In-depth analysis of biomass and pyrolysis oils using high-resolution mass spectrometry

Authors: Terrell, Evan; DUFOUR, ANTHONY - National Council For Scientific Research-Cnrs; CARRE, VINCENT - University Of Lorraine; AUBRIET, FREDERIC - University Of Lorraine; BARTOLOMEI, ERIKA - National Council For Scientific Research-Cnrs; GARCIA-PEREZ, MANUEL - Washington State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Biomass pyrolysis is a promising technology by which renewable biomass resources, like wood and agriculture residues, can be converted into liquid fuels and chemicals. A major challenge with this technology is in measuring and understanding the liquid oil resulting from pyrolysis reactions. Specifically, this oil contains a large fraction of heavy molecules (oligomers), which are difficult to analyze in a typical laboratory setting. In this work, an advanced analytical method called high resolution mass spectrometry is used to directly measure these heavy molecules both in unreacted biomass and in pyrolysis products. While there is a good amount of published research using this type of technique for analyzing petroleum and water samples, its applications to biomass and pyrolysis products is much more limited. In this presentation, the direct analysis of biomass before and after pyrolysis, with high resolution mass spectrometry, will be shown. The focus will be on giving ideas about how to best analyze and visualize the data from high resolution mass spectrometry and understanding some important things that can be seen and concluded from high resolution mass spectrometry analysis. Additionally, this talk will show how to connect high resolution mass spectrometry analysis with the present body of knowledge about biomass pyrolysis in order to make more advanced reaction models. Ultimately, the approaches that will be presented represent a new way to look at the pyrolysis process using analytical laboratory methods that are relatively unexplored for biomass.

Technical Abstract: Introduction: Biomass pyrolysis reactions produce a wide range complex and diverse products, which makes the characterization of bio-oils challenging. A popular, emerging technique for petroleomic analysis of bio-oils (and biomass directly) is Fourier transform ion cyclotron resonance-mass spectrometry (FT ICR-MS). FT ICR-MS possesses high resolution capability and high mass measurement accuracy that allows for the assignment of a chemical formula (i.e., CxHyOz) based on solely its measured m/z ratio. Consequently, one great strength of FT ICR-MS lies in its ability to probe the nature of oligomeric molecules that occur in bio-oils1, which are difficult to accurately measure with more limited “traditional” MS techniques like GC/MS. Aim: In this work, we will present the analysis of lignin, whole biomass pyrolysis oils, and lignin-derived pyrolysis products using FT ICR-MS. Various different data treatments and visualizations will be explored. Particular emphasis is given to the analysis of lignin and its pyrolysis products. Methods: The direct analysis of hybrid poplar milled wood lignin was carried out using matrix assisted laser desorption/ionization (MALDI) FT ICR-MS (9.4 T, positive ion detection mode, 355 nm, Metz, France). Measurements on pyrolysis products were conducted by electrospray ionization (ESI) FT ICR-MS (9.4 T, Pullman, WA, US). Further details on the pyrolysis product assessments can be found in two published studies, from which some data is derived.2,3 In-depth data analysis and visualization is conducted with both Microsoft Excel and Python softwares. Results: Based on FT ICR-MS analysis of lignin and its pyrolysis products3, it is possible to observe a clustered nature of detected features in a H/C ratio vs. nominal mass plot (Figure 1). These clusters are the result of the polymeric nature of lignin, which is made up of aromatic subunits. Using structural information from other techniques (e.g., NMR, Py-GC/MS), it is also possible to propose candidate structures. For example, a nominal mass of 662 (from C33H42O14) can be attributed to a syringyl-type trimer connected by ß-O-4 bonds (among other potential matching structures). For direct lignin analysis, 160 unique structures are proposed for 80 unique MS peaks. This can be carried out similarly for lignin pyrolysis products. Additionally, using van Krevelen diagrams it is possible to visualize various reaction and/or functional group loss patterns (Figure 2). Ongoing work will explore analyses for whole bio-oils and other data visualization modes, such as through Kendrick mass defect analysis. Conclusion: In-depth analysis of biomass and its pyrolysis products (and for other carbonaceous feedstocks, like coals and plastics) can enable greater understanding of pyrolysis reactions. Furthermore, FT ICR-MS is shown to be robust and fast, requiring very small sample amounts, for gaining significant insight on molecular-level details of pyrolysis liquids. These results represent an important advance in analytical capabilities for pyrolysis research.