Study On The Thermal Stability Of Benzotriazole With Impurities

In chemical synthesis reaction,thermal risk is an important point which people need pay more attention to,because so many accidents are caused by thermal runaway reactions.On the other hand,some processes of chemical compounds,especially hazardous chemicals,such as mixing,storage,disposal,etc.,the environment of handling materials needs to be controlled strictly,for their stabilities are often influenced by thermal effects brought by environment.In 2015,an explosion accident happened in a chemical plant near Taizhou.According to accident analysis,the decomposition of benzotriazole(BTA)affected by some impurities under abnormal conditions was the main reason.Therefore,three impurities o-phenylenediamine(A),sodium nitrite(B)and sodium sulfate anhydrous(C)are chosen for effective study of BTA stability,and the decomposition mechanism of BTA is also researched after.Firstly,some DSC experiments are used to obtain target samples’ thermal parameters,such as heat generation,onset temperature,peak temperature,etc.It is found that impurities sodium nitrite(B)and o-phenylenediamine(A)have a catalytic effect for the decomposition of BTA.The onset decomposition temperature of the mixture of impurities A and BTA is 259℃,and there are two peaks appeared in the DSC curves of the mixture of impurities B and BTA,the onset temperature of the first peak is 195 ℃.Both the onset temperatures are lower than that of the BTA pure,which is about 277 ℃.While impurity C does not effect on BTA decomposition.Based on this,in order to further study the impact of impurities on the decomposition of BTA,mixtures with three different percentages(i.e.2%,6%and 10%)of the three impurities are measured by DSC respectively.The results showed that with higher percentage of impurity A,the onset temperature of impurity A with BTA decreases,indicating that the higher the percentage of impurity A,the easier the decomposition of BTA.As the percentage of impurity B increases,the DSC results of the mixture of impurity B and BTA almost the same,but a second peak appeared,indicating that impurity B affects the decomposition mechanism of BTA.Percentage of comp C almost cannot affect the BTA.In addition,temperature and pressure during decomposition are also important,which are measured by rapid scanning calorimeter(RSC)and accelerating rate calorimeter(ARC).The thermal parameters calculated from test results are very similar with DSC’s,and pressure results are able to calculate gas generation of sample decomposition.Finally,using AKTS software to deal with DSC data,the decomposition kinetics of each target sample is acquired successfully.Based on kinetics,the initial temperature from which the temperature rate rises up to the maximum need 24 hours or 8 hours is predicted(TD8 and TD24).Analyzing ARC results,theoretical calculation and simulation are used separately to calculate TD8 and TD24,the theoretical results are close to DSC’s,while simulation results are a bit larger.By comparing the results between BTA pure and BTA-A/BTA-B mixtures,the TD8 and TD24 of mixtures are lower than pure one’s.For example,TD8 and TD24 of BTA-A predicted in AKTS are 207 ℃ and 173 ℃,TD8 and TD24 of BTA-B are 206 ℃ and 194 ℃,respectively.While TD8 and TD24 of BTA pure are 216 ℃ and 198 ℃.The results mean the worse stability and higher thermal risk of mixtures will be.Dealing with ARC data,the kinetic parameters are similar with DSC kinetic results,from which the conclusions by DSC analysis are also evidenced.The investigation in this paper will be of some help and reference for relevant process design and safety evaluation.