FT-IR analysis
FTIR spectra for SCG and the crude bio-oil derived from SCG
liquefaction under the liquefaction conditions of 275 C, 10 min,
water/feedstock mass ratio of 20:1 with 2.0 MPa initial N2 pressure
are illustrated in Fig. 4. Similar functional groups presented in both
the SCG and crude bio-oil. A broad absorbance was displayed at
around 3400 cm1 for the raw material, which indicated a high
content of carbohydrates and proteins [51]. The crude bio-oil
showed a weaker absorbance at the wavenumber of 3400 cm1,
suggesting that both carbohydrates and proteins were decomposed
in HTL process. Absorption between 2700 cm1 and 3000 cm1 was
ascribed to OeH stretching vibration and the bond of OeH, mainly
from long-chain carboxylic acids in the bio-oil. The absorption
peaks between 1650 and 1750 cm1 were attributed to the C]O
stretching from carboxylic acids and ester groups in the crude biooil.
A weaker absorbance in this wavenumber range was also
observed for the raw material, indicating that more carboxylic acid
groups were formed during HTL process. The bands from
1350 cm1e1470 cm1 were ascribed to CeH bending, which
indicated alkyl groups in the obtained oil. Absorption between
1020 cm1 and 1340 cm1was attributed to CeN bands, most likely
showing the presence of amines groups which might be in nonvolatile
compounds thus were not detected by GCeMS. Meanwhile,
the absorption profiles between 670 cm1 and 870 cm1
implied the presence of phenyl rings and substituted phenyl rings
[27]. The bond at 1050 cm1only appeared in the absorption profile
of SCG, which could be CeO connected with hydroxyl groups and
were dehydrated after liquefaction.