Non-isothermal Thermogravimetric Analysis Research Articles

Stability of cationic and amphoteric derivatives of mannan from the yeast Candida albicans

Infection with Candida albicans can prove lethal in immuno-compromised patients. It is imperative to develop a vaccine against this common organism. The amphoteric derivatives of the mannan component of the Candida cell wall may present a prospective target for the development of such a vaccine; however, the radical processing by antigen-presenting cells of the immune system is not fully understood. In this work a set of tailor-made cationic and amphoteric derivatives of three different degrees of quaternization (DSQ 0.14–0.38) has been prepared by chemical modification of ultrasonically-treated mannan and three carboxymethylated mannan derivatives (DSCM 0.13–0.32). These were exposed to free-radical attack by OH, generated in situ by the Fenton reaction. Potential changes in composition, DSQ, and molar mass distribution due to free-radical degradation were monitored by elemental analysis, NMR and FTIR spectroscopies, and size exclusion chromatography. A protective effect of quaternization against OH degradation was found. Non-isothermal thermogravimetric analysis found that the thermal stability of this mannan was also improved by chemical modification.

Thermokinetics of SO3H-functionalized dicationic ionic liquids: Effect of anions

In this study, the kinetics of thermal degradation of three ionic liquids (ILs) were investigated using non-isothermal thermogravimetric analysis to investigate the thermal stability of ILs with various anion. Di(4-sulfonic acid) dibutyltriethylene diammonium di(hydrogen sulfate, ([DABCODBS][HSO4]2), di(4-sulfonic acid) dibutyltriethylene diammonium di(trifluoromethanesulfonate) ([DABCODBS][CF3SO3]2) and di(4-sulfonic acid) dibutyltriethylene diammonium di(chloride) ([DABCODBS][Cl]2) were subjected to thermogravimetric analysis (TGA) in the temperature range of 50-800°C at four heating rates of 10, 15, 20 and 25°C/min using nitrogen at a flow rate of 20 L/min as purge gas. The average activation energies (Ea) calculated using Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Starink methods are 163.49, 173.33 and 162.58 kJ/mol for [DAB CODB S][HSO4]2, 119.59, 130.41 and 119.07 kJ/mol for [DABCODBS][CF3SO3]2, and 199.72, 210.50 and 198.63 kJ/mol for [DABCODBS][Cl]2, respectively. The results presented through all kinetic methods are in close agreement with each other and showed a decreasing thermal stability trend of [DABCODBS][Cl]2 > [DABCODBS][HSO4]2 > [DABCODBS][CF3SO3]2. The results also showed that intermediates were formed for [DABCODBS][CF3SO3]2 and [DABCODBS][HSO4]2 until achieved total decomposition, while there was no intermediate formed for the pyrolysis kinetic of [DABCODBS][Cl]2. This study shows the effect of nature of anion towards the thermal stability and decomposition mechanism of ILs.

A surface activation function method to determine the intrinsic reactivity of coal char oxyfuel conversion

The kinetics of coal/char oxyfuel combustion by isothermal and non-isothermal thermogravimetric analysis is still controversial. The two methods were compared according to the kinetics of two coal chars (NCP anthracite, DT bituminous) combustion in kinetics-controlled regime I under different O2/CO2 and O2/N2 atmospheres. We have developed a surface activation function (SAF, F(X)) to describe the reactive specific surface area of char conversion, and then the intrinsic reaction rate can be expressed by R(X)=kPO2mF(X), the autocatalysis model (ACM) of FX=Xa1-Xc was found to be suitable under both isothermal and non-isothermal conditions, however, the exponents a and c in ACM as well as the activation energies (E) differ under these two conditions. These controversial results may be caused by the exponential function exp(−E/RT), which changes with the conversion ratio under non-isothermal conditions, which in turn affects the nonlinear modeling results of SAF. According to the isothermal study, temperature has no effect on the form of SAF in Regime I. Thus it is reasonable to use the intrinsic SAF obtained from isothermal experiments (F(X)iso) to fit the non-isothermal data. The modeled results show that ENCP = 207–220 kJ/mol under different O2/CO2 and O2/N2 atmospheres, greater than those under isothermal conditions (178–179 kJ/mol). While EDT = 159–165 kJ/mol, this agrees well with the isothermal result (163–167 kJ/mol). Furthermore, it indicates that the O2 partial pressure (PO2) has no influence on E, even though increasing PO2 or replacing CO2 in the O2/CO2 mixture with N2 increases the intrinsic reaction rate.

A comprehensive kinetics study on non-isothermal pyrolysis of kerogen from Green River oil shale

Fundamentally understanding the pyrolysis kinetics of kerogen is of prime scientific and industrial importance. Herein, bitumen- and carbonates-free kerogen sample is prepared through Soxhlet extraction followed by decarbonation of Green River oil shale, and its pyrolysis is studied by non-isothermal thermogravimetric analysis. The systematic analyses show that both the Popescu and master plots methods are not applicable to describe the kerogen pyrolysis process due to the changed reaction model and the varied activation energy over certain conversion range, respectively, while the piecewise non-linear least squares analysis is identified as an effective method to discriminate the most probable kinetic model from commonly used 15 reaction models based on four solid-state pyrolysis mechanisms. Two-stage reaction model, i.e., F1 at the early stage and F2 at the later one, is proposed to well describe the kerogen pyrolysis process, which demonstrates a wide applicability owing to their insensitivities on the heating rate and estimation methods of the activation energies. The methodology revealed here could be applicable to determine other solid-state pyrolysis kinetics and reaction mechanism.

Kinetic analysis of nanodiamonds oxidation

This study examines the oxidation kinetics of nanodiamonds (NDs) and carbon black (CB), taken for comparison, in air oxygen . The oxidation rate constants and parameters of the Arrhenius equation were determined under isothermal conditions within a temperature range from 430 to 560 °C. Thermal behavior of both carbon nanomaterials was investigated using non-isothermal thermogravimetric analysis (TGA) experiments in air and argon. Powders of NDs and CB were characterized by nitrogen adsorption, scanning electron microscopy and energy dispersion X-ray microanalysis, ATR Infrared spectroscopy, and the total titration. The effect of various parameters of the carbon nanomaterials on the oxidation rate, such as oxygen content, surface area, ash and admixture contents, and functional groups coverage, was investigated. Overall, this study confirms that the oxygen-containing surface groups generating active sites upon thermal decomposition have a major impact on the oxidation ability of NDs and CB.

A comparative study of Schiff base chelating resins: synthesis, uptake of heavy metal ions, and thermal studies

Two new chelating resins (Rciaa91 and Rciaa73) with different compositional chelating groups and degree of cross-linking were prepared by free radical copolymerization of Schiff bases obtained from condensation reaction of cinnamaldehyde (ci) with anthranilic acid (aa) and 1,4-phenylenediamine (pn) monomers. The synthesized materials were characterized using CHN analyses, FTIR, 1H-NMR, and thermal analyses (TGA, DTA). Batch technique was applied, and the contact time, pH and initial concentration of the metal ions were investigated as factors affecting the uptake behavior. The results obtained indicated that the chelating resin with larger compositional ratio of chelating moieties and lower degree of cross-linking showed lower optimum reaction time and higher uptake affinity towards the metal ions Cu(II), Cd(II), Co(II), Zn(II), Hg(II), and Pb(II), under the same conditions. Both the chelating resins showed uptake behavior of the metal ions in the following order Hg2+ > Cu2+ > Zn2+>Pb2+>Co2+ > Cd2+ each metal at its optimum pH and at the same reaction time and ion concentration. The thermal degradation behavior and stability of the resins were investigated by using non-isothermal thermogravimetric analysis (TGA/DTG/DTA), at 10 °C min-1 heating rate and under nitrogen. The Coats-Redfern method was used to evaluate the kinetic and thermodynamic parameters (ΔG*, ΔH* and ΔS*) for the prominent degradation steps in the TGA curves at 450-660 °C range.

Co-combustion characteristics and kinetic study of anthracite coal and palm kernel shell char

The non-isothermal thermogravimetric analysis was conducted to evaluate the combustion characteristics of Yangquan anthracite coal (YQ), palm kernel shell char (PC) and their blends with different mass ratios. The physical and chemical characteristics of YQ and PC were also studied systematically. The investigation shows that, compared to YQ, PC was more reactive due to the higher content of the alkali metal oxides, lower ordering degree and more developed porous structures. The combustion reactivity of YQ can be improved effectively by mixing with PC, and a synergetic effect between YQ and PC can be observed. The experimental results of the thermal degradation experiments were represented with both the random pore model (RPM) and the volume model (VM), and the activation energies and pre-exponential factors were further determined. The performance of the RPM model is slightly better than that of the VM model. The activation energies of all samples are in the range of 90.2–121.8 kJ/mol, where the lowest value of 90.2 kJ/mol is for the sample of PC at 60% mass ratio.

Dehydration Study of Piracetam Co-Crystal Hydrates

A hydrate of co-crystal of piracetam and 3,5-dihydroxybenzoic acid was obtained via crystallization from water. Single-crystal X-ray data show that piracetam/3,5-dihydroxybenzoic acid tetrahydrate (P35TH) crystallizes in the triclinic system with a P1 space group. The physicochemical properties of co-crystal hydrate were characterized using powder X-ray diffractometry, differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA), and FTIR spectroscopy. The dehydration kinetics of P35TH was monitored at various temperatures and heating rates by DSC and TGA. Activation energy of P35TH dehydration was obtained using temperature ramp DSC, isothermal and nonisothermal TGA methods. Kinetic analysis of isothermal TGA data was fitted to various solid-state reaction models. Mechanistic models derived from isothermal dehydration kinetic data are best described as a 2-dimensional diffusion mechanism. A correlation was noted between the dehydration behavior and the bonding environment of the water molecules in the crystal structure. This study is a good demonstration of complexity of co-crystal hydrate and their dehydration behavior.

Non-isothermal thermogravimetric analysis of heavy oil in an O2/CO2 atmosphere

Abstract Although heavy oil is an abundant and promising energy source, its processing and utilization are complicated due to its high density, low hydrogen/carbon ratio, and high asphaltene content. Fortunately, these problems can be mitigated by the application of oxy-fuel combustion. To gain deeper insights into the above technology, the characteristics of heavy oil combustion in an O2/CO2 atmosphere was investigated using non-isothermal thermogravimetric analysis. We demonstrate that the combustion process consisted of four stages. Low-molecular-weight hydrocarbons reacted at low temperature, whereas heavy ones required a higher temperature. Increasing the concentration of oxygen resulted in increased TGA and DSC peak intensities and decreased peak widths, and these peaks were shifted to lower temperatures. Coat-Redfern and Flynn-Wall-Ozzawa methods were used to evaluate the kinetic parameters (E, A) of the oxidation process, showing that the high-temperature activation energy was much higher than the low-temperature one due to the different molecular weights of the oxidized substrates in each region. The reaction was demonstrated to be diffusion-controlled, as reflected by the lower activation energy at high oxygen concentration and high temperature, with the influence of oxygen concentration on QO processes being much more obvious than that on SO ones.

Non-isothermal thermogravimetric analysis of pyrolysis kinetics of four oil shales using Sestak–Berggren method

In this study, the non-isothermal pyrolysis method was used to investigate the pyrolysis characteristics of oil shale from four areas: namely Nongan, Fuyu, Mongolia, and North Korea, with special emphasis on Fuyu oil shale. X-ray diffraction was performed to determine the mineral composition of the oil shale. The pyrolysis behaviours of the oil shale at different heating rates were determined by thermogravimetric analysis and differential thermogravimetric analysis. During pyrolysis, as the heating rate increased, the oil shale reaction zone moved to a higher temperature due to thermal hysteresis. The activation energies of the oil shale samples from four areas were obtained by the Flynn–Wall–Ozawa (FWO), Starink, and Friedman methods. The results showed that the activation energy was not stable throughout the conversion stage, and the overall trend showed an increase with an increase in temperature. The average activation energy in the second stage was 304, 307, and 342 kJ mol−1 for Fuyu oil shale; 328, 333, and 348 kJ mol−1 for Nongan oil shale; 341, 347, and 422 kJ mol−1 for North Korea oil shale; and 362, 363, and 379 kJ mol−1 for Mongolia oil shale by the FWO, Starink, and Friedman methods, respectively. The fluctuation of activation energy showed that thermal degradation in oil shale was a complicated multistep reaction, regardless of the area. The quality and characteristics of organic matter and mineral impacted the pyrolysis process and kinetic characteristics. The Sestak–Berggren method was used to fit the data from oil shale pyrolysis. The results indicated that the main mass loss phase of oil shale pyrolysis was controlled by a nucleation mechanism.

Non-isothermal decomposition kinetics of pyridinium nitrate under nitrogen atmosphere

The thermal stability and decomposition kinetics of the ionic liquid pyridinium nitrate was investigated by non-isothermal thermogravimetric analysis in an inert atmosphere (nitrogen). For the kinetic experiments, the thermal behavior of the sample was studied in the temperature interval from 360 up to 600 K at different heating rates (5, 10, 15 and 20 K/min).The kinetic parameters of decomposition including activation energy and pre-exponential factor under nitrogen atmosphere were evaluated by menace of two model-free methods – Friedman and Kissinger-Akahira-Sunose. Depending on the used calculation model, the obtained activation energy and pre-exponential factor values with respect to the degree of sample conversion during the kinetic experiment for method ranged in the intervals of 76.36–112.56 kJ/mol and 1.72×105–1.42×1010 min–1, respectively. Based on the attained kinetic parameter values it was established that the process of pyridinium nitrate decomposition occurred as a first-order reaction. Considering the calculated kinetic parameters, a decomposition mechanism for pyridinium nitrate was proposed.

Effects of CO2 enriched atmosphere on chars from walnut shells pyrolysis in a drop tube reactor

A laminar drop tube reactor (DTR) was used to perform fast pyrolysis of walnut shells, a ligno-cellulosic biomass sample, in nitrogen and carbon dioxide atmospheres. The DTR reached the temperature of 1300 °C and the heating rate of 104–105 °C/s. Char samples collected at different residence times along the reactor were characterized by ultimate and proximate analysis and by SEM. Char combustion reactivity was then measured by non-isothermal thermogravimetric analysis (TGA) in air.The analyses show that at residence times of 66 ms pyrolysis in N2 is not complete, whereas it is complete in CO2. For residence times of 115 ms the differences between samples produced in N2 and CO2 atmospheres level off.The derivative thermogravimetric (DTG) curves of the char combustion show the existence of multiple peaks. Notably, early combustion peaks progressively fade in the chars collected at increasing reactor residence time, confirming the completion of pyrolysis. A kinetic model of char combustion is proposed which includes multiple parallel reactions.

Drying and thermal decomposition kinetics of sugarcane straw by nonisothermal thermogravimetric analysis

This work aims the study of the drying (25 ± 3 °C–150 °C) and thermal decomposition (150–900 °C) of sugarcane straw kinetics in inert and oxidative atmospheres by nonisothermal thermogravimetry (TG) analysis using heating rates of 2.5, 5 and 10 °C/min. The drying kinetic analysis was carried out using five models, Lewis, Page, Henderson and Pabis, Midilli and Logaritmic, obtaining the activation energy of 1.25 kJ/mol, in which the Page’s model showed to be the most accurate description for both atmospheres. The thermal decomposition kinetics was analyzed through three consecutive reactions scheme, obtaining activation energies of 130, 200 and 56 kJ/mol as well as 200, 350 and 100 kJ/mol for both atmospheres, respectively. The consecutive reaction scheme allowed an excellent agreement between experimental and modeled data, providing a quality of fit similar than the obtained with independent parallel reactions scheme.

Modeling of the co-pyrolysis of rubber residual and HDPE waste using the distributed activation energy model (DAEM)

The kinetic analysis for rubber residual i.e. rubber seed shell, high density polyethylene (HDPE) waste and its mixture are investigated using distributed activation energy model (DAEM) reaction model. Furthermore, the pyrolysis characteristics from these materials are investigated by non-isothermal thermogravimetric analysis from temperature 323 K to 1173 K at varying heating rates range of 10–200 K/min in inert argon atmosphere. The average value determined for activation energy, Ea and pre-exponential factor, k0 are 54.888 kJ mol−1 and 6.923 × 104 s−1 respectively for RSS, 75.396 kJ mol−1 and 1.346 × 106 s−1 respectively for HDPE and 64.010 kJ mol−1 and 8.444 × 104 s−1 respectively for binary mixture of RSS/HDPE. By taking these values as the initial guess for Gaussian distribution, and assuming the standard deviation, σ is at 15 kJ mol−1, as well as constant k0 value for all first order reactions, the mean activation energy, E0 determined from the distribution curve for RSS, HDPE and RSS/HDPE are 55.0 kJ mol−1, 75.5 kJ mol−1 and 64.0 kJ mol−1 respectively. The values of E0 and k0 in pyrolysis of binary mixture of RSS/HDPE are found to be lower compared to the individual component of RSS and HDPE in pyrolysis process.

Biocomposites based on cellulose and starch modified urea‐formaldehyde resin: Hydrolytic, thermal, and radiation stability

Two biocomposites based on cellulose (UFC) and starch modified urea formaldehyde (UFS) resin (F/U ratio of 0.8) were synthesized using the same procedure. The hydrolitical, thermal, and radiation stability of biocomposites are determined. Also, released formaldehyde during the acid hydrolysis is determined. Biocomposites based on modified UF resin have been irradiated with (50 kGy). Cellulose modified UF resin after γ‐radiation has 1.38% released formaldehyde; unmodified UF resin has 2.21% released formaldehyde. Thermal stability of biocomposites is determined using nonisothermal thermogravimetric analysis, differential thermal gravimetry (DTG), and differential thermal analysis with IR spectroscopy. Moving the DTG peak to higher temperatures indicates an increased thermal stability of cellulose modified UF resin, which is confirmed by the FTIR analysis. Gamma radiation most often causes a decrease in the intensity of the peaks in the FTIR spectrum. POLYM. COMPOS., 40:1287–1294, 2019. © 2018 Society of Plastics Engineers

Analyzing the pyrolysis kinetics of several microalgae species by various differential and integral isoconversional kinetic methods and the Distributed Activation Energy Model

The pyrolysis kinetics of the microalgae Chlorella vulgaris (CV), Isochrysis galbana (IG), Nannochloropsis gaditana (NG), Nannochloropsis limnetica (NL), Phaeodactylum tricornutum (PT), and Spirulina platensis (SP) were studied by non-isothermal thermogravimetric analysis conducted at nine different constant heating rates. The kinetic parameters of each microalgae species were calculated using several kinetic methods, such as those of Kissinger, Friedman, Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), Vyazovkin, and the simplified Distributed Activation Energy Model (DAEM). The results show that the kinetic parameters calculated from the integral isoconversional methods OFW, KAS and Vyazovkin are similar to those determined by applying the simplified DAEM. In contrast, application of the differential isoconversional method of Friedman led to moderate deviations in the activation energies and pre-exponential factors computed, whereas the unique values of the kinetic parameters determined by the Kissinger method resulted in the highest deviations.

Higher Performance and Safer Handling: Formulation Based on 2,2,2-Trinitroethyl Formate and Nitrocellulose.

A new, green propellant formulation based on the high-energy dense oxidizer (HEDO) 2,2,2-trinitroethyl formate (TNEF) and nitrocellulose (NC) was prepared and thermally investigated using non-isothermal thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) was used to check the crystals of the oxidizer and the homogeneity of the new propellant formulation (NC-TNEF). The burning behavior of NC-TNEF was recorded by high-speed camera to observe the smoke produced. A high specific impulse (Is =257.4 s) was obtained from the characteristics calculation of the new propellant formulation by using EXPLO5_V6.03 software. The NC-TNEF mixture did not show any endothermic peak and its exothermic peak was at 204.6 °C, which means that a composite might be formed. The activation energy of the NC-TNEF was in the range of 184-190 kJ mol-1 . NC-TNEF has a higher performance and a lower hazard compared with the double-base propellant.

Thermal decomposition mechanisms of coal and coal chars under CO2 atmosphere using a distributed activation energy model

The thermal decomposition characteristics of Sanxing (SX) coal and coal chars (C500 and C850, produced at 500 and 850 °C, respectively) were tested by nonisothermal thermogravimetric analysis and a distributed activation energy model used to determine the kinetic parameters. The effects of char-making temperature were investigated. A sharp peak was seen in the relationship between X and activation energy (E) of the SX and C500 samples; no evident peak, but a ladder-shaped decline, was shown by C850. The temperatures at which E was maximized were relatively close for SX coal and C500, while the minimum value of activation energy was almost the same for the three samples. This showed the char-making process had less influence on the gasification reaction under high-temperature conditions. The results of the kinetic compensation effect between E and the pre-exponential factor (k0) showed that different kinetic compensation mechanisms occurred for the pyrolysis- and gasification-dominated stages.

Thermal stability and thermal decomposition kinetics of Ginkgo biloba leaves waste residue

Non-isothermal thermogravimetric (TG) analysis was used to investigate the thermal stability and kinetics of three types of Ginkgo biloba leaves. These three types of Ginkgo biloba leaves included: Ginkgo biloba leaves before enzymolysis and ultrasound extraction (G1), Ginkgo biloba leaves after enzymolysis and ultrasound extraction (G2), and Ginkgo biloba leaves after soxhlet extraction (G3). Thermogravimetric/dynamic thermogravimetric, (dynamic TG) experiments indicated that the thermal stability of G2 and G3 were weaker than G1. Kissinger, Flynn-Wall-Ozawa, Friedman, and Coats-Redfern methods were firstly utilized to calculate the kinetic parameters and predicted decomposition mechanism of G1, G2, and G3. The thermal decomposition of G1, G2, and G3 were all corresponded to random nucleation and growth, following the Avrami-Erofeev equation, and activation energy of which were 191.4, 149.9, and 201.6 kJ/moL, respectively. In addition, the thermal decomposition G1, G2, and G3 were endothermic, irreversible and non-spontaneous.

Study of temperature and irradiation influence on the physicochemical properties of Aspirin

Pure Aspirin samples were treated with a wide spectrum of light (γ-ray, UV- lamp and sunlight) and 40 °C temperature at various time of exposure. The changes in the thermal degradation parameters, crystalline structure, morphology and purity due to radiation and temperature treatments of Aspirin were pursued by comparing their TGA, XRD, SEM and HPLC results. The non-isothermal thermogravimetric analysis curves (TG, DTG and DSC) at 10 °C min−1 heating rate, under nitrogen flow and overheating range of 25–650 °C showed two degradation steps for the treated and untreated Aspirin samples. Accordingly, their thermal behavior and thermal stability were determined. Aspirin samples treated with 40 °C and UV-12 h were proven to be of the lowest thermal stability as their TDTG values (166.7 and 168.8 °C) were lower than that of the untreated sample (TDTG = 181 °C). The degradation kinetics parameters (i.e. activation energy, pre-exponential factor and order of reaction), life time prediction and thermodynamic parameters (ΔG*, ΔH* and ΔS*) were worked out using the Coats-Redfern (CR) expression and standard equations. The lowest activation energy (104.3 kJ mol−1) associated with the highest degradation rate was observed for the UV-12 h treated Aspirin sample. Crystallinity percentage was estimated from XRD and DSC, whereas, morphology and purity changes due to treatments were detected by scanning electron microscopy (SEM) and HPLC. The significant change in crystallinity from the XRD results of the treated Aspirin samples occurred in the (32.2%–58.7%) range. The photocatalytic degradation of Aspirin samples before and after treatments was carried out using TiO2/sunlight system. The photocatalytic degradation of all samples followed pseudo first order kinetics and the shelf life, rate of reaction and efficiency of degradation were determined and discussed. The highest degradation percentage (∼99%) and the associated lowest shelf life (4.3–5.8 min) were observed in the photocatalytic degradation of the 40 °C, UV-12 h, γ-ray-aqueous and sunlight treated samples.