M.L. Savaliya, B.Z. Dholakiya / Applied Catalysis A: General 494 (2015) 12–21
15
Table 2
conversion. The percentage conversion of oil to biodiesel was
affected drastically by changing the oil: methanol molar ratio
under the identical reaction conditions. The highest biodiesel
yield obtained is 98.00% at 1:10 oil to methanol molar ratio.
Whereas, the lowest biodiesel yield obtained is 71.22% at 1:40 oil
to methanol molar ratio. It can be clearly seen from Table 2 that, on
increasing in oil to methanol molar ratio, decreasing in biodiesel
% yield was observed. This may be attributed to polar nature of
catalyst and methanol. In case of 1:10 oil to methanol molar ratio,
catalyst does not strongly attracted towards methanol. While, as
oil to methanol molar ratio is increase, the catalyst directly comes
in strong attraction with methanol. So, on increasing the methanol
quantity, the attraction of catalyst towards methanol becomes
more and stronger due to polar nature of one another. But the fact
is catalyst should be remain in the oil phase during reaction rather
than methanol phase, as the first step of transesterification reac-
tion suggests that protonation of triglycerides proceeds first and
foremost. However, as the methanol quantity increases, the attrac-
tions of catalyst in methanol phase are much more than attraction
towards oil phase. Whereas, in case of 1:05 oil to methanol molar
ratio shows lower yield compare to 1:10 oil to methanol molar
ratio. This may be due to reversible nature of transesterification
reaction; oil to methanol molar ratio below 1:10 can directly
affect the biodiesel yield by facilitating reversible reaction and
suppressing the forward reaction. Another reason for decreasing in
biodiesel % yield is may be due to increasing in quantity of reaction
mass. As all reactions were performed by keeping quantity of oil,
catalyst, reaction temperature and reaction time uniform for all
four reactions. But only oil to methanol molar ratios was varied.
Therefore, on increasing oil to methanol molar ratio, reaction
mass also goes on increases. But the catalyst quantity was uniform
for all for reactions. So, the catalyst activity may be affected by
varying quantity of reaction mass and it directly affects the % yield
of biodiesel. The distribution of catalyst was much more in case of
1:40 oil to methanol molar ratio compare to 1:10 oil to methanol
molar ratio. Therefore, at higher oil to methanol molar ratio, the
interaction catalyst with oil is comparatively lower than the lower
oil to methanol molar ratio and hence lowers the yield of biodiesel.
Results of percentage conversion of TGs of WCO to corresponding DG, MG and FAME
(130 ◦C Reaction temperature, 5% (w/w) SMTSA catalyst and 10 hrs Reaction time).
Entry
Oil:methanol
molar ratio
% Conversions
% TG
% DG
% MG
% Biodiesel
1
2
3
4
5
1:05
1:10
1:20
1:30
1:40
0.12
0.11
0.70
3.63
10.65
1.66
1.60
3.10
6.22
17.67
0.31
0.29
0.18
0.60
0.46
97.91
98.00
96.02
89.55
71.22
Where, TG = Triglyceride, DG = Diglyceride, MG = Monoglyceride.
Where R1, R2 and R3 are carbon chain of fatty acid.
identified on comparison with the peaks obtained in the GC chro-
matogram for the above standard used) and their representative
chromatogram is demonstrated in Fig. S2.
2.4. FAME content and yield measurement
The biodiesel samples were stored under nitrogen at 4 ◦C in
internal standard for quantitative determination. Once the FAMEs
of the biodiesel samples were identified, the peak areas were
employed to determine the FAME content of each sample by fol-
lowing equation [34].
ꢀ
A − AIS
CIS × VIS
C =
×
× 100
(1)
AIS
m
ꢀ
Where,
A is the total peaks area, AIS is the internal standard
(methyl heptadecanoate) peak area, CIS is the concentration of the
internal standard solution (mg/mL), VIS is the volume of the inter-
nal standard solution used (mL) and m is the mass of the biodiesel
sample (mg).
MBiodiesel
Yield(%) =
× 100
(2)
Moil
Where MBiodiesel is the mass of purified methyl esters obtained,
Moil the mass of oil employed and C is the fatty acid methyl ester
content determined as described in above equation.
3.2. SMTSA catalyzed biodiesel derived raw glycerol to
triglyceride of lauric acid
3. Results and discussion
Biodiesel derived raw glycerol represent a copious and inexpen-
sive source which can be used as raw material for variety of value
added products such as 1,3-propanediol, poly hydroxyalkanoate,
hydrogen, epichlorohydrin and also lactic acid [36,37]. Glycerol
obtained as a side stream at the end of the transesterification
reaction along with three biodiesel molecules. Furthermore, the
world is facing the problem of disposal of glycerol obtained from
biodiesel synthesis as a byproduct and simultaneously they are
facing the problem of the abundance of feedstocks for biodiesel
synthesis. The purification of crude glycerin from the biodiesel
plants is a major issue. Also, the disposal of glycerol by the emerg-
ing biodiesel industry is therefore a new engineering challenge. So,
in this present study, a little effort was made to utilize prepared
solid acid catalyst (SMTSA) for the synthesis of triglycerides of
lauric acid under reaction conditions such as 100 ◦C reaction tem-
perature, 600 rpm stirring speed and 0.8 g catalyst via esterification
of lauric acid and biodiesel derived raw glycerol. Methanol free
glycerol is produced by distillation of crude glycerol obtained at
the end of transesterification reaction. The best catalyst amount
was chosen based on the yield of maximum triglycerides with
minimum unreacted glycerol and lauric acid content in the final
product. During the esterification reaction, it has been found that
reaction is easy, clean and needs no special work-up procedure.
Finally, the reaction mixture was cooled to ambient conditions;
3.1. SMTSA catalyzed transesterification of waste cooking oil to
biodiesel
The acid catalyzed transesterification process does not having
the same efficiency as the base catalyzed process. The fact that
the acid catalyzed reaction is about 4000 times lower than the
alkali catalyzed reaction has been one of the main reason [35].
However, acid catalyzed transesterification imparts an important
advantage with respect to base catalyzed ones. The performance of
acid catalyst is not strongly affected by the presence of FFAs in the
feedstock. In fact, acid catalyst can simultaneously catalyze both
esterification and transesterification of FFA and TGs respectively to
biodiesel. Accordingly, instead of starting with a TG molecule, as in
the transesterification reaction, the starting molecule is FFA. Thus, a
great advantage with acid catalyst is that they can directly produce
FFA concentrations and thus, lowering the cost of production. To
achieve this WCO was used as a feedstock and the maximum yield of
biodiesel at optimum molar ratio of oil:methanol was studied. The
results of percentage conversion of FFA and TGs to corresponding
DG, MG and biodiesel are summarized in Table 2.
In present study best results were achieved with the 1:10
oil: methanol molar ratio at fixed 10 hrs reaction time for 98%