Non-isothermal Kinetic Analysis Research Articles

Non-Isothermal Kinetic Analysis of the Dehydroxylation of Kaolinite in Dynamic Air Atmosphere

Abstract A non-isothermal kinetic analysis of kaolinite dehydroxylation was carried out using thermogravimetric analysis on powder samples with heating rates from 1 to 30 °C・min-1 in a dynamic air atmosphere. The mechanism of the reaction, values of overall activation energy and pre-exponential factor were determined from a series of thermogravimetric experiments by the Coats- Redfern method. The results show that the dehydroxylation of kaolinite is controlled by the rate of the third-order reaction (F3) with the mean values of overall activation energy (EA) 255 kJ・mol-1 and pre-exponential factor (A) 25.56 × 1014 s-1.

Thermal stability and crystallization process in a Fe-based bulk amorphous alloy: The kinetic analysis

In this work, the thermal stability and non-isothermal kinetic analysis of crystallization process in (Fe41Co7Cr15Mo14Y2C15)94B6 amorphous alloy were investigated. The research findings revealed that crystallization process was done in four stages whereby the crystalline phases including Fe23 (B, C)6, Fe3Mo3C, and Mo3Co3C were formed. In order to determine the activation energy of every crystallization stages, the isoconversional methods were used. The activation energies were calculated about 550, 620, 550, and 820kJ/mol for I, II, III, and IV crystallization stages, respectively. Also, values of the rate constant at the peak temperature of crystallization, Kp; Avrami exponent, n; and growth dimensional, m; were determined by means of Augis-Bennett and Gao-Wang methods. Furthermore, for a more accurate determination of kinetic parameters including n, and m, these kinetic parameters were obtained by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) and Matusita. The values of m were calculated equal to 2, 1, 2, and 3 for I, II, III, IV crystallization stages, respectively. Also, the obtained nucleation index, showed that the rate of nucleation in I, II, and III crystallization stages were zero. Therefore, it can be acceptable that a large number of nuclei related to these stages already exist in the specimen.

Kinetic analysis of ceria nanoparticle catalysed efficient biomass pyrolysis for obtaining high-quality bio-oil

Bio-oils obtained from biomass pyrolysis are being recognized as the next generation energy source. However, this technology has not yet been fully employed in real practice because of highly viscous and complex chemical nature of pyrolytic products and also due to lack of adequate understanding of such non-isothermal reactions. Catalysts can be used to upgrade the quality of bio-oils by enhancing the pyrolysis reaction efficiency and breaking down higher molecular weight compounds into simpler products. The study of the kinetics of this pyrolysis process explicates in depth knowledge about the reaction mechanism to have a better control over the efficiency of pyrolysis conversion of the biomass constituent. In this study, we focus on the kinetic analysis of ceria nanoparticles catalysed pyrolysis of cellulose, the major constituent of lignocellulosic biomass, for production of high-quality bio-oil. A non-isothermal kinetic analysis method identifies the reaction to be following a ‘one and a half order’ pathway and establishes significant lowering of activation energy after addition of the nanocatalyst. The merit of the nanocatalyst was again ascertained by performing qualitative analysis of pyrolytic liquids from cellulose in the presence of both bulk and nanosized ceria catalysts. It was observed that CeO2 nanoparticles improved the pyrolysis process enhancing the C–C bond scission reactions. As a result, percentage amount of lower molecular weight (96–144) compounds in the pyrolytic liquids increased with the addition of nanocatalyst (highest being 100% for 7% ceria nanocatalyst).

Synthesis and characterization of poly(ester ether urethane)s block copolymers based on biodegradable poly(butylene succinate) and Poly(ethylene glycol)

A series of poly(ester ether urethane)s (PEEUs) block copolymers composed of dihydroxy-terminated poly(butylene succinate) (HO-PBS-OH) as the hydrophobic part and poly(ethylene glycol) (PEG) as the hydrophilic part were successfully synthesized and investigated with various PEG mass fraction using isophorone diisocyanate (IPDI) as a chain-extender. Nonisothermal melt-crystallization kinetics and subsequent melting behavior of PEEUs have been investigated by differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny and Mo's method were applied to describe the kinetics of the crystallization process. Meanwhile, the effects of PEG on the crystalline morphology and crystal structure of PEEUs were studied by wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM). The analysis of nonisothermal crystallization kinetics showed that the crystallization rate of PBS segment within PEEUs was improved by the introduction of high PEG. content. Additionally, banded spherulites were observed regardless of composition for all copolymers. Their biodegradability was investigated by the enzymatic degradation using pseudomonas cepacia lipase. Experimental data showed that biodegradation rate increased with the increasing of PEG content, and a significant rate of degradation was occurred in the PEEU sample with 60 wt% PEG content.

Non-isothermal kinetic analysis of nano-crystallization process in (Fe41Co7Cr15Mo14Y2C15)94B6 amorphous alloy

In this work, non-isothermal kinetic analysis of the crystallization process was performed on a (Fe41Co7Cr15Mo14Y2C15)94B6 amorphous alloy heated by DSC at various heating rates (5, 10, and 20°C/min) up to 1200°C. The research findings revealed that three crystalline phases including Fe23 (B, C) 6, Fe3Mo3C, and Mo3Co3C were formed during the crystallization process; furthermore, the presence of nano-crystalline grains was confirmed by FE-SEM. Two isoconversional methods including Starink, and Friedman (FR) were used to determine the variation of activation energy with a (Eα). Moreover, the invariant kinetic parameters (IKP) method and free model were used to calculate the empirical kinetic triplets (E, A, and g(α)). The best reaction models, chosen by fitting methods to describe the mechanism of four crystallization steps were A2, A3/2, A2, and A4, respectively.

Structural and Computational Study of 4 New Solvatomorphs of Betulin: A Combined X-Ray, Hirshfeld Surface, and Thermal Analysis

Four new solvatomorphs of betulin were reported and characterized by X-ray diffractometry as well as thermal and vibrational spectroscopic analyses. Single-crystal X-ray diffraction was used to analyze the X-ray structures of the compounds and confirmed the stoichiometric ratio between the host and guest molecules from thermal data. Results indicated that solvatomorphism occurred in several betulin solvates. Changes in intermolecular arrangements, stoichiometry, and hydrogen-bonding interactions of solvatomorphs were due to solvent incorporation to solvates. Hirshfeld surface analyses, especially dnorm surface and fingerprint plots, were used to determine intermolecular interactions in the crystal network. Solvent molecules played an important role in the construction of a 3D architecture. The stabilities of these solvates were evaluated by thermal analyses. Nonisothermal kinetic analysis was used to explain the kinetics of solid–solid phase transition (desolvation) of betulin solvates. The apparent activation energies were evaluated using Kissinger and Ozawa methods. Moreover, phase transitions were visually investigated by hot-stage microscopic analysis.

Thermal Valorization of Pulp Mill Sludge by Co-processing with Coal

At the pulp and paper industries, large volumes of primary and secondary sludge are generated from wastewater treatment. Aiming to assess the co-processing of each type of sludge with coal, thermogravimetric (TG) analysis has been used in this work. First, combustion and pyrolysis TG curves of coal (C), primary (L1) and secondary (L2) pulp mill sludge were obtained under oxidizing and inert atmosphere, respectively. Then, under identical experimental conditions, TG analysis was carried out on the primary sludge–coal (CL1) and the secondary sludge–coal (CL2) blends. The corresponding differential thermogravimetric (DTG) curves showed evident differences between C, L1 and L2, which were mainly related to the relative large fixed carbon and low volatiles content of C. However these differences, the combustion of CL1 and CL2 mostly resembled that of C. Meanwhile, the pyrolysis of CL1 and CL2 showed lower devolatilization temperatures and char yields than that of C. Non-isothermal kinetic analysis of TG data showed slightly lower apparent activation energy (E) for the combustion of C than for the combustion of either CL1 or CL2. Contrarily, much lower E values were determined for the pyrolysis of CL1 and CL2 than for the pyrolysis of C. Yet, lower E values than the weighted calculated ones were determined for the combustion and, especially, for the pyrolysis of the blends.

Non-isothermal kinetic analysis of crystallization of vacuum prepared Se90In9.9Cu0.1 alloy thin films

Amorphous Se90In9.9Cu0.1 alloy thin films were prepared by conventional thermal evaporation method under high vacuum. The crystallization kinetics were studied by differential thermal analysis at various heating rates 5, 10, 15, 20 and 25K/min. The glassy nature of the alloy films and the chemical composition were investigated by X-ray diffraction and energy dispersive X-ray analysis, respectively. From the heating rate dependence of glass transition, the onset crystallization activation energy, the crystallization activation energy and the glass transition activation energy were calculated. The results indicated that the obtained value of activation energy, using Kissinger's relation, is greater than those obtained by Moynihan's relation based on the concept of thermal relaxation. The crystallization kinetics were measured using mainly non-isothermal treatment. The effective activation energy of crystallization and the frequency factor were found to be 170.83kJ/mol and 4.655×1023min−1, respectively.

Explosive Properties of 4,4’,5,5’-Tetranitro-2,2’-bi-1H-imidazole Dihydrate

This paper reports measured explosive properties of 4,4',5,5'-tetranitro-2,2'-bi-1H-imidazole dihydrate (TNBI center dot 2H(2)O). Non-isothermal kinetics analysis, calorimetric measurements, detonability tests, small-scale shock reactivity tests (SSRT), detonation velocity measurements and cylinder tests were performed. The results of the cylinder tests were used to determine the acceleration ability of TNBI center dot 2H(2)O. Some experiments were conducted also with TNT, NTO, FOX-7 and RDX. Our experimental studies have shown that TNBI center dot 2H(2)O is a thermodynamically stable compound, surpassing TNT with regard to its energetic and detonation parameters. The results of the SSRT indicate that this material has better performance in small charges than RDX, FOX-7 and NTO.

Effect of different nanofillers on non-isothermal crystallization kinetics and electric conductivity of dynamically-vulcanized PP-EPDM Blends

In this study, nanofillers composed of hydroxylated carbon nanotubes (h-CNT), carbon nanotubes (CNT) and graphene (GR) were separately added into the dynamically-vulcanized polypropylene (PP)/ethylene-propylenediene monomer (EPDM) blend. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and electrical resistivity measurements were employed to study the effect of nanofillers on the melt behavior, non-isothermal crystallization behavior and electrical conductivity of the prepared composites. WAXD results showed that h-CNT had a better induction effect of β-PP in the nanocomposites. The sequence of the activity in inducing the formation of β-PP was h-CNT>GR>CNT. However, the total crystallinity of the nanocomposites nearly remained constant. Non-isothermal crystallization kinetic analysis indicated that the presence of nanofillers improved the crystallization rate of the nanocomposites. The consequence of nucleation activity was as follows: CNT>GR>h-CNT. Although EPDM hindered the macromolecular motion of PP, interestingly it could increase the crystallization rate to an extent. Besides, the influence of nanofillers on enhancing the conductive property of the nanocomposites can be ranked as follow: CNT>GR>h-CNT.

Specific Features of Solid Fuels Combustion in Oxygen Atmosphere with Recirculation of CO2

<p>Aspects of coal combustion have been experimentally studied under oxyfuel conditions, one of the promising technologies for carbon capture and storage (CCS). Here, the thermogravimetric analysis (TGA) method was chosen as an experimental technique. Coal pyrolysis tests performed under an O<sub>2</sub>/CO<sub>2</sub> atmosphere were compared with a conventional O<sub>2</sub>/N<sub>2</sub> environment in terms of reaction rate and total volatile yield. Combustion of the resulting chars in the corresponding atmospheres revealed somewhat different combustion rates with a less vigorous reaction in the O<sub>2</sub>/CO<sub>2</sub> medium. The two manipulated factors – namely, the inherently different char reactivities due to the different atmospheres they were obtained in and the different atmospheres of the actual combustion process – were distinguished by performing another series of tests with chars pyrolysed under identical conditions using a standard routine. These chars also showed a weaker reaction in O<sub>2</sub>/CO<sub>2</sub> atmosphere, which was attributed to the lower binary diffusion coefficient of the O<sub>2</sub>/CO<sub>2</sub> pair. The activity of the char – CO<sub>2 </sub>gasification reaction in an O<sub>2</sub>/CO<sub>2</sub> environment was also investigated and revealed some contribution of this reaction to the conversion process. This was particularly noticeable at temperatures above 750 °C and under an internal diffusional controlled regime (zone II), implying displacement of oxygen out of the char particle pore volume, which allowed free reaction of CO<sub>2</sub> on the developed pore surface. Non-isothermal kinetic analysis of the intrinsic kinetics of the oxidation reaction in O<sub>2</sub>/CO<sub>2</sub> revealed no particular difference compared to the O<sub>2</sub>/N<sub>2</sub> medium, at least when the char-CO<sub>2 </sub>reaction was inhibited. The obtained data were used to develop a coal combustion model under O<sub>2</sub>/CO<sub>2</sub> conditions, which was then incorporated as a combustion module into circulating fluidized bed (CFB) computation software.</p>

Kinetic and structural analyses for the formation of anatase nanocrystals in barium titanoborate glasses

Transparent barium titanoborate glass-ceramics bearing TiO2 (anantase) nanocrystals were prepared by the conventional melt-quenching and subsequent heat treatment of 35BaO–xTiO2–110B2O3 (in mol) (x = 20, 25, and 30) glasses. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results clearly reveal the formation of highly-crystalline anatase nanocrystals in glass matrices. The average crystal size ranges from ∼10 to 20 nm according to TiO2 contents. Non-isothermal kinetic analyses were performed to understand the crystallization behavior of each glass using differential scanning calorimetry (DSC) scan curves. With the increase of TiO2 contents in the glass, the crystallization peak temperature of TiO2 decreases, while the activation energy for crystallization increases. We propose a possible mechanism for the formation of TiO2 nanocrystals based upon kinetic analysis results and structural changes in barium titanoborate glass matrices according to TiO2 contents. The nanocrystalline glass-ceramics show ∼60–75% visible light transmittance and sharp UV-light absorption edges at ∼387 nm, corresponding to the energy band gap of anatase (3.2 eV). They show apparent photocatalytic properties and ∼70% of methylene blue solution was decomposed within 180 min.

Thermogravimetric analysis of the co-pyrolysis of a bituminous coal and pulp mill sludge

Thermal valorization of organic wastes by co-processing with coal may be a management option for such wastes. In this work, the separate pyrolysis of coal and primary and secondary pulp mill sludge was assessed by thermogravimetric (TG) analysis. Then, under the same experimental conditions, the pyrolysis TG curves of the coal blends with a 10 mass% of either primary or secondary pulp mill sludge were obtained. The corresponding differential thermogravimetry curves made evident that the devolatilization of coal starts at higher temperature and reaches higher char yields than that of primary or secondary paper mill sludge. Under blending, lower devolatilization temperatures and char yields, close to the weighted calculated ones, are observed. Non-isothermal kinetic analysis showed that the Arrhenius activation energy (E) corresponding to the pyrolysis of coal was lower than that corresponding to either L1 or L2. Moreover, lower E than the weighted calculated ones was determined for the co-pyrolysis of the blends.

Effect of cyclic freeze–thawing process on the structure and properties of collagen

The influence of freeze–thawing cycles (named ‘N’) on the rheological and thermal properties of bovine skin collagen solution was investigated using a rheometer and differential scanning calorimetry (DSC). The results of dynamic frequency sweep tests showed that the elasticity of collagen increased as N increased to 3, 5 and 7. Especially, after the freeze–thawing cycles of N=7, the recovery capacity of collagen remarkably increased (from 17.76% to 74.98%) and the hysteresis loop areas of collagen also became larger (from 95.53 to 218.24Pa/s). Moreover, DSC and non-isothermal kinetic analysis revealed that although the freeze–thawing process had little impact on the thermal denaturation temperature, the endothermic enthalpy was increased by 73% when N=7, as estimated from the area under the endothermic peak and from the Friedman isoconversional method. In addition, as observed by atomic force microscopy (AFM), the fibers of collagen became thicker after the process of freeze–thawing cycles, indicating that the aggregation of collagen molecules was enhanced in the process of freeze–thawing. Meanwhile, the morphology of freeze–thawed collagen sponge examined by scanning electron microscopy (SEM) exhibited a porous network structure, and the pores became more regular with increasing N.

Combustion of primary and secondary pulp mill sludge and their respective blends with coal: A thermogravimetric assessment

Properties of primary and secondary pulp mill sludge are unalike and are also very different from those of coal. Thermogravimetric analysis was used to assess the separate combustion of coal, primary and secondary pulp mill sludge. Then, the co-combustion of coal with primary and with secondary pulp mill sludge was studied under identical experimental conditions. Both Differential Thermogravimetry burning profiles (DTG) and Differential Scanning Calorimetric analysis (DSC) showed remarkable differences between the combustion of coal, primary and secondary paper mill sludge. However, compared with the combustion of coal, the effects of adding a 10 wt.% of either primary or secondary paper mill sludge were not relevant in terms of weight loss or heat release. This was further proved by non-isothermal kinetic analysis, which was used to evaluate the apparent activation energy corresponding to the single combustions and to the co-combustion of blends.

Kinetic pathway for thermal exfoliation of pyrophyllite

The thermal exfoliation of pyrophyllite on heating above 600°C was studied to discern its kinetic pathway and correlate it with dehydroxylation. The irreversible thermal expansion data of pyrophyllite was collected from a thermomechanical analyzer at different heating rates (β). Detailed kinetic analysis was performed on the data using model-free and regression analysis (both linear and non-linear) methods. Multivariate non-isothermal kinetic analysis was used to fit the expansion data at all heating rates simultaneously using eighteen kinetic models. It is found that, the exfoliation of pyrophyllite can be successfully fitted with three kinetic models, viz., n-dimensional Avrami (An), two-dimensional diffusion (D2) and three-dimensional diffusion (D3) model with acceptable kinetic parameters. D2 model (Ea, activation energy=392kJ·mol−1, regression coefficient=0.998) provides the most realistic mechanistic pathway by considering the planar geometric constraint of nucleation and growth in the layered structure of pyrophyllite. Electron microscopic images of exfoliated pyrophyllite shows distinct exfoliated layers indicating escape route for heated gas and supports the choice of D2 model. Although this exfoliation process is a consequence of dehydroxylation reaction, its complexity due to diffusional and geometric constraints is reflected by the high energy barrier (Ea) reported consistently by every kinetic model compared to that of dehydroxylation.

Influence of TiB2 Addition on the Precipitation Kinetics in Al-7Si-0.3Mg In Situ TiB2 Composites

Precipitation behavior of the Al-7Si-0.3Mg/TiB2in situ composites was investigated using differential scanning calorimetry and transmission electron microscopy, and it was found that Si precipitation is accelerated with increase in TiB2 content. Non-isothermal kinetic analysis clearly showed a decrease in the precipitation kinetics of the overaged metastable precipitates in the Mg2Si precipitation sequence.

Effects of cooling rates on crystallization behavior and melting characteristics of isotactic polypropylene as neat and in the TPVs EPDM/PP and EOC/PP

Non-isothermal crystallization behavior and melting characteristics of polypropylene (PP) in EPDM/PP and EOC/PP TPVs were studied at various cooling rates using differential scanning calorimetry (DSC). The results revealed that the crystallization of PP in the TPVs occurs at a lower degree of undercooling, relative to neat PP, with smaller size PP crystals. The vulcanized EPDM and EOC particles could accelerate the crystallization of the PP phase either by providing nucleation or by promoting interfacial crystallization. The crystallization exotherm and melting endotherm peaks of the TPVs were broad, and they shifted towards lower temperatures as the cooling rate was increased. The analysis of non-isothermal crystallization kinetics indicates that the crystallization of the PP in the TPVs is heterogeneous nucleation, with two or three-dimensional growth during primary and secondary crystallization. Furthermore, the vulcanized EPDM and EOC particles promote the initial crystallization activation energy of the PP in TPVs to exceed that of the neat PP. The developed mathematical models show an approximately power-law dependence on the cooling rate for the crystallization behavior and the melting characteristics of PP in the TPVs.

Mechanism of vanadium slag roasting with calcium oxide

Thermodynamic analyses, XRD characterization and non-isothermal oxidation kinetic analyses were conducted to find the mechanism of vanadate formation when vanadium slag was roasted with calcium oxide. The effects of heating rate, added amount of CaO, holding temperature and holding time on oxidation efficiency were investigated. Thermodynamic calculations show that the fayalite is more likely to be oxidized than vanadium spinel, formation of calcium vanadates is easier than that of Mn(VO3)2 and Mg(VO3)2 and the oxidation of Fe2+ in augite is hindered by the presence of diopside. TGA results show that lowering the heating rate can improve the oxidation efficiency of vanadium. The maximum vanadium recovery of 93.3% was achieved when the vanadium slag with a ratio of m(CaO)/m(V2O5) of 0.42 was roasted at 850°C for 2.5h. Dynamic heating experiments indicate that oxidations of vanadium spinel and augite overlap within 608–959°C with a heating rate of 3°C·min−1, while only oxidation of spinel occurs within 657–914°C at 5°Cmin−1. The oxidation was controlled by a 3/2 reaction and a third order reaction, with corresponding overall apparent activation energy values of 140.3 and 247.8kJ·mol−1 for the heating rates of 3°C·min−1 and 5°C·min−1, respectively.

Thermogravimetric analysis of the behavior of sub-bituminous coal and cellulosic ethanol residue during co-combustion

The influence of the addition of cellulosic ethanol residue (CER) on the combustion of Indonesian sub-bituminous coal was analyzed by non isothermal thermo-gravimetric analysis (TGA). The effect of blends ratio (5%, 10%, 15% and 20%), interaction mechanism, and heating rate (5°C/min, 10°C/min, 15°C/min, 20°C/min) on the combustion process was studied. The results show that the increase of the blending ratio allows to achieve the increase of the combustibility index from 7.49E−08 to 5.26E−07 at the blending ratio of 20%. Two types of non-isothermal kinetic analysis methods (Ozawa–Flynn–Wall and Vyazovkin) were also applied. Results indicate that the activation energy of the blends decreases with increasing the conversion rate. In particular, the blending ratio of 20% confirms to have the better combustion performance, with the average value of the activation energy equal to 41.10kJ/mol obtained by Ozawa–Flynn–Wall model and 31.17kJ/mol obtained by Vyazovkin model.