Reaction Kinetic Model Research Articles

Observation and modeling of the thermal runaway of high-capacity pouch cells due to an internal short induced by an indenter

Owing to the complexity of coupling mechanical and electrical solvers for finite element analysis (FEA) of mechanical abuse of a battery, the simulation should be performed by incorporating a local short circuit model activated based on the status of battery elements. However, the approach should also consider various other conditions of the battery simulated, such as the initial state of charge (SOC), for precise simulations of the internal short. This study proposes an approach developed with a mechanical model and single-particle battery model, along with a reaction kinetics model for thermal abuse using LS-DYNA. Several key parameters were selected, such as the activation criteria, kinetic abuse and element integration points during the internal short circuit induced by the indenter. The impact of these key parameters in the FEA on thermal runaway response for various initial SOCs from 25to 100 % were analyzed. The FEA results obtained were compared against experimental results with various parameters such as activation criterion of internal short, kinetic abuse based on accelerating rate calorimetry (ARC) data. Finally, the root causes of the discrepancy between the FEA and experimental results are discussed regarding integration point what solver can make difference during calculation.

Hypocoercivity and Reaction-Diffusion Limit for a Nonlinear Generation-Recombination Model

A reaction-kinetic model for a two-species gas mixture undergoing pair generation and recombination reactions is considered on a flat torus. For dominant scattering with a non-moving constant-temperature background the macroscopic limit to a reaction-diffusion system is carried out. Exponential decay to equilibrium is proven for the kinetic model by hypocoercivity estimates. This seems to be the first rigorous derivation of a nonlinear reaction-diffusion system from a kinetic model as well as the first hypocoercivity result for a nonlinear kinetic problem without smallness assumptions. The analysis profits from uniform bounds of the solution in terms of the equilibrium velocity distribution.

Study on the reduction of Fe2O3 pellets by CO-CO2 and H2-H2O: Reaction kinetics and pore network model

The steel industry contributes to creating an environmentally friendly society by providing high-quality steel and working to develop low-carbon processes. Using hydrogen produced from renewable energy to replace part of coke in blast furnaces is one of the measures to reduce fossil carbon dioxide emissions in the process of steelmaking. In this paper, a series of reduction experiments of Fe2O3 pellets at different temperatures were carried out under three conditions of hydrogen-rich in blast furnace. The variation law between reduction degree and apparent activation energy was calculated. The result shows that when the reduction degree reaches 11% and 70%, the apparent activation energy reaches the peak, which are 38.9 kJ/mol and 19.5 kJ/mol, respectively. This suggests that the reduction process is affected by two or more mechanisms. Then, on the basis of the typical single interface reaction kinetics model, the multistep reduction kinetics model of hydrogen-rich reduction Fe2O3 pellets was established. In addition, based on the results of industrial computerized tomography (CT) analysis, the three-dimensional pore network model and velocity model of Fe2O3 pellets after reduction were established. The coupling relationship between the fractal dimension of pellet pores and reduction atmosphere was studied by introducing fractal theory. Under hydrogen-rich reduction condition, the volume fractal dimension of pore structure of Fe2O3 pellets increases from 2.41 to 2.58. Therefore, the pore structure formed by hydrogen-rich reduction is conducive to the diffusion of reducing gas in the pellet, so as to improve the reduction degree of pellet.

State-space model construction and dynamic analysis for a space thermionic nuclear reactor

The space nuclear reactor (SNR) is an important energy pattern for spacecrafts due to its high power density, long life and stabilization. A linear dynamic model is necessary to analyze the dynamics and design the appropriate control system analytically. A simplified nonlinear model based on conservation equations including point reactor kinetics model, thermal-hydraulic model, coolant model and heat pipe and radiator model was constructed. The state-space linear model was derived using perturbation theory. To verify the linear model, comprehensive comparisons were made in both time domain and frequency domain. The dynamic characteristics with respect to reactor power and reactivity were obtained in frequency and time domains. It is concluded that the reactor is an unstable system with a large time delay and strong nonlinearity at different power levels. This study provides solid foundation for future control system design.

New insight into the oxidation of propene at elevated pressure

Comprehensive experimental and kinetic studies of propene (C3H6) oxidation were conducted by using a jet-stirred reactor at 12.0 atm within 725–1020 K under both fuel-lean (Φ = 0.5) and fuel-rich (Φ = 3.0) conditions. Molecular species concentration profiles were obtained by using online gas chromatography and gas chromatography-mass spectrometry, including CO, CO2, CH4, C2H4, C2H6, A-C3H4, C3H8, 1,3-C4H6, 1-C4H8, nC4H10, CH3CHO, C2H3CHO, CH3COCH3, C3H6O1-2 CH3CH2CHO, and C6H6. Sixteen products and intermediates including light hydrocarbons, oxygenated and aromatic species were identified and quantified. Based on Aramco Mech 3.0 and previous works, the rate coefficients of some key elementary reactions were updated, and a detailed kinetic reaction model was developed with reasonable predictions involving 587 and 3037 reactions. Rate-of-production analysis indicates the four main pathways for high-pressure oxidation of C3H6, namely hydrogen atom abstraction reactions, OH addition reactions, H atom addition reactions, and the formation of C3H6O1-2. Sensitivity analysis reveals that H2O2(+M) <=> 2OH(+M) and the H-abstraction of C3H6 by OH radicals are the most promoting and inhibiting reactions for C3H6 consumption, respectively. The benzene formation during C3H6 oxidation was analyzed, mainly generated by the C1 + C5 channel and consumed by OH addition. It was found that increasing pressure can decrease the initial reaction temperature and increase the conversion of C3H6. The importance of addition and hydrogen abstraction reactions in the oxidation of C3H6 was identified by analyzing the pressure effect. To confirm its validity, the proposed kinetic model could be used to the previous literature data, including JSR oxidation at around 1 atm and ignition delay times for C3H6. These experimental and modeling efforts provide a basis for gaining a more comprehensive insight into the oxidation of propene.

Degradative solvent extraction of cyanobacteria: From reaction kinetics to potential organic matter evolution mechanism

This study proposed a new continuous lumped reaction kinetics model to accurately reveal the control mechanism of cyanobacteria at each stage of degradative solvent extraction and discussed the potential evolution mechanism of organic matter. Results showed that degradation solvent extraction successfully separated nitrogen and phosphorus from cyanobacteria. The solute has high carbon and volatile contents, is almost ash-free, and forms a phosphorus-rich residue. The lowest fitting degree of the continuous lumped reaction model kinetics was 94.5%, suggesting that this model worked well. The depolymerization of the residue dominated between 200 and 350 °C, whereas solute decomposition dominated at 400 °C. Nitrogen-containing compounds, which originate from protein decarboxylation or deamination to generate amides, are the main components of the solute, and amino acids react with reducing sugars to generate nitrogen heterocyclic compounds, which are useful for preparing nitrogen-containing chemicals.

Oxidation behaviors of Hongqian heavy crude oil characterized by TG-DSC-FTIR-MS within full temperature regions

To better understand in-situ combustion (ISC) theory and reveal the oxidation behavior and mechanism of Hongqian (HQ) heavy crude oil, the thermo-oxidative characteristics and kinetics of HQ heavy oil were studied under air conditions using TG-DSC-FTIR-MS technique. According to the TG/DTG-DSC curves, the oxidation reactions of HQ heavy oil can be divided into low temperature oxidation (LTO), fuel deposition (FD) and high temperature combustion (HTC) stages. The reaction mechanism for each reaction interval was comprehensively analyzed by online FTIR and MS analysis. In FTIR spectra, H2O, hydrocarbon, CO2, CO, –COOH, and aromatic ring were observed during the oxidation process, which are used to explain the occurrence of the possible decomposition/isomerization of hydroperoxides in the later stage of LTO and the important role of light hydrocarbons evaporation, thermal oxidative cracking and polycondensation for coke formation at FD stage, coke combustion at HTC stage, as well as the possible hysteresis of dehydrogenation and aromatization at FD and HTC stages. The strong variation of activation energy with conversion degree confirms the complex oxidation reactions. MS analysis of H2, CH4, H2O, CO, O2, and CO2 produced during oxidation process helps to verify these reaction mechanisms; and provide more information about the in-situ H2 generation and the conditions where H2 generation may occur as well as the generation of CO and its possible reaction mechanism in LTO reactions. These obtained data aid in a deeper insight into crude oil oxidation mechanism and provide reference for establishing accurate reaction scheme and reaction kinetic model for the precise simulation of ISC processes.

Influence of Electromagnetic Inductive Microcapsules on Self-Healing Ability of Limestone Calcined Clay Cement (LC3) Mortar.

In order to promote the sustainability of cementitious materials, it is imperative to reduce the level of environmental pollution and energy consumption during their production, as well as extend the service life of building elements. This study utilized limestone, calcined clay and gypsum as supplementary cementitious materials to prepare LC3 mortar, replacing 50% of ordinary silicate cement. Three types of microcapsules (M1, M2 and M3) were prepared using IPDI as a healing agent and polyethylene wax, polyethylene wax/nano-CaCO3 or polyethylene wax/ferrous powder as shell materials. The microcapsules were added to the LC3 mortar and tested for their effects on the mechanical properties, pore structure and permeability of mortars. Pre-loaded and pre-cracked mortar specimens were subjected to room temperature or under an applied magnetic field to evaluate the self-healing ability of the microcapsules on mortars. The kinetics of the curing reaction between IPDI and moisture were investigated using quasi-first-order and quasi-second-order reaction kinetic models. The experimental results showed that the mortar (S3) mixed with electromagnetic inductive microcapsules (M3) exhibited the best self-healing ability. The compressive strength retention, the percentage of pores larger than 0.1 μm, recovery of chloride diffusion coefficient and maximum amplitude after self-healing of S3 were 92.2%, 42.6%, 78.9% and 28.87 mV, respectively. Surface cracks with an initial width of 0.3~0.5 mm were healed within 24 h. The curing reaction between IPDI and moisture during self-healing followed a quasi-second-order reaction kinetic model.

Experimental and Simulation Analysis of Siloxane Mixtures Used in Organic Rankine Cycle with Thermal Stability Limits

The thermal stability of siloxanes has significant influence on the selection of working fluid and the performance of organic Rankine cycle systems. In this study, a thermal decomposition experimental apparatus was designed to measure the thermal stability of hexamethyldisiloxane (MM), octamethyltrisiloxane (MDM), and their mixtures; a reaction kinetics model based on first order reaction theory was built to analyze the thermal stability of siloxane mixture fluids in a long operation period. And the influence of the mass fraction and evaporation temperature on the net power and thermal efficiency of the system was analyzed under the constraints of thermal stability. The results showed that the thermal stability of MDM was worse than that of MM, and the mixture of MM and MDM had significant inhibition effects on the de-composition of pure fluids. The activation energy of decomposition reaction was 50.50 kJ/mol, and the pre-exponential factor was 5.80 × 10−3 s−1. With the evaporation temperature limit, the net power and thermal efficiency were both lower than those without the evaporation temperature limit. Comparing the obvious decrease in the thermal efficiency, the change of the net power was limited. Siloxane mixtures emerged as a superior choice for ORC systems in the conditions of this paper. MM/MDM (0.6/0.4) improved the net power and heat efficiency of the system by 8.1% and 1.7%, respectively, comparing with that of the pure working fluids.

A study on nitrile rubber/polyvinyl chloride blend vulcanization kinetics with different fillers by using single isothermal rheograph

An attempt has been made to establish a reasonably accurate microkinetics model for accelerated sulfur vulcanization of commonly used acrylonitrile rubber/polyvinyl chloride (NBR/PVC 70/30) blend (NVC73) from a single, isothermal rheograph data of torque versus time. The effect of three different types of fillers, such as pre-exfoliated organically modified montmorillonite (OMMT) clay, graphite (GRT) powder, and high abrasion furnace (HAF) carbon black (CB), were studied. The kinetics study was done with six solid-state reaction kinetics models. Among these, Sestak-Berggren (SB) equation was found to be the best model for the present compositions. The SB kinetic rate expressions were evolved after several iterations using empirical values of autocatalytic and non-autocatalytic orders of ‘ m’ and ‘ n’, respectively. The gum vulcanizate and OMMT clay-loaded compositions were found to have comparable conversion function f (α) and almost identical reaction rate constants at 150°C, under isothermal conditions. In comparison, HAF CB and GRT rate expressions differed from clay-loaded compositions. The validity of the reaction rate equations obtained was confirmed by comparison of plots for experimental and derived conversions with time.

Numerical Analysis of Tar and Syngas Formation during the Steam Gasification of Biomass in a Fluidized Bed

A sequential modular hydrodynamic model integrated with detailed reaction kinetics (SMHM-RK) was developed and validated to predict tar and syngas components produced by the steam gasification of biomass in a fluidized bed gasifier. The simulations showed that the prediction accuracy is sensitive to both models for hydrodynamics and reaction kinetics. The simulations showed that the tar composition predicted by the SMHM-RK was more close to the measured values than those predicted by the well-mixed hydrodynamic model integrated with the same reaction kinetics (WMHM-RK). The predictions showed that the total tar decreased, but the polycyclic aromatic tar compounds increased with the increase in gasification temperature. There was an optimum steam-to-biomass ratio (SBR) for minimizing tar formation. The simulations found that the contents of total tar and heavy tar compounds decreased by increasing the SBR from 0.3 to 0.9, and then increased by further increasing the SBR. The injection of a small amount of oxygen in steam gasification cannot reduce tar formation. The injection of oxygen in steam gasification changed the reaction pathways of naphthalene to produce more naphthalene in the syngas. The de-volatilization rate affects pyrolytic volatile compositions and subsequent tar formation. Therefore, biomass devolatilization and homogeneous gas reactions should be solved simultaneously to accurately predict the syngas and tar composition.

Perovskite nanomaterials with exceptional photocatalytic properties for oxidative desulfurization of dibenzothiophene

LaTiO3, LaZnO3, and Zn-doped LaTiO3 (LaZn0.5Ti0.5O3) perovskite catalysts are used for the aerobic photocatalytic oxidative desulfurization (APODS) of organosulfur compounds such as dibenzothiophene (DBT). Several techniques were used to characterize the synthesized photocatalyst, XRD, SEM, TEM, EDX, UV–Vis, DRS, PL, and XPS physisorption analyses. XRD patterns of LaZn0.5Ti0.5O3 is similar to pure LaTiO3 without any impurities confirming the insertion of atomic zinc into the LaTiO3 lattice structure. According to the obtained results, synthesized doped perovskite exhibits a more significant photocatalytic reaction than pure perovskite in removing DBT in the following order LaZn0.5Ti0.5O3 > LaZnO3 > LaTiO3 in the values 99.97, 91.38 and 76.05 % within 180 minutes under sunlight. The pseudo-first-order kinetic reaction model fits well with the results of the kinetic study. A reaction mechanism for LaZn0.5Ti0.5O3 was proposed using UV– Vis and XPS. At wavelengths above 400 nm, UV–Vis DRS confirms the absorption edges of the compound, which in this case equates to a visible light absorber with a band gap of 2.9 (eV). Superoxide radicals and holes were determined to be the primary active species in the photocatalytic process due to the reactive species and oxygen bubbles acting as trapping agents. The developed photocatalytic material was also highly regenerative and recyclable. The photocatalyst LaZn0.5Ti0.5O3 is first utilized in the photocatalytic oxidation of DBT. LaZn0.5Ti0.5O3 is a promising photocatalyst for environmental control and relevant applications, especially in solar energy.

Dynamics of quality change in process of shiitake mushroom (Lentinus edodes) cooking

AbstractTo better predict quality changes during food heating, a kinetic approach was used to determine and analyze the reaction kinetics of changes in ripening quality factors (color and hardness). The moisture content as a superheated quality factor was superheated to improve the quality of shiitake dishes during the cooking of shiitake mushroom. The results showed that the changes in L*, a*, hardness, and moisture content of the shiitake mushroom followed the first‐order reaction kinetics model, and the changes in h* and △E of the shiitake mushroom followed the zero‐order reaction kinetics model as the temperature increased during cooking. The z values of L*，a*，h*, and △E were 56.22,42.19,45.02 and 47.90°C and the Ea values were 34.20, 34.78, 41.33, and 26.43 kJ/mol, respectively. The z value for hardness was 49.67°C and Ea value was 25.92 kJ/mol. The z value for moisture content was 67.31°C and Ea value was 37.32 kJ/mol, which was greater than the z values of color and hardness. The z values of mature quality factors were less than the z value of overheating quality factor, which was in accordance with the requirement of cooking operation optimization. Our results proved that there was room for optimization of shiitake mushroom in the cooking process.Practical applicationThis study investigated the kinetics of quality changes of shiitake mushroom during cooking. In practical application, it could better predict the quality changes of shiitake mushroom during heating, determine the optimal cooking time by monitoring the changes of ripeness factor and overheating factor during cooking, facilitate food enterprises to design heat supply more scientifically, and provide basic data to promote the industrial production of shiitake pre‐prepared dishes.

Hydrolytic Hydrogen Production from Severely Plastic Deformed Aluminum-Based Materials: An Overview

The development of hydrogen energy will help to reduce the use of nonrenewable energy sources and achieve global carbon neutrality. The aluminum-water reaction is an important method of producing hydrogen because aluminum has abundant reserves, a high yield, and no pollution. However, the dense passive oxide film on the surface of aluminum, on the other hand, often obstructs this reaction, which is the primary issue limiting the development of aluminum-based hydrolytic materials. Mechanochemical activation by processing severely plastic deformed aluminum-based materials is one effective approach and has been developed in recent years. This article reviews recent progress of hydrogen production from hydrolysis of severely plastic deformed aluminum-based materials. The kinetic model of aluminum-water reaction, aging protection of the materials, catalytic mechanism and stable rate control for the hydrolysis of aluminum-based materials are reviewed. Furthermore, some existing problems as well as some suggestions for future research on hydrogen production from aluminum-based materials are also discussed.

Numerical investigation of the flame suppression mechanism of porous muzzle brake

An excellent flame suppression effect can be achieved using a novel porous brake. To understand the flame-suppression mechanism of a porous brake, combustion using a muzzle brake is investigated. A set of internal ballistic equations is employed to provide accurate velocity and pressure for a projectile moving to the muzzle. The multispecies transport Navier–Stokes equations, which incorporate complex chemical reactions, are solved by coupling a real gas equation of state, the Soave–Redlich–Kwong model, and a detailed chemical reaction kinetic model. The development of muzzle flow with a chemical reaction is simulated, and the interaction between chemical reactions with the muzzle flow field is numerically calculated to explain the muzzle combustion mechanism with a porous brake. The underlying mechanism is analyzed in detail. The results demonstrate that, first, the gas is fully expanded in the brake, leading to a reduction in pressure and temperature at the muzzle, thereby reducing the initial flame. In addition, the shock wave weakens due to the expansion and separation process, leading to a reduction in the mixture of gas and air, ultimately resulting in a reduction in the intermediate and secondary flames.

Solvent-free oxidation of p-tert-butyl toluene catalyzed with cobalt 4-tert-butylbenzoate in an internal circulation bubbling bed reactor

P-tert-butyl benzoic acid (PTBA) was synthesized by solvent-free oxidation of p-tert-butyl toluene (PTBT) at atmospheric pressure using cobalt 4-tert-butylbenzoate as catalyst and oxygen as an oxidant in a self-made internal circulation bubbling bed reactor (ICBBR). The effects of different catalysts and reactors on the reaction were investigated. The results show that the catalytic performance of cobalt 4-tert-butylbenzoate is superior, and the performance of the ICBBR is distinctly better than that of the batch stirred tank reactor (BSTR). The effects of reaction conditions such as flow rate, reaction temperature, and catalyst concentration on the oxidation of PTBT were studied. According to the distribution and kinetics of oxidation products, the oxidation mechanism of PTBT was analyzed. The results show that under the conditions of the oxygen flow rate of 2.5 L/min, reaction temperature of 150 °C and Co mass fraction of 250 ppm, the conversion rate of PTBT is 45.63% and the selectivity of PTBA is 97.8% after 4 h reaction without solvent. The reaction kinetics model of oxidation of PTBT to PTBA was established, and the reaction kinetics equation was obtained. The experimental values were close to the predicted values of the model.

Performance analysis of methanol steam micro-reformers for enhanced hydrogen production using CFD

Present study shows the performance analysis of methanol steam reforming considering different miniature-scale reformer geometries. Three different types of 3D models of steam reformers have been considered: straight annular, spiral, and serpentine-type reactors. Each reformer is packed with a copper-based catalyst to enhance the reaction between steam and methanol. Methanol steam reforming is an endothermic reaction with a two-step mechanism, whose reaction kinetic models were mathematically implemented. The study shows different hydrodynamic aspects of the flow fields through the catalyst bed, the conversion of methanol, and production of hydrogen for each type of reactors. Simulations were carried out at different temperatures and inlet velocities to study the methanol conversion and identify the most optimized reformer design. It was found that in the spiral and serpentine-type reformer, the methanol conversion was more due to the bending in the tubular reactor, which disturbs the flow field with an enhancement of mixing, causing more conversion. Spiral reformer exhibited conversion up to 91.16% at 650 K and producing 0.15 mass fraction of hydrogen, which was found to be 3% more than the conversion achieved in serpentine type and almost 8% more than the straight annular type geometry when the inlet velocity was kept at 0.1 m/s for all the cases.

Design and Development of Neutronics and Thermal Hydraulics Modeling Code for ACP1000 Nuclear Reactor Dynamics in LabVIEW

An advanced neutronics and thermal hydraulics nuclear code, called GNTHACP code, is designed and developed in LabVIEW as Graphical Neutronics and Thermal Hydraulics toolkit for 1100 MWe Advanced Chinese PWR (ACP-1000) nuclear power plant. The reactor neutronics model is developed using a nonlinear point reactor kinetics model, while, the reactor thermal hydraulics model is developed based on nonlinear fuel and coolant temperature dynamics. The heart of the GNTHACP code is the control rod reactivity model. Control rod reactivity banks are comprised of four power compensation banks G1, G2, N1, N2 and one temperature compensation bank R. The reactivity control configuration of these banks is highly nonlinear, complex and challenging in nature. The control rod reactivity model as a function of G1, G2, N1, N2 and R banks is optimized using two distinct techniques. The control rod reactivity model is optimized using Simplex Linear Programming (SLP) technique under constraints of reactor power as safety limit and control rod speed as maximum speed limit in LabVIEW. The control rod reactivity model is also optimized and investigated using nonlinear Sequential Quadratic Programming (SQP) technique under same constraints in LabVIEW. All the models are integrated and the state-of-the-art virtual instruments (VIs) are designed for cost function optimization, configuring models and calibration of model parameters in LabVIEW. The integrated model as graphical coupled neutronics and thermal hydraulics modeling code is optimized and validated against the Final Safety Analysis Report (FSAR) and different parameters of interest are investigated and proved within design limits as reported with CORCA and CORTH benchmark nuclear codes. The proposed code is stable, highly efficient and accurate as compared to other nuclear codes.

Mechanism study of the N-butoxycarbonyl-2,5-dimethylpyrrole synthesis reaction based on in-situ FTIR monitoring

The reaction pathway of many Paal-Knorr reactions for pyrrolic compounds hasn’t been thoroughly studied and remains controversial. In this work, the synthesis of an important anti-ultraviolet agent N-butoxycarbonyl-2,5-dimethylpyrrole based on the Paal-Knorr reaction was studied via in-situ Fourier transform infrared (FTIR) analysis combined with density functional theory (DFT) calculation. The online spectral data were analyzed using K-means clustering in order to find the characteristic wavenumbers of intermediates. It was found that the reaction with 2,5-hexadione and butyl carbamate are more favorable to form the imine and enamine intermediates by nucleophilic addition, which is different from another Paal-Knorr reaction with 2, 5-hexadione and ethanolamine. In addition, the reaction kinetic model was established through chemometric methods, with parameters of two rate-limiting reaction steps calculated. This approach of FTIR analysis is proven to be an effective tool for mechanism study of organic synthesis.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials