MoO3 catalyst
supported on synthesized mesoporous SBA-15
matrix was employed in the hydrothermolysis of Kraft lignin in a basic-subcritical
water system. Experiments were carried out in a batch reactor at 350
°C for 1 h under N2 atmosphere using two different
solvent systems of sub-H2O and 0.5% NaOH. At 10% (w/w)
of synthesized MoO3/SBA-15 catalyst with lignin, the highest
total crude bio-oil yield (∼56.40 wt %) and lowest char formation
(∼8.60 wt %) were observed in basic medium, in comparison to
the subcritical water system. The GC-MS analysis of the produced bio-oil
indicated that the major products in the crude bio-oil were phenol-rich
monomers such as guaiacols (19.50%), alkyl-guaiacols (24.83%), catechol
(26.76%), and alkyl-catechols (17.82%) under subcritical water condition.
Alternatively, catechols (42.07%) and alkyl-catechols (34.59%) were
the primary products in the basic solvent system with the presence
of MoO3/SBA-15 catalyst. Additionally, monophenols (5.0%)
were also produced as a result of the demethoxylation of guaiacol
or hydrodeoxygenation of catechol. MoO3/SBA-15 catalyst
significantly reduced the oxygen–carbon ratio (O/C) from 0.72
(in original Kraft lignin) to 0.29 (in basic-subcritical water system).
Decreased oxygen and increased carbon and hydrogen contents enhanced
the calorific value of the produced bio-oil, whereby a higher heating
value (HHV) of 32.00 MJ/kg was achieved. The synthesized catalysts
were characterized through BET, XPS, ICP-OES, and HR-TEM analyses.
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