Modeling thermal analysis for predicting thermal hazards relevant to transportation safety and runaway reaction for 2,2′-azobis(isobutyronitrile)

The pure decomposition behavior of 2,2′-azobis (isobutyronitrile) (AIBN) and its physical phase transformation were examined and discussed. The thermal decomposition of this self-reactive azo compound was explored using differential scanning calorimetry (DSC) to elucidate the stages in the progress of this chemical reaction. DSC was used to predict the kinetic and process safety parameters, such as self-accelerating decomposition temperature (SADT), time to maximum reaction rate under adiabatic conditions (TMR_ad), and apparent activation energy (E_a), under isothermal and adiabatic conditions with thermal analysis models. Moreover, vent sizing package 2 (VSP2) was applied to examine the runaway reaction combined with simulation and experiments for thermal hazard assessment of AIBN. A thorough understanding of this reaction process can identify AIBN as a hazardous and vulnerable chemical during upset situations. The sublimation and melting of AIBN near its apparent onset decomposition temperature contributed to the initial steps of the reaction and explained the exothermic attributes of the peaks observed in the calorimetric investigation.     

Thermal research on the uncontrolled behavior of styrene bulk polymerization

Thermal runaway can occur during the styrene bulk polymerization process because of easily formed local hotspots resulting from the high viscosity of reactants and the difficulty of heat dissipation. To obtain the thermal hazard characteristics, the polymerization behavior of styrene was investigated using differential scanning calorimetry (DSC) at a scanning rate of β = 2 °C/min. Experimental results showed that the exothermic peaks obtained for heat initiation were different from those obtained when initiator was added. The exothermic peak changed from one to two after the initiator was added. The exothermic onset temperature (T₀) was also reduced. Phi-tech II was utilized to study the bulk polymerization of styrene in an adiabatic environment. The adiabatic temperature rise (ΔT_ad), starting temperature of uncontrolled polymerization (T_star), maximum temperature (T_end), and heat of polymerization (ΔH) under different conditions were acquired. When the dose of the additive was increased, the starting temperature of uncontrolled polymerization (T_star) decreased and the adiabatic temperature rise (ΔT_ad) increased gradually. Severity grading was performed based on the severity evaluation criteria of runaway reaction. The results can help designers decide whether it is necessary to take certain measures to reduce risk.     

The thermal hazard evaluation of 1,1-di (tert-butylperoxy) cyclohexane by DSC using non-isothermal and isothermal-kinetic simulations

1,1-Di (tert-butylperoxy) cyclohexane (DTBPH) has been widely employed in the chemical industry. Unfortunately, organic peroxides have been involved in many serious fires and explosions in manufacturing processes, storage, and transportation. This study investigated the thermokinetic parameters by isothermal kinetic and non-isothermal-kinetic simulation, using differential scanning calorimetry (DSC) tests. DSC was applied to assess the kinetic parameters, such as kinetic model, frequency factor (ln k₀), activation energy (E_a), reaction order, and heat of reaction (ΔH_d). Comparisons of non-isothermal and isothermal-kinetic model simulation led to a beneficial kinetic model of thermal decomposition to predict the thermal hazard of DTBPH. Simulations of a 0.5 L Dewar vessel and 25 kg barrel commercial package in liquid thermal explosion models were performed and compared to the results in the literature. From the results, the optimal conditions for use of DTBPH to avoid violent runaway reactions during the storage and transportation were determined. This study established the features of thermal decomposition that could be executed as a reduction of energy potential and storage conditions in view of loss prevention.     

Research on thermal decomposition characteristics of H foaming agent with different moisture contents

N, N-Dinitroso pentamethylene tetramine, also known as H foaming agent, is a self-reactive chemical substance commonly used in the rubber industry. Decomposition, explosion and combustion may be caused by the presence of fire or high temperature. As a high-risk chemical that is strictly regulated in China, H foaming agent has ever triggered multiple accidents. During the study of the decomposition thermal process of H foaming agent, it was found that the presence of moisture content at different levels had a significant effect on its thermal stability. The thermal characteristics of H foaming agent under different moisture contents was studied through the test means such as adiabatic calorimetry and high-pressure differential scanning calorimetry. Through isothermal calorimetry experiment, it was found that the decomposition of H foaming agent had obvious auto-catalytic characteristics. In the moisture content within the range of 0–40%, with the increase of moisture content, the initial exothermic temperature T_onset of the mixture system of H foaming agent and water decreased, while the time from initial heat release to rapid temperature rise of the reaction system (induction period) was gradually prolonged, and the temperature increment of the reaction system was increased gradually. As the proportion of moisture content in the system increased, the adiabatic temperature rise ΔT_ad of the mixture system of H foaming agent and water gradually decreased, meanwhile the time to maximum rate under adiabatic condition (TMR_ad) gradually decreased. The research results have guiding significance for finding the reasonable moisture content of H foaming agent in the drying process and determining the upper temperature limit during storage and transportation.     

Evaluation of thermal hazard characteristics of four low temperature reactive azo compounds under isothermal conditions

The polymerization reaction can lower the threshold of the required energy by the initiator to improve the efficiency of the overall process reaction. Emerging polymerization initiators are also a major focus of process improvement and technological progress. Azo compounds (azos), which used in dyeing applications, are subsequently used in polymerization reactions due to their highly exothermic reaction characteristics. Although higher heat release can promote polymerization and modify the product, heat generation may also cause process hazards.These thermal hazard parameters were studied by selecting dimethyl 2,2′-azobis(2,4-dimethylvaleronitrile) (ABVN), 2,2′-azobis(2-methyl propionate) (AIBME), 2,2′-azobis(2-methylpropionamide) dihydrochloride (AIBA), and 2,2′-azobis(isobutyronitrile) (AIBN), which are common azo initiators at present. Thermal hazards are closely related to the reaction kinetics of the substance itself. The form of the reaction, the apparent activation energy and the thermodynamic parameters of the exothermic mode were also obtained.Kinetic analysis of the actual process using the experimental data of the isothermal calorimetry model is rarely used in the evaluation of related thermal hazard characteristics. The simulation results revealed the kinetic azo models and were further applied to calculate the runaway situations of azo under specific boundary conditions.     

Reaction hazard and mechanism study of H2O2 oxidation of 2-butanol to methyl ethyl ketone using DSC,Phi-TEC II and GC-MS

Methyl ethyl ketone (MEK) oxidation via H₂O₂ with tungsten-based polyoxometalate catalysts has gained much attention with an ever-growing body of knowledge focusing on the development of environmentally benign processes in chemical industry. In this study, two calorimetry techniques, differential scanning calorimetry (DSC) and Phi-TEC II adiabatic calorimetry, were employed to analyze the thermal hazards associated with the 2-butanol oxidation reaction system. Hydrogen peroxide was the oxidant and a tungsten-based polyoxometalate as the catalyst. Gas chromatography-mass spectrometry was used for identification of the organic products. Important thermal kinetic data were obtained including “onset” temperature, heat of reaction, adiabatic temperature rise and self-heat rate. From DSC results, three exothermic peaks were detected with a total heat generation of approximately 1.26 kJ/g sufficiently to induce a thermal runaway. Possible reaction pathway for three stages were proposed based on both DSC and GC-MS results. One exotherm was detected by Phi-TEC II calorimeter and the pressure versus temperature profile together with the DSC and GC-MS data demonstrate the complexity of 2-butanol reaction system under both thermal screening and adiabatic conditions.     

Thermal runaway reaction for highly exothermic material in safe storage temperature

Highly exothermic materials have caused many serious accidents involving storage and transportation, due to being thermally reactive. The safe storage and management of these materials is still a critical problem in many countries. Our aim was to study the thermal hazard of thermal reactive materials, such as a propellant, by employing differential scanning calorimetry (DSC) non-isothermal tests and isothermal tests, and then comparing the kinetic parameters by isothermal and non-isothermal of kinetics. The chosen approach was to obtain reliable thermal decomposition by a safe and effective method, which acquired the kinetic and safety parameters of storage conditions that could be applied as highly exothermic materials' reduction of loss prevention and energy potential for safer design during storage transport and processing operations.     

Process hazard assessment of energetic ionic liquid with kinetic evaluation and thermal equilibrium

With the continuous development of battery technology, there are new research investments in materials of various parts. In the field of electrolytes, ionic liquids (IL) are considered to be excellent electrolytes and have been widely studied in distinct energy fields. However, it is necessary to pay attention to the safety characteristics of ionic liquids at high temperature due to the application of energy, but there is little research on the reaction and kinetics of ionic liquids. To ensure the safety of ionic liquids, such as high temperature, the common ionic liquid 1-Ethyl-3-methylimidazolium nitrate ([Emim] NO₃) was selected for analysis. The exothermic mode is obtained from the data of differential scanning calorimetry. The basic reaction parameters of [Emim] NO₃ were determined with thermodynamic equation simulation. For ionic liquids in the actual situation, consider adding a heat balance model to estimate its temperature change pattern and find out the hazard temperature and related safety parameters. Temperature changes were estimated by constructing 25.0 g and 50.0 g packages to simulate material reactions and heat transfer in the external environment. The results showed that [Emim] NO₃ had shorter TMR_ad and TCL (<1 day) when the temperature was above 180 °C.     

Thermal hazard analysis of triacetone triperoxide (TATP) by DSC and GC/MS

Thermal degradation of triacetone triperoxide (TATP) was studied using differential scanning calorimetry (DSC) and gas chromatography/mass spectrometry (GC/MS). TATP, a potential explosive material, is powerful organic peroxide (OP) that can be synthesized by available chemicals, such as acetone and hydrogen peroxide in the laboratory or industries. The thermokinetic parameters, such as exothermic onset temperature (T₀) and heat of decomposition (ΔH_d), were determined by DSC tests. The gas products from thermal degradation of TATP were identified using GC/MS technique.In this study, H₂O₂ was mixed with propanone (acetone) and H₂SO₄ catalysis that produced TATP. The T₀ of TATP was determined to be 40 °C and E_a was calculated to be 65 kJ/mol. A thermal decomposition peak of H₂O₂ was analyzed by DSC and two thermal decomposition peaks of H₂O₂/propanone were determined. Therefore, H₂O₂/propanone mixture was applied to mix acid that was discovered a thermal decomposition peak (as TATP) in this study. According to risk assessment and analysis methodologies, risk assessment of TATP for the environmental and human safety issue was evaluated as 2-level of hazard probability rating (P) and 6-level of severity of consequences ratings (S). Therefore, the result of risk assessment is 12-point and was evaluated as “Undesirable” that should be enforced the effect of control method to reduce the risk.     

Effects of metal ions on thermal hazard of tert-butyl peroxy-3,5,5-trimethylhexanoate

As a commonly used initiator for polyethylene, tert-butyl peroxide 3,5,5-trimethylhexanoate (TBPTMH), with the molecular formula of C₁₃H₂₆O₃, is more likely to decompose and cause fires and explosions. Understanding the thermal risks of TBPTMH mixed with common metal ions, potentially in containers and pipes, is important. In this work, by using differential scanning calorimetry (DSC) and Phi-Tec adiabatic calorimetry, the effects of CuCl₂, FeCl₃, CuBr_2, and FeBr₃ on the thermal decomposition of TBPTMH were investigated. Adiabatic kinetic analysis was performed and the apparent activation energy (E_a) was calculated by thermodynamic analysis. Time to maximum rise under adiabatic conditions (TMR_ad) and the self-accelerating decomposition temperature (SADT) under different packing qualities were reckoned. It was found that the thermal risk of TBPTMH was increased while mixing these metal ions, especially CuBr₂. To ensure the safety of the substance in process industry, the temperature of TBPTMH in the presence of metal should be governed below 39.48 °C. This work was expected to provide some guidance for improving the process safety of TBPTMH.     

Thermal hazard and decomposition kinetics of 1-butyl-2,3-dimethylimidazolium nitrate via TGA/DSC and FTIR

1-Butyl-2,3-dimethylimidazolium nitrate ([Bmmim][NO₃]), a kind of versatile and novel ionic liquids, is widely applied in the modern petrochemical industry. Nevertheless, its thermal hazard safety data at high temperature or thermal disturbance conditions are currently unavailable. Therefore, this study aimed to characterize the thermal risk of [Bmmim][NO₃] through auto-ignition temperature measurements, flash point analysis, thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC), TGA-Fourier transform infrared spectroscopy (TGA-FTIR) and thermal decomposition kinetics analysis. Additionally, [Bmmim][NO₃] was examined using isothermal thermogravimetric analysis at different temperatures (220, 230, 240, 250, 260 and 270 °C). The experimental results show that the flash point of [Bmmim][NO₃] is 305.70 ± 9.30 °C and the auto-ignition temperature is 341.00 ± 21.60 °C with an ignition delay time of 8.6 s. In addition, using the nitrogen atmosphere TGA data to calculate the activation energy according to the Friedman, Kissinger and Flynn-Wall-Ozawa methods, roughly the same results were obtained. Finally, TGA-FTIR results show that [Bmmim][NO₃] produced acetylene, butane, butanol and carbon dioxide during the thermal decomposition process. This study could provide data support and some guidance for the thermal hazard assessment and safety control of [Bmmim][NO₃] during its use and storage.     

Thermal hazard evaluation for iso-octanol nitration with mixed acid

2-Ethylhexyl nitrate (2-EHN), an important additive to diesel fuel, is produced from the nitration of iso-octanol with HNO₃–H₂SO₄ mixed acid. In this study, the differential scanning calorimeter (DSC), accelerating rate calorimeter (ARC) and reaction calorimeter were used to analyze the thermal stability of 2-EHN and the thermal hazard of iso-octanol nitration. Four samples with different ratios of 2-EHN to mixed acid were tested using DSC. The results indicated that more mixed acid could catalyze the decomposition of 2-EHN. Three samples were tested using ARC and the results showed that sample 4 contained the lowest onset temperatures, T_D8 and T_D24. This shows that there is a higher probability of triggering the decomposition of the product 2-EHN from the iso-octanol nitration process. This conclusion was verified using RC1e tests at different temperatures. The RC1e experiments also indicated that the overall heat generation of these reactions was considerably large despite the high yields of the nitration process at 45 °C and 55 °C. This heat generation makes these semi-batch processes difficult to control, especially on a pilot or plant scale. Based on the maximum temperature of the synthesis reaction (MTSR) corrected by the yield, the only acceptable semi-batch process is the nitration reaction at 10 °C.     

Thermal safety assessment for solid organic peroxides

The thermal hazards of dicumyl peroxide (DCP) and benzoyl peroxide (BPO), self-reactive chemicals are identified and characterized using high-pressuredifferential scanning calorimeter, and simultaneous thermogravimetric analyzer, a C80 micro-calorimeter is used. The apparent exothermic onset temperature of DCP is found to be between the range of 112–122 °C for different heating rates in DSC tests. There are two coupled peaks of BPO around 105 °C at both the heating rates of 4.0 and 8.0 °C/min while no endothermic peak showed at lower heating rates. Furthermore, another endothermic peak appears immediately after the exothermic peak at about 211 °C of DCP under high-pressure conditions. For BPO, the endothermic peak before the exothermic peak disappears as the pressure increases to 1.0 and 1.5 MPa. The average values of apparent activation energy calculated by Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods during the conversion rate between 15 and 75% of DCP are 80.69 and 74.05 kJ/mol, and that of BPO are 119.96 and 112.93 kJ/mol, respectively. According to the isothermal tests, the thermal decomposition of DCP behaviors is an n-th order reaction while BPO conforms to the laws of autocatalytic reaction.     

Green thermal analysis for predicting thermal hazard of storage and transportation safety for tert-butyl peroxybenzoate

Liquid organic peroxides, such as tert-butyl peroxybenzoate (TBPB), have been widely employed in the petrifaction industry as a polymerization formation agent. This study investigated the thermokinetic parameters of TBPB by isothermal kinetic algorithms and non-isothermal kinetic equations, using thermal activity monitor III (TAM III) and differential scanning calorimetry (DSC), respectively. Simulations of 0.5 L, 25 kg, 55 gallon, and 400 kg reactors in liquid thermal explosion models were performed and compared to the results in the literature. A green thermal analysis was developed for a reactor containing TBPB to prevent pollution and reduce the energy consumption by thermal decomposition. It is based on the thermal hazard properties, such as the heat of decomposition (ΔH_d), activation energy (E_a), self-accelerating decomposition temperature (SADT), control temperature (CT), emergency temperature (ET), and critical temperature (TCR). From the experimental results, the optimal conditions to avoid violent runaway reactions during the storage and transportation of TBPB were determined.     

Thermal decomposition kinetic of liquid organic peroxides

This study demonstrates the application of isothermal calorimeter for investigating the thermal decomposition of several liquid organic peroxides, such as t-Butyl peroxy acetate (TBPA), Di-tert butyl peroxide (DTBP), and Cumene hydroperoxide (CHP). The decomposition mechanism and kinetic can be identified from case to case. TBPA and DTBP undergo first order reaction, whereas CHP occurs autocatalysis. Accurate kinetic can be assessed on the basis of discerning these various schemes of given samples. Consequently, the thermal runaway or reactive hazards potential of organic peroxides can be determined, for instance as a self accelerating decomposition temperature (SADT).     

Calorimetric behaviors of N2H4 by DSC and superCRC

The objective of this study is to obtain information about the thermal decomposition behaviors of hydrazine (N₂H₄) caused by metals, using differential scanning calorimeter (DSC) and SuperCRC. The DSC measurements revealed that the exothermic reactions of N₂H₄ were caused by the reaction conditions such as the type of cells; the T_DSC with a gold pan is 485.2 K and that with a glass capillary is 620.5 K. Besides, the activation energy of the thermal decomposition of N₂H₄, calculated from the Kissinger and Ozawa methods, were found to be about 38±2 kJ mol⁻¹ in the gold pan and 141±8 kJ mol⁻¹ in the glass capillary. Moreover, a heat flow profile was observed with SuperCRC during the mixing of N₂H₄ and the metal ion solution at 298 K. The maximum heat flow was related to the metal ion oxidative characters. The higher oxidative characters would provide a faster acceleration for the exothermic behavior than the lower oxidative ions. Based on this study, Mn(VII) and Cr(VI) were considered to exhibit strongly oxidative characteristics during mixing with N₂H₄.     

Assessment of the thermal hazards and oxidization mechanism of coloured corn starch dust by TG–FTIR

Starch is widely used in industrial production and in every life, and an increasing number of accidents of starch dust burning and explosions are occurring and have caused serious casualties and economic losses. Previous studies on the oxidative properties and microscopic characterization of coloured corn starch dust have been less systematic than the present study. To prevent coloured corn starch dust explosion accidents more effectively, thermogravimetry and Fourier transform infrared spectroscopy were applied to study the oxidation characteristics of coloured corn starch dust. Seven characteristic temperatures were determined from the thermogravimetric curves and derivative thermogravimetric curves of coloured corn starch dust. The entire oxidation process of coloured corn starch dust was divided into five stages, and a 60% mass loss occurred in the rapid oxidation stage. Three iso-conversion methods were used to calculate the apparent activation energy (E_a) and pre-exponential factor (A) at different oxidation stages. The value of E_a was found to be related to the difficulty of the reaction, and it had a positive correlation with lnA. Six kinds of gases were detected during the oxidation process. The oxidation mechanism was further analysed by the macro and micro characterization of the oxidation process. The findings provide a theoretical basis for preventing and controlling explosion accidents that involve coloured corn starch dust.     

The influence of ClO− and acidity in the reaction between H2O2 and CuCl2

The potentially explosive reaction of hydrogen peroxide (H₂O₂) and copper chloride (CuCl₂) was investigated. Pressure tests revealed that the reaction was strongly temperature - dependent and can easily undergo runaway reaction. Nevertheless, there was only a slight pressure increase at the low temperatures studied or when using low concentrations of CuCl₂. Under the conditions generating the slight pressure increase, hypochlorite anions (ClO⁻) are generated and the acidity increases. As the reaction reaches completion, ClO⁻ disappears, and the acidity decreases. Interestingly, the addition of phosphate buffer to maintain the weakly acid conditions led to a runaway reaction, and the use of basic ClO⁻ promoted the exothermic reaction. Based on the results, acidity has a strong impact on the reaction behaviour.     

Thermal hazard assessment for synthesis of 3-methylpyridine-N-oxide

The exothermic oxidation of 3-methylpyridine with hydrogen peroxide was analyzed by Reaction Calorimeter (RC1e) in semi-batch operation. Heat releasing rate and heat conversion were studied at different operating conditions, such as reaction temperature, feeding rate, the amount of catalyst and so on. The thermal hazard assessment of the oxidation was derived from the calorimetric data, such as adiabatic temperature rise (ΔT_ad) and the maximum temperature of synthesis reaction (MTSR) in out of control conditions. Along with thermal decomposition of the product, the possibility of secondary decomposition under runaway conditions was analyzed by time to maximum rate (TMR_ad). Also, risk matrix was used to assess the risk of the reaction. Results indicated that with the increase of the reaction temperature, the reaction heat release rate increased, while reaction time and exotherm decreased. With the increase of feeding time, heat releasing rate decreased, but reaction time and exotherm increased. With the amount of the catalyst increased, heat releasing rate increased, reaction time decreased and exothermic heat increased. The risk matrix showed that when the reaction temperature was 70 °C, feeding time was 1 h, and the amount of catalyst was 10 g and 15 g, respectively, the reaction risk was high and must be reduced.