EFFECTIVE SOLUTION METHOD OF CHEMICAL REACTION KINETICS WITH DIFFUSE

The time integration method with four-order accuracy, self-starting and implicit for the diffuse chemical reaction kinetics equation or the transient instantaneous temperature filed equation was presented. The examples show that both accuracy and stability are better than Runge-Kutta method with four-order. The coefficients of the equation are stored with sparse matrix pattern, so an algorithm is presented which combines a compact storage scheme with reduced computation cost. The computation of the competitive and consecutive reaction in the rotating packed bed, taken as examples, shows that the method is effective.

Effects of Chemical Reactions in the Hypersonic Reacting Flow around Blunt Bodies

The effects of chemical reactions in the hypersonic reacting flow are investigated using an integrated algorithm considering simultaneously two different reaction mechanisms,i.e.,including the high temperature air nonequilibrium chemical reactions and the H_2-air combustion reactions. The program is validated by the air non-equilibrium flow at Mach number of 25.9 with the RAM C-II configuration and the shock-induced combustion flow at Mach number of 4.512 6 around a sphere,respectively. Furthermore,the mixed reacting flow with the Mach number of 10.0 with an opposing jet of hydrogen is numerically analyzed. The results show that the program is reliable,and the effects of chemical reactions engender in the decrease of peak temperature along characteristic lines,as well as on the surface. The production of water is augmented in the region with high ratio of oxygen to hydrogen and weakened in the area with low ratio of oxygen to hydrogen by the air chemical non-equilibrium effects.

Simple Program for Step-by-Step Time Integration in Chemical Kinetics, Applied to Simple Model for Hydrogen Combustion

A simple algorithm is proposed for step-by-step time integration of stiff ODEs in Chemical Kinetics. No predictor-corrector technique is used within each step of the algorithm. It is assumed that species concentrations less than 10-6 mol·L-1 do not activate any chemical reaction. So, within each step, the time steplength Δt of the algorithm is determined from the fastest reaction rate maxR by the formula Δt = 10-6mol·L-1/max R. All the reversible elementary reactions occur simultaneously;however, by a simple book-keeping technique, the updating of species concentrations, within each step of the algorithm, is performed within each elementary reaction separately. The above proposed simple algorithm for Chemical Kinetics is applied to a simple model for hydrogen combustion with only five reversible elementary reactions (Initiation, Propagation, First and Second Branching, Termination by wall destruction) with six species (H2, O2, H, O, HO, H2O). These five reversible reactions are recommended in the literature as the most significant elementary reactions of hydrogen combustion [1] [2]. Based on the proposed here simple algorithm for Chemical Kinetics, applied to the global mechanism of proposed five reversible elementary reactions for hydrogen combustion, a simple and short computer program has been developed with only about 120 Fortran instructions. By this proposed program, the following are obtained: 1) The total species concentration of hydrogen combustion, starting from the sum of initial reactants concentrations [H2] + [O2], gradually diminishes, due to termination reaction by wall destruction, and tends to the final concentration of the product [H2O], that is to the 2/3 of its initial value, in accordance to the established overall stoichiometric reaction of hydrogen combustion 2H2 + O2 → 2H2O. 2) Time-histories for concentrations of main species H2, O2, H, H2O of hydrogen combustion, in explosion and equilibrium regions, obtained by the proposed program, are compared to corresponding ones obtained by accurate computational studies of [3]. 3) In the first step of the algorithm, the only nonzero species concentrations are those of reactants [H2], [O2]. So, the maximum reaction rate is that of the forward initiation reaction max R = Rif = kif[H2] [O2], where the rate constant kif is very slow. Thus, the first time steplength Δt1 = 10-6mol·L-1/max R results long in sec. After the first step, the sequences of all the following Δt’s are very short, in μsec. So, the first time steplength Δt1 can be considered as ignition delay time. 4) It is assumed that explosion corresponds to ignition delay time Δt1 t1 = 10 sec., can be considered as explosion limit curve. This curve is compared to the corresponding one obtained by the accurate computational studies of [2].

Light-Controlled Chemical Reaction Pathways in Disulfide-Based Nonequilibrium Systems

Pathway selection in a complex chemical reaction network(CRN)enables organisms to adapt,evolve,and even learn in response to changing environments.Inspired by this,herein we report an artificial system,where light signal was used to manipulate the reaction pathways in a disulfide-based nonequilibrium CRN.By changing the photon energy and irradiation window,the anion or new radical-mediated pathways were selectively triggered,resulting in a user-defined evolution pathway.Additional photodissipative cycles were achieved by UV(365 nm)irradiation,increasing the total number of reactions from 3 to 7.The emerging pathway selection of the CRN is accurately predictable and controllable even in complex organo-hydrogel materials.We demonstrate up to five-state autonomous sol-gel transitions and the formation of fuel-driven dissipative organo-hydrogel through both chemical and light input.This work represents a new approach to allowing CRNs to communicate with the environment that can be used in the development of materials with lifelike behaviors.

Discovery and Preparation of Organic Molecular Crystal via Vapor Phase Chemical Reaction

Chemical vapor deposition has been widely used to prepare the films of silicon, diamond and other inorganic species. Preparation of molecular crystal from chemical reactions in the vapor phase is seldom reported. Hepta-condensed form of 1-propyne-1. 3-diol molecular crystal produced via vapor phase chemical reaction is reported and

Chemical looping oxidative propane dehydrogenation controlled by oxygen bulk diffusion over FeVO_(4)oxygen carrier pellets

The oxygen distribution and evolution within the oxygen carrier exert significant influence on chemical looping processes.This paper describes the influence of oxygen bulk diffusion within FeVO4 oxygen carrier pellets on the chemical looping oxidative propane dehydrogenation(CL-ODH).During CL-ODH,the oxygen concentration at the pellet surface initially decreased and then maintained stable before the final decrease.At the stage with the stable surface oxygen concentration,the reaction showed a stable C3H6 formation rate and high C3H6 selectivity.Therefore,based on Fick’s second law,the oxygen distribution and evolution in the oxygen carrier at this stage were further analyzed.It was found that main reactions of selective oxidation and over-oxidation were controlled by the oxygen bulk diffusion.C3H8 conversion rate kept decreasing during this stage due to the decrease of the oxygen flux caused by the decline of oxygen gradient within the oxygen carrier,while C3H6 selectivity increased due to the decrease of overoxidation.In addition,reaction rates could increase with the propane partial pressure due to the increase of the oxygen gradient within the oxygen carrier until the bulk transfer reached its limit at higher propane partial pressure.This study provides fundamental insights for the diffusion-controlled chemical looping reactions.

Chemical equilibrium controlled synthesis of polyoxymethylene dimethyl ethers over sulfated titania

The chemical equilibrium and reaction kinetic behavior in the synthesis of polyoxymethylene dimethyl ethers （DMMn） were investigated over sulfated titania in order to reveal the decisive factor controlling the reaction. The results showed that the molar ratio of adjacent DMMn products in equilibrium solution had the same value, which depended absolutely on the reaction temperature. Meanwhile, the reactions had the same DMMn products distributions under varied reaction conditions. The equilibrium constants of the related step-wise reactions for DMMn formation were equal, which were calculated based on the bulk compositions of the reaction solution. And thus, the selectivity to DMMn was mainly controlled by the chemical equilibrium, i.e., thermodynamic control. In brief, the present results provide some guidance for future synthesis of DMMn.

Monte Carlo Simulation of Electron Velocity Distribution and Gas Phase Process in Electron-Assisted Chemical Vapor Deposition

The gas phase process of diamond film deposition from CH4/H2 gas mixture by electron-assisted chemical vapor deposition is simulated by the Monte-Carlo method. The electron velocity distribution under different E/P (the ratio of the electric field to gas pressure) is obtained, and the velocity profile is asymmetric. The variation of the number density of CH3 and H with different CH4 concentrations and gas pressure is investigated, and the optimal experimental parameters are obtained: the gas pressure is in the range of 2.5 kPa - 15 kPa and the CH4 concentration is in the range of 0.5% - 1%. The energy carried by the fragment CH3 as the function of the experiment parameters is investigated to explain the diamond growth at low temperature. These results will be helpful to the selection of optimum experimental conditions for high quality diamond films deposition in EACVD and the modeling of plasma chemical vapor deposition.

Chemical Kinetic Aspects of Solid State Reaction Producing Wollastonite from Rice Husk Silica and Limestone

An industrial mineral wollastonite (CaSiO3) was produced under solid state conditions from rice husk silica and limestone. Reaction was carried out at 900'C to 1300'C for 1 h. The product batches were subjected to XRD and chemical analysis techniques specific for wollastonite. Mole fractions of different product batches were calculated on the basis of accumulated data to study the kinetics. Specific rate constants and reaction rate were also found out. Various probable models of mechanism for reaction were considered and testified with the laid down criterion for suggesting the suitable one. The resulting data were treated with Arrhenius equation as well and activation energy was calculated--therefrom. In addition to finding it's value from the slope of Arrhenius curve, an alternate method was also applied for this purpose. Both of the values were observed to be comparable. The activation energy required for performed reaction was found to be almost one third of that reported for synthesizing CaSiO3 by using quartz. This referred to the economical preparation of wollastonite by using rice husk as a source of silica instead of quartz.

Influence of arc current and pressure on non-chemical equilibrium air arc behavior

The influence of arc current and pressure on the non-chemical equilibrium （non-CE） air arc behavior of a nozzle structure was investigated based on the self-consistent non-chemical equilibrium model. The arc behavior during both the arc burning and arc decay phases were discussed at different currents and different pressures. We also devised the concept of a non- equilibrium parameter for a better understanding of non-CE effects. During the arc burning phase, the increasing current leads to a decrease of the non-equilibrium parameter of the particles in the arc core, while the increasing pressure leads to an increase of the non-equilibrium parameter of the particles in the arc core. During the arc decay phase, the non-CE effect will decrease by increasing the arc burning current and the nozzle pressure. Three factors together-- convection, diffusion and chemical reactions--influence non-CE behavior.

The Chemical Channel of Earthquake Reactions and Decrease in the Magnitude of Earthquakes

The first necessary condition for the onset of an earthquake is the penetration of explosive gas into an explosive zone as a result of physical or chemical reaction. The second necessary condition is to ensure the subsequent propagation of the flame after ignition. The latter condition has made it possible to explain the impact of a cyclone on the emergence of 42 strongest earthquakes in the 21st century. If violation of this condition can be achieved with the help of vibrators or explosions, this will result in a decrease in the magnitude of an earthquake or even a complete prevention of earthquakes. Thus, the second condition is essentially a “pressure lock” that opens (with a decrease in the pressure caused by a cyclone), which leads to an earthquake or closes (with an increase in the pressure caused by an anticyclone or human interference using vibrators or explosions), which leads to earthquake prevention. Kinetic equations of the 2nd type were used to describe chemical reactions and obtain formulas for the precursor time, which made it possible to describe earthquakes of the chemical channel. The set of experimental time values of the earthquake precursor described by the physical model includes about 20% of all earthquakes;80% of earthquakes can be attributed to the chemical channel for earthquakes that occurred in Dushanbe in 1983. All earthquakes in Tiberias in June 2018 passed through the chemical channel, which can be concluded from the small magnitude of these earthquakes. Several proposals have been made, including: 1) creating a new sensor for the geochemical method, which allows determining the epicenter of a future earthquake;2) creating a network of stations with a new sensor for determining the epicenter and an atmospheric pressure meter installed at each station (this will determine if the “pressure lock” is closed by an anticyclone, which can lead to a decrease in the magnitude of an earthquake or even prevent an earthquake);3) installing vibrators in epicenters (or making daily explosions with explosives delivered by trucks, drones, airplanes or helicopters, which should lower the magnitudes of future dangerous earthquakes);4) alerting the public to the expected future earthquake;5) developing specialized vibrators for reducing the magnitude of an impending catastrophic earthquake. Thus, this article is a breakthrough, describing a new mechanism in earthquakes for understanding and theory of earthquakes, which are used for the vast majority of earthquakes, including for program to reduce the magnitude of dangerous earthquakes.

Chemical kinetic studies on interfacial reaction in SCS-6 SiC/Ti matrix composites

Interfacial reaction and its mechanism of SiC/Ti composite were revealed by chemical kinetic studies. A two-step dynamic model of interfacial reaction in SCS-6 SiC/Ti composites was built up, and the rate constant and the activation energy of the interfacial reactions were obtained based on the quantum chemistry calculation. The results show that the first step, in which the atomic Ti, C and Si are decomposed from Ti matrix and SiC fiber, respectively, is a rate-determined step because the activation energy of the step is much larger than that of the second one in which deferent interfacial reaction products form. The theoretically predicted result of the interfacial reaction is coincident with that of experimental observation.

Reactivity study and kinetic evaluation of CuO-based oxygen carriers modified by three different ores in chemical looping with oxygen uncoupling(CLOU)process

In the chemical looping with oxygen uncoupling(CLOU)process,CuO is a promising material due to the high oxygen carrier capacity and exothermic reaction in fuel reactor but limited by the low melting point.The combustion rate of carbon is faster than the decoupling rate of oxygen carrier(OC).Hence,high temperature tolerance and rapid oxygen release rate of CuO modified by three different ores were investigated in this study.The kinetics analysis of oxygen decoupling with Cu-based oxygen carriers was also evaluated.Results showed that CuO modified by chrysolite had faster oxygen release rate than that of CuO.Limestone showed obvious positive effect on the oxidization process.The selected OCs could keep stable in at least 20 cycles,for about 1200 min.Shrinking core model(SCM)fitted well for the decoupling process in the temperature range of 1123-1223 K.Reduction rate kinetic information may aid in the development of chemical looping with oxygen uncoupling(CLOU)technologies during reactor design and process modeling.Ternary doped copper oxide with chrysolite and limestone could improve the reactivity of CuO in decoupling and coupling process and also improve the high temperature tolerance.

Chemical looping gasification of maceral from low-rank coal: Products distribution and kinetic analysis on vitrinite

The product distribution and kinetic analysis of low-rank coal vitrinite were investigated during the chemical looping gasification(CLG)process.The acid washing method was used to treat low-rank coal,and the density gradient centrifugation method was adopted to obtain the coal macerals.By combining thermogravimetric analysis and online mass spectrometry,the influence of the heating rate and oxygen carrier(Fe2O3)blending ratio on product distribution was discussed.The macroscopic kinetic parameters were solved by the Kissinger-Akahira-Sunose(KAS)method,and the main gaseous product formation kinetic parameters were solved by the iso-conversion method.The results of vitrinite during slow heating chemical looping gasification showed that the main weight loss interval was 400–600℃,and the solid yield of sample vitrinite-Fe-10 at different heating rates was 64.30%–69.67%.When b=20℃·min^(-1),the maximum decomposition rate of vitrinite-Fe-10 was 0.312%min1.The addition of Fe2O_(3)reduced the maximum decomposition rate,but by comparing the chemical looping conversion characteristic index,it could be inferred that the chemical looping gasification of vitrinite might produce volatile substances higher than the pyrolysis process of vitrinite alone.The average activation energy of the reaction was significantly reduced during chemical looping gasification of vitrinite,which was lower than the average activation energy of 448.69 kJ·mol^(-1) during the pyrolysis process of vitrinite alone.The gaseous products were mainly CO and CO_(2).When the heating rate was 10℃·min^(-1),the highest activation energy for CH4 formation was 21.353 kJ·mol^(-1),and the lowest activation energy for CO formation was 9.7333 kJ·mol^(-1).This study provides basic data for exploring coal chemical looping gasification mechanism and reactor design by studying the chemical looping gasification process of coal macerals。

Reaction mechanism and kinetics of pressurized pyrolysis of Chinese oil shale in the presence of water

A study of reaction mechanisms and chemical kinetics of pressurized pyrolysis of Chinese Liushuhe oil shale in the presence of water were conducted using an autoclave for simulating and modeling in-situ underground thermal degradation.It was found that the oil shale was first pyrolyzed to form pyrobitumen,shale oil,shale gas and residue,then the pyrobitumen was further pyrolyzed to form more shale oil,shale gas,and residue.It means that there are two consecutive and parallel reactions.With increasing temperature,the pyrobitumen yield,as intermediate,first reached a maximum,then decreased to approximately zero.The kinetics results show that both these reactions are first order.The activation energy of pyrobitumen formation from oil shale is lower than that of shale oil formation from pyrobitumen.

Reaction kinetics of isopropyl palmitate synthesis

In this study, the kinetics of isopropyl palmitate synthesis including the reaction mechanism was studied based on the two-step noncatalytic method. The liquid-phase diffusion effect on the reaction process was eliminated by adjusting the stirring rate. The results showed that the two-step reaction followed a tetrahedral mechanism and conformed to second-order reaction kinetics. Nucleophilic attack on the carbonyl carbon afforded an intermediate, containing a tetrahedral carbon center. The intermediate ultimately decomposed by elimination of the leaving group, affording isopropyl palmitate. The experimental data were analyzed at different temperatures by the integral method. The kinetic equations of the each step were deduced, and the activation energy and frequency factor were obtained. Experiments were performed to verify the feasibility of kinetic equations, and the result showed that the kinetic equations were reliable. This study could be very signi ficant to both industrial application and determining the continuous production of isopropyl palmitate.

Reaction kinetics determination based on microfluidic technology

Microfluidic technology has been successfully applied to determine the reaction kinetics relying on its great characteristics including narrow residence time distribution,fast mixing,high mass and heat transfer rates and very low consumption of materials.In this review,the recent progresses about the reaction kinetics measured in microreactors are comprehensively organized,and the kinetic modeling thoughts,determination methods and essential kinetic regularities contained in these studies are summarized according to the reaction types involving nitration,oxidation,hydrogenation,photochemical reaction,polymerization and other reactions.Besides,the significant advances in the innovation of microplatform are also covered.The novel reactor configuration methods were established mainly to achieve rapid and efficient data collection and analysis.Finally,the advantages of microfluidic technology for the kinetic measurement are summarized,and a perspective for the future development is provided.

Mechanism and Kinetics Analysis of NO/SO_2/N_2/O_2 Dissociation Reactions in Non-Thermal Plasma

The kinetics mechanism of the dissociation reactions in a NO/SO2/N2/O2 system was investigated in consideration of energetic electrons＇ impacts on a non-thermal plasma. A model was derived from the Boltzmann equation and molecule collision theory to predict the dissociation reaction rate coefficients. Upon comparison with available literature, the model was confirmed to be acceptably accurate in general. Several reaction rate coefficients of the NO/SO2/N2/O2 dissociation system were derived according to the Arrhenius formula. The activation energies of each plasma reaction were calculated by quantum chemistry methods. The relation between the dissociation reaction rate coefficient and electron temperature was established to describe the importance of each reaction and to predict relevant processes of gaseous chemical reactions. The sensitivity of the mechanism of NO/SO2/N2/O2 dissociation reaction in a non-thermal plasma was also analysed.

Vibrational Nonequilibrium in the Hydrogen-Oxygen Reaction at Different Temperatures

A theoretical model of chemical and vibrational kinetics of hydrogen oxidation is suggested based on the consistent account for the vibrational nonequilibrium of HO2 radical which forms in result of bimolecular recombination H + O2 = HO2 in the vibrationally excited state. The chain branching H + O2 = O + OH and inhibiting H + O2 + M = HO2 + M formal reactions are considered (in the terms of elementary processes) as a general multi-channel process of forming, intramolecular energy redistribution between modes, relaxation, and monomolecular decay of the comparatively long-lived vibrationally excited HO2 radical which is capable to react and exchange of energy with another components of the mixture. The model takes into account the vibrational nonequilibrium for the starting (primary) H2 and O2 molecules, as well as the most important molecular intermediates HO2, OH, O2(1D), and the main reaction product H2O. The calculated results are compared with the shock tube experimental data for strongly diluted H2-O2 mixtures at 1000 T p < 4 atm. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods. It is shown that the hydrogen-oxygen reaction proceeds in absence of vibrational equilibrium, and the vibrationally excited HO2 radical acts as a key intermediate in the principally important chain branching process. For T < 1500 K, the nature of hydrogen-oxygen reaction is especially nonequilibrium, and the vibrational nonequilibrium of HO2 radical is the essence of this process.

聚甲氧基二甲醚-2燃烧动力学模型及试验研究

采用试验研究与动力学建模相结合方法,对聚甲氧基二甲醚-2(polyoxymethylene dimethyl ethers-2,PODE_(2))的中低温燃烧特性进行了研究。基于二甲氧基甲烷(dimethoxymethane,DMM)详细反应机理,遵循基于反应类的速率准则构建了PODE_(2)详细化学反应动力学机理,并与文献试验数据进行了验证;在快速压缩机试验平台测量了PODE_(2)在温度范围为550~900 K,当量比为0.5、1.0、2.0时着火延迟时间,结合所构建的详细反应机理,对PODE_(2)中低温条件下自着火过程控制因素进行了分析。结果表明,所构建的PODE_(2)反应机理可以很好地再现试验测量的着火延迟时间,对文献中现有的试验数据均能给出合理的预测。PODE_(2)自着火过程呈现明显的两阶段着火现象,没有表现出负温度系数(negative temperature coefficient,NTC)行为;PODE_(2)第一阶段着火延迟时间在低温段随温度呈线性变化,在720~820 K的中温范围内呈“平台”状,几乎不随温度变化。PODE_(2)低温反应活性来自于3个替代性通道,由氧加成反应开启的典型低温链分支反应序列作用被抑制。