Date of Award
Doctor of Philosophy
In recent decades, thermochemical conversion of lignocellulosic biomass has gained popularity as a means to supplement or replace petroleum. Fast pyrolysis bio-oils have emerged as a potential source for transportation fuels and value-added chemicals. A lack of molecular-level understanding has stalled progress toward fast pyrolysis as an economically feasible option. To address this roadblock, this research focuses on high resolution mass spectrometry (HRMS) applications to molecular-level understanding of biomass pyrolysis.
Negative mode atmospheric pressure photionization (APPI) and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS) are applied to nitrogen-rich switchgrass bio-oil and gasification tar for characterization and comparison. When compared with (+) APPI and positive and negative electrospray ionization, (-) APPI ionizes a wider range of compounds and provides a more comprehensive overview of the compounds present. The compounds accessed by (-) APPI are also generally accessed by one of the other ionization methods, but (-) APPI ionizes them with less specificity for a single group of compounds.
A novel HRMS system for biomass pyrolysis analysis is introduced. Gas chromatography is coupled with dopant-assisted atmospheric pressure chemical ionization (dAPCI) for analysis by a time-of-flight mass spectrometer (TOF MS). Ammonia gas serves as the dopant. The ammonium adduct ions prevent the fragmentation observed in dopant-free APCI. Water plays a crucial role in the ionization process; thus, a humidification system for dAPCI is created to provide constant humidity. All compounds demonstrate improved signal and ionization with controlled humidity.
A micropyrolyzer (μPy) is attached to the dAPCI-TOF MS system and thin-film glucose labeled on carbons 1, 3, or 6 with 13C is pyrolyzed and analyzed in real-time to study reaction pathways. The real-time data acquired validates or invalidates previously proposed mechanisms. Alternative reaction pathways are suggested when the mechanism is invalidated. Glyceraldehyde, a C3 compound difficult to detect with traditional analytical methods, is shown to play an important role.
Single particles of whole biomass are pyrolyzed and analyzed with the μPy-dAPCI-TOF MS for a unique comparison of herbaceous, softwood, and hardwood lignocellulosic biomass. Different temporal profiles for holocellulose and lignin decomposition products are observed. A series of the most dominant phenolic compounds occurs at m/z 133, 163, and 193, related to the monolignol monomers. Smaller, highly oxygenated compounds are more abundant for the hemicellulose-rich herbaceous feedstock whereas levoglucosan is dominant in both hardwood and softwood.
Carolyn P. Hutchinson
Hutchinson, Carolyn P., "High resolution mass spectrometry to explore molecular-level understanding of biomass pyrolysis" (2017). Graduate Theses and Dissertations. 15535.