Two-step Reaction Model Research Articles

Numerical analysis of mixing performance in Y-junction mixers and its impact on yields from supercritical water hydrolysis

This study investigates the mixing behavior in a Y-junction mixer for supercritical water hydrolysis using large eddy simulation with a discrete phase model. Yield changes were simulated using a two-step reaction model with first-order kinetics, based on particles’ temporal temperature data. Effective mixing produced closely matched mass and particle flow temperature distributions, both exhibiting bell-shaped profiles near the mixed temperature. Although variations in flow rate within ±25 % and changes in the inlet temperatures of supercritical water from 350 °C to 430 °C and subcritical water from 100 °C to 170 °C did not significantly affect the overall mixing performance, they did alter the mixed temperature and, subsequently, yield changes. Additionally, backflow occurred when Richardson number for the subcritical inlet reached approximately 7. In effective mixing, simulated yields were approximately 15 % lower than the ideal theoretical yields, calculated using the reaction rate constant at the mixed temperature.

Corrosion behavior and mechanism of Cr10Mo1 steel subjected to different corrosive ions in simulated concrete pore solution

The corrosion of pre-passivated Cr10Mo1 steels in simulated concrete pore solution of saturated Ca(OH)2 induced by different corrosive ions were investigated, namely Cl−, SO2- 4, and combination of Cl− and SO2- 4. Electrochemical methods, Pourbaix analysis of Fe–Cr–H2O system and DFT calculation were adopted to characterize corrosion behavior and reveal underlying mechanism. Results showed that while sulfate may induce corrosion at higher threshold value, the scenario of chloride alone leads to lowest corrosion potential, linear polarization resistance and highest corrosion rate, and the presence of SO2- 4 ions mitigate corrosion risk under the coexistence condition of chloride and sulfate. A two-step reaction model of competitive adsorption-catalytic corrosion was proposed based on theoretical analysis and DFT calculation results.

Thermal Decomposition and Combustion Analysis of Malaysian Peat Soil Samples Using Coats Redfern Model-free Method

This research investigates the thermal decomposition behaviour of Malaysian peat soil through thermogravimetric analysis at varying heating rates. The study aims to analyse the thermal kinetics of decomposition for distinct peat soil types under inert and oxidative atmospheres while considering the role of available oxygen. The investigation encompasses virgin and agricultural peat, employing a non-isothermal thermogravimetric analysis technique to evaluate thermal decomposition characteristics and compute kinetic parameters using the Coats Redfern model-free approach. The pyrolysis profiles reveal three primary stages: moisture evaporation (30–180°C), organic component decomposition (200–500°C), and mineral decomposition (600–800°C). Virgin peat experiences a 43% mass loss during pyrolysis, while agricultural peat shows a 46% mass loss, emphasising insights into thermal behaviour and consistent decomposition patterns across peat types. Combustion profiles exhibit three main stages: dehydration (30–180°C), oxidative pyrolysis transforming organic matter into volatiles and char (200–300°C), and subsequent char oxidation (300–500°C). The study determines average activation energy trends, measuring 14.87 kJ/mol for virgin peat and 5.37 kJ/mol for agricultural peat under an inert atmosphere, and 28.89 kJ/mol for virgin peat and 36.66 kJ/mol for agricultural peat under an oxidative atmosphere. The research introduces an innovative two-step reaction model elucidating peat thermal decomposition kinetics (excluding dehydration), including a discussion on the impact of oxygen availability on kinetic parameters. These findings essential peat fire smouldering modelling, contributing to peat combustion behaviour for effective strategies to reduce peat fire risks.

Evolution of weakly unstable oblique detonation in disturbed inflow

The surface instability of oblique detonation waves (ODWs) without perturbations has been extensively investigated, yet the impact of external perturbations remains under-explored. Utilizing reactive Euler equations coupled with a two-step induction-exothermic reaction model, this study conducts a numerical examination of the evolution of unstable ODW surfaces subjected to a continuous sinusoidal density/temperature perturbation inflow. The results show that, without inflow perturbations, the ODW can evolve into triple points in the downstream due to detonation instability, similar to previous work. However, a small continuous perturbation can induce a significant forward movement of the ODW unstable position. Surprisingly, as the perturbation magnitude increases, the changes in the unstable position become progressively less pronounced. By increasing the perturbation frequency, the oscillation amplitude first increases, but a decreasing period/stage occurs with a modest frequency. To investigate the response of ODW to the increase in perturbation, the frequency characteristics and numerical smoked cells of detonation surfaces are examined and analyzed using Fast Fourier Transformation. The power spectral density indicates the presence of two distinct oscillation modes within oblique detonation. Low-frequency, small-amplitude perturbations serve to amplify the instability of the detonation, and more irregular oscillations could be observed. Conversely, high-frequency, large-amplitude perturbations suppress the development of small-scale waves on the detonation wavefront and lead to a relative regular oscillation, indicating that the wavefront pressure oscillations are entirely determined by inflow perturbations and become predictable. These findings have significant implications for the control of intrinsically unstable ODWs, providing valuable insights into the regulation of ODW dynamics.

Investigating the Phase Transition Kinetics of 1-Octadecanol/Sorbitol Derivative/Expanded Graphite Composite Phase Change Material with Isoconversional and Multivariate Non-Linear Regression Methods.

Organic composite phase change materials (PCMs) have been extensively studied, and it is important to investigate the effect of added components on the phase change process of the organic matrix. Herein, the phase transition process of the composite PCM with 1-octadecanol (OD) as the matrix adsorbed by a network framework composed of 1,3:2,4-di-(3,4-dimethyl) benzylidene sorbitol (DMDBS) and expanded graphite (EG) was measured using differential scanning calorimetry (DSC) at several linear heating rates. Using isoconversional and multivariate non-linear regression methods, a two-step consecutive reaction model for the composite PCM was established, while the apparent activation energies and pre-exponential factors were determined. The reaction mechanism of the first step was altered compared to pure OD, while the activation energies significantly decreased at the initial stage of the phase transition process and increased at the later stage. Combined with microscopic morphology analysis, the main reasons were the size and nanoconfinement effect. The predictions of the composite PCM under various conditions suggested that the composite PCM had a wider available temperature range compared to pure OD. This research provided a new idea for the in-depth study of the phase transition process of organic composite PCMs, which was helpful for the evaluation of organic composite PCMs.

Diffusion Coupling Kinetics in Multisite Catalysis: A Microkinetic Framework

Multicomponent (or multisite) catalysts are gaining increasing importance and popularity in heterogeneous catalysis and yet the cooperation mechanism among them remains obscure and intriguing. In this work, a vital and characteristic phenomenon in the two-component catalytic systems, the diffusion of surface intermediates, and the induced activity enhancement by coupling with the surface reactions is systematically investigated with both rigorous theoretical deduction and microkinetic simulations. By virtue of the proposed pseudo-fluctuation method, a general analytical framework is established with the two-step reaction model and the influence and origin of intermediate diffusion are elaborated. We quantify that the difference of the chemical potential of surface intermediates on different sites leads to the diffusion and determines the diffusion flowing from the strong adsorption site to the weak adsorption site. More importantly, we demonstrate that an enhancement in the overall reaction rate can be achieved by integrating the advantages of different components. Specifically, the optimum promotion effect would appear when the adsorption abilities of the two-component catalysts for the surface intermediate are around the chemical potential of the reactant and product, respectively. From the aspect of practical preparation methods, the coupling kinetics of the mechanically mixed catalysts and the alloy-typed catalysts are theoretically compared and a preliminary strategy for choosing the coupled components is proposed. We believe that this work provides a fundamental insight into the understanding and manipulation of the intermediate diffusion process.

Behaviors and non-isothermal kinetics of Chlorella pyrenoidosa fodder pyrolysis by a modified kinetic compensation effects and a parallel two-step reaction model

Behaviors and non-isothermal kinetics of Chlorella pyrenoidosa fodder pyrolysis by a modified kinetic compensation effects and a parallel two-step reaction model

Evolution and mechanisms of low-temperature oxidation and coal–oxygen coupling processes of a specific low-rank bituminous coal with various microscale particle sizes

ABSTRACT Coal fires are very typical hazards caused most significantly by uncontrolled spontaneous combustion processes in coal mines, seams, and the like. By thermogravimetry (TG) experiments, evolution behaviors and properties of thermal oxidation processes at low temperature of a bituminous coal with five microscale particle sizes (L1 215.20 μm; L2 151.90 μm; L3 80.22 μm; L4 43.71 μm; and L5 19.21 μm) were investigated. A two-step reaction model was developed by using Coats–Redfern method and pyrolysis kinetics parameters were calculated. Results show that in stage 1 (65.0–160.0°C) segments of water evaporation and gas desorption dominate, while in stage 2 (160.0–320.0°C) segments of generation of coal–oxygen complex and structure oxidation contribute most. Five macro-characteristic temperatures (critical temperature T1, xerochasy temperature T2, activity temperature T3, mass peak temperature T4, and ignition temperature T5) move to the low temperature direction with decreasing particle sizes except T4. Reaction processes during coal–oxygen interactions are proposed. Activation energies decrease as particle sizes reduce during both stage 1 (15.01–32.47 kJ·mol−1) and stage 2 (64.29–96.34 kJ·mol−1) since specific surface areas are augmented and more active groups are exposed. This work is expected to better monitoring of temperature thresholds for coal spontaneous combustion processes.

STUDY ON EVOLUTION MODEL OF GASEOUS DETONATION WAVE IN PERIODIC INHOMOGENEOUS MEDIUM

The initiation, steady propagation and failure mechanism of gaseous detonation wave in periodic inhomogeneous media are very complex, and many physical mechanisms are still unclear, which is an active topic in detonation physics. Numerical simulation of propagation of gaseous detonations in the inhomogeneous medium is studied by using the reactive Euler equations coupled with a two-step chemical reaction model. The inhomogeneity is generated by placing artificial temperature perturbations with different wavelengths and amplitudes. The influence of temperature disturbance with different wavelength and amplitude on the structure of wave front is analyzed. The results show that, the transition of ZND detonation to cellular detonation under artificial temperature disturbance is mainly controlled by two competitive factors: one is the intrinsic instability of detonation wave, the other is the wavelength and amplitude of artificial disturbance, the former is the internal factor, the latter is the external factor. The existence of artificial temperature disturbance delays the evolution of ZND detonation to cellular detonation by suppressing the development of shear wave, and the increase of internal instability can slow down this delay phenomenon. This shows that the artificial temperature disturbance can restrain the development of cell instability in a certain range, but it cannot stop the process. The discontinuity of temperature makes the detonation wave front more distorted, which leads to the existence of a weak triple-wave structure near the shear wave, which is, the artificial disturbance increases the inherent instability of detonation wave and changes the propagation mechanism of detonation wave front. The propagation of detonation and the instability of detonation are restrained by the artificial temperature disturbance with large amplitude. The formation of detonation front cellular structure depends on the artificial temperature disturbance and its own instability.

Dependence of total ionizing dose effect of nMOS transistors on the on/off duty ratio of a gate voltage

The dependence of the total ionizing dose effect of continuously operating nMOS transistors, irradiated with gamma-ray from a Co60 source, on the on/off duty ratio of a gate voltage was studied. The transistors were manufactured by a 180 nm process. It was found that the maximum leak current in the case of 10% duty ratio was by a factor of about 100 less than the case of 90% duty ratio. To explain the observed result, a two-step reaction model was adopted, which describes the increase in the density of positively charged taps in an oxide layer and negatively charged interface traps. It was shown that a set of rate equations based on the proposed model can explain the observed dependence of the leak current on the duty ratio.

A potassium responsive numerical path to model catalytic torrefaction kinetics

To assess the potassium catalytic influence on the kinetic behavior of non-oxidative biomass torrefaction, two woody biomass samples (Amapaí and Eucalyptus), as well as Miscanthus samples impregnated with three different K2CO3 concentrations (0.003 M, 0.006 M, and 0.009 M) were comprehensively studied. The solid thermal degradation kinetics were analyzed through thermogravimetric analysis in usual torrefaction conditions (275 °C during 68min and 10 °C.min−1 heating rate) and an original Potassium Responsive Numerical Path (PRNP). Therefore, a two-step reaction model with unified activation energies was integrated within a numerical method that considers the torrefaction severity influence for each potassium-loading content in all three biomasses. The proposed PRNP enables an accurate solid yield prediction (R2 > 0.9995). A strong (R2 between 0.91 and 0.99) and a significant (p≤0.0463) linear correlation was highlighted between the potassium content in biomass, the increasing reaction rates, and pre-exponential factors. The solid and volatile product distribution depicted faster and marked degradation for solid pseudo-components and anticipated a higher volatile release. The catalytic torrefaction severity factor determination enabled correlating treatment severity and kinetic rates showing better correlations than K% for wood biomass. The accurate results are conducive to developing numerical models that are essential for assessing solid fuel upgrading under catalytic effect in torrefaction plants.

A Simplified Model for Reversible Solid Oxide Fuel Cells

A simplified reversible steady-state solid oxide cell model is formulated and solved analytically with only a few calibration parameters to match experimental performance data. A Butler-Volmer type model is used for the hydrogen electrode while a two-step single pathway reduced-order oxygen reduction reaction model is applied in the oxygen electrode. It is shown that this simple model is capable of accurately predicting the trends of V-I data produced experimentally at various gas concentrations in both fuel cell and electrolysis modes.

Degradation and deactivation of plasmid-encoded antibiotic resistance genes during exposure to ozone and chlorine

Degradation and deactivation kinetics of an antibiotic resistance gene (ARG) by ozone (O3) and free available chlorine (FAC) were investigated in phosphate-buffered solutions at pH 7 for O3 (in the presence of tert‑butanol), and pH 6.8 or 8.1 for FAC. We used a plasmid (pUC19)-encoded ampicillin resistance gene (ampR) in both extracellular (e-) and intracellular (i-) forms. The second-order rate constant (kO3) for degradation of 2686 base pair (bp) long e-pUC19 toward O3, which was determined by quantitative polymerase chain reaction assay, was calculated to be ~2 × 105 M−1s−1. The deactivation rate constants of e-pUC19 by O3 measured with various recipient E. coli strains were within a factor of 2 compared with the degradation rate constant for e-pUC19. The degradation/deactivation kinetics of i-pUC19 were similar to those of e-pUC19, indicating only a minor influence of cellular components on O3 reactivity toward i-pUC19. For FAC, the degradation and deactivation rates of e-pUC19 were decreased in the presence of tert‑butanol, implying involvement of direct FAC as well as some radical (e.g., •OH) reactions. The degradation rates of e-ampR segments by direct FAC reaction could be explained by a previously-reported two-step sequential reaction model, in which the rate constants increased linearly with e-ampR segment length. The deactivation rate constants of e-pUC19 during exposure to FAC were variable by a factor of up to 4.3 for the different recipient strains, revealing the role of DNA repair in the observed deactivation efficiencies. The degradation/deactivation of e-pUC19 were significantly faster at pH 6.8 than at pH 8.1 owing to pH-dependent FAC speciation variation, whereas i-pUC19 kinetics exhibited much smaller dependence on pH, demonstrating intracellular plasmid DNA reactions with FAC occurred at cytoplasmic pH (~7.5). Our results are useful for predicting and/or measuring the degradation/deactivation efficiency of plasmid-encoded ARGs by water treatment with ozonation and chlorination.

Thermal hazards of benzaldehyde oxime: Based on decomposition products and kinetics analysis by adiabatic calorimeter

As a self-reactive substance, benzaldehyde oxime (BO) is prone to a highly exothermic runaway reaction and thermal hazard analysis and the reaction kinetics calculation of BO have great significance. In this work, the decomposition products of BO in nitrogen atmosphere were identified by GC–MS and HPLC techniques. The impact of the decomposition products on the decomposition behaviors of BO were analyzed by comparison of the ARC test results of pure BO and mixture of BO and decomposition products. It was found that N-benzylidene benzylamine was the intermediate decomposition product and benzoic acid, benzamide, N-benzyl benzamide, and 2,4,5-triphenylimidazole were the final products of BO. A two-step continuous autocatalytic reaction model was established to depict the decomposition process of BO. The kinetic parameters of the model were calculated by applying the nonlinear optimization method. Finally, thermal behaviors under different process temperature were predicted based on the kinetic model, and the time to maximum rate (TMRad) was predicted as 112.04 °C under 24 h, and 122.19 °C of 8 h, which offer crucial safety information to optimize the safety conditions of BO during usage, storage and transportation, which minimizes the industrial disasters.

Two-step model for reduction reaction of ultrathin nickel oxide by hydrogen

Nickel (Ni) is used as a catalyst for nitric oxide decomposition and ammonia production but it is easily oxidized and deactivated. Clarification of the reduction process of oxidized Ni is essential to promote more efficient use of Ni catalysts. In this study, the reduction processes of ultrathin oxide films formed on Ni(111) surfaces by thermal oxidation under vacuum and a hydrogen atmosphere were investigated by in situ time-resolved photoelectron spectroscopy. On the basis of these results, we propose a reaction model for the reduction of Ni oxide films. Our results show that the reduction of Ni oxide films on heating under vacuum does not yield a clean Ni(111) surface owing to formation of a residual stable suboxide structure on the Ni(111) surface. Conversely, in a hydrogen atmosphere of 1 × 10−5 Pa, the Ni oxide was completely reduced and a clean Ni(111) surface was obtained, even when heating below 300 °C. The reduction in a hydrogen atmosphere was best described by a two-step reaction model. The rate of the first step depends on the reduction temperature, and the rate of the second step depends on the H2 pressure. The rate-limiting process for the first step is surface precipitation of O atoms and that of the second step is dissociation of H2 molecules.

Influences of incoming flow on re-initiation of cellular detonations

The study of detonation initiation under supersonic incoming flow is of significance for the supersonic air-breathing propulsion based on detonation waves. By high-resolution simulations based on the 5th order weighted essentially non-oscillatory (WENO) and a two-step reaction model, this paper addresses the effect of incoming flow on re-initiation as a detonation generated in a pre-detonator propagates into semi-infinite free or confined space. Results show that detonation re-initiation is promoted by incoming flow because the leading shock wave is strengthened at the upstream side. Furthermore, the role of the promotion is quantitatively compared between stable and unstable detonations. Responses of detonation re-initiation to incoming flow velocity are different, which associates with the instability of detonations. Since responses of ignition delay time to the variation of post-shock temperature are different, the unstable detonation is more sensitive than the stable detonation.

Degradation Kinetics of Antibiotic Resistance Gene mecA of Methicillin-Resistant Staphylococcus aureus (MRSA) during Water Disinfection with Chlorine, Ozone, and Ultraviolet Light.

Degradation kinetics of antibiotic resistance genes (ARGs) by free available chlorine (FAC), ozone (O3), and UV254 light (UV) were investigated in phosphate buffered solutions at pH 7 using a chromosomal ARG (mecA) of methicillin-resistant Staphylococcus aureus (MRSA). For FAC, the degradation rates of extracellular mecA (extra-mecA) were accelerated with increasing FAC exposure, which could be explained by a two-step FAC reaction model. The degradation of extra-mecA by O3 followed second-order reaction kinetics. The degradation of extra-mecA by UV exhibited tailing kinetics, which could be described by a newly proposed kinetic model considering cyclobutane pyrimidine dimer (CPD) formation, its photoreversal, and irreversible (6-4) photoproduct formation. Measured rate constants for extra-mecA increased linearly with amplicon length for FAC and O3, or with number of intrastrand pyrimidine doublets for UV, which enabled prediction of degradation rate constants of extra-mecA amplicons based on sequence length and/or composition. In comparison to those of extra-mecA, the observed degradation rates of intracellular mecA (intra-mecA) were faster for FAC and O3 at low oxidant exposures but significantly slower at high exposures for FAC and UV. Differences in observed extra- and intracellular kinetics could be due to decreased DNA recovery efficiency and/or the presence of MRSA aggregates protected from disinfectants.

Intensification of Biomass Thermal Deoxygenation via a Two-Stage Process

Thermal deoxygenation (TDO) is a promising reaction scheme for producing low oxygen bio-oil from biomass carbohydrate. The primary step in bio-oil production involves pyrolysis of alkaline earth metal-neutralized biomass hydrolysates at 723 K yielding bio-oil, chars, carbonates, and light gases. Reactor scaling from bench to floor-scale, however, reduced carbon yields from 80% to 48% of theoretical, respectively. This paper details a two-stage process to intensify the TDO process, improving carbon yields to 79% of theoretical. The scheme involves a 523 K thermal pretreatment (stage I) to yield a polysalt and transition of a melt-phase. The resulting solid polysalt is reduced to powder to improve material handling and reaction rates during decomposition at 723 K (stage II). Resulting bio-oil yield is shown to improve from 0.082 to 0.16 kg-oil/kg-feed. A two-step reaction model is developed detailing the reaction rates and regimes which can guide continuous process design efforts.

Wedge-induced oblique detonation waves in supersonic kerosene-air premixing flows with oscillating pressure

The oblique detonation wave (ODW) induced by a wedge in the supersonic pre-evaporated kerosene-air flow is investigated via the numerical simulation based on the Navier-Stokes equations with a two-step reaction model. The unsteady inflow feature is subject to a continuous sinusoid pressure disturbance. The influence of oscillating amplitudes and disturbance cycle numbers of the unsteady pressure on the stabilization of wedge-induced ODW is analyzed. Based on a smooth transition with a curved shock from the shock-induced deflagration to oblique detonation, the increasing fluctuating amplitude results in the unsteady dynamics for the ODW stabilization. It is found that both the formation wave structure and the transition pressure are changed due to the unsteady inflow, and a double-V wave structure appears. The interaction between the pressure disturbance and the stabilization wave structure leads to the oscillating ODW with convex and concave fronts. In particular, the low-pressure wave induces a larger wave angle with convex ODW and the concave one with unstable cellular wave structures is due to the high-pressure disturbance. The decrease of the disturbance cycle number results in a gradual evolution process of ODW stabilization, and the increase leads to the complex interactions of transverse waves, during which local quenching could occur. In general, the present results indicate that the stabilization wave structure of ODW is expected to re-adjust itself with local unstable features during a dynamic process and tends to be resilient to the inflow pressure disturbances.

Numerical study on stabilization of wedge-induced oblique detonation waves in premixing kerosene-air mixtures

The initiation and stabilization features of oblique detonation wave (ODW) in kerosene-air premixing flows are investigated numerically based on the Navier-Stokes equations with a two-step reaction model. The effects of fuel-air equivalence ratios and inflow Mach numbers are considered by a parametric study. The present results indicate that the dependence of ODW initiation distance for kerosene fuel with high density on the equivalence ratio, Φ0, is quasi-linear, which is different from the previous study on the low-density fuel such as hydrogen, but the local transition pressure from the oblique shock wave (OSW) to ODW is non-linear with a critical equivalence ratio around 1.0. In particular, as the equivalence ratio increases from the fuel-lean to fuel-rich conditions, the transition pattern from the OSW to ODW varies: a smooth transition with a curved shock shifts to an abrupt one with a multi-wave point, and the initiation distance decreases, associated with the increase of transition pressure and the unstable detonation front. These are due to combined effects of the increasing inflow Mach number and the increasing fuel-rich mixtures for the exothermic reaction. The former accelerates the chemical reaction rate due to the increase of pressure/temperature of the post-OSW flow, and the latter enlarges the heat release. In particular, a double-ODW wave structure occurs for the fuel-rich mixture with Φ0=1.4, since the inflow reactive mixture cannot be consumed as it crosses the first ODW, resulting in a downstream second ODW. The increasing inflow Mach number results in the acceleration of ODW initiation and stabilizes the ODW within the inflow conditions in this study.