(124c) Ab Initio Studies of the Mechanism and Kinetics of Polymerization Fouling in Ethylene Plants

Polymerization fouling of butadiene and/or styrene can happen under favorable conditions in downstream separation sections of ethylene plants and is a major cause of shutdowns and safety issues. In this work, the mechanism and kinetics of initiation and propagation reactions of butadiene-styrene system were investigated using density functional theory (DFT) methods. The overwhelmingly dominant initiation mechanism under typical plant conditions was found to be peroxide decomposition over thermal initiation at ppm levels of peroxide impurities. The similarity between isoprene and butadiene in fouling chemistry was unveiled, such as monomer reactivity ratios in the copolymerization with styrene. The results suggested that isoprene is a good analogue of butadiene in lab studies for copolymerization fouling with the advantages of reducing the risk of chemical exposure and fire/explosion. Furthermore, DFT predictions of the instantaneous relative monomer consumption rates of isoprene-styrene system were validated by experimental results at different initial monomer compositions. It is predicted that in a butadiene-styrene system, butadiene will be consumed faster than styrene even at 70% of styrene in monomer composition, and the overall propagation rate constant will increase with higher styrene fractions. We recommend that anti-fouling treatments should focus on eliminating initiators such as peroxides, and aggressively tailoring additive programs based on radical-forming monomers such as styrene. Overall, this study built a basis for integrating computational study with experimental efforts in understanding the fundamentals of polymerization fouling, which could eventually help provide more effective anti-fouling strategies in the production of light hydrocarbons.