Preparation of nano-CaO and catalyzing tri-component coupling transesterification to produce biodiesel

Article abstract of DOI:10.1080/24701556.2020.1720726

Nano-CaO with different particle sizes and crystallinity was prepared by sol-gel method. A tri-component coupling transesterification of rapeseed oil/dimethyl carbonate (DMC)/methanol was used to determine the viability of prepared nano-CaO as a basic catalyst for biodiesel synthesis. Nano-CaO exhibits better catalytic performance than commercial CaO for biodiesel production under same reaction condition. At 1:1:8 molar ratio of oil to DMC to methanol, 5 wt% nano-CaO catalyst (calcined at 800 °C), and 65 °C reaction temperature, the reaction gave the best results, and the fatty acid methyl ester yield exceeded 92% at 4 h which was 2 h shorter than that of commercial CaO. The catalyst calcined under different temperature has been characterized by BET, CO₂-TPD, TGA, XRD, and SEM. As the results shows that nano-CaO calcined at 800 °C exhibited the most active which should be contributed to the presence of good dispersivity, large surface area and pore volume.

Full text of DOI:10.1080/24701556.2020.1720726

Inorganic and Nano-Metal Chemistry
ISSN: 2470-1556 (Print) 2470-1564 (Online) Journal homepage: https://www.tandfonline.com/loi/lsrt21
Preparation of nano-CaO and catalyzing tri-
component coupling transesterification to
produce biodiesel
Ying Tang, Ying Yang, Huan Liu, Tianlan Yan & Zhifang Zhang
To cite this article: Ying Tang, Ying Yang, Huan Liu, Tianlan Yan & Zhifang Zhang (2020):
Preparation of nano-CaO and catalyzing tri-component coupling transesterification to produce
biodiesel, Inorganic and Nano-Metal Chemistry, DOI: 10.1080/24701556.2020.1720726
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INORGANIC AND NANO-METAL CHEMISTRY
https://doi.org/10.1080/24701556.2020.1720726
Preparation of nano-CaO and catalyzing tri-component coupling
transesterification to produce biodiesel
a
a
a
a
b
Ying Tang , Ying Yang , Huan Liu , Tianlan Yan , and Zhifang Zhang
a
b
College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, Shaanxi, China; School of Chemistry and Chemical
Engineering, Yulin University, Yulin, China
ABSTRACT
ARTICLE HISTORY
Nano-CaO with different particle sizes and crystallinity was prepared by sol-gel method.
A tri-component coupling transesterification of rapeseed oil/dimethyl carbonate (DMC)/methanol
was used to determine the viability of prepared nano-CaO as a basic catalyst for biodiesel synthe-
sis. Nano-CaO exhibits better catalytic performance than commercial CaO for biodiesel production
under same reaction condition. At 1:1:8 molar ratio of oil to DMC to methanol, 5 wt% nano-CaO
catalyst (calcined at 800 C), and 65 C reaction temperature, the reaction gave the best results,
and the fatty acid methyl ester yield exceeded 92% at 4 h which was 2 h shorter than that of
Received 27 October 2019
Accepted 9 January 2020
KEYWORDS
Nano-CaO; tri-component
coupling transesterification;
biodiesel; heterogeneous
ꢀ
ꢀ
commercial CaO. The catalyst calcined under different temperature has been characterized by BET,
ꢀ
CO
2
-TPD, TGA, XRD, and SEM. As the results shows that nano-CaO calcined at 800 C exhibited the
most active which should be contributed to the presence of good dispersivity, large surface area
and pore volume.
An efficient transesterification reaction has been developed over nano-CaO which
possessing good dispersivity, larger surface area and pore volume. Dimethyl carbon-
ate as a green methylating reagent, has been added aiming to turn rapeseed oil to
biodiesel with no glycerol by-product.
Introduction
[
3]
sodium or potassium methoxides. Although the reaction
rates for this process are high, recovery of catalysts is
difficult and treatment of wastes containing catalysts, water,
Associated with the diminishing fossil fuel supplies and
increasing environmental concerns, researchers have focused
on the renewable energy resources.
considered as a renewable fuel derived from triglycerides by
transesterification of triglycerides, typically of chain lengths
[
1]
[
4]
Biodiesel has been
glycerol and oils presents challenges. Furthermore, these
heterogeneous catalytic process still produces glycerol by-
product, and its separation from the fatty acids and esters
with 16, 18 or 20 carbon atoms, or their mono-alkyl esters adds to overall cost of biodiesel production. Glycerin, as
[
2]
with alcohols. The prevailing commercial method of bio- a by-product, is not very valuable as that obtained from
diesel production is transesterification of glycerol triglyceride biodiesel production simply adds to the over-supply of the
with short-chain alcohols, such as methanol or ethanol, in commodity from other sources and thus contribute to
[
5,6]
the presence of soluble inorganic bases as catalysts, such as a depression of its price.
Glycerol production can be
CONTACT Ying Tang
tangying78@xsyu.edu.cn
College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, Shaanxi 710065, China.
ß 2020 Taylor & Francis Group, LLC

2
Y. TANG ET AL.
avoided if rapeseed oil and DMC are reacted to produce gly- centrifugation, and the excess methanol was distilled off
cerol carbonate as a secondary product that is not required to under vacuum. Samples were analyzed for composition on
be separated from the fatty acid esters. Some researchers have an HP-7890 gas chromatograph equipped with a flame ion-
used enzymes as catalyst to produce biodiesel by introducing ization detector and a fused-silica capillary column (HP-5;
[
7]
DMC as reactant. In our previous research, an indirect 0.32 mm ꢁ 30m, 0.1 mm film thickness) using methyl hepta-
reaction between DMC and triglycerides can be established if decanoate as the standard. The nitrogen was the carrier gas
[
8]
methanol is added as a third reacting component.
at a flow rate of 20 mL/min. The oven temperature was kept
ꢀ
The application of calcium oxide as transesterification constant at 260 C. Yield of FAME was defined as a ratio of
catalyst for biodiesel production is restricted due to the the weight of FAME in samples, as determined using the gas
requirement of long reaction time and high molar ratio of chromatography, to the weight of equivalent FAME that the
methanol to oil. To solve these problems, we expanded oil used in the reaction would have contained.
the specific surface area of CaO to obtain a relatively high
[
9]
[
10]
fatty acid methyl ester (FAME) yield.
Presented in this
Catalyst characterizations
article are results on the application of nano-CaO prepared
by sol-gel method as catalysts for the coupling transesterifi-
cation of rapeseed oil, dimethy carbonate and methanol
to produce biodiesel at moderate condition. The catalytic
activities were investigated and the effect of nano-CaO
preparation condition on the yield of biodiesel was examined.
Textural characteristics were investigated by means of surface
area determined by BET including mean pore diameter and
pore volume using desorption isotherms on a Micromeritics
ASAP2010. Temperature-programmed desorption patterns of
carbon dioxide (CO -TPD) for the products were measured
2
with an automated chemisorption analyzer (AutoChem II
2
920, Micromeritics, USA) at the temperature range from 40
Experimental
ꢀ
ꢀ
ꢂ1
to 800 C with a heating rate of 10 C min . The crystalline
structures of the products of calcination were analyzed using
an X-ray diffraction device (JDX-3530, JEOL, Japan) with an
X-ray tube that has copper Cu as target and released K radi-
ation when accelerated at 30mA and 40kV). Thermo gravi-
metric analyses (TGA) of catalyst samples were performed in
the static air condition 20–1000 C with a heating rate of 5 C
min , using a thermo-gravimetric analyzer/simultaneous dif-
ferential thermal analyzer (TGA/SDTA 851 , Mettler-Toledo,
Switzerland). Scanning Electron Microscopy (SEM) was used
for the investigation of surface morphology of catalyst sam-
ples. Before being submitted to SEM characterization, the
solid sample was coated with gold in order to achieve suffi-
cient conductivity.
Materials
Refined rapeseed or canola oil was purchased from Xi’an Coal
Co., Ltd. Dimethyl carbonate (DMC), methanol, absolute ethyl
alcohol, cyclohexnae, Ca(NO ) , citric acid (analytical grade).
a
3
2
ꢀ
ꢀ
ꢂ1
Catalyst preparation
The mixture that absolute ethyl alcohol/Ca(NO ) /citric
acid/water was prepared in a 100 mL round-bottomed
flask and was heated to gelatinous by water bath. Then the
production was aging at room temperature for 24 h and was
dried in vacuum oven. Finally, the nano oxide catalyst was
e
3
2
ꢀ
obtained after calcinating for 6 h at 900 C in muffle stove.
Results and discussion
Preparation of biodiesel
The comparative study
The coupling transesterification of rapeseed oil, dimethy
carbonate and methanol to produce biodiesel has been The catalytic performances of 10 wt% nano-CaO powder for
established based on our previous research work as shown biodiesel production have been investigated at refluxing
ꢀ
in Scheme 1. The reaction was performed in a three necked temperature (65 C) with a molar oil/DMC/methanol ratio
round bottomed flask equipped with a reflux condenser of 1:1:8. For comparison, FAME yield of commercial CaO
and methanol were charged into the flask. After 30 g rape- has also been investigated. As indicated in Figure 1, over
seed oil, 6.0 g methanol and 2.8 g DMC adding, the mixture 90% yield of FAME can be obtained over nano-CaO after
ꢀ
was heated and maintained at 65 C temperature with 4 h which is better than that of commercial CaO with the
continuous stirring for hours. Samples were taken out yield of FAME below 80%. Similar result has been proved
from the reaction mixture every one hour and quenched by other researchers that commercial CaO catalyst shows a
to room temperature, then the catalyst was separated by lower catalytic activity in normal reaction condition for
O
O
O
O
O
R1
R2
R3
O
O
O
O
O
Catal
+
+
O
CH OH
H CO
3
OCH3
R
OCH3
+
3
OH
Scheme 1. The tri-component coupling transesterification to produce biodiesel.

INORGANIC AND NANO-METAL CHEMISTRY
3
1
00
100
80
1
3
%
%
CaO
Nano CaO
5%
8
6
4
2
0
0
0
0
0
8
1
%
0%
60
4
2
0
0
0
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Time/(h)
Time/(h)
Figure 2. Effect of the amount of catalyst on biodiesel yield.
Figure 1. Catalytic performance comparison of different CaO samples.
[11]
biodiesel production. This results indicated that large surface
area of nano powder provided more active sites which gave
great chance for the high transesterification reaction rate.
Effect of catalyst amounts
To explore the influence of the amount of catalyst in the
reaction, catalytic performance in presence of various
concentration nano-CaO catalysts were tested under the same
ꢀ
reaction condition at refluxing temperature (65 C) with a
molar oil/DMC/methanol ratio of 1:1:8 and the results were
shown in Figure 2. From the results summarized in Figure 2,
it can be seen that the yield of FAME markedly increased at
the beginning with the increase of catalyst dosage from 1 to
5
% (weight to oil). The yield of FAME attained the maximum
value of 85.5% when 5% catalyst was introduced at 4 h.
However, with further increase of the catalyst content, the
FAME yields decrease due to the decrease of contact between
the reactants and the catalyst as a result of agglomeration
of nano particle catalyst. Moreover, the higher viscosity of
the reaction system due to the more the dosage of the nano
particle catalyst leads to the influence of the mass transfer
Figure 3. Effect of calcination temperature on biodiesel yield.
2þ
formed complex of citric acid and Ca
during catalyst
preparation process. The organic matter failed to decompose
completely led to less effective constituent CaO at low
calcination temperature, on the contrary, catalytic surface
was sintered leading to covering active sites at high
[
12,13]
so as to the difficulty of the reaction.
So the optimum
amount of the catalyst was selected as 5%.
[
14,15]
calcination temperature.
By drawing on the results, the
ꢀ
optimum calcination temperature was selected as 800 C.
Effect of calcination temperature
To study the influence of the calcination temperature
of nano-CaO in FAME yield, the catalytic performances
Effect of alcohol solvent
of nano-CaO calcinated under various temperatures have Since the amount of alcohol has great effect on the structure
been investigated under the optimal conditions obtained of formed gel so as to the physic-chemical properties
ꢀ
in the previous section (65 C refluxing temperature, a of obtained nano-CaO particles, the influence of alcohol
molar oil/DMC/methanol ratio of 1:1:8 and 5 wt% nano- content on catalytic properties was investigated under the
CaO catalysts). From the result as shown in Figure 3, it was optimal reaction conditions and shown in Figure 4. From
found that the yield of FAME varied from 38.7 to 90.8% the results, it was found that biodiesel yield varied from
ꢀ
with rising of calcination temperature from 600 to 900 C increase to decrease with the increasing of absolute molar
ꢀ
and reaches the optimal value of 92.82% after 4 h at 800 C. ratio of ethyl alcohol/Ca(NO ) /citric acid/water from 0.2/5/
3
2
These results may be due to the high thermal stability of the 5/50 to 2/5/5/50, and the high ratio of ethanol at 1/5/5/50

4
Y. TANG ET AL.
1
00
100
80
60
40
20
0
1
1
1
1
:1:6
0
0
.2:5:5:50
.5:5:5:50
:1:8
:1:10
:1:12
8
6
4
2
0
0
0
0
0
1.0:5:5:50
.0:5:5:50
2
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Time/(h)
Time/(h)
Figure 4. Effect of the alcohol solvent on biodiesel yield.
Figure 5. Effect of the amount of the methanol on biodiesel yield.
indicating low ratio of Ca(NO ) /citric acid/water gave the
3
2
highest biodiesel yield of 92.4%. It is concluded from this
results that a critical concentration of water should be noted
which affecting the formation of gel probably due to the
excess of water causes a very fast hydrolysis of the alcoxide
by consuming all the disposable alcoxide groups. The near-
complete removal of alcoxide groups from the molecular
structure causes the condensation of the particles in these sys-
tems, because the presence of a small amount of alcoxide
[
16]
groups is necessary to produce the solubility in alcohol.
However, as the molar ratio of ethanol increases, an occlusion
of ethanol and water inside the pores happened. Hence, the
pores of formed nano-CaO precursor would be blocked which
lead to a decrease in the values of surface area and pore
[17,18]
volume of formed gel so to its catalytic performance.
Effect of molar ratio
The influence of the molar ratio in the proposed trans-
esterification of rapeseed oil was investigated at refluxing
temperature (65 C) using 5 wt% nano-CaO and the results
were shown in Figure 5. In general, such a high proportion
of methanol, usually 15:1 molar ratio of methanol to oil,
was used in transesterification between methanol and oil to
2
Figure 6. CO -TPD curves of different CaO samples.
ꢀ
nano-CaO particles are similar with major diffraction peaks
ꢀ
ꢀ
ꢀ
ꢀ
for CaO at 2h angles of 32.3 , 37.4 , 53.9 , 64.2 , and
ꢀ
[19]
6
7.4 .
Peaks of Ca(OH) and CaCO were also visible
2 3
promote thigh equilibrium conversion of vegetable oil to that obtained nano-CaO is partially hydrated and carbo-
esters. However, in this work, from Figure 5, it showed that nated. Furthermore, the characteristic diffraction peaks of
the optimal proportion of the feed reactants, on a molar CaCO
basis, is oil: DMC: methanol of 1:1:8 under the refluxing was set at 900 C, which indicated that the complete decom-
were still existed even the calcination temperature
3
ꢀ
condition. The results suggested that the proposed method position of CaCO required high temperature.
3
containing three reactants greatly reduce the amount
of methanol, which gives more potential to the widely
application for biodiesel production.
BET
The BET surface, pore size and average volume of different
nano-CaO are characterized and listed in Table 1. As shown,
a reasonable increase of the SBET and the pore volume were
observed over nano-CaO, which benefit the mass transform
Characterizations of samples
XRD
The X-ray diffraction patterns for all calcium oxide samples between catalysts and reactants in the heterogeneous
calcined under different temperature have been shown in reaction. Therefore reasons for the tremendous variation in
Figure 6. The plots show that the crystal structures of all the catalytic efficiency of the sample prepared using sol–gel

INORGANIC AND NANO-METAL CHEMISTRY
5
Table 1. Pore structure property of the CaO samples.
4
00
Commercial CaO
Nano CaO
BET surface area
Pore volume
Pore size
(nm)
2
3
ꢂ2
(
m /g)
(cm /g ꢁ 10
)
CaO
Nano-CaO
443.3695
659.3303
0.4414
0.5868
39.8189
35.5979
300
method in this experiment. Moreover, pores in both samples
belong to the mesopores class with their dimension of mag-
2
1
00
00
0
[
20]
nitude larger than the triglyceride dimensions,
thus any
significant diffusion restriction should not be expected.
According to Figure 7, the hysteresis curve of common CaO
is more similar to Type H1 and put up adsorption limit in
the low relative pressure, while the hysteresis curve of nano-
CaO is corresponding to Type H3 with more obvious hys-
teresis loop, which shows that the pore pattern is vary from
narrow seam pore to ampuliform pore with small caliber
0
.0
0.2
0.4
Relative pressure/(p/p0)
2
Figure 7. N adsorption curves of the catalyst.
0.6
0.8
1.0
[
7,21]
and large lumen.
CO -TPD
2
For solid basic catalysts, the amount of CO2 irreversibly
adsorbed reflects the population of basic sites on exposed surfa-
ces. The desorption temperature indicates that the strengths of
adhesion at the base site. Results for temperature-programmed
desorption are presented in Figure 8. According to the result,
ꢀ
above 615 C desorption peak indicated that nano oxides
exhibit stronger base than commercial oxides. With increasing
of calcination temperature, desorption curves of nano-CaO
move to high temperature attributed to the strong basic sites of
2
ꢂ
O
anions, which indicated that the low calcination tempera-
2ꢂ
2ꢂ
ture led to weak effect of O , while the effect of O was
[22]
strengthened with increasing calcination temperature. This is
similar to previously claimed that the required calcination tem-
perature to generate maximum amounts electron donating sites
2
Figure 8. CO -TPD curves of different CaO samples.
ꢀ
[23]
on CaO surface should be high than 700 C.
TGA
In order to investigate the influence of temperature of the
catalyst activation on biodiesel yield, the thermal behavior of
the prepared samples were investigated using TGA from
ꢀ
room temperature to 800 C. Figure 9 exhibits TGA curves
of nano-CaO and commercial CaO. In the thermograph
of both samples two major steps for the mass loss
with changing temperature indicating two endothermal
ꢀ
effects. The first step from 350 to 420 C is due to loss of
decomposing Ca(OH)2, known to perform less efficiently
in the transesterification reaction in comparison to its
counterpart oxide. The second step occurred in the range of
ꢀ
5
00–600 C corresponding to the release of CO from
2
CaCO due to the easily react of CaO with carbon dioxide
3
as it was exposed to the air. Based on these thermogravimet- Figure 9. TGA plot for different CaO samples.
ric properties it seems that a much more pronounced
ꢀ
endothemic effect at 400 C for prepared nano-CaO particles FT-IR
indicating much more hydration of this sample. The decom- The Fourier transform infrared spectra of the commercial
ꢀ
pose temperature for CaCO3 around 600 C suggest that CaO and nano-CaO calcinated at different temperatures were
ꢂ1
the complete decarbonation of carbonates over nano-CaO shown in Figure 10. The absence of the band at 1645 cm ,
requires higher temperature and the thermal stability of usually assigned to the bending of OH-groups of physisorbed
nano-CaO has been improved.
water molecules, on all of nano-CaO samples, indicates that

6
Y. TANG ET AL.
the complete dehydration of nano-CaO over calcination tem-
ꢀ
perature of 600 C. For all the samples, the spectra bands at
8
ꢂ1
50 and 1460 cm correspond to vibration modes of mono
and bidentate carbonates which provide the poisoning of CO2
over their surface. The nano-CaO appeared stronger vibration
a mode indicates that it was eroded more easily by CO than
2
commercial CaO as exposed to the air. Although results of
thermal analysis presented in TGA (Figure 8) suggest that
ꢀ
6
00 C should be the temperature high enough for the com-
plete decarbonation, it is obvious that in reality this process
requires higher temperatures. On the other side, the vibration
peaks of mono and bidentate carbonates have diminished with
increasing calcination temperature, which indicate the surface
sintering of nano-CaO under high calcination temperature.
SEM
The SEM images of commercial and nano-CaO samples cal-
cined under different temperature were shown in Figure 11.
Figure 10. IR spectra of the commercial and nano-CaO.
Figure 11. SEM photographs of commercial and nano-CaO.

INORGANIC AND NANO-METAL CHEMISTRY
7
These images of nano-CaO show a good morphology that par-
ticles are more homogeneous than commercial CaO. However,
nano-CaO particles calcined at 900 C were column like indi-
[7] Seong, P.-J.; Jeon, B. W.; Lee, M.; Cho, D. H.; Kim, D.-K.; Jung,
K. S.; Kim, S. W.; Han, S. O.; Kim, Y. H.; Park, C. Enzymatic
Coproduction of Biodiesel and Glycerol Carbonate from
Soybean Oil and Dimethyl Carbonate. Enzyme Microb. Technol.
ꢀ
cating sintering of the surface so as to its relatively low yield of
2
011, 48, 505–509. DOI: 10.1016/j.enzmictec.2011.02.009.
ꢀ
biodiesel, while nano-CaO particles calcined at 800 C which
[8] Tang, Y.; Cheng, Q. T.; Cao, H.; Zhang, L.; Zhang, J.; Li, H. F.
Coupling Transesterifications for No-Glycerol Biodiesel
Production Catalyzed by Calcium Oxide. J. C. R. Chim. 2015,
are concentrated in spheres and the particle size distribution is
more uniform indicating the good dispersivity which have
good relationship with its best catalytic performance.
1
8, 1328–1334. DOI: 10.1016/j.crci.2015.08.003.
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[
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Conclusion
[
10] Kouzu, M.; Kasuno, T.; Tajika, M.; Sugimoto, Y.; Yamanaka, S.;
In this research, nano-CaO obtained by sol-gel method
exhibited high activity in the transesterification of rapeseed
oil with DMC and methanol to produce biodiesel. At 1:1:8
molar ratio of oil to DMC to methanol, addition of 5 wt%
Hidaka, J. Calcium Oxide as Solid Base Catalyst for
a
Transesterification of Soybean Oil and Its Application to
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1016/j.fuel.2007.10.019.
ꢀ
[11] Zhang, J.; Cai, D.; Wang, S. S.; Tang, Y.; Zhang, Z.; Liu, Y.;
Gao, X. Q. Efficient Method for the Synthesis of Fatty Acid
Amide from Soybean Oil Methyl Ester Catalysed by Modified
CaO. Can. J. Chem. Eng. 2014, 92, 871–875.
nano-CaO catalyst (calcined at 800 C), gave the best results
ꢀ
with FAME yield exceeded 92% at 4 h under 65 C reaction
temperature, which shorten 2 h of reaction time than com-
mercial CaO at the same reaction condition. The large sur- [12] Reyero, I.; Arzamendi, G.; Gand ꢀı a, L. M. Heterogenization of
face area and strong basic properties results in a remarkable
high activity of nano-CaO. Based on this highly efficient
and low-cost catalyst, the production of biodiesel could be
greatly enhanced and the production cost could be reduced.
the biodiesel synthesis catalysis: CaO and novel calcium com-
pounds as transesterification catalysts . J. Chem. Eng. Res. Des.
2
014, 92, 1519. DOI: 10.1016/j.cherd.2013.11.017.
13] Liu, S.; Ma, J.; Guan, L.; Li, J.; Wei, W.; Sun, Y. Mesoporous
CaO–ZrO Nano-Oxides: Novel Solid Base with High
Activity and Stability. J. Microporous Mesoporous Mater. 2009,
17, 466–471. DOI: 10.1016/j.micromeso.2008.07.026.
14] Yaakob, Z.; Mohammad, M.; Alherbawi, M.; Alam, Z.; Sopian,
K. Overview of the Production of Biodiesel from Waste
Cooking Oil. J. Renew. Sustain. Energy Rev. 2013, 18, 184–193.
DOI: 10.1016/j.rser.2012.10.016.
[
[
[
[
[
2
A
1
Acknowlegement
We are thankful for the work of Modern Analysis and Testing Center
of Xi’an Shiyou University.
15] Intarapong, P.; Iangthanarat, S.; Phanthong, P.; Luengnaruemitchai,
A.; Jai-In, S.; Jai-In, A. Activity and basic properties of KOH/mor-
denite for transesterification of palm oil. J. Energy Chem. 2013, 22,
Funding
690–700. DOI: 10.1016/S2095-4956(13)60092-3.
The work was supported financially by National Science Foundation of
China (No. 21763030), Scientific Research Plan Projects of Shaanxi
Science and Technology Department (2019GY-136) and Xi’an Science
and Technology Project (201805038YD16CG22(3)).
16] Soetaredjo, F. E.; Ayucitra, A.; Ismadji, S.; Maukar, A. L. KOH/
Bentonite Catalysts for Transesterification of Palm Oil to
Biodiesel. J. Appl. Clay Sci. 2011, 53, 341–346. DOI: 10.1016/j.
clay.2010.12.018.
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Uemura, Y. Production of Biodiesel Fuel from Canola Oil with
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