(104bf) Preventing Runaway Polymerization of Vinyl Acetate in Storage Vessels

During the production of vinyl acetate (VA), the runaway polymerization of VA and VA /acetic acid solutions in storage vessels might occur at the storage temperature, especially under the conditions of free inhibitor for maintaining the polymerization activity of VA in polymerization reactors. The influence on the polymerization of VA by oxygen, polymerization inhibitor, acetic acid dilution, impurities including Fe₂O₃, water, and acetaldehyde/water mixture, was investigated with C80 calorimeter in closed cell, respectively. The onset exotherm temperature of VA free polymerization inhibitor is 230°C under nitrogen compared to 125°C under oxygen. There existed two segments in the process of VA polymerization, including low temperature polymerization and high  temperature polymerization. The low temperature polymerization is related to the presence of oxygen, while the high temperature polymerization was caused by plenty of free radicals due to high temperature. Either under nitrogen or under oxygen, the high temperature polymerization existed. The onset exotherm temperature of VA with 10 ppm hydroquinone (HQ) rose to 165°C under oxygen, whose onset exotherm temperature of  the high temperature polymerization is the same as VA without HQ. The onset exotherm temperature of the two segments polymerization of VA /acetic acid solutions hadn’t altered remarkably as the dilution of acetic acid. As impurities, both water and Fe₂O₃ could stabilized VA, while acetaldehyde/water mixture quite the contrary. As a result, Isoconversional differential Frieman analysis was taken to determine the time to maximum rate under adiabatic conditions(TMR) of VA free inhibitor in the presence of oxygen, and predict the induction period at certain temperature.