Ultrasound Intensified Biodiesel Production from Mixed Non–Edible Oil Feedstock
4.4 Results and discussion
4.4.1 Characterization of catalyst
model–predicted profile is compared with the experimental data. The objective function (Obj) for minimizing root mean square (RMS) error is expressed as: Objmin
in1eri
,where n – the number of data points of experimental concentrations of four species. The error function (er) is described as:
exp model
2 3 exp 3 model
2 exp model
2 exp model
2 1/ 2i i i i i i i i i
er T T CH OH CH OH F F G G
The other low intensity peak at 2θ = 39o–43o 1 0 0 represents graphitic structure observed in both sulfonated and chloro–sulfonated catalysts. Moreover, the intensities of both peaks were relatively smaller in sulfonated catalyst as compared to chloro–
sulfonated catalyst. This indicated higher activated (amorphous) sulfonated carbon with predominant graphitic structure [11,24,25,35].
XPS analysis: The broad XPS spectrum of sulfonated catalyst and chloro–sulfonated catalyst between the binding energies of 0 to 1200 eV is shown in Fig. 4.2 (A). The XPS spectrum of both catalysts confirmed the presence of oxygen, carbon and sulfur on the surface.
(A)
(B) (C)
Figure 4.2: XPS scan spectrum (A) sulfonated and chloro–sulfonated catalyst; (B) Narrow scan in C 1s region for chloro–sulfonated catalyst and (C) Narrow scan in S 2p region for chloro–sulfonated catalyst
The narrow XPS scans for C 1s region (binding energy 270–300 eV) and S 2p region (binding energy 155–185 eV) for chloro–sulfonated catalyst are also shown in Figs. 4.2 (B) and (C), respectively. The peak corresponding to binding energy 168 eV is characteristic of S (2p1/2) in sulfonated materials and validates the existence of ˉSO3H group on catalyst surface. The two distinguishing peaks identified at binding energy of 283 eV (the large one) and 286.8 eV (the small one) in narrow C 1s scan (shown in Fig.
4.2 (B)), correspond to elemental carbon from support material and to carboxylic acid on catalyst’s surface formed due to carboxylation side reaction, respectively. These results are similar to those reported earlier [2,11,24,41]. Presence of chlorine was not confirmed by the XPS analysis of chloro–sulfonated catalyst, which indicates the absence of chlorine or chlorine is present below detectable limits.
FE–SEM and EDX analysis: FE–SEM micrographs of sulfonated and chloro–
sulfonated catalysts are shown in Fig. 4.3. These micrographs showed the catalysts surface as highly porous and irregular in shape. The chloro–sulfonated catalyst has greater and large number of pores as compared to the sulfonated catalyst. This probably due to the disappearance of chlorine as Cl2 gas during the calcination at 573 K, resulting in larger and bigger porous structure for chloro–sulfonated catalyst.
(A) (B)
Figure 4.3: FE–SEM image of synthesized carbon catalyst (A) sulfuric acid treated
Energy–dispersive X–ray spectroscopy (EDX) for both catalyst was also carried out by FE–SEM to analyse the elemental distribution present at the catalyst surface as shown in Fig. 4.4. The EDX data as depicted in Table 4.3 shows that chloro–sulfonated catalyst has higher elemental sulfur composition than sulfonated catalyst and traces of chlorine. The values of elemental sulfur composition on catalyst surface were slightly higher than the values reported in literature by Galhardo et al. [2], Dehkhoda et al. [24]
and Lou et al. [41] for similar type of catalyst. This may be perhaps due to excess sulfonation of carbon support due to high strength of the acid.
Table 4.3: Elemental analysis of synthesized heterogeneous acid catalyst from rubber de–oiled seed cake
Sample C O S Cl Total acid density (mmol/g)
Sulfonated catalyst 59.0 36.9 4.1 Nil 2.92 Chloro–sulfonated catalyst 58.4 36.1 5.4 0.1 3.76
(A) (B)
Figure 4.4: EDX spectrum of synthesized carbon catalyst (A) sulfuric acid treated and (B) chloro–sulfonic acid treated
Surface area and pore size analysis: N2 adsorption–desorption isotherm obtained for both catalysts as shown in Fig. 4.5, predicted the combination of type I and IV isotherms representing the characteristic of mesoporous and microporous material. The BET surface area of sulfonated and chloro–sulfonated catalyst was found to be 10.208 m2/g and 16.187 m2/g, respectively. The average pore diameter and total pore volume of
sulfonated catalyst was found to be 3.21 nm and 0.09 cc/g, respectively, whereas for chloro–sulfonated catalyst average pore diameter and total pore volume of sulfonated catalyst was 8.16 nm and 0.13 cc/g, respectively. These results of surface area, average pore diameter and pore volume are similar to the results reported by Dehkhoda et al.
[24], but lower as compared with the reported results of Lui et al. [25].
Figure 4.5: Nitrogen adsorption–desorption isotherm of synthesized acid catalyst
Total acidity: The total acidic site concentration was calculated from back titration method as described earlier. The results showed that the sulfonated catalyst has the total acidic site density of 2.92 mmol/g, whereas chloro–sulfonated catalyst have total acidic site density of 3.76 mmol/g. For chloro–sulfonated catalyst, the total acidic site density obtained was slightly higher as compared to sulfonated catalyst, but the values are analogous to those reported by Konwar et al. [11,35] and Luo et al. [41]. This is perhaps due to the existence of two–functional groups in chloro–sulfonic acid resulting in higher acidic strength than sulfuric acid.
The above characterization of both heterogeneous acid catalysts showed excellent surface properties required for transesterification of non–edible oil. Chloro–
sulfonated catalyst showed better surface properties and morphology as compared to sulfonated catalyst. Thus, chloro–sulfonated catalyst was selected for transesterification
process for producing biodiesel from mixed non–edible oil feedstock.