As observed in Table 3, the main organic compounds in the biooil
are phenols, which are formed in the decomposition of lignin
macromolecules above 350 C, and their yields increase considerably
at 600 C (12 wt.%). The high yield of phenolic compounds in
the bio-oil is consistent with other results from the literature for
the RH fast pyrolysis [34,57,58]. These compounds have been
grouped into three lumps: catechols (benzenediols), guaiacols
(methoxyphenols) and alkyl-phenols. Table 3 shows that guaiacols
are the main phenolic compounds at low temperatures, although
their yields decrease slightly at higher temperatures. Nevertheless,
alkyl-phenols and catechols increase sharply with temperature,
especially at 600 C. These results are consistent with the lignin
pyrolysis mechanism proposed by Demirbas [59], i.e., the monomolecular
dissociation of guaiacols into the corresponding radicals
(catechols and cresols) at higher temperatures. According to Amutio
et al. [20], similar trends are observed in pine wood sawdust
fast pyrolysis in a CSBR. Once they have been isolated, phenol
and phenolic derivatives are a valuable and useful chemical source
of phenolic resins [60] for the synthesis of antiseptics, antioxidants,
dyes and pharmaceuticals [61]. Currently, phenol is synthesized
from the partial oxidation of benzene, according to the cumene
process, or the Raschig–Hooker process. These typical synthesis
methods are usually very complex, and the phenol produced by
these methods is expensive.