Bio-oils obtained from lignocellulosic biomass pyrolysis are regarded as a promising solution to replace petroleum-based fuels. At the molecular level, these materials are highly complex mixtures comprising thousands of species covering a large range of mass and polarity. In fact, they contain significant oxygenated compounds and amount of water, which is responsible for corrosiveness and storage issues, as well as a low energetic density. Consequently, they cannot be directly used as biofuels, but must undergo upgrading processes in order to obtain a material whose physicochemical properties are close to conventional fuels. To understand and improve both the conversion and upgrading processes, a deep molecular characterization of the raw of upgraded bio-oils is required. Some of the studies performed on bio-oils involve direct-infusion ultra-high-resolution mass spectrometry that allows detecting and assigning thousands of molecular formulae. However, only isobaric level is well-described by this approach, and neither structural nor isomeric information is obtained. This latter dimension was shown to be relevant in the upgrading catalytic process of petroleum fractions, but it is still poorly documented regarding bio-oils. Therefore, we are currently developing an analytical method coupling supercritical fluid chromatography to ion mobility spectrometry - mass spectrometry (SFC-IMS-MS). The first step is aimed at reducing the bio-oil complexity, but it also helps to differentiate isomers, whereas ion-mobility spectrometry enables to separate isomers and to obtain the collision cross section (CCS) of given ion, which is an intrinsic property linked to its three-dimensional structure. The comparison of experimental and theoretical CCS values can provide valuable structural information from real unknown molecules. This novel method was applied to a pyrolysis bio-oil and to standard compounds relevant to species identified in bio-oils. Thus, both the retention time and the CCS, respectively achieved by SFC and IMS, for these standards will help to identify some bio-oil components, bringing complementary isomeric dimension for the bio-oil characterization.

Insight into the isomeric diversity of the pyrolysis bio-oil components

ACS Fall 2021

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