reaction temperature, and liquid/solid ratio on the calcium leaching rate was discussed in detail by means of experiment optimal design. A kinetic model developed from the shrinking core model was given to describe the leaching process. The apparent kinetic activation energy(Ea) of the leaching reaction was calculated to be 10.58 kJ·mol^-1.展开更多
Cold-bonded pellets, to which a new type of inorganic binder was applied, were reduced by H2~CO mixtures with different HJCO molar ratios （1：0, 5：2, 1：1, 2：5, and 0：1） under various temperatures （1023, 1123, 1...Cold-bonded pellets, to which a new type of inorganic binder was applied, were reduced by H2~CO mixtures with different HJCO molar ratios （1：0, 5：2, 1：1, 2：5, and 0：1） under various temperatures （1023, 1123, 1223, 1323, and 1423 K） in a daermogravimetric analysis appaxatus. The effects of gas composition, temperature, and binder ratio on the reduction process were studied, and the microstxucture of re- duced pellets was observed by scanning electron microscopy-energy-dispersive spectrometry （SEM-EDS）. The SEM-EDS images show that binder particles exist in pellets in two forms, and the form that binder particles completely surround ore particles has a more significant hin- der effect on the reduction. The reduction equilibrium constant, effective diffusion coefficient, and the reaction rate constant were calculated on the basis of the unreacted core model, and the promotion effect of temperature on reduction was further analyzed. The results show that no sintering phenomenon occurred at low temperatures and that the increasing reaction rate constant and high gas diffusion coefficient could main- tain the promotion effect of temperature; however, when the sintering phenomenon occurs at high temperatures, gas diffusion is hindered and the promotion effect is diminished. The contribution of the overaJl equilibrium constant to the promotion effect depends on the gas composition.展开更多
The CuO/γ-Al2O3/cordierite catalyst, after being sulfated by sulfur dioxide (SO2) at 673 K, exhibits high activities for selective catalytic reduction (SCR) of nitrogen oxide (NO) with ammonia (NH3) at 573-723 K. The...The CuO/γ-Al2O3/cordierite catalyst, after being sulfated by sulfur dioxide (SO2) at 673 K, exhibits high activities for selective catalytic reduction (SCR) of nitrogen oxide (NO) with ammonia (NH3) at 573-723 K. The intrinsic kinetics of SCR of NO with NH3 over CuO/γ-Al2O3/cordierite catalyst has been measured in a fixed-bed reactor in the absence of internal and external diffusions. The experimental results show that the reaction rate can be quantified by a first-order expression with activation energy Eá of 94.01 kJ·mol-1 and the corresponding p re-exponential factor A′ of 3.39×108 cm3·g-1·s-1 when NH3 is excessive. However, when NH3 is not enough, an E ley-Rideal kinetic model based on experimental data is derived with Ea of 105.79 kJ·mol-1, the corresponding A of 2 .94×109 cm3·g-1·s-1, heat of adsorption-Hads of 87.90 kJ·mol-1 and the corresponding Aads of 9.24 cm3·mol-1. The intrinsic kinetic model obtained was incorporated in a 3D mathematical model of monolithic reactor, and the agreement of the prediction with experimental data indicates that the present kinetic model is adequate for the reac-tor design and engineering scale-up.展开更多
A modern approach to model reduction in chemical kinetics is often based on the notion of slow invariant manifold.The goal of this paper is to give a comparison of various methods of construction of slow invariant man...A modern approach to model reduction in chemical kinetics is often based on the notion of slow invariant manifold.The goal of this paper is to give a comparison of various methods of construction of slow invariant manifolds using a simple Michaelis-Menten catalytic reaction.We explore a recently introduced Method of Invariant Grids(MIG)for iteratively solving the invariance equation.Various initial approximations for the grid are considered such as Quasi Equilibrium Manifold,Spectral Quasi Equilibrium Manifold,Intrinsic Low Dimensional Manifold and Symmetric Entropic Intrinsic Low Dimensional Manifold.Slow invariant manifold was also computed using the Computational Singular Perturbation(CSP)method.A comparison between MIG and CSP is also reported.展开更多
The effect of magnesia on calcium ferrite(CaO.Fe2O3)reduction by CO was examined by isothermal thermogravimetry.Samples of calcium ferrite added with 0,2,4,and 8 wt.%magnesia(abbreviated as CF,CF2M,CF4M,and CF8M)were ...The effect of magnesia on calcium ferrite(CaO.Fe2O3)reduction by CO was examined by isothermal thermogravimetry.Samples of calcium ferrite added with 0,2,4,and 8 wt.%magnesia(abbreviated as CF,CF2M,CF4M,and CF8M)were prepared.Phase composition was analyzed by X-ray diffraction,and the results indicated that CF2M and CF4M are reduced to lower reduction degree and with lower apparent activation energy than CF;and CF8M with more MgO.Fe2O3 is reduced to a lower degree and with more difficulty compared with CF.Reduction rate analysis revealed that CF,CF2M,CF4M,and CF8M reductions are all typical two-step reactions with the order of CF→CWF(CaO.FeO.Fe2O3)→Fe.The apparent reduction activation energies of CF,CF2M,CF4M,and CF8M are 46.89,37.30,17.30,and 29.20 kJ/mol,respectively.Sharp analysis depicted that CF2M,CF4M,and CF8M reductions are all described by 2D Avrami–Erofeev(A–E)equation(A2)in the whole process,while CF reduction is first expressed by A2 and then by 3D A–E equation(A3).Different from shrinking core model,a new kinetic model for powdery samples reduction was proposed to illustrate the relationship among reduction rates,reduction routes,and model functions.展开更多
To solve the technical problems of hot metal desulfurization by injecting magnesium particulate,a new idea of hot metal desulfurization by bottom-blowing magnesium vapor was put forward.The reaction mechanism of hot m...To solve the technical problems of hot metal desulfurization by injecting magnesium particulate,a new idea of hot metal desulfurization by bottom-blowing magnesium vapor was put forward.The reaction mechanism of hot metal desulfurization with magnesium vapor injection was analyzed,and the kinetic model of the desulfurization rate during the process of hot metal desulfurization with magnesium vapor injection was established.The dimensionless equation of the gas–liquid mass transfer coefficient under the injection conditions was obtained by the dimensional analysis method.And the theoretical calculation results were in good agreement with the experimental measurements.The results show that the diameter of the bubbles and the viscosity of the melt significantly affect the desulfurization rate of hot metal injected with magnesium vapor.When the temperature is 1573 K and the gas flow rate is 3 L/min,the desulfurization rate can reach 79%and the utilization rate of magnesium can reach 83%.展开更多
Reduction of complex protein networks models is of great importance.The accuracy of a passivity preserving algorithm (PRIMA) for model order reduction (MOR) is here tested on protein networks,introducing innovative va...Reduction of complex protein networks models is of great importance.The accuracy of a passivity preserving algorithm (PRIMA) for model order reduction (MOR) is here tested on protein networks,introducing innovative variations of the standard PRIMA method to fit the problem at hand.The reduction method does not require to solve the complete system,resulting in a promising tool for studying very large-scale models for which the full solution cannot be computed.The mathematical structure of the considered kinetic equations is preserved.Keeping constant the reduction factor,the approximation error is lower for larger systems.展开更多
Chemical looping reforming of methane is a novel and effective approach to convert methane to syngas,in which oxygen transfer is achieved by a redox material.Although lots of efforts have been made to develop high-per...Chemical looping reforming of methane is a novel and effective approach to convert methane to syngas,in which oxygen transfer is achieved by a redox material.Although lots of efforts have been made to develop high-performance redox materials,a few studies have focused on the redox kinetics.In this work,the kinetics of SrFeO_(3−δ)–CaO∙MnO nanocomposite reduction by methane was investigated both on a thermo-gravimetric analyzer and in a packed-bed microreactor.During the methane reduction,combustion occurs before the partial oxidation and there exists a transition between them.The weight loss due to combustion increases,but the transition region becomes less inconspicuous as the reduction temperature increased.The weight loss associated with the partial oxidation is much larger than that with combustion.The rate of weight loss related to the partial oxidation is well fitted by the Avrami–Erofeyev equation with n=3(A3 model)with an activation energy of 59.8 kJ∙mol^(‒1).The rate law for the partial oxidation includes a solid conversion term whose expression is given by the A3 model and a methane pressure-dependent term represented by a power law.The partial oxidation is half order with respect to methane pressure.The proposed rate law could well predict the reduction kinetics;thus,it may be used to design and/or analyze a chemical looping reforming reactor.展开更多
In the present work,we develop in detail the process leading to reduction of models in chemical kinetics when using the Method of Invariant Grids(MIG).To this end,reduced models(invariant grids)are obtained by refinin...In the present work,we develop in detail the process leading to reduction of models in chemical kinetics when using the Method of Invariant Grids(MIG).To this end,reduced models(invariant grids)are obtained by refining initial approximations of slow invariant manifolds,and used for integrating smaller and less stiff systems of equations capable to recover the detailed description with high accuracy.Moreover,we clarify the role played by thermodynamics in model reduction,and carry out a comparison between detailed and reduced solutions for a model hydrogen oxidation reaction.展开更多
Kinetics of hot metal desulfurization were studied using CaO-SiO2-Al2O3-Na2O-TiO2 slag in the range of 1400-1500℃on a laboratory scale.The results of kinetic experiments indicate that the desulfurization rate increas...Kinetics of hot metal desulfurization were studied using CaO-SiO2-Al2O3-Na2O-TiO2 slag in the range of 1400-1500℃on a laboratory scale.The results of kinetic experiments indicate that the desulfurization rate increases as the temperature,Al2O3 content,Na2O content,and TiO2 content increase and basicity increases from 1.01 to 1.75,but decreases when basicity increases from 1.75 to 2.02.The melting effect of slag is promoted as the temperature,Na2O content,and TiO2 content increase and Al2O3 content increases from 12.13 to 17.17 mass%,but worsened as basicity increases and Al2O3 content increases from 17.17 to 22.27 mass%.A kinetic model of hot metal desulfurization has been developed to calculate the mass transfer coefficient and the mass transfer resistance of sulfur in slag.The mass transfer coefficient of sulfur increases as the temperature,Al2O3 content,Na2O content,and TiO2 content increase and basicity decreases.Total mass transfer coefficients of sulfur were in the range of(5.02-23.78)×10^-7 m s^-1.The activation energy was estimated to be 464.06 kJ mo1^-1 at the temperature from 1400 to 1450℃and 176.35 kJ mol-1 at the temperature from 1450 to 1500℃.The sulfur distribution at the slag-metal interface was observed using a mineral liberation analyzer.The result shows that the mass transfer of sulfur in slag is the controlling step at high temperature during the desulfurization process.展开更多
The kinetics of isothermal reduction of Ag2O with graphite under argon atmosphere for a non-activated sample and mechanically activated sample was investigated.It is found that Johnson-Mehl-Avrami model appropriately ...The kinetics of isothermal reduction of Ag2O with graphite under argon atmosphere for a non-activated sample and mechanically activated sample was investigated.It is found that Johnson-Mehl-Avrami model appropriately explained the thermal and mechanochemical synthesis of Ag from Ag2O＋ghraphite mixture.The process kinetics was investigated using the same approach for milled and unmilled samples.The results show that the Avrami exponent of mechanochemical reduction is higher than that of high temperature thermal reduction.Also,the mechanisms of nuclei growth in thermal and mechanochemical reduction are diffusion controlled and interface controlled,respectively.展开更多
文摘Simulation of the direct reduction conditions was performed in a laboratory furnace. Lump samples from natural hematite iron ore were reduced by a gas mixture of H2 and CO (H2/CO =1.5) at temperatures of 700°C, 800°C and 900°C. The effect of reduction temperature on the reduction degree, reduction rate of samples and carbon deposition were investigated and discussed in this study. The thermo-gravimetric data obtained from the reduction experiments was run in a programme that calculates the solid conversion rate. Also, three models: 1) Grain Model (GM), 2) Volumetric Model (VM), and 3) the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. It was found that the RPM model result agreed best with the obtained experimental results. Furthermore, it gave better predictions of the natural iron oxide conversion and thereby the reduction kinetics.
基金Supported by the National Natural Science Foundation of China.
文摘The kinetics of H<sub>2</sub>S removal by zinc oxide desulfurizer was studied through thermogravimetricanalysis.The experimental results show that desulfurization rate was controlled,at high temperatureand low conversion,by the chemical reaction rate,and at low temperature and high conversion by thegrain diffusion rate.The reaction is first order with respect to H<sub>2</sub>S concentration in the differentcontrolled stages.The kinetic behavior can be modeled through the employment of the shrinking coremodel.The values of the model parameters were determined.The variation tendencies with temperatureand concentration of H<sub>2</sub>S at the controlled stages were discussed.
基金financially supported by the National Natural Science Foundation of China (Nos. 51104014 and 51134008)
文摘Reduction of hematite pellets using H2-CO mixtures with a wide range of H2/CO by molar （1：0, 3：1, 1：1, 1：3, and 0：1） at different reducing temperatures （1073, 1173, and 1273 K） was conducted in a program reducing furnace. Based on an unreacted core model, the effective diffusion coefficient and reaction rate constant in several cases were determined, and then the rate-control step and transition were analyzed. In the results, the effective diffusion coefficient and reaction rate constant increase with the rise in temperature or hydrogen content. Reduction of iron oxide pellets using an H2-CO mixture is a compound control system; the reaction rate is dominated by chemical reaction at the very beginning, competition during the reduction process subsequently, and internal gas diffusion at the end. At low hydrogen content, increasing temperature takes the transition point of the rate-control step to a high reduction degree, but at high hydrogen content, the effect of temperature on the transition point weakens.
基金financially supported by the National Basic Research Program of China (No. 2012CB720401)the National Key Technology Research and Development Program of China (No. 2011BAC01B02)
文摘Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.
基金Supported by the Natural Science Foundation of Fujian Province (No.E0310019) and Key Project of Science and Technology of Fujian Province (No.2003H023).
文摘The kinetics of asymmetric production of R-（-）-mandelic acid （R-MA） from phenylglyoxylic acid （PGA） catalyzed by Saccharomyces cerevisiae sp. strain FD11b was studied by fed-batch cultures. The concentrations of glucose and PGA were controlled respectively with a dual feeding system. When the electron donor glucose was supplied at the rate of 0.0833mmol·gdw^-1·h^-1, the specific production rate （qp） and the enantiomeric excess of R-MA reached the maximum 0.353mmol·gdw^-1·h^-1 and 97.1%, respectively. The apparent reduction activity of yeast FD 11 b was obviously affected by both substrate PGA and product MA. The qp value reached the maximum 0.36-0.38mmol·gdw^-1·h^-1 when the PGA concentration was controlled between 25 and 35mmol·L^-1. The obvious substrate inhibition of bioconversion was observed at the PGA concentrations higher than 40mmol·L^-1. The accumulation of product MA also caused a severe feed-back inhibition for its production when the product concentration was above 60mmol·L^-1. The kinetic model with the inhibition effect of both substrate and product was simulated by a computer-based least-square arithrnatic. The established kinetic model was in good agreement with the experimental data.
基金Supported by the National Natural Science Foundation of China(51206096)
文摘An experimental study of thermal de-NOx using NH3 as reductant in 02/C02 atmosphere with the effect of S02 and different additives was performed in a drop tube furnace. Results show that the optimum temperature win- dow is 841-1184 ℃, and the optimum reaction temperature is about 900 ℃ with a de-NOx efficiency of 95.4%. A certain amount of S02 has an inhibiting effect on NO reduction. The effect of additives, including Na2C03, C2H5OH and FeCI3, on NO reduction by NH3 is also explored. The addition of Na2CO3 and FeCI3 is useful to widen the tem- perature window and shift the reaction to lower temperature for the efficiency is increased from 30.5% to 74.0% and 67.4% respectively at 800 ℃. Qualitatively, the modeling results using a detailed kinetic modeling mecha- nism represent well most of the process features. The effect of Na2CO3, C2H5OH and FeCI3 addition can be reproduced well by the Na2C03, C2H5OH and Fe（CO）5 sub-mechanism respectively. The reaction mechanism analysis shows that the effects of these additives on NO reduction are achieved mainly by promoting the produc- tion of OH radicals at lower temperature.
基金supported in part by a grant from National Science Foundation of the United States(DMR-1505441)startup funds from the Georgia Institute of Technology
文摘In this letter, we report a quantitative analysis of how a Pt（II） precursor is reduced to atoms at different temperatures for the formation of Pt nanocrystals with different morphologies and sizes. Our results suggest that in the early stage of a synthesis, the Pt（II） precursor is reduced to atoms exclusively in the solution phase, followed by homogeneous nucleation to generate nuclei and then seeds. At a relatively low reaction temperature such as 22℃, the growth of the seeds is dominated by autocatalytic surface reduction that involves the adsorption and then reduction of the Pt（II） precursor on the surface of the just-formed seeds. This particular growth pathway results in relatively large assemblies of Pt nanocrystals. When the reaction temperature is increased to 100 ℃, the dominant reduction pathway will be switched from surface to solution phase, producing much smaller asselnblies of Pt nanocrystals. Our results also demonstrate that a similar trend applies to the seed-rnediated growth of Pt nanocrystals in the presence of Pd nanocubes.
文摘Using high temperature carbon tube furnace, reduction of manganese ore pellets containing carbon was investigated. The reaction was divided into two stages at five minutes after reaction, and the kinetics model of reduction process was established. The experimental results showed that, the reaction rate in the earlier stage was controlled by the chemical reactions between FeO, MnO and carbon reductant, and the activation energy was 28.85 KJ/mol. In the later stage, as the carbon reductant replaced by CO, the reaction rate was controlled by CO-diffusing in solid products, and the cor- responding activation energy was 86.56 KJ/mol. Reaction rate of the later stage was less than the earlier one.
文摘In metallurgical processes, more and more usage of hydrocarbons is encouraged to bring down the carbon emissions. In this regard, numerous investigations on reduction of oxides by C-O-H-N gas mixture have been reported. Attempts to simulate these reduction processes using shrinking core model, one of the common models used for such studies, have under predicted the reduction rates. This may be owing to the fact that the homogeneous reaction in the gas phase is not being considered. If the reaction temperatures are above 1,000 K, generally so for many reduction processes, the homogeneous gas reaction rates are expected to be high enough that local equilibrium in the gas phase can be assumed. In the present study, reduction of wustite in a C-O-H-N gas mixture has been modeled using shrinking core model considering the water gas shift equilibrium in the gas while it diffuses through the product layer.
基金Supported by Young Teachers Scientific Research Foundation Project of Sichuan University(2014SCU11020)National Key Research Project(2017YFB0307504)Sichuan Science and Technology Planning Project(2019YFH0149).
文摘Phosphogypsum(PG) desulfurization slag is a calcium-rich residue from reductive decomposition of PG using sulfur as the reductant. We proposed a technology of preparation light calcium carbonate with PG desulfurization slag, which mainly contains two steps: leaching and carbonizing. In this work, we concentrated on the former, in which ammonium chloride aqueous solution was utilized as leaching agent to extract calcium from the slag, and conducted thermodynamics and kinetics study on it. Fact Sage software was employed to do thermodynamic and phase equilibrium diagram calculations. The influence of leaching conditions including agitation speed, initial concentration of leaching solution, reaction temperature, and liquid/solid ratio on the calcium leaching rate was discussed in detail by means of experiment optimal design. A kinetic model developed from the shrinking core model was given to describe the leaching process. The apparent kinetic activation energy(Ea) of the leaching reaction was calculated to be 10.58 kJ·mol^-1.
基金financially supported by the National Key Research and Development Program of China(2017YFB0304300 and 2017YFB0304302)the 111 Project(No.B13004)
文摘Cold-bonded pellets, to which a new type of inorganic binder was applied, were reduced by H2~CO mixtures with different HJCO molar ratios （1：0, 5：2, 1：1, 2：5, and 0：1） under various temperatures （1023, 1123, 1223, 1323, and 1423 K） in a daermogravimetric analysis appaxatus. The effects of gas composition, temperature, and binder ratio on the reduction process were studied, and the microstxucture of re- duced pellets was observed by scanning electron microscopy-energy-dispersive spectrometry （SEM-EDS）. The SEM-EDS images show that binder particles exist in pellets in two forms, and the form that binder particles completely surround ore particles has a more significant hin- der effect on the reduction. The reduction equilibrium constant, effective diffusion coefficient, and the reaction rate constant were calculated on the basis of the unreacted core model, and the promotion effect of temperature on reduction was further analyzed. The results show that no sintering phenomenon occurred at low temperatures and that the increasing reaction rate constant and high gas diffusion coefficient could main- tain the promotion effect of temperature; however, when the sintering phenomenon occurs at high temperatures, gas diffusion is hindered and the promotion effect is diminished. The contribution of the overaJl equilibrium constant to the promotion effect depends on the gas composition.
基金Supported by the National Natural Science Foundation of China （20821004 20736001 21076008） the Research Fund for the Doctoral Program of Higher Education of China （2090010110002）
文摘The CuO/γ-Al2O3/cordierite catalyst, after being sulfated by sulfur dioxide (SO2) at 673 K, exhibits high activities for selective catalytic reduction (SCR) of nitrogen oxide (NO) with ammonia (NH3) at 573-723 K. The intrinsic kinetics of SCR of NO with NH3 over CuO/γ-Al2O3/cordierite catalyst has been measured in a fixed-bed reactor in the absence of internal and external diffusions. The experimental results show that the reaction rate can be quantified by a first-order expression with activation energy Eá of 94.01 kJ·mol-1 and the corresponding p re-exponential factor A′ of 3.39×108 cm3·g-1·s-1 when NH3 is excessive. However, when NH3 is not enough, an E ley-Rideal kinetic model based on experimental data is derived with Ea of 105.79 kJ·mol-1, the corresponding A of 2 .94×109 cm3·g-1·s-1, heat of adsorption-Hads of 87.90 kJ·mol-1 and the corresponding Aads of 9.24 cm3·mol-1. The intrinsic kinetic model obtained was incorporated in a 3D mathematical model of monolithic reactor, and the agreement of the prediction with experimental data indicates that the present kinetic model is adequate for the reac-tor design and engineering scale-up.
基金supported by SNF,Project 200021-107885/1(E.C.)and by BFE,Project 100862(I.V.K.)。
文摘A modern approach to model reduction in chemical kinetics is often based on the notion of slow invariant manifold.The goal of this paper is to give a comparison of various methods of construction of slow invariant manifolds using a simple Michaelis-Menten catalytic reaction.We explore a recently introduced Method of Invariant Grids(MIG)for iteratively solving the invariance equation.Various initial approximations for the grid are considered such as Quasi Equilibrium Manifold,Spectral Quasi Equilibrium Manifold,Intrinsic Low Dimensional Manifold and Symmetric Entropic Intrinsic Low Dimensional Manifold.Slow invariant manifold was also computed using the Computational Singular Perturbation(CSP)method.A comparison between MIG and CSP is also reported.
基金the financial support of the National Natural Science Foundation of China(51234010 and 51522403)the Program for New Century Excellent Talents in University and the Program for the Youth Top-Notch Talents of Chongqing(20151001)Ultrasonic Assisted Iron Ore Sintering Technology Research(cstc2014kjrc-qnrc90001),and China Scholarship Council.
文摘The effect of magnesia on calcium ferrite(CaO.Fe2O3)reduction by CO was examined by isothermal thermogravimetry.Samples of calcium ferrite added with 0,2,4,and 8 wt.%magnesia(abbreviated as CF,CF2M,CF4M,and CF8M)were prepared.Phase composition was analyzed by X-ray diffraction,and the results indicated that CF2M and CF4M are reduced to lower reduction degree and with lower apparent activation energy than CF;and CF8M with more MgO.Fe2O3 is reduced to a lower degree and with more difficulty compared with CF.Reduction rate analysis revealed that CF,CF2M,CF4M,and CF8M reductions are all typical two-step reactions with the order of CF→CWF(CaO.FeO.Fe2O3)→Fe.The apparent reduction activation energies of CF,CF2M,CF4M,and CF8M are 46.89,37.30,17.30,and 29.20 kJ/mol,respectively.Sharp analysis depicted that CF2M,CF4M,and CF8M reductions are all described by 2D Avrami–Erofeev(A–E)equation(A2)in the whole process,while CF reduction is first expressed by A2 and then by 3D A–E equation(A3).Different from shrinking core model,a new kinetic model for powdery samples reduction was proposed to illustrate the relationship among reduction rates,reduction routes,and model functions.
基金This research was supported by the National Natural Science Foundation of China(U1702253,51774078)the Fundamental Research Funds for the Central Universities(N172506009.N170908001).
文摘To solve the technical problems of hot metal desulfurization by injecting magnesium particulate,a new idea of hot metal desulfurization by bottom-blowing magnesium vapor was put forward.The reaction mechanism of hot metal desulfurization with magnesium vapor injection was analyzed,and the kinetic model of the desulfurization rate during the process of hot metal desulfurization with magnesium vapor injection was established.The dimensionless equation of the gas–liquid mass transfer coefficient under the injection conditions was obtained by the dimensional analysis method.And the theoretical calculation results were in good agreement with the experimental measurements.The results show that the diameter of the bubbles and the viscosity of the melt significantly affect the desulfurization rate of hot metal injected with magnesium vapor.When the temperature is 1573 K and the gas flow rate is 3 L/min,the desulfurization rate can reach 79%and the utilization rate of magnesium can reach 83%.
文摘Reduction of complex protein networks models is of great importance.The accuracy of a passivity preserving algorithm (PRIMA) for model order reduction (MOR) is here tested on protein networks,introducing innovative variations of the standard PRIMA method to fit the problem at hand.The reduction method does not require to solve the complete system,resulting in a promising tool for studying very large-scale models for which the full solution cannot be computed.The mathematical structure of the considered kinetic equations is preserved.Keeping constant the reduction factor,the approximation error is lower for larger systems.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.21978230)Shaanxi Creative Talents Promotion Plan−Technological Innovation Team(Grant No.2019TD-039).
文摘Chemical looping reforming of methane is a novel and effective approach to convert methane to syngas,in which oxygen transfer is achieved by a redox material.Although lots of efforts have been made to develop high-performance redox materials,a few studies have focused on the redox kinetics.In this work,the kinetics of SrFeO_(3−δ)–CaO∙MnO nanocomposite reduction by methane was investigated both on a thermo-gravimetric analyzer and in a packed-bed microreactor.During the methane reduction,combustion occurs before the partial oxidation and there exists a transition between them.The weight loss due to combustion increases,but the transition region becomes less inconspicuous as the reduction temperature increased.The weight loss associated with the partial oxidation is much larger than that with combustion.The rate of weight loss related to the partial oxidation is well fitted by the Avrami–Erofeyev equation with n=3(A3 model)with an activation energy of 59.8 kJ∙mol^(‒1).The rate law for the partial oxidation includes a solid conversion term whose expression is given by the A3 model and a methane pressure-dependent term represented by a power law.The partial oxidation is half order with respect to methane pressure.The proposed rate law could well predict the reduction kinetics;thus,it may be used to design and/or analyze a chemical looping reforming reactor.
基金partially supported by SNF(Project 200021-107885/1)(E.C.)CCEMCH(I.V.K.).
文摘In the present work,we develop in detail the process leading to reduction of models in chemical kinetics when using the Method of Invariant Grids(MIG).To this end,reduced models(invariant grids)are obtained by refining initial approximations of slow invariant manifolds,and used for integrating smaller and less stiff systems of equations capable to recover the detailed description with high accuracy.Moreover,we clarify the role played by thermodynamics in model reduction,and carry out a comparison between detailed and reduced solutions for a model hydrogen oxidation reaction.
基金The authors would like to acknowledge the National Key R&D Program of China(No.2017YFC0210301)the National Natural Science Foundation of China(No.51474021)for financial support.
文摘Kinetics of hot metal desulfurization were studied using CaO-SiO2-Al2O3-Na2O-TiO2 slag in the range of 1400-1500℃on a laboratory scale.The results of kinetic experiments indicate that the desulfurization rate increases as the temperature,Al2O3 content,Na2O content,and TiO2 content increase and basicity increases from 1.01 to 1.75,but decreases when basicity increases from 1.75 to 2.02.The melting effect of slag is promoted as the temperature,Na2O content,and TiO2 content increase and Al2O3 content increases from 12.13 to 17.17 mass%,but worsened as basicity increases and Al2O3 content increases from 17.17 to 22.27 mass%.A kinetic model of hot metal desulfurization has been developed to calculate the mass transfer coefficient and the mass transfer resistance of sulfur in slag.The mass transfer coefficient of sulfur increases as the temperature,Al2O3 content,Na2O content,and TiO2 content increase and basicity decreases.Total mass transfer coefficients of sulfur were in the range of(5.02-23.78)×10^-7 m s^-1.The activation energy was estimated to be 464.06 kJ mo1^-1 at the temperature from 1400 to 1450℃and 176.35 kJ mol-1 at the temperature from 1450 to 1500℃.The sulfur distribution at the slag-metal interface was observed using a mineral liberation analyzer.The result shows that the mass transfer of sulfur in slag is the controlling step at high temperature during the desulfurization process.
文摘The kinetics of isothermal reduction of Ag2O with graphite under argon atmosphere for a non-activated sample and mechanically activated sample was investigated.It is found that Johnson-Mehl-Avrami model appropriately explained the thermal and mechanochemical synthesis of Ag from Ag2O＋ghraphite mixture.The process kinetics was investigated using the same approach for milled and unmilled samples.The results show that the Avrami exponent of mechanochemical reduction is higher than that of high temperature thermal reduction.Also,the mechanisms of nuclei growth in thermal and mechanochemical reduction are diffusion controlled and interface controlled,respectively.
