Production of biodiesel through esterification of palmitic acid using 12-tungestoposphoric acid supported on nanocavity of aluminium incorporated mesoporous SBA-15

Article abstract of DOI:10.1134/S1070427215040217

The main aim of this research is to develop efficient and environmentally benign heterogeneous catalysts for biodiesel production. For this purpose, H₃PW₁₂O₄₀ (PW₁₂) supported on Al-functionalized SBA-15 mesoporous molecular sieve featuring a well-defined three-dimensional (3D) mesoporosity were studied, and the prepared catalyst (PW₁₂/Al-SBA-15) was tested for the esterification process of palmitic acid to produce methyl palmitate as a kind of biodiesel. The effects of the methanol/oil ratio, catalyst amounts, reaction time, and reaction temperature on the conversion are also reported in this paper. More importantly, by using a 35 wt % of PW₁₂/Al-SBA-15 with methanol/oil molar ratio of 20: 1 at reflux of methanol, the oil conversion of 98% after 8 h of reaction, could be achieved over the solid catalyst for at least 6 cycles under mild conditions.

Full text of DOI:10.1134/S1070427215040217

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2015, Vol. 88, No. 4, pp. 676−681. © Pleiades Publishing, Ltd., 2015.
VARIOUS
TECHNOLOGIES
Production of Biodiesel through Esterification of Palmitic Acid
Using 12-Tungestoposphoric Acid Supported on Nanocavity
of Aluminium Incorporated Mesoporous SBA-151
*
Razieh Fazaeli and Hamid Aliyan
Department of Chemistry, Shahreza Branch, Islamic Azad University, 86145-311, Iran
*
e-mail: fazaeli@iaush.ac.ir
Received May 5, 2015
Abstract—The main aim of this research is to develop efficient and environmentally benign heterogeneous
catalysts for biodiesel production. For this purpose, H PW O (PW ) supported onAl–functionalized SBA-15
3
12 40
12
mesoporous molecular sieve featuring a well-defined three-dimensional (3D) mesoporosity were studied, and
the prepared catalyst (PW /Al–SBA-15) was tested for the esterification process of palmitic acid to produce
1
2
methyl palmitate as a kind of biodiesel. The effects of the methanol/oil ratio, catalyst amounts, reaction time,
and reaction temperature on the conversion are also reported in this paper. More importantly, by using a 35 wt %
of PW /Al–SBA-15 with methanol/oil molar ratio of 20 : 1 at reflux of methanol, the oil conversion of 98% after
1
2
8
h of reaction, could be achieved over the solid catalyst for at least 6 cycles under mild conditions.
DOI: 10.1134/S1070427215040217
INTRODUCTION
thicker pore walls, and higher hydrothermal stability. For
these reasons, the discovery of SBA-15 provides a po-
tential for the material as versatile catalysts and catalyst
support for conversion of large molecules [12]. Since pure
siliceous SBA-15 materials lack acidity, active centers
must be introduced into their framework (mesoporous
wall). Generally, incorporation of heteroatoms, such asAl
into microporous zeolites will introduce a charge imbal-
ance in the framework which is balanced by protons, thus
generating bridging hydroxyl groups (SiOHAl, Bronsted
acid sites) on these materials [13].
Biodiesel is an environmentally sustainable fuel
composed of alkyl esters of long-chain fatty acids. It
can be made from vegetable oils, animal fat, and waste
oils from the food industry [1–5]. Currently, the most
common process used for biodiesel production is through
esterification of free fatty acids (FFAs) or catalytic
transesterification of triglyceride with alcohols in the
presence of a suitable catalyst [6–8].
Different heterogeneous base catalysts have been
investigated for the production of biodiesel [9]. Some
of these solid catalysts include alkali-metal and alkaline
earth metal carbonates and oxides [5], lithium base ceram-
ics [6], transition metal oxides [7], basic ion-exchange
resins [8], layered double hydroxides [9] and zeolites [10].
In continuation of our work on the catalytic properties
of heteropoly acids (HPAs) [14,15], we focus our attention
on the influence of PW /Al–SBA-15 as a catalyst in
the esterification reaction of palmitic acid, where the
parameters of temperature, time and reagent: catalyst
molar ratios were examined.
1
2
In 1998, Zhao et al. synthesized a new type of meso-
porous material SBA-15 with uniform two-dimensional
hexagonal structure [11]. Compared with microporous
zeolites, this material possesses significantly larger pores,
EXPERIMENTAL
Synthesis of unmodified Al–SBA-15. Al–SBA-15
materials were prepared according to the direct synthesis
procedure reported by Yue et al. [16] using aluminium
1
The text was submitted by the authors in English.
6
76

PRODUCTION OF BIODIESEL THROUGH ESTERIFICATION
677
isopropoxide as aluminium source and working with
Si/Al molar ratios equal to 60.
Synthesis of 35% PW /Al–SBA-15. The supported
(a)
T, %
PW /A1–SBA-15
12
1
2
A1–SBA-15
PW12 catalysts were prepared using the method of
incipient wetness. In a typical process, a 560 mg portion of
PW was dissolved in deionized water and impregnated
12
drop wise into 1960 mg support (Al–SBA-15) in 25 mL
methanol, with constant agitation. The resulting pastes
were dried for 4 h at 110°C and calcined for 4 h at 350°C.
4
000
3000
2000
1000
360
–
1
Wavenumber, cm
Esterification procedures. The activity of the catalyst
was examined through esterification of palmitic acid with
methanol. All the esterification runs were carried out in
a 250 mL round-bottom flask equipped with a reflux
condenser and a magnetic stirrer. In a typical experiment,
(b)
PW /A1–SBA-15
0
.15 g of palmitic acid was introduced into the flask, and
12
then the temperature was increased to 95–100°C. After
the palmitic acid had melted, 5 g of warm methanol and
0
.2 g of 35 wt % PW /SBA-15 catalyst were quickly
12
added and stirred rapidly by a magnetic bar at 600 rpm.
The weight ratio of palmitic acid to methanol was
: 20). The temperature of this liquid-phase esterification
reaction was kept at 100°C for 8 h. Sample solutions were
collected periodically from the flask during the reaction,
and the concentration of the produced methyl palmitate
was analyzed using a gas chromatograph. Ar was used
as the carrier gas.
(
1
A1–SBA-15
0
.7
1
2
2
3
4
θ, deg
Fig. 1. (a) FTIR spectrum, (b) XRD patterns of Al–SBA-15
RESULTS AND DISCUSSION
and PW /Al–SBA-15.
1
2
Catalysts characterization. Figure 1a presents the
–
1
Figure 1b shows XRD patterns of parent Al–SBA-
5 within the 2θ range of 0.7–5. Small-angle X-ray
diffraction patterns of parrent Al–SBA-15 materials
represent intensive well-resolved peaks, which can be
indexed as the (100), (110), and (200) reflections of a
FTIR spectra in the skeletal region of 4000–400 cm for
theAl–SBA-15 and PW /Al–SBA-15 materials. For both
1
12
–1
–1
of samples, a band at 3429 cm and 1636 cm assigned to
the O–H stretching and bending vibration of physisorbed
water [17]. Besides, the primary infrared bands related
to the molecular sieves framework were the asymmetric
2
-D hexagonal lattice with p6mm symmetry [20]. PW12
–
1
introduction leads to a significant decrease in the intensity
of the reflections. All patterns in the figures show a main
diffraction peak due to d(100) reflection of SBA-15
hexagonal space group p6mm.At higher 2θ angles, d(110)
and d(200) reflections are not observed, indicating that
the adopted synthesis procedure leads to less ordered
materials than traditional Al–SBA-15 [21].
and symmetric stretching of Si–O–Al at 1080 cm and
–1
–1
8
03 cm , and the absorption peak at 463 cm could be
ascribed to the Si–O–Al bending stretching vibration [18].
Both of spectra of Al–SBA-15 and PW /Al–SBA-15
1
2
–
1
exhibit intensive absorption bands at 1080 and 803 cm ,
which arise from the silica host matrix [19]. The FT-IR
spectra of the PW /Al–SBA-15 indicate that most of
1
2
the characteristic bands of the parent Keggin structure,
TEM images of selected PW /Al–SBA-15 are
1
2
which could be found in the PW fingerprint region
presented in Fig. 2.Awell-resolved contrast characteristic
of certain silica mesopore structure symmetry is still
observed, which is an indication for the preservation of
the long ordered arrangement of the channels in the silica
1
2
–1
(1250–500 cm ), are not shown or appeared in the same
assignable position of the bands corresponding to the
ordered mesoporous silica host materials.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 4 2015

678
RAZIEH FAZAELI, HAMID ALIYAN
2
0 nm
2
0 nm
Fig. 2. TEM images of PW /Al–SBA-15.
12
host matrix after the aluminium deposition. The places
with darker contrast could be assigned to the presence of
PW particles with different dispersion. The small dark
PW /Al–SBA-15 showed very similar isotherm pattern
12
and pore size distribution compared to bare Al–SBA-15,
indicating that the mesopore structure of mesoporous
silica was still maintained even after the surface
modification step and the subsequent immobilization
step of PW . Physical properties of parent Al–SBA-
12
spots in the images could be ascribed to PW particles,
1
2
probably located into the support channels. The larger
dark areas over the channels most likely correspond to
PW agglomerates on the external surface.
1
2
12
15, PW (bulk) and modified Al–SBA-15 are listed in
12
The content of PW12 on the Al–SBA-15 supports,
which was calculated from W content in supported Al–
SBA-15 was determined by neutron activation analysis
Table 1. As expected, the BET surface areas and total
pore volumes of bareAl–SBA-15 are decreased after the
functionalization with PW12. These changes reflect that
part of the mesopore volume in the Al-SBA-15 matrix is
filled with PW .
(NAA). The good distribution of elements analyzed is in
agreement with the neutron activation analysis (NAA) and
ICP results with deviation in the range of ±0.09.
1
2
Catalytic performance. Effect of molar ratio of
alcohol to acid on the esterification reaction. The
esterification is a reversible reaction so that excessive
alcohol was usually added in order to improve the
conversion. In the present work, the effect of different
molar ratios of palmitic acid to methanol (12 : 1–24 : 1)
was studied (Fig. 4a). The decrease of conversion
was observed when the molar ratio exceeded 20 : 1. It
N adsorption–desorption isotherms. Figure 3
2
shows the N adsorption–desorption isotherms and pore
2
size distributions of Al–SBA-15 and PW /Al–SBA-
1
2
1
5. All the samples exhibited typical IV type isotherms
and H1 type hysteresis loops at high relative pressures
according to the IUPAC nomenclature [22], which are the
typical characteristics of mesoporous materials [23]. The
The texture parameters of bare Al–SBA-15 and PW /Al–SBA-15 in comparison with the bulk PW materials
1
2
12
2
–1
3
–1
Entry
Sample
Al–SBA-15
PW12
BET, surface area, m g
Pore volume, cm g
Pore diameter, nm
1
2
3
1041
6
1.2
–
4.6
–
PW /Al–SBA-15
75
0.71
3.61
1
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 4 2015

PRODUCTION OF BIODIESEL THROUGH ESTERIFICATION
679
1
000
A1–SBA-15 ∆▲
PW /A1–SBA-15
8
6
4
2
00
00
00
00
0
A1–SBA-15 ∆▲
1
2
PW /A1–SBA-15
1
2
0
10
Pore size, nm
20
0
.0
0.2
0.4
0.6
0.8
1.0
p/p0
Fig. 3. (a) N -Adsorption-desorption isotherms and (b) pore size distributions calculated by the BJH method of Al–SBA-15 and
2
PW /Al–SBA-15.
1
2
(a)
(c)
(b)
Fig. 4. Effect of (a) molar ratio of methanol to oil on the esterification reaction; (b) catalyst loading on the esterification reaction and
(c) temperature on the esterification reaction.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 4 2015

680
RAZIEH FAZAELI, HAMID ALIYAN
reaction is endothermic in nature, it favors a higher
reaction temperature for biodiesel synthesis [27]. When
the reaction temperature is increased to above 100°C, the
biodiesel yield (%) decreases. There was a chance of loss
of alcohol and increasing of darkness color of the product
at higher temperature [28].
Recycling of the catalyst. The catalyst reusability is
an important feature for determining its commercial
viability. The catalyst was recycled to test its activity
as well as stability. The catalyst was separated from the
reaction mixture by filtration, washed with methanol
until the filtrate is free from the acid, e.g., unreacted
palmitic acid if any, followed by washing with double
distilled water and then dried at 110°C and calcined at
Run no.
Fig. 5. Reusability study after five reaction cycles for 35 wt %
PW /Al–SBA-15 catalyat, reaction conditions: catalyst amount
g, methanol/oil molar ratio 20 : 1, reaction time 8 h, reaction
1
2
2
3
50°C. No appreciable change in activity was noticed
temperature 100°C.
after four cycles (Fig. 5).
continues to decrease upon the ratio is further increased
to 24 : 1. It is speculated that the further excess methanol
molecules may flood the active sites of the catalyst which
hinder the protonation of palmitic acid at the active sites
CONCLUSIONS
The performance of H PW O -supported on
3
12 40
aluminum-mesoporous silica (Al–SBA-15) as catalyst
prepared by impregnation method in esterification
of palmitic acid is outstanding. It demonstrates high
catalytic activity and long durability in esterification of
palmitic acid, in which the fatty acid methyl ester yield
reached 98% consecutively for 4 cycles even under mild
conditions (methanol/palmitic acid = 20 : 1, 35 wt % of
catalyst, 100°C, 8 h). From the results of this study, it is
[3, 24 ].
Effect of catalyst dosage. Another important parameter
that affects the ester yield is the catalyst dosage. In a
screening experiment, different PW12 loading (final
PW content of 25–45 wt %) were used for the catalyst
12
preparation, and the esterification reaction was carried
out over the as-prepared solid catalysts. Based on
the experimental results, the 35% PW /Al–SBA-15
proposed that PW /Al–SBA-15 is a suitable catalyst for
12
1
2
the production of methyl palmitate by the esterification of
palmitic acid owing to the high acid site density.
(
Fig. 4b) was found to be the most active catalyst for
the esterification reaction. The increase in the reaction
rate (from 25 to 35 wt %) was due to the increase in
the total number of acive sites available for the reaction
with increasing catalyst loading [25]. The decrease in the
reaction rate (from 35 to 45 wt %) was perhaps attributed
to the blocking of the active sites due to formation of
multilayer on the support, and the multilayer formation
can hinder the reactant molecules to react with the active
sites. Thus, there is decrease in the conversion [26].
ACKNOWLEDGMENTS
We gratefully thank Shahreza Branch, Islamic Azad
University, for financial support.
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