Values Of Reaction Order Research Articles

Kinetic models for the methanation of COx gases to produce methane: A critical analysis

An exhaustive review of the available literature regarding the kinetic models for the methanation of COx gases to produce natural gas (CH4) is reported. Since the oldest and recent reported kinetic studies about this topic were discussed and analyzed. The characteristics of the experimental studies such as the reaction system, operating conditions, catalyst used, and the experimental procedure, as well as the derived reaction rate equations, reaction rate coefficients and activation energies are highlighted. The results of the various kinetic models are also discussed in order to identify appropriate approaches that can be used as reference to develop new kinetic models. Most of the works reported values of reaction order of 0.2–1 and activation energies of 75–110 kJ/mol in a temperature range of 220–450 °C. Average absolute error (ε) values were calculated to evaluate the accuracy of the predicted data, which resulted to be in the range of 0.15 %–8.08 % showing generally a good agreement.

Isothermal low-temperature oxidation kinetics of heavy crude oil and its oxidized oils

A large amount of heavy oil inevitably encountered different degrees of isothermal low-temperature oxidation (LTO) reactions in the processes of in-situ combustion, storage, and transportation, so it was of vital importance to study the isothermal LTO kinetics of heavy oil that was still less well-understood. In this study, a thermogravimetry was used to study the isothermal LTO characteristics of heavy crude oil and its oils oxidized at 120, 160, and 200 °C, and four LTO temperatures of 125, 200, 275, and 350 °C with 1 h heating treatment were taken into account. The isothermal kinetic models were then established based on the n-order reactions. Subsequently, the comparisons of conversion degree between experiments and predictions were conducted to ensure the reliability of the established kinetics. The results showed that the mass losses for all the oil samples were almost linearly proportional to the LTO duration at 125 °C, indicating that the LTO time generated a significant effect on the thermal deposition. The shift rightward of the LTO peak with the elevated LTO temperature verified that the structures of all the oil samples were affected by LTO to a certain extent. After thermal degradation at 350 °C, 49.5% of LTO residue remained for the oxidized at 200 °C, obviously more than that for the other three oil samples. This gave a hint that the oils oxidized at higher LTO temperatures could be transformed into more fuel serving for combustion reactions. The appropriate values of reaction order of crude oil and its oils oxidized at 120, 160, and 200 °C were determined to be 4, 5, 5, and 7, respectively. There was no apparent difference in the values of activation energy, indicating that all the oil samples had close mass loss rates that determined the entire mass loss during isothermal LTO. The oil oxidized at 200 °C had fairly higher frequency factor than the other three oil samples, due primarily to its stronger polar molecular structure that resulted in higher molecular collision frequency. The prediction lines matched well with the experimental ones for all the oil samples, demonstrating that the developed isothermal kinetics was a useful tool to predict the LTO behavior of heavy oils.

Thermal degradation and kinetic studies of redwood (Pinus sylvestris L.)

AbstractIn this scientific paper, thermochemical conversion of redwood (RW) was studied. Using the thermogravimetric analysis' technique (TGA), the thermal behavior of RW samples was examined at four heating rates ranging from 5 to 20 K min−1 in inert atmosphere between 300 and 900 K. Two main objectives have been set for this study; the first one was the determination of the kinetic decomposition parameters of RW (Pinus sylvestris L.), and the second one was the study of the variation of characteristic parameters from the TG-DTG curves of the main RW's components, such as; cellulose, hemicellulose and lignin. The kinetic analysis was performed using three isoconversional methods (Vyazovkin (VYA), Friedman (FR) and Flynn-Wall-Ozawa (FWO)), Avrami theory method and the Integral master-plots (Z(x)/Z(0.5)) method to estimate activation energy (Ea), reaction order (n), pre-exponential factor (A) and model kinetic (f(x)) for the thermal decomposition of cellulose, hemicellulose and lignin components.The DTG and TG curves showed that three stages identify the thermal decomposition of RW, the first stage corresponds to the decomposition of hemicellulose and the second stage corresponds to the cellulose, while the third stage corresponds to the lignin's decomposition. For the range of conversion degree (x) investigated (0.1 ≤ x ≤ 0.7), the mean values of apparent activation energies for RW biomass were 127.60–130.65 KJ mol−1, 173.74–176.48 KJ mol−1 and 197.21–200.36 KJ mol−1 for hemicellulose, cellulose and lignin, respectively. Through varied temperatures from 550 to 600 K for hemicellulose, from 600 to 650 K for cellulose and from 750 to 800 K for lignin, the corresponding mean values of reaction order (n) were 0.200 for hemicellulose, 0.209 for cellulose and 0.047 for lignin. The pre-exponential factor's average values for three components of RW ranges from 0.08 × 1012 s−1 to 2.5 × 1012 s−1 (Ahemicellulose = 1.09 × 1012 s−1), 0.10 × 1014 s−1 to 0.28 × 1014 s−1 (Acellulose = 0.17 × 1014 s−1) and 3.07 × 1016 s−1 to 3.69 × 1016 s−1 (Alignin = 3.33 × 1016 s−1), respectively. The experimental data of RW had overlapped the D4, D2 and F3 in the conversion degree of 10–30%, 30–55% and 55–70% for the three components, respectively.

Exploring aging kinetic mechanisms of bio-oil from biomass pyrolysis based on change in carbonyl content

Bio-oil from biomass pyrolysis offers a wide range of applications such as transport fuels, value-added chemicals, materials, or heat and power generation. However, fresh bio-oil is unstable due to its physicochemical properties, chemical composition, and multiphase behaviors changing with time. The bio-oil aging kinetic model based on the change in carbonyl content was developed, and the pattern search method was proposed to optimize the model parameters. The accelerated and long-term aging kinetic behaviors of two bio-oil samples could be described accurately by the carbonyl-based aging kinetic model. The reaction rate constant values for the long-term and accelerated aging of bio-oil 1 were 1.694 × 10−4 and 4.589 × 10−2 h−1, whereas 3.084 × 10−4 h−1 and 1.329 × 10−1 h−1 were reported for bio-oil 2, respectively. The reaction order values of the long-term aging (2.452 for bio-oil 1 and 3.973 for bio-oil 2) were higher than that of the accelerated aging (0.943 for bio-oil 1 and 1.000 for bio-oil 2). Two bio-oil samples showed different aging kinetic characteristics due to different raw materials, pyrolysis reactor types and conditions, and bio-oil phases for aging tests. The hydration, hemiacetal, acetal and polymerization reactions of carbonyl compounds were the primary mechanisms for the change in carbonyl content during bio-oil aging.

Synergistic mechanism and decopperization kinetics for copper anode slime via an integrated ultrasound-sodium persulfate process

An eco-friendly synergistic decopperization method via ultrasound and sodium persulfate was developed from copper anode slime (CAS), a hazardous solid waste. The advanced oxidation process was applied to the field of metal leaching/enrichment in hydrometallurgy. Electron paramagnetic resonance (EPR) spectroscopy was used to trace the free-radical quenching mechanism in the leaching experiment. The influence of different conditions on copper leaching efficiency was studied. A total of 98.11% of copper was removed by the synergistic process from CAS. By comparison, the leaching efficiency of copper by persulfate leaching under the same conditions was only 66.64%. The kinetics model fitting results indicate that ultrasound reduced the threshold of the leaching reaction. The leaching reaction order values of the H2SO4 and Na2S2O8 concentrations are 0.11 and 0.69, respectively, which shows that persulfate plays a major role in leaching efficiency in the decopperization process. Mineralogical analysis demonstrated that the insoluble copper was effectively transformed into copper sulfate via ultrasound and sodium persulfate. In addition, hazardous solid waste was converted to valuable high-grade metallurgical stock through the enrichment of rare noble metals in CAS using a cooperative process. The novel decopperization method via integrated ultrasound/sodium persulfate has wide application prospects in waste management and recycling in a clean and economical hydrometallurgical process.

A Simple Direct Method to Obtain Kinetic Parameters for Polymer Thermal Decomposition

In a fire, the polymer combustion occurs when gaseous fuels react with oxygen. The heating of a material could force the release of gaseous fuels during thermal decomposition and pyrolysis. The rate of pyrolysis to define the gaseous fuels is usually interpreted by means of the Arrhenius expression and a reaction model expression, which are characterized by an activation energy, a pre-exponential factor, and a reaction order value. Many methods are available for determining kinetic parameters from thermogravimetric experimental data. However, the most challenging issue is achieving an adequate balance between accuracy and simplicity. This work proposes a direct method for determining the kinetic parameters with only a thermogravimetric experiment at a single heating rate. The method was validated with six polymers, and the results were compared with those from similar procedures, such as the Lyon method and generalized direct method. The results achieved using the simpler approach of the proposed method show a high level of accuracy.

The Curing Kinetics of E-Glass Fiber/Epoxy Resin Prepreg and the Bending Properties of Its Products.

The curing kinetics can influence the final macroscopic properties, particularly the three-point bending of the fiber-reinforced composite materials. In this research, the curing kinetics of commercially available glass fiber/epoxy resin prepregs were studied by non-isothermal differential scanning calorimetry (DSC). The curing kinetic parameters were obtained by fitting and the apparent activation energy Ea of the prepreg, the pre-exponent factor, and the reaction order value obtained. A phenomenological nth-order curing reaction kinetic model was established according to Kissinger equation and Crane equation. Furthermore, the optimal curing temperature of the prepregs was obtained by the T-β extrapolation method. A vacuum hot pressing technique was applied to prepare composite laminates. The pre-curing, curing, and post-curing temperatures were 116, 130, and 153 °C respectively. In addition, three-point bending was used to test the specimens’ fracture behavior, and the surface morphology was analyzed. The results show that the differences in the mechanical properties of the samples are relatively small, indicating that the process settings are reasonable.

Kinetic analysis of the pyrolysis of wood/inorganic composites under non-isothermal conditions

The pyrolysis kinetics of wood/inorganic composites was measured using one or two kinds of inorganic modifiers (CaCO3, SiO2–TiO2, and Mg–Al compounds) to study the pyrolysis behavior. Thermogravimetric experiments were carried out under nitrogen conditions and operated at different heating rates, ranging from 10 to 40 K/min. Model-free methods (Starink, Flynne-Wall-Ozawa, and modified Coats-Redfern) were used to evaluate the kinetic parameters, including apparent activation energy (Ea) and reaction order. For the range of conversion fractions investigated (20%-80%), the results yielded Ea values of 114–117 kJ/mol, 151–158 kJ/mol, 174–175 kJ/mol, and 153–156 kJ/mol for the unmodified poplar wood and modified poplar wood composites with CaCO3, SiO2–TiO2, and Mg–Al inorganic compounds, respectively. The corresponding reaction order values were 0.4485–0.8677, 0.0150–0.3694, 0.2021–0.5579, and 0.4336–0.8293, respectively. Wood impregnated with inorganic substances had good chemical modification effect. In addition, the kinetic mechanism function of the wood pyrolysis reaction was also studied. Results show that the heating diffusion mechanism model better describes the entire pyrolysis process of the modified wood compared with the control wood, which could be attributed to difficulty in the heat transfer process because of the thermal barrier effect of the inorganic layer and the resistance of gaseous products during pyrolysis. The stability of the wood/inorganic composites is therefore effectively improved.

Catalytic combustion of propane on Pd-modified Al–La–Ce catalyst – from reaction kinetics and mechanism to monolithic reactor tests and scale-up

Abstract A propane combustion catalyst was prepared by supporting of Pd on optimized multiphase composition, containing Al2O3, La2O3 and CeO2 aiming for possible application in catalytic converters for abatement of propane in waste gases. The catalyst characterization has been made by N2- physisorption, XRD, SEM/EDX, TEM and XPS. The obtained values for reaction order towards propane and oxygen are 0.57 and 0.14, respectively. The negative reaction order towards the water vapour (−0.26) shows an inhibition effect of the water molecules. According to the kinetics model calculations, the reaction pathway over Pd-modified La–Ce catalyst proceeds most probably through Langmuir–Hinshelwood mechanism with adsorption of propane and oxygen on different types of sites, dissociative adsorption of oxygen, whereupon water molecules compete with propane molecules for one and the same type of adsorption sites. For practical evaluation of the synthesized material, a sample of Pd/Al2O3–La2O3–CeO2, supported on rolled Al-containing stainless steel (Aluchrom VDM®) to form a single monolithic channel was prepared and tested. Two-dimensional heterogeneous models were used to simulate the propane combustion from laboratory reactor to full-scale adiabatic monolithic converter for ensuring an effective abatement of propane emissions.

Pyrolytic Characteristics and Kinetic Parameters Evaluation of Cassava Stalks Using Thermogravimetric Analyzer

Pyrolytic characteristics and kinetics of cassava stalks as a renewable energy source were delved via a thermogravimetric (TG) analyzer. About 10 mg powder of the sample was heated up in the TG cavity under inert conditions with 50 ml.min-1 nitrogen flow rate and operated at 20 °C min-1 of heating program. The pyrolysis process of cassava stalks was taken place into three main stages, in which the peak reaction occurred at the second stage with 70% of the mass was degraded. The differential method of Arrhenius kinetic evaluation resulted in the values of reaction order (n) that was 0.99, activation energy that was 89.46 kJ/mol and logarithmic frequency factor (log A) was 7.7 min-1.

Overcoming the Limitations of Transient Photovoltage Measurements for Studying Recombination in Organic Solar Cells

Transient photovoltage (TPV) measurements are frequently used to study recombination processes in thin‐film solar cells by probing the decay of a small optically induced voltage perturbation to infer the charge carrier dynamics of devices at open circuit. However, the validity of this method to probe organic semiconductors has recently come into doubt due to large discrepancies in the reported carrier lifetime values for the same systems and the reporting of unrealistic reaction order values. Herein, the validity of TPV to extract reliable charge carrier lifetimes in thin‐film solar cells is explored through the use of time‐dependent drift‐diffusion simulations and measurements. It is found that in low‐mobility materials, TPV serves primarily as a probe of charge carrier redistribution in the bulk rather than bulk recombination dynamics and that the extracted time constant is highly mobility dependent. To address this shortcoming, transient photocharge, a new technique to measure the charge carrier density during photovoltage decay, is introduced and applied to study the recombination dynamics in a series of (fullerene and nonfullerene) organic solar cell systems. It is shown that using this technique the charge carrier recombination lifetime in the active layer is more accurately determined.

Al2O3 based Co-Schiff Base complex catalyst in hydrogen generation

This work presents the study of the catalytic activity of aluminum oxide supported Co-Schiff Base complex derived from 4,4′-Methylenebis(2,6-diethylaniline)-3,5-ditertbutylsalicylaldimine-Co-Schiff Base complex in sodium borohydride hydrolysis. This catalyst is characterized with XRD, FT-IR, SEM, TEM, and BET. The respective reaction kinetics have been calculated. With the catalyst condition, maximum reaction (initial) rate is 106540 and 147193,3 mL H2/gcat..min. at 30 °C and 50 °C. For this reaction apparent activation energy is 44,7792 kJ.mol−1 with 20–50 °C. The reaction order value (n) for this catalytic system is 0,31. Additionally when Al2O3 supported Co-Schiff Base complex compared with pure Co-Schiff Base complex, the experimental results show that the aluminum oxide support exhibits enhancing effect with 106540 and 64147 mL H2/gcat. min respectively in sodium borohydride hydrolysis to Hydrogen production.

Stochastic Analysis of Multi-Reaction Model for Non-Linear Thermal History

Abstract This paper investigates the effect of non-linear thermal profile on the numerical solution of the multi-reaction model. According to the practical perspective, the temperature distribution at a different section of pyrolysis reactor is not necessarily following the ideal thermal history; therefore, it is necessary to predict the behaviour of the system for the higher degree of freedom. TG thermogram is obtained by the thermal degradation of pine needles sample in the thermogravimetric analyser (TGA). The activation energy, frequency factor, reaction order and the scale, shape and location parameters of a stochastic function are estimated for the non-linear parabolic thermal profile. The conventional Laplace integral is used to approximate the multi-reaction model. Activation energy obtained for the non-thermal profile lies in the range of 57.5–60 kJ·mol−1, whereas the frequency factor varies from 103–105 min-1. The obtained value of reaction order (n) lies in the domain of (0.9, 1.6).

Preparation and Characterization of Graphite Substrate Manganese Dioxide Electrode for Indirect Electrochemical Removal of Phenol

Manganese dioxide rotating cylinder electrode prepared by anodic deposition on a graphite substrate using MnSO4 solution in the presence of 0.918 M of H2SO4. The influence of different operational parameters (MnSO4 concentration, current density, time, and rotation speed) on the structure, and morphology of MnO2 deposit film was examined widely. The structure and crystal size determined by X-ray diffraction (XRD), the morphology examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The γ-MnO2 obtained as the main product of the deposition process. It found that the four parameters have a significant influence on the structure, morphology, and roughness of the prepared MnO2 deposit. The crystal size increases with MnSO4 concentration, current density, and rotation speed, and decreasing with time, while the roughness decreases with increasing all of four parameters. It found that the optimum conditions used in preparing MnO2 rotating electrode that gave the smallest crystal size, low roughness and less cracking were 0.33 M of MnSO4, 6 mA/cm2, 2 h, and 200 rpm. Electrochemical oxidation of phenol in a batch reactor was carried out in the presence of NaCl to examine the performance of the prepared MnO2 electrode for degrading phenol and any organic byproducts at different current densities. The results indicate that as the current density increased from 25 to 100 mA/cm2, the chemical oxygen demand (COD) removal efficiency was increased from 59.26 to 99.90%. Kinetics and the effect of temperature on the COD disappearance have been studied. It was clear that COD decreases with time and as the temperature increases, and the value of reaction order equals to 1 as has been found.

A further study of pyrolysis of carbon fibre-epoxy composite from hydrogen tank: Search optimization for kinetic parameters via a Shuffled Complex Evolution.

The study of hydrogen fuel cell vehicles is currently one of the popular research topics. However, a vital issue for hydrogen fuel cell vehicles is the hydrogen tank safety when hydrogen tank catch fires. In this paper, the carbon fibre-epoxy composite from hydrogen tank was investigated by thermogravimetric analysis. Thermogravimetric experiments were carried out at three heating rates (20, 30 and 40 K/min) in a nitrogen atmosphere. A two-step parallel reaction scheme was developed for the decomposition of the carbon-fibre epoxy composite based on the K-K method and previous studies. The kinetic reaction scheme was coupled to Shuffled Complex Evolution (SCE) method to obtain optimized kinetic parameters. The predicted values using the optimized kinetic parameters show a good agreement with the experimental data, which shows the potential promising application of the reaction scheme and optimized kinetic parameters of the carbon-fibre epoxy composite.

Influence of Aging Temperature on Precipitation Kinetics, Morphology and Hardening Behavior of Al-7475 Alloy

In this research, the precipitation hardening behavior of Al-7475 alloy is investigated by a comprehensive experimental study on the relationship between thermal aging and evaluation of the kinetics and hardening properties of the alloy. The investigation was carried out using X-ray diffraction analysis (XRD), differential scanning calorimetry, scanning and transmission electron microscopy investigations and Vickers hardness (HV) test. The XRD results show that increasing the aging temperature, from 273 to 620 K, enhances the coarsening and evolution of precipitates which leads to an increase in the particle size. The thermal analysis shows the precipitation kinetics of the observed phases such as $$\upeta '$$ , $${T}'$$ , and $$\upeta $$ , based on the correlation between migration and diffusion of spread atoms in the Al matrix. In addition, the TEM micrographs indicate that needle-shaped precipitates distinguish the development of $$\upeta '$$ and/or $${T}'$$ - precipitates which at most contribute to the material strengthening. Moreover, the reaction order values of $$\upeta '$$ and $$\upeta $$ -precipitate nucleation indicate that the developed phases are radially grown.

Kinetics of photocatalytic, self-cleaning surfaces: A decision tree approach for determination of reaction order

Self-cleaning photocatalytic surfaces have several decades of application, yet satisfactory rate equations for analyzing the kinetics of reactions on such solid surfaces are lacking, due in large part to the many configurations of the catalyst and the deposited contaminants.We analyze the existing literature and show that nearly all studies can be described by application of the power law for rate of reaction:Rate = kcat [C] nwhere n = apparent reaction order, and kcat is a fundamental constant of the catalytic material. The value of reaction order, n, we show requires answers to the following six questions. In each case, the observed apparent kinetic order depends upon interplay among the distributions of photocatalyst, reactant, and irradiance.1. Is the photocatalyst porous or non-porous?Example: Stearic acid on/within non-porous/porous photocatalyst layer.2. Is the photocatalytically active layer optically thin or thick?Example: Dye conversion in TiO2 layers vs. 10% TiO2/SiO2?3. Is the probe reactant deposit a submonolayer or multilayer?Examples: Dye sub/multilayers with TiO24. Is probe reactant light absorption negligible or important?Example: Stearic acid vs. soot5. Is the probe reactant present as a continuous film or as a distribution of discrete islands?Example: Long chain carboxylic acids on TiO26. If distributed, what is breadth of distribution?Example: Stearic acid on TiO2For contaminant removal we demonstrate apparent reaction orders of 0, ½, 1, and 2! Simple analysis is used to explain this diversity of apparent reaction orders. We use the six questions posed to construct a decision tree for determination of the apparent reaction order, n, as a function of responses to the six questions.

The Study on the Reaction Order and Kinetics of Total Oxidation Reaction of m-xylene over LaMnO3 Perovskite Catalyst

Gases of m-xylene is one of the popurlar toxic pollutants in the exhaust gases, it is emitted into the environment from factories and engines because the fuel in the engine does not burn completely. The best solution in order to remove this toxic gases of m-xylene to protect the environment is transforming them completely into CO2 and H2O by catalysts. Perovskite of LaMnO3 is one of the catalysts that was synthesized and studied the catalytic properties in total oxidation of m-xylene in our previous report. Obtained results showed that the LaMnO3 perovskite has good catalytic characterizations such as large surface area and the amount of α-oxygen adsorbed on the catalyst is large too. So, it exhibits a good catalytic activity in total oxidation of m-xylene at relatively low reaction temperature. In present work, the reaction order and kinetics of this reaction are determined. The obtained results demonstrated that the reaction order value with respect to m-xylene is equal to about 1, to oxygene is proximately equal to 0 and the order of reaction is equal to about 1. Based on reaction order data, it was thought that the pathway of m-xylene oxidation by air oxygen over LaMnO3 may be followed through which the Langmuir - Hinshelwood mechanism.
 Keywords
 Catalyst, perovskite, oxidation, m-xylene, kinetics
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Reliable method for determining the complete kinetic and thermodynamic information for thermal degradation of polymers in a multi-step process

Proposed approach enables a reliable determination of kinetic and thermodynamic behaviors for thermal degradation of polymers. As a model polymer, poly(ethylene oxide) with average molecular weight Mv ~ 100.000 (PEO100) was used. Two-component continuous distribution kinetics best describes PEO100 thermal degradation, involving two main reactions with different values of reaction orders. Procedure enables the check of existence of true or real enthalpy–entropy compensation (EEC). It was established that in the case of random scission reaction step, the artificial EEC emerges. For second reaction step which involves β-scission reaction step (“slow” step), true (real) EEC emerges. It was found that this reaction step is responsible for occurrence of successive micro-phase transitions. These transitions are associated with significant reduction of PEO100 crystallinity through a hinder effect on polymer chains. It was concluded that these transitions are cyclic and reversible, related to the change of mechanical properties of the polymer.

Kinetic study on iso-concentration hydrogen peroxide bleaching of poplar chemi-thermomechanical pulp by the process of continuous chemical supplement

In the authors’ previous studies, a bleaching process based on continuous chemical supplementation (CCS) was proposed to improve the effectiveness of peroxide bleaching of chemi-thermomechanical pulp (CTMP). In this study, the kinetic model of the CCS process of peroxide bleaching was applied to poplar CTMP to explore how the bleaching rate was affected. The model was based on the rate of chromophore elimination characterized by the brightness gains of bleached pulp. The reaction rate of chromophore destruction proceeded via a rapid initial phase followed by a slow phase. The equation of reaction rate was confirmed. The value of reaction order was -3.62, and the activation energy was 288.8 kJ/mol. The developed kinetic model was a good fit for the experimental results.