Reaction Study of Guaiacylglycerol-Beta-Guaiacyl Ether

Lignin, a biopolymer found in woody and other plant biomass, is a potential energy source that can offset the demand for fossil fuels by providing a new pathway for making reagents—such as bio-aromatics and olefins—and aviation fuel. However, Lignin is historically underutilized primarily due to a plethora of recalcitrant chemical bonds that inhibit lignin from depolymerizing. One such prolific bond is the beta-O-4, connecting various compounds within Lignin.

For the project, Guaiacylglycerol-beta-guaiacyl ether (GGE) was used as the model compound, containing the beta-O-4 bond. The research regards GGE and the reactionary steps needed to depolymerize it into its monomer components, coniferyl alcohol and guaiacol. By identifying the best reaction conditions for depolymerizing GGE, this research can support the eventual creation of a techno-economically sound, lignin-focused biorefinery.

For experimentation, solvolysis reactions were conducted, consisting of GGE in various concentrations of water and methanol and at varying lengths of time. These reactions occurred in batches utilizing a fluidized sand bath reactor held at different temperatures. After spending time in the reactor, the samples were cooled in an ice bath, and a vial of the solution was taken for gas chromatography analysis afterward.

The gas chromatography data from the differing solvent concentration experiments indicate positive relationships between temperature and GGE conversion and another between solvent polarity and product selectivity. The data from the differing times experiment displays a positive correlation between reaction time and GGE conversion but a negative one between reaction time and product yield.

In addition, a byproduct of the reaction processes was identified; a solid precipitate was present in the final samples of some of the reactions. The concluding hypothesis is that coniferyl alcohol, and potentially guaiacol, are repolymerizing into unknown oligomers at some stage in the reaction process. This is leading to various experiments to isolate the solid product and identify its molecular structure through techniques, such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) imaging.