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