Fig. 1 to Fig. 4 show the TGA and DTG curves for both EFB and OPT, pyrolyzed at heating rate of
50o
C/min and 80o
C/min. TGA curve displays weight loss as a function of temperature in a controlled
atmosphere, whereby DTG curve emphasizes the zone of reaction where various reaction steps are taking
place over the entire temperature range. The weight loss started at 150-500°C and terminated around
650°C at all operating conditions for both OPT and EFB samples. Fig. 1 shows a TGA-DTG curves of
OPT and EFB at a heating rate of 50 °C/min for particle size of < 0.25 mm (dp1). In general, the pyrolysis
of any biomass can be divided into three phases which are drying and evaporation of light components
(phase I), devolatilization of hemicellulose and cellulose (phase II) and decomposition of lignin (phase
III). Phase I occurs at temperature below 150°C, phase II starts from 150o
C to 450°C and finally phase III
is attained at temperature above 450°C.
Fig. 1 shows that for particle size dp1 heated at 50°C/min, the amount of char left at the end of pyrolysis
process is 22.47% for EFB and 24.49% for OPT. Larger particle size decreases the amount of biomass
conversion whereby the final residue is 32.28 % and 25.35% for EFB and OPT respectively as shown in
Fig. 3. It is well agreed in the literature that larger particle sizes yields more residue because of poor heat
transfer to the inner biomass surfaces which leads to low average particles temperature [1,2]. Previous
study conducted by Sukiran et al. [3] shows that optimum bio-oil yield was obtained for particle size of
0.091-0.106 mm, and Ruengvilairat et al. [4] concluded that optimum EFB particle size is > 1.180 mm.
Larger particle size is favourable for char and gas production.
Higher heating rate is expected to increase the amount of volatiles in pyrolysis process. In this study
however, the effect is adverse. At heating rate of 50°C and particle size of dp1, the volatiles yield for OPT
is 73.41%, while at 80°C/min the amount of volatiles was reduced by 2.57%. Same result is reported for
EFB which recorded 11.20% decrement. At dp2 the results is not significant for OPT but EFB recorded a
2.42% increment when pyrolyzed at higher heating rate. While the effect of heating rate towards volatile
content production is inconsistent, it does increases the peak degradation rate for each tested samples. For
dp1, the degradation rate increases by 1.42 mg/s at heating rate 50°C/min, while at heating rate 80°C/min,
the increment is 1.56 mg/s. Larger particle size (dp2) shows greater changes with 3.13 mg/s and 4.93 mg/s
respectively. It can be concluded that higher heating rate helps in degradation speed but insignificantly
affects the amount of volatiles produces.
A study has shown that biomass with more cellulose and hemicellulose contents (or holocellulose
content) will produces more volatiles compared to woody biomasses [5]. OPT and EFB constitutes of
76.30% and 65.5% of holecellulose accordingly [6]. Under different tested parameters, OPT produces
5.46-8.93% more volatiles, except during dp1 and heating rate=50°C/min where EFB yields 2.02% more
volatiles. DTG graphs for EFB display two distinctive peaks, in which the first peak is 0.22-0.62 mg/s
lower than the next. The first peak corresponds to the degradation of lower molecular weights
components (hemicellulose) from 180o
C to 310°C and second peaks indicates cellulose degradation
which occurs between 320o
C and 410°C. OPT on the other hand show a ‘shoulder’ pattern, which is
caused by the amount of cellulose and hemicellulose in each type of biomass. It is noted that when the
temperature reaches 650°C, the degradation rates are no longer significant as most volatiles had already
been pyrolysed