Polymer fouling is a ubiquitous problem in ethylene cracking plants. 1,3 Butadiene is an active conjugated diene that readily polymerizes at typical process conditions in the presence of active oxygen or free radical species. 1,3 Butadiene along with other compounds can form polymers that deposit in downstream equipment resulting in impaired heat transfer, flow blockages, and eventual plant shut down. A variety of empirical approaches have been developed and used, with mixed success, to ameliorate process fouling. However, there is a limited fundamental understanding of the mechanism responsible for fouling. In this work, we construct a mechanism to understand the polymerization of 1,3 butadiene under reboiler conditions (115○C, 15 bar). The mechanism was built with Reaction Mechanism Generator (RMG), which uses a rate and flux-based algorithm to generate reaction mechanism. RMG automatically identified the dimerization and isomerization pathways of 1,3-butadiene to 4-vinylcyclohexene, 1,5-cyclooctadiene, and 1,2-divinylcyclobutanein addition to step polymerization pathways. The mechanism then passed to Automatic Reaction Calculator (ARC) spinoff quantum mechanical calculations of species at CBS-QB3. ARC is an in-house software which carries out quantum chemistry calculations using popular electronic structure programs with minimum human intervention. Transition states and connected local minima were verified with Intrinsic Reaction Coordinate (IRC) calculations followed by Transition State Theory (TST) calculations with the Automated Reaction Kinetics and Network Exploration (Arkane) package in RMG. We validate our reaction mechanism and kinetic model using stainless steel batch reactor experiments with pure butadiene at 115 ○C. The experiments were repeated for 2, 5, 16, and 22 hr reaction times. The liquid phase products from the batch reactor experiments were analyzed using a GCxGC-qMS. The results from the experiments show that the kinetic model created with the aid of RMG accurately predict dimerization, isomerization, and trace polymerization pathways of 1,3 butadiene.

Automated reaction mechanism generation and automatic quantum chemical calculations: Initial stages of butadiene oligomerization and polymerization

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.