3. RESULTS AND DISCUSSION
Physicochemical Characterization of Silica-Based
Heterogeneous
Catalyst
The physicochemical characterization of the calcined ash (RHA),
activated ash (ARHA),Huskcatacid andHuskcatbase was perfomed using XRD analysis as shown in Fig. 1.
The calcination of rice husk at 800 ºC afforded calcined ash as a white
silica powder (Arzamendi, et al., 2007). All samples showed similar
crystallinity pattern with the decrease in intensity of certain peaks,
which indicate good dispersion of H2SO4and NaOH on silica (Taufiq-Yap, et al., 2011). The calcined ash (Fig.
1a) showed a strong and sharp peak of cristobalite silica
(SiO2) at 2θ=21.68 (Taufiq-Yap, et al., 2011). A series
of small peaks were detected at 2θ=28.11, 31.21 and 35.87 in the
calcined ash which corresponded to traces of metal elements (Kumar et
al., 2013). These peaks were reduced in the activated ash (Fig. 1b)
ascribed the effects of NaOH to the activated ash. A sharp and
well-defined peaks at 2θ=25.05, 29.38, 34.93, 37.21, 48.08, 52.02 and
65.68 were observed in Huskcatbase (Fig. 1c) due to cement effect
of sodium loading on the activated ash during mineralization and
crystallization of larger crystallites (Taufiq-Yap, et al., 2012; Kumar
et al., 2013). Cement effect of sodium and
H2SO4 acted by filling up the
intergranular porosity of the silica and sticking the particles
together, resulting of larger crystallites or crystalline structure of
the catalysts (Zabeti, et al., 2009; Taufiq-Yap, et al., 2011). The XRD
analysis shows a broad diffraction peak in Huskcatacid (Fig. 1d),
which indicated that no substantial difference in the XRD pattern before
and after sulfonation by H2SO4 on the
activated ash. Similar observation has also been reported during
impregnation of H3PO3 and
H2SO4 onto carbon-based materials (Fu,
et al., 2011; Fu, et al., 2012)
Figure 1
SEM analysis was performed on the calcined ash, activated ash,Huskcatacid and Huskcatbase to examine the surface
morphology of the samples before and after treatment. SEM micrograph of
activated ash (Fig. 2b) showed agglomerated particles and increased
pores network and surface area after underwent activation process. SEM
micrograph of Huskcatbase after impregnation with NaOH is shown
in Fig. 2c with some assembled needle-like structures (Fu, et al., 2011;
Arzamendi, et al., 2007). The morphology observed could be due to
repeated washing of the sample which caused exfoliation to the outer
surface and thus, exposing the internal structure. SEM micrograph ofHuskcatacid (Fig. 2d) after sulfonation showed a disintegration
of the surface caused by the partial destruction of the porous structure
during impregnation, which resulted in larger pores (Janaun and Ellis,
2011). Large pore structure has been reported to indirectly improve
catalytic activity (Shu, et al., 2009) during esterification.
Figure 2
The EDX analysis on the elemental composition of the calcined ash,
activated ash, Huskcatacid and Huskcatbase showed the
presence of silica (SiO2) as the main element detected
in all the samples (Table 1). The successful impregnation showed by the
presence of sulfur (3.25%) and sodium (0.40%) inHuskcatacid andHuskcatbase , respectively.
Table 1
BET analysis showed that the surface area and total pore volume of
calcined ash was increased from 1.914 m2/g to 18.947
m2/g after activation process (Table 2). The
activation process has apparently caused the formation and enlargement
of pores, as observed in SEM, which increase the surface area of the
activated ash. The surface area of Huskcatbase (14.493
m2/g) and Huskcatacid (7.362
m2/g) was found to be lower than the activated ash.
The introduction of active species such as alkali metals and sulfonation
onto a support material has reduced the surface area of the catalyst
(Perrichon and Durupty, 1988; Janaun and Ellis, 2011).
Table 2
Esterification of PFAD with
Methanol
Effect of Catalyst
Loading
The nature of PFAD with higher FFA content has undergone a two-step
process which are esterification of PFAD, followed by
transesterification of the oil with methanol (MeOH) (Shu, et al., 2009).
In the initial stage, the esterification of PFAD was performed in 1:5
wt% (PFAD:MeOH) using Huskcatacid (1 wt%) under reflux for 24 h
(Gole and Gogate, 2012). The effect of Huskcatacid loading during
esterification of PFAD is illustrated in Fig. 3. The FTIR spectra showed
two peaks at 1706 cm-1 and 1743 cm-1attributed to -COOH and –COOR, respectively, which indicated an
incomplete esterification of the carboxyl group (Fig. 3b) (Yong-Ming, et
al., 2014). An increased amount ofHuskcatacid to 5 wt%
showed a complete formation of ester by the appearance of a sharp peak
at 1742 cm-1 and desappearnce of peak at 1706
cm-1 (Fig. 3c).
Figure 3
Effect of PFAD to Methanol
A minimum amount of MeOH was investigated for the esterification of PFAD
using 5 wt% Huskcatacid under reflux for 24 h. Incomplete
esterification was observed in 1:0.5 (PFAD:MeOH) by the appearance of
-COOH peak at 1709 cm-1. A
complete formation of ester (Fig.
4b) occurred in 1:1 (PFAD:MeOH) in the presence of 5 wt%Huskcatacid . The influence of PFAD to MeOH ratio is illustrated
in Fig. 4.
Figure 4
Effect of reaction time
Reaction time is crucial and incur the production cost of biodiesel. The
esterification was optimized hourly with constant ratio 1:1 wt%
(PFAD:MeOH) and 5 wt% Huskcatacid (Fig. 5). FTIR spectra showed
a mixture of COOH and COOR (ester) peaks presence after 1-1.5 h (Fig.
5a). Further increased of the reaction time to 2 h (Fig. 5b) afforded
esterified oil at 1741 cm-1 with yield 91.6%. A
reversible reaction is believed to occur during 24 h esterification
(Moser, 2009; Chongkhong, et al., 2007; Kumar, et al., 2013).
Figure 5
The esterified oil was characterized using GCMS and shown in Table 3. No
significance carboxyl group was detected in the esterified oil as
compared to PFAD. The palmitic acid, for instance, was completely
converted into methyl palmitate (Table 4).
The acid value of the esterified oil was 6 mgKOH/g with 3% of FFA. FFA
value in the range of 3% indicates that the sample is suitable to
undergo base catalysed-transesterification reaction (Meher, et al.,
2006).
Transesterification of
PFAD
Effect of catalyst
loading
Huskcatbase was employed in
the transesterification of the esterified oil at various catalyst
loading (0.5 -5%) with constant reaction temperature and oil to
methanol ratio (Table 5). Further increase ofHuskcatbase (5 wt%) was
observed to produce undesirable viscous, jelly-like oil, and turned
cloudy upon addition of water during separation of biodiesel (Fig.6a).
This could be due to saponification phenomenon (Moser, 2009) owing to
the possible sodium leaching from the catalyst during reaction
(Arzamendi, et al., 2007). The optimum amount of Huskcatbase (1
wt%) for 1 h contributed to the formation of biodiesel and glycerol as
by-product (Fig. 6b).
Effect of reaction time
Reaction time is another crucial factor in biodiesel production process.
Different reaction times were monitored for
the transesterification of
esterified oil with methanol
(1:1) and Huskcatbase (1 wt%) as a catalyst (Gole and Gogate,
2012). The conversion of esterified oil to biodiesel was monitored with
the gradual formation of glycerol, which formed after 15 min and
constant at 30-60 min. The
formation of biodiesel was increased from 96.7% (15 min) to 97.5% (30
min) and decreased after 60 min (Fig. 7). Reusability of the catalyst up
to three times afforded biodiesel ranging from 90-97% w/w. The
percentage conversion (%) of biodiesel from esterified oil was
determined based on Equation 4 (Banani, et al., 2015).
Conversion, % =\(\frac{Weight\ of\ biodiesel\ produced,\ \ g}{Weight\ of\ feedstock,\ g}\)x 100% Eq.4
Figure 7
Calorific Value of Biodiesel
The efficiency of the PFAD biodiesel was characterized based on the
calorific values (CV) of the neat biodiesel (B100), 5% biodiesel to
95% commercial diesel (B5), commercial B5 (CB5) and commercial diesel
fuel (CD) using Oxygen Bomb Calorimeter (Parr 6400) (Sivaramakrishnan
and Ravikumar, 2012; Lang, et al., 2001). The CV of B100 was 39.35 MJ/kg
while CV of B5 was increased to
45.07 MJ/kg. Based on the CV
obtained for CB5 (45.53 MJ/kg) and CD (45.67 MJ/kg), it can be deduced
that B5 showed a comparable CV and efficiency which is acceptable as a
diesel substitution.
Table 6
GCMS analysis
The composition of the biodiesel produced via two step reactions
(esterification and transesterification) was analyzed using GCMS.
Table 7 shows higher percentage of
methyl palmitate (34.43%) and methyl oleate (57.86%) from the PFAD
biodiesel. This phenomenon is not surprising as PFAD has higher amount
of palmitic acid (73.99%) and oleic acid content (13.25%) in as
compared to other types of fatty acids (Sugiarto, et al., 2015). No
significant carboxyl group was detected in PFAD biodiesel. In other
words, initial esterification of PFAD improved the ability to form
complete transesterification of PFAD for a high biodiesel yield (Ngaini
et al, 2026).
Table 7
Combustion capability
test
The combustion capability test of PFAD biodiesel (B100) was demonstrated
on the alternative diesel engine (Megatech- Mark III) (Fig. 8). Ethanol
was initially introduced into the combustion chamber to achieve
400-500°C before B100 was introduced. A bright orange flame with less
smoke was released upon combustion of B100 in the chamber in 10-15 mins
as compared to CD, which normally emitted black smoke due to incomplete
combustion (Akihama, et al., 2002). A slight, odourless smoke was
produced during combustion of B100 indicated a sufficient and complete
combustion of the engine.
Figure 8
The performance of fuel using
diesel combustion engine was demonstrated based on torque, ɽ, load and
revolution per minute (rpm) (Fig. 9), where torque was proportionally
increased with the B100 loading. This observation indicated that the
engine was able to operate up to the maximum load of 100 lbs using B100
PFAD. The rpm was decreased when the load of B100 increased. This is
because high force (torque) is needed to endure the load and cause the
rpm to decrease (Ngaini et al, 2016).
Figure 9