(SEM) and are presented in Fig. 6. The structure appears very irregular
and the material is fragmented in smaller particles due to
breakage of originally big particles during the recovery process
from the reactor. Although the bio-coke particles kept an irregular
shape they appear to have a relatively dense structure similar to
that of petroleum coke from vis-breaking or delayed coking where
quick volatilization of volatile compounds leaves a skeleton of
fixed carbon. This indicates that low-density biomass can be transformed
into high density bio-coke that can logistically be treated
like coal.
3.4. TGA and DTG analysis
Fig. 7 shows the derivative thermo-gravimetric (DTG) curves of
different bio-cokes from WSG and RSM carried out under nitrogen
from 105 to 800 C. The volatilization of the RSM bio-coke started
at 130 C and finished at 545 C and had one main peak at 287 C
and a second main peak at 487 C. The rate of volatilization was almost
the same for both the peaks. The WSG bio-coke with no water
added also had two peaks at 287 and 497 C where the second peak
was more dominant. For the WSG bio-coke with 5 wt.% water addition
the first peak has disappeared and had only one peak at
527 C. This indicates that the RSM bio-coke may have had a larger
proportion of small aromatic moieties, such as phenols, that were
volatilised at lower temperatures. In contrast, the WSG showed
higher reactivity at higher temperature possibly due to a more
cross-linked nature, where the addition of water appears to have
targeted the low molecular species during reaction. The release
profiles of volatiles for the bio-cokes that spread