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Pyrolysis bio-oils have great potential for the future use as biofuels and source of oxygenated chemicals. To optimize a pyrolysis process, detailed knowledge about the chemical composition of bio-oils is necessary. In recent years, high-resolution mass spectrometry (HRMS) has successfully been used to the characterization of pyrolysis bio-oils from lignocellulosic biomass. This method enabled to detect thousands of semivolatile and nonvolatile, high-molecular-weight bio-oil compounds and provided partial information about their structure. In this work, we used high-resolution orbitrap mass spectrometry to characterize semivolatile and nonvolatile, high-molecular-weight compounds of four bio-oils obtained from the ablative flash pyrolysis of different biomass sources. Before the analyses of these bio-oils, we analyzed model bio-oil compounds and commercially available bio-oil from fast pyrolysis of wood using positive-ion and negative-ion electrospray (ESI) and positive-ion and negative-ion atmospheric pressure chemical ionization (APCI) orbitrap mass spectrometry and compared the results. Based on this comparison, a combination of negative-ion ESI and APCI was found to be well suited for the characterization of pyrolysis bio-oils; these techniques were thus used for the study of bio-oils from different biomass sources and the obtained results were compared. In the studied bio-oils, mostly compounds with 1–8 oxygen atoms per molecule were detected and their degree of unsaturation (DBE) was about 1–10 (negative-ion ESI) and 1–17 (negative-ion APCI), respectively. Among the studied bio-oils, the differences were observed mostly in abundances of their major compounds (compound classes). The analyses of model bio-oil compounds brought valuable information about their behavior during the HRMS characterization of bio-oils. The presented results could help to improve the understanding of bio-oil composition and HRMS characterization of bio-oils and facilitate their further utilization

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Bio-oil upgrading through its hydrodeoxygenation (HDO) using sulfided catalysts has attracted significant attention because of its potential to provide advanced biofuels. Although many studies have been undertaken, a detailed understanding of the changes in the chemical composition on the molecular level that would allow the better design of catalysts for bio-oil upgrading is still insufficient. Therefore, we have subjected straw bio-oil and products obtained from its hydrotreatment over a broad range of experimental conditions to a detailed quantitative chemical analysis. Most of the volatile compounds were quantified by GC-MS. Among them, 115 compounds were quantified directly (i.e., using the appropriate standards) and more than 100 indirectly (i.e., based on their structural similarity with corresponding standards). Moreover, the total concentrations of carboxylic acids, carbonyls and phenols were quantified by the carboxylic acid number (CAN), Faix, and Folin–Ciocalteu methods, respectively, to obtain complementary and supporting information on the chemical composition to the GC-MS data. The detailed quantification of most volatile compounds in the feed and the products allowed us to create a reactivity order of the oxygen-containing functional groups present and to understand the origin of some of the compounds. On the basis of the results, the upgrading of straw bio-oil from ablative fast pyrolysis at 340 °C and 4 MPa seems to be optimal when evaluating the severity of the reaction conditions and hydrogen consumption, on the one hand, and the products quality, on the other hand. This provides a good starting point for further catalyst development and optimization allowing the long-term upgrading of the bio-oil for obtaining petroleum-refinery-compatible feedstock.

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