Research on the critical temperature of thermal decomposition for large cartridge emulsion explosives

Emulsion explosives are one type of main industrial explosives. The emergence of the large cartridge emulsion explosives has brought new security incidents. The differential scanning calorimeter (DSC) and the accelerating rate calorimeter (ARC) were selected for the preliminary investigation of the thermal stability of emulsion explosives. The results showed that the initial thermal decomposition temperatures were in the range of 232–239 °C in nitrogen atmosphere (220–232 °C in oxygen atmosphere) in DSC measurements and 216 °C in ARC measurements. The slow cook-off experiments were carried out to investigate the critical temperature of the thermal decomposition (T_c) of the large cartridge emulsion explosives. The results indicated that the larger the diameter of the emulsion explosives, the smaller the T_c is. For the large cartridge emulsion explosives with diameter of 70 mm, the T_c was 170 °C at the heating rate of 3 °C h⁻¹. It is a dangerous temperature for the production of the large cartridge emulsion explosives and it should cause our attention.     

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 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.     

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.     

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 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.     

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 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.     

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.     

Using thermal analysis with kinetic calculation method to assess the thermal stability of 2-cyanopropan-2-yliminourea

Azo compounds, which are commonly used as initiators and blowing agents, are also typical self-reactive materials capable of undergoing runaway reaction during storage and transportation, which can cause severe fires and accidents. To ensure the thermal safety of azo compounds in the process, transportation, and applications, this study investigated 2-cyanopropan-2-yliminourea, which can also be called V-30. First, thermal decomposition characteristics under the non-isothermal conditions were obtained using differential scanning calorimetry. Second, the collected data were combined with a mathematical model to evaluate the primary thermal hazard during the process for V-30. Then, based on a heat-transfer model, the self-accelerating decomposition temperature (SADT) was extrapolated for consideration and non-consideration of consumption of chemicals. The results showed that SADT of V-30 was less than 80 °C. Therefore, it is essential to avoid a temperature beyond SADT or the cooling system will fail. The influence of consumption was also considered for SADT in this study.     

Effects of environmental temperature on the thermal runaway of lithium-ion batteries during charging process

Lithium-ion batteries with relatively narrow operating temperature range have provoked concerns regarding the safety of LIBs. In this work, a series of experiments were conducted to explore the thermal runaway (TR) behaviors of charging batteries in a high/low temperature test chamber. The effects of charging rates (0.5 C, 1 C, 2 C, and 3 C), and ambient temperature (2 °C, 32 °C and 56 °C) are comprehensively investigated.The results indicate that the cell exhibited greater thermal hazard at the high charging rate and ambient temperature conditions. As the charging rate increased from 0.5 C to 3 C, more lithium intercalated in the anode prompt the TR triggered in advance, the TR onset temperature decreased from 297.5 °C to 264.7 °C. In addition, the charging time decreased with the elevated ambient temperature, resulting in a relatively higher TR onset temperature and lower maximum temperature, and the average TR critical time declined by 115–143 s. Finally, the TR required less heat accumulation with increasing of charging rate and ambient temperature, and the heat generation of side reaction played a substantial role that accounted for approximately 54%∼63%. These results provide an insight into the charging cell thermal runaway behaviors in complex operation environments and deliver valuable guidance for improving the safety of cell operation.     

Preoptimal analysis of phase characteristic indicators in the entire process of coal spontaneous combustion

To accurately predict the development degree of coal spontaneous combustion (CSC), the CSC process was investigated using a programmed high-temperature-heating experimental system, and the variation law of index gas concentration in the holistic process of CSC and oxidation is formulated. Additionally, the accuracy of the experimental system was evaluated using experimental design for thermal analysis, and the correlation between gas index and apparent activation energy was determined using grey correlation analysis. The results indicated the following. In the critical temperature stage (0–100 °C), φ(CO)/φ(CO₂) should serve as the main index and C₂H₄ should serve as the auxiliary index; in the crack-active-speedup temperature stage (100–260 °C), CO and φ(C₂H₄)/φ(C₂H₆) should serve as the main index and R₁, the Graham index, and φ(C₂H₄)/φ(CH₄) should serve as auxiliary indexes; in the speedup-ignition temperature stage (260–370 °C), R₂ and the Graham index should serve as main indexes and φ(CO)/φ(CO₂), C₂H₄, and R₁ should serve as auxiliary indexes; in the ignition temperature (370–500 °C), R₃ should serve as the main index and R₂, the Graham index and C₂H₄ should serve as auxiliary indexes. Among them, the grey correlation degrees among the Graham index, Grignard fire coefficient, and apparent activation energy were the highest, reaching 0.91.     

Thermal hazard evaluation for γ-valerolactone production by using formic acid as hydrogen donor

Aiming at the green and sustainable energy substitution and supply, biomass valorization has become a potential strategy to face the energy crisis and increasing demand all over the world from long-term perspectives. Among the bio-based chemicals, γ-valerolactone (GVL) production from hydrogenation of levulinic acid (LA) and its esters has attracted great interests due to its wide applications, such as fuel, solvent, and additives. However, the safety evaluation for this hydrogenation reaction has received few attentions. To fill this gap, thermal hazard evaluation for GVL production from LA hydrogenation by using formic acid (FA) as hydrogen donor was first performed. The process conditions were optimized by using orthogonal experimental method for further calorimetry study. Thermal stability of chemicals and thermal risk of reaction process under adiabatic conditions were investigated by applying differential scanning calorimetry and accelerating rate calorimeter Phi-Tec II, respectively. The results revealed that the chemicals were stable in temperature range from 30 to 250 °C except FA due to its evaporation and decomposition with endothermic behaviors. The reaction process under isothermal and adiabatic conditions demonstrates that the decomposition of FA was rapid and followed by the hydrogenation of LA to GVL. Based on kinetic model under adiabatic conditions and risk matrix, the thermal runaway risk was found to be medium, indicating that certain safety measures should be properly designed and taken for loss prevention. This work could benefit the safety design and thermal risk prevention for GVL production by using FA as hydrogen donor.     

Dilute Acid Hydrolysis of Cellulose and Cellulosic Bio-Waste Using a Microwave Reactor System

The dilute acid hydrolysis of grass and cellulose with phosphoric acid was undertaken in a microwave reactor system. The experimental data and reaction kinetic analysis indicate that this is a potential process for cellulose and hemi-cellulose hydrolysis, due to a rapid hydrolysis reaction at moderate temperatures. The optimum conditions for grass hydrolysis were found to be 2.5% phosphoric acid at a temperature of 175°C. It was found that sugar degradation occurred at acid concentrations greater than 2.5% (v/v) and temperatures greater than 175°C. In a further series of experiments, the kinetics of dilute acid hydrolysis of cellulose was investigated varying phosphoric acid concentration and reaction temperatures. The experimental data indicate that the use of microwave technology can successfully facilitate dilute acid hydrolysis of cellulose allowing high yields of glucose in short reaction times. The optimum conditions gave a yield of 90% glucose. A pseudo-homogeneous consecutive first order reaction was assumed and the reaction rate constants were calculated as: k₁ = 0.0813 s⁻¹; k₂ = 0.0075 s⁻¹, which compare favourably with reaction rate constants found in conventional non-microwave reaction systems. The kinetic analysis would indicate that the primary advantages of employing microwave heating were to: achieve a high rate constant at moderate temperatures: and to prevent ‘hot spot’ formation within the reactor, which would have cause localised degradation of glucose.     

Explosion parameters of wood chip-derived syngas in air

The wood gasification process poses serious concerns about the risk of explosion. The design of prevention and mitigation measures requires the knowledge of safety parameters, such as the maximum explosion pressure, the maximum rate of pressure rise and the gas deflagration index, K_G, at standard ambient temperature (25 °C) and pressure (1 bar) conditions. However, the analysis at specific process conditions is strongly recommended, as the explosion behavior of gas mixtures may be completely different.In the work presented in this paper, the explosion behavior of mixtures with composition representative of wood chip-derived syngas (CO/H₂/CH₄/CO₂/N₂ mixtures with and without H₂O) was experimentally studied in a closed combustion chamber. Experiments were run at two temperatures, 300 °C and 10 °C, and at atmospheric pressure. Test conditions were requested by the safety engineering designer of an existing industrial-scale wood gasification plant. In order to identify the specific fuel–air ratios to be analyzed, thus reducing the number of experimental tests, a preliminary thermo-kinetic study was performed.Results have shown that the mixtures investigated can be classified as low-reactivity mixtures, the higher value of K_G found (∼36 bar m/s) being much lower than the K_G value of methane (55 bar m/s @ 25 °C).     

Case study on prevention of fire hazards in coating epoxy-based FRP work with illumination

In this study, we investigated and analyzed the causes of fire hazards on the basis of actual accidents that occurred during epoxy resin fiberglass-coating operations. Results of this study showed that during this process, two major factors could cause a fire. One factor was related to the heat produced during the mixing of the epoxy resin and a polyamide curing agent. From the results of thermal analysis, it was found that the T_onset of the epoxy resin and the polyamide curing agent was 52.8 °C by DSC and T_d10 was 58.9 °C by DT/TGA, causing an exothermic hazard. Further, the results of a pseudo-adiabatic analysis performed in a Dewar vessel showed that the temperature increased from 23.5 °C to 177 °C.The other factor that could increase fire hazard was the illumination source used during the coating operation. Depending on the type of illumination source used, the temperature could increase above 350 °C. The decomposition temperature (T_d10) of PVC was 276.3 °C. The experiments involving epoxy resin fiberglass coating using an illumination source showed serious burn marks, and the polyvinyl chloride (PVC) electrical cable emitted small flames. Therefore, it can be concluded that fire was caused by the combination of two factors—the exothermic reaction between epoxy resin and the polyamide curing agent and the effect of prolonged illumination, both of which caused an increase in temperature leading to auto-ignition of the PVC electric cable.     

Evaluation of thermal properties and process hazard of three ionic liquids through thermodynamic calculations and equilibrium methods

Industrial and new energy applications of ionic liquids (ILs) may have to be used at high temperatures conditions, such as in batteries and fuel applications, which may cause thermal hazards. However, there are few studies on the thermal hazards of ILs. To ensure the thermal safety of ILs processes, three commonly used ILs were selected for analysis: 1-butyl-3-methylimidazolium nitrate ([Bmim]NO₃), 1-butyl-2,3-dimethylimidazolium nitrate ([Bmmim]NO₃), and 1,3-dimethylimidazolium nitrate ([Mmim]NO₃). The process hazards under adiabatic conditions demonstrated that [Bmmim]NO₃ and [Mmim]NO₃ have extensive explosion hazards. The self-reaction characteristics determined by the isothermal test indicated that the ILs are nth reactions, and the thermal decomposition features were also determined by thermogravimetric analysis. The data were obtained with a nonlinear thermodynamic model and used to establish the basic thermal hazards of the three ILs. In addition, based on the thermal equilibrium theory, the critical safety parameters can be inferred. The effects of heat transfer in 25.0 g and 50.0 g containers were discussed. The results show that [Mmim]NO₃ will produce a thermal runaway reaction at a lower temperature (<100 °C) and has the shortest reaction time (<1 day), which means [Mmim]NO₃ is considered to be the most hazardous material among the three ILs studied.     

MIE determination and thermal degradation study of PA12 polymer powder used for laser sintering

Pulverized materials such as metallic or polymer powders play a considerable role in many industrial processes. Their use requires the introduction of preventive safeguards to control the plant's safety.PA12 polymer powder processing by laser sintering is characteristic of this tendency. The present work concerns PA12 powder (bimodal particle size distribution: 10 μm and 55 μm) and relates to explosion sensitivity and the thermal degradation of this powder, which can occur during laser sintering. Minimum Ignition Energy is determined using a modified Hartmann tube combined with the Langlie method developed in the PRISME Laboratory. This study shows the influence of parameters such as distance between the electrodes, powder concentration and arc power on MIE values. Theses parameters vary in the range of 3–6 A for the current intensity of the spark and the electrode gap in the range of 2.5–4 mm. The MIE is obtained for a spark gap of 3 mm and current intensity of the 4 A spark in our device. It shows that the MIE is less than 40 mJ for concentrations approaching 1000 g/m³. At lower concentrations (under 150 g/m³) the MIE increases but discrepancies in measurements appear, probably because of the static electricity that creates strong irregularities in dust dispersion. The second part of this study concerns the thermal degradation of the PA12 which is performed by thermogravimetric experiments coupled with mass spectrometric (MS) analysis for gas investigation. The mass loss measurement combined with the gas analysis allows the principal stages of degradation to be determined so as to calculate the kinetics parameter PA12. Experiments have been performed for different heating rates between 1 and 30 K min^?1 and the reproducibility of experiments has been verified. The activation energy is determined using two methods: Freidman and KAS. For a reaction rate of between 0.2 and 0.6, the activation energy is nearly constant. The KAS method gives a value of E_a = 250 kJ mol^?1 and the Friedman method gives E_a = 300 kJ mol^?1. The gas analysis by MS shows that oxidation begins at over 350 °C and finishes at under 650 °C with the formation of CO₂ and H₂O. Other major peaks with an m/z ratio of 29, 28 and 30 are noticed in this range of temperature. They show the presence of intermediate species such as C₂H₆, NO or CH₂O. The presence of HCN is also detected (m/z ratio of 27).     

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.