Kinetic study of template removal of Al-MCM-41 synthesized at room temperature

The Al-MCM-41 molecular sieve with Si/Al = 20 molar ratio was synthesized at room temperature and characterized by X-ray diffractometry, surface area, thermogravimetry, and infrared spectroscopy. The kinetic study was conducted by Vyazovkin and Ozawa method, in order to verify the activation energy during the Hofmann degradation between 130 and 370 °C, in which most of surfactant removal occurs. The results suggest that the activation energy for template removal is close to 80 kJ mol^?1 lower in Al-MCM-41 synthesized at room temperature, when compared to results obtained for mesopores Al-MCM-41 and MCM-41 synthesized by hydrothermal method. This lower activation energy may be understood as consequence of textural properties, such as higher pore size.     

New findings on thermal degradation properties of fluoropolymers

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 ± 11 and 268 ± 13 kJ mol^?1, respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 ± 14 kJ mol^?1. The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 °C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 °C would be underestimated for >20%.     

Kinetic study of degradation of heavy oil over MCM-41

Thermogravimetry was applied in order to investigate the catalytic degradation of heavy oil (15.4^oAPI) over silica-based MCM-41 mesoporous molecular sieve. This material was synthesised by the hydrothermal method, using cetyltrimethylammonium bromide as organic template. The physicochemical characterization by nitrogen adsorption, X-ray diffraction, and thermogravimetry, showed that the obtained material presents well-defined structure, with a uniform hexagonal arrangement. The thermal and catalytic degradation of heavy oil was performed by thermogravimetric measurements, in the temperature range from 30 to 900 °C, at heating rates of 5, 10, and 20 °C min⁻¹. By using the model-free kinetics, proposed by Vyazovkin, it was determined that the activation energy to degrade the heavy oil was ca. 128 kJ mol⁻¹, and for degradation of oil in presence of MCM-41, this value decreased to 69 kJ mol⁻¹, indicating the performance of the mesoporores catalyst for the degradation process.     

Studies on the thermal behavior and decomposition kinetic of drugs cetirizine and simvastatin

Understanding the response of drugs and their formulations to thermal stresses is an integral part of the development of stable medicinal products. In the present study, the thermal degradation of two drug samples (cetirizine and simvastatin) was determined by differential scanning calorimetery (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the cetirizine occurs during two temperature ranges of 165–227 and 247–402 °C. The TG/DTA analysis of simvastatin indicates that this drug melts (at about 143 °C) before it decomposes. The main thermal degradation for the simvastatin occurs during two endothermic behaviors in the temperature ranges of 238–308 and 308–414 °C. The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of both the drug samples was verified. The results showed that as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by ASTM E696 method, the values of activation energy for cetirizine and simvastatin were 120.8 and 170.9 kJ mol^?1, respectively. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Thermal stability of ionene polymers

Two different cationic polymers of the same chemical type and with very similar chemical structures were reacted with a natural bentonite over a wide range of polymer/clay ratios. This study involved the synthesis of cationic aliphatic ammonium polyionenes, specifically 3,6-ionene and 3,6-dodecylionene. Ionenes are ion-containing polymers that contain quaternary nitrogen atoms in the main macromolecular chain as opposed to a pendant chain. The CHN content, basal spacing, and elemental composition of each of the polymer–clay complexes were analyzed by X-ray diffraction, X-ray fluorescence, and thermogravimetry. All the polycations reacted to form interlayer complexes with clay, which displaced more Na⁺ and little Ca²⁺. Sodium and calcium were both present as interlayer cations in the clay and its complexes. The TG/DTG curves show that both polymers underwent thermal degradation in more than one stage. Specifically, 3,6-ionene was found to undergo two stages of decomposition and 3,6-dodecylionene undergo three stages. The behavior of the TG/DTG curves and the activation energy values suggest that 3,6-dodecylionene (E = 174,85 kJ mol^?1) complexes have greater thermal stability than 3,6-ionene (E = 115,52 kJ mol^?1) complexes. The mechanism of degradation suggests a direct interaction with the dodecyl chain containing 12 carbons, which are present in 3,6-dodecylionene but not in 3,6-ionene.     

Thermoanalytical and NMR investigation of NaBH<Subscript>4</Subscript> × 2H<Subscript>2</Subscript>O thermolysis process

This paper describes the thermal investigations and kinetic analysis regarding the solid-state degradation of three compounds used as mental disorder therapeutic agents (antidepressants), namely amitriptyline, desipramine and imipramine. The study was carried according to ICTAC 2000 recommendations, by using three isoconversional methods, namely Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Friedman. The differential method of Friedman indicated multistep degradation, which was later confirmed by the nonparametric kinetic method (NPK). NPK method showed that all three tricyclic antidepressants are degraded by two processes. In terms of apparent activation energies for decomposition, the NPK method indicated 123.4 kJ mol^?1 for imipramine, 112.3 kJ mol^?1 for desipramine and 82.9 kJ mol^?1 for amitriptyline, and the results are in good agreement with the ones suggested by isoconversional methods.     

Thermogravimetric analyses revealed the bioenergy potential of <Emphasis Type="Italic">Eulaliopsis binata</Emphasis>

The present study was focused on the thermal degradation of Eulaliopsis binata biomass produced on a salt-affected soil without any fertilizer or pesticide applications. The plant biomass was subjected to thermal degradation experiments at three heating rates, 10, 30 and 50 K min^?1. The kinetic analyses were performed through isoconversional models of Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa, followed by the calculation of thermodynamic parameters of activation. The high heating value was calculated as 15.10 MJ mol^?1. The activation energy values of the grass were shown to be ranging from 118 through 240 kJ mol^?1. Energy difference of enthalpies of activation between the reagent and the activated complex was in accordance with activation energies. Pre-exponential factors indicated the reaction to follow first-order kinetics. Gibbs free energy for the grass was measured to be ranging from 171 to 174 kJ mol^?1. Our data have shown that E. binata biomass offers remarkable potential as a low-cost biomass for bioenergy.     

Performance of birnessite-type manganese oxide in the thermal-catalytic degradation of polyamide 6

Birnessite-type manganese oxide (BMO) was prepared by oxidation of Mn(NO₃)₂ with H₂O₂ in KOH solution. The nature and the extent of degradation of polyamide 6 (PA6) in the presence of samples were analysed by thermogravimetric analysis under static air atmosphere at several heating rates between 5 and 30 °C min^?1. The surface and structure of BMO were characterized using infrared (IR) spectroscopy, X-ray diffraction, and thermal analysis techniques. The acid sites of BMO were investigated by IR using pyridine as a molecular probe. The activation energy for degradation estimated by Kissinger method for PA6 and BMO/PA6 system containing 10 mass% of BMO was found to be 212 and 144 kJ mol^?1 under air, respectively. The catalytic activity observed in BMP catalyst was associated to a high lattice oxygen mobility.     

Thermogravimetric analysis of walnut shell as pyrolysis feedstock

Thermal degradation behavior and kinetics of a biomass waste material, namely walnut shell, were investigated by using a thermogravimetric analyzer. The desired final temperature of 800 °C was achieved at three different heating rates (2, 10, and 15 °C min^?1) under nitrogen flow (50 mL min^?1). The TG and DTG curves exhibited three distinct zones that can mainly be attributed to removal of water, decomposition of hemicellulose + cellulose, and decomposition of lignin, respectively. The kinetic parameters (activation energy, pre-exponential factor, and reaction order) of active pyrolysis zone were determined by applying Arrhenius, Coats?CRedfern, and Horowitz?CMetzger methods to TG results. The values of activation energies were found to be between 45.6 and 78.4 kJ mol^?1. There was a great agreement between the results of Arrhenius and Coats?CRedfern methods while Horowitz?CMetzger method yielded relatively higher results. The existence of kinetic compensation effect was evident.     

Advanced isoconversional and master plot analyses on solid-state degradation kinetics of a novel nanocomposite

The decomposition kinetics of glycerol diglycidyl ether (GDE)/3,3-dimethylglutaric anhydride/nanoalumina composite have been investigated by thermogravimetry analysis under nonisothermal mode. The activation energy, E _a, of the solid-state decomposition process was evaluated using the advanced isoconversional method. From the experimental data, the dependence of conversion on temperature and activation energy was constructed allowing calculating the master plots. Our results showed that the decomposition mechanism at temperatures below 400 °C could be fitted by R2 kinetic model with E _a = 143 kJ mol^?1. The information about the kinetic parameters based only on thermal degradation data has been used for quick lifetime estimation at different temperatures. The Vyazovkin method was also employed to predict the times to reach α = 0.5 at isothermal mode using the activation energy calculated by the advanced isoconversional approaches. Scanning electron microscopy (SEM) analysis was carried out to investigate the fracture surface morphology. It was revealed from the SEM images that the presence of nanoalumina results in reinforcement of GDE matrix.     

Study on thermal decomposition and oxidation kinetics of cation exchange resins using non-isothermal TG analysis

Kinetics of two successive thermal decomposition reaction steps of cationic ion exchange resins and oxidation of the first thermal decomposition residue were investigated using a non-isothermal thermogravimetric analysis. Reaction mechanisms and kinetic parameters for three different reaction steps, which were identified from a FTIR gas analysis, were established from an analysis of TG analysis data using an isoconversional method and a master-plot method. Primary thermal dissociation of SO₃H⁺ from divinylbenzene copolymer was well described by an Avrami–Erofeev type reaction (n = 2, g(α) = [?ln(1 ? α)]^1/2]), and its activation energy was determined to be 46.8 ± 2.8 kJ mol^?1. Thermal decomposition of remaining polymeric materials at temperatures above 400 °C was described by one-dimensional diffusion (g(α) = α ²), and its activation energy was determined to be 49.1 ± 3.1 kJ mol^?1. The oxidation of remaining polymeric materials after thermal dissociation of SO₃H⁺ was described by a phase boundary reaction (contracting volume, g(α) = 1?(1 ? α)^1/3). The activation energy and the order of oxygen power dependency were determined to be 101.3 ± 13.4 and 1.05 ± 0.17 kJ mol^?1, respectively.     

Kinetics and Mechanism of the Exothermic First-stage Decomposition Reaction of Dinitroglycoluril

Introduction Dinitroglycoluril (DINGU) is a typical cyclourea nitramine. Its crystal density is 1.94 gcm-3. The detonation velocity corresponding to =1.94 gcm-3 is about 8450 ms-1. Its sensitivity to impact is better than that of cyclotrimethylenetrinitramine. It has the potential for possible use as high explosive from the point of view of the above-mentioned high performance. Its preparation,1-4 properties1-4 and hydrolytic behavior4 have been reported. In the present paper, we report i…     

Synthesis, structure analysis and thermodynamics of [Ni(H2O)4(TO)2](NO3)2·2H2O (TO = 1,2,4-triazole-5-one)

A novel complex [Ni(H₂O)₄(TO)₂](NO₃)₂·2H₂O (TO = 1,2,4-triazole-5-one) was synthesized and structurally characterized by X-ray crystal diffraction analysis. The decomposition reaction kinetic of the complex was studied using TG-DTG. A multiple heating rate method was utilized to determine the apparent activation energy (E _a) and pre-exponential constant (A) of the former two decomposition stages, and the values are 109.2 kJ mol^?1, 10^13.80 s^?1; 108.0 kJ mol^?1, 10^23.23 s^?1, respectively. The critical temperature of thermal explosion, the entropy of activation (ΔS ^≠), enthalpy of activation (ΔH ^≠) and the free energy of activation (ΔG ^≠) of the initial two decomposition stages of the complex were also calculated. The standard enthalpy of formation of the new complex was determined as being ?1464.55 ± 1.70 kJ mol^?1 by a rotating-bomb calorimeter.     

Thermal properties and kinetics of new-generation posterior bulk fill composite cured light-emitting diodes

In this study, the thermal behavior in terms of glass transition (T _g), degradation, and thermal stability of four commercial new-generation posterior bulk fill composites (Surefill SDR, Dentsply; Quixfill, Dentsply; Xtrabase, Voco; and Xtrafill, Voco) activated by light-emitting diodes (LEDs) was analyzed by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The activation energies (E _a) for the decomposition of the dental resins were calculated based on the Kissinger and Doyle kinetic models from the peaks of the endothermic curves obtained when the specimens were heated at four different temperatures (5, 10, 15, and 20 °C min^?1) during DSC. The results show that the Xtrabase composite displayed the highest T _g (120 °C at a 5 °C min^?1 heating rate) and E _a (157.64 kJ mol^?1) values associated with thermal degradation from the main chain of the polymer.     

Thermal decomposition kinetic evaluation and its thermal hazards prediction of AIBN

AIBN (2,2′-azobis (isobutyronitrile)), widely used for blowing agent and initiator, is a typical self-reactive material, being capable of undergoing runaway reaction due to its self-heating during storage or transportation. In this study, the thermal decomposition process of AIBN was studied by differential scanning calorimetry at different heating rates. The kinetic parameters including the activation energy and pre-exponential factor at different stages were calculated, and the laws of parameter variation were analyzed using the software, named as Advanced Kinetics and Technology Solutions, which can also predict the thermal stability of decomposition process at actual situations, such as ton and kg scale. The results show that heating rate can influence evidently the thermal behavior of AIBN, which can decompose in liquid phase or in liquid–solid co-existing phase, or, even decomposes in solid phase; according to Friedman method, the value of the calculated activation energy is 122 kJ mol^?1; according to Ozawa method, the value decreases gradually with the reaction process, and the smallest one is 124 kJ mol^?1. By mg-scale prediction under isothermal condition, it is known that AIBN decomposes at 30 °C (room temperature), very slowly; by ton-scale prediction under adiabatic condition, the safety diagram of AIBN is acquired, which shows how the time to the maximum rate changes with the initial temperature under ideal adiabatic condition (Φ = 1), for example, for TMR_ad = 24 h, the corresponding mean temperature (i.e., TD₂₄) is 71.23 °C, and for the initial temperature 71.23 °C, the lower and upper limits of the confidence intervals (95 % probability) are 18.5 and 31 h; by kg-scale prediction, it is obtained that the self-accelerating decomposition temperature of 50 kg AIBN with standard package is 63 °C, which is close to that of ARC.     

Study of the Thermal Stability Properties of Pyridoxine Using Thermogravimetric Analysis

The thermal decomposition behavior and kinetics of pyridoxine in nitrogen-only and air atmospheres were studied using thermogravimetry analysis (TGA). Kinetic interpretation of thermal analysis data for pyridoxine decomposition was carried out using Ozawa and ASTM E698 isoconversional methods. The activation energy of the decomposition process varied with the degree of decomposition and was different in the nitrogen and air atmospheres. At a 5% decomposition level, the activation energy and the pre-exponential factor were found to be 28.3 kcal mol^?1 and 1.2 × 10¹⁴ min^?1, respectively, in the nitrogen-only atmosphere. Thermal stability was determined by calculating the time for 5% of the pyridoxine vitamer to decompose at 25°C. The calculated shelf life for the pyridoxine vitamer obtained via TGA was surprisingly smaller in nitrogen (0.9 years) than in air (1.5 years). This is speculated to be the result of a more complex decomposition mechanism in air, involving thermo-oxidative decomposition in the presence of oxygen.     

Kinetic and thermodynamic parameters of volatilization of biodiesel from babassu, palm oil and mineral diesel by thermogravimetric analysis (TG)

The boiling point and volatility are important properties for fuels, as it is for quality control of the industry of petroleum diesel and biofuels. In addition, through the volatility is possible to predict properties, such as vapor pressure, density, latent heat, heat of vaporization, viscosity, and surface tension of biodiesel. From thermogravimetry analysis it is possible to find the kinetic parameters (activation energy, pre-exponential factor, and reaction order), of thermally simulated processes, like volatilization. With the kinetic parameters, it is possible to obtain the thermodynamic parameters by mathematical formula. For the kinetic parameters, the minor values of activation energy were found for mineral diesel (E = 49.38 kJ mol^?1), followed by babassu biodiesel (E = 76.37 kJ mol^?1), and palm biodiesel (E = 87.00 kJ mol^?1). Between the two biofuels studied, the babassu biodiesel has the higher minor value of activation energy. The thermodynamics parameters of babassu biodiesel are, ΔS = ?129.12 J mol^?1 K^?1, ΔH = +80.38 kJ mol^?1 and ΔG = +142.74 kJ mol^?1. For palm biodiesel ΔS = ?119.26 J mol^?1 K^?1, ΔH = + 90.53 kJ mol^?1 and ΔG = +141.21 kJ mol^?1, and for diesel ΔS = ?131.3 J mol^?1 K^?1, ΔH = +53.29 kJ mol^?1 and ΔG = +115.13 kJ mol^?1. The kinetic thermal analysis shows that all E, ΔH, and ΔG values are positive and ΔS values are negative, consequently, all thermodynamic parameters indicate non-spontaneous processes of volatilization for all the fuels studied.     

Kinetics of the thermal decomposition of anhydrous cobalt nitrate by SCRT method

It has been shown the ability of the Sample Controlled Reaction Temperature (SCRT) method for both discriminate the kinetic law and calculate the activation energy of the reaction. This thermal decomposition is best described by a Johnson–Mehl–Avrami kinetic model (with n = 2) with an activation energy of nuclei growth which fall in the range 52–59 kJ mol^?1. The process is not a single-step because the initial rate of decomposition is likely to be limited by nucleation. The results reported here constitute the first attempt to use the new SCRT method to study the kinetic of the thermal decomposition of cobalt nitrate.     

Coordination of extraframework Li+ cation in the MCM-22 and MCM-36 zeolite: FTIR study of CO adsorbed

Nature and population of Li⁺ cationic sites in MCM-22 zeolite and its pillared form (MCM-36) were investigated by means of adsorption of CO as a probe molecule. CO stretching frequency and adsorption heat were measured by FTIR spectroscopy and adsorption microcalorimetry. Intrazeolitic carbonyl complexes on Li⁺ cations in MCM-22 and MCM-36 are characterized by two main vibrational bands at 2,195 and 2,188 cm^?1. Band at higher wavenumbers is ascribed to carbonyls on Li⁺ ions coordinated only to two oxygen atoms at the intersection of 10-ring channels and interacting with CO molecule by energy around 45 kJ mol^?1. Band at 2,188 cm^?1 was assigned to the carbonyls on Li⁺ cations located on top of 5 or 6-rings on the channel walls and coordinated to three or four oxygen atoms, interacting with CO molecule by energy 33–36 kJ mol^?1. Effect of pillaring and layered form of zeolite on nature and population of Li⁺ cationic sites is also discussed, as well as the formation of dicarbonyl complexes.     

Kinetic analysis of co-pyrolysis of cellulose and polypropylene

The present research work focuses on understanding the kinetics and mechanism of co-pyrolysis of cellulose, a major constituent of biomass, and polypropylene (PP) that is abundantly present in waste plastics. Co-pyrolysis of cellulose and PP of different compositions, viz., 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 (mass%/mass%), was carried out in a thermogravimetric analyzer at various heating rates from 5 to 180 K min^?1. The kinetics of slow to medium heating rate pyrolysis was analyzed using first Kissinger and Kissinger–Akahira–Sunose techniques. Cellulose and PP decomposition occurred in two distinct temperature regimes, viz., 575–650 and 675–775 K, respectively. However, apparent activation energies of thermal decomposition of the mixtures clearly indicated the presence of interaction between cellulose and PP. The presence of cellulose in the mixture decreased the apparent activation energy of PP decomposition from 210 to 120 kJ mol^?1, while the presence of PP did not affect the apparent activation energy of cellulose decomposition (E _a = 158 ± 3 kJ mol^?1). A significant decrease in apparent activation energy was observed in the conversion regime corresponding to the completion of cellulose pyrolysis and beginning of PP pyrolysis. Differential scanning calorimetry data clearly showed the shift of exothermic char formation to higher temperatures with PP incorporation in the mixture. The presence of PP also resulted in reduction of final char content. Based on the above analyses, a new interaction step that involves a bimolecular reaction of activated PP with volatiles from cellulose pyrolysis to form interaction products and char is proposed, and the rate limiting steps for char formation are clearly identified.