Bio-mass for biomass: biological mass spectrometry techniques for biomass fast pyrolysis oils
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Biomass fast pyrolysis oils, or bio-oils, are a promising renewable energy source to supplement or replace petroleum-based products and fuels. However, there is a current lack of understanding about the pyrolysis process which creates a bottleneck towards making biomass pyrolysis an economically feasible option. In order to address this bottleneck, this research focuses on developing high resolution mass spectrometry (HRMS) techniques to address biomass pyrolysis at the molecular-level.
The first attempt at analyzing bio-oils with HRMS employs laser desorption ionization and LTQ-Orbitrap MS to successful identify over 100 compounds. These compounds consist of 3-6 oxygens and have double-bond equivalents (DBE) of 9-17. A petroleomic analysis and comparison of the bio-oil to the low-mass components in hydrolytic lignin suggest that these compounds are dimers and trimers of depolymerized lignin. A wider variety of bio-oil compounds, specifically volatile and non-volatile compounds, could be characterized with electrospray ionization (ESI). Specifically, (-) ESI allows for the characterization of over 800 molecular compounds, of which about 40 of these were previously known in GC-MS. These compounds include cellulose- and hemicellulose-derived pyrolysis products as well as lignin-derived pyrolysis products.
A comparative study of three common HRMS was also performed to validate the methodology and to investigate differences in mass discrimination and resolution. This led to the development of a novel spectral stitching technique that combines datasets from different HRMS together. By stitching the datasets together inherent instrument limitations (e.g. like mass discrimination and resolution) can be addressed. The resulting stitched mass spectrum gives rise to a more comprehensive picture of bio-oil.
Lastly, a pioneering technique that utilizes HRMS to monitor biomass fast pyrolysis in real-time has been developed. A fast-scanning time-of-flight mass spectrometer with a soft ionization source and a drop-in micropyrolyzer is used to provide insights into biomass pyrolysis that are not possible with traditional techniques. For example, metastable intermediates of cellulose pyrolysis could be identified and monitored with this novel approach. Also, fundamental pyrolysis studies, such as the effect of biomass shape and thickness, are possible with this technique due to the high sensitivity and time resolution of the time-of-flight mass spectrometer.