Transesterification catalyzed by superhydrophobic-oleophilic mesoporous polymeric solid acids: An efficient route for production of biodiesel

Article abstract of DOI:10.1007/s10562-013-1030-6

We report here an efficient mesoporous polymeric solid acid catalyst (p-PDVB-SO₃H) with superhydrophobic-oleophilic properties synthesized from copolymerization of divinylbenzene (DVB) with sodium p-styrene sulfonate under solvothermal conditions. N₂ isotherm showed that p-PDVB-SO ₃H has large BET surface area and uniform mesopore. Contact angle tests showed that p-PDVB-SO₃H exhibits superhydrophobic-oleophilic property for triolein and methanol, which results in its good miscibility and high exposition degree of active sites for various organic reactants. Catalytic tests showed that p-PDVB-SO₃H has much better catalytic activities and recyclability toward transesterification to biodiesel than those of H-form mesoporous ZMS-5 zeolite, carbon solid acid and commercially acidic resin of Amberlyst 15, which will be very important for its wide applications for biodiesel production in industry.

Full text of DOI:10.1007/s10562-013-1030-6

Catal Lett (2013) 143:792–797
DOI 10.1007/s10562-013-1030-6
Transesterification Catalyzed by Superhydrophobic–Oleophilic
Mesoporous Polymeric Solid Acids: An Efficient Route
for Production of Biodiesel
Iman Noshadi
Baishali Kanjilal
Hua Liu Jiantao Li
•
Ranjan Kamat Kumar
Richard Parnas
Fujian Liu
•
•
•
•
•
Received: 7 March 2013 / Accepted: 24 May 2013 / Published online: 6 June 2013
Ó Springer Science+Business Media New York 2013
Abstract We report here an efficient mesoporous polymeric
solid acid catalyst (p-PDVB-SO H) with superhydrophobic–
1 Introduction
3
oleophilic properties synthesized from copolymerization of
Increase in energy demand and environmental concerns
coupled with depletion in world petroleum reserves have
been the primary drivers for the development of alternative
and renewable sources of energy. Biodiesel is a renewable
fuel comprising of alkyl esters. It is made from vegetable oil
and animal fat and offers advantages of renewability, better
lubricity and biodegradability. Additionally, in comparison
to petrodiesel, its use results in decreased particulate emis-
sion, unburned hydrocarbons and carbon monoxide [1–6].
The production of biodiesel was usually achieved toward
transesterification of triolein with short-line alcohol catalyzed
by acid or base catalysts [7–10]. Compared with base cata-
lysts, acid catalysts can simultaneously catalyze both esteri-
fication and transesterification without forming any soap,
unlike base catalysts [7–10]. Thus they can be employed to
produce biodiesel from low-quality and low cost feedstock
such as waste cooking oil or renewable plants oil [7–10].
Although conventional mineral acids such as H SO or HCl
divinylbenzene (DVB) with sodium p-styrene sulfonate under
solvothermal conditions. N isotherm showed that p-PDVB-
2
SO H has large BET surface area and uniform mesopore.
3
Contact angle tests showed that p-PDVB-SO H exhibits su-
3
perhydrophobic–oleophilic property for triolein and methanol,
which results in its good miscibility and high exposition degree
of active sites for various organic reactants. Catalytic tests
showed that p-PDVB-SO H has much better catalytic activi-
3
ties and recyclability toward transesterification to biodiesel
than those of H-form mesoporous ZMS-5 zeolite, carbon solid
acidandcommercially acidicresin ofAmberlyst15, whichwill
be very important for its wide applications for biodiesel pro-
duction in industry.
Keywords Solid acids Á Transesterification Á Biodiesel Á
Hydrophobic mesoporous polymers Á Recyclability
2
4
are excellent catalysts for converting crude oils to biodiesel,
they are environmentally unfriendly and difficult to recycle in
addition to being highly corrosive, which strongly restricts
their wide applications [11–16]. On the other hand, solid acids
suchassulfated zirconia, heteropolyacidsand acidicresins, on
the other offer advantages of recyclability and reduced cor-
rosion. Additionally, being environmental friendly, they have
been widely used for production of biodiesel at laboratory
scale [11–16]. However their poor porosity restricts their
catalytic capabilities and largely constrains their application
in biodiesel production [11–16]. Mesoporous solid acids, with
high BET surface areas, abundant and uniform mesoporosity
overcome the disadvantage of porosity limitations [17–19],
which exhibit very good catalytic activities in various acid-
catalyzed reactions. Typical mesoporous solid acids such as
I. Noshadi Á R. K. Kumar Á B. Kanjilal Á R. Parnas
Department of Chemical and Biomolecular Engineering,
University of Connecticut Storrs, Storrs, CT 06269-3222, USA
H. Liu Á F. Liu (&)
Key Laboratory of Alternative Technologies for Fine Chemicals
Process, Shaoxing University, Shaoxing 312000, Zhejiang,
People’s Republic of China
e-mail: liufujian1982@yahoo.cn
J. Li
Fushun Research Institute of Petroleum and Petrochemicals,
SINOPEC, Fushun 113001, People’s Republic of China
e-mail: lijiantao.fshy@sinopec.com
1
23

Superhydrophobic–Oleophilic4 Mesoporous Polymeric Solid Acids
793
sulfonic group functional mesoporous silicas (SBA-15-
SO H), mesoporous sulfated ZrO acidic resins and carbon
by using AIBN initiator under solvothermal conditions. As
a typical run, 2.0 g of DVB and 0.5 g of SVBS functional
monomer were added to a mixture of 0.065 g of AIBN,
25 mL of THF and 2.5 mL of distilled water, after stirring
of the reaction mixture for 2 h at room temperature, the
mixture was treated by autoclaving at 100 °C for 1 day and
evaporating of the solvents at room temperature. The
resultant solid obtained is white in color. Then the resulted
sample was ion exchanged by using sulfuric acid as fol-
lows: 1.0 g of resulted Na-form solid acid was added into a
mixture of 30 mL of distilled water, 10 mL of ethanol and
5 mL of sulfuric acid, vigorously stirred for 24 h, filtered
and washed with large amount of water until neutral. The
sample was dried at 80 °C for 6 h prior to use, giving the
3
2
based solid acids [10, 20, 21] have been studied with good
results in esterifications and transesterifications [10, 20, 21].
The limitation on their catalytic activity arises from their
inorganic hydrophilic framework and hence low miscibility
for various organic substrates [22–24].
Very recently, Liu et al. [24] have successfully synthe-
sized mesoporous polydivinylbenzene (p-PDVB-SO H)
3
based solid acids with superhydrophobicity and good
oleophilicity, which exhibits excellent catalytic activities in
esterification and condensation. The superhydrophobicity
and good oleophilicity result in its superior wettability and
good miscibility with organic substrates, which were
favorable characteristics for the enhancement of its cata-
lytic activity. Thus, synthesis of mesoporous solid acids
with good oleophilic polymer network can significantly
improve its catalytic activities for biodiesel production
toward transesterification. In this work, we demonstrate an
efficient route for production of biodiesel by transesterifi-
sample of p-PDVB-SO H. For comparison, mesoporous
3
ZMS-5 zeolite and carbon solid acid were synthesized
according to the literature [25, 26].
The acid-exchange capacity of various catalysts was
determined by acid–base titration with standard NaOH
solution. As a typical run, 0.1 g of catalyst was added into
25 mL of 2 M aqueous NaCl solution, after stirring for
24 h at room temperature until equilibrium was reached,
the resulted suspension was titrated by drop wise addition
of standard NaOH solution.
cation reaction catalyzed by p-PDVB-SO H. The
3
improvement in catalytic efficiency and recyclability have
been correlated with surface area, good stability, and
excellent hydrophobicity of p-PDVB-SO H, which was
3
much better than those of mesoporous ZMS-5 zeolite,
carbon based solid acid and commercial Amberlyst 15. The
superior catalytic activity and recyclability of p-PDVB-
2.3 Characterizations
SO H in transesterification will be potentially important for
3
Nitrogen isotherms were measured using a Micromeritics
ASAP 2020 M system. The samples were outgassed for 10 h
at 150 °C before the measurements. The Barrett–Joyner–
Halenda (BJH) model was used to calculate the pore-size
distributionfor mesopores. A Bruker66 V FTIRspectrometer
wasusedfor FTIR spectralmeasurements. Acid–basetitration
with standard NaOH solution was employed to estimate the
acidexchangecapabilitiesofthecatalysts. Elementalanalyses
(C, H, N and S) were performed on a Perkin-Elmer series II
CHNS analyzer 2400. Thermogravimetric analysis (TG) were
performed on a Perkin-Elmer TGA7 and a DTA-1700 in
flowing air, respectively. The heating rate was 20 °C/min.
its wide applications for biodiesel production in industry.
2
Experimental Section
2
.1 Chemicals and Reagents
All chemicals were of analytical grade and used as purchased
without further purification. Sodium p-styrene sulfonate,
nonionic block copolymer surfactant poly(ethyleneoxide)-
poly(propyleneoxide)-poly(ethyleneoxide) block copolymer
(
P123, molecular weight of about 5,800), 3-mercaptopropyl-
trimethoxysilane (3-MPTS), tetrapropyl ammonium hydrox-
ide (TPAOH) and Amberlyst 15 were purchased from
Sigma-Aldrich Company, Ltd. (USA). DVB monomer, initi-
ator of azobisisobutyronitrile (AIBN), tetraethyl orthosilicate
2.4 Catalytic Reactions
Model transesterification reactions were carried out on
triolein with methanol. As a typical run, 2 g (2.26 mmol)
of triolein was added into a three-necked round flask
equipped with a condenser and a magnetic stirrer, then the
temperature was rapidly increased to 65 °C. 10.9 mL of
methanol and 0.05 g of catalyst were quickly added under
vigorous stirring, the reaction was kept at 65 °C for 16 h.
The molar ratio of triolein/methanol was 1:120 and the
mass ratio of catalyst/triolein was 0.05. The reaction
products were analyzed by gas chromatography (Agilent
5390) with a flame ionization detector (FID).
(
TEOS), sodium aluminate, methanol, triolein and sulfuric
acid were obtained from Tianjin Guangfu Chemical Reagent.
H-form of Beta zeolite and ultrastable Y zeolite (USY) were
supplied by Sinopec Catalyst Co.
2
.2 Preparation of p-PDVB-SO H
3
The p-PDVB-SO H was synthesized from copolymeriza-
3
tion of sodium 4-vinylbenzenesulfonate (SVBS) with DVB
123

7
94
I. Noshadi et al.
The recycling experiment of p-PDVB-SO H was per-
3
the sample, which exhibits relative high BET surface area
2
3
formed by separation of p-PDVB-SO H from reaction
3
(171 m /g) and large pore volume (0.52 cm /g), much higher
than those of Amberlyst 15 and carbon based solid acid
media by centrifugation, washing with large amount of
ethanol for removing of adsorbed reactants or products, and
(Table 1). Correspondingly, p-PDVB-SO H shows very uni-
3
drying at 80 °C for 4 h. The recycled p-PDVB-SO H was
form pore size centered at 21.2 nm, in good agreement with
the results published by uspreviously [22]. Additionally, the S
3
activated by 0.1 M H SO at room temperature for 4 h
2
4
before the next time use.
content and H concentration of p-PDVB-SO H were 1.3 and
3
1.8 mmol/g respectively, higher than those H form meso-
porous ZSM-5 (0.92 mmol/g), lower than those of Amberlyst
3
Results and Discussion
.1 Catalyst Characterization
15 (4.7 mmol/g) and C–SO H (2.0 mmol/g). Interestingly,
3
only a little decreasing of S content and H concentration could
3
be observed in p-PDVB-SO H after recycled for five times,
3
which should be attributed to partial deactivation and cover-
age of active sites during recycling experiment. It should also
be noted here that the increasing of the concentration of active
sites usually results in the decreasing of BET surface areas of
the samples [22].
Figure 1 shows the N isotherms and pore size distribution of
2
p-PDVB-SO H. Clearly, p-PDVB-SO H shows a type-IV
3
3
curve with a sharp capillary condensation step at P/P =
0
0
.8–0.95, indicating the formation of obviously mesopores in
Fig. 1 N
size distribution of p-PDVB-
SO
2
isotherms and pore
0.7
3
3
2
2
1
1
50
00
50
00
50
00
3
H
0.6
0.5
0.4
0.3
0.2
0.1
0.0
50
0
0.0
0.2
0.4
0.6
0.8
1.0
0
20 40 60 80 100 120 140
Relative pressure (P/P0)
Pore diameter (nm)
Table 1 The textural and acidic parameters of various solid acid catalysts
a
b
2
3
(cm /g)
c
Run
Samples
S content (mmol/g)
Acid sites (mmol/g)
S
BET (m /g)
V
p
p
D (nm)
1
2
3
4
5
a
p-PDVB-SO
p-PDVB-SO
3
H
H
1.30
1.26
4.30
1.91
–
1.8
171
165
45
0.52
0.50
0.31
–
21.5
22.3
40
d
3
1.68
4.70
2.0
Amberlyst 15
C–SO
Mesoporous ZMS-5
3
H
10\
368
–
e
0.92
0.31
14.5
Measured by CHNS elemental analysis
Measured by acid–base titration
b
c
d
e
Pore size distribution estimated from BJH model
The sample after being recycled for two times in transesterification of triolein with methanol
Si/Al ratio at 40
1
23

Superhydrophobic–Oleophilic4 Mesoporous Polymeric Solid Acids
795
Figure 3 shows the contact angles of p-PDVB-SO H for
3
9
8
7
6
5
4
3
2
0
0
0
0
0
0
0
0
water and triolein. Notably, the water droplet contact angle
of 150°, on the surface of p-PDVB-SO H indicates its su-
3
1
368
perhydrophobic nature; On the contrary, the contact angle of
1043
1091
soybean oil or methanol droplet on the surface of p-PDVB-
SO H is nearly 0° indicating its super wettability for oil and
3
methanol. Interestingly, the contact angle of 120° for glyc-
erin on the same surface indicates a good anti-wettability for
glycerin. The super wettability of p-PDVB-SO H for oil and
3
good anti-wettability for glycerin and water were favorable
for enhancement of its catalytic activities in transesterifica-
tion of oil with methanol. To the best of our knowledge,
solid acids with good hydrophobic and oleophilic properties
have not been reported previously.
700
800
900
1000
1100
1200
1300
1400
-1
Wave number (cm )
Fig. 2 FT-IR spectrum of p-PDVB-SO
Figure 4 shows TG curves of p-PDVB-SO H and Am-
3
3
H
berlyst 15, both of them demonstrate the weight loss
associated with the desorption of adsorbed water, destruc-
tion of sulfonic group and polymeric network ranged from
30 to 150, 200 to 440 and 440 to 540 °C; Notably, the
weight loss assigned to destruction of sulfonic group and
polymeric network were centered at around 364 and
497 °C, which were much higher than those of Amberlyst
15 (295–439 °C), indicating the better thermal stability of
Figure 2 shows the FT-IR spectrum of p-PDVB-SO H.
3
-
1
Notably, the peak at 1,042 cm
associated with C–S
bond could also be clearly observed in p-PDVB-SO H; In
3
the meanwhile, other peaks at around 1,092 and
-
,368 cm associated with S=O bond could be clearly
1
1
observed; Above results confirmed that the sulfonic group
has been successfully grafted onto the network of
p-PDVB-SO H than that of commercial Amberlyst 15.
3
p-PDVB-SO H.
3
Similar results have also been reported previously [22, 23].
A
CA=150°
B
CA=0°
D
CA=120°
C
CA=0°
3
Fig. 3 Contact angles of a water droplet, b triolein droplet, c methanol and d glycerin on the surface of p-PDVB-SO H
123

7
96
I. Noshadi et al.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
8
7
6
0
0
0
50
40
30
20
10
b
a
0
50
100 150 200 250 300 350 400 450 500 550 600 650 700
Fresh
1st
2nd
°
Temperature ( C)
Recycle numbers
Fig. 4 TG-DTA curves of a p-PDVB-SO
3
H and b Amberlyst 15
Fig. 6 p-PDVB-SO H catalyst recyclability for transesterification of
3
triolein with methanol (T = 65 °C, time = 16 h)
3
.2 Catalytic Reactions
when compared with various conventional solid acids. The
Figure 5 shows the catalytic kinetics curves in transesterifi-
cationoftrioleinwithmethanolcatalyzedbyvariouscatalysts.
excellent catalytic performance per sites in p-PDVB-SO H
3
should be attributed to its unique hydrophobic–oleophilic
property. The superhydrophobic network results in the good
anti-wettability for the byproduct of glycerin (Fig. 3d), which
largely constrains the reverse reaction, further resulting in the
high yields of biodiesel [23, 27]. On the other hand, the super-
oleophilic property results in the good dispersion of p-PDVB-
Clearly, p-PDVB-SO H showed very good catalytic activities
3
when compared with those of mesoporous ZMS-5 zeolite,
carbon based solid acid and Amberlyst 15. After only 4 h of
reaction, the conversion of triolein catalyzed by p-PDVB-
SO H was much higher than those of H-form mesoporous
3
ZSM-5, Amberlyst 15, and carbon based solid acid (Fig. 5).
After 16 h of reaction time, the conversion of triolein cata-
SO H in reaction media [24], which leads to the high expo-
3
sition degree of active sites in p-PDVB-SO H [28], further
3
lyzed by p-PDVB-SO H was up to 78.3 %, which was much
3
resulting in its excellent catalytic activities for biodiesel
production.
higher than those of H-form mesoporous ZSM-5, Amberlyst
1
5 and carbon solid acid (57.32, 43.23 and 40.23 % respec-
Figure 6 shows the recyclability of p-PDVB-SO H in
3
tively), suggesting the excellent catalytic activities of
transesterification of triolein with methanol. Compared
p-PDVB-SO H in transesterification for production of bio-
3
with fresh p-PDVB-SO H (conversion at 78.3 %), after
3
diesel. It should be also noted here that the TOF value of
recycled for one time, the sample showed the conversion of
triolein at 72.3 %, further recycled for two times, the
conversion of triolein was still up to 71.0 %. The little
-1
p-PDVB-SO H was 1.71 h , much higher than those of
3
-1
-1
Amberlyst 15 (0.28 h ) and carbon solid acid (0.60 h ),
-1
similar with that of H-form mesoporous ZSM-5 (1.75 h ),
decrease in catalytic activities of p-PDVB-SO H should be
3
which indicates good activities per sites in p-PDVB-SO H
3
attributed to partially coverage of active sites during
recycling processes, which confirms that p-PDVB-SO H
3
do not suffer instant deactivation. The good recyclability of
p-PDVB-SO H comes from its opened and abundant
3
mesoporosity, good thermal stability.
4
Conclusions
In summary, an efficient solid acid of p-PDVB-SO H with
3
hydrophobic and good oleophilic network was successfully
prepared through copolymerization of DVB with sodium
4-vinylbenzenesulfonate. The solid acid exhibited the
characteristics of high BET surface area, large pore vol-
ume, a stable and hydrophobic network and a high con-
centration of active sites, which result in their superior
Fig. 5 Catalytic kinetics curves in the transesterification of triolein
with methanol catalyzed by a p-PDVB-SO H, b H-form mesoporous
3
ZMS-5 zeolite, c Amberlyst 15 and d carbon solid acid
1
23

Superhydrophobic–Oleophilic4 Mesoporous Polymeric Solid Acids
797
catalytic activities and recyclability in transesterification of
triglyceride or plant oil with methanol for production of
biodiesel as compared with those of conventional solid acid
including H-form mesoporous zeolite, Amberlyst-15 and
carbon based solid acid. The successful synthesis of
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3
of biodiesel toward transesterification in industry.
Acknowledgments This work was supported by the National Nat-
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Science and Technology of Shaoxing Bureau (2012B70018) and
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