Estimation of biomass pyrolysis oil oligomer properties through anlaysis with high resolution mass spectrometry coupled with reaction modeling

Authors: Terrell, Evan; GARCIA-PEREZ, MANUEL - Washington State University

Submitted to: American Institute of Chemical Engineers Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/2020
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 properties of 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. This work used an advanced analytical technique (high resolution mass spectrometry) to measure these heavy molecules. The reactions that lead to the production of these molecules is also modeled and compared to laboratory analysis. With a better understanding of what these molecules look like, it then becomes possible to estimate some of their important properties, like boiling point and solubility characteristics. This work shows progress toward understanding the properties of heavy molecules in pyrolysis oil and proposes some of the reactions responsible for producing these molecules. A better understanding of the pyrolysis process at a molecular level makes it easier to design and implement renewable energy technologies that make fuels and chemicals from biomass.

Technical Abstract: The oligomeric fraction of biomass pyrolysis oil makes up a significant component of pyrolysis products, comprising the majority of the overall liquid product mass. These high molecular weight molecules present an interesting and important engineering challenge regarding the characterization and final valorization of liquid products from biomass pyrolysis. In order to more fully understand the nature of the pyrolysis oil oligomeric fraction, it is necessary to estimate the structures of the molecules comprising this fraction. In this presentation, we will use results from high-resolution FT-ICR MS analysis of bio-oils coupled with simple combinatoric modeling to simulate pyrolysis fragmentation to propose molecular structures for abundant bio-oil oligomers. The fragmentation modeling is used to build up a library of oligomers to which FT-ICR MS-detected peaks can be matched. Once these molecular structures have been proposed, then their properties can be estimated (via group contribution methods and other possible correlations). Some of these properties include normal boiling point, heat of vaporization, and solubility parameters. At present, a total of 50 structures have been assigned to detected MS peaks with high abundance among three contrasting bio-oils. Importantly, we show that these structures can be reached beginning from unmodified cellulose-derived oligomers, while at the same time producing H2O, CO and C2-C3 light volatile organics. Figure 1 depicts a potential fragmentation pathway that yields C8H14O7, one of the top-abundance peaks in FT-ICR MS analysis. Based on the resulting structure, it is then possible to estimate properties of the molecule with the prescribed structure. For example, cellobiosan (another abundant bio-oil product) has been estimated to have normal boiling point of 555 C and total solubility parameter of 41 MPa1/2. Ongoing work will extend this property prediction analysis to further assigned/proposed oligomeric structures corresponding to high-abundance peaks detected in FT-ICR MS analysis of bio-oil.