Thermal decomposition of AIBN Part C: SADT calculation of AIBN based on DSC experiments
Introduction
This article continues the work from paper [1]. Purpose of the work: kinetic analysis of the data measured in BAM [2] by methods DSC, calculation of self-acceleration decomposition temperature (SADT) based on this analysis and verification by the experiments H.4 and H.1 [1] for real scale packages.
Steps:
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Description of experimental DSC data: dynamic and isothermal.
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Development of kinetic model based on DSC data.
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Verification of kinetic model based on H.4 experiments.
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Simulation for conditions of H.1 and H.4 experiments and comparison with experimental data.
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Calculation of self-acceleration decomposition temperature (SADT).
Section snippets
Experimental
The experimental DSC data will be used for the construction of a kinetic model, which will in turn be used for further simulations. Therefore, the experimental conditions for this task depend on the temperature range and heating rates of the target simulation. Ideally, the DSC experiment should cover the ranges of temperatures and heating rates which will be used during simulation. For azobisisobutyronitrile (AIBN), the SADT is about 50 °C [2]. During self-heating due to decomposition, the
Kinetic analysis of DSC data
Kinetic analysis is carried out in the NETZSCH Thermokinetics 3.1 software; a description of the principles can be found in [12]. For kinetic analysis, we should take the following experimentally registered kinetic processes into account:
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Exothermal decomposition peak in liquid phase with maximal thermal effect. Registered at 95–180 °C on all dynamic measurements. Reaction heat of this effect can be calculated as the difference between total reaction heat of dynamic measurements including all
Simple model for melting and decomposition in liquid phase
The simple kinetic model has two steps: melting and decomposition from the liquid phase.
The first step in this model is endothermal melting, and the second one is exothermal decomposition in the liquid phase. Melting step A → B exhibits auto-acceleration behavior to obtain a quasi-AC type of total reaction, described by [11]. The second step, B → C, is a reaction of the n-th order [9]. This simple two-step model describes melting and decomposition in the liquid phase for dynamic data with low
Verification of the kinetic model
Verification of the kinetic model and further SADT calculations are carried out in the NETZSCH Thermal Simulation 2.0 software. Verification of the kinetic model is necessary if the simulation is planned for conditions where the temperature or heating rate is outside of the range of experimental data. The current model was created for the calculation of SADT with a long initial period of an almost-zero self-heating rate at temperatures below the phase transition at 80 °C. All isothermal
Comparison of simulation with H.1 experiments for 5, 20 and 50 kg packages
Additional H1 UN-Tests are done and by BAM and described in [1] for 5 kg at 47 and 49 °C, for 20 kg at 48 °C and for 50 kg at 47 °C. Experiments for 5 kg do not exhibit the self-heating due to decomposition, but they have a temperature maximum after 15 days, then a temperature decrease. This long time to the temperature maximum is noted in the correspondence with a long induction time for H.4 experiments. Experiments and simulated data are presented in Fig. 7, Fig. 8, Fig. 9, where data order in
Calculation of SADT and temperature of safe storage for 60 days for 5, 20 and 50 kg packages
This chapter solves two different tasks. First of it is the calculation of SADT. SADT is the ambient temperature, if the temperature increase of 6 K occurs in sample within a period of 7 days, starting when the sample temperature reaches 2 K below the ambient temperature. The three-step kinetic model is used for the calculation of SADT values for 5, 20 and 50 kg packages and Dewar 500 ml. Simulation is done for distributed heat transfer model for the spheres with diameters 51, 38, 24 and 9.3 cm for
Conclusion
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The kinetic model for AIBN decomposition has been created. It contains both exothermal (decomposition) and endothermal (melting) kinetic processes.
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The kinetic model contains reactions for decomposition from both the solid and the liquid phases. For the temperatures below the melting range, only solid decomposition occurs. For the fast dynamic heating to the temperatures above melting range, the melting and subsequent decomposition from the liquid phase take place. For the long time in the
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