Comparative Study On Thermal Behavior Of Similar Structure Azo Compounds

The production scale of azo compounds in future will inevitably increase with the ever-increasing requirement sourcing from people' consumption.Due to the characteristics of azo compounds' own structure,they are prone to thermal decomposition.Once they get out of control,fire and explosion accidents are triggered easily,resulting in massive loss of people and property.In this work,the thermal safety of new azo compounds was focused.In term of the similarity of R functional groups,four azo compounds with similar structure were selected,including diethyl azodicarboxylate(DEAD),diisopropyl azodicarboxylate(DIAD),ditertbutyl azodicarboxylate.Ester(DBAD)and dibenzyl azodicarboxylate(DDAD),etc.The thermal behavior,decompostion mechanism and thermal hazard evaluation were studied by using C80 microcalorimeter and TG-FTIR-MS.The effects of R functional structure on apparent activation energy were revealed.The conclusions are as follows:(1)The thermal decomposition process of four kinds of azo compounds is very complicated,and there is a multi-step exothermic reaction in the thermal decomposition process.Both DBAD and DDAD are solids,and there is a melting endothermic process before exotherm.At the same heating rate,the ordering of initial decomposition temperature of four substances is: DIAD>DEAD>DBAD>DDAD;the ordering of peak temperature of liberation heat peak is:DIAD>DEAD>DDAD>DBAD.The total calorific values of decomposition reaction decreased in turn,which were 1146±70 J/g,946±23 J/g,680±35 J/g,and 295±133 J/g,respectively.(2)There are the same breaking mode at the initial decomposition stage of DIAD,DBAD and DDAD,that is,the R-O bond is broken firstly,and the R group is released.The breaking mode of DEAD is different from that of other three azo compounds,and the RO-C bond is broken firstly.,O-R group is released;subsequrently,there are complex subsequent cracking processes and rearrangement phenomena,thereby producing complex and variable pyrolysis products.(3)Under the same breaking condition,the ordering of electronegativity and spatial volume of R group is negatively correlated with that of apparent activation energy.As the electronegativity and space volume of R group increase,the apparent activation energy of the species decreases.(4)The SADTs of four substances based on the Semenov model are 48.9°C,89.0°C,17.1°C,and 61.1°C.The SADT of four substances obtained based on the Frank-Kamenetskii model are 45.0°C,65.6°C,7.2°Cand 51.1°C;Special attention should be paid to the preservation of DEAD.