Properties of the resulting crude bio-oil
The crude bio-oil obtained from the HTL process of SCG were
coffee-brown, viscous and possessed a coffee-aromatic odor with a
water content of 2.1% and pH of 4.8. The elemental composition (C,
H and N) of the raw material and the representative crude bio-oil
product was determined by an elemental analyzer and presented
in Table 1. The results showed that the SCG crude bio-oil contained
a higher content of carbon and a less oxygen content than those of
the raw materials. The oxygen content of SCG was greatly reduced
from approximately 40% down to 19% mass fraction, and the O/C
molar ratio dropped from 0.6 to 0.2. This was expected since the
oxygen was removed in the form of CO or CO2 through decarbonylation
reaction and decarboxylation reaction, respectively, in the
process of liquefaction. This resulted in a significant increase in the
higher heating value, as presented in Table 1, in which the HHV of
the bio-oil was 31.0 MJ kg1, much higher than that of SCG
(20.2 MJ kg1). Additionally, the energy recovery of the resulting oil
at such conditions was fairly high with a value of 72.6%, indicating
that a large percentage of the energy in the feedstock was recovered
in the oil phase. It was thus concluded that HTL is a suitable
technology to convert SCG to a more energy-rich bio-oil with the
potential to be used as a renewable energy source.