Research On The Method For Calculating Decomposition Kinetics And Thermal Explosion Parameters Of Adiabatic Systems

Adiabatic calorimetry is one of the most important methods to study the thermal runaway behavior and kinetic parameters of substances and chemical reactions under adiabatic conditions.However,due to the measured sample often reacts with large heat release,large gas production and strong temperature rise rate or strong pressure rise rate,there are the phenomena of uneven temperature distribution and insufficient heat compensation tracking rate of furnace in the current adiabatic test which lead to the inaccurate adiabatic test data.In addition,the uncertainty of the reaction kinetic mechanism and the initial decomposition state of the sample could result in the failure to accurately obtain the kinetic parameters in the theoretical analysis of the adiabatic test data.Therefore,it is quite necessary to innovate and expand the current test procedures and mathematical processing methods of experimental data to obtain accurate reaction kinetic mechanism and thermal safety parameters,so as to facilitate the accurate assessment of thermal risk in the reaction system.First of all,based on the basic adiabatic theory,the adiabatic heat-quench-heat method was proposed by changing the experimental procedure to slow down the reaction rate and ensure the temperature uniformity and heat balance of the system and the initial temperature criterion was proposed to determine the reaction model.In order to verify the feasibility of the adiabatic heat-quench-heat method,numerical simulation of n-order model and autocatalytic model and experiments of four typical substances（dit-butyl peroxide（DTBP）,diisopropyl hydrogen peroxide（DCP）,isopropyl hydrogen peroxide（CHP）and benzaldehyde oxime（BO））were carried out.The result shows that,compared with the current adiabatic method,this method can reduce the reaction rate effectively to ensure the accuracy of experimental data acquisition,and determine the reaction model accurately through the initial temperature criterion.Then,based on the adiabatic theory and adiabatic pressure correction method,the full-time equivalent adiabatic model was established.In this model,"heat-wait-search"（HWS）process is equivalent to adiabatic process reasonably,and its initial temperature was defined as equivalent adiabatic temperature.Based on the model,a pressure determination method was proposed to verify the reaction model.In this method,the initial conversion rateα_Pi from the pressure data and the conversion rateα_ti under multiple mechanism models from the temperature data were calculated.Compareα_ti withα_Pi to screen the more accurate mechanism model and kinetic parameters.In order to verify the feasibility of the pressure determination method,adiabatic experiments of 20%DTBP in toluene solution and 25%CHP in isopropylbenzene solution were carried out,respectively.The result shows that combined with the current thermal determination method,the pressure determination method can verify the reaction model accurately.Secondly,through the comparision of d²T/dt² in the n-order model and the autocatalytic model under adiabatic condition,the adiabatic E/n method was proposed to determine the reaction model.In this method,at least two sets of adiabatic experiments with different thermal inertia（φ）or different thermal history（different initial conversion rate（α₀）or initial decomposition temperature（T₀））were carried out to obtain the final temperature（T_f）and the temperature at the maximum temperature rise rate（T_p）,and the value of RT_p²/（T_f-T_p）need to be calculated.If the values of RT_p²/（T_f-T_p）calculated by different adiabatic experimental curves are constant,then the reaction follows the n-order reaction mechanism.Otherwise,the reaction follows the autocatalytic reaction mechanism.The adiabatic E/n method was verified by numerical simulation of n-order model and the autocatalytic model,and multiple adiabatic experiments based on differentφand thermal history of four typical materials（20%DTBP,DCP,CHP and BO）.The result shows that the reaction model can be determined by E/n method accurately.Thirdly,based on the reaction characteristics of the Benito-Perez autocatalytic model,the product addition method was proposed to determine the complex decomposition reaction model.This method requires the repeated adiabatic experiments with each product added in the reactants after the analysis of products.The catalysis of the products can be determined by the change of T₀ or the time to reach the maximum temperature rise rate under or adiabatic conditions(TMR_ad),so that the reaction model can be determined.The decomposition reaction of BO was taken as an example to verify the product addition method.The result shows that the complex decomposition reaction model can be determined by product addition method.Finally,the reseach on thermal explosion hazard parameters was carried out.Based on the reaction kinetics model and parameters calculated by adiabatic heat-quench-heat method,pressure determination method,and product addition method,thermal explosion hazard parameters such as the TMR_ad,the accelerating decomposition temperature（SADT）and cook-off temperature were calculated.The results of the proposed methods were compared with the results of current adiabatic method to verify the reliability of the proposed methods.The result shows that the thermal explosion hazard parameters based on adiabatic heat-quench-heat method are more reliable than that of the current method.Combined with current method,pressure determination method is quite important to the determination of reaction mechanism model and calculate thermal explosion hazard parameters.For complex reactions,the calculation result based on the the product addition method is more accurate than the current method and the adiabatic heat-quench-heat method although it has a larger workload.The four adiabatic methods proposed in this paper have good theoretical guiding significance and engineering application value for the accurate acquisition of adiabatic data,the establishment of kinetic model of thermal decomposition reaction,the calculation of kinetic parameters,and the evaluation of thermal risk,etc.