Biodiesel production via esterification of oleic acid catalyzed by MnO2@Mn(btc) as a novel and heterogeneous catalyst

Article abstract of DOI:10.1002/jccs.201800288

The main objective of this study is to develop efficient and environmentally benign heterogeneous catalysts for biodiesel production. For this purpose, a heterogeneous MnO₂@Mn(btc) catalyst was prepared by the solvothermal method, and the prepared catalyst was tested for the esterification of oleic acid. Various techniques such as X-ray diffraction, scanning and transmission electron microscopy, Brunauer–Emmett–Teller (BET) method, infrared spectroscopy, thermogravimetry, and NH₃-TPD (temperature programmed desorption) analysis were employed for the characterization of the solid catalyst. The solid catalyst with MnO₂@Mn(btc) loading of 15% showed high catalytic activity and long durability in the esterification of oleic acid, in which the fatty acid methyl ester yield reached 98% consecutively for at least five cycles under mild conditions.

Full text of DOI:10.1002/jccs.201800288

Received: 24 July 2018
Revised: 30 November 2018
Accepted: 18 December 2018
DOI: 10.1002/jccs.201800288
A R T I C L E
Biodiesel production via esterification of oleic acid catalyzed
by MnO2@Mn(btc) as a novel and heterogeneous catalyst
Elham Amouhadi | Razieh Fazaeli | Hamid Aliyan
Department of Chemistry, Shahreza Branch,
The main objective of this study is to develop efficient and environmentally benign
Islamic Azad University, Shahreza, Isfahan, Iran
heterogeneous catalysts for biodiesel production. For this purpose, a heterogeneous
Correspondence
Razieh Fazaeli, Department of Chemistry,
MnO2@Mn(btc) catalyst was prepared by the solvothermal method, and the pre-
pared catalyst was tested for the esterification of oleic acid. Various techniques
such as X-ray diffraction, scanning and transmission electron microscopy,
Shahreza Branch, Islamic Azad University,
86145-311, Shahreza, Isfahan, Iran.
Email: raziehfazaeli@yahoo.com
Brunauer–Emmett–Teller (BET) method, infrared spectroscopy, thermogravimetry,
Funding information
Islamic Azad University, Shahreza Branch
and NH3-TPD (temperature programmed desorption) analysis were employed for
the characterization of the solid catalyst. The solid catalyst with MnO2@Mn(btc)
loading of 15% showed high catalytic activity and long durability in the esterifica-
tion of oleic acid, in which the fatty acid methyl ester yield reached 98% consecu-
tively for at least five cycles under mild conditions.
KEYWORDS
biodiesel, esterification, heterogeneous catalyst, metal-organic frameworks
(MOFs), oleic acid
strong acidity,[9] waste silicone solid base,[10] fe3o4@gly,[11]
LiFe5O8-LiFeO2,[12] Li2TiO3,[13] or Li4SiO4.[14]
1
| INTRODUCTION
Methyl and ethyl esters derived from vegetable oils or ani-
mal fat, known as biodiesel, have acceptable ability as an
alternative to diesel fuel. Biodiesel consisting of long-chain
fatty acid methyl esters (FAMEs) has appeared as a usable
alternative fuel with the benefits of non-toxicity, renewabil-
ity, biodegradability, and low emission profiles.[1,2] The con-
ventional method of producing biodiesel from vegetable oils
involves the use of alkali catalysts, which, in the presence of
free fatty acids (FFAs), form soap, which is undesirable, as
it consumes the catalyst, makes separation of products more
complicated, and decreases the biodiesel yield. Instead of
using an alkali catalyst, an acid catalyst can be employed to
convert the FFAs into biodiesel through the esterification
reaction.[3–5] In recent years, many surveys on catalysts for
the esterification or transesterification step have indicated
the use of sulfated alumina,[6] carbon-based solid acid,[7]
supported heteropolyacids,[8] cation-exchange resins with
These catalysts can replace sulfuric acid and thereby
solve process problems such as environmental pollution and
tool corrosion. However, the synthesis of these catalysts is
quite complicated, they are hard to recycle, and their produc-
tion cost is high. Therefore, it is vital to develop efficient,
environmentally friendly, and novel catalysts for the synthe-
sis of biodiesel by esterification.[15]
Metal-organic frameworks (MOFs) are a novel class of
inorganic–organic hybrid materials constructed from inor-
ganic metal nodes and organic linkers. Their structurally
sequenced and molecularly tunable aspects make them a per-
fect framework to assimilate distinct functional moieties.
The integration between various individual doped species
will provide such composite materials with excellent poten-
tial applications, notably in the catalytic field. High surface
areas, controllable pore sizes, and tunable pore environments
of MOFs would promote the MOF supports to trap different
nanoparticles (NPs).[16–20] Moreover, the crystalline porous
© 2019 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2019;1–6.
http://www.jccs.wiley-vch.de
1

2
AMOUHADI ET AL.
structure, together with heteroatom donors on MOFs, would
effectively limit the accumulation and migration of small,
active catalytic NPs in the solid state, thereby making the
NPs involved in NPs@MOFs catalysts to be highly active
and reusable.[21]
proved by the absence of the absorption bands in the region
1,680–1,800 cm−1 [28]
.
The X-ray diffraction (XRD) patterns of hollow MnO2,
Mn(btc), and MnO2@Mn(btc) are displayed in Figure 2.
The similarity of the diffraction peaks of Mn(btc) and
MnO2@Mn(btc) suggests that the loading of the MnO2 spe-
cies has hardly changed the framework of Mn(btc). Because
of relatively low concentration and the good dispersion of
the MnO2 species on Mn(btc), the characteristic diffraction
peaks attributed to MnO2 on the catalysts are not observed.
The scanning and transmission electron microscopy
(SEM and TEM) images of the MOF-derived MnO2@Mn
(btc) particles, shown in Figure 3, suggest they are well-
MnO2 with the benefits of environmental friendliness,
ideal cycle stability, natural abundance, low cost, and effi-
cient charge–discharge characteristics has turned out to be a
promising material for catalysts. Wang et al. expanded the
synthesis of mesoporous MnOx for catalytic oxidation
removal of low-concentration HCHO.[22] The MnOx/HZSM-
5 system served as catalyst for the oxidation of toluene,[23]
and decontamination of sulfur mustard was reported by
MnO2-ZnO.[24] The aim of this work was to examine solid
MnO2@Mn(btc) catalysts’ use in biodiesel production and
evaluate the optimum values of the ethanol/oil ratio, catalyst
amounts, reaction time, and reaction temperature. Further-
more, the MnO2@Mn(btc) catalyst was highly active and
air-insensitive and could be reused for at least 10 cycles
without loss of activity.
12000
Hollow MnO2
Mn(btc)
MnO2@Mn(btc)
10000
8000
6000
4000
2
| RESULTS AND DISCUSSION
2000
c
b
a
0
2.1 | Physicochemical characterization
10
20
30
40
50
60
70
2θ(°)
The Fourier transform infrared (FT-IR) spectra of the
Mn(btc) and MnO2@Mn(btc) are shown in Figure 1. The
FIGURE 2 XRD patterns of (a) hollow MnO2, (b) Mn(btc), and
Mn–O stretching vibration appears at 690 cm−1 [25]
.
The
broad band due to the symmetric stretching vibration of
water is at 3,406 cm−1 [26]
The asymmetric and symmetric
stretching vibrations of the bound carboxylic groups
(c) MnO2@Mn(btc)
.
(CO2M) appear at 1,631–1,500 and 1,441–1,372 cm−1
,
respectively.[27] The bands occurring at 853 and 759 cm−1
are clearly related to the stretching and out-of-plane defor-
mation vibrations of the of benzene C–C and C–H groups,
respectively. Complete deprotonation of the btc ligand is
(b)
(a)
4000
3000
2000
1000
Wavenumber (cm-1)
FIGURE 3 (a–e) SEM image with different magnifications. (f) TEM
FIGURE 1 FTIR spectra of (a) Mn(btc) and (b) MnO2@Mn(btc)
image of MnO2@Mn(btc)

AMOUHADI ET AL.
3
shaped rectangular bars with smaller broken particles in the
range 3–16 μm in length, 0.2–2 μm in width, and
150–200 nm in thickness, with a comparatively smooth
surface.
Figure 4 shows the thermal decomposition of the
MnO2@Mn(btc) catalyst precursor. As can be seen from the
thermogravimetry (TG) curves, the TG profile shows two
mass loss events. The initial mass loss of 22.85% accompa-
nied by an endothermic event occurs in the temperature
range 25–240ꢀC and is due to the loss of physically
absorbed water and dimethylformamide (DMF). The second
mass loss of 71.41%, overlapping a broad endothermic DTA
peak over a wide temperature range of 240–665ꢀC, refers
mainly to the thermal decomposition of MnO2@Mn(btc)
into their corresponding metal oxides. Beyond 665ꢀC, there
is almost no mass loss detected in the TG curve. These ther-
mal analysis results suggest that the thermal decomposition
of metal oxide precursors is completed at a temperature
of 665ꢀC.
The Brunauer–Emmett–Teller (BET)-Barrett Joyner
Halenda (BJH) adsorption isotherms are depicted in
Figure 5. The N2 adsorption curves (Figure 5) of
MnO2@Mn(btc) obviously represent type IV isotherms,
which prove that the samples would include both micropo-
rous (diameter < 20 Å) and mesoporous materials, based on
the IUPAC categorization [29]. MnO2@Mn(btc) gives a BET
surface area of 10.867 m2/g and a pore volume of
0.039 cm3/g.
(b) dif.TG [mg/mln]
0.5
0.0
22.85%
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
2.0
1.5
(c) DTA
71.41%
1.0
0.5
0.0
-0.5
-1.0
-1.5
200
200
400
600
400
800
(a) TG [mg]
600
800
Temperature [oC]
FIGURE 5 (a) TG (b) DTG, and (c) DTA analysis of MnO2@Mn(btc)
2.2 | Effects of esterification reaction conditions on the
The NH3 temperature programmed desorption (TPD)
curve of MnO2@Mn(btc) (Figure 6) shows three peaks. The
two peaks at around 414 and 456ꢀC imply the weak acidic
sites and the third peak at around 540ꢀC displays the strong
acidic sites. These strong acidic sites are due to the Lewis
acidity of MnO2 NPs. It should be noted that Mn(btc)
decomposed at about 300ꢀC, so there exists the possibility
that the NH3 adsorption could destroy the structural integrity
of Mn(btc).[30]
catalytic activity of MnO2@Mn(btc)
2.2.1
| Effect of molar ratio between ethanol and oleic acid
The molar ratio of ethanol to oleic acid is one of the signifi-
cant parameters that influence the ester yield. As displayed
in Figure 7, with the other experimental conditions main-
tained constant, the molar ratio of ethanol to oleic acid was
1.0
30
0.0035
540
0.0030
25
20
15
10
5
0.0025
0.0020
0.0015
0.0010
0.0005
0.0000
0.8
0.6
0.4
Ads
0
20
40
60
80
r
p
/nm
0.2
414
456
Ads
Des
0.0
0
200
400
600
800
0.0
0.2
0.4
0.6
0.8
1.0
Temperature (oC)
p/po
FIGURE 4 N2 adsorption–desorption isotherms and (insert) pore size
distributions calculated by the BJH method of Pd@Mn(btc)
FIGURE 6 NH3-TPD spectra of MnO2@Mn(btc) measured between
100 and 900ꢀC

4
AMOUHADI ET AL.
2.2.2
| Effect of catalyst dosage
90
80
70
60
50
Catalyst dosage is another essential parameter that deter-
mines the ester yield. As illustrated in Figure 8, the
MnO2@Mn(btc) amount is varied from 1% to 5% w/w of
oleic acid. The results demonstrate that when the catalyst
dosage is increased from 1 to 3 wt%, the FAME yield
increases from 82% to 100%. It may be that there are not suf-
ficient active sites for the reaction at low catalyst dosages
and extra catalyst is required. However, upon further
increase of the catalyst dosage from 3 to 5 wt%, no enhance-
ment in the FAME yield is detected. This means 3 wt% of
the catalyst is optimal for this reaction.
2
4
6
8
10
12
14
16
18
20
22
Time (min)
2.2.3
| Effect of reaction temperature
FIGURE 7 Molar ratio experiments run at 100ꢀC and catalyst amount of
The effect of reaction temperature on the FAME yield in
MnO2@Mn(btc)-catalyzed esterification of oleic acid was
examined, and the results are shown in Figure 9. The reac-
tion temperatures considered were 80, 100, and 120ꢀC. It
can be seen that the activity of MnO2@Mn(btc) is nearly the
same at 100 and 120ꢀC. One possible cause for the reduction
in activity at 80ꢀC may be the accumulation of the water
molecules generated on the surface that block the active
sites. It is seen that a temperature higher than the boiling
point of water may help decrease the chance of the as-
formed water molecules remaining on the surface of the cat-
alyst, which finally becomes strongly bounded to the active
sites and is hard to remove even when the catalyst is washed
and regenerated. As a low reaction temperature has consider-
able economic advantage, 100ꢀC is chosen as the optimal
reaction temperature. In short, in the MnO2@Mn(btc)-
catalyzed esterification of oleic acid, the FAME yield could
reach 98% consecutively for at least five cycles under the
following optimal conditions: the molar ratio of ethanol to
oleic acid 12:1, 3 wt% catalyst, reaction temperature 100ꢀC,
and reaction time 12 hr.
3% with the final conversion shown for each separate experiment with ratios
between moles of ethanol and moles of fatty acid of 4:1, to 20:1
varied from 4:1 to 20:1. The conversion of oleic acid is
enhanced because the excess ethanol moved the equilibrium
to the product side when the molar ratio is increased from
4:1 to 12:1. However, when the molar ratio is further
increased to 12:1, the conversion of oleic acid reduced. It
continues to decrease when the ratio is further increased to
20:1. It is considered that further increase in ethanol mole-
cules may overfill the active sites of the catalyst, thus
obstructing the protonation of oleic acid at the active
sites.[25] Therefore, besides the excess of the reactant shifting
the equilibrium, the higher conversion could be ascribed to
the accessibility of the active sites. In addition, further
excess of ethanol may also insert more water, which may
react with the FAME to transform it back to oleic acid. Thus,
the ratio 12:1 was found to be the optimal ethanol/oleic acid
molar ratio.
100
120
80oC
1%
3%
5%
100oC
100
80
120oC
80
60
60
40
20
0
40
20
0
20
40
60
80
100
120
140
160
180
20
40
60
80
100
120
140
160
180
200
Time (min)
Time (min)
FIGURE 8 Catalyst amount experiments run at 100ꢀC and the ratio
between moles of ethanol and moles of fatty acid of 12:1 with catalyst
amount at 1, 3, and 5%
FIGURE 9 Effect of reaction temperature on MnO2@Mn(btc)-catalyzed
esterification of oleic acid with ethanol. Reaction conditions: 3%
MnO2@Mn(btc), molar ratio of ethanol to oleic acid 12:1

AMOUHADI ET AL.
5
3
|
EXPERIMENTAL
Teflon-lined stainless autoclave for 6 hr at 80ꢀC. The result-
ing black precipitate was filtered under vacuum, washed sev-
eral times with deionized water, and finally dried at 120ꢀC
for 12 hr.
A Perkin Elmer Spectrum 65 spectrophotometer was used to
record the infrared spectra in the range 400–4,000 cm−1
using KBr pellets. Cu Kα (1.54056 Å) radiation with auto-
matic control was employed to obtain the powder XRD dif-
fraction patterns on Bruker D8 ADVANCE and PW1830
instruments. Adsorption/desorption of nitrogen at liquid
nitrogen temperature was carried out to determine the BET
specific surface areas and pore volumes of the catalysts,
using a Micromeritics BELSORT mini II instrument. The
samples were outgassed at 623 K for 12 hr under a vacuum
of 10−4 Pa prior to the adsorption measurements. The cata-
lyst’s pore sizes were arrived at from the peak positions of
the distribution curves detected by the adsorption branches
of the isotherms. In NH3-TPD (Nano sort-NS91), 0.1 g of
the catalyst was taken in a U-shaped, flow-through quartz
sample tube. Thermogravimetric analysis (TGA) and differ-
ential thermal analysis (DTA) were carried out on a BAHR-
STA-504 apparatus. Thermal analyses were carried out in
the range of 25–800ꢀC, at the heating rate of 10 K/min.
4
| CONCLUSIONS
In summary, novel and efficient catalyst MnO2@Mn(btc)
was prepared under hydrothermal conditions and character-
ized by XRD, SEM, BET, IR, TGA, and NH3-TPD analyses.
The catalytic activity of MnO2@Mn(btc) was investigated
for biodiesel production from the esterification of the FFA
oleic acid. The significant advantages of this procedure are
short reaction times, high yields, mild reaction conditions,
and reusability of catalyst for several times.
ACKNOWLEDGMENT
This work was supported by the Islamic Azad University,
Shahreza Branch.
3.1 | Preparation of Mn(btc)
Synthesis of mesoporous Mn(btc) was done according to the
literature procedure [31]. Initially, a mixture of MnCl2ċ4H2O
(3.0 mmol, 0.5937 g), H3BTC (1.0 mmol, 0.210 g), DMF
(5.0 mL), and distilled water (5.0 mL) was placed in a
25-mL Teflon-lined stainless autoclave and heated to 120ꢀC
at a rate of a 10ꢀC/hr under autogenous pressure for 5 days.
Then, the autoclave was cooled to room temperature at a rate
of 5ꢀC/hr. Finally, the obtained colorless crystals were fil-
tered, washed with DMF and distilled water, and then dried
in air.
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How to cite this article: Amouhadi E, Fazaeli R,
Aliyan H. Biodiesel production via esterification of
oleic acid catalyzed by MnO2@Mn(btc) as a novel
and heterogeneous catalyst. J Chin Chem Soc. 2019;
1–6. https://doi.org/10.1002/jccs.201800288