| In the context of the ever-growing need for various polymers in modem society,free-radical polymerization(FRP)plays a progressively momentous role in the petrochemical industry.Polymers manufactured by FRP has manipulated approximately 40-45%of all industrial polymers.The dominant position of FRP stems from its extraordinary peculiarities compared with ionic or coordination polymerization,FPR can be executed in polar solvents even when monomers are not fully dried or the system is mixed with a small quantity of impurities.Industrially important radical initiators can be categorized into peroxide initiators and azo-initiators depending on their decomposition mechanism.While azo-initiators are superior in that they have higher chain transfer constants and lower initiating efficiencies,peroxide initiators are now being phased out.Despite the superior performance of azo-initiators,a series of accidents due to the thermal instability of azo-initiators have occurred even in the very recent past.Numerous deflagration or explosion accidents induced by elements such as external ignition,friction,and mechanical impact denoted apparent drawbacks brought by the thermal unreliability and self-accelerating decomposition character of azo-initiators.From a safety point of view,azo-initiators would release numerous heats under elevated ambient temperature,thus hampering their application in a wider market.Therefore,the evaluation of the thermal hazards and identification of hazardous scenarios are of great significance for the safe production,storage,and application of azo compounds.2-(1-Cyano-1-methylethyl)azocarboxamide(CABN)and azodicarbonamide(ADC)were adopted as examples for identifying the hazardous scenarios in the production,storage,and application of azo compounds.CABN is one of a few asymmetrical azo-initiators that are commonly used for polymerization,organic synthesis,and foaming.From the aspect of its molecular structure,CABN has an oil-soluble structure on one side of the-N=N-,but the formamide which links to the other side is a hydrophilic group.The asymmetric structure enables CABN to be dissolved in both oil and water,and makes it possible for industry to initiate polymerization in various application environments.The one purpose of this paper is to decode the thermal hazards of CABN by kinetic-based numerical simulation and identify hazardous scenarios in its applications.Initially,the thermokinetic parameters for CABN were investigated using simultaneous thermogravimetric analyzer(STA)and differential scanning calorimetry(DSC).The model-free equations including the Kissenger-Akahira-Sunose and Flyn-Wall-Ozawa methods were used to determine the apparent activation energy(Ea)and pre-exponential factor(A).Then,based on the experimental results and thermokinetic analysis,the optimal thermokinetic model of CABN was suggested by verifying the selected thermal decomposition mechanism functions.Subsequently,kinetics-based simulation of the thermal explosion and adiabatic runaway reaction for CABN stored in a 55 gallon 304 stainless drum was accomplished.Furthermore,several process safety parameters,such as the time to maximum rate under adiabatic conditions and induction period were estimated.Ultimately,CABN was used as an example for the identification of hazardous scenarios in the production,storage,and application of azo-initiators to provide references for the FPR industry to forestall the azo-initiators involved thermal accidents.ADC is a type azo compound with outstanding application performance and thermal stability,always used as a food additive in bread baking and blowing agent in the production of foamed plastics.It was considered harmless in its practical application from previous literature.Nevertheless,our research has overturned this standpoint and denoted the special exothermic behavior of ADC,especially when it was placed in high-pressure system.For further understanding of this peculiar phenomenon,STA was employed to have a preliminary evaluation of thermal stability for ADC under different atmospheres.Followed with calorimetric experiments by high-pressure differential scanning calorimetry,the exothermic behaviors of ADC under different ambient pressures were investigated.The results revealed that the thermal decomposition rate of ADC will linearly increase along with the elevation of the testing pressure.The peak power of DSC curves has breathtakingly researched 73.0 W/g when the testing pressure was set at 4 MPa,and the overall decomposition heat has reached 1261 J/g with the scanning rate at 4.0?/min.Furthermore,advanced thermokinetic investigation was employed to make a thorough inquiry of how pressure influences the decomposition mechanism of ADC.The results were expected to settle the problem of how pressure influence the thermal behavior of ADC and provide references for the industry in designing new-type functional azo compounds.Figure[32]Table[25]Reference[113]... |
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