Research On The Isoconversional Method In Adiabatic Accelerating Rate Calorimetry And Its Application

Thermal runaway is one of the most interesting risks in chemical industry.Adiabatic accelerating rate calorimetry is an important method to analyze the thermal behavior of exothermic reaction under adiabatic condition,which is widely used in the research on thermal safety of chemical substances.At present,the kinetic analysis method applied for adiabatic accelerating calorimetry mainly adopts the model fitting method.There are problems such as difficulty in analyzing the reaction mechanism,large uncertainty in solving kinetic parameters,and high requirements for researchers’experience.It is of great significance and application value to further understand exothermic reaction mechanism,optimize chemical process and assess thermal risk by exploring the isoconversional method applied for adiabatic accelerating rate calorimetry and its prediction application.This dissertation first introduces the theory of thermal analysis kinetics and systematically analyzes the reaction rate equation,reaction type and the connotation of thermal analysis kinetics.Then the principle of isoconversional method is expounded and the isoconversional methods are classified from differential and integral forms.The application scope,advantages and disadvantages of typical isoconversional methods are compared and analyzed.On this basis,combined with the working principle and data characteristics of adiabatic accelerating rate calorimetry,the influence of thermal inertia on the reaction process is studied,and the thermal inertia is determined as the adjusted physical quantity of the temperature control program.The Friedman and Vyazovkin isoconversional methods are selected for the kinetic analysis of adiabatic accelerating rate calorimetry.The influencing factors of isoconversional methods in adiabatic accelerating rate calorimetry are studied.Through numerical simulations and experimental tests,the influences of temperature selection,noise,data points,thermal inertia and reaction types on the solution of activation energy was revealed,and the range of core parameters are determined.The differences between Friedman and Vyazovkin methods are compared and analyzed.Based on the statistical methods of corrected Student’s distribution and F distribution,the confidence intervals of the two isoconversional methods are evaluated respectively.These provide experimental and theoretical guidances for the application of isoconversional methods in adiabatic accelerating rate calorimetry.Based on the linear correlation between activation energy and pre-exponential factor in kinetic compensation effect,combined with typical reaction mechanism models and calorimetric data,the pre-exponential factor and reaction mechanism model are proposed.Through in-depth research on the core influencing factors and parameter solving approaches,the isoconversional kinetic analysis methods for the kinetic triplet oriented to adiabatic accelerating rate calorimetric data are proposed.In order to solve the problems of model selection and local optimization in the model-fitting method of multi-step complex reaction,the isoconversional method and the model fitting method are combined to solve the multi-step reaction kinetics parameters.First,the activation energy and ln[A_αf（α）]are calculated using Friedman’s method,and the pre exponential factor A_αand apparent reaction mechanism model f（α）are obtained through compensation effect.It provides reference for the selection of reaction model and initial value of model fitting.Then,the activation energy and rate equation formula are used for model-fitting in steps.The decoupling of E_αand A_αis carried out,and the dimensions of parameter data are reduced,so that the kinetic parameters of a single step in a complex reaction can be solved.The results of numerical simulations and experimental researches show that the combination method is effective and accurate.It can reduce the possibility of falling into local optimization of kinetic parameters and lower the experience requirements for researchers.Aiming at the calculation of thermal explosion parameters,the model-free kinetic prediction equations based on the isoconversional methods are established.The time to maximum rate under adiabatic condition(TMR_ad),the self accelerating decomposition temperature（SADT）and the cook-off temperature of di-tert-butyl peroxide（DTBP）,azobisisobutyronitrile（AIBN）and cumyl hydroperoxide（CHP）are predicted.First,the validity and accuracy of the model-free kinetic prediction methods are verified by numerical simulations.Then,based on the experimental data of three substances,TMR_adare calculated.Finally,the model-free kinetic prediction equations are used to predict the heat release of the reaction process of the three substances.Combined with the finite element analysis method,the heat transfer characteristics of different specifications of packaging are analyzed,and the prediction of SADT and cook-off temperatures are realized.The experimental results show that the maximum relative errors of T_D8 and T_D24 are 5.8%and 6.3%respectively,the maximum relative errors of SADT prediction are 12.8%,the maximum relative errors of the initial decomposition temperature and the ambient temperature corresponding to the peak value are 6.0%and 6.2%respectively.The prediction accuracy of the model-free method is good.The higher the packaging volume of chemical substances,the lower the SADT and cook-off temperatures,and it is recommended to use smaller packaging volume for higher thermal safety.As an alternative and beneficial supplement to the traditional kinetic analysis method of adiabatic accelerating rate calorimetry,the isoconversional methods and its prediction application methods established in this dissertation will provide important theoretical support and practical guidance for thermal risk assessment of chemical processes,thermal stability analysis of chemical substances,establishment of thermal disaster model and accident prevention.