Non-isothermal Kinetic Models Research Articles

Thermal Decomposition and Kinetic Parameters of Three Biomass Feedstocks for the Performance of the Gasification Process Using a Thermogravimetric Analyzer

Thermogravimetric analysis (TGA) is a powerful technique and useful method for characterizing biomass as a non-conventional fuel. A TGA apparatus has been utilized to experimentally investigate the impact of biomass feedstock diversity on the performance of the gasification of hardwood (HW), softwood (SW) pellets, and refuse-derived fuel (RDF) materials. The solid conversion rate and the volatile species formation rate have been estimated to quantify the rates of devolatilization for each material. In addition, the combustion kinetic characteristics of the three biomass feedstocks were investigated using TGA at different heating rates, and a thermal kinetic analysis was conducted to describe the gasification process. Therefore, the kinetic parameters have been evaluated for different thermal reactions and non-isothermal kinetic models that depend on the relationships between heating rates and temperature profiles. The results show that the amount of tar content from the RDF was higher than that of pure hardwood and softwood feedstocks. Hence, tar removal must be part of any process using syngas produced from RDF feedstocks in a gas engine to produce electricity.

PYROLYSIS KINETICS OF KEYBOARD PLASTIC WASTE USING THERMOGRAVIMETRIC ANALYSER TO ASSESS ITS ENERGY POTENTIAL

In this paper, the kinetic parameters of discarded computer keyboard plastic waste are estimated using thermogravimetric analysis (TGA) with four different non-isothermal kinetic models at a wide range of heating rates 5, 10, 15, 20, 40, 60 and 100 °C/min. The gross calorific value of waste computer keyboard plastic is 38.96 MJ/Kg. FT-IR analysis confirms the presence of alcohol, phenol, ether, ester, carboxylic acid, aromatic, and alkene compounds in keyboard plastic waste. The average values of activation energy are calculated as 158.1668, 198.883, 193.612, and 197.765 kJmol−1 from Kissinger, Friedman, FWO, and Coats-Redfern methods, respectively. The kinetic data obtained in this work would be useful for accurate prediction of reaction behaviour and in the design of efficient commercial process for the conversion of such plastic wastes to energy.

Thermochemical characteristics and non-isothermal kinetics of camphor biomass waste

To enhance the understanding of conversion processes and decomposition characteristics, the mass losses, intermediates evolved and products formed during pyrolysis of camphor biomass waste were determined by coupling DSC/TGA-DTG/GC-MS/FTIR. The non-isothermal kinetics of pyrolysis and combustion processes under the heating rates of 10, 15 and 20 °C/min were studied by the improved Coats-Redfern method. The activation energies and the pre-exponential factors were estimated iteratively by regression to improve their accuracy. The results indicated the mass losses could be divided into the different phases and the exothermic and/or endothermic reactions occurred. The functional groups and condensable/non-condensable gases such as O‒H, C˭O, C‒O, C‒O‒C, C‒H benzene skeleton, CO, H2, CO2, CH4, etc. were detected at different temperatures. The non-isothermal kinetic models based on improved iterative Coats-Redfern method fitted the experiments adequately in each phase both pyrolysis and combustion of camphor biomass waste. The nucleation and one-dimensional diffusion were found the suitable models, and the values of activation energy on main mass loss in the second phase of pyrolysis and combustion were obtained 39.98–56.25 and 109.26–135.84 kJ/mol, respectively.

Thermal Characteristics, Kinetic Models, and Volatile Constituents during the Energy Conversion of Bituminous SARA Fractions in Air.

To understand the thermal characteristics, nonisothermal kinetic models, and volatile constituents during the energy conversion of bituminous materials at the fraction level, differential scanning calorimetry–mass spectrometry tests were performed on bituminous four fractions, including saturates, aromatics, resins, and asphaltenes (SARA). Then, three-dimensional (3D) nonisothermal kinetic models of SARA fractions were established and volatile constituents of SARA fractions were discussed. Results indicate that when the heating rate is increased, the decomposition temperature ranges in each stage increase and the initial decomposition, peak, and burn-out temperatures of each SARA fraction all shift to high temperatures. Also, the whole energy conversion processes of SARA fractions are mainly exothermic reactions. Additionally, the energy conversion mechanism in each stage of saturates and aromatics accords with different nonisothermal kinetic models. However, the energy conversion mechanisms of resins and asphaltenes are similar and both accord with the 3D diffusion models. Further, the established nonisothermal kinetic models in each decomposition stage of SARA fractions are feasible to describe the energy conversion processes of SARA fractions. The released small molecular volatiles from saturates and aromatics increase when the heating rate is increased, but the macromolecular volatiles are decreased. The opposite is true for resins, but all volatiles emitted from asphaltenes are increased. Finally, the heating rate has little influence on the constituents of emitted gaseous products from SARA fractions but shows an effect on the release amount of volatiles from SARA fractions. The main common volatiles of SARA fractions are CO2, H2O, methanol, hydrazine, propyne, acetaldehyde, and propane. This study contributes to further reveal the energy conversion mechanisms of bituminous materials.

Surface engineering of nanoparticles anchored meso-macroporous silica heterostructure: An efficient adsorbent for DNA

The present article for the first time puts forth the adsorption of genomic deoxyribonucleic acid (DNA) onto the copper oxide nanoparticles impregnated meso-macroporous silica (MMS) framework and sets the stage for formulating MMS as carriers of nucleic acids. Prior to the adsorption of DNA, the silica surface was made compatible by aminosilanization of the MMS surface using aminopropyltriethoxysilane (APTES). The present methodology resulted in high-density amination of the MMS material as pointed out by the elemental and thermal gravimetric analysis. FTIR spectrum, FESEM micrograph, and zeta potential value confirmed the surface passivation of the MMS surface. Non-isothermal kinetic models validated that APTES modified composite was thermally stable. Mesopore ordering and the surface area of the functionalized material were estimated by small-angle X-ray scattering (SAXS) and N2 adsorption-desorption analysis respectively. Modified material offered us a convenient platform for adsorption-desorption of calf thymus-DNA (CT-DNA). Adsorption efficiency of the APTES grafted MMS for CT-DNA has been found as high as 95.96%. Adsorption isotherms affirmed monolayered chemisorption of CT-DNA on the APTES@MMS. APTES grafted MMS can act as a potent, reusable, economical, and highly efficient adsorbent for CT-DNA. In summary, this work highlights the mechanistic and kinetic aspects underlying the adsorption behavior of DNA onto the MMS framework.

Simple synthesis, kinetics and thermodynamics of rod-like Cu2(OH)PO4 microparticles and rod-like Cu4O(PO4)2 nanoparticles

Rod-like Cu2(OH)PO4 microparticles were synthesized via a simple wet chemical reaction by mixing the solutions of CuSO4·5H2O and Na3PO4·12H2O at 90 °C for 24 h. Thermal transformation of the prepared Cu2(OH)PO4 microparticles were related to endothermic dehydroxylation and its final decomposed product rod-like Cu4O(PO4)2 nanoparticles were obtained. The XRD results indicated that Cu2(OH)PO4 and Cu4O(PO4)2 crystallize orthorhombic (space group Pnnm, D2h12) and triclinic (space group P1‾, Ci1) phases, respectively. The thermal transformation mechanisms from Cu2(OH)PO4 to Cu4O(PO4)2 were expressed thought the relation of the graphical shape of isothermal combined with the non-isothermal multi-heating rate equation and kinetic models (P3/2 and R2) to discuss the change of morphologies from microparticles to nanoparticles. Kinetic parameters and triplet thermodynamic functions of activated compound were determined and fully discussed. The obtained data will be useful for academic scientists and industrial researchers to apply these copper phosphates for special applications.

Volatilization characteristics of high-lead slag and its influence on measurement of physicochemical properties at high temperature

Volatilization causes measurement deviations of physicochemical properties for volatiles-containing slag at high temperature. Hence, investigating the degree of volatilization and identifying the volatilization mechanism and deviation rules are crucial to improve the accuracy of the measured properties. Here, PbO-FeOx-CaO-SiO2-ZnO slag system was selected as a research subject. The volatile characteristics and non-isothermal intrinsic kinetic models of high-temperature volatilization for lead slag were established by thermogravimetric analysis (TGA), and the volatilization mechanism and deviation in the measured properties were determined by analyzing the phase and chemical composition of the residues. In addition, experimental measurements of the melting temperature/ viscosity were compared with theoretically calculated results. The volatilization of PbO decreased the lead-containing phase, but increased the amount of precipitated spinel phase, which led to the deviation in the measured physicochemical properties of the studied slags. The volatilization kinetics for PbO in the slags followed three-dimensional diffusion. The diffusion of PbO gas from PbO-FeOx-CaO-SiO2-ZnO slag was the restrictive step of volatile reaction, and mechanism function was g(?)=1-(1-?)1?3. Moreover, during the slag properties measurement at high temperatures, a high heating rate and protective gas can be used to reduce volatilization of lead slag and avoid consequent properties deviation.

Synthesis, crystal structure, theoretical calculations and thermal characterization of two heterodinuclear NiII–ZnII complexes prepared from ONNO-type symmetrical Schiff base and its reduced derivative

Two complexes in NiII–ZnII heterodinuclear form were prepared in DMF medium by the use of an ONNO-type symmetrical Schiff base bis-N,N′(salicylidene)-1,3-diaminopropane (LH2) and the reduced derivative of this ligand bis-N,N′(2-hydroxybenzylidene)-1,3-diaminopropane (LHH2). The fact that the complexes are in [NiL·ZnCl2·DMF2] and [NiLH·ZnCl2·(DMF)2] stoichiometry was verified with elemental and thermogravimetric analyses and IR spectroscopy. The structures of the complexes were determined by the use of X-ray diffraction. The two complexes were very similar, almost isostructure, and it was observed that Ni(II) ions in both complexes coordinated with two phenolic oxygens and two iminic nitrogen of organic ligand and formed an octahedral coordination between two DMF molecules. On the other hand, the Zn(II) ion was observed to be located in a tetrahedral coordination sphere coordinated with two phenolic oxygens between two halides. Although the molecular structures of the complexes are very similar, their thermal properties are quite different from of each other. The decomposition of [NiL·ZnCl2·(DMF)2] was observed between 140 and 190 °C by the removal of coordinative DMF molecules, leaving a residue of a mixture of NiL and ZnCl2 behind. The complex of the reduced ligand [NiLH·ZnCl2·(DMF)2] was observed to be stable up to 250 °C. After this temperature, the coordinative DMF molecules rapidly leave the structure before the degradation of NiLH. That is why the activation energies of the thermal reactions were evaluated by the use of isothermal and nonisothermal kinetic models: Coats–Redfern, Ozawa, Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose. Also the thermal differences between these two complexes were examined by the use of theoretical programs included in Gaussian 09 package. The ground-state energies calculations were carried out by the use of density functional theory method 631G(d) basis set. The calculated theoretical bond energies and angles were observed to be different compared with the experimental data. The HOMO and LUMO values of the complexes were also calculated. The difference between these two complexes was evaluated.

Thermal and kinetic behaviors of pyrolytic carbon black and gas coal in co-combustion

In this study, a combustion study of tire pyrolytic carbon black (CBp), gas coal (GC), and their blends was carried out by thermogravimetric analysis with four heating rates under air atmosphere. And the structure characteristics of CBp and GC were studied using particle size distribution, scanning electron microscope, X-ray diffraction, Raman spectra followed by peak deconvolution and data analysis. The results demonstrated that the structural differences between CBp and GC directly affected their thermal behavior trends. GC with low graphitization degree had more combustibility reactivity than that of CBp, while the mean reaction rate and maximum reaction rate of CBp were larger than GC due to its bigger specific surface area and higher porosity. For blends, the combustibility reactivity could be improved by blending with GC, and there was obviously synergetic effect for the co-combustion of CBp and GC. The combustion reaction mechanisms and kinetic parameters were carried out using three non-isothermal kinetic models: random nucleation nuclei growth model (RNGM), volume reaction model, and unreacted core model. The kinetic analysis demonstrated that the RNGM model had a better performance than other models for describing the thermal behavior of the selected samples. In addition, the synergetic effect between CBp and GC was observed from the kinetics data calculated by RNGM. The activation energies of CBp and GC calculated by RNGM model were 119.6 kJ mol−1 and 126.4 kJ mol−1, respectively, whereas the lowest activation energy for their blends was 104.3 kJ mol−1 when CBp ratio was 40%.

Effect of pyrolysis temperature on pine sawdust chars and their gasification reactivity mechanism with CO2

AbstractThe mechanism on CO2 gasification reactivity of pine sawdust chars (PS chars) obtained from the different pyrolysis temperatures (873, 973, and 1073 K) is studied on the basis of nonisothermal thermogravimetric method. The order of gasification reactivity is PS char‐873 > PS char‐973 > PS char‐1073. The effect of pyrolysis temperature is depicted by microstructure characterization, and the gasification reactivity is analyzed with nonisothermal kinetic models. The microstructure characterizations of chars are characterized by scanning electron micrograph, Brunauer–Emmett–Teller, Fourier transform infrared, and X‐ray diffraction. Results show that the microcrystalline structure of biomass char is the dominant factor for the effect of gasification reactivity with the pyrolysis temperature rising. The kinetic models of Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose are applied to describe the kinetics of gasification process. The average values of activation energy are in close agreement with the two methods. Both of the methods prove that F2 mechanism is applicable to the gasification of PS chars at lower pyrolysis temperature and F1 mechanism at higher pyrolysis temperature. Besides, there is a compensation effect between activation energy and preexponential factor in the CO2 gasification process.

Non-isothermal crystallization kinetics and degradation kinetics studies on barium thioglycolate end-capped poly(ε-caprolactone)

The poly(e-caprolactone) (PCL) was synthesized by ring-opening polymerization at 160 °C under nitrogen atmosphere for 2 h by bulk polymerization method in the presence of barium thioglycolate (Ba-TG) as an initiator and stannous octoate as a catalyst. The monomer-to-initiator ratio was maintained at 400. The Ba-TG end-capped PCL was characterized by various analytical tools like FTIR spectroscopy, NMR spectroscopy, AFM, DSC, TGA, POM and HRTEM. The non-isothermal crystallization kinetic study was executed with the help of DSC in order to determine the rate at which nucleation formation and spherulitic growth take place. The thermal degradation kinetic studies were performed with the help of TGA to know the degradation rate as well as energy of activation (Ea) using different non-isothermal kinetic models. The main aim of the present investigation is to determine the role of chain end-capping agent (Ba-TG) on the crystallization and degradation process of PCL. It was found that the Ba-TG induced the 3D spherulitic crystal growth of PCL.

Non-isothermal reduction kinetics of oolitic iron ore in ore/coal mixture

Mixtures of oolitic iron ore and coal with different C/O molar ratios (1.5, 2.0, 2.5, and 3.0) were heated from 600 to 1300 °C at four heating rates (5, 10, 15, and 20 °C min−1). The degree of reduction and reduction rate were calculated from the measurements of weight loss and off-gas composition using thermogravimetry technique and NDIR gas analyzer. The kinetic parameters (the activation energy, pre-exponential factor, and reduction model) were determined by Ozawa–Flynn–Wall kinetic method and by Satava–Sestak method. It was found that, as temperature increased, the degree of reduction increased, while the reduction rate rapidly increased first, subsequently stabilized, and then decreased. The non-isothermal reduction of oolitic iron ore with coal was significantly influenced by both heating rate and C/O molar ratio, although the impact of the latter was much less. The values of activation energy estimated by Ozawa–Flynn–Wall method ranged from 159.2 to 169.6 kJ mol−1. The mechanism function for the non-isothermal coal-based reduction of oolitic iron ore was D5 reaction model. The non-isothermal kinetic models for coal-based reduction of oolitic iron ore were proposed based on the obtained kinetic parameters. The iron oxide in the oolitic ore was reduced to metallic iron in the sequence of Fe2O3 → Fe3O4 → FeO (FeAl2O4, Fe2SiO4) → Fe. Phase change and reduction mechanism shift were observed during the reduction.

Thermal hazard evaluation of the autocatalytic reaction of benzoyl peroxide using DSC and TAM III

A new approach was used to monitor the autocatalytic reaction of benzoyl peroxide (BPO) by non-isothermal and isothermal kinetic models constructed using differential scanning calorimetry and thermal activity monitor III analyses, respectively. Autocatalytic reactions generally start slowly and then accelerate as the reactant is consumed and the autocatalyst is produced. Consequently, an autocatalytic reaction may require special design considerations to avoid certain upset conditions, such as runaway exothermic reactions.We conducted a thermal hazard analysis of various products, including benzoic acid, benzene, and phenol, which were deliberately selected and individually mixed with BPO to investigate their thermal hazards. Model fitting can be applied to predict the amount of time required to achieve the maximum rate under isothermal conditions at any temperature of interest. The proposed procedure was effective and accurate for evaluating the autocatalytic reaction of BPO.

Kinetic Analysis of Tar’s Separation from Lump Coal

The tar separated out from the lump coal has an important effect on COREX process. In this paper, a designed experimental method is used to study the kinetics of tar’s separation from lump coal. The weight percent gain of the tar was defined as the tar’s separation conversion using the weight-loss ratio in TGA for reference, and then the isothermal and non-isothermal kinetic models were used to analyze the dynamics mechanism of tar’s generation. Based on the characteristic of tar’s generation, we suppose that the shrinking core model is suited to the early heating process of lump coal, and the mid-term and later stage of tar’s generation are respectively controlled by the coal pyrolysis and the spread of the tar molecule. Thus, the equation of non-isothermal unreacted core model, the first order reaction model and the Anti-Jander diffusion equation are respectively established to describe the tar’s generation. The fitting results of these three models showed a good linear dependence relation illustrating that the experimental method and the hypothetical models in this paper are reliable. What’s more, a way is provided to study the tar’s or other substances’ dynamic separation through the experiment method.

Hydrogen desorption kinetics of MgH2 synthesized from modified waste magnesium

Abstract In the present study, hydrogen desorption properties of magnesium hydride (MgH2) synthesized from modified waste magnesium chips (WMC) were investigated. MgH2 was synthesized by hydrogenation of modified waste magnesium at 320 °C for 90 min under a pressure of 6 × 106 Pa. The modified waste magnesium was prepared by mixing waste magnesium with tetrahydrofuran (THF) and NaCl additions, applying mechanical milling. Next, it was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques in order to characterize its structural properties. Hydrogen desorption properties were determined by differential scanning calorimetry (DSC) under nitrogen atmosphere at different heating rates (5, 10, and 15 °C/min). Doyle and Kissenger non-isothermal kinetic models were applied to calculate energy (Ea) values, which were found equal to 254.68 kJ/mol and 255.88 kJ/mol, respectively.

Calorimetric Techniques Combined with Various Thermokinetic Models to Evaluate Incompatible Hazard of tert-Butyl Peroxy-2-ethyl Hexanoate Mixed with Metal Ions

tert-Butyl peroxy-2-ethyl hexanoate (TBPO), an organic peroxide broadly used as initiator for polymerization of ethylene, styrene, methyl methacrylate, and acrylonitrile, has the characteristic of triggering a highly exothermic reaction. Mixing with a contaminant, such as metal ions, may result in a runaway reaction and acceleration decomposition under an abnormal situation. We investigated how Cu2+, Ni2+, and Fe2+ individually affected the thermal decomposition of TBPO. Our aim was to explore the thermal hazard of TBPO mixed with metal ions by calorimetric techniques combined with thermokinetic models. We employed nonisothermal and isothermal calorimeters to determine various thermokinetic and safety parameters, including exothermic onset temperature (To), peak temperature (Tp), final temperature (Tf), heat of decomposition (ΔHd), and maximum heat flow (Qmax) by differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III). Moreover, the isothermal and nonisothermal kinetic models we...

Non-isothermal kinetic parameters and models of crystallization for amorphous Fe–Co–Nb–Cu–B alloys

The non-isothermal differential scanning calorimetry (DSC) measurements are often used to study kinetics of amorphous alloys. However non-isothermal kinetic parameters and models of amorphous alloy crystallization process were unclear. In our research, amorphous (FexCo1−x)NbCuB (x=0.33, 0.5 and 0.75) alloys were produced in the form of ribbon by a single roller melt-spinning method. DSC curves at heating rate 5, 10, 15, 20 and 25K/min were obtained. Kissinger, Ozawa and model-free methods obtain identical activation energies at each exothermic peak of all compositions. We conclude that first exothermic reaction is determined by the migration activation energy of Fe or Co atom; second reaction determined by the energy between parent and product boride phases; and the third reaction determined by the energy between parent α-FeCo phase and product bcc-Fe/fcc-Co phases. We hypothesized a non-isothermal kinetic modelf(α)=αm(1−α)n, which fit our experiment results well. In this model, m depends on nucleus shape and growth dimension, and n are determined by lattice positions participated in new phase formation.

Characterization and thermal behavior of PrMO3 (M = Co or Ni) ceramic materials obtained from gelatin

Metal oxides with perovskite-type structure have attracted considerable interest in recent years due to their magnetic and electrical properties, as well as their catalytic activity. In this study, oxides with PrNiO3 and PrCoO3 composition were prepared by using gelatin powder as a precursor agent for its use as a catalyst. The powders obtained were calcined at 700°C and 900°C and characterized using the X-ray diffraction, thermal analysis (thermogravimetry and differential thermal analysis), infrared spectroscopy, temperature programed reduction and scanning electron microscopy techniques. Thermogravimetric data using the non-isothermal kinetic models of Flynn and Wall and “Model-free Kinetics” were used to determine the activation energy to study the decomposition kinetics of the ligand groups with system's metallic ions that takes part in the synthesis of PrMO3 (M=Ni or Co).

Prediction of thermal hazard of liquid organic peroxides by non-isothermal and isothermal kinetic model of DSC tests

Abstract Liquid organic peroxides (LOPs) have been widely used as initiators of polymerization, hardening, or cross-linking agents. We evaluated a beneficial kinetic model to acquire accurate thermokinetic parameters to help preventing runaway reactions, fires or explosions in the process environment. Differential scanning calorimetry was used to assess the kinetic parameters, such as kinetic model, reaction order, heat of reaction (ΔHd), activation energy (Ea), frequency factor (lnk0), etc. The non-isothermal and isothermal kinetic models were compared to determine the validity of the kinetic model, and then applied to the thermal hazard assessment of commercial package contaminated with LOPs. Simulations of a 0.5-L Dewar vessel and 25-kg commercial package were performed. We focused on the thermal stability of different liquid system properties for LOPs. From the results, the optimal conditions were determined for avoiding violent heat effects that can cause a runaway reaction in storage, transportation...

Devolatilization non-isothermal kinetic analysis of agricultural stalks and application of TG-FT/IR analysis

Abstract Devolatilization behavior of several types of agricultural stalks (sunflower, rice, corn, and wheat) was studied using thermogravimetric system (TG) under nitrogen atmosphere at different heating rates (10, 15, and 20 °C min−1). Coats&Redfern, Horowitz&Metzger, and Arrhenius non-isothermal kinetic models were applied to calculate the devolatilization kinetic parameters and the devolatilization rate equations have been established. In addition, the kinetic compensation effect (KCE) has also been used to correlate pre-exponential factor (ko) with activation energy (Ea) and an existence of the KCE is accepted. TG-FT/IR analyses were applied of the different stalks and FT/IR stack plot used to analyze the devolatilization gas products (CO2, CH4, HCOOH, CH3OH). Infrared vibrational frequencies, micro structure and crystallinity of stalks were investigated by Fourier transform infrared spectroscopy (FT/IR), scanning electron microscope (SEM), and X-ray diffraction analysis (XRD), respectively.