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Wednesday, May 08

The Chemistry of Lignin Model Compounds:
A Computational Approach

Ariana Beste, University of Tennessee/Oak Ridge National Laboratory, Oak Ridge
Joint Institute for Computational Sciences Seminar
1:00 PM — 2:00 PM, Joint Institute for Computational Sciences (Building 5100), Auditorium (Room 128)
Contact: Donna Wilkerson (djx@ornl.gov), 865.574.5493

Abstract

The main part of the talk will focus on the computational study of the thermal decomposition of ß-O-4 model compounds, representing the most common linkage in lignin. While experimental work determines overall product distributions and total rates of reaction, kinetic parameters of individual reactions and details of substituent effects on equilibrium and transition state structures are difficult to obtain experimentally. Computational methods allow the location of transition states and the calculation of activation barriers and entropical pre-factors for targeted chemical reactions. We launched a systematic computational study of the kinetic details of the pyrolysis of phenethyl phenyl ether (PPE) and various oxygen substituted derivatives, which are model compounds for the ß-O-4 linkage in lignin. Using density functional methods, we investigate relevant reaction steps including homolytic cleavage, competitive hydrogen abstraction, radical rearrangement, and ß-scission reactions. Electronic structure analysis of reactants, intermediates, products, and transition states is used to explain the effect of naturally occurring substituents, which can perturb multiple steps of the pyrolysis mechanism. We calculate relative rate constants using transition state theory, apply analytic kinetic models and kinetic Monte Carlo techniques to obtain experimentally observed product selectivities and monitor reaction progress as a function of time.

The presentation will be concluded by an introduction to our recent work relevant to the production of low-cost carbon fiber from lignin. Here we use a reactive force field within molecular dynamics to describe pyrolysis and oxidation processes of representative lignin models for softwood.

This research was sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy and was performed in part using the resources of the Center for Computational Sciences at Oak Ridge National Laboratory under contract DE-AC05-00OR22725. It was also supported by an allocation of advanced computing resources at the National Institute for Computational Sciences provided by the National Science Foundation. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.