Kinetic Compensation Effect Research Articles

Literature Review on Thermodynamic and Kinetic Limitations of Thermal Decomposition of Methane

The state of the art in methane pyrolysis does not yet provide a definitive answer as to whether the concept of an elementary reaction is universally applicable to the apparently simple process of methane dissociation. Similarly, the literature currently lacks a comprehensive and unambiguous description of the methane pyrolysis process and, in particular, a single model that would well represent its course at both the micro and macro scales. Given the wide range of conditions under which this reaction can occur—whether thermal or thermo-catalytic, in solid or fluidized bed reactors—it is crucial to evaluate the usefulness of different kinetic models and their compatibility with basic thermodynamic principles and design assumptions. To address these research gaps, the authors analysed the thermodynamic and kinetic dependencies involved in the thermal decomposition of methane, using the synthesis of methane from its elemental components and its reversibility as a basis for exploring suitable kinetic models. Using experimental data available in the literature, a wide range of kinetic models have been analysed to determine how they all relate to the reaction rate constant. It was found that regardless of whether the process is catalytic or purely thermal, for temperatures above 900 °C the reversibility of the reaction has a negligible effect on the hydrogen yield. This work shows how the determined kinetic parameters are consistent with the Kinetic Compensation Effect (KCE) and, by incorporating elements of Transition State Theory (TST), the possibility of the existence of Entropy–Enthalpy Compensation (EEC). The indicated correspondence between KCE and EEC is strengthened by the calculated average activation entropy at isokinetic temperature (∆SB=−275.0 J·(mol·K)−1). Based on these results, the authors also show that changes in the activation energy (E=20–421 kJ·mol−1) can only serve as an estimate of the optimal process conditions, since the isoconversion temperature (Tiso=1200−1450 K>Teq) is shown to depend not only on thermodynamic principles but also on the way the reaction is carried out, with temperature (T) and pressure (P) locally compensating each other.

Usefulness of insights into the kinetic compensation effects in the kinetic analysis of the coal gasification process

AbstractIn this paper, an attempt has been made to understand the kinetic compensation effects and their usefulness in the kinetic analysis of a lab‐based gasification study. The gasification experiment was carried out in two different gasifying environments, that is, 0.4%O₂ + 8%H₂O‐Ar and 8%H₂O‐Ar, for two different particle sizes of Loy Yang brown coal. Analysis of kinetic values with the change in particle size and gasifying environment was investigated. This provides information on the path of product gas formation and how the overall controlling factor affects the path of char gasification, including the rate‐limiting step. Furthermore, the results indicate that having multiple sets of kinetic parameters caused by the inclusion of the change in char properties into kinetics during solid–gas heterogeneous reactions opens up the scope for wider applications in chemical reaction engineering. This includes the design of a reactor with a proper kinetic model, optimization of feedstock, and process parameters with the identification of pathways for product gas formation, which ultimately plays a key role in scaling up technology from bench‐scale to plant‐scale. In contrast, the study of kinetics with having a single set of kinetic data based on the initial change in char properties limits its applications.

Cyclohexane dehydrogenation: Critical evaluation of parameter estimation procedures for kinetic modeling

In the present paper a comparison between different parameter estimation procedures commonly used for the kinetic modeling of chemical reaction is performed, based on experimental measurements of the cyclohexane dehydrogenation to benzene. The obtained results show that, when the Arrhenius equation parameters are estimated from estimates of the rate constant taken at different temperatures, larger parameter uncertainties and correlations are obtained, particularly when the variances of the experimental measurements are not considered during the estimation process. It is also observed that an apparent kinetic compensation effect occurs when the experimental data are separated according to the inlet partial pressure and catalyst mass in the reactor, mainly due to the existing and unavoidable experimental uncertainties and parameter correlations. Additionally, it is shown that larger uncertainties and correlations are obtained when the parameter estimates are computed through the differential method, which can also lead to poorer model predictions of the experimental data. Finally, it is shown that the simultaneous one-step estimation of all model parameters through the integral method and considering the available experimental uncertainties can provide the most accurate parameter estimates, making use of mathematical expressions that describe how variances of the experimental measurements depend on the experimental conditions.

Pyrolysis kinetics and reaction mechanism studies of 5-Amino-1H-Tetrazole with thermogravimetry/ differential scanning calorimetry/ Fourier transform infrared analysis

5-Amino-1H-Tetrazole (5AT) is extensively utilized in explosives, propellants and pyrotechnics as a high-nitrogen fuel or energetic material. Thermo-analysis is an efficient method to investigate the thermal decomposition characteristics of fuels or energetic materials, aiding in improving the safety and environmental performances of 5AT. In this study, the entire decomposition process of 5AT was explored using TG-DSC (thermogravimetry-differential scanning calorimetry) text. To accurately obtain the complete kinetic triplets, the iso-conversion activation energy for each stage was calculated using three conventional model-free approaches including KAS, Advanced Vyazovkin, and Starink methods, the results show that the activation energy results keep a good agreement by the three methods. Two different model-fitting methods (multiple heating rates CR method and the master-plots Criado method) were also introduced to predict the reaction model and calculate pre-exponential factors based on the iso-conversion activation energy results for the corresponding stages. The similarities and differences of the predicted results from these two different methods were compared, showing almost consistent findings that the first and third stages are controlled by the Fn and Dn model, respectively. Furthermore, the validity and the relationships were effectively verified and corrected based on the obtained kinetic parameters using the kinetic compensation effect, indicating the rationality of the selected kinetic methods and the calculated kinetic parameters for studying the pyrolysis characteristics of 5AT. Additionally, TG-FTIR (thermogravimetry combined with Fourier transform infrared) analysis was also conducted to identify characteristic groups and determine a potential pyrolysis pathway for 5AT. The findings in this paper can be used as input data for thermal safety, combustion, explosion and environmental protection model simulations.

A Study on the Pyrolysis Behavior and Product Evolution of Typical Wood Biomass to Hydrogen-Rich Gas Catalyzed by the Ni-Fe/HZSM-5 Catalyst

The thermo-chemical conversion of biomass wastes is a practical approach for the value-added reclamation of bioenergy in large quantities, and pyrolysis plays a core role in this process. In this work, poplar (PR) and cedar (CR) were used as staple wood biomasses to investigate the apparent kinetics of TG/DTG at different heating rates. Secondly, miscellaneous wood chips (MWC), in which PR and CR were mixed in equal proportion, were subjected to comprehensive investigations on their pyrolysis behavior and product evolution in a fixed bed reactor with pyrolysis temperature, catalyst, and the flow rate H2O steam as influencing factors. The results demonstrated that both PR and CR underwent three consecutive pyrolysis stages, the TG/DTG curves shifted to higher temperatures, and the peak temperature intervals also enhanced as the heating rate increased. The kinetic compensation effect expression and apparent reaction kinetic model of CR and PR pyrolysis were obtained based on the law of mass action and the Arrhenius equation; the reaction kinetic parameter averages of Ea and A of its were almost the same, which were about 72.38 kJ/mol and 72.36 kJ/mol and 1147.11 min−1 and 1144.39 min−1, respectively. The high temperature was beneficial for the promotion of the pyrolysis of biomass, increased pyrolysis gas yield, and reduced tar yield. This process was strengthened in the presence of the catalyst, thus significantly increasing the yield of hydrogen-rich gas to 117.9 mL/g-biomass. It was observed that H2O steam was the most effective activator for providing a hydrogen source for the whole reaction process, promoted the reaction to proceed in the opposite direction of H2O steam participation, and was beneficial to the production of H2 and other hydrocarbons. In particular, when the flow rate of H2O steam was 1 mL/min, the gas yield and hydrogen conversion were 76.94% and 15.90%, and the H2/CO was 2.07. The yields of H2, CO, and CO2 in the gas formation were significantly increased to 107.35 mL/g-biomass, 53.70 mL/g-biomass, and 99.31 mL/g-biomass, respectively. Therefore, H2 was the most dominant species among gas products, followed by C-O bond-containing species, which provides a method for the production of hydrogen-rich gas and also provides ideas for compensating or partially replacing the fossil raw material for hydrogen production.

Extended kinetic approach to reversible thermal decomposition of solids: A universal description considering the effect of the gaseous product and the kinetic compensation effect

The kinetics of the reversible thermal decomposition of solids, simplified as A(s) ⇌ B(s) + C(g), is universally described, as a function of temperature (T), degree of reaction (α), and partial pressure of gaseous product (p(C(g))) concerning the equilibrium pressure (Peq(T)) of the reaction, with the aid of an accommodation function (h(p(C(g)), Peq(T))). The kinetic curves of the reaction at different p(C(g)) values form a specific surface in the extended three-dimensional kinetic coordinate (T−1, α, ln[(dα/dt)/h(p(C(g)), Peq(T))]). The coordinate surface is characterized in terms of isoconversional and isothermal kinetic relationships. The apparent Arrhenius parameters that characterize the coordinate surface are related to the intrinsic Arrhenius parameters by considering the thermodynamic parameters of the reaction. In addition, all sets of Arrhenius parameters determined using the extended kinetic approach are correlated with the kinetic compensation effect. Herein, the extended kinetic approach was demonstrated, as exemplified by the thermal decomposition of CaCO3.

Thermogravimetric analysis and pyrolysis characterization of expanded–polystyrene and polyurethane–foam insulation materials

Expanded polystyrene (EPS) and polyurethane foam (PUF) are commonly used as building insulation material for energy savings; however, the fire risk is high because insulation material ignites easily and combusts upon exposure to external heat sources. Insulation materials are regarded as solid fuels, which undergo pyrolysis before combustion. Therefore, elucidating insulation material pyrolysis is an important aspect of efforts to predict combustion and fire phenomenon in these materials. Thermogravimetric analysis (TGA) was conducted to investigate the pyrolysis behavior of EPS and PUF in a nitrogen atmosphere using four heating rates. The results showed that the pyrolysis of EPS and PUF in nitrogen occurred through one- and two-weight loss reactions, respectively. Based on the pyrolysis temperatures obtained via TGA, the effective activation energies were determined using multiple model-free methods. The pre-exponential factors were calculated by applying the kinetic compensation effect from the reaction mechanism established using the model-fitting method. Additionally, the material activation energies and pre-exponential factors determined from experiments could be used as pyrolysis properties for numerical predictions of fire using the Fire Dynamics Simulator (FDS). Numerical simulations were conducted to validate the material activation energies and pre-exponential factors determined from experiments based on the FDS pyrolysis model.

Unlocking the potential of pequi (Caryocar brasiliense) residues for bioenergy and renewable chemicals: Multicomponent kinetic modeling, thermodynamic parameter estimation, and characterization of volatile products through TGA and Py-GC/MS experiments

The first study in the literature on the pyrolysis of pequi (Caryocar brasiliense) residues, focusing on the kinetic triplet, thermodynamic parameters, and characterization of volatile products utilizing TGA and Py−GC/MS techniques, is presented in this paper. Slow pyrolysis experiments were conducted on a thermogravimetric scale in a controlled atmosphere of pure nitrogen, with five distinct heating rates (5, 10, 20, 30 and 40 ºC min−1). The pyrolysis progress profiles were fitted using the Asym2Sig function to deconvolute the devolatilization rates of individual biomass pseudo-components, including extractives, hemicellulose, cellulose, and lignin. The average activation energies for pequi peel pyrolysis, as determined by the isoconversional methods of Friedman, Flynn−Wall−Ozawa, Kissinger−Akahira−Sunose and Starink, were higher (114.30 −319.13 kJ mol−1) than those estimated for pequi seeds (88.05 −168.39 kJ mol−1). The pre-exponential factors, obtained through the kinetic compensation effect method, exhibited a range of values between 3.6 × 1011 and 2.4 × 1030 min−1 for pequi peel and between 1.2 × 107 and 9.4 × 108 min−1 for pequi seeds. Utilizing the master-plots method revealed the involvement of F-type, A-type, and D-type reaction models in the pyrolysis of pequi residues. A slight difference between the Ea and ΔH values, less than 5 kJ mol−1, indicates the facile formation of reaction products during pyrolysis. The main organic volatile products obtained from the fast pyrolysis of pequi peel, as revealed by Py−GC/MS analysis, include furans, ketones, aldehydes, and ethers, constituting up to 52% of the total yield of the condensable fraction at 550 °C. Aliphatic hydrocarbons are the major organic volatile products derived from the fast pyrolysis of pequi seeds, accounting for approximately 74% of the total condensable fraction yield at 650 °C. This study provides new insights into the valorization of residues resulting from pequi fruit processing. As a result, a novel pathway for bioenergy and biobased chemical production via pyrolysis is established, aligning with the circular economy principle and capable of promoting energy matrix diversification.

Pyrolysis of cashew nutshell residues for bioenergy and renewable chemicals: Kinetics, thermodynamics, and volatile products

The present study's motivation and novelty are related to the potential of raw (RCNS) and pressed (PCNS) cashew nutshell residues for producing bioenergy and renewable chemicals through their physicochemical characterization and pyrolysis processing (multicomponent kinetic analysis, thermodynamic study, and volatile product analysis). A thermogravimetric analyzer and an analytical pyrolyzer coupled with gas chromatographymass spectrometry (Py–GC/MS) were used to perform the pyrolysis reactions. The pyrolysis behavior of RCNS and PCNS was accurately modeled with the help of the Asym2sig deconvolution function through five and four parallel devolatilization events, respectively. The average activation energies for the pyrolysis of RCNS and PCNS fell in the ranges of 63.8 − 249.3 and 91.1 − 167.4 kJ mol−1, respectively, as determined by four isoconversional methods (Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink). Pre-exponential factors ranging from 4.2 × 108 to 6.9 × 1016 min−1 (RCNS) and 4.8 × 108 to 3.2 × 1011 min−1 (PCNS) were estimated from the kinetic compensation effect. The master plots method evidenced that the most likely reaction models involved in the pyrolysis pertain to the nucleation-growth and n-order reaction mechanisms. Based on the multiple kinetic triplets acquired, the verification step of the summative rate expressions indicated excellent agreement between the simulated behavior and the experimental data, with a minimum quality of fit of 93.1%. The pyrolysis route can valorize both cashew nutshell residues to obtain renewable chemicals promoting the circular economy, as verified by Py-GC/MS analysis. Aliphatic hydrocarbons were the dominant components of the condensable volatile products at 650 °C, while reaction temperatures of 450 and 550 °C favored the production of oxygenated compounds. Due to the low potential energy barrier, the thermodynamic study attests to the viability of converting the studied residues into valuable products. The present results play an essential role in the utility of both cashew nutshell residues as inexpensive feedstocks for pyrolysis, possibly leading to bioenergy and biobased chemicals, which fall under the principle of valorization of lignocellulosic residues.

Assessing the impact of thermal maturation on the evolution of organic chemistry of Bakken Shale: Insights into oil generation

Early development of the Bakken Petroleum System recognized the significance of source rock maturation and the onset of oil generation in determining the geographic limits of production. The process of oil generation kinetics within source rocks involves intricate chemical reactions, where the nature of organic matter and thermal history influence the production of petroleum products. While simple models work well for some kerogen types (Type I), they fail for others (Type II and III), revealing the limitations of assuming invariant kinetic properties. This study explores the complexity of oil generation kinetics and its significance, particularly in the context of the Bakken Formation. Various methods have been used to identify the boundaries of oil sources, yet many are inductive. This research introduces a novel method to distinguish between catagenesis and diagenesis in Bakken's organic matter.A common linear relationship between activation energy (Ea) and frequency factor (ln(A)) appears in kinetic studies of source rocks, often attributed to statistical errors. This study investigates these relationships, revealing non-statistical compensation effects. Furthermore, extended kinetic models uncover a range of behaviors, highlighting the complexity of oil generation pathways. Notably, a kinetic compensation effect (KCE) is observed in the Bakken Formation, closely resembling findings for Type II kerogen. These compensation effects are not statistically forced, emphasizing their physiochemical origins. This research sheds light on the diverse KCEs within the Bakken Formation through a combination of experimental maturation, core analyses, and kinetic modeling. The study suggests that provenance, particularly for Type II kerogen, plays a crucial role in these effects. The data reveal multiple KCE patterns, including linear, inclined arch, and random clusters, with some transitioning between patterns during the oil generation process. These findings underscore the complexity of oil generation kinetics and its dependency on organic provenance. They also provide valuable insights for understanding oil reservoirs in the Bakken Formation and beyond.

Physicochemical investigation and thermogravimetric analysis of bamboo and poplar wood residues and tire rubber waste: Kinetic and thermodynamic analyses

This work conducted a physicochemical investigation of bamboo and poplar wood residues and tire rubber waste and their potential for conversion by pyrolysis from kinetic and thermodynamic aspects. The activation energies were obtained by means of a modified Friedman isoconversional method, with varying values of 133.0–248.4 kJ mol−1, 162.7–235.2 kJ mol−1, and 111.5–275.2 kJ mol−1 for the pyrolysis of bamboo and poplar wood residues and tire rubber waste, respectively. A combination of the kinetic compensation effect and a general empirical reaction model was used for the simultaneous determination of the frequency factors and empirical reaction models. The frequency factors of the pyrolysis of bamboo and poplar wood residues and tire rubber waste ranged from 1.5 × 109 to 4.7 × 1018 s−1, 1.2 × 1012 to 2.3 × 1018 s−1 and 1.3 × 107 to 3.4 × 1020 s−1, respectively. The effective thermodynamic parameters for the pyrolysis of bamboo and poplar wood residues and tire rubber waste were calculated, which indicated that these samples exhibited significant potential as raw materials for pyrolysis conversion.

Insights into pyrolysis of pearl millet (Pennisetum glaucum) straw through thermogravimetric analysis: Physico-chemical characterization, kinetics, and reaction mechanism

Millets and millet crop residues are gaining increasing attention. Present work provides insights into thermal degradation characteristics, pyrolysis indices, kinetic triplets, and thermodynamic parameters for pearl millet straw (PMS) pyrolysis. Pyrolysis indices revealed suitability of higher heating rates for PMS in terms of enhanced pyrolysis performance and shorter reaction time. Combined approach, encompassing model-free methods and model-based method, i.e. distributed activation energy model (DAEM) was employed to study kinetics. Average activation energy through Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, Friedman, Starink, Vyazovkin, and DAEM was found to be 189.61, 190.84, 192.71, 187.84, 193.33, and 191.08 kJ/mol, respectively. Statistical analysis through ANOVA using Tukey test demonstrated insignificant deviation for obtained activation energies. Kinetic compensation effect was employed to determine pre-exponential factor. Master plots revealed prevalence of random nucleation (R1 and R2) for α < 0.5 and diffusion (D1) and power law (P2) models for α > 0.5. Thermodynamic parameters revealed endothermic, non-spontaneous, and high degree of randomness for PMS pyrolysis.

Non-isothermal thermal decomposition behavior and reaction kinetics of acrylonitrile butadiene styrene (ABS)

Environmental concerns associated with the rapid rising plastic consumption have led to the search for better waste utilization and management. Pyrolysis has emerged as an ideal and promising technique for energy extraction from plastic waste. The aim of this work is to explore the waste plastic pyrolysis behavior under non-isothermal heating conditions. The decomposition characteristics, reaction mechanism, kinetics and thermodynamics of a typical widely used thermosetting plastic, acrylonitrile butadiene styrene (ABS), were studied via coupled thermogravimetry, Fourier transform infrared spectrometry and gas chromatography-mass spectrometry analysis (TG-FTIR-GC/MS). Kinetic analysis showed the average Eα values are estimated to be 187.02, 188.55, 187.04 and 185.67 kJ/mol via advanced Vyazovkin, Flynn-Wall-Ozawa (FWO), Tang and Starink model-free method, respectively. Model-fitting CR and master-plots method indicated that f(α)=(1-α)n is the most probable reaction mechanism. The equation of kinetic compensation effect was further developed as lnA = −3.1955 + 0.1736 Eα. Based on these initial inferences, a new reaction scheme coupled with Particle Swarm Optimization (PSO) was put forward for modeling ABS pyrolysis. The optimized values of E, A and n are 198.07 kJ/mol, 7.61 × 1012 s−1 and 1.56, respectively. The predicted results showed that the experimental data can be well characterized by the optimized parameters from PSO, validating the effectiveness and accuracy of the inverse modeling procedure. Moreover, it is found that the volatile products are mainly composed of aromatic compounds, ketones, amines, esters, nitrile compounds, alkenes and amines. Based on the FT-IR and GC-MS results, the possible chemical reactions for ABS pyrolysis from molecular structure were proposed. Finally, thermodynamic analysis was carried out, the calculated values of enthalpy ΔH, Gibb's free energy ΔG and entropy ΔS indicated that non-spontaneous reactions with low favorability exists during ABS decomposition, the process is complex therefore extra energy is needed to promote the reaction. The obtained results should offer as an important reference for future disposal and thermochemical management of such polymer waste.

Kinetic compensation effects of non-isothermal gasification in the diffusion control region

The aim of this study is to investigate the kinetic compensation effect during the non-isothermal gasification of coffee char and lignite char in a CO2 environment. The non-isothermal gasification experiments were carried out using a thermogravimetric analyzer in the temperature range of 321 K–1273 K. The activation energies (E) and pre-exponential factors (A0) of different diffusion control zones were determined, and the relationship between kinetic compensation effects and diffusion was investigated. This study shows that different kinetic parameter calculation methods have no influence on the kinetic compensation effect; intrinsic reaction or external diffusion has a very weak kinetic compensation effect, and only bed diffusion has a more obvious kinetic compensation effect. The kinetic compensation effect shows a dependence on bed diffusion.

Some new insights into the kinetic compensation effect in different diffusion-controlled domain for char-CO2 gasification

The CO2 gasification reaction of lignite and coffee char are conducted at 1098–1173 K and 0.025–0.1 MPa CO2 via thermogravimetry analysis (TGA). The calculation methods of the activation energy and pre-exponential factor are further compared and analyzed. The activation energy and pre-exponential factor in the chemical-controlled domain, the external diffusion-controlled domain and the bed diffusion-controlled domain are measured to investigate the relationship between the kinetic compensation effect and mass transfer limitations. Results reveal that the normalized power-law rate equation can provide reliable kinetic parameters due to PCO2n ≠ constant (PCO2n represents the partial pressure term) at different temperatures and f(X) ≠ constant (f(X) represents the mechanism function term) at different char conversion. In the chemical-controlled or the external diffusion-controlled domains, coffee grounds char (CGC) and lignite char (LC) exhibit similar activation energies and pre-exponential factors in the char conversion range of 0.2–0.8. In the bed diffusion-controlled domain, the activation energy and pre-exponential factor increase and then decrease during the reaction process. An evident kinetic compensation effect was observed between E and ln(A0) throughout the conversion process with bed diffusion and among data from experiments with and without diffusional limitations, showing its dependence on mass transfer limitations.

Isokinetic and Compensation Temperature in the Analysis of Thermal Dissociation of the Solid Phase under Dynamic Conditions

Sets of Arrhenius parameters, determined according to known different equations for dynamic conditions, in the vast majority form the Kinetic Compensation Effect (KCE). Converting these data to the simplified components of the Eyring equation comes down to Enthalpy–Entropy Compensation (EEC), which is consistent with the second law of thermodynamics. It has been proved that the impact of the generally known Coats−Redfern solution on the equation in differential form results in an isokinetic form of the equations and a very important coordinate T0;α0 (initial temperature and conversion degree), depending on the heating rate. This makes it possible to determine the parameters of Arrhenius’ law for both in silico and experimental data. An analytical method for determining this coordinate has been proposed. These considerations have given rise to an analysis of the relationship between two temperatures: initial and isokinetic. The sense of isokinetic temperature has been verified by the parameters CQF and K. Going further, it was found that the effects of EEC can be transformed into KCE and vice versa, which means that the two temperatures should be identical, i.e., Tiso=Tc. However, the experimental data indicate that the analyzed temperatures form a sequence T0↔Tiso↔Tc≤Teq, where Teq is the equilibrium temperature.

Assessing the potential of the invasive grass Cenchrus echinatus for bioenergy production: A study of its physicochemical properties, pyrolysis kinetics and thermodynamics

The current study aims to investigate the physicochemical properties and pyrolysis characteristics (kinetic triplet and thermodynamic parameters) of the invasive grass Cenchrus echinatus to assess its bioenergy potential. A thermogravimetric analyzer was employed to obtain the pyrolysis behavior of the grass under slow non-isothermal conditions. First, a multi-component deconvolution analysis of differential thermogravimetry (DTG) curves using the Fraser–Suzuki function was performed, aiming to quantify the individual devolatilization reactions of hemicellulose (P–HC), cellulose (P–CL), and lignin (P–LG). The survey of the activation energy employing four isoconversional methods (Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink) indicated the following devolatilization order: P–LG (329.9 − 376.7 kJ mol−1) > P–CL (178.4 − 188.2 kJ mol−1) > P–HC (157.8 − 161.2 kJ mol−1). With values of pre-exponential factors from 1.1 × 1015 to 1.4 × 1031 min−1, as estimated from the kinetic compensation effect, it was deduced that the chemical reactions with simpler nature are predominant. With the method of integral master plot, a geometrical contraction mechanism matched the devolatilization of P–CL, and an nth-order-based reaction model matched the devolatilizations of P–HC and P–LG. Besides, the thermodynamic study suggested that the conversion process is endothermic (ΔH≠ = 153.4 to 245.2 kJ mol−1) and nonspontaneous (ΔG≠ = 146.8 to 174.4 kJ mol−1). With the three kinetic triplets, one overall rate expression for the pyrolysis of invasive grass C. echinatus was established. The simulation results were then compared to experimental kinetic curves, and the agreement was deemed satisfactory. The outcomes from this research recommend the C. echinatus as a promising feedstock for bioenergy production and are decisive for scheming large-scale pyrolysis reactors for this invasive grass.

Thermal decomposition mechanism analysis of circulating solids sampled from Ende pulverized‐coal gasifier

AbstractEnde pulverized‐coal gasifier (EPCG) is a type of circulating fluidized bed gasifier, in which the circulating solids are resent into the furnace through a return conduit for regasification. Since the solid circulation in the return conduit mainly relies on gravity self‐balancing, it is easy to cause low and unstable solid circulation rate and increase unburned combustible of fly ash. To solve these problems, a circulation enhancement technique using an ejector to provide a stable pressure barrier to promote solid circulation was proposed. To verify its feasibility, considering that the circulating solid‐CO2 reaction is a rate‐controlling step in the gasification process, it is of great significance to explore the reactivity characteristics of the circulating solids under CO2 atmosphere. In this work, thermal decomposition characteristics of Hailar circulating solids (HLE‐CS), Hailar char (HLE‐C), and Shenhua circulating solids (SH‐CS) were investigated by non‐isothermal thermogravimetric analysis to compare the gasification reaction characteristics of circulating solids and char. The HLE‐CS and SH‐CS used in the experiments were taken from the return conduit of 45,000 and 20,000 Nm3/h EPCGs, respectively, while HLE‐C was made from the raw coal of 45,000 Nm3/h EPCG. The effects of different samples under the same thermal decomposition temperature range were investigated. The kinetic parameters were determined by the distributed activation energy model. The results indicated that remarkable peaks were found in the relationship between temperature (T) and activation energy (E) for HLE‐CS and SH‐CS, but there was no significant peak for HLE‐C, and kinetic compensation effects also existed between ln(k0) and E for different samples. The circulating solids of HLE‐CS and SH‐CS were more easily gasified than that of HLE‐C in the lower temperature ambience. Moreover, HLE‐CS and SH‐CS have obvious pyrolysis and gasification stages, which can be completely introduced into EPCG for regasification, and increasing the circulating solid rate and temperature within a certain range is beneficial to enhance the gasification rate.

A Physical Basis for Kinetic Compensation.

Kinetic compensation is a strong, positive correlation between the Arrhenius activation energy E and the frequency factor A for a reaction between the same reactants under similar experimental conditions or similar reactants under the same conditions, even though these parameters are supposed to be independent. The kinetic compensation effect (KCE) is demonstrated by a linear relationship between ln[A] and E/R in the eponymous Constable plot and has been the subject of more than 50 000 publications over the past 100 years, with no consensus opinion about the cause of this effect. In this paper, it is suggested that the linear relationship between ln[A] and E is the result of a real or spurious path dependence of the reaction history between the initial state of the pure reactant(s) and the final state of the pure product(s) having standard enthalpy and entropy differences, ΔH° and ΔS°, respectively. The single-step rate law approximation of a reversible reaction leads to T0 = H°/ΔS° as the dynamic thermal (thermodynamic) equilibrium temperature and 1/T0 = (ln[A̅/k0])/(E̅/R) as the slope of a Constable/KCE plot or the crossover temperature of Arrhenius lines in an isokinetic relationship (IKR), where A̅ and E̅ are mean values for the ensemble of compensating {Ei, Ai} pairs and k0 is a constant that accounts for the path dependence of the reaction history and reconciles the KCE with the IKR. This proposed physical basis for the KCE and IKR is supported by qualitative agreement between ΔH° and ΔS° calculated from the statistics of compensating {Ei, Ai} pairs in the literature, and the difference in the standard enthalpies and entropies of formation of the products and reactants for thermal decomposition of organic peroxides, calcium carbonate, and poly(methyl methacrylate).

A non-isothermal thermokinetic degradation study of the mesoporous Ni–Co layered double hydroxide using isoconversional approaches

The present study describes the phenomenological thermokinetic behavior of the mesoporous Ni–Co layered double hydroxide (LDH) and determines three basic parameters called ‘kinetic triplets’. The non-isothermal kinetic heating program was carried out at four different heating rates, viz. 5,10,15, and 20oC.min−1, respectively, in the temperature range of 50−800oC. Various isoconversional or model-free kinetics involving integral and differentials like Kissinger–Akahira–Sunose, Flynn-Wall-Ozawa, Friedman, and non-linear Vyazovkin methods were utilized. Due to the presence of physisorbed gas or moisture phases, the temperature integral from 50−198oC was excluded from the present study. The experimental and simulation results described the consistency in depicting the effective activation energies by either Friedman or non-linear Vyazovkin isoconversional methods. Also, it was observed that the variation in activation energies was found to differ by 9–10%, which confirms the Ni–Co LDH degradation undergoes a kinetically complex process. The evaluation of the preexponential factor and master plot determination of reaction models f(α) showed that the mesoporous Ni–Co LDH degradation pathway strongly depends on kinetic compensation effect and undergoes a reaction process governed by nucleation models. Furthermore, the kinetics of pseudo-components of Ni–Co LDH (mathematical deconvolution analysis) showed that the second (three subtransitions) and third stage (two subtransitions) degradation process are controlled by a number of individual peak components in the thermodynamic temperature range 536–727 K (second) and 727–803 K (third).