Bio-Oil from Waste: A Comprehensive Analytical Study by Soft-Ionization FTICR Mass Spectrometry

Organic solid wastes are potential feedstocks for the production of liquid biofuels, which could be suitable alternatives to fossil fuels for the transport and heating sectors and for industrial use as well. By hydrothermal liquefaction (HTL), the wet biomass is partially transformed into a water-immiscible oil-like organic matter called bio-oil. In this study, three different mass spectrometric ionization techniques, namely, ESI, APCI, and APPI, in combination with a high-resolution FTICR mass analyzer were used in a comparative approach for the characterization of HTL bio-oil. In terms of the number of assigned molecular formulas, the three ionization techniques gave comparable results but with different distributions of the molecular classes. APPI, in particular, was demonstrated to be the ionization technique that best fits the actual elemental composition of the bio-oil sample. Our results, obtained by the integration of the three mass spectrometric ionization techniques, offer the opportunity to detect and identify by FTICR mass spectrometry the heteroaromatic compounds in bio-oil. Both aromatic molecules and nitrogen-containing species raise concern for the subsequent upgrading process of the bio-oil into a diesel-like fuel

Amides in Bio-oil by Hydrothermal Liquefaction of Organic Wastes: A Mass Spectrometric Study of the Thermochemical Reaction Products of Binary Mixtures of Amino Acids and Fatty Acids

Among biofuels, the bio-oil produced by hydrothermal liquefaction of waste biomass can be considered an alternative to fossil fuels in industry as well as transport and heating compartments. The bio-oil complex composition is directly dependent upon the specific biomass used as feedstock and the process used for the chemical conversion. The coexistence of proteins and lipids can explain, in principle, the high percentage of fatty acid amides found in the produced bio-oil. In the present study, the amides in a sample of bio-oil have been separated by gas chromatography and identified at first on the basis of their electron impact (EI) mass spectra. To distinguish between <i>N</i>-alkyl isomers, standard amides have been synthesized and analyzed. Because the most reasonable origin of fatty acid amides in hydrothermal bio-oils is the condensation reaction between fatty acids and the decarboxylation products of amino acids, a series of model experiments have been carried out by reacting hexadecanoic acid, at high temperature and pressure, with each of the 20 amino acids constitutive of proteins, looking for the formation of fatty acid amides. Remarkably, by such experiments, all of the amides present in the bio-oil have been recognized as hydrothermal coupling compounds of the decomposition products of amino acids with fatty acids, thus allowing for their structural elucidation and, also important, confirming their (bio)­chemical origin