Novel H3PW12O40: Catalysed esterification reactions of fatty acids at room temperature for biodiesel production

Article abstract of DOI:10.1007/s10562-010-0294-3

The catalytic activity of Bronsted acids on fatty acid (FA) esterification at room temperature has been investigated. Noticeably, the H ₃PW₁₂O₄₀ heteropolyacid (HPW) showed a very high activity than other catalysts herein evaluated, i.e. p-toluene sulfonic acid and sulfuric acid. High yields in ethyl esters (ca. 90%) were reached after a 4 h reaction at 25 °C on a HPW catalysed reactions. Despite the fact that HPW catalyst was used in a homogeneous phase, it could be efficiently recovered and reused through out a simple recycling protocol, without any activity loss. The effects of alcohol and the FA nature on yield reaction were also investigated.

Full text of DOI:10.1007/s10562-010-0294-3

Catal Lett (2010) 135:207–211
DOI 10.1007/s10562-010-0294-3
Novel H3PW12O40: Catalysed Esterification Reactions of Fatty
Acids at Room Temperature for Biodiesel Production
•
Vinıcius Wilker de Godoi Silva Letıcia Oliveira Laier
•
´
Marcio Jose da Silva
´
´
´
´
Received: 9 November 2009 / Accepted: 29 January 2010 / Published online: 12 February 2010
Ó Springer Science+Business Media, LLC 2010
Abstract The catalytic activity of Brønsted acids on fatty
acid (FA) esterification at room temperature has been
investigated. Noticeably, the H3PW12O40 heteropolyacid
(HPW) showed a very high activity than other catalysts
herein evaluated, i.e. p-toluene sulfonic acid and sulfuric
acid. High yields in ethyl esters (ca. 90%) were reached
after a 4 h reaction at 25 °C on a HPW catalysed reactions.
Despite the fact that HPW catalyst was used in a homo-
geneous phase, it could be efficiently recovered and reused
through out a simple recycling protocol, without any
activity loss. The effects of alcohol and the FA nature on
yield reaction were also investigated.
well as ester separation steps and product neutralization
represent significant problems [6, 7]. A more interesting
alternative for lower biodiesel prices, is to produce it
directly from low cost lipidic raw materials, which are
normally rich in free fatty acids (FFA) [8]. However, it’s
conversion into biodiesel is only compatible with acid
catalysts [9]. Indeed, traditional Brønsted acids such as
sulfuric acid are inexpensive catalysts able to take part in
these processes. Nevertheless, in addition to their high
corrosiveness, they are also not reusable and its use results
in large generation of acid effluents and salts to be disposed
off into the environment [10, 11]. Thus, catalysts with nice
characteristics such as recyclability, less corrosiveness and
higher activity under mild condition reactions are extre-
mely welcome [12–14]. Moreover, in sight of a green
chemistry, the substitution of harmful liquid acids by solid
reusable acids as catalysts is in fact attractive to both
organic synthesis and industrial processes [15]. In this
sense, catalysis by heteropolyacids is one of the most
important and growing areas of research in the recent years
and has been successfully used in both homogeneous and
heterogeneous processes [16–18]. Heteropolyacid catalysts
are more attractive because they are commercially avail-
able, less corrosive, easy to handle when compared to
mineral acids, and can be used in recyclable processes [19,
20]. Highlighted, the Keggin series heteropolyacid
H3PW12O40, has been shown to be a similar or higher
catalytic activity on reactions esterification than traditional
acid catalysts [21–23].
Keywords Fatty acids Á
Esterification at room temperature Á
Dodecatungstophosphoric acid Á Ethanol Á Biodiesel
1 Introduction
The biodiesel occupies a prominent position among alter-
native fuels from others proposed nowadays [1, 2]. How-
ever, it’s production has over come several technological
drawbacks [3]. Presently, most of the biodiesel production
is via edible or non-edible vegetable oils transesterification,
under homogeneous alkaline catalysis conditions [4].
During these industrial processes, biodiesel is manufac-
tured with high yieldings using methanol, which is
obtained mainly via fossil sources [5]. Furthermore, the
high cost of raw materials, larger effluent generation as
In this work, the utilization of heteropolyacid
H3PW12O40 (HPW) as catalyst on FA esterification at room
temperature is described. The comparison between it’s
catalytic activity and those of the traditional Brønsted acids
on ethanol esterification reactions at room temperature
reveals that HPW is a lot more efficient than other catalysts
´
V. W. de Godoi Silva Á L. O. Laier Á M. J. d. Silva (&)
Chemistry Departament, Federal University of Vic¸osa, Vic¸osa,
Minas Gerais State zip code 36570-000, Brazil
e-mail: silvamj2003@ufv.br
123

´
V. W. de Godoi Silva et al.
208
herein evaluated. In addition to that, the HPW can be
recovered and reused without catalytic activity loss via
simple and efficient recycle protocols. The effects of
reaction variables such as the temperature, the type of fatty
acid and the type of alcohol were investigated.
H2SO4, 0.0288 mmol and PTSA, 0.0576 mmol) and then
the reaction started. All acid catalysts were used with the
equal hydrogen ions concentration (0.0576 mmol) consid-
ering the total ionization.
2.4 Effect of FA nature on HPW–Catalysed
Esterification with Ethanol
2 Experimental Section
The effect of both carbon chain length and double bonds
number FA in the yield and selectivity of ethyl esters for-
mation at room temperature (ca. 25 °C) was investigated.
The FA selects were myristic, palmitic and stearic acids
(saturated acids) and oleic, linoleic and linolenic acids
(unsaturated acids).
2.1 Chemicals
All chemicals were purchased from commercial sources
and used as received unless otherwise stated. Ethanol was
acquired from Sigma–Aldrich (99.9% w/w). The
H3PW12O40 x H2O heteropolyacid hydrate (HPW- do-
decatungstophosphoric acid, 99, 995%) was purchased
from Sigma–Aldrich (Milwaukee, WI), whereas sulfuric
acid (H2SO4, 98% w/w) and p-toluene sulfonic acid
2.5 Effect of Alcohol Nature on HPW–Catalysed
Esterification of FA
´
(PTSA) that were acquired from Quımica Moderna (Sa˜o
The catalytic activity of the HPW on esterification of dif-
ferent alcohols at room temperature was also investigated.
Typically, 10 mL of substrate alcohol selects (methanol,
ethanol, n-propanol, isopropanol or buthanol) were stirred
and then reacted with stearic or linolenic acids (2.5 mmol)
at room temperature in the presence of solved HPW cata-
lyst (0.0192 mmol).
Paulo, Brazil). Hexane and others solvents were purchased
from Vetec (Sa˜o Paulo, Brazil), and utilized without prior
handling. The myristic, palmitic, stearic, oleic, linoleic and
linolenic acids besides their respective esters were acquired
from Sigma–Aldrich and used as received.
2.2 HPW- Catalysed Esterification of FFA
with Ethanol: Effect of Temperature
2.6 Recovery/Reutilization of HPW Catalyst
Catalytic tests were conducted in a 50 mL three-necked
glass flask, equipped with sampling system, a reflux con-
denser, in thermostatic bath and under magnetic stirrer. The
reactions were performed under atmospheric pressure. In
all runs, ethanol was used in a large amount to shift the
equilibrium towards the esters formation. In a typical run,
oleic acid (1 mmol) and ethanol (164 mmol, 9.4 mL) were
stirred yet complete dissolution at room temperature. The
HPW catalyst (0.0192 mmol) was added to only then begin
the reaction. The heteropolyacid amount used as catalyst
was calculated without considering the water hydration. All
catalytic tests were performed in triplicate.
Herein, we intend to show that although this catalyst has
been used in a homogenous phase, it’s recovery can be
easily performed via simple recycle protocols. Thus, oleic
acid (1.0 mmol) was reacted with ethanol (164 mmol,
9.4 mL) in presence of HPW catalyst (0.0192 mmol) dur-
ing a 4 h reaction at room temperature. Furthermore, at the
end of the reaction, hexane was added to the solution. The
alcoholic layer containing the catalyst was isolated from a
non-polar organic layer, washed with several small por-
tions of water. The aqueous/alcoholic extract was then
evaporated till it dried under reduced pressure. The HPW
catalyst was then collected and reutilized in another cata-
lytic test. This recovery/reutilization procedure was repe-
ated for three times.
2.3 Brønsted Acids–Catalysed Esterification of FFA
with Ethanol at Room Temperature: Effect
of Catalyst Nature
2.7 Reaction Monitoring
A comparison between the HPW catalytic activity to
Brønsted acids more commonly used on FA esterification
at room temperature (ca. 25 °C) was performed. Again, the
same excess of ethanol has been used toward equilibrium
onto product formations and kept the catalyst in solution.
In a typical run, oleic acid (1 mmol) and ethanol
(164 mmol, 9.4 mL) were stirred and heated, and the cat-
alyst appropriated was then added (HPW, 0.0192 mmol;
The reaction progress was continuously monitored taking
aliquots at regular intervals of 30 min with a syringe and
diluted with hexane (5.0 mL), and analyzing them via gas
chromatography (Shimadzu GC17A fitted with a DB5
capillary column and FID detector) [21]. Reaction yields
were calculated by matching the areas of the esters GC
peaks into the corresponding calibration curves.
123

Novel H3PW12O40
209
2.8 Reaction Products Identification
Table 1 Brønsted acids-catalysed esterification of oleic acid with
ethanol at room temperature
The reaction products were identified via analysis carried
out on a Shimadzu GC17A gas chromatograph coupled
with a MS-QP 5050A mass spectrometer (Tokyo, Japan)
with a DB5 capillary column and helium as the carrier gas
at 2 mL/min [21]. The MS detector was operated in the EI
mode at 70 eV, with a scanning range of m/z 50–500.
Entry Catalyst Total conversion (%) Ethyl oleate yielding (%)
1
2
3
4
–
\5
19
8
99
97
98
94
H2SO4
PTSA
HPW
92
Reaction conditions: oleic acid (1 mmol); H2SO4 (0.0288 mmol);
PTSA (0.0576 mmol); HPW (0.0192 mmol); ethanol (167 mmol);
temperature (ca. 25 °C); 4 h
3 Results and Discussion
Both total conversion based on FFA reacted and ethyl oleate yielding
were determinate by GC analysis
3.1 HPW- Catalysed Esterification of Oleic Acid
with Ethanol: Effect of Temperature
Average of the results of three assays
Oleic acid, one FA normally present in large amounts on
most of the vegetable oils was the selected substrate. The
kinetic curves of HPW—catalysed esterification of oleic
acid with ethanol were obtained at different temperatures
are displayed in Fig. 1.
acids catalysts commonly used on FA esterification at room
temperature were performed. In Table 1, the results of
oleic acid esterification with ethanol in absence or presence
of catalysts such as HPW, PTSA or sulfuric acid obtained
at room temperature is shown. Firstly, as expected, in
absence of any acid catalysts very low conversion into
ethyl oleate was achieved (Table 1, entry 1, ca. \5%).
Conversely, in presence of acid catalysts a different
behavior was observed. Although Brønsted acids catalysts
have been used in the same hydrogen concentration, it was
found that both PTSA and sulfuric acid were noticeably
less active than HPW catalyst.
Remarkably, the catalytic activity of the HPW was not
affected by lowering the temperature. As a fact, high oleic
acid to ethyl oleate conversion (ca. 90%) was achieved
after a reaction time as long as 4 h for any temperature
studied (Fig. 1). As far as we know, this is an auspicious
result in heteropolyacid-catalysed FA esterification
reactions.
This is an unexpected result if we take in account that
both sulfuric acid and HPW are Brønsted acids equally
strong in solvent such as water [24]. Nevertheless, pKa
measurements revealed that those acids have different
behaviors in polar or non-polar organic solvents [25].
3.2 Comparative Analysis of HPW Activity Against
Commonly Used Acid Catalysts on FA
Esterification Reactions
In view to the results obtained on Sect. 3.1, a comparison
between the HPW catalytic activity against others Brønsted
Indeed, we think that probably, as suggested by Misono
-3
and co-workers, the high softness of the bulky PW12O
2-
conjugated base, in comparison to SO4 anion, seems to
40
favor the equilibrium shifts towards a higher concentration
of H? cations in the reaction solution [26]. Consequently,
with a higher concentration of protonated species, a higher
esters formation on HPW—catalysed reactions is achieved
[27]. Similar results were reported elsewhere which indi-
cate that HPW is more active than sulfuric acid in a wide
variety of acid-catalyzed reactions [28, 29].
100
80
25 oC
60
35 oC
45 oC
55 oC
3.3 HPW–Catalysed Esterification Reactions at Room
Temperature: Effect of FA nature
40
20
0
The effects of the presence of double bonds and the carbon
chain length in FA on HPW -catalysed ethanol esterifica-
tion are presented in Table 2.
0
1
2
3
4
5
6
7
8
Note that such yields and selectivities at the end reaction
seem not to be affected by the FA nature. For instance, the
myristic acid esterification (bearing a saturated carbonic
chain with 14 carbon atoms) and linolenic acid (bearing a
time (hs)
Fig. 1 Effect of temperature on HPW—catalysed esterification of
oleic acid with ethanol
123

´
V. W. de Godoi Silva et al.
210
Table 2 HPW–catalysed ethanol esterification of FFA at room
temperature
ethyl oleate yield (%)
catalyst recovery (%)
100
90
80
70
60
50
40
30
20
10
0
Entry
Fatty
acids Cn:m
Conversion (%)
Ethyl ester
selectivity (%)
a
1
2
3
4
5
6
C14:0
C16:0
C18:0
C18:1
C18:2
C18:3
95
95
94
92
96
97
97
96
96
94
95
96
Reaction conditions: substrate (1 mmol); ethanol (164 mmol); HPW
catalyst (0.0192 mmol); temperature (ca. 25 °C); 4 h
Conversion and selectivities determinate by GC analyses
Average of the results of three assays
a
Subscripts n = carbon number; m = double bonds number
1
2
3
runs
Fig. 2 Ethyl esters yields obtained for the 1st, 2nd and 3rd
consecutive recovery/reuse on esterification reactions of linolenic
and stearic acids in presence of HPW as catalyst. Reaction conditions:
ethanol (167 mmol); HPW (0.192 mmol); room temperature (ca.
25 °C); 2 hs reaction
carbonic chain with 18 carbon atoms and three double
bonds) produced similar yields and quite analogous selec-
tivities (95 and 97%, respectively) for the corresponding
ethyl esters (97 and 96%, respectively).
3.5 Recycling Catalysts
In recent work, we reported some preliminary results of a
simple procedure for recycling HPW catalyst on FFA
esterification reactions being carried out at ethanol reflux
temperature [21]. Herein, those protocols were used to
evaluate the recovery/reutilization of the HPW catalyst in
FA esterification reactions at room temperature.
3.4 HPW–Catalysed Esterification of FA: Effect
of Alcohol Nature
The result in Table 3 reveals that a drastic lowering on the
conversion of the alcohols into their respective esters was
been observed when the carbon chain of alcohol is higher.
Likewise, the alcohol reactivity also was strongly affected
by bulky hindrance on the hydroxyl group. For instance,
only a low conversion into isopropyl stearate or isopropyl
linoleate was reached after a 4 h reaction (Table 3, entries
4, 5). Probably with the increase of hindrance bulky on
secondary hydroxyl, the attack onto FA carbonyl became
more difficult, lowering the formation of esters.
A high catalyst load was employed, aiming a more ease
recovery and a lower time reaction. The Fig. 2 shows that
the HPW catalyst can be efficiently recovered and reused
without activity loss. Regard that a very high yield
recovery of the catalyst was achieved by their extraction
from the reaction medium. Additionally, another positive
aspect is that the after distillation and water removal from
ethanol with Na2SO4 its solvent can be again employed in
another catalytic run.
Table 3 HPW–catalysed alcoholysis of FFA at room temperature
4 Conclusion
Entry
Alcohol substrate
Stearate alkyl
yielding (%)
Linoleate alkenyl
yielding (%)
The HPW catalyst (H3PW12O40), the highest acid hetero-
polyacid of Keggin series, efficiently promotes the FA
esterification with ethanol at room temperature. It dem-
onstrated a higher catalytic activity compared to PTSA and
sulfuric acid catalysts at room temperature. This activity is
attributed to a higher acid strength and conjugated base
softness. High yields and selectivity were achieved on the
ethanolysis of saturated and unsaturated FA. Additionally,
the HPW activity on alcoholysis of oleic acid also was
investigated. The alcohol reactivity was strongly affected
1
2
3
4
5
Methyl
Ethyl
94
87
63
17
46
97
89
73
25
56
n-propyl
Isopropyl
Buthyl
Reaction conditions: alcohol substrate (10.0 mL); FFA (2.50 mmol);
HPW catalyst (0.0192 mmol); temperature (25 °C); 4hs reaction
Yielding determinate by GC analysis
Average of the results of three assays
123

Novel H3PW12O40
211
8. Lou W-Y, Zong M-H, Duan Z-Q (2008) Bioresour Technol
99:8752
9. Patil PD, Deng S (2009) Fuel 88:1302
10. Di Serio M, Tesser R, Santacesaria E, Dimiccoli F, Cammarota F,
Nastasi M (2005) J Mol. Catal A 239:111
11. Dash SS, Parida KM (2007) J Mol Catal A 266:88
12. Lotero E, Liu Y, Lopez DE, Suwannakaran K, Bruce DA,
Goodwin JG Jr (2005) Ind Eng Chem Res 44:5353
13. Chongkhong S, Tongurai C, Chetpattananondh P (2009) Renew.
Energ. 34:1059–1063
14. Misono M (2005) Catal Today 100:95
15. Xu L, Wang Y, Yang X, Yu X, Guo Y, Clark JH (2008) Green
Chem 10:746
16. Timofeeva MN (2003) Appl Catal A 256:19
17. Misono M, Ono I, Koyano G, Aoshima A (2000) Pure Appl
Chem 72:1305
18. Kozhevnikov IV (2009) J Mol Catal A 305:104
19. Alizadeh MH, Kermani T, Tayebee R (2007) Monatsh Chem
138:165
by bulky hindrance on the hydroxyl group and by
increasing carbon chain length. Finally, after a simple and
efficient recycle protocol, it was verified that the HPW
catalytic activity remained unaltered even after several
recovery/reutilization cycles. Relevant advantages such as
the reusability, less corrosive and high activity under room
temperature, are positive aspects for the heteropolyacid
catalyst. In conclusion, the utilization of HPW represents a
remarkable improvement compared to homogeneous cata-
lysts traditionally used to produce biodiesel via FFA
esterification.
Acknowledgments The authors are grateful to FUNARBE,
CAPES, CNPq, and FAPEMIG for financial support.
20. Caetano CS, Fonseca IM, Ramos AM, Vital J, Castanheiro JE
(2008) Catal Commun 9:1996
References
21. Cardoso AL, Augusti R, da Silva MJ (2008) J Am Oil Chem Soc
85:555
22. Misono M (2008) Catal Today 144:285
23. Miao X, Li R, Yao H (2009) Energ Convers Manage 50:2680
24. Morin P, Hamad B, Sapaly G, Rocha MGC, de Oliveira PGP,
Gonzalez WA, Sales EA, Essayem N (2007) Appl Catal A 330:69
25. Okuhara T, Hu C, Hashimoto M, Misono M (1994) Bull Chem
Soc Japan 67:1186
26. Mizuno N, Misono M (1994) J Mol Catal A 86:319
27. Lyu Y, Lotero E, Goodwin JG Jr (2006) J Mol Catal 245:132
28. Sepulveda JH, Yori JC, Vera CR (2005) Appl Catal A 288:18
29. Macht J, Carr RT, Iglesia E (2009) J Am Chem Soc 131:6554
1. Di Serio M, Tesser R, Pengmei L, Santacesaria E (2008) Energ
Fuel 22:207
2. Marchetti JM, Miguel VU, Errazu AF (2007) Renew Sust Energ
Rev 11:1300
3. Kulkarni MG, Gopinath R, Meher LC, Dalai AK (2006) Green
Chem 8:1056
4. Sakai T, Kawashima A, Koshikawa T (2009) Bioresour Technol
100:3268
5. Zabeti Z, Daud WMAW, Aroua MK (2009) Fuel ProcessTechnol
90:770
6. Haas MJ (2005) Fuel Process Technol 86:1087
7. Bozbas K (2008) Renew Sust Energ Rev 12:542
123