Reaction Model Screening And Thermal Behavior Evaluation For Autocatalytic Decomposition Based On Isothermal Test Method

In the chemical industry,the autocatalytic reaction is a very important part.In recent years,accidents related to autocatalytic reactions have occurred frequently,and there is an urgent need for research on this reaction.At present,the research on autocatalytic reaction at home and abroad mainly focuses on the judgment of reaction type and the choice of reaction model,but there is insufficient research on the strength or degree of autocatalytic reaction.Determining the correct reaction model is the first step in studying the thermal decomposition reaction of substances.It is of great significance for understanding the reaction characteristics of substances and providing correct and scientific guidance for various safety measures in the production process.More essential information about the reaction can be obtained by using the isothermal method in thermal analysis.Based on isothermal conditions,this paper proposes a simple method for screening reaction models,and investigates the thermal behavior of the autocatalytic reaction from the perspective of different models,and tries to give a criterion for the strength of the autocatalytic reaction.First,through theoretical derivation,it is found that the normalized curve of the single-step reaction model under isothermal conditions has the same shape as the measured normalized curve of the isothermal model.Based on this,a standard curve library of 41common solid-phase thermal decomposition reaction mechanisms was established.Furthermore,the feasibility of the screening method was studied from the theoretical and differential scanning calorimetry（DSC）experimental perspectives.It was found that,in theory,whether the reaction model in the standard library is followed or not,the normalized curve gives useful information for the reaction model;the experimentally measured DCP thermal decomposition is a decelerating exothermic reaction,and the reaction model is f（α）=（1-α）ⁿ,the first dehydration reaction of calcium oxalate monohydrate is an endothermic and reversible self-accelerating reaction,the reaction model is f（α）=（1-α）^m[-ln（1-α）]ⁿ;Further kinetic fitting shows that the exact reaction model of the two is f（α）=（1-α）^0.96,f（α）=（1-α）^0.66[-ln（1-α）]^0.41,theoretical and experimental results shows that it is feasible to screen the reaction model based on the normalized curve.Secondly,using TSS（Thermal Safety Series）software to simulate the heat release curve based on the isothermal method,the characteristics of the autocatalytic thermal decomposition behavior of the Prout-Tompkins model,the Avrami-Erofeev model and the Benito-Perez model are studied.The results show that the isothermal induction period of the Prout-Tompkins model and the Avrami-Erofeev model is proportional to the activation energy,and inversely proportional to the pre-digital factor and the isothermal temperature.The Benito-Perez model exhibits autocatalytic behavior characteristics when the autocatalytic factor is greater than 1,and its degree of autocatalysis increases as the autocatalytic factor becomes larger.The isothermal induction period of this model depends on the rate constant of the two-step reaction.The parameters indicating the strength of autocatalysis were analyzed from different angles,and finally based on（dα/dt）_max-TMRO and the scale of different reactors,the classification method of autocatalytic strength is preliminarily established and the strength levels of three autocatalytic substances are given.The work in this paper provides a convenient method for screening reaction models and facilitates the use of model fitting methods.At the same time,the thermal behavior of different autocatalytic models under isothermal conditions and the influencing factors of the strength of the autocatalytic reaction were investigated,which provided guiding significance for further exploration of the autocatalytic reaction.