Clean and Green Procedure for the Synthesis of Biodiesel from the Esterification of Free Fatty Acids and Alcohol Catalyzed by 6-O-(sulfobutyl)-Β-cyclodextrin

Article abstract of DOI:10.1134/S1070427218070091

The catalyst of 6-O-(sulfobutyl)-β-cyclodextrin (SB-CD) is renewable, non-toxic, environmentally benign and biocompatible, which could be used as efficient and recyclable catalyst for the synthesis of biodiesel from free long-chain fatty acids with low-chain alcohols as substrates. The reaction was accomplished at 60°C for 1.5 h, while the products were separated from the catalyst system by liquid/liquid at room temperature with good conversion of 91–98%. The catalyst can be reused for 10 times. The novel and clean procedure offers advantages including short reaction time, good conversion, operational simplicity, and environmentally benign characteristics.

Full text of DOI:10.1134/S1070427218070091

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2018, Vol. 91, No. 7, pp. 1123−1128. © Pleiades Publishing, Ltd., 2018.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Clean and Green Procedure for the Synthesis of Biodiesel
from the Esterification of Free Fatty Acids and Alcohol Catalyzed
by 6-O-(sulfobutyl)-β-cyclodextrin1
Guangqing Zhanga, Leqin Hea, Mingxia Yuana, Hui Li, Tao Changa,*, and Shenjun Qina
a Key Laboratory for Resource Exploration Research of Hebei Province, Hebei University of Engineering,
Handan 056038, China
*e-mail: changtao@hebeu.edu.cn
Received January 2, 2017
Abstract—The catalyst of 6-O-(sulfobutyl)-β-cyclodextrin (SB-CD) is renewable, non-toxic, environmentally
benign and biocompatible, which could be used as efficient and recyclable catalyst for the synthesis of biodiesel
from free long-chain fatty acids with low-chain alcohols as substrates. The reaction was accomplished at 60°C for
1.5 h, while the products were separated from the catalyst system by liquid/liquid at room temperature with good
conversion of 91–98%. The catalyst can be reused for 10 times. The novel and clean procedure offers advantages
including short reaction time, good conversion, operational simplicity, and environmentally benign characteristics.
Keywords: Cyclodextrin; biodiesel; esterification; free fatty acid; heterogeneous separation
DOI: 10.1134/S1070427218070091
INTRODUCTION
as raw materials, which were massive in China and other
developing countries [8–10]. However, the low-cost
feedstocks also contain significant amounts of free fatty
acids, which pose significant processing problems in the
standard biodiesel manufacturing. FFAs are saponifed by
alkali catalysts, leading to a depletion of the catalysts as
well as to increased purification costs [11]. Generally, the
problem can be circumvented by an esterification pretreat-
ment of FFAs to alkyl esters in the presence of an acid
catalyst. However, the catalyst of H2SO4 involves high
consumption of energy, and the separation of the catalysts
from the homogenous reaction mixtures is costly and
produces chemical wastes [12]. Solid acidic and basic
catalysts also have such disadvantages as low activity,
easy deactivation, and adsorption of products, which result
in their limited application [13–20]. Functional acidic ionic
liquids (FILs) are designed to replace traditional mineral
liquid acids and used for the synthesis of biodiesel [21–32].
Accordingly, the aim of numerous recent research efforts is
to develop novel catalysts. Certainly, these catalysts must
be active, selective, reusable, stable and reproducible via
simple viable procedures.
For several decades, energy crisis have being con-
fronting the world due to the excessive utilization of
the world’s depleting oil reserves by the ever-increasing
human population.Apart from the ever-increasing prices
of petroleum fuels, more worrying issues associated with
utilizing these fuels include deteriorating health standards
and environmental degradations. These concerns have led
to the search for sustainable biofuel alternatives [1].Are-
newable and sustainable fuel currently receiving renewed
interests and intensive experimentations since the work
of Rudolf Diesel is biodiesel [2, 3]. Prominent amongst
them is the simultaneous esterification and transesteri-
fication of feedstocks especially those containing high
amounts of free fatty acids (FFAs) [4–6]. The product
is fatty acid alkyl ester (FAME), the biodiesel fuel, is
a perfect biodegradable and renewable clean fuel [7].
In order to reduce the production costs and to facilitate
competition with petroleum diesel, low-cost feedstocks,
such as waste fried oils and non-edible oils, can be used
1 The text was submitted by the authors in English.
1123

1124
GUANGQING ZHANG et al.
Scheme 1. General structure of SB-CD.
β-Cyclodextrin (β-CD) is type of cyclic oligosaccha-
was characterized by FTIR spectrum and NMR spectrum.
SB-CD: 1H NMR (400 M, D2O) (one glucose unit): δ =
1.53 (d, 4H), 2.71 (s, 2H), 3.10–3.62 (m, 8H), 4.91–5.25
(m, 1H); 13C NMR (100 M, D2O): 20.90, 28.25, 36.58,
50.77, 60.49, 72.83, 81.51, 100.88; FTIR (KBr): 3421,
1159, 1043, 607, 533.
rides consisting of seven glucose units with lipophilic
central cavities and a hydrophilic outer surface, which
bind substrates and catalyze reactions by supramolecular
catalysis involving reversible formation of host-guest
complexes by noncovalent bonding as seen in enzymes. In
addition, there have been many reports about cyclodextrin
as co-catalyst [33]. For instances, Rao et al. have used
β-CD as co-catalyst for the addition reactions of olefins,
ring-opening reaction, and oxidation reactions [34–35].
Cyclodextrins derivatives have been playing important
roles in the artificial enzymes [36]. Thus, β-CD deriva-
tives are attractive catalysts and they are highly desirable
on the way to improve the catalytic activity.
General procedure for the synthesis of biodiesel.
To a flask was added different volume of SB–CD
solution, the solvent was evaporated by evaporator
and dried under vacuum at 40°C for 24 h, methanol and
FFAs were added into the flask. The esterification was
then typically carried out for a length of time at a specific
temperature with vigorous stirring.After the reaction, the
unreacted alcohol was recovered by distillation. After
the residue was cooled and kept for a while, the reaction
mixture became biphasic. The upper phase containing the
desired biodiesel could be collected by decantation; the
bottom phase, a mixture of catalyst and water generated
from the reaction, could be reused after removal of water
(Fig. 1). Conversion data were calculated based on FFAs
through KOH titration [24].
As discussed above, many catalysts have been
developed for the esterification reaction. However, it is
still very interesting to develop efficient catalytic systems
for the reaction using cheap and non-toxic reagents. In
the present work, we designed and synthesized sulfonic
acid functionalized β-CD as novel catalysts in an efficient
and convenient procedure for biodiesel (Scheme 1). The
esterification reaction that was studied can be summarized
as follows:
RESULTS AND DISCUSSION
SB-CD
Synthesis and characterization of SB-CD. The
6-O-(sulfobutyl)-β-cyclodextrin sodium salt can be
changed into SB-CD by the resin of Amberlite 732
resin through ion-exchange (Scheme 1).
R–COOH + R'OH
R COOR' + H2O,
where R and R' are the carbon chains. R' represents a
primary alcohol.
The structure of SB-CD was examined by NMR
spectrum and FTIR spectrum, which are shown in
Figs. S1–S3 in supporting information. The NMR
spectrums indicate that SB-CD possesses glucose
units. The vibrational bands at 1159 (O=S=O stretching
in SO3H), 1043 (SO3-stretching) and 607 (C–SO3H
stretching) in the FTIR spectrum indicate that the catalyst
possesses –SO3H groups.
EXPERIMENTAL
Preparation of SB-CD. To a solution of 6-O-(sulfo-
butyl)-β-cyclodextrin sodium salt (2.4 g) in 30 mL of
methanol was added Amberlite 732 resin (8 g). The
mixture was then stirred for 2 h to give the solution of
catalyst of SB-CD. The concentration of the SB-CD
solution was titrated by standard KOH solution. The
solvent was evaporated by evaporator and dried under
vacuum at 40°C for 24 h to give a white powder, which
Effect of the amount of methanol on esterification.
Generally, an excess of reactant methanol is necessary
for the esterification of FFA because it can increase the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 7 2018

CLEAN AND GREEN PROCEDURE FOR THE SYNTHESIS OF BIODIESEL
1125
rate of methanolysis. The mole ratio of methanol to oleic
acid varied from 2 : 1 to 16 : 1, and the conversions
obtained are shown in Table 1. The more the methanol
was added, the higher the conversion of oleic acid to
methyl oleate was obtained in the same time (entry 1–6).
The highest conversion of oleic acid achieved was 94.5%
with methanol to oleic acid mole rate of 10 : 1 in 1.5 h.
Further increase of methanol did not result in an increase
in conversion. Unfortunately, the unmodified catalyst can
not be realized the reaction (entry 7).
Fig. 1. Esterification reaction procedure.
Effect of the catalyst amount on esterification. The
catalyst amount was also of great importance for the
esterification. Figure 2 shows the effect of the catalyst
amount with increasing of the molar ratio of catalyst
SB–CD. When the loading of the catalyst increased from
0.6 to 1.7 mol %, the conversion of product increased
from 85.2 to 94.8%. At a catalyst loading of 1.3 mol %,
the best result can be obtained. Further increasing the
amount of catalyst, the conversion increase slightly,
therefore 1.3 mol % was selected as the best loading of
catalyst amount.
Fig. 2. Effect of the catalyst amount on esterification. Reaction
Effect of reaction temperature. The effect of reaction
temperature on esterification is shown in Fig. 3. When the
reaction temperature was 40°C, 90.4% of the oleic acid
was converted into methyl oleate in 1.5 h. The conversion
of oleic acid was found to increase with temperature
from 40 to 60°C. Further increase temperature had no
significant effect on conversion, at which the reaction
system exhibited a slightly yellow color and a state of
reflux. Considering conversion and cost, the optimum
reaction temperature is 60°C.
conditions: 79 mmol methanol, 7.9 mmol oleic acid, 60°C, 1.5 h.
after removal of water under vacuum.As shown in Fig. 5,
SB–CD could be reused at least ten times. The catalyst
structure did not change after the reactions, according
to the NMR and FTIR spectrum (Figs. S4 and Fig S5
in supporting information). Compared with traditional
catalysts, efficient recycling performance is an attractive
property of the proposed catalysts from the environmental
protection and economic perspectives.
Effect of reaction time on esterification. The effect
of reaction time on oleic acid conversion is shown in
Fig. 4. As shown in Fig. 4, SB-CD was very efficient for
the reaction of methanolysis of oleic acid, over 78.9%
of oleic acid was converted into methyl oleate within
0.5 h. The rate of methanolysis became slow, extending
from 0.5 h to 1.5 h, and the conversion of oleic acid
was 94.5%. The reaction of methanolysis approached
equilibrium after 1.5 h, and the conversion of oleic acid
did not increase when the reaction was prolonged. The
trend was consistent with the previous report [21]. The
optimum reaction time is 1.5 h.
Table 1. Effect of the amount of methanol on esterificationa
Conversion,
Entry
Ratio of methanol to oleic acid
%
1
2
3
4
5
6
7b
1 : 2
38.3
59.1
70.9
82
1 : 4
1 : 6
1 : 8
1 : 10
1 : 16
1 : 10
94.5
95.1
NR
Reusability of SB-CD for esterification. The recy-
cling performance of SB-CD was investigated using the
above model reaction. After the reaction, the products
were isolated from the catalytic system by centrifugation
and decantation, the catalyst was reused in the next time
a Reaction conditions: 7.9 mmol oleic acid, 0.11mmol SB-CD, 60°C,
1.5 h.
b Unmodified catalyst (I), no reaction.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 7 2018

1126
GUANGQING ZHANG et al.
Fig. 3. Effect of reaction temperature on esterification. Reaction
conditions: 79 mmol methanol, 7.9 mmol oleic acid, 0.11 mmol
SB-CD, 1.5 h.
Fig. 5. Reusability of SB-CD for esterification with methanol.
Reaction conditions: 79 mmol methanol,7.9 mmol oleic acid,
0.11 mmol SB-CD, 60°C, 1.5 h.
acid and palmitic acid, which are key components in
waste oils for biodiesel production, as well as alcohols,
were tested as the substrates. The results are listed in
Table 2. Excellent conversion rates were obtained in all
cases (entry 1–6). Notably, the length of the alkyl chains
of alcohols had a significant effect on the conversion of
FFAs (entry 1–3). Our investigation showed that SB-
CD could be a good candidate for biodiesel production
from non-edible oils.
CONCLUSIONS
Fig. 4. Effect of reaction time on oleic acid conversion. Reaction
conditions: 79 mmol methanol, 7.9 mmol oleic acid, 0.11 mmol
SB-CD, 60°C.
In conclusion, the catalyst of SB-CD is renewable,
non-toxic, environmentally benign and biocompatible,
which was found to be novel catalyst for the synthesis of
biodiesel from various FFAs and alcohols with satisfactory
conversion of 91–98% under optimal reaction conditions.
The catalyst has the advantages of high activity as well as
practical convenience in the product separation from the
catalytic system. The SB-CD can be reused for 10 times,
which renders the method as a potential application in the
production of biodiesel.
Catalytic performance of SB-CD for the esteri-
fication of other FFAs and short-chain alcohols. To
investigate the scope of SB-CD in terms of the prepa-
ration of FAME related to biodiesel production, stearic
Table 2. Results of esterification for different FFAs and
alcoholsa
Entry
Fatty acids
Oleic acid
Oleic acid
Oleic acid
Lauric acid
Stearic acid
Alcohol
Methanol
Ethanol
Conversion, %b
ACKNOWLEDGMENTS
1
2
3
4
5
6
94.5
93.8
90.7
97.0
92.4
98.0
We acknowledge financial support by the National
Natural Science Foundation of China (no. 21403051), the
Science Foundation of Hebei province (no. B2016402030,
D2014402046), and the Science and Technology
Foundation of Universities of Hebei Province
(no. ZD2015113).
Propanol
Methanol
Methanol
Palmitic acid Methanol
a Reaction conditions: 79 mmol alcohols. 7.9 mmol FFAs, 0.11 mmol
SB-CD, 60°C, 1.5 h.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 7 2018

CLEAN AND GREEN PROCEDURE FOR THE SYNTHESIS OF BIODIESEL
1127
25. Guo, F., Fang, Z., Tian, X.F., Long, Y.D., and Jiang, L.Q.,
REFERENCES
Bioresour. Technol., 2011, vol. 102, p. 6469.
1. Knothe, G., Prog. Energy Combust. Sci., 2010, vol. 36,
26. Zhao, Y.W., Long, J.X., Deng, F.G., Liu, X.F., Li, Z.,
Xia, C.G., and Peng, J.J., Catal. Commun., 2009, vol. 10,
p. 732.
p. 364.
2. Zabeti, M., Dual, W.M.A.W., and Aroua, M.K., Fuel
Process. Technol., 2009, vol. 90, p. 770.
27. Elsheikh, Y.A., Man, Z., Bustam, M.A., Yusup, S., and
Wilfred, C.D., Energy Convers. Manage., 2011, vol. 52,
p. 804.
3. Karatepe, Y., Nese, S.V., Kecebas, A., and Yumurtaci, M.,
Renewable Energy, 2012, vol. 44, p. 17.
4. Xua, L., Xia, Y., Yua, X., and Guomaynurkader, Y., Catal.
Commun., 2008, vol. 9, p. 1607.
28. Liang, X.Z. and Yang, J.G., Green Chem., 2010, vol. 12,
p. 201.
5. Lopez, D.E., Goodwin, J.G., Bruce, D.A., and Lotero, E.,
29. Cui, X., Zhang, S., Shi, F., Zhang, Q., Ma, X., Lu, L., and
Appl. Catal. A: Gen., 2005, vol. 295, p. 97.
Deng, Y.Q., ChemSusChem, 2010, vol. 3, p. 1043.
6. Park, Y.M., Lee, D.W., Kim, D.K., Lee, J.S., and Lee, K.Y.,
30. Tong, X. and Li, Y., ChemSusChem, 2010, vol. 3, p. 350.
Catal. Today, 2008, vol. 131, p. 238.
31. Chippe, C., Rajamani, S., Andrea, F.D., Green Chem.,
7. Helwani, Z., Othman, M.R., Aziz, N., Fernande, W.J.N.,
2013, vol. 15, p. 137.
and Kim, J., Fuel Process. Technol., 2009, vol. 90, p. 1502.
32. Hayyan, A., Hashim, M.A., Hayyan, M., Mjialli, F.,
Alnashef, I.M., J. Clean. Prod., 2014, vol. 65, p. 246.
8. Moser, B.R., Fuel, 2012, vol. 92, p. 231.
33. Sun, T., Hao,A.Y., and Shen, J., Chin. J. Org. Chem., 2009,
9. Bankovi-Ili, I.B., Stamenkovi, O.S., and Veljkovi, V.B.,
vol. 29, p. 681.
Renew. Sus. Energy Rev., 2012, vol. 16, p. 3621.
34. Krishnaveni, N.S., Surendra, K., and Rao, K.R., Adv. Synth.
Catal., 2006, vol. 348, p. 696.
10. Wang, Y., Ou, S., Liu, P., Xue, F., and Tang, S., J. Mol.
Catal. A: Chem., 2006, vol. 252, p. 107.
35. Surendra, K., Krishnaveni, N.S., Sridhar, R., Rao, and K.R.,
11. Marchetti, J.M., Miguel, V.U., and Errazu,A.F., Fuel, 2007,
J. Org. Chem., 2006, vol. 71, p. 5819.
vol. 86, p. 906.
36. Hu, S., Li, L., Xiang, J., Pan, J., Luo, S.Z., and Cheng, J.P.,
12. Toda, M., Takagaki, A., Okamura, M., Kondo, J.N.,
Domen, K., Hayashi, S., and Hara, M., Nature, 2005, vol.
438, p. 178.
J. Am. Soc. Chem., 2010, vol. 132, p. 7216.
APPENDIX
13. Su, F. and Guo, Y.H., Green Chem., 2014, vol. 16, p. 2934.
14. Shuit, S.H., Yee, K.F., Lee, K.T., Subhash, B., and
Tan, S.H., RSC Adv., 2013, vol. 3, p. 9070.
15. Ozbay, N., Oktar, N., and Tapan, N.A., Fuel, 2008, vol. 87,
p. 1789.
16. Sani, Y.M., Daud, W.M.A.W., and Aziz, A.R.A., Appl.
Catal. A: Gen., 2014, vol. 470, p. 140.
17. Singh, S. and Patel,A., J. Clean. Prod., 2014, vol. 72, p. 46.
18. Tang, Y., Xu, J.F., Zhang, J., and Lu, Y., Clean. Prod.,
2013, vol. 42, p. 198.
19. Farooq, M., Ramli, A., and Subbarao, D., J. Clean. Prod.,
2014, vol. 59, p. 131
20. Nair, P., Singh, B., Upadhyay, S.N., and Sharma, Y.C.,
J. Clean. Prod., 2014, vols. 29–30, p. 82.
21. Zhang, L., Xian, M., He, Y.C., Li, L.Z., Yang, J.M., Yu, S.T.,
and Xu, X., Bioresour. Technol., 2009, vol. 100, p. 4368.
22. Ghiaci, M., Aghabarari, B., Habibollahi, S., and Gil, A.,
Bioresour. Technol., 2011, vol. 102, p. 200.
23. Fang, D., Yang, J.M., and Jiao, C.M., ACS Catal., 2011,
5.0
0
vol. 1, p. 42.
ppm
24. He, L.Q., Qin, S.J., Chang, T., Sun, Y.Z., and Gao, X.R.,
Fig. S1. The 1H NMR spectrum of SB-CD.
Catal. Sci. Technol., 2013, vol. 3, p. 1102.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 7 2018

1128
GUANGQING ZHANG et al.
10.0
5.0
ppm
0
150
100
50
0
ppm
Fig. S2. The 13C NMR spectrum of SB-CD.
Fig. S4. The 1H NMR spectrum of recycled SB-CD.
60
50
40
30
20
10
0
1 Fresh catalyst
2 Recycled catalyst
2
1
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber, cm–1
Fig. S5. The IR spectrum of fresh catalyst and recycled catalyst.
Fig. S3. The IR spectrum of SB-CD.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 7 2018