Bio-oils after hydrotreatment can still contain significant amount of phenols and cyclic olefins as the products of an incomplete deoxygenation. The removal of these compounds would be necessary to produce suitable components for automotive fuels. However, no routine method currently exists for the reliable determination of these groups in hydrotreated bio-oils (HBOs). In this paper, we analyzed 140 different pure oxygenates as model compounds using the bromine number method (ASTM D1159) observing that most compounds present in HBOs react with one equivalent of bromine. The determination of phenols using bromine number method in crude bio-oil is complicated especially by the presence of guaiacols and syringols that react with more than one equivalent of bromine and, thus, the obtained result is significantly overestimated. Further we optimized the chromatographic separation of hydrocarbons from HBOs for the selective determination of olefins content. As no other reactive compounds under the conditions of the method, besides phenols and olefins, were observed in HBOs, the difference between HBO bromine number (before hydrocarbons separation) and olefins content correspond to the total amount of phenols. The method was finally applied to 11 HBOs with different content of oxygen, providing a good correlation between phenols and oxygen content.
Keywords: Bio-oils; Bromine number; Hydrotreated; Olefins; Phenols; Pyrolysis.
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