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 N-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.

Solid wastes of organic origins are potential feedstocks for the production of liquid biofuels, which could be suitable alternatives to fossil fuels for the transport and heating sectors, as well as for industrial use. By hydrothermal liquefaction, the wet biomass is partially transformed into a water-immiscible, oil-like organic matter called bio-oil. In this study, an integrated NMR spectroscopy/mass spectrometry approach has been developed for the characterization of the hydrothermal liquefaction of bio-oil at the molecular level. (1)H and (13)C NMR spectroscopy were used for the identification of functional groups and gauging the aromatic carbon content in the mixture. GC-MS analysis revealed that the volatile fraction was rich in fatty acids, as well as in amides and esters. High-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) has been applied in a systematic way to fully categorize the bio-oil in terms of different classes of components, according to their molecular formulas. Most importantly, for the first time, by using this technique, and for the liquefaction bio-oil characterization in particular, FT-MS data have been used to develop a methodology for the determination of the aromatic versus aliphatic carbon and nitrogen content. It is well known that, because they resist hydrogenation and represent sources of polluting species, both aromatic molecules and nitrogen-containing species raise concerns for subsequent upgrading of bio-oil into a diesel-like fuel.

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.

In the conversion of heavy oil into valuable fuels by thermal processes, one of the main problems is the formation of soft coke-like substances that can cause equipment fouling and catalyst deactivation. Asphaltenes are present in large quantity in heavy crude oil and are known to be coke precursors. The objective of the present study was to obtain chemical structure information about the asphaltene molecules when they undergo a thermal treatment and to investigate the mechanism of coke formation. Asphaltenes were separated from two industrial thermal treated heavy crude oils and characterized by elemental analysis, NMR, FTIR, and FT-ICR MS. Analytical data were then compared with that obtained from asphaltene samples after thermal treatment at 400 °C. From complementary and comparative use of the different analytical techniques, we demonstrated that asphaltenes thermally treated at 400 °C tend to aromatize to form coke precursors. We found that the species rich in saturated rings and/or alkyl chains are less stable than the one containing aromatic rings; the main reaction in thermal treatment is the intramolecular cyclization/aromatization and not the cleavage of residual aliphatic chains. Moreover, asphaltene classes containing sulfur atoms present a lower stability than the other species.