Global Activation Energy Research Articles

Exploring Corymbia torelliana hydrochar combustion kinetics through thermogravimetric analysis, peak deconvolution and reaction profile modelling.

This study aims to conduct an applied and innovative investigation to enhance the energy quality of wood residues through hydrothermal carbonization pretreatment. For this purpose, the treatment was carried out at three different temperatures: 180, 220, and 240°C under autogenous pressure. The in natura material and the hydrochars were characterized, and thermogravimetric analyses were performed in an O2 atmosphere with heating rates of 2.5, 5, 10, and 20°Cmin-1. The global activation energy for natura biomass combustion was determined to be 112.49kJ.mol-1. On the other hand, the hydrothermal carbonization process promoted a reduction in this value for the 94.85kJ.mol-1. The conversion function for the in natura biomass was characterized as , order 1, while the hydrochars was 2(1-α) [-ln(1-α)] (1⁄2), Avrami-Erofe'ev I. Triple kinetic parameters were ascertained, and the conversion curves along with their respective derivatives were modeled, exhibiting minimal deviations between theoretical and experimental data. This facilitated the mathematical representation of the reaction processes and allowed for a comprehensive comparison of the results.

Ignition Delay and Reaction Time Measurements of Hydrogen–Air Mixtures at High Temperatures

Induction and reaction times of hydrogen–air mixtures (ϕ = 0.5–2) have been measured behind reflected shock waves at temperatures of 1000–1600 K, pressures of 0.1, 0.3, 0.6 MPa in the domain of the extended second explosion limit. The measurements were performed in the shock tube with a completely transparent test section of 0.5 m long, which provides pressure, ion current, OH and high-speed chemiluminescence observations. The experimental induction time plots demonstrate a clear increasing of the global activation energy from high- to low temperature post-shock conditions. This trend is strongly pronounced at higher post-shock pressures. For a high-temperature range of T > 1200 K, induction time measurements show an activation energy for the global reaction rate of hydrogen oxidation of 64–83 kJ/mole. Detected reaction times exhibit a big scatter and a weak temperature dependence. The minimum reaction time value was nearly 2 µs. Obtained induction time data were compared with calculations carried out in accordance with the known kinetic mechanisms. For current and former shock-tube experiments within a pressure range of 0.1–2 MPa, critical temperatures required for strong (1000–1100 K), transient and weak auto-ignition modes behind reflected shock waves were identified by means of the pressure and ion-probe measurements in stoichiometric hydrogen-air mixture. The transfer from the strong volumetric self-ignition near the reflecting wall to the hot spot ignition (transient) was established and visualized below <1200 K with a post-shock temperature decreasing.

A tractable methodology for assessing the pressure scaling of sooting processes in a counterflow diffusion flame from 1 to 6 bar

A parametric study using ethylene as fuel was undertaken which examines the efficacy of concentration based and soot production rate (SPR) based parameters for assessing the pressure scaling of sooting processes in a counterflow diffusion flame. Two experimental designs pertaining to constant flow residence times (Case A), and constant carbon mass flux (Case B) were respectively implemented for pressures between 1 to 6 bars and across peak temperatures ranging from ∼2300−2600 K for Yf=Yox=0.35, ∼2100−2400 K for Yf=Yox=0.30, and ∼1800−2100 K for Yf=Yox=0.25 flames. A diffuse line-of-sight based extinction imaging diagnostic was employed for the measurement of soot concentrations. The evaluation of SPR follow a transport based coupling of inferred gaseous precursors, temperatures and velocity fields from detailed 1D OpenSMOKE++ simulations and soot concentrations from extinction measurements. The use of concentration based parameters, namely peak (∼p2.5−4.5) and integrated soot volume fractions (∼p2.1−3.9), is noted to be dependent on the Case A or B with little information discernible about the pressure effects in an experimental setting. The use of production rate based parameters, namely mean SPR (∼p2.2−3.4) removes the disparity of pressure scaling exponents across cases A and B but inherits the dependency to peak flame temperature, and gaseous precursor concentrations. An empirical fit of local SPR to acetylene and pyrene concentrations reveals a universal Arrhenius activation energy parameter in the high-temperature region (1300–2000 K) of the studied flames. The global activation energy is noted to remain roughly constant across varying peak flame temperatures, fuel flux, flow residence times and pressure. Consequently, we propose a soot yield parameter (Ω), calculated as the mean soot production rate normalized to acetylene and pyrene mass fractions which is noted to universally scale with pressure as Ω∼p1.7.

Role of O2 on nitrous oxide fuel blend ethylene auto-ignition sensitivity

An experimental and kinetic modeling study of the influence of O2 addition on the ignition behaviors of Ar diluted nitrous oxide/ethylene blend was performed. Ignition delay time (IDT) measurements were taken by detecting pressure evolution profiles in a heated rapid compression machine (RCM) at temperatures and pressures ranging from 910–1500 K to 35–45 bar. Results show that the addition of O2 significantly promotes the ignition of N2O/C2H4/Ar blend. With the O2 blending ratio increase from 10 % to 100 %, the IDT first decreases and then increases. Subsequently, the IDT data were employed to validate several kinetic models in literature. A reaction model developed in our previous work [Combustion and Flam, 2020, 221: 64-73] can reproduce the measured data and predict the promotion effect of O2 on N2O/C2H4/Ar blend well. Reaction pathway and rate of production (ROP) analyses show that high decomposition temperature of N2O inhibits the ignition of N2O/C2H4/Ar blend, whose ignition is mainly driven by reactions of N2O (+M) = N2 + O (+M) and N2O + H = N2 + OH. The dominant pathway is chain branching process: C2H4 + H/OH→C2H3 (+M)→C2H2 + O→HCCO + H2→CH2CO + H→CH3CO (+M)→CO + CH3. However, the presence of O2 in mixture induces reaction flux changes and decreases the global activation energy for chemical reaction. C2H3 radical is the main intermediate product during the ignition initial stage of C2H4 blends, whose ROP can reflect ignition process of C2H4 blends. For N2O/C2H4/O2/Ar and C2H4/O2/Ar ignition, C2H3 radical pool can be rapidly established via H-abstraction reaction of C2H4. However, the reaction of N2O + H = N2 + OH enhances the ROP of OH radical in N2O/C2H4/O2/Ar blends, resulting in C2H3 radical pool rapid establishment and a faster ignition.

Evidence of interstitial-mediated boron self-diffusion in boron carbide

Boron carbide is an important high-temperature material with interesting structural and functional properties. However, self-diffusion is very poorly known on this material, and also the few impurity diffusion studies, devoted in particular to helium and lithium, overlook the possible diffusion coupling with intrinsic defects. In this paper we present a study of boron self-diffusion in boron carbide based on first principles calculations and kinetic cluster expansion. Our results show that boron self-diffusion may occur with a migration activation energy on the order of 1.5–1.6 eV and with a global activation energy between 4 and 5.5 eV, depending on the doping conditions, which is significantly lower than the self-diffusion activation energies in other semiconducting carbides, like silicon carbide.We believe that our results are of interest for many applications of boron carbide and for tuning the best conditions for controlling the synthesis routes at specific stoichiometries for boron carbide.

Study on Pyrolysis Behaviors and Characteristics, Thermodynamics, Kinetics, and Volatiles of Single-Base Propellant, a Typical Energy-Containing Material

The widespread use of single-base propellant may contribute to serious pollution of the environment. The study of single-base propellant pyrolysis could provide an in-depth understanding of the combustion mechanism, reveal the key steps and reaction kinetics of the combustion process, and reduce the damage when using single-base propellant to the environment. In the present study, the pyrolysis behaviors, pyrolysis characteristic parameters, kinetics, thermodynamics, and volatiles of single-base propellant pyrolysis in an argon atmosphere were studied. The results showed that the main temperature ranges of pyrolysis and heat variation were 400–700 K and 450–520 K, respectively. With the increase in the heating rate, the maximum/average reaction rate of pyrolysis increased, the maximum instantaneous heat flow and the heat flow integral increased, the pyrolysis and combustion performance increased, and the thermal stability decreased. The average global activation energy and pre-exponential factor of the pyrolysis were 202.82 kJ and 9.48 × 1021, respectively. Thermodynamic analysis showed that the single-base propellant pyrolysis was a spontaneous endothermic reaction with a low energy barrier and fast reaction rate, which was beneficial to the formation of active complexes. In addition, information on the main volatiles was obtained, including H2, CH4, C2H4, C2H6, H2O, HCN, HCOOH, NO2, HONO, and CO2.

Thermal evaluation of plant biomass from the phytostabilisation of soils contaminated by potentially toxic elements

The combination of phytoremediation of soils contaminated by potentially toxic elements with energy production by combustion of the generated biomass can be a sustainable land management option, combining the production of renewable bioenergy with soil restoration while minimising energy consumption and CO2 emission. In this work, plant biomass from phytoremediation of soils contaminated by potentially toxic elements was studied as solid biofuel for combustion by thermal analysis and biomass composition. Six plant species were grown in two soils with differing degrees of contamination: Brassica juncea, Cynara cardunculus, Atriplex halimus, Nicotiana glauca, Dittrichia viscosa, Retama sphaerocarpa and Salvia rosmarinus. The composition of the plant biomass was characterised chemically and thermogravimetric analyses were performed for the mass loss (TG), derivative curves of mass loss (DTG) and temperature difference (DTA) signal. The cellulose concentration correlated with the parameters of the thermal analysis in the low temperature range (150–350 °C), while lignin correlated with the thermal parameters of the second peak in the high temperature range. Salvia rosmarinus and R. sphaerocarpa showed the best combustion characteristics according to the thermal profile and mineral residue results. The accumulation of potentially toxic elements in B. juncea grown in heavily contaminated soil led to a higher amount of residue at 750 °C, with a global activation energy lower than the one obtained when this species was grown in a soil with lower contamination. Therefore, the most beneficial combination of soil phytoremediation and energy production (combustion) that can be suggested would depend on the level of soil contamination: in heavily contaminated soil, phytostabilisation using R. sphaerocarpa and S. rosmarinus; in slightly contaminated soil, B. juncea due to its high energy of activation, although the concentrations of potentially toxic elements in the residue must be controlled, as well as possible particulate matter emissions during combustion.

Determining the global activation energy of methane–air premixed flames

In this work, the determination of the apparent activation energy of a global chemical reaction mechanism of the methane–air flames is revisited. The one-step formulation allows to derive the theoretical background for the method to measure the activation energy within the burner stabilised flame setup. The validity of this approach is demonstrated by using the numerical simulations with the detailed reaction model and direct thin filament pyrometry measurements of the temperature distribution in flame. The combination of numerical and experimental approaches allows us to find the activation energy for various mixture compositions. The prediction of numerical simulations and measured values of the activation energy is found to be in good agreement with each other and the data known from the literature. It is demonstrated that two critical phenomena need to be taken into account to obtain a reliable estimate of the activation energy: the flame blow-off and the onset of the diffusive-thermal instabilities. The effect of these critical events on the accuracy of the measurements is discussed as well as prospects of further investigation.

Distributed heat release effects on entropy generation by premixed, laminar flames

This article studies the generation of entropy disturbances by laminar premixed flames. The total entropy generation equals the integrated ratio of the local heat release rate and the local temperature, namely, [Formula: see text]. Due to this path dependency, evaluating this integral requires an understanding of how the heat release is distributed in the temperature space. Several studies evaluate the local entropy generation as [Formula: see text], where [Formula: see text] refers to the burned gas temperature, implicitly assuming all the heat release occurs at [Formula: see text]. Such an approximation is motivated by the high activation energy nature of combustion chemistry. This work evaluates this assumption by comparing it to results from one-dimensional premixed flame calculations for hydrogen, methane, and propane-air flames over a range of pressures, equivalence ratios, and preheat temperatures, quantified via the ratio [Formula: see text]. We show that this assumption is quite reasonable for methane and propane-air flames (with errors ranging from 5% to 25%) but deviates significantly from the exact results for hydrogen flames (where errors can be as high as 50%). In general, the peak heat release moves to lower temperatures as preheat temperature is increased. Noting that the temperature sensitivity of heat release is directly related to the activation energy, we use Law's approach to extract global activation energies and show that the deviations of [Formula: see text] from unity can be approximately correlated with [Formula: see text]. Finally, we show that significant improvements in entropy generation calculations can be obtained by estimating [Formula: see text] using [Formula: see text], where [Formula: see text] is the temperature at which the reaction rate peaks. This estimation leads to predictions of ∼5% within the exact value for the hydrocarbon cases but can still be in significant error for hydrogen at certain conditions.

Determination of Pyrolysis and Kinetics Characteristics of Chicken Manure Using Thermogravimetric Analysis Coupled with Particle Swarm Optimization

The valorization of chicken manure via pyrolysis can give biowaste a second life to generate value and contribute to the circular economy. In the present study, the thermal degradation and pyrolysis characteristics of chicken manure pyrolysis were investigated via thermogravimetric analyses (TGA) coupled with optimization methods. Thermogravimetric data were obtained for the samples at five heating rates of 5, 10, 20, 30 and 50 °C/min over a range of temperature under inert conditions. The manure devolatilization process was initiated at between 328 and 367 °C to overcome the global activation energy barrier. The determined activation energy of the manure via Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), Friedman and Kissinger methods was in the range of 167.5–213.9 kJ/mol. By using the particle swarm optimization (PSO) method, the pyrolytic kinetic parameters of the individual component present in the manure were calculated, in which the activation energy for cellulose (227.8 kJ/mol) was found to be higher than that of hemicellulose (119 kJ/mol) and lignin (134.3 kJ/mol). Based on intrinsic transition-state theory, the pre-exponential factor and activation energy of the manure can be correlated through a linear equation ln Aα = 0.2006 Eα − 1.2847. The devolatilization characteristics of the chicken manure were elucidated via the optimization process, paving the way for the design of thermochemical conversion reactors and processes.

Characterization and its curing behaviors of rigid phenolic foams based on cardanol

Cardanol/phenol-based foaming resol resins were prepared successfully by reacting formaldehyde with cardanol/phenol. Phenolic foams were fabricated with the above foaming resol resin and certain foaming agents. Two kinds of resol resins were characterized with Fourier transform infrared spectroscopy, rheological analysis and Scanning electron microscope. Meanwhile, the nonisothermal curing reactions of these resol resins were studied in detail using a dynamic Differential scanning calorimetry technique at a series of heating rates. The global activation energies of the reactions were determined with the Ozawa methods. The results indicated that the peak temperatures of the exothermic reactions and global activation energies of cardanol-based foaming resol resin were higher than those of phenol-based foaming resol resin, which indicated that the more complex molecular structure of cardanol-based foaming resol resin has a negative effect on the curing speed of resin.

Curing Kinetics of Bioderived Furan-Based Epoxy Resins: Study on the Effect of the Epoxy Monomer/Hardener Ratio

The potential of furan-based epoxy thermosets as a greener alternative to diglycidyl ether of Bisphenol A (DGEBA)-based resins has been demonstrated in recent literature. Therefore, a deep investigation of the curing behaviour of these systems may allow their use for industrial applications. In this work, the curing mechanism of 2,5-bis[(oxiran-2-ylmethoxy)methyl]furan (BOMF) with methyl nadic anhydride (MNA) in the presence of 2-methylimidazole as a catalyst is analyzed. In particular, three systems characterized by different epoxy/anhydride molar ratios are investigated. The curing kinetics are studied through differential scanning calorimetry, both in isothermal and non-isothermal modes. The total heat of reaction of the epoxy resin as well as its activation energy are estimated by the non-isothermal measurements, while the fitting of isothermal data with Kamal's autocatalytic model provides the kinetic parameters. The results are discussed as a function of the resin composition. The global activation energy for the curing process of BOMF/MNA resins is in the range 72-79 kJ/mol, depending on both the model used and the sample composition; higher values are experienced by the system with balanced stoichiometry. By the fitting of the isothermal analysis, it emerged that the order of reaction is not only dependent on the temperature, but also on the composition, even though the values range between 0.31 and 1.24.

Characteristics of Hydrothermal Carbonization Hydrochar Derived from Cattle Manure

The characteristics of hydrothermal carbonization hydrochar derived from cattle manure including excrements and lignocellulosic biomass were analyzed. The effects of hydrothermal carbonization were evaluated by varying the reaction temperatures in the range of 180~240 °C. The hydrochars were evaluated with respect to their usefulness as renewable fuels via physicochemical analysis and pyrolysis processes. As reaction temperatures increased, the fractions of fixed carbon in proximate analyses, carbon elements in ultimate analyses, and higher heating values of hydrothermally carbonized biochars increased in correlation with the primary reactions of coalification. Various correlations were derived with the characteristics of hydrochars in order to be utilized for operating and designing HTC reactors for cattle manure. The correlation between the O/C and H/C ratios was deduced on the basis of a van Krevelen diagram. The interaction equation was represented with the increased fraction of HHV compared to the reaction temperature of hydrothermal carbonization. The ultimate correlation for the estimation of higher heating values was suggested for HTC hydrochars. Moreover, the pyrolysis characteristics and kinetic parameters of the cattle manure and hydrochar were deduced by utilizing a multi-step kinetic model scheme. As the HTC reaction temperature increased, the global activation energy and the pre-exponential factors of hydrochars decreased in the low-temperature section and increased in the high-temperature section.

Green coconut fiber thermal behaviour under the presence of a cobalt spinel catalyst

With increasing environmental concerns, much effort has been spent in research regarding development ofsustainable processes for production of fuels and chemical products. In this context, hydrothermal liquefaction (HTL)has gained increasing attention, as a possible route for the chemical transformation of organic raw-materials, some sortof biomass, for example, into liquid oils at temperatures usually below 400 °C, under moderate to high pressures (5–25MPa), usually in the presence of a suitable catalyst. In the present work the thermogravimetric (TG) behavior underinert atmosphere of pure green coconut fiber and mixtures thereof with a spinel phase (Fe2CoO4), acting as catalysthas been studied. Spinel samples have been produced at 1,000 °C and different calcination times (3 h, 6 h and 9 h). Bothraw and synthesized materials were characterized through different techniques, such as scanning electron microscopy(SEM), X-ray diffraction (XRD) and Infrared Absorption Spectroscopy (FTIR). According to the TG data, the catalystproduced during a calcination time of 9 h showed a superior behavior regarding the lignin full thermal decomposition,which developed without fixed carbon formation. The results further suggest that the mixing process has a significanteffect over the measured degradation kinetics, as it has a direct influence over the contact between catalyst and fibers.The kinetic modelling applied to the dynamic TG signal allowed a quantitative representation of the experimental data.The global process activation energy and order have proven to be respectively, 85.291 kJ/mol and 0.1227.

Effect of losses on hydrogen–oxygen–argon detonation cell sizes

This work revisits the effect of losses on detonation characteristic length scales. Low-pressure experiments of the very regular hydrogen–oxygen–argon detonations in the straight narrow channel and along the exponentially diverging ramp were reported, demonstrating the significant role of losses in increasing detonation velocity deficits and cell sizes. Both the theoretically established and experimentally obtained relationships show the exponential sensitivity of detonation cell sizes to losses in terms of flow divergence, which is controlled by the global activation energy. The presence of losses modulates the lengthening of the characteristic detonation reaction zones and thus results in larger cell sizes, as indicated by the linear correlation characterizing the amplification of cell sizes and induction length. Moreover, the present work proposed an effective method for calibrating the ideal Chapman–Jouguet (CJ) detonation cell size from experiments, by adopting a revised formulism of Mirels' laminar-boundary-layer theory and also the generalized Zeldovich–von Neumann–Doering (ZND) model in the presence of flow divergence. Comparisons of the ZND-model calibrated ideal CJ detonation cell sizes from experiments with those from detailed numerical simulations show that, while differences still exist for the relatively high pressure cases, accounting for wall losses could excellently reconcile the discrepancy for the lower pressure cases, which appears to suggest no evident influence of the vibrational non-equilibrium effects for the hydrogen–oxygen–argon reactive system.

Application of general third-order Gaussian distribution activation energy model in the combustion of solid waste

ABSTRACT Solid waste had a variety of components, and its complex and obscure combustion behavior brought challenges to calculate the kinetic parameters accurately. Therefore, the thermogravimetric experiments of municipal solid waste and sewage sludge were carried out and a general third-order Gaussian distributed activation energy model was built. The combustion components of solid waste could be divided into three categories: light volatile components, heavy volatile components, and fixed carbon. The kinetic model matched the experimental data well, the adjR2 was above 0.9994 and the global activation energy was within a reasonable range of 54.85 kJ/mol-178.04 kJ/mol. Local sensitivity analysis found that the average activation energy had a strong influence on the stability of the model, and the degree of influence was positively correlated with the content of combustion components. In addition, the model had the ability to predict experimental data under unknown conditions.

Elucidation of the Diels–Alder Reaction Kinetics between Diphenylfulvene and Maleimide by Mechanochemistry and in Solution

The Diels–Alder reaction kinetics between diphenylfulvene and maleimide using mechanochemistry and in liquid state is described. This reaction was carried out in solid state using a modified vibratory ball-mill with temperature control and in solution with toluene as solvent. The effect of temperature, ball mass, material, additives, and aging reaction were studied. We reported for the first time the kinetics of a mechanochemical reaction depending on the ratio ball mass/mass of the reagent. A new kinetic model has been established that corresponds well to our experimental data and allows an estimation of the global activation energy. In solution, the retro Diels–Alder reaction was observed. The reaction was second order for the formation of endo and exo and first order for the retro Diels–Alder reaction. The grinding method shows many advantages compared to solution: shorter reaction time, total reaction, and better selectivity.

Experimental investigation of burning characteristics of porous combustible soaked in liquid oxidizer

Experimental investigations of burning characteristics of a tested specimen consisting of a polyethylene foam soaked in 100 wt% hydrogen peroxide are made. All experiments are carried out in a large volume chamber, which newly introduced in our previous work at an initial pressure range from p = 0.1 to p = 0.35 MPa in absolute with various fuel porosity range from ε = 0.6 to ε = 0.9, which corresponds to global equivalence ratios from φ = 0.51 to φ = 3.8. Temperature measurements using an R-type thermocouple embedded into the specimen are then conducted to investigate thermal structure (e.g., profiles of temperature and temperature gradients and burning surface temperature) of the burning specimen for deep understandings of the burning process. Following forced ignition at top surface of the specimen, steady successive-burning process is successfully observed for all conditions studied in this work. Burning rates (a rate at which the top surface moves downward) are measured by carefully tracking the top surface of the specimen by adopting an image processing software. Findings show that overall burning rates at the rate from 1 to 3.2 mm/s are obtained and influenced by pressure and the fuel porosity. Additionally, results of the direct temperature measurements reveal that the temperature gradient in the gas-phase layer near the top surface (burning surface) of the specimen increases as pressure increases, resulting in an increase in the overall burning rate. The top surface temperature and its pressure dependency, and a global activation energy at the top surface temperature of the specimen are experimentally measured accordingly.

Effect of nitrogen dioxide addition on ethane auto-ignition at different pressures and equivalence ratios: Experiments and chemical kinetic modeling

Ignition delay times of C2H6/O2/Ar mixtures with NO2 concentration changing from 0 to 2100 ppm were measured at T = 772–980 K, φ = 0.5–2.0 and p = 15–30 bar in a rapid compression machine. In general, the results show that NO2 addition significantly promotes ethane ignition and reduces its global activation energy. And NO2 promoting effect is more remarkable at fuel-lean and low-pressure condition at given NO2 concentration. The results also demonstrate that pressure shows smaller effect on the ignition of mixtures doped with NO2 than those on neat ethane ignition. Three literature NOx models are selected to validate against the new measured data set to evaluate their performances. Finally, sensitivity and flux analyses are conducted to identify the key reaction classes controlling the ignition of C2H6-NO2 mixtures.

Kinetic Study of the Herrmann–Beller Palladacycle-Catalyzed Suzuki–Miyaura Coupling of 4-Iodoacetophenone and Phenylboronic Acid

This article presents an experimental kinetic study of the Suzuki–Miyaura reaction of 4-iodoacetophenone with phenylboronic acid catalyzed by the Herrmann–Beller palladacycle. This catalyst, together with the solvent (ethanol) and the base (sodium methylate), were chosen to ensure catalyst stability and reactants solubility all along the reaction. Based on the study of initial reaction rates, a quasi-first-order was found for 4-iodoacetophenone with a first-order dependence on the initial concentration of palladium. A zero-order was found for the base and the phenylboronic acid. The oxidative addition step of the mechanism was thus considered as the rate determining step. A global rate law was derived and validated quantitatively. A global activation energy, with an average value of ca. 63 kJ/mol was determined.