1,3-butadiene monomer undergoes thermally initiated, reversible dimerization / trimerization reactions with essentially the same kinetics in both the gaseous and liquid phases. Kinetics for formation of the dimer and the trimer are available from the open literature. The rate of reaction becomes significant (0.02°C/min = 29°C/day) at temperatures above 70-80°C. Inhibitors (t-butylcatechol, et al.) are used to prevent / minimize free-radical polymerization reactions in the liquid phase and to maintain product quality at ambient or subambient temperatures. These inhibitors do not prevent the dimerization / trimerization reactions.
Unless adequate emergency relief is provided, the adiabatic temperature rise from the dimerization / trimerization reactions can lead to both a free-radical polymerization, initiated by adventitious peroxides, and a thermal decomposition of the resultant polymer to produce residues, volatiles, and noncondensable gases. Temperatures of 600°C and pressures of over 2000 psig are possible. Heat rates of 10,000°C/min and pressure rise rates of 10,000 psig/min are also possible in unvented / undervented vessels.
Emergency relief devices protecting vessels containing high concentrations of 1,3-butadiene should be reviewed to identify potentially reactive cases. This review is recommended to ensure that current emergency relief system designs are adequate and that equipment is being operated with an adequate margin of safety.
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