Simulation approach to decomposition kinetics and thermal hazards of hexamethylenetetramine

The thermal stability of HMT under dynamic, isothermal and adiabatic conditions was investigated using differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC), respectively. It is found from the dynamic DSC results that the exothermic decomposition reaction appears immediately after endothermic peak, a coupling phenomenon of heat absorption and generation, and the endothermic peak and exothermic peak were indentified at about 277–289 and 279–296 °C (T_peak) with the heating rates 1, 2, 4 and 8 °C min⁻¹. The ARC results reveal that the initial decomposition temperature of HMT is about 236.55 °C, and the total gas production in decomposition process is 6.9 mol kg⁻¹. Based on the isothermal DSC and ARC data, some kinetic parameters have been determined using thermal safety software. The simulation results show that the exothermic decomposition process of HMT can be expressed by an autocatalytic reaction mechanism. There is also a good agreement between the kinetic model and kinetic parameters simulated based on the isothermal DSC and ARC data. Thermal hazards of HMT can be evaluated by carrying out thermal explosion simulations, which were based on kinetic models (Isothermal DSC and ARC) to predict several thermal hazard indicators, such as T_D24, T_D8, TCL, SADT, ET and CT so that we can optimize the conditions of transportation and storage for chemical, also minimizing industrial disasters.

     

Thermal decomposition and kinetics studies on the 2,2-dinitropropyl acrylate–styrene copolymer and 2,2-dinitropropyl acrylate–vinyl acetate copolymer

In the present work, kinetics of thermal decomposition of 2,2-dinitropropyl acrylate–styrene copolymer (DNPA/St) and 2,2-dinitropropyl acrylate–vinyl acetate copolymer (DNPA/VAc) was investigated by differential scanning calorimetry (DSC). The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of the copolymer was verified. The results showed that, as the heating rate was increased, decomposition temperature of the copolymer was increased. Also, the kinetic parameters such as activation energy and frequency factor of the copolymer were obtained from the DSC data by the isoconversional methods proposed by Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). Average activation energy obtained by KAS and FWO methods for the thermal decomposition reaction of DNPA/St and DNPA/VAc are 157.38 ± 0.27 and 147.67 ± 0.57 kJ mol^?1, respectively. The rate constants for thermal decomposition calculated from the activation parameters showed the structural dependency. The relative stability of two copolymers under 50 °C was in this order: DNPA/St > DNPA/VAc. The results of thermogravimetry (TG) analysis revealed that the main mass changes for DNPA/St and DNPA/VAc occurred in the temperature ranges of 200–270 °C. The DSC-FTIR analysis of DNPA/St indicates that the band intensity of nitro and other groups increased haphazardly from 230 °C due to thermal decomposition.     

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.     

Improvement of thermal decomposition properties of ammonium perchlorate particles using some polymer coating agents

This research aimed to investigate the optimum conditions for modification of thermal decomposition properties of ammonium perchlorate (AP) particles through microencapsulation techniques. A solvent/non-solvent method has been used to perform microencapsulation of AP particles with some polymer-coating agents such as viton A and nitrocellulose (NC). Differential scanning calorimetry, thermogravimetry, and scanning electron microscopy have been exploited to investigate the thermal properties, heat of decomposition, and coating morphology of pure and coated samples. The preliminary results revealed that AP microparticle could be effectively coated with both NC and viton, but the latter significantly and unfavorably attenuated heat of decomposition of AP so NC was chosen as an appropriate coating agent for modification of thermal properties of AP. The thermal analysis of NC-coated samples, prepared at optimized coating conditions, showed that its first stage decomposition temperature increases about 12 °C with respect to uncoated sample and reaches to 305 °C. Also, the apparent activation energy (E), ΔG ^≠, ΔH ^≠, and ΔS ^≠ of the decomposition processes of the pure and coated AP particles at the optimum conditions were obtained by non-isothermal methods that proposed by ASTM and Ozawa. Finally, the results of this investigation showed that microencapsulation of AP particles with fibrous NC enhance its heat of decomposition (~120 J g^?1) with no obvious effect on kinetic parameters and thermal decomposition temperature.     

The simulation of the thermal behavior of energetic materials based on DSC and HFC signals

Two small calibre and four medium calibre types of propellants were investigated non-isothermally (0.25–4K min⁻¹) by differential scanning calorimetry (DSC) in the range of RT-260°C and isothermally (60–100°C) by heat flow calorimetry (HFC). The data obtained from both techniques were used for the calculation and comparison of the kinetic parameters of the decomposition process. The application of HFC allowed to determine the kinetic parameters of the very early stage of the reaction (reaction progress α below 0.02) what, in turn, made possible the precise prediction of the reaction progress under temperature mode corresponding to real atmospheric changes according to STANAG 2895. In addition, the kinetic parameters obtained from DSC data enabled determination of self-accelerating decomposition temperature (SADT) and comparison of the predicted ignition temperature during slow cook-off with the experimental results. The study contains also the results of the calculation of the time to maximum rate (TMR_ad) of the propellants under adiabatic conditions.     

过氧化苯甲酸叔丁酯的热分解动力学研究及SADT推算

研究了过氧化苯甲酸叔丁酯的热分解动力学及不同包装规格下的自加速分解温度(SADT),利用C600微量热仪测试了过氧化苯甲酸叔丁酯的热分解特征,得到升温速率分别为0.1 K/min、0.2 K/min、0.5 K/min、1 K/min下热流随时间的变化曲线,并使用Friedman等转化率法对所得的实验数据进行分析处理,得到了过氧化苯甲酸叔丁酯的分解反应活化能、指前因子等热动力学参数,推算了不同包装规格的过氧化苯甲酸叔丁酯的SADT。结果表明TBPB分解活化能及指前因子随转化率变化而变化,活化能范围为42-135.5 kJ/mol,指前因子范围为0.25-33.5,在25L聚乙烯桶包装下的SADT为59℃,50L下为52℃,200L下为46℃。     

Kinetics of Thermal Decomposition of Solid Propellant Based on Aluminum and Ammonium Perchlorate

Kinetic regularities of the mass loss and heat and-gas release were studied in the thermal decomposition of a solid propellant composed of aluminum, ammonium perchlorate, and a polymer binder. It was shown that, under heating from 40 to 340°C under permanent vacuum conditions, propellant samples decompose without ignition, with the limiting mass loss in the decomposition being 48%. When experiments were performed in air, the propellant formulation decomposes with sharp ignition, with the inflammation temperature (270–287°C) and amount of volatiles released by this instant of time (10–16 wt %) dependent on the heating rate. The kinetic regularities of the mass loss in the decomposition of a solid propellant were described in terms of the polychromatic kinetics model that assumes that the reaction system has ensembles of particles differing in reactivity. The distribution functions of the mass fractions of the propellant by activation energies of decomposition were calculated. The heat release kinetics in the decomposition of a propellant formulation in the temperature range 153–270°C in a closed evacuated system is described by a sum of equations for two parallel reactions: 1st-order reaction with a heat effect Q₁ = 200 ± 5 kJ kg^–1 and 1st-order autocatalysis with heat effect Q₂ = 1900 ± 50 kJ kg–1. The rate constants and the activation parameters of the process were determined.

     

Influence of some lime-containing additives on the thermal behavior of urea

Urea is one of the main nitrogen fertilizers used in agriculture. But being well soluble in water, hardly 50% of its nitrogen is assimilated by plants. One possibility to eliminate this disadvantage is to use coating agents for modification of urea to obtain a controlled-realized fertilizer. The aim of this research was to study the influence of different lime-containing additives on the thermal behavior and decomposition kinetics of urea in oxidizing atmosphere. Commercial fertilizer-grade urea (46.4% N) and analytical-grade CaO, MgO, CaCO₃, MgCO₃ were used in the experiments. In addition, one Estonian limestone and one dolomite sample were used as additive or coating material. The experiments with a Setaram Setsys 1750 thermoanalyzer coupled to a Nicolet 380 FTIR Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 900 °C at the heating rate of 5 °C min^?1 and to calculate kinetic parameters, additionally, at 1, 2, and 10 °C min^?1 in the atmosphere containing 80% of Ar and 20% of O₂. The differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results obtained indicate that thermooxidative decomposition of urea as well as the blends of urea with lime-containing materials and urea prills coated with limestone or dolomite powder follows a complex reaction mechanism.     

Thermal behavior and decomposition kinetics of Formex-bonded explosives containing different cyclic nitramines

Thermal behavior and decomposition kinetics of Formex-bonded PBXs based on some attractive cyclic nitramines, such as 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Actually, cis-1,3,4,6-tetranitrooctahy droimidazo-[4,5-d]imidazole (BCHMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10, 12-hexaazaisowurtzitane (CL-20), was investigated by means of nonisothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that the mass loss rate of PBXs involved in this research depends greatly on heating rate and the residue of the decomposition of these PBXs decreases with the heating rate. The onset of the exotherms was noticed at 215.4, 278.7, 231.2 and 233.7 °C with the peak maximum at 235.1, 279.0, 231.2 and 233.7 °C for RDX-Formex, HMX-Formex, CL-20-Formex, and BCHMX-Formex, respectively. Their corresponding exothermic changes were 1788, 1237, 691, and 1583 J g^?1. It was also observed that the dependence on the heating rate for onset temperatures of HMX- and BCHMX-based PBXs was almost the same due to their similar molecular structure. In addition, based on nonisothermal TG data, the kinetic parameters for thermal decomposition of these PBXs were calculated by isoconversional methods. It was shown that the Formex base has great effects on the activation energy distribution of nitramines. It was further found that the kinetic compensation effects occurred during the thermal decomposition of nitramine-based PBXs, and they almost have the same compensation effects due to similar decomposition mechanism.     

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.     

Thermal decomposition properties of double-base propellant and ammonium perchlorate

The thermal decomposition properties and the heat of combustion (ΔH) of samples with different ammonium perchlorate (AP)/double base propellant (DB) mass ratios under argon atmosphere were studied by the thermogravimetry–differential scanning calorimetry–mass spectrometry–Fourier transform infrared spectroscopy (TG–DSC–MS–FTIR) and automatic calorimeter method. The results show that decomposition process of AP/DB samples in negative and zero oxygen balance (OB) is different from that in positive OB. With the increasing of AP in the AP/DB samples, the decomposition of the samples becomes more and more severe. When the OB of the samples is positive, the phenomenon of deflagration or explosion could be observed in the decomposition process. The sample with OB = 0 has the greatest heat of combustion.     

A facile synthesis of boron nanostructures and investigation of their catalytic activity for thermal decomposition of ammonium perchlorate particles

In this research, ultrasound irradiation as a simple method was used to produce boron nanostructures. Reaction conditions such as boron concentration and sonication time show important roles in the size, morphology and growth process of the final products. The boron nanostructures (nanoparticles and nanorods) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, small-angle X-ray scattering and inductively coupled plasma atomic emission spectroscopy techniques. Primary evaluation of results showed that nanoparticles and nanorods of boron successfully have been prepared with 25–40 and 50–100 nm average particle size, respectively. These nanostructures (nanoparticles and nanorods) were studied as an additive for promoting the thermal decomposition of ammonium perchlorate (AP) particles. Thermochemical decomposition behaviors of treated samples were characterized by thermal gravimetric analysis and differential scanning calorimetry techniques. Also, the kinetic parameters of thermal decomposition processes of pure and treated samples were obtained by nonisothermal methods proposed by Kissinger and Ozawa. However, boron nanoparticles with the smallest average particle size (25–40 nm) have the most significant catalytic effect including the decrease in decomposition temperature of AP + B nanocomposite by 100 °C, increase in the heat of decomposition from 580 to 1354 J g^?1 and decrease in activation energy from 207 to 110 kJ mol^?1.     

Effect of the catalyst MCM-41 on the kinetic of the thermal decomposition of poly(ethylene terephthalate)

The aim of this work is to determine the activation energy for the thermal decomposition of poly(ethylene terephthalate)—PET, in the presence of a MCM-41 mesoporous catalyst. This material was synthesized by the hydrothermal method, using cetyltrimethylammonium as template. The PET sample has been submitted to thermal degradation alone and in presence of MCM-41 catalyst at a concentration of 25% in mass (MCM-41/PET). The degradation process was evaluated by thermogravimetry, at temperature range from 350 to 500 °C, under nitrogen atmosphere, with heating rates of 5, 10 and 25 °C min^?1. From TG, the activation energy, determined using the Flynn–Wall kinetic method, decreased from 231 kJ mol^?1, for the pure polymer (PET), to 195 kJ mol^?1, in the presence of the material (MCM-41/PET), showing the catalyst efficiency for the polymer decomposition process.     

Thermal behaviour and kinetic study of some triazoles as potential anti-inflammatory agents

Thermogravimetric (TG), differential thermogravimetric analysis and differential scanning calorimetry had been used to characterize the thermal stability of four new heterocyclic compounds with triazolic structure. The four analysed compounds have similar thermal behaviours, namely the thermal mal curves of these new compounds show three thermal events. These compounds were thermally stable up to 110 °C. Above this temperature, the evolution of hydrochloric acid took place as observed by EGA. Identification and the monitoring of gaseous species released during thermal decomposition of pure triazoles in air atmosphere have been carried out by coupled TG–FTIR. Between 110 and 220 °C the main gaseous product is HCl which was identified on the basis of these FTIR spectra. Arguments for a rapid thermooxidation of the four molecules were brought by EGA by identifying the substances which arise from both the destruction of side chains and of triazolic ring. The kinetic analysis of the destruction process of triazolic structure was investigated using the TG data in air for the substance’s decomposition in non-isothermal conditions. The isoconversional methods, Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Friedman, were applied to determine the activation energy from the analysis of four curves measured at different heating rates. In order to obtain realistic kinetic parameters, even if the decomposition process is a complex one, the non-parametric kinetics method was also used. A good agreement between the data obtained from the four applied methods was found.     

Devolatilization behaviour and pyrolysis kinetic modelling of Spanish biomass fuels

The basic pyrolysis behaviour of eight different biomass fuels has been tested in a thermogravimetric analyser under dynamic conditions (5, 20 and 50 °C min^?1 heating rates) from room temperature up to 1,000 °C. Their decomposition was successfully modelled by three first-order independent parallel reactions, describing the degradation of hemicellulose, cellulose and lignin. Hemicellulose would be the easiest one to pyrolyse, while lignin would be the most difficult one. Experimental and calculated results show good agreement. The reactivity of the different biomass type functions of various thermal, kinetic and composition parameters are discussed. The effect of the heating rate on pyrolysis behaviour was studied, and a comparison between slow and fast heating rate reveals a small displacement of the DTG profiles to higher temperatures. The heating rate not only affects the highest mass loss rate temperature but also influences the mass loss rate value.     

Synthesis and thermal decomposition of ditetrazol-5-ylamine

Ditetrazol-5-ylamine (DTA) was synthesized from cyanuric chloride in four steps. The thermal decomposition of DTA in the solid state was studied by thermogravimetry, volumetry, mass spectrometry, IR spectroscopy, and calorimetry. Under isothermal conditions at 200–242 °C, thermal decomposition obeys the first order autocatalytic kinetics. The kinetic and activation parameters of DTA decomposition were determined. The composition of gaseous reaction products and the structure of condensed residue were studied. The thermal effect of thermal DTA decomposition is 281.4 kJ mol⁻¹. The nitrogen content in a mixture of gaseous products formed by the reaction in a temperature interval of 200–242 °C exceeds 97 vol.%. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1660–1664, July, 2005.     

Thermal behavior of coffee oil (Robusta and Arabica species)

Coffee seeds are a source for obtaining oil which is used in the candy, soluble coffee, and cosmetics industries. The main purpose of this study was the investigation of the lipid profile and thermal behavior of the roasted and in nature coffee oil of Arabica and Robusta species, using thermogravimetry, differential thermal analysis, derivative thermogravimetry, differential scanning calorimetry (DSC), and modulated DSC. Details concerning the thermal decomposition as well as data of the kinetic parameters have been described here. The kinetic studies were evaluated from several heating rates with a sample mass of 10 mg in open crucible under nitrogen atmospheres. The obtained data were evaluated with the isoconversional kinetic method, where the values of activation energy (E _a/kJ mol^?1) were evaluated in function of the conversion degree (α). In addition, this oil was evaluated by modulated DSC from 25 to ?60 °C, where the transition phase behavior was verified.     

Thermal parameters study of 1,1-bis(tert-butylperoxy)cyclohexane at low heating rates with differential scanning calorimetry

Having two active peroxide groups, 1,1-bis(tert-butylperoxy)cyclohexane (BTBPC) has a certain degree of thermal instability. It is usually used as an initiator in a chemical process, and therefore, careless operation could result in severe accidents. This study emphasized the runaway reactions of BTBPC 70 mass% (4.5–5.2 mg), the relevant thermokinetic parameters, and the thermal safety parameters. Differential scanning calorimetry was used to evaluate the above-mentioned thermokinetic parameters, using four low heating rates (0.5, 1, 2, and 4 °C min^?1) combined with kinetic simulation method. The results indicated that apparent exothermic onset temperature (T _o), apparent activation energy (E _a), and heat of decomposition (ΔH _d) were ca. 118 °C, 156 kJ mol^?1, and 1,080 kJ kg^?1, respectively. In view of process loss prevention, at the low heating rates of 0.5, 1, 2, and 4 °C min^?1, storing BTBPC 70 mass% below 27.27 °C is a more reassuring approach.     

Thermal stability of ketoprofen��active substance and tablets

Simultaneous thermoanalytical techniques were used for the characterization of the thermal decomposition of ketoprofen??active substance and tablets. DTA and DSC curves showed that ketoprofen melts before the decomposition. A kinetic study regarding the ketoprofen??active substance??s thermal decomposition was performed under non-isothermal conditions and in a nitrogen atmosphere at five heating rates: 2.5, 5, 7.5, 10 and 15 °C min^?1. The kinetic parameters of thermal decomposition process were obtained from TG/DTG curves using the following differential methods: Friedman isoconversional, Chang, respectively, integral methods: Flynn?CWall?COzawa, Kissinger?CAkahira?CSunose, Coats?CRedfern and Madhusudanan. The careful treatment of the kinetic parameters obtained in certain thermal conditions was confirmed to be necessary as well as a different strategy of experimental data processing.