Bio-oil Fractionation According to Polarity and Molecular Size: Characterization and Application as Antioxidants

Bio-oil obtained
from biomass pyrolysis has great potential for
several applications after being upgraded and refined. This study
established a method for separating bio-oil into different fractions
based on polarity and molecular size to extract phenolic and polyphenolic
compounds with antioxidant properties. The fractions were analyzed
using various spectroscopic and chromatographic techniques, such as
GC/MS, FTIR, UV–vis, SEC, DOSY-NMR, 13C-NMR, and 31P-NMR. The antioxidant properties of these fractions were
tested by examining their ability to improve the oxidative stability
of biodiesel. The results strongly connected the bio-oil’s
chemical functionalities and antioxidant power. During solvent fractionation,
dichloromethane could extract phenolic structures, which were subsequently
size-fractionated. The subfractions with lower molecular weight (in
the order of monomers and dimers) outperformed the antioxidant potential
of the crude bio-oil. Heavier subfractions from dichloromethane extraction
did not show good antioxidant abilities, which was related to the
low hydroxy group content. After solvent extraction, phenolic oligomers
remained in the water-insoluble/dichloromethane-insoluble fraction,
which showed good antioxidant potential despite its low solubility
in biodiesel.