(151a) The Study of Thermal Hazard Evaluation of Polymerizing Substances at Storage

Polymerizing substances have potential hazards of chemical reaction, and they will begin polymerization reaction that is caused by heat, light or acid. Although “Polymerization-inhibitor” is added in the container to prevent polymerization during shipment and storage, unintended accidents sometimes occur. The explosion and fire accident in the acrylic acid middle tank occurred at Nippon Shokubai, Japan in 2012, and the accidents brought very serious damage. It's difficult to judge directly whether polymerizing substances have the thermal hazard by an experiment during storage. Because the actual experiment takes 2-3 months, and needs to test each kind of polymerization-inhibitor, hence the number of experiments are required. Therefore rapid and easy evaluation method and experimental technique are desired.

Standard thermal hazard evaluation for self-reactive substances is the estimation of temperature rise under adiabatic condition by using the kinetics parameters that calculated from result of thermal analysis. These materials begin polymerization reaction after polymerization-inhibitor consumes. So a presence of polymerization-inhibitor in the liquid influences very big for thermal stability. Therefore there is possibility that thermal behavior of polymerizing substances is different, if the polymerization-inhibitor amount and the heating history for experimental sample, and the atmosphere at experiment are different. So wrong evaluation is sometimes carried out because correct kinetic parameters cannot be obtained when standard evaluation is applied.

For example, polymerizing materials begin polymerization reaction at room temperature, but there are cases that onset temperature of these materials with inhibitor which is obtained by thermal analysis is higher than 100℃. Therefore because there is a possibility of the underestimate by using standard thermal evaluation techniques, we will study about the evaluation technique which considered material reaction mechanism. At first, thermal analysis were carried out under different experimental condition to confirm the difference of thermal behavior. A consumption mechanism of polymerization-inhibitor was considered from result of thermal analysis, and appropriate experimental condition for thermal hazard evaluation of polymerizing materials was found. Next the method to evaluate time until polymerization reaction begins was considered. As polymerization reaction occurs after polymerization-inhibitor disappeared, it's possible to regard induction time as time until polymerization-inhibitor is consumed. So to obtain induction time, an acceleration test by thermal analysis and a short storage test were carried out. And from relation between the temperature and induction time, the way to estimate induction time by the storage temperature was considered.

In our presentation, the study of thermal analysis method that considered a polymerization-inhibitor consumption mechanism, and estimation of induction time to polymerization reaction will be presented. Polymerizing substance is designated by UN transport of hazardous goods. Therefore this study is very useful for dangerous goods judgment.