decreasing in O/C and H/C in a classical coalification fashion where
the bituminous coal has an O/C of about 0.10 and H/C of about 0.80.
The bio-oils show molar ratios much similar to those of starting
biomass than coal or even lignite.
All of the bio-cokes from the RSM are in the same area as the
bituminous coal but with somewhat lower O/C ratios.
On the other hand, the bio-cokes produced from WSG have H/C
ratios around 1.70 that is more related to heavy crude oil than coal
(Fig. 4). This indicates that bio-cokes from the RSM may be having
a high content of smaller aromatics compounds while the biocokes
from WSG probably are cross-linked long-chain hydrocarbons.
Fig. 4 suggests that the RSM cokes lost both oxygen and
hydrogen rich compounds while becoming increasingly aromatic.
On the contrary, the WSG coke lost almost the same amount of
oxygen but was able to retain most of its hydrogen probably due
to decarboxylation [36–38].
The nature of the RSM bio-coke was further studied by FTIR
analysis in Fig. 5 and compared with it corresponding py-char.
The bands are similar to that reported for other solid fuels [35].
For the bio-coke there is a reduction in the intensity of the
3424 cm1 OH band compared to the py-char indicating the decrease
in oxygen content (Table 1). However, there is a strong increase
in the CH band between 3000 and 2860 cm1 suggesting a
stronger hydrocarbon structure of the bio-coke compared to the
py-char. This is further confirmed by an increase in the aromatic
ring band at 1590 cm1 for the py-char and 1603 cm1 for biocoke.
It is interesting to note that the carbonyl bands at 1660
and 1725 cm1 were not present in both samples. The FTIR spectra
confirm the removal of oxygen from the bio-coke and its conversion
into a hydrocarbon like structure.
The morphologies of the WSG bio-coke only and WSG with 5%
additive were analysed using a scanning electron microscopy