Microalgae and oilseeds demonstrated themselves as excellent
feedstocks for the HTL process. As shown in Table 3, microalgae,
Nannochloropsis sp,was liquefied at 350 C, giving a fairly high yield
of the crude bio-oil (43.0%) and a HHV of 39.0 MJ kg1. HTL of
L. cubeba seed achieved an even higher yield of the oil product
(56.9%) with a HHV value of 40.8 MJ kg1, both of which are much
higher than those of the crude bio-oil from SCG liquefaction (oil
yield of 47.3%, HHV of 31.0 MJ kg1). This is not surprising because
Nannochloropsis sp, and L. cubeba seed contains high contents of
lipid (28.0% and 41.0%, respectively) and protein (52.0% and 35.0%,
respectively), which was believed to be able to enhance the crude
bio-oil yield in the HTL processes [44e48,51,52]. However, high
lipid content materials can be converted into biodiesel comparable
to petro-diesel, through a process known as transesterification, less
costly than HTL. More concerning, the cultivation of algae and L.
cubeba requires additional energy inputs. On the contrary, SCG, a
waste stream does not require extra energy for the feedstock
plantation. The above comparison suggests that SCG can become a
promising feedstock for HTL. The yield of crude bio-oil from HTL of
SCG is much higher than those of lignocellulose feedstock and its
HHV is comparable or slightly lower than that of lignocellulose
feedstock. However, SCG bio-oil is still not competitive to the biooils
derived from the protein/lipid rich biomass such as microalgae
and oilseeds in terms of yield and higher heating value.