Detailed Multiphase Chemical Kinetic Model for Polymer Fouling in a Distillation Column

Abstract

Polymer fouling is a ubiquitous but unsolved problem in the separation train downstream of a steam cracker. A mechanistic understanding of polymer fouling would guide mitigation. We present a multiphase chemical kinetic model to predict the polymer film growth rate in an industrial "debutanizer" distillation column. Modeling innovations are introduced, which allow us to construct models including thousands of chemical reactions occurring in the liquid and film phases, vapor−liquid equilibria of hundreds of species, transport between the phases, and flows between the trays. All of these significantly affect the fouling rate. Most of the critical model parameters are derived from quantum chemistry calculations. The modeling method is validated using experimental film growth measurements made with a quartzcrystal microbalance. The debutanizer fouling model clarifies the mechanistic details of the fouling process. Challenges in more accurately predicting polymer fouling in industrial units are discussed.

Oxygen Chemistry in Polymer Fouling: Insights from Multiphase Detailed Kinetic Modeling

“…Literature experimental investigations have shown that dissolved oxygen can affect fouling significantly, − where dissolved oxygen was measured to accelerate fouling , even at parts per million (ppm) level concentrations, while the fouling rate becomes independent of oxygen concentration near air saturation . The effects of dissolved oxygen on fouling rates were recently measured using quartz crystal microbalance with dissipation monitoring (QCM-D), similar to the prediction by our detailed fouling model for QCM-D cell fouling …”

“…In our prior research, we took the initial step of creating a predictive multiphase detailed chemical kinetic model for polymer fouling in an industrial distillation column that separates C4 and lighter species from heavier ones (“debutanizer”), as illustrated in Figure . That model only considered the base case scenario, which includes alkanes, alkenes, conjugated dienes, and aromatics from steam cracker effluents and excluded any impurities or industrial additives.…”

“…In this work, we extend the base case model for debutanizer fouling in our previous work toward oxygen chemistry (“oxygen-perturbed model”), as illustrated in Figure . We follow a similar modeling method as presented in our previous work . A general flowchart of this work can be found in Figure .…”

“…The film growth mechanism at the surface of each tray, condenser, and reboiler is modeled using a variant of fragment-based modeling, a type of lumping well suited for modeling unselective chemistry of mixtures containing macromolecules. We update the fragment-based reaction template presented previously to include important autoxidation reactions. We simulate the oxygen-perturbed fouling model with a simulation scheme similar to our previous work using ReactionMechanismSimulator.jl (RMS), , a Julia software package for simulating large chemical kinetics models developed recently by the MIT Green Group.…”

“…We update the fragment-based reaction template presented previously to include important autoxidation reactions. We simulate the oxygen-perturbed fouling model with a simulation scheme similar to our previous work using ReactionMechanismSimulator.jl (RMS), , a Julia software package for simulating large chemical kinetics models developed recently by the MIT Green Group. As shown below, the new oxygen-perturbed model predicts a faster fouling rate in some trays of the column and prompts us to consider diffusion limits when simulating the fouling growth.…”