Model-fitting Methods Research Articles

Studies on the thermal stability and decomposition kinetics of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide via density functional theory and experimental methods

• The types of decomposition products of [Emim][NTf 2 ] were analyzed through the TGA-FTIR technology. • Model-free and model-fitting methods were utilized to analyze reaction kinetics of [Emim][NTf 2 ] under inert gas. • The E α and f (α) of [Emim][NTf 2 ] under inert gas were obtained by thermal analysis kinetic calculation. • DFT theory coupled with thermal analysis methods provided a significant reference for investigating ionic liquids. Imidazole ionic liquids have potential applications in gas capture processes such as carbon dioxide capture carried out under high-temperature conditions. Therefore, it is of great significance to explore the thermal stability and thermal decomposition of imidazole ionic liquids. In this work, the thermal stability and decomposition characteristics of an imidazole ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][NTf 2 ]) were investigated by thermogravimetric analysis combined with Fourier transform infrared spectroscopy experiments under nitrogen conditions. The structure of [Emim][NTf 2 ] was optimized by density function theory (B3LYP/M06-2X) with a 6–311++G(d,p) basis set. In the reaction kinetics section, model-free methods (Friedman, FWO, KAS) and a model-fitting method (Coats-Redfern) were utilized for the evaluation of kinetic data for [Emim][NTf 2 ] following ICTAC recommendations. The optimum mechanism model of [Emim][NTf 2 ] under nitrogen conditions was determined from these different kinetic methods. Decomposed gaseous products of [Emim][NTf 2 ], which were obtained from thermogravimetric experiments, were simultaneously analyzed by Fourier transform infrared spectroscopy. Finally, the possible decomposition mechanism and gaseous products of [Emim][NTf 2 ] were also discussed. The whole work was meant to combine the experimental and theoretical results to provide a feasible research route for the thermal composition stability and mechanism of ionic liquid [Emim][NTf 2 ] and a significant reference for further investigations into the thermal decomposition characteristics of universal ILs.

Influence of Organic-Inorganic Composition on the Adsorption of Niutitang Formation Shale in Huijunba Syncline

To study the influence of different organic-inorganic composition on the adsorption in shale, taking the Niutitang Formation shale in the Huijunba syncline in southern Hanzhong as the research object, based on acid treatment to extract kerogen and wet chemicals. Extracting mineral components by oxidation method, a series of isothermal adsorption experiments were carried out on the original rock, kerogen, and mineral components of the samples. Through the three-dimensional Langmuir model fitting and adsorption thermodynamic calculation method, the adsorption thermodynamic parameters such as the isometric heat of adsorption and the standard adsorption entropy are obtained. The research results show that organic matter is the primary factor affecting the methane adsorption of shale and clay minerals also affect the adsorption to a certain extent. When the burial depth is relatively shallow, diagenesis has a promoting effect on the total amount of adsorption. As the depth increases, the diagenesis will turn into an inhibitory effect on the total amount of adsorption. Through the component weighting method, the lower limit ratio of the adsorbed amount of organic matter to the total amount in the shale is 29.3%~46.7% when the depth reaches to 3000 m, while the upper limit ratio of the adsorption of mineral components is 66.4%~73.6%.

Visual Art Design of Digital Works Guided by Big Data

With the rapid development of digital technology, the development speed of digital media is also relatively fast. Digital media technology has a great impact on people’s lifestyles and aesthetic concepts, and it also has a greater impact on visual art, creative thinking communication methods, and expression methods. In this study, the quality enhancement of digital images has been intensively studied based on the guidance of big data of eye-movement gaze points. A large amount of visual data are collected from public social resources, and the optimization research of image sensory quality is carried out in-depth using the acquired big data. Next, the region of interest (ROI) is obtained by combining the data with a two-dimensional Gaussian distribution model-fitting method, and the obtained data clustered and improved based on the K-means clustering algorithm to obtain ROI fixation points. Finally, discontinuities in the choice of sharpness in graphics and video playback are pointed out, and the final fixation data analysis is utilized. Results show that targeted optimization is very effective in improving the quality of digital images and saving space, enabling users to enjoy higher-quality visual digital images. The proposed method can be used to improve the dynamic resolution of images and videos.

Determination of potential thresholds for N-ethyl-N-nitrosourea and ethyl methanesulfonate based on a multi-endpoint genotoxicity assessment platform in rats

The main goal of the study was to investigate the genotoxic response of N-ethyl-N-nitrosourea (ENU) and ethyl methanesulfonate (EMS) at low doses in a multi-endpoint genotoxicity assessment platform in rats and to derive potential thresholds and related metrics. Male Sprague–Dawley rats were treated by daily oral gavage for 28 consecutive days with ENU (0.25 ~ 8 mg/kg bw) and EMS (5 ~ 160 mg/kg bw), both with six closely spaced dose levels. Pig-a gene mutation assay, micronucleus test, and comet assay were performed in several timepoints. Then, the dose–response relationships were analyzed for possible points of departure (PoD) using the no observed genotoxic effect level and benchmark dose (BMD) protocols with different critical effect sizes (CES, 0.05, 0.1, 0.5, and 1SD). Overall, dose-dependent increases in all investigated endpoints were found for ENU and EMS. PoDs varied across genetic endpoints, timepoints, and statistical methods, and selecting an appropriate lower 95% confidence limit of BMD needs a comprehensive consideration of the mode of action of chemicals, the characteristics of tests, and the model fitting methods. Under the experimental conditions, the PoDs of ENU and EMS were 0.0036 mg/kg bw and 1.7 mg/kg bw, respectively.

Effect of coal grade and heating rate on the thermal degradation behavior, kinetics, and thermodynamics of pyrolysis of low-rank coal

ABSTRACT The work investigates the thermal degradation characteristics, kinetics, and thermodynamics of low-rank coals of three different grades selected from coal mines of Odisha, India by thermogravimetric analysis in temperatures ranging from 30°C to 1000°C under a nitrogen atmosphere at five heating rates of 5, 10, 15, 20, and 25°C min−1. The kinetic parameters are computed using model-fitting methods assuming first-order kinetics in the 250–635°C temperature range of major weight loss. The average activation energy of the reaction at different heating rates is found to be in the range of 55–65 kJ/mol. The average entropy change is found to vary from −180.03 to −165.887 J/K/mol1, the average enthalpy change varies from 51.1758 to 57.574 kJ/mol and that of free energy change varies from 189.718 to 177.9 kJ/mol. In addition, the composition of the oil obtained by pyrolysis of the coal in a semi-batch reactor at different temperatures is analyzed by FTIR and GC-MS techniques. The composition of the oil is found to be affected by the pyrolysis temperature.

In-depth study on reaction kinetics of porous charred layer with high temperature alumina deposition in solid rocket motor

Current understanding of insulators abnormal ablation caused by alumina deposition in solid rocket motors (SRMs) is limited. The ability to calculate its thermochemical kinetic parameters and establish the corresponding ablation model determines the height of the thermal protection system design for advanced SRMs. In this work, the reaction mechanism of interaction between α-alumina and porous charred layer under deposition conditions was proposed firstly. Then the isothermal thermogravimetric experiments at 1750-1900 °C were carried out for the reaction system. The TG and DTG curves under various reaction conditions were treated by isoconversional method and model-fitting method, respectively, and the corresponding kinetic parameters and reaction models were calculated. Finally, based on the above research results, a deposition ablation model was established and the corresponding calculation code was compiled. Results show that the reaction of α-alumina/ porous charred layer system is formed by the superposition of four steps. The reaction model and kinetic parameters of each step reaction are as follows: steps 1 and 4 follows the diffusion control model (D3) with activation energies Ea of 109.6 kJ·mol−1, 47.9 kJ·mol−1 and frequency factors A of 47.9 min−1, 0.4 min−1, respectively, step 2 follows the chemical reaction control model (F1) with Ea of 48.5kJ·mol−1 and A of 14.8 min−1, and step 3 follows the contracting area model (R2) with Ea of 41.9kJ·mol−1 and A of 3.9 min−1. The insulator's ablation thickness calculated by the deposition ablation model established in this paper has an error of 16.01% compared to that in the experiment, indicating that it can be used to accurately calculate the ablation characteristics of insulators under the alumina deposition conditions in the future work.

Kinetics mechanism of inert and oxidative torrefaction of biomass

Torrefaction of biomass is a promising pre-treatment process capable of substantially improving the properties of raw biomass for its use as a solid biofuel, among many other potential applications. Oxygen-lean torrefaction can effectively reduce the cost and complexity of inert torrefaction. In this work, torrefaction tests of crushed olive stones were conducted in a thermogravimetric analyzer in various oxygen concentrations, under both non-isothermal and isothermal conditions. Non-isothermal torrefaction measurements were used to gain fundamental knowledge on the inert and oxidative torrefaction processes by applying a model-fitting kinetics method. Analysis of these measurements showed that an accurate description of inert torrefaction based on a two-step reaction mechanism is possible, whereas a three-step reaction mechanism is necessary for oxidative torrefaction. The new three-step mechanism was found to be accurate for describing the global mass loss during isothermal torrefaction, obtaining average root mean squared errors between the model predictions and the TGA measurements below 2.0 % for inert and oxidative torrefaction of olive stones. Furthermore, predictions using the extended mechanism were in good agreement with the more fundamental torrefaction reactions derived from the kinetics analysis of the non-isothermal torrefaction measurements.

Investigation of Synergistic Effects and Kinetics on Co-Pyrolysis of Alternanthera philoxeroides and Waste Tires.

A thermogravimetric analysis is used to analyze the thermal kinetics and investigate the synergistic effects between Alternanthera philoxeroides (AP) and waste tires (WTS) in a temperature range of 50–900 °C under three heating rates (15, 25, and 35 °C/min). Two model-free methods (FWO and KAS) and a model-fitting method (CR) were applied to calculate the activation energy. Results revealed that heating rates had no significant effect on the pyrolysis operation. The addition of WTS improved the thermal degradation of the samples as the samples had more than one stage during the main reaction period. A promoting synergistic effect was found in the blend 75A25WT and obtained the lowest activation energy among all the blends without a catalyst, while the blend 50A50WT exhibited an inhibiting effect. On the other hand, the addition of HZSM-5 accelerated the reaction time and obtained the lowest activation energy among all the blends without a catalyst. Furthermore, ΔW of 75A25WT+C was the lowest, indicating that the blend with a catalyst exhibited the strongest synergistic effect. This research confirmed that the addition of WTS improved the thermal parameters of the samples and clarified the capacity of HZSM-5 to reduce the activation energy.

Detecting crop phenology from vegetation index time-series data by improved shape model fitting in each phenological stage

Crop phenology provides important information for crop growth management and yield estimations. The popular shape model fitting (SMF) method detects crop phenology from vegetation index (VI) time-series data, but it has two limitations. First, SMF assumes the same “relative position” of phenological stages for the pixels of the same crop type. This assumption is valid only if all target pixels, relative to the shape model, display a synchronized increase (or decrease) in length between any two phenological stages, which is uncommon in practice. Second, the variance in the resulting phenology estimates for a particular phenological stage is related to the stage itself; this makes it challenging to simulate spatial and temporal variations in crop phenology using SMF. Here, we address both limitations by developing the shape model fitting by the Separate phenological stage method (“SMF-S"). SMF-S uses a modified fitting function and an iterative procedure to match the shape model with the VI time series for each phenological stage in an adaptive local window. Comparisons between SMF-S and SMF in simulation experiments show the superior performance of SMF-S in different scenarios, regardless of noise. Comparisons involving winter wheat field observations from the North China Plain showed that the RMSE values averaged over nine phenological stages were smaller for SMF-S (RMSE = 9.5 d) than for SMF (RMSE = 13.4 d) and one variant of SMF (the shape model with accumulated growing degree days (SM-AGDD); RMSE=33.6 d). Moreover, SMF-S better described the spatial variations (i.e., variance) in the results and captured the temporal shifts in multiple phenological stages. In the derived regional phenology maps of winter wheat on the North China Plain, SMF-S generated more reasonable spatial patterns, whereas SMF underestimated (overestimated) the variance in the early (late) phenological stages. We expect that the improved crop phenology estimates obtained with SMF-S could benefit various agricultural activities.

Fusion method of model-free and model-fitting for complex reactions in accelerating rate calorimetry

At present, the kinetic approaches of accelerating rate calorimetry (ARC) are restricted to model-fitting methods, and the n-order reaction model is mainly used to estimate the kinetic parameters. However, the model-fitting method has the problems related to model selection and falling into a local optimum. To address these issues, kinetic analysis methods are introduced into ARC data treatment, and the kinetic parameters of complex reactions are solved by a model-free and model-fitting fusion method. First, the Friedman method is used to calculate the activation energy Eα. Then, Aα and the overall mathematical function f(α) are obtained through the compensation effect. It provides references for the selection of the reaction model and initial values of model fitting, and the kinetic parameters are estimated through two-step model fitting. The fitting in steps realizes the decoupling of E and A and reduces the data dimensions. These help to reduce the chance of falling into a local optimum and lower the experience requirements. Finally, numeric simulations and the experimental results showed the effectiveness of the method.

Pyrolysis Evaluation of Tennis String Polyurethane and Water-Borne Polyurethane Wastes through Isoconversional Kinetic Analysis.

A detailed kinetic analysis of pyrolysis processes of Tennis string polyurethane (TSPU) waste and waterborne polyurethane (WPU) waste was carried out in the present paper. Non-isothermal pyrolysis characterizations of two wastes were acquired through thermogravimetric determinations under the constant heating rates of 5, 10, 15 and 20 K/min. Experimental results showed that the pyrolysis processes of TSPU and WPU were mainly characteristic of three stages and two stages, respectively. Two pyrolysis performance indices, the devolatilization index (DI) and heat-resistance index (HRI), were used to interpret the heating rate effect on the pyrolysis features and different thermal dependences of TSPU and WPU. Isoconversional kinetic analysis was thoroughly performed with model-free and model-fitting methods. By using Starink, Vyazovkin–Dollimore and Coats–Redfern methods, the activation energies thus obtained were in the range of 103.3~148.3 kJ/mol and 92.5~204.3 kJ/mol, respectively, for TSPU and WPU, over the entire pyrolysis process. Their respective pre-exponential factor lnA values were determined to be within 17.94~33.42 min−1 and 16.56~20.82 min−1. Thermodynamic parameters in terms of ΔG#, ΔH# and ΔS# throughout the entire pyrolysis process were also calculated. Finally, by means of the model-fitting Coats–Redfern method, the most appropriate mechanism functions were ascertained for, respectively, describing multi-stage pyrolysis degradations of TSPU and WPU waste. These results may offer meaningful support for designing any industrial pyrolysis reactor to dispose of polyurethane wastes.

Kinetic Study on The Slow Pyrolysis of Isolated Cellulose and Lignin from Teak Sawdust

This study was conducted to explicate the stages of biomass pyrolysis by using a comprehensive kinetics study. The pyrolysis was performed on teak sawdust and its isolated klason lignin and cellulose. Pyrolysis experiments were carried out on Thermogravimetric Analysis (TGA) with 3 different heating rates at 5, 10, and 20 K min−1. The results were analyzed with 2 model-free methods of Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW), and a model-fitting method of nth-order Distributed Activation Energy Model (DAEM). The model-free kinetics analyses using KAS and OFW methods gave consistent activation energy trends for all samples. In teak sawdust pyrolysis, the activation energy fluctuates with the increase of conversion between 235-252 kJ mol−1. For cellulose, the activation energy increased along with the conversion from 208 to 240 kJ mol−1. Whereas for lignin, the activation energy widely ranges between 80-250 kJ mol−1. Further exploration using the multi-component nth-order DAEM was conducted to provide deeper insight on multistage pyrolysis reaction. The 4 components DAEM successfully provided a satisfying mathematical fit to the experimental data of teak sawdust pyrolysis. The proposed model was able to capture the two stages of lignin pyrolysis. The method that has been demonstrated here gave a broader insight to the application of DAEM in describing lignocellulosic biomass pyrolysis.

Computationally efficient parameter estimation for spatial individual-level models of infectious disease transmission

Individual-level models incorporate individual-specific covariate information, such as spatial location, to model infectious disease transmission. However, fitting these models with traditional Bayesian methods becomes cumbersome as model complexity or population size increases. We consider a spatial individual-level model with a binary susceptibility covariate. A method for fitting this model to aggregate-level data using traditional Metropolis–Hastings MCMC and then disaggregating the results to obtain individual-level estimates for epidemic metrics is proposed. This so-called “Cluster–Aggregate–Disaggregate” (CAD) method is compared to two approximate Bayesian computation (ABC) algorithms in a simulation study. The methods are also applied to a data set from the 2001 U.K. foot and mouth disease epidemic. While the CAD and ABC methods both performed reasonably well at capturing epidemic metrics, the CAD method was found to be much easier to implement and reduced computation time (relative to the traditional model-fitting method) more consistently than the ABC methods.

Nonisothermal kinetic analysis of decomposition of CuCO3.Cu(OH)2 and 2ZnCO3.3Zn(OH)2

Thermal decomposition of copper (II) carbonate hydroxide (CCH), CuCO3.Cu(OH)2 and zinc hydroxide carbonate (ZHC), 2ZnCO3.3Zn(OH)2 is widely used for the synthesis of copper and zinc oxides. Kinetic modelling, identification of the rate-controlling step and change in thermodynamic properties of these decomposition reactions have not been reported adequately in the literature. In the present work, the kinetic behaviour of nonisothermal thermal decomposition of CuCO3.Cu(OH)2, and 2ZnCO3.3Zn(OH)2 has been investigated using thermogravimetric (TG) analysis, employing model-free iso-conversional as well as model-fitting methods. Mean apparent activation energy (Ea) values, estimated by various iso-conversional methods (KAS, Starink, FWO, Kissinger and Vyazovkin), were found to be in close agreement (104.9-111.2 kJ.mol-1 for CuCO3.Cu(OH)2 and 192.8-197.9 kJ.mol-1 for 2ZnCO3.3Zn(OH)2). Ea decreased significantly with an increase in conversion for CuCO3.Cu(OH)2, while it increased, peaked and then decreased with conversion for 2ZnCO3.3Zn(OH)2. It indicates that both decomposition reactions are not single-step. Avrami-Erofeev model of order 2.5 was found to explain the experimental TG data well for CuCO3.Cu(OH)2 decomposition, while 2ZnCO3.3Zn(OH)2 decomposition followed the chemical reaction model of order 1.75. Positive changes in the thermodynamic properties, enthalpy and Gibbs free energy for both samples showed that these endothermic decomposition reactions were not spontaneous. The difference between Ea and H was found to be low; 3.9-4.5 kJ.mol-1and 4.0-4.6 kJ.mol-1 for CuCO3.Cu(OH)2 and 2ZnCO3.3Zn(OH)2 respectively, indicating the reactions to be favourable. The thermodynamic properties, though not influenced by the iso-conversional method and the rate of heating, varied significantly with the conversion. FTIR analysis of the gases evolved from decomposition showed that dehydration started before the initiation of decarboxylation, followed by simultaneous progress of both these reactions for CuCO3.Cu(OH)2 and 2ZnCO3.3Zn(OH)2.

Comparative Study on Pyrolysis Kinetics Behavior and High-Temperature Fast Pyrolysis Product Analysis of Coastal Zone and Land Biomasses.

The pyrolysis characteristics of land biomass (corn stalks (Cs), pine sawdust (Ps)) and coastal zone biomass (Jerusalem artichoke stalks (JAs) and reed (Re)) were investigated based on thermogravimetric analysis (TGA) and products’ analysis. The kinetic parameters were obtained by three isoconversional methods (Friedman, KAS, and FWO) and one model-fitting method (DAEM). The simultaneous effect of high temperature (700–900 °C) and high heating rate (1000 °C/s) on the pyrolysis product simulating the typical conditions of a fluidized bed gasifier was studied. TGA showed that high heating rates deepen the thermal cracking process of biomass. Compared with the land biomass, the initial decomposition temperature (Ti) of the coastal biomass is reduced significantly owing to its higher proportion of hemicellulose. These methods agree with the trends shown by the activation energy (Ea) distribution calculated, with fluctuations between 160 and 350 kJ/mol. The mean value activation energies of Re and JAs were higher than those of Cs and Ps between 10% and 90% conversion. The DAEM model showed that Cs and JAs have a good linear relationship between ln A and Eα during the main pyrolysis stage, while Ps and Re are relatively weaker. The kinetic compensation effect was evident for Cs and JAs during the main thermal cracking stage. Py-GC-MS results confirmed that phenols, hydrocarbons, PAHs, and oxygen heterocycle compounds were strongly present in the released volatile products. High-temperature fast pyrolysis of JAs produced a larger amount of PAH compounds than from Cs, Ps, and Re. A larger amount of hydrocarbons and phenols was generated from high-temperature fast pyrolysis of Ps. Some oxygen-containing volatiles are easily converted into aromatic products with higher stability under high temperature.

Degradation mechanism and oxidation kinetics of C60 fullerene

Despite a great deal of research on the basic properties of C60 to the present, no detailed and comprehensive reports are available concerning its degradation mechanism and oxidation kinetics. However, a deeper understanding of the oxidation mechanism of the most common fullerene broadens the horizons of potential applications, especially at high temperatures. Therefore, this study attempted to investigate the fullerene oxidation process using kinetic analysis under non-isothermal conditions. Initially, the powder was structurally and morphologically characterized accurately via XRD, Raman spectroscopy, FESEM, and TEM analyses. This was followed by simultaneous thermal analysis (STA) (i.e., TG and DSC) at four different heating rates (2.5, 5, 10, and 15 °C min−1) in airflow, and kinetic analysis was subsequently conducted to evaluate the thermal oxidation of C60. The activation energy as evaluated by model-free methods turned out to be almost invariant within the specified range of reaction fraction (α). Model-fitting methods were also employed to identify the oxidation mechanism involved, from which emerged two models (i.e., R3 (g(α) = 1-(1-α)1/3) and F1 (g(α) = −ln(1-α))) as possible reaction mechanisms. However, further investigation using the Z(α) master plot method revealed that the kinetic model R3, a phase-boundary process, is the controlling mechanism of C60 oxidation with E ≈ 96 kJ mol−1 and lnA ≈ 9.1 min−1. Further examinations were conducted in the neutral atmosphere, and the partial oxidation process based on TEM and FESEM images revealed that oxygen and heat applied during the process play a central role in the deagglomeration of C60 particles and the consequent oxidation. In fact, considering the spherical morphology and the agglomerates present in the C60 powder, the contracting sphere kinetic model (R3) was found to capture the oxidation process due to attacks by the oxygen molecules at the interface of C60 powder agglomerates.

Novel adamantane-based dicyanate ester: Synthesis, polymerization kinetics, and thermal properties of resulting polymer

A new adamantane-based dicyanate ester has been synthesized. The kinetics of its thermal polymerization is studied by means of conventional and temperature-modulated differential scanning calorimetry. The kinetics is analyzed comprehensively by a combination of an advanced isoconversional and model-fitting method. Polymerization proceeds via transition from a kinetic- to diffusion-control regime, which becomes operative at the later stages of the process. The kinetically-controlled regime manifests itself as a quasi-one-step auto-catalytic reaction. A contribution of diffusion to the overall kinetic is accounted for by means of the Fournier model. The polymerization product possesses excellent thermal properties (the glass transition temperature of ∼370 °C and 5% mass loss temperature of ∼480 °C), which makes it a promising candidate for application in hot-section components for aerospace and military industry.

Kinetic study on high-temperature gasification of medical plastic waste coupled with hydrogen-rich syngas production catalyzed by steel-converter ash

In order to dispose medical plastic waste (MPW) with aim of producing hydrogen-rich syngas, converter ash (CA) produced from the converter steelmaking process was used as the catalyst to promote MPW gasification coupled with the hydrogen-rich syngas production in a fixed-bed reactor at 900–1100 °C, and the kinetics on the MPW gasification were also analyzed based on Friedman and model-fitting method. The results indicated that the hydrogen-rich syngas was generated during the MPW high-temperature gasification due to the synergistic catalytic of the Fe2O3 and CaO in the CA. The CA had a significant catalytic effect on the reaction rates for the H2, CO and CH4 formation, whereas the steam had no significantly effect on the reaction mechanism for the H2, CO and CH4 formation during the MPW CO2 gasification. The kinetic models for the H2, CO and CH4 formation during the MPW non-catalytic CO2 gasification were in sequence as three-dimensional diffusion, chemical reaction (n = 1), and nucleation and growth (n = 1/2). However, the nucleation and growth (n = 2/3), chemical reaction (n = 0) and chemical reaction (n = 1) were the optimum models for the H2, CO and CH4 formation during MPW CO2 gasification in the presence of CA.

A generalized Mallows model based on [formula omitted]-divergence measures

Rankings occur when a set of items is ordered in agreement with some criteria or personal opinions and can be found in various problems ranging from voting and elections to food preferences. Distances on permutations are commonly used in rank data analysis and are an efficient tool for constructing probability models for rankings. In this paper, we consider the optimal property of the distance-based Mallows model in terms of the Kullback–Leibler divergence and propose a generalization based on the ϕ-divergence. In the sequel, we focus on a special parametric family of models induced by the Cressie–Read power divergence. For the suggested models, we provide parameter estimating algorithms and model fitting methods. Furthermore, we propose a simple approach for the specification of the consensus ranking, based on modal complete or partial rankings modal rankings, that could be used alternatively to complete search algorithms. As an illustration, the described procedures are applied to three examples of rank data.

Non-isothermal kinetics of coal char oxyfuel combustion by isothermal model-fitting method

Non-isothermal kinetics of coal/char conversion obtained by model-fitting and model-free methods are always very different, and the effect of heating rate β on the kinetics is unclear. In this study, the oxyfuel combustion kinetics of two coal chars (NCP anthracite, DT bituminous) at βs of 2.5–40 K/min are investigated through thermogravimetric analysis. The direct model-fitting methods (DMFMs), the isothermal model-fitting method (IMFM) and the model-free methods (MFRMs) were used to obtain the non-isothermal kinetics. The results show that all the above models can fit experimental data well, due to the coefficients of determination values of these models are all above 0.99. However, the activation energies, Es, at different βs obtained by the DMFMs differ greatly from the isothermal kinetic parameters, the maximum differences in Es are 43–57 and 22–35 kJ/mol for the NCP and DT chars, respectively; while the Es obtained by the IMFM are almost same for each char, and more consistent with the isothermal experimental results, indicating β has little influence on the E. Moreover, the MFRMs are difficult to distinguish the influence of coal rank, due to the obtained mean (E¯) values of both chars conversion are practically equal, and much lower than the isothermal experimental results. Therefore, the IMFM is more suitable than DMFMs and MFRMs, for determining the non-isothermal kinetics of char oxyfuel conversion.