Date of Award
Doctor of Philosophy
Julie Carrier, Paul Frymier, Douglas Hayes, Xiaofei Ye
The lignocellulosic biorefinery is a visionary concept that endeavors to provide an alternative to fossil-based refineries by producing biobased fungible fuels and specialty chemicals almost exclusively derived currently from petroleum refineries. This vision of the lignocellulosic biorefinery can only be realized if all fractions of lignocellulosic biomass are efficiently deconstructed and valorized to generate a diverse portfolio of products to sustain it against market vicissitudes. Of the three main structural constituents of lignocellulosic biomass (i.e., cellulose, hemicellulose, and lignin), lignin is underutilized despite being the most abundant renewable source of aromatic platform chemicals, representing a growing 250 billion dollar market. One pathway for lignin valorization includes its efficient fractionation followed by controlled deconstruction. Through the thermochemical deconstruction route, the focus of this dissertation project, greater understanding of the thermal deconstruction or depolymerization reactions and their associated kinetics is necessary to control competing reaction pathways to improve selectivity toward desirable products and increase yields. In this project, we seek to deepen our mechanistic understanding of the prevalent reaction pathways during the thermal deconstruction of lignin by computationally and experimentally investigating model lignin oligomers with important linkages found in lignin. Insight of the thermal deconstruction pathways of oligomeric lignin fragments with diverse linkages is a key missing piece of the puzzle required to develop fuller and generalizable lignin thermal deconstruction mechanisms. We will employ density functional theory (DFT), a computational quantum chemistry investigative tool, to assess the reactivity of a combination of important lignin linkages in the model oligomers. We will then experimentally pyrolyze commercially available model compounds with closely related to the model compounds used in the DFT investigation using a pulse heated pyrolysis reactor (PHPR) system developed for this project. The PHPR system overcomes transport limitations found in commercial pyroprobe systems used in milligram-scale biomass pyrolysis studies. We will use this system to identify major products and intermediates and validate the results obtained from the computational calculations. The computational and experimental findings will be used to identifying general reactivity trends between the major interunit linkages of lignin and propose and validate reaction mechanisms and kinetics for each model oligomer.
Houston, Ross Wesley, "Understanding lignin’s fast pyrolysis through examination of the thermolysis mechanisms of model oligomers. " PhD diss., University of Tennessee, 2023.