Biodiesel production using a carbon solid acid catalyst derived from β-cyclodextrin

Article abstract of DOI:10.1007/s11746-015-2621-8

A novel carbon solid acid catalyst was prepared by incomplete hydrothermal carbonization of β-cyclodextrin into small polycyclic aromatic carbon sheets, followed by the introduction of -SO₃H groups via sulfonation with sulfuric acid. The physical and chemical properties of the catalyst were characterized in detail. The catalyst simultaneously catalyzed esterification and transesterification reactions to produce biodiesel from high free fatty acid (FFA) containing oils (55.2%). For the as-prepared catalyst, 90.82% of the oleic acid was esterified after 8 h, while the total transesterification yield of high FFA containing oils reached 79.98% after 12 h. By contrast, the obtained catalyst showed comparable activity to biomass (such as sugar, starch, etc.)-based carbon solid acid catalyst while Amberlyst-15 resulted in significantly lower levels of conversion, demonstrating its relatively high catalytic activity for simultaneous esterification and transesterification. Moreover, as the catalyst can be regenerated, it has the potential for use in biodiesel production from oils with a high FFA content.

Full text of DOI:10.1007/s11746-015-2621-8

J Am Oil Chem Soc
DOI 10.1007/s11746-015-2621-8
ORIGINAL PAPER
Biodiesel Production Using a Carbon Solid Acid Catalyst Derived
from β‑Cyclodextrin
Xiao‑bo Fu1 · Jie Chen1 · Xue‑li Song1 · Yuan‑ming Zhang1 · Yi Zhu1 · Jun Yang1 ·
Cheng‑wu Zhang2
Received: 30 March 2014 / Revised: 22 February 2015 / Accepted: 23 February 2015
© AOCS 2015
Abstract A novel carbon solid acid catalyst was pre-
pared by incomplete hydrothermal carbonization of
β-cyclodextrin into small polycyclic aromatic carbon
sheets, followed by the introduction of –SO3H groups via
sulfonation with sulfuric acid. The physical and chemical
properties of the catalyst were characterized in detail. The
catalyst simultaneously catalyzed esterification and trans-
esterification reactions to produce biodiesel from high free
fatty acid (FFA) containing oils (55.2 %). For the as-pre-
pared catalyst, 90.82 % of the oleic acid was esterified after
8 h, while the total transesterification yield of high FFA
containing oils reached 79.98 % after 12 h. By contrast, the
obtained catalyst showed comparable activity to biomass
(such as sugar, starch, etc.)-based carbon solid acid catalyst
while Amberlyst-15 resulted in significantly lower levels
of conversion, demonstrating its relatively high catalytic
activity for simultaneous esterification and transesterifica-
tion. Moreover, as the catalyst can be regenerated, it has the
potential for use in biodiesel production from oils with a
high FFA content.
Introduction
At their current usage rates, petroleum, coal and natural
gas, which are currently the world’s major energy sources,
will soon be depleted [1]. Therefore, the need to find tech-
nically feasible, low-cost, environmentally benign, and
readily available alternatives has become one of our most
important energy issues. One promising alternative to fossil
oil is biodiesel, which was originally derived from triglyc-
eride oils [2]. It is well known that there are minor differ-
ences in flow and combustion properties between biodiesel
and petroleum-derived diesel. Moreover, biodiesel has
many advantages over petro-diesel, including biodegrada-
bility, nontoxicity, low emission of greenhouse gases and
better lubricity. From an ecological point of view, biodiesel
combustion has no net effect on global warming, as it is
a means to recycle CO2 (CO2 produced by combustion of
biodiesel is converted back into oils by plants) [3]. Even
though biodiesel has a number of promising features, its
actual commercialization has been limited due to the high
cost of triglyceride oil feedstocks.
Keywords Biodiesel · Solid acid · Esterification ·
Transesterification · β-Cyclodextrin
The main component of biodiesel is fatty acid methyl
ester (FAME), which is derived from fatty acid esterifi-
cation and triglyceride transesterification. In these reac-
tions, catalysts play a key role [4]. The main catalysts used
include basic catalysts and acidic catalysts. Generally, com-
monly used basic catalysts, such as KOH and NaHCO3,
are considered to be highly efficient. However, formation
of soaps typically occurs when the levels of free fatty acid
in the oil exceed 1 %. Moreover, the high cost of the oil
feedstock may hinder biodiesel commercialization. These
issues may be addressed by utilizing less expensive and
more readily available alternate feedstocks, such as waste
cooking oils or high FFA oil, and to utilize acidic catalysts.
* Yuan-ming Zhang
tzhangym@jnu.edu.cn
1
Department of Chemistry, Jinan University,
510632 Guangzhou, China
2
Research Center of Hydrobiology, Jinan University,
510632 Guangzhou, China
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J Am Oil Chem Soc
Although biodiesel production from waste cooking oil and
other high-FFA feedstocks can only meet a small fraction
of global demand for diesel, biodiesel from high-FFA feed
stocks is certainly still worth developing. Sulfuric acid was
first proposed as a homogeneous acidic catalyst for produc-
tion of biodiesel. Although the free fatty acids and H2O in
the feedstock can be ignored in homogeneous acid cata-
lyzed processes, new problems in the use of such catalysts
have emerged, such as difficulty in separating and recycling
the catalyst, operation at high temperatures, and equipment
corrosion.
Recently, the use of solid acid catalysts was reported
as an optimal solution for biodiesel production, because
it can eliminate such separation, corrosion, toxicity, and
environmental considerations [4]. Ideally, a solid acid cat-
alyst for biodiesel production should possess a high den-
sity of strongly acidic sites, excellent stability, large pore
size, low cost and hydrophobic surfaces [5]. Among solid
acidic catalysts reported to be studied for biodiesel pro-
duction are inorganic-based solid acids such as zeolite [6],
niobic acid [7], and sulfonated zirconia [8]. However, these
catalysts have small pore size, which limit the diffusion of
the large fatty acid molecules, and thus they are not suit-
able for the production of biodiesel. While strongly acidic
ion-exchange resins, i.e., Amberlyst-15 and Nafion-NR50
[9], possess a large number of sulfonic acid groups, their
application is limited due to their high cost and low sta-
bility. While solid acid catalysts derived from sulfonated
polystyrene compounds [10] and polyvinyl alcohol cross-
linked with sulfosuccinic acid [11] also show high activity
for esterification of fatty acids with methanol, leaching of
active species into the reaction system are an issue. There-
fore, it is desirable to develop high stability solid acid cata-
lysts with a high density of strongly acidic sites.
Recently, significant attention has been given to carbon-
based solid acid catalysts, as they can provide a high den-
sity of strong acid sites while resisting H2O deactivation
during the esterification reaction [12]. These carbon solid
acid catalysts displayed remarkable catalytic properties
and stability for biodiesel production [5, 13–18]. Gener-
ally, the carbon-based catalysts were produced by the fol-
lowing steps. Biomass, such as sugar, glucose, or starch,
is incompletely carbonized to create polycyclic aromatic
carbon sheets. These incomplete carbonized sheets are then
sulfonated. It has been demonstrated that this method can
synthesize the carbon solid acid catalyst effectively, cast-
ing new light on solid carbon acidic catalyst preparation.
Moreover, recent studies related to carbon solid acid cata-
lysts suggest that their performance is strongly depend-
ent on their starting materials [16]. Cyclodextrins (CDs)
are cyclic oligosaccharides of R-D-glucopyranose that are
formed by cyclomaltodextrin glucano-transferase cata-
lyzed degradation of starch and can accumulate during the
fermentation process. Shin et al. [19] demonstrated for the
first time that CDs can be converted into aromatic carbon
spheres by incomplete hydrothermal carbonization. These
carbon structures were reported to be support anchoring of
sulfuric groups with high density on the edges of the car-
bon solid acid catalyst. Thus, the goal of this work is to
prepare a new carbon solid acidic catalyst with a high den-
sity of strong acid sites for biodiesel production using CD
as a precursor. For the first time, β-CD-derived solid-acid
catalysts were evaluated for oleic acid esterification. The
catalyst was also studied for production of biodiesel from a
mixed oil containing 50.2 % FFAs by simultaneous esteri-
fication and transesterification. In addition, recyclability of
the catalyst was also evaluated.
Experimental
Materials
β-Cyclodextrin (CD) (≥98 % reagent grade) was purchased
from Aladdin Reagent Database (Shanghai, China). metha-
nol (99.9 % reagent grade containing <0.04 % water) and
sulfuric acid (95–98 % AR grade) were purchased from
Guangzhou Chemical Reagent (Guangzhou, China). Oleic
acid, triolein, methyl palmitate, n-dodecane, methyl oleate,
methyl linoleate, and methyl stearate were supplied by
Sigma-Aldrich (United States). The solvents and reagents
were HPLC grade or AR grade.
Catalyst Preparation
The precursors for the carbon solid acid catalyst were pre-
pared through incomplete hydrothermal carbonization of
β-CD and sulfonation of the carbon precursor according
to the following procedure: a mixture of β-CD (8 g), water
(50 mL) and sulfuric acid (0.1 g) in a 100-mL Teflon-lined
autoclave was heated to 180 °C for 4 h, and then cooled
to room temperature. The slurry was filtered and washed
with approximately 1000 mL deionized water. The residue
was dried under vacuum at 120 °C for 4 h and the collected
product was ground to a powder. The powder (5 g) was
boiled in 200 mL of H2SO4 (98 %) at 150 °C under N2 for
15 h, and then cooled to room temperature. A black precip-
itate formed after addition of 1000 mL of deionized water
to the mixture. The catalyst was filtered and washed repeat-
edly with hot deionized water (>80 °C) to remove impuri-
ties (sulfate ions) and was dried under vacuum at 120 °C
for 12 h. Three samples, the carbonization product of β-CD
with only water, the carbonization product of β-CD with
diluted H2SO4 and the sulfonated carbonization product
of β-CD with H2SO4, were prepared and denoted as CD-1,
CD-2 and CD-3.
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J Am Oil Chem Soc
Catalyst Characterization
autoclave. The reaction mixture of 300 mmol methanol and
10 mmol triolein with 5 wt.% catalyst based on the weight
of triolein was reacted at 80 °C for 12 h. Samples for GC
analysis were prepared as described above.
Fourier transform infrared spectra (FT–IR) of the carbon
solid acid catalysts were obtained using a Nicolet 380 FT–
IR spectrometer using the KBr technique (MA, USA). The
measured range was 400–4000 cm−1. X-ray photoelectron
spectra (XPS) were obtained using a Thermo-VG ESCA
LAB-250 spectrometer with monochromatic Al Ká radia-
tion (MA, USA). Powder X-ray diffraction (XRD) pat-
terns were obtained using a MSAL XD2 X-ray diffractom-
eter (Cu Ká, 36 kV, 20 mA, and λ = 1.54056 Å) (Beijing,
China). The measured angle (2θ) was 10–80° at a scanning
rate of 8°/min. The morphologies were tested with a scan-
ning electron microscope (SEM; Philips SEM-XL30S;
Amsterdam, Netherlands). The textural properties of the
sample were analyzed by N2 adsorption. After degassing
the sample under vacuum at 130 °C overnight, the BET
specific surface area and pore structure was carried out
using a Micromeritics ASAP 2000 system at 77 K (Atlanta,
USA). Strong acid density was determined using a sulfur
elemental analyzer (Elementar Vario, EL III; Hanau, Ger-
many). The total levels of functional groups, including
SO3H + COOH and SO3H + COOH + OH, were inves-
tigated according to Na+ exchange in NaHCO3 and NaOH
solutions. Typically, ~0.2 g of carbon material was ground
into powder and then mixed with 20 mL of 0.05 M solu-
tions of NaHCO3 and NaOH for 24 h. Finally, 0.05 M
NaOH was used to back titrate an excess of 0.05 M HCl
solution after acidifying.
Biodiesel Production
Biodiesel were produced by esterification and transesteri-
fication of high FFA-containing triolein. The process was
performed by adding prepared carbon solid acid catalyst to
a blend of triolein (50.2 wt.% oleic acid) stirred at a speed
of 500 rpm at 80 °C for 12 h. A sample was prepared and
analyzed as described.
Catalyst Regeneration
To investigate the stability of the prepared catalyst, the
regeneration method and the operational stability were
investigated by esterifying oleic acid with methanol with
5 wt.% catalyst for five runs. After each reaction, the
catalyst was regenerated by filtration and washing with
excess methanol. The two methods for regeneration of
catalyst were: (1) washing of spent catalyst with 98 %
H2SO4, and (2) washing of the the spent catalyst with
methanol.
GC Analysis
Samples were analyzed using a gas chromatograph (Agi-
lent 7890A) (Palo Alto, USA) equipped with a DB-1701
capillary column (30 m × 0.25 mm; J&W Scientific Agi-
lent Tech., USA) to determine FAME concentration. An
internal standard of n-dodecane was used; about 0.5 g of
sample and 5 mL of 0.5 M n-dodecane/cyclohexane solu-
tion were mixed with cyclohexane. Then, 2 uL of sample
was injected and N2 was used as the carrier gas. A split
ratio of 100:1 was used at 523 K. A flame ionization detec-
tor (FID) was set at 523 K. The initial oven temperature
was 373 K and elevated at a rate of 5 K/min to 493 K, and
then held at 493 K for 25 min. The total operation time was
51 min.
Catalytic Testing
Catalytic esterification of oleic acid with methanol was
performed in a flask equipped with a water condenser. The
reaction mixture was 100 mmol of methanol and 10 mmol
of oleic acid with carbon solid acid catalyst (5 wt% on the
basis of the oleic acid weight). The reaction temperature
was 60–80 °C for 12 h. Aliquots (0.2 mL) were taken at
regular intervals. After the reaction was completed, the
mixture was centrifuged (16,000 rpm, 10 min) to sepa-
rate the spent solid catalyst and then dried under vacuum
at 70 °C for 10 min to remove the methanol, followed by
addition of 200 μL of anhydrous n-hexane with 1.0 mM of
n-dodecane for the GC analyses.
FAME yield was obtained by the following equation:
ꢁ
ꢂ
WD
ꢀ
AFAME
ADfFAME
FAME yield (wt%) =
× 100
Catalytic transesterification of triolein with methanol
was also conducted in a flask with a condenser. The reac-
tion mixture of 300 mmol methanol and 10 mmol with
5 wt% catalyst on the basis of the triolein weight was
reacted at 80 °C for 12 h with a stirring rate of 500 rpm.
Samples (0.5 mL) were prepared for GC analysis, as
described above.
S
ꢁ
ꢂ
ꢀ
AGlyerol
WD
ADfGlycerol
Glycerol yield (wt%) =
× 100
S
where AFAME and AGlycerol are the area of FAME and glyc-
erol, AD is the area of n-dodecane, fFAME and fGlycerol are the
coefficient for each FAME and glycerol, calculated from
Catalytic transesterification of triolein with methanol
under high pressure was performed in a 50-mL Teflon-lined
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J Am Oil Chem Soc
4000
3500
3000
2500
2000
1500
1000
500
(a)
(b)
(c)
0
10
20
30
40
50
60
70
80
2 ( )
Fig. 1 XRD patterns of the samples: a CD-1, b CD-2 and c CD-3
the calibration curve, WD is the weight of n-dodecane and S
is the sample weight.
Results and Discussion
Characterization of the Solid Acid Catalysts
The catalysts were first characterized by XRD. The XRD
patterns of CD-1, CD-2 and CD-3 presented two weak
diffraction peaks. Figure 1 shows that their 2θ values are
between 10º–30º and 30º–50º, respectively, assigned to
the (002) and (101) planes of the carbon. It is likely that
the stacks of parallel carbon sheets and the regular struc-
ture within the individual carbon sheet that produces these
structures [12] clusters with small fragments of graphene
planes and disordered carbon, which are characteristic of
carbon states and indicate the formation of the polycylic
aromatic structures. These structures are known to be
favorable for anchoring of the –SO3H groups. After sul-
fonation, as shown by Fig. 1c, the structure of CD-3 was
still maintained, indicating that the catalyst remains amor-
phous and has no graphitization.
Morphologies of the samples were characterized with
SEM, as shown in Fig. 2. The CD-1 sample showed homo-
geneous carbon spheres with narrow size distribution and
an average particle size of about 1 μm. The results were
identical to those reported by Shin et al. [19]. Without using
H2SO4, the reaction rate for carbonization was very slow,
leading to a slower growth rate and smaller particle size.
After addition of H2SO4, the CD-2 sample contained some
microspheres with particle sizes larger than 8 μm. It is
obvious that the addition of H2SO4 can accelerate the car-
bonization of the CD, leading to a larger particle size. After
Fig. 2 SEM images of (a) CD-1, (b) CD-2 and (c) CD-3 samples
further sulfonation, although more –SO3H groups may be
anchored to the catalyst, no significant change of morphol-
ogy was observed. It still retained its original microsphere
morphology, suggesting that the sulfonation process did no
damage and that the carbon solid catalyst can be prepared
by this two-step method. Moreover, the BET surface areas
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J Am Oil Chem Soc
(a)
(b)
(a)
C1s
O1s
(c)
(d)
1384
1620
628
1037
S2p
3401
1202
1720
1157
4000
3000
2000
1000
900
600
300
0
Wavenumber (cm-1)
Binding Energy (eV)
Fig. 3 FT-IR spectra of the catalyst: a CD-1, b CD-2 and c CD-3;
and the recycled catalyst after five runs (d)
(b)
S2p
of the CD-1, CD-2 and CD-3 samples were determined to
be 38.2, 8.0 and 5.6 m2/g, which are in agreement with the
results observed from SEM.
FT–IR spectra of the CD-1, CD-2, CD-3 and recycled
(CD-3) catalyst after five runs in Fig. 3a captures bands
at 1620 and 1384 cm−1, confirming the structure of poly-
cylic aromatic carbon sheets (owing to their assignment to
C=C stretching in a carbon matrix) and their good agree-
ment with the XRD results. Additionally, Fig. 3c highlights
the absorption bands at 1037 and 1157 cm−1. The bands’
assignment to the –SO3H groups and the ascription to S=O
vibration [14, 15, 18] of the peak at 1037 cm−1 indicate the
presence of –SO3H groups on the catalyst, suggesting that
the –SO3H groups can be introduced into the carbon frame-
work. Moreover, the O–H stretching of the phenolic groups
contributed to the strong peak at 3401 cm−1. The presence
of –COOH functional groups was confirmed by bands
at 1202 and 1720 cm−1, representing the C–O and C=O
stretching in the carboxyl. The levels of the groups were
determined by a combination of titration and elemental
analysis. The titration results show that the concentrations
of the –OH and –COOH functional groups on CD-1, CD-2
and CD-3 were about 0.012, 0.380 and 0.600 mmol/g,
respectively. The results from elemental analysis indicated
that the concentrations of S in CD-1, CD-2 and CD-3 sam-
ples were about 0.047, 0.085 and 0.860 mmol/g, respec-
tively. The results were consistent with FT–IR analysis.
Through the two-step process, a high density of –SO3H
functional groups was successfully introduced onto the
catalyst derived from β-CD. The process also demonstrated
the superiority of using β-CD as a precursor.
175
170
165
Binding Energy (eV)
Fig. 4 Overall (a) and S2p (b) XPS spectra of the CD-3 catalyst
the only peak emerged at 186.0 eV, corresponding to the
bonded –SO3H groups rather than any other sulphur moi-
ety when the S2p region of the catalyst is taken by a narrow
scan (Fig. 4b).
The above characterizations suggested that the –SO3H
groups can be effectively incorporated into the framework
of the catalyst derived from β-CD by this two-step process.
Catalytic Activity
The catalytic activity was first investigated in oleic acid
esterification with methanol using 5 % carbon solid acid
catalyst at different temperatures. Figure 5a shows the cata-
lytic performance of the carbon-based catalyst compared to
a well-known solid acid catalyst, Amberlyst-15. The CD-1
and CD-2 catalysts showed lower catalytic activity, owing
to the lower density of their acid groups. The CD-3 showed
much higher catalytic activity for esterification, especially
The XPS analysis further confirmed that only –SO3H
functional groups are present on the CD-3 catalyst surface.
Only the elements of C, S and O were found (Fig. 4a) and
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J Am Oil Chem Soc
100
80
60
40
20
0
accessibility of reactants to the –SO3H groups and more
importantly, to the activity-promoting hydrophilic –COOH
and –OH groups [12]. The high catalytic activity of the –
SO3H, –COOH and phenolic –OH groups could possibly
be attributed to the strong affinity of the hydrophilic por-
tions of the reactants with the neutral –OH groups on the
surface [21], favoring catalyst dispersion in methanol and
resulting in high catalytic activity.
The CD-3 catalyst was also evaluated by transesterifi-
cation with triolein. This reaction showed lower catalytic
performance as compared to the catalytic activity observed
during esterification of oleic acid, as shown in Fig. 5b. On
the oil–methanol interface, the solid-acid catalyst always
showed lower activity during transesterification, owing to
lower accessibility of oil and methanol to the acid cata-
lyst [22]. It is reported that the carbon solid acid catalyst
showed comparable yields of methyl oleate under the same
reaction conditions [13], confirming the high catalytic
activity of the CD-3 catalyst. Considering the lower yield
of methyl oleate, a higher reaction pressure was adopted to
accelerate the reaction rate. Thus, transesterification of tri-
olein in an autoclave maintained at a reaction temperature
of 80 °C was performed, as seen in Fig. 5b. A high methyl
oleate yield (90 %) was obtained after 8 h of reaction time
with 5 wt.% catalyst loading, demonstrating a high level of
catalytic activity sufficient for biodiesel production.
(a)
CD-1 80 C
CD-2 80 C
CD-3 60 C
CD-3 70 C
CD-3 80 C
Amberlyst-15 80 C
0
2
4
6
8
10
12
Reaction time (h)
100
80
60
40
20
0
(b)
Atmosphere
Autoclave
Biodiesel Production from High Free Fatty Acid
Containing Oil
0
2
4
6
8
10
12
Reaction time (h)
Utilization of lower-cost high free fatty acid-contain-
ing feedstocks, such as animal fats, inedible oils, waste
food oils and byproducts of vegetable oil refining, is one
way to decrease production costs. Considering its supe-
rior catalytic performance, the CD-3 catalyst was further
investigated for conversion of mixed oils with high FFAs
(50.2 wt.% FFAs). In mixed oils, esterification proceeded
with ease. It is commonly known that transesterification
is a three step reaction. The first step involves the reaction
between one fatty acid from a triglyceride and one mole-
cule of methanol, leading to formation of a diglyceride and
one methyl ester. In the second step, one of the remaining
fatty acids on the diglyceride reacts with a second mole-
cule of methanol to produce a monoglyceride and another
methyl ester. In the third reaction step, the reaction of the
remaining fatty acid on the monoglyceride with a third
molecule of methanol takes place, leading to glycerin and
a third methyl ester. In addition, each of these are revers-
ible reaction and the reaction rate for transesterification of
triglycerides when using heterogeneous acid catalysts is
slow. For these reasons, an excess of methanol is used to
drive the reaction to the right, maximizing the yield of fatty
acid methyl esters [23]. Thus, higher production rates for
Fig. 5 Esterification of oleic acid (a) (with CD-1, CD-2, CD-3 at
60, 70, 80 °C and amberlyst-15 catalysts) and transesterification of
triolein (b) [reaction at atmosphere and reaction in autoclave (high
presure)]. (reaction conditions: atmosphere: oleic acid: 10 mmol,
methanol: 100 mmol, catalyst: 5 %, reaction temperature: 333–358 K,
reaction time: 12 h. Autoclave: oleic acid: 10 mmol; methanol:
300 mmol; catalyst: 5 %; reaction temperature: 368 K; pressure: less
than 2 MPa)
at the initial stage. Furthermore, higher yields of methyl
oleate can be achieved with higher reaction temperatures,
indicating that higher temperatures increase esterification
rates. This is because the higher temperature increases oil–
solvent miscibility in both phases [20]. Moreover, the cata-
lytic activity of the CD-3 is much higher than that of the
commonly used Amberlyst-15 solid acid catalyst, which
is an ion exchange resin bearing macropores. Although
Amberlyst-15 has a high acid density (about 5.3 mmol/g),
its catalytic activity is significantly reduced with large
molecules such as oleic acid, as they cannot penetrate the
poorly swelling network in which most acid sites resided.
Compared with Amberlyst-15, the carbon solid acid cata-
lyst possesses a higher density of –SO3H groups and better
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J Am Oil Chem Soc
100
100
80
60
40
20
0
Glycerol
Methyl ester
80
60
40
20
0
1
2
3
4
5
6
Runs
0
2
4
6
8
10
12
Fig. 7 Regenerability of the CD-3 catalyst in methyl oleate forma-
tion by oleic acid esterification with methanol. The recovered catalyst
was reused after washing with methanol (white) or H2SO4 (black) and
dried at 403 K) (Reaction conditions: oleic acid: 10 mmol; methanol:
100 mmol; catalyst: 5 %; reaction temperature: 358 K; reaction time:
12 h)
Reaction time (h)
Fig. 6 Methyl ester and glycerol yield versus time from mixed
oil containing 50.2 wt.% FFAs using CD-3 solid acid catalysts.
(Reaction conditions: atmosphere: triolein (50.2 wt.% oleic acid):
10 mmol; methanol: 300 mmol; catalyst: 5 %; reaction temperature:
358 K; reaction time: 12 h)
factor is the loss of –SO3H groups from polycylic aromatic
carbon sheets during the washing process. According to
the XRD results, the catalyst was mainly comprised of
polycyclic aromatic carbon sheets, leading to a relatively
hydrophobic catalyst surface, and as the water layer sel-
dom forms on its surface, the more hydrophobic fatty acids
or glycerides have greater access to the catalyst surface.
Therefore, the methanol washing process may cause the
deactivation of the catalyst, which was previously reported
by Mo et al. [24].
An improvement in regenerability reported by Chen
et al. [13] is made through cleaning the used catalyst with
98 % H2SO4 followed by drying. During subsequent esteri-
fication reactions, the regenerated catalyst demonstrated a
high level of stability, as shown in Fig. 7 (black). This is
confirmed by FI–IR characterization and elemental analy-
sis. After five runs, the FI-IR spectrum of the spent cata-
lyst showed no decrease in peak intensity at the band of
1037 cm−1 in Fig. 2d. Obviously, the 98 % H2SO4 helped
anchor the –SO3H groups on the catalyst while it was
recovering the sulfur, which is shown in the element analy-
sis. However, the mechanism of catalyst regeneration by
concentrated sulfuric acid is still unknown and should be
further studied.
biodiesel produced with beta-CD-derived carbon-based cat-
alysts was achieved with a high methanol-to-oil molar ratio
of 30:1. Yields of methyl ester and glycerol versus reaction
time are shown in Fig. 6. It can be seen that, for the reaction
containing both triglyceride and FFA, the catalyst showed
high activity. The yield of methyl ester can reach about
80 % after 12 h of reaction time, which is slightly lower
than the reported results of Zong et al. [16]. This may be
due to the higher FFA content (50.2 wt.%) in our raw mate-
rial versus the rapeseed oil (about 27.8 wt.% FFA) used by
Zong, who reported that higher FFA in the raw material can
suppress transesterification [18]. Moreover, water produced
by esterification pushes the equilibrium toward the left.
Stability of the Catalyst
The stability of the catalyst is a key parameter in evaluat-
ing its efficiency. In order to examine the regenerability of
the carbon solid acid catalyst, the used CD-3 catalyst was
washed with methanol and hot water prior to reuse. The
catalytic activity decreased to 79 % of its original conver-
sion rate after six runs, as shown in Fig. 7 (white), which
shows the deactivation of the catalyst after multiple cycles.
It has been reported that the deactivation of carbon solid
acid catalyst may be governed by two factors. One factor
is the formation of water during the reaction, resulting in a
water layer on the hydrophilic surface of the carbon-based
catalyst, preventing the access of the relatively hydropho-
bic substrate to the hydrophilic functionalities. The second
Conclusions
A carbon solid acid catalyst produced from β-CD via
incomplete hydrothermal carbonization followed by sul-
fonation was demonstrated to be an efficient catalyst for
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J Am Oil Chem Soc
10. Soldi RA, Oliveira ARS, Ramos LP, Cesar-Oliveira MAF (2009)
Soybean oil and beef tallow alcoholysis by acid heterogeneous
catalysis. Appl Catal A-Gen 361:42–48
11. Caetano CS, Guerreiro L, Fonseca IM, Ramos AM, Vital J,
Castanheiro JE (2009) Esterification of fatty acids to biodiesel
over polymers with sulfonic acid groups. Appl Catal A-Gen
359:41–46
12. Hara M (2010) Biodiesel Production by amorphous carbon bear-
ing So(3)H, COOH and phenolic OH groups, a solid bronsted
acid catalyst. Top Catal 53:805–810
13. Chen G, Fang BS (2011) Preparation of solid acid catalyst from
glucose-starch mixture for biodiesel production. Bioresour Tech-
nol 102:2635–2640
biodiesel production. The catalytic activity of the carbon-
based catalyst was high for esterification of oleic acid to
ester. More importantly, the catalyst showed good catalytic
performance for biodiesel conversion from high-FFA oil by
simultaneous esterification and transesterification. Addi-
tionally, this catalyst also showed excellent regenerability
and stability, demonstrating further its potential for use
in the production of biodiesel. Therefore, the CD-derived
catalysts may be potentially applicable as heterogeneous
strong acid catalysts.
14. Devi B, Gangadhar KN, Prasad PSS, Jagannadh B, Prasad RBN
(2009) A glycerol-based carbon catalyst for the preparation of
biodiesel. Chem Sus Chem 2:617–620
15. Liang XZ, Yang JG (2009) Synthesis of a novel carbon based
strong acid catalyst through hydrothermal carbonization. Catal
Lett 132:460–463
16. Lou WY, Zong MH, Duan ZQ (2008) Efficient production of
biodiesel from high free fatty acid-containing waste oils using
various carbohydrate-derived solid acid catalysts. Bioresour
Technol 99:8752–8758
17. Okamura M, Takagaki A, Toda M, Kondo JN, Domen K, Tat-
sumi T, Hara M, Hayashi S (2006) Acid-catalyzed reactions on
flexible polycyclic aromatic carbon in amorphous carbon. Chem
Mat 18:3039–3045
18. Zong MH, Duan ZQ, Lou WY, Smith TJ, Wu H (2007) Prepara-
tion of a sugar catalyst and its use for highly efficient production
of biodiesel. Green Chem 9:434–437
19. Shin Y, Wang LQ, Bae IT, Arey BW, Exarhos GJ (2008) Hydro-
thermal syntheses of colloidal carbon spheres from cyclodex-
trins. J Phys Chem C 112:14236–14240
20. da Silva CAS, Sanaiotti G, Lanza M, Follegatti-Romero LA,
Meirelles AJA, Batista EAC (2010) Mutual solubility for sys-
tems composed of vegetable oil plus ethanol plus water at differ-
ent temperatures. J Chem Eng Data 55:440–447
21. Geng L, Wang Y, Yu G, Zhu YX (2011) Efficient carbon-based
solid acid catalysts for the esterification of oleic acid. Catal
Comm 13:26–30
Acknowledgments The authors are grateful to the support from
Natural Science Foundation of Guangdong (No. S2011040001667),
National Natural Science Foundation of China (No. 21306061),
National High Technology Research and Development Program 863
(No. 2009AA064401) and Fundamental Research Funds for the Cen-
tral Universities (No. 11612328).
References
1. Steinfeld JI (2006) Energy futures and green chemistry: compet-
ing for carbon. Sust Sci 1:123–126
2. Ma FR, Hanna MA (1999) Biodiesel production: a review.
Bioresour Technol 70:1–15
3. Meher LC, Sagar DV, Naik SN (2006) Technical aspects of bio-
diesel production by transesterification—a review. Renew Sust
Energ Rev 10:248–268
4. Lotero E, Liu YJ, Lopez DE, Suwannakarn K, Bruce DA, Good-
win JG (2005) Synthesis of biodiesel via acid catalysis. Ind Eng
Chem Res 44:5353–5363
5. Okuhara T (2002) Water-tolerant solid acid catalysts. Chem Rev
102:3641–3665
6. Van Rhijn WM, De Vos DE, Sels BF, Bossaert WD, Jacobs PA
(1998) Sulfonic acid functionalised ordered mesoporous mate-
rials as catalysts for condensation and esterification reactions.
Chem Commun (3):317–318
7. Harmer MA, Farneth WE, Sun Q (1998) Towards the sulfuric
acid of solids. Adv Mater 10:1255–1257
8. Yadav GD, Nair JJ (1999) Sulfated zirconia and its modified ver-
sions as promising catalysts for industrial processes. Micropo-
rous Mesoporous Mat 33:1–48
22. Furukawa S, Uehara Y, Yamasaki H (2010) Variables affecting
the reactivity of acid-catalyzed transesterification of vegetable
oil with methanol. Bioresour Technol 101:3325–3332
23. Furuta S, Matsuhashi H, Arata K (2004) Biodiesel fuel produc-
tion with solid superacid catalysis in fixed bed reactor under
atmospheric pressure. Catal Commun 5:721–723
24. Mo X, Lopez DE, Suwannakarn K, Liu Y, Lotero E, Goodwin
JG, Lu CQ (2008) Activation and deactivation characteristics of
sulfonated carbon catalysts. J Catal 254:332–338
9. Harmer MA, Sun Q, Vega AJ, Farneth WE, Heidekum A, Hoe-
lderich WF (2000) Nafion resin-silica nanocomposite solid
acid catalysts. Microstructure-processing-property correlations.
Green Chem 2:7–14
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