Study for Thermal Hazard Evaluation of Polymerizing Substance at Storage Tank

The polymerization reactions are inhibited by the polymerization inhibitors during storage in tanks, but when the polymerization inhibitors are consumed, unwanted exothermic reactions might occur. Due to the explosion accident of acrylic monomer storage tank occurred in 2012 in Japan, it was necessary to review prevention and emergency measures against runaway reactions of polymerizing substances. The standard for storage of polymerizing substances in tanks is should be instituted properly in the aspect of the concentration of polymerization inhibitor and storage period, nevertheless, experimental method is the only way to quantify the induction period for runaway reaction. As there are many tanks which storage temperature of polymerizing substances are room temperature or about 40℃, therefore, experimental method by actual storage temperature needs long term for evaluation. Furthermore, emergency measures assumed reaction runaway are important to prevent and mitigate serious damage, but it is difficult to say that the methods for estimating effect of added polymerization inhibitor are established.

The purpose of this study is to establish a “fast” and “accurate” method for estimating the induction period until occurrence of runaway reaction and effect of shortstopping in an emergency.

For the estimation of the induction period, the acceleration tests which small amount of polymerizing substances were hold at a high temperature were carried out by C80 and ARC (Accelerating Rate Calorimeter), and the induction period was estimated by the consumption rate of polymerization inhibitor. However, the different results of induction period between estimation by acceleration test and verification test at the actual storage temperature were obtained, and it is suggested that the reaction mechanism is different between the high temperature range and the low temperature range. An estimation method of the induction period is established by the minimum number tests combined with acceleration test and verification test.

For the estimation of effect of added polymerization inhibitor, the thermal equipment was improved for that could measure a series of phenomena from detection of the start of runaway reaction to the effect of shortstopping by added polymerization inhibitor. An appropriate concentration of an inhibitor and timing of addition are clarified by the equipment, it would be possible to propose to more effective emergency measures quantitatively.

Establishing estimation method in this study can be useful for improving safety handling in storing polymerizing substances and evaluation of the risk for runaway reaction fast and accurately.