Thermogravimetry Experiments Research Articles

The competitive adsorption behavior of CO and H2 molecules on FeO surface in the reduction process

The competitive adsorption behavior of CO and H2 molecules on FeO surface in the reduction process was investigated by TG (thermogravimetry) experiments and MD (molecular dynamics) simulation. The model based on the Langmuir adsorption equations was built to describe the adsorption ability of CO and H2 molecules on the FeO surface. The results show that: oxygen atoms cooperate with iron atoms to have influences on the adsorption ability of CO molecules. When the Fe mole fraction is higher than the critical value of 0.57, the governed factor of carbon monoxide's adsorption is converted from oxygen atoms to iron atoms, but the hydrogen's adsorption is only governed by oxygen atoms on the FeO surface. The experimental results is offered by the explanations that there exist a attractive force between carbon atoms and iron atoms and carbon monoxide could be spontaneously adsorbed on the iron shell of FeO surface while the adsorption of hydrogen on the iron shell is unstable. The high temperature will weaken strength of carbon monoxide's adsorption because of a negative effect on the adsorption energy.

The influence of soluble components on spontaneous combustion risk of sawdust samples

Sawdust is a common by-product of wood processing industry. Spontaneous combustion would even take place under unfavorable conditions of storage and transportation. In this study, self-heating substances test experiments, Thermogravimetry (TG) experiments and Frank-Kamenetskii (FK) theory were used to compare the spontaneous combustion risk of three sawdust samples (DCP, CFE, and LOH). The results revealed that the Critical Ambient Temperatures (CATs) of DCP, CFE and LOH were 81.2 (±0.3), 96.0 (±0.4) and 125.9 (±0.3)°C respectively when the stack dimension reached 1.6 m. Lower CAT for sample indicated that it had a higher spontaneous combustion risk. On the other hand, the relationship between spontaneous combustion risk and soluble components of three sawdust samples was studied with Gas Chromatographic and Mass Spectrometric (GC–MS) experiments. The results found that if a sawdust sample contained more soluble components than other sawdust samples, the spontaneous combustion risk of this sample would also higher than other sawdust samples, and vice versa.

Thermal behavior and structural study of ZrO2/poly(ε-caprolactone) hybrids synthesized via sol-gel route

The thermal behavior of pure ZrO2 and four ZrO2-based organic-inorganic hybrids (OIHs) containing increasing amount (6, 12, 24 and 50 wt%) of poly(ε-caprolactone) (PCL) (named Z, ZP6, ZP12, ZP24 and ZP50 respectively) has been studied by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The FTIR analysis of the gas mixture evolved at defined temperatures from the samples submitted to the TG experiments identified the mechanism of each thermally activated process. The obtained results suggest that the inorganic matrix of the OIHs prepared by this method exerts a stabilizing effect on the polymer, in particular for poor-PCL hybrid materials. In fact, the different thermal behavior of the ZP50 sample suggests that the polymer is not entirely bonded to the -OH groups of the zirconia matrix due to their saturation. For this reason a part of PCL is not affected by the stabilizing effect of the matrix and is subjected to thermal degradation. Finally, by observing their thermal behavior it was possible to select the most suitable temperatures for thermal pretreatment: 400, 600 and 1000 °C. The structural analysis by X-ray diffraction (XRD) revealed that at 400 °C the materials are amorphous, while at 600 °C they are mostly tetragonal, and the content of the tetragonal phase decreases with increasing the amount of PCL in the OIHs. All the materials treated at 1000 °C are monoclinic, but their crystallinity decreases with increasing the PCL content.

Thermal Properties of Multilayer Nanocomposites Based on Halloysite Nanotubes and Biopolymers

This paper reports a novel procedure to fabricate multilayer composite biofilms based on halloysite nanotubes (HNTs) and sustainable polymers. Among the biopolymers, the non-ionic (hydroxypropyl cellulose) and cationic (chitosan) molecules were selected. The nanocomposites were prepared by the sequential casting of ethanol solutions of hydroxypropyl cellulose and aqueous dispersions of chitosan/HNTs. The composition of the bio-nanocomposites was systematically changed in order to investigate the effect of the hydroxypropyl cellulose/HNTs ratio on the thermal properties of the films, which were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). DSC studies were conducted in the static air (oxidative atmosphere), while TG measurements were carried out under nitrogen flow (inert atmosphere). The analysis of DSC data provided the enthalpy and the temperature for the oxidative degradation of the bio-nanocomposites. These results were helpful to estimate the efficacy of the well-compacted middle layer of HNTs as a flame retardant. TG experiments were performed at a variable heating rate and the collected data were analyzed by the Friedman’s method (non-isothermal thermogravimetric approach) with the aim of studying the kinetics of the hydroxypropyl cellulose degradation in the multilayer nanocomposites. This work represents an advanced contribution for designing novel sustainable nanocomposites with excellent thermal behavior as a consequence of their peculiar multilayer structure.

Low-temperature oxidation of light and heavy oils via thermal analysis: Kinetic analysis and temperature zone division

This research is intended to investigate low-temperature oxidation (LTO) behavior and kinetics of light and heavy oils and to divide their LTO intervals. Ramped thermogravimetry/derivative thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC) experiments and isothermal TG experiments with different temperature intervals were used to characterize LTO behavior and to obtain kinetic parameters determined by Ozawa–Flynn–Wall (OFW) and general reaction rate models. The results indicated that there were three (two) distinct variation trends about the conversion rate versus temperature for light (heavy) oil in the LTO region, manifesting the LTO interval of light (heavy) oil should be controlled by multiple-step mechanisms and divided into at least three (two) reaction subintervals. The LTO interval of both light and heavy oils used could be subdivided into three temperature intervals inferred from the variation trend of activation energy over temperature for ramped experiments. Additionally, the LTO region of both light and heavy oils held three subzones in the aspect of isothermal tests. For light oil, the reaction rate augmented from 50 to 250 °C where the activation energy was positive, while it reduced from 250 to 350 °C coupled with negative activation energy. As for heavy oil, the reaction rate presented an increasing trend in the first and third subintervals (50–150 °C and 250–350 °C) with positive activation energy and a declining trend in the second subinterval (150–250 °C) with negative activation energy. It is believed that this research can add new insights to the LTO interval division of crude oil regarding to the isothermal and non-isothermal conditions, which are of significance for understanding LTO reaction pathways and mechanisms.

Effect of different humectants on the thermal stability and fire hazard of nitrocellulose

In order to ensure the thermal safety of nitrocellulose (NC) mixtures in the process of handing, storage, and usage, it is necessary to obtain the thermal stability and fire hazard of NC with different humectants. In this study, the thermogravimetry experiments with four heating rates (5, 10, 15, 20 C min−1) under nitrogen and air atmospheres were performed to investigate the thermal stability of two NC-humectants, namely NC-water and NC-ethanol mixtures, and pure NC. Moreover, the influence of humectants on the fire hazard of NC was evaluated by the ISO 5660 Cone Calorimeter test. The humectant, water or ethanol, can increase the activation energy and reduce the fire risk of NC. Compared with the NC with water, the NC with ethanol exhibits lower activation energy and higher fire hazard.

Reduction Characteristics of Carbon-Containing REE–Nb–Fe Ore Pellets

To separate and recover the valuable metals from low-grade REE (rare earth elements)–Nb–Fe ore in China, the reduction characteristics of carbon-containing REE–Nb–Fe ore pellets, including mineral phase variation, reduction degree, and reaction kinetics, were observed based on thermogravimetry experiments. The results showed that the reduction and separation efficiency of valuable metals in the carbon-containing pellets were superior to the ones in the previous non-compact mixture. After the reduction roasting of the pellets at 1100 °C and a subsequent magnetic separation, the iron powder with a grade of 91.7 wt % was separated, and in magnetic separation tailings the grades of Nb2O5 and (REE)O were beneficiated to approximately twice the grades in the REE–Nb–Fe ore. The reaction rate of the reduction of the carbon-containing pellets was jointly controlled by the carbon gasification reaction and the diffusion of CO in the product layer with an activation energy of 139.26–152.40 kJ·mol−1. Corresponding measures were proposed to further improve the kinetics condition.

Pyrolytic behavior of waste extruded polystyrene and rigid polyurethane by multi kinetics methods and Py-GC/MS

The utilization of polymer wastes for volatile fuel production has been considered as a sustainable and environmental-friendly approach for achieving better waste management, pollution protection, and renewable energy security. Polymer pyrolysis, as an ideal method for polymer waste converted into storable fuel, was explored thoroughly in this study from pyrolysis kinetics to evolved gas analysis. Two typical building-used polymer wastes, extruded polystyrene (XPS) and rigid polyurethane (RPU), were selected to conduct a series of thermogravimetry (TG) experiments. Then commonly-used isoconversional methods were employed to calculate the kinetic parameters of the pyrolysis during the whole conversion. Kinetic models of XPS and RPU thermal degradations were identified from nineteen reaction models by Coats-Redfern and masterplots methods. Then accommodation function was employed to adjust the theoretical model for reconstruction. Considering the complexities of RPU component and degradation process, Py-GC/MS was used to identify the volatile product component at 250, 340, and 460 °C, respectively. Results showed that there are large parts of volatile alcohols and ethers escaped during RPU pyrolysis process. The results of this study have implications concerning kinetic triplet determination method and escaped gas analysis during polymer waste pyrolysis process.

Identification of Compounds Released During Pyrolysis of Palm Kernel Shell (PKS) Using Pyrolysis-GC/MS

Pyrolysis is one of thermochemical conversion to convert biomass into bio-oil. The higher energy content in bio-oil suggests its potential as a raw material in the production of energy, bio-fuels, and other chemicals. Pyrolysis of PKS and the chemicals released were studied using pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) at 400-600°C. Prior to pyrolysis, thermogravimetry experiments were carried out to monitor the degradation temperature of hemicellulose, cellulose, and lignin in the PKS. Degradation of hemicellulose occurred within a temperature range of 150-330°C, whereas the cellulose was degraded in temperatures range between 330-400°C. Degradation of lignin took place within a broad range of temperatures, which reached maximum at temperatures range of 200-500°C. Based on the Py-GC/MS results, pyrolysis of PKS at 400°C produced bio-oil that can be used as biofuel due to its high aromatic compounds but low carboxylic acids contents. Keywords: bio-oil; chemical; palm kernel shell; Py-GC/MS; thermogravimetry .

Low-temperature oxidation and thermal kinetics analysis of light and medium crude oils

ABSTRACTIn this research, low-temperature oxidation (LTO) and thermal kinetics analysis of light and medium crude oils were analyzed by static isothermal experiments and thermogravimetry (TG). The results elucidated that, during LTO process, medium oil possessed stronger oxygen consumption capability than light oil and oxygen addition was the dominating reaction path for both light and medium oils; more heavy components contained in medium oil were oxidized to form higher molecular-weight material with lower H/C. In TG experiments, three main reaction zones were identified known as LTO, fuel deposition (FD) and high-temperature oxidation (HTO). Compared with light oil, LTO range and corresponding mass loss were lowered for medium oil with more oxygenated compounds left behind to be converted into coke materials. The activation energy for medium oil were higher than that for light oil in LTO stage while less in HTO stage owing to the difference of oil components.

Thermal Behavior and Structural Study of SiO₂/Poly(ε-caprolactone) Hybrids Synthesized via Sol-Gel Method.

SiO2-based organic-inorganic hybrids (OIHs) are versatile materials whose properties may change significantly because of their thermal treatment. In fact, after their preparation at low temperature by the sol-gel method, they still have reactive silanol groups due to incomplete condensation reactions that can be removed by accelerating these processes upon heating them in controlled experimental conditions. In this study, the thermal behavior of pure SiO2 and four SiO2-based OIHs containing increasing amount (6, 12, 24 and 50 wt %) of poly(ε-caprolactone) (PCL) has been studied by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The FTIR analysis of the gas mixture evolved at defined temperatures from the samples submitted to the TG experiments identified the mechanisms of thermally activated processes occurring upon heating. In particular, all samples already release ethanol at low temperature. Moreover, thermal degradation of PCL takes place in the richest-PCL sample, leading to 5-hexenoic acid, H2O, CO2, CO and ε-caprolactone. After the samples’ treatment at 450, 600 and 1000 °C, the X-ray diffraction (XRD) spectra revealed that they were still amorphous, while the presence of cristobalite is found in the richest-PCL material.

Thermochemical assessment of the load-bearing capacity of steel-reinforced elastomeric bearings subjected to fire loading

This paper addresses the characterization and analysis of the thermochemical behavior of steel-reinforced elastomer (polychloroprene) bearings during fire loading. Based on results obtained from thermogravimetry (TGA) and differential scanning calorimetry (DSC) experiments, a thermochemical model capturing the effective behavior of the elastomer is proposed. The obtained material model is implemented in a finite element program for evaluating the evolution of temperature and material degradation within steel-reinforced elastomeric bearings commonly employed in engineering practice. In a first step, the analysis tool is applied to the re-analysis of experiments, where sections of a steel-reinforced elastomeric bearing are subjected to a pre-specified temperature load while measuring the temperature increase within the steel and elastomer layers. Measured data and simulation results show good agreement, finally paving the way for the application of the proposed analysis tool to the analysis of the time-dependent heat penetration of steel-reinforced elastomeric bearings in the course of a fire incident. The obtained results provide useful information on the remaining load-bearing capacity of elastomeric bearings finally entering the safety analysis of buildings and bridges supported by these bearings.

Organic modification of montmorillonite and effect of catalytic selectivity on the dimerization of unsaturated fatty acid

This study describes the selective synthesis of C36-dimer fatty acids, by reacting unsaturated fatty acid at 533 K for 6 h in the presence of montmorillonite and lithium chloride as the catalyst and cocatalyst, respectively. The catalytic performance of different montmorillonite and organic modified montmorillonite catalysts was investigated in the dimerization of technical grade unsaturated fatty acid, and the influence of the catalyst structure and composition on the catalytic performance was analyzed. All the samples were characterized by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetry (TG), and dispersion experiments. The results show that the layer spacing and dispersion property of the montmorillonite crystal have important effects on its catalytic performance and the yield of the product. In the dimerization experiments, the maximum yield of the dimer acid is found to be 70.15%, while the lowest yield is 32.37%. It is thought that the larger interlayer spacing in the montmorillonite provides more reaction space for the unsaturated fatty acid, allows the generation of a large volume of dimeric molecules, and helps the product molecules to diffuse out from the layered structure.

Characterization of CO2 Absorption and Carbamate Precipitate in Phase-Change N-Methyl-1,3-diaminopropane/N,N-Dimethylformamide Solvent

A phase-change solvent for CO2 absorption was prepared by mixing N-methyl-1,3-diaminopropane (MAPA) and N,N-dimethylformamide (DMF). In this MAPA/DMF solvent, MAPA-carbamate precipitate was formed after CO2 absorption to facilitate reducing energy consumption of amine regeneration. The CO2 uptake of MAPA/DMF solvent (14.8 mg/g solvent) was increased by 22% compared with that of MAPA/water solvent (12.1 mg/g solvent). For MAPA/DMF solvent, time was reduced by 22% to reach the CO2 absorption equilibrium. The maximum CO2 uptake rate of MAPA/DMF solvent was 30% higher than that of MAPA/water solvent because DMF displayed higher CO2 solubility and lower MAPA-carbamate solubility than water. Differential scanning calorimetry and thermogravimetry experiments revealed that MAPA(H+)2 and MAPA(CO2–)2 compositions in MAPA-carbamate precipitate first decomposed (peak temperature = 59.9 °C). Subsequently, the MAPACO2 compositions in precipitate also decomposed (peak temperature = 124.2 °C).

Thermal behavior and dehydration kinetic study of SiO2/PEG hybrid gel glasses

Six different silica‐polyethylene glycol (SiO2/PEG) organic‐inorganic hybrid nanocomposites with different amounts of PEG 400 (6, 12, 24, 50, 60 and 70 wt.%) were synthesized by the sol‐gel technique. Their thermal behavior was studied by thermogravimetry (TG) and differential thermal analysis (DTA) under a flowing argon atmosphere in a wide temperature range and their behavior was compared with those of the related materials with 60 and 70 wt.% of PEG, whose results were reported in a previously study. To identify all physical and chemical processes occurring in these promising materials, the gases evolved during TG experiments were analyzed at characteristic constant temperatures by FTIR. These measurements revealed that all the materials undergo a two‐step dehydration (loosing water physically bound at temperature lower than 100°C) with overlapping of both TG and DTA curves, thus suggesting an identical behavior up to 200°C regardless the different content of PEG. A different behavior is observed at higher temperature, where three different exothermic effects were observed in the range 200–450°C accompanied by mass losses ranging from 6 to 37% for the SiO2/PEG hybrid materials. POLYM. ENG. SCI., 57:606–612, 2017. © 2017 Society of Plastics Engineers

Thermal Decomposition Kinetics of Wood and Bark and Their Torrefied Products

The pyrolysis kinetics of Norway spruce, its bark, and their torrefied products was studied. Thermogravimetry (TGA) was employed with linear and stepwise heating programs. Altogether 36 TGA experiments were evaluated simultaneously by the method of least-squares. Part of the kinetic parameters could be assumed common for the studied samples without a considerable worsening of the fit quality. This process results in better defined parameters and emphasizes the similarities between the studied materials. Three pseudocomponents were assumed. Two of them were described by distributed activation energy models (DAEM), while a simpler kinetics was assumed for the pyrolysis of the cellulose content of the samples. The pyrolysis kinetics of the wood and the torrefied wood showed remarkable similarities to the bark and torrefied bark, though essential differences were also observed.

Thermophysical and transport properties of blends of an ether-derivatized imidazolium ionic liquid and a Li+-based solvate ionic liquid

The ‘solvate’ ionic liquid (IL), comprising of a 1:1 complex of lithium bis(trifluoromethanesulfonyl)amide (LiTf2N) and tetraglyme (G4), denoted herein by [Li(G4)][Tf2N], is promising as a relatively nonvolatile, nonflammable, and safer electrolyte for lithium-ion batteries. It, however, suffers from the drawback of low ionic conductivity compared with the conventional organic carbonate electrolytes. We report herein the enhancement in the thermal and transport properties of [Li(G4)][Tf2N] by blending it with an ether-derivatized imidazolium IL, namely 1-(2-methoxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [mEtMeIm][Tf2N]. The volumetric and transport properties of [mEtMeIm][Tf2N], and its blends with [Li(G4)][Tf2N], were investigated at temperatures in the range of 10–85 °C using oscillating U-tube densitometry, cone and plate viscometry, and electrochemical impedance spectroscopy. The addition of [mEtMeIm][Tf2N] to [Li(G4)][Tf2N] lowered the viscosity and increased the ionic conductivity of the blends. The blends also exhibited improved thermal stability in thermogravimetry experiments. Notwithstanding the complex intermolecular interactions existing in the mixture of the [mEtMeIm][Tf2N], LiTf2N, and G4, the density, viscosity, and conductivity data could be modeled assuming the blend to be a simple binary mixture of [Li(G4)][Tf2N] and [mEtMeIm][Tf2N], instead of a ternary mixture of [mEtMeIm][Tf2N], LiTf2N, and G4. The addition of unchelated LiTf2N to [mEtMeIm][Tf2N] resulted in a decrease in ionic conductivity at all temperatures of measurement. However, when LiTf2N was added as a 1:1 complex with G4, the conductivity was higher, at the same molar concentration of LiTf2N. The implications of these results are discussed in view of developing thermally and chemically stable IL-based electrolytes for Li ion batteries, especially for operation at elevated temperatures.

Investigation on the ignition, thermal acceleration and characteristic temperatures of coal char combustion

Through using a new thermal analysis model and a method of coal/char combustion, the minimum ignition temperature and minimum ignition heat of three different ranks of pulverized coal char were measured by simultaneous Thermogravimetry and Differential Scanning Calorimetry (TG-DSC) experiments. The results show that the ignition of coal char occurs in the range between the minimum ignition temperature and the inflection-point temperature. The thermal acceleration and its gradient GT increase with increasing heating rate and decrease with increasing coal char rank. The higher the GT of the coal char, the more easily the ignition occurs and more rapidly the burning and burnout occur. The data show that the GT of coal char of SLH lignite is 1.6 times more than that of coal char of ZCY bituminous and JWY anthracite in ignition zone, and 3.4 times in burning zone. The characteristic temperatures increase with increasing temperature of prepared char, heating rate and char rank. Moreover, the Tig,max calculated in DSC experiment is approximately in line with the ignition temperature obtained in the entrained flow reactor, which demonstrates the feasibility of the proposed theory.

Thermal decomposition of Tatarstan Ashal’cha heavy crude oil and its SARA fractions

In this research, heavy crude oil from Ashal’cha field, Republic of Tatarstan, and its SARA (saturate, aromatic, resin and asphaltene) fractions were analyzed by differential scanning calorimetry (DSC) and thermogravimetry (TGA) methods. The experiments were performed at three different heating rates (10, 20, 30°C/min) for DSC and at single heating rate for TGA analysis, all under the air atmosphere. In DSC experiments, two main reaction regions were detected at each heating rate known as low and high temperature oxidation reactions. On the other hand, in TGA experiments, one main region was observed. For all the SARA fractions studied, highest heat of reaction was observed in lowest heating rate. The kinetic analysis of the crude oils and their fractions was also performed using ASTM E-698 and Arrhenius methods, respectively. Activation energy values of the crude oil sample and the fractions varied between 69.2 and 201.8kJ/mol in LTO region and 82.9–182.1kJ/mol in HTO regions, respectively. In Arrhenius method, the activation energy values were in the range of 33.1–108.9kJ/mol.

Experimental study on the corresponding relationship between the index gases and critical temperature for coal spontaneous combustion

The critical temperature is a key parameter in coal spontaneous combustion. To acquire variation of the critical temperature and the corresponding relationship between the index gases and critical temperature, we gleaned the coal samples from No. 3 seam in Yanzhou coalfield, Shandong Province, China. Thermogravimetry (TG) was used to analyze the effects of particle size, heating rate, and oxygen concentration on critical temperature. The index gases were determined by 15-t experimental furnace of coal spontaneous combustion. The results showed that the critical temperature measured by TG experiment indicates a trend that is augmented with the increase in particle size. When the heating rate was set up with 5 °C min−1 and the oxygen concentration was 14.9 mass% (13 vol%), the critical temperatures of coal samples with different particle sizes reached the maximal values. When the heating rate rose to 20 °C min−1 and the oxygen concentration was 14.9 mass% (13 vol%), the critical temperatures of coal samples with particle sizes 0.105 mm. As the particle was smaller than 0.098 mm, the difference in critical temperatures during two kinds of heating rate tended to first increase, then decrease, and reached a maximum under the condition that the oxygen concentration was 14.9 mass% (13 vol%), while it reached a minimum when the particle size was larger than 0.098 mm and presented a style of “M.” The critical temperature as measured by TG experiment was in the range of 45.4–103.2 °C. The critical temperature is, respectively, achieved in coal spontaneous combustion by the 15-t experimental furnace, in which the concentrations of CO and CO2 increased obviously and the value of CO2/CO reached its maximum.