Thermal and evolved gas analyses on Michael addition oligomers of acrylic acid

Abstract

Michael addition reaction of acrylic acid has caused thermal runaway of acrylic acid, thereby causing many explosion and fire accidents in the chemical industries. The aim of the present study is to gain a better understanding of the reaction mechanisms of Michael addition oligomers of acrylic acid (MAO) during a runaway polymerization on the basis of thermal and evolved gas analysis. The Michael addition reaction of acrylic acid occurs at a temperature lower than the temperature at which thermal polymerization occurs, triggering the initiation of thermal polymerization and the associated thermal runaway, and after the thermal runaway, the pressure generated by the reaction with the product, MAO, can cause tank rupture. We discussed the reaction mechanisms of MAO including thermal polymerization and thermal decomposition on the basis of high-sensitivity reaction calorimetry and evolved gas analysis of MAO and its thermal polymer. From the results of the thermal analysis using Calvet-type calorimeter and thermogravimetry–differential scanning calorimetry-mass spectrometry-infrared spectrometry (TG-DSC-MS-IR), MAO can be polymerized exothermically at more than 180 °C, and its thermal polymer decomposes to propanoic acid, carbon dioxide, ethylene and low-molecular hydrocarbons such as methane, ethane, and cyclopropane at more than 195 °C. Michael addition oligomerization of acrylic acid was found to not only thermally initiate free radical polymerization due to its heat generation but also increase the possibility of the tank explosion after runaway polymerization due to the large pressure generation induced by thermal decomposition of MAO polymer.