Hydrothermal effect on synthesis, characterization and catalytic properties of calcium methoxide for biodiesel production from crude Jatropha curcas

Article abstract of DOI:10.1039/c4ra11936c

Hydrothermal synthesis is a well-suited approach for preparing bulk metal catalysts with high purity as it is cost-effective and easy to control in terms of temperature and time. In the current study, an effective catalyst for transesterification of high fatty acid content of crude Jatropha curcas oil (JCO) was appraised. Calcium methoxide (Ca(OCH₃)₂) has been successfully synthesized via a green and economical hydrothermal process at different synthesis times. CaO was used as a precursor as it is abundant, inexpensive and environmentally friendly. Ca(OCH₃)₂ can form on the surface of CaO and its active basic surface is very well developed. This facile experimental strategy without any surfactant or template produced porous Ca(OCH₃)₂ with a high surface area and high basicity, which leads to a superior catalytic reaction and is a promising alternative for short-reaction-time solid-based catalysts in biodiesel production in terms of excellent transesterification performance and long durability. The performance of synthesized Ca(OCH₃)₂ was examined by characterizing it using analytical techniques such as TG-DTA, XRD, BET, FT-IR, TEM and SEM. Ca(OCH₃)₂ catalysts had three types of morphologies, i.e. (a) irregular round shape particles, (b) a well arrangement of plate-like structures with rough surface and (c) a cluster of tiny plate-like architectures with smooth surfaces. The correlation between synthesis time, surface area and morphology of catalysts and the biodiesel yield was studied. Ca(OCH₃)₂ was able to maintain the FAME content above 86% after a fifth cycle, at optimum reaction conditions of 2 h reaction time, 12:1 methanol/oil molar ratio, 2 wt% catalyst loading and 65°C reaction temperature. Ca(OCH₃)₂ is a solid heterogeneous catalyst for the transesterification reaction of non-edible Jatropha curcas oil for biodiesel production. The catalyst can be separated easily from the reaction mixture and reused to give a consistent transesterification activity.

Full text of DOI:10.1039/c4ra11936c

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Hydrothermal effect on synthesis, characterization
and catalytic properties of calcium methoxide for
biodiesel production from crude Jatropha curcas
Cite this: RSC Adv., 2015, 5, 4266
abc
Siow Hwa Teo,ab Yun Hin Taufiq-Yap,
Umer Rashidd and Aminul Islamab
*
Hydrothermal synthesis is a well-suited approach for preparing bulk metal catalysts with high purity as it is
cost-effective and easy to control in terms of temperature and time. In the current study, an effective
catalyst for transesterification of high fatty acid content of crude Jatropha curcas oil (JCO) was
appraised. Calcium methoxide (Ca(OCH3)2) has been successfully synthesized via
a green and
economical hydrothermal process at different synthesis times. CaO was used as a precursor as it is
abundant, inexpensive and environmentally friendly. Ca(OCH3)2 can form on the surface of CaO and
its active basic surface is very well developed. This facile experimental strategy without any surfactant
or template produced porous Ca(OCH3)2 with a high surface area and high basicity, which leads to a
superior catalytic reaction and is a promising alternative for short-reaction-time solid-based catalysts
in biodiesel production in terms of excellent transesterification performance and long durability. The
performance of synthesized Ca(OCH3)2 was examined by characterizing it using analytical techniques
such as TG-DTA, XRD, BET, FT-IR, TEM and SEM. Ca(OCH3)2 catalysts had three types of
morphologies, i.e. (a) irregular round shape particles, (b) a well arrangement of plate-like structures
with rough surface and (c) a cluster of tiny plate-like architectures with smooth surfaces. The
correlation between synthesis time, surface area and morphology of catalysts and the biodiesel yield
was studied. Ca(OCH3)2 was able to maintain the FAME content above 86% after a fifth cycle, at
optimum reaction conditions of 2 h reaction time, 12 : 1 methanol/oil molar ratio, 2 wt% catalyst
loading and 65 ꢀC reaction temperature. Ca(OCH3)2 is a solid heterogeneous catalyst for the
transesterification reaction of non-edible Jatropha curcas oil for biodiesel production. The catalyst
can be separated easily from the reaction mixture and reused to give a consistent transesterification
activity.
Received 7th October 2014
Accepted 25th November 2014
DOI: 10.1039/c4ra11936c
www.rsc.org/advances
Kranjar oil (India) and soybean oil (USA). In order to solve the
problems related to food-based biodiesel, non-edible oils have
attracted increasing attention as potential feedstocks.2
The Jatropha curcas L. seed kernel has about 60% oil content.
Jatropha curcas L. is attracting increasing attention as a poten-
tial feedstock as it is non-edible and easy to produce, it has low
cost and its seeds are available in abundance. Therefore, this
makes its use as an energy or fuel source very attractive, espe-
cially for biodiesel production. The overall reaction of meth-
anolysis of vegetable oil is shown in Scheme 1.
Introduction
Biodiesel, also called fatty acid methyl ester (FAME), is a
promising alternative energy source for the transportation
sector. Numerous advantages are associated with biodiesel,
such as renewability, low/zero net CO2 emission, low sulfur and
higher biodegradability.1 Additionally, biodiesel is superior to
fossil diesel fuel in terms of cetane number, ash point and
lubricity characteristics. Biodiesel can be produced by the
transesterication with alcohol of various feedstocks such as
vegetable oils (Europe), palm oil (South East Asia), Jatropha oil,
aCatalysis Science and Technology Research Centre, Faculty of Science, Universiti
Putra Malaysia, 43400, Serdang, Selangor, Malaysia. E-mail: tauq@upm.edu.my;
Fax: +60-3-89466758; Tel: +60-3-89466809
bDepartment of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400,
Serdang, Selangor, Malaysia
cCurtin Sarawak Research Institute, Curtin University, Miri, Sarawak, Malaysia
dInstitute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang,
Malaysia
Scheme 1 Transesterification of triglyceride with methanol.
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Due to their advantages of corrosion resistance, environ- calculated based on the acid value (AV) and saponication value
mental benignancy and easy separation from liquid products, (SV) of crude JCO obtained using the following correlation:14
heterogeneous solid catalysts are being widely used for the
M ¼ 56.1 ꢁ 1000 ꢁ 3/(SV ꢂ AV)
(1)
transesterication of triglycerides. Calcium oxide (CaO) is the
most widely used and exhibits good catalytic properties for
transesterication of triglycerides to biodiesel from an
economic point of view.3,4 However, the reaction rate is slow and
it seems not to be adaptable for industrial application, because
extensive leaching of, for example, Ca2+ may reduce the reus-
ability and the environmental sustainability of the catalyst.5,6
Recently, hydrothermal synthesis has turned out to be well-
suited for the preparation of bulk metal catalysts with high
purity as it is low-cost and easy to control (i.e. temperature and
time). The variety of micro/nano-materials with unique
morphologies can be obtained, such as nanocable,7 nanorod,8
star-shaped and ower-like9 products. Up to now, this tech-
nique has been successfully applied in preparing Ca(OCH3)2
solid catalyst.10–12 However, morphology and structure-
controlled growth of micro/nanoarchitectures of Ca(OCH3)2
has not been achieved. The synthesized Ca(OCH3)2 exhibited
various unique physical and chemical properties, such as high
surface area, ideal porosity and strong basicity. Nanoparticle
catalysts could be an important factor for improving the cata-
lytic properties by exposing catalytically active –OCH3 on the
surface of the catalyst, which would favor the transesterication
reaction.13
Herein, we report a simple hydrothermal approach without
using any surfactant or template to prepare Ca(OCH3)2 catalyst.
By varying the synthesis time, heterogeneous catalysts exhibit-
ing different effectiveness in the transesterication of crude
Jatropha curcas oil (JCO) with methanol have been obtained. The
active phase of Ca(OCH3)2 was characterized with data obtained
from physico-chemical properties of the catalysts. The inuence
of varying the synthesis time on the size and structural and
textural properties of the prepared Ca(OCH3)2 is appraised.
Also, the correlative effect between transesterication activity
and catalyst surface area is discussed. This is the rst report in
which the catalytic performance of Ca(OCH3)2 for the trans-
esterication of non-edible crude JCO is presented. Moreover,
the efficiency and reusability of the catalyst in biodiesel
production is also studied.
Ca(OCH3)2 catalyst was prepared by heating CaO in excess
dehydrated methanol under 65 ꢀC at a range of durations (2 to
12 h) under N2 ow (50 ml minꢂ1). The reaction can be
expressed as shown in Scheme 2.
CaO was used without removing any hydroxide phase.
Typically, 1 g of CaO was dispersed rapidly into 20 ml of anhy-
drous methanol in a three-neck round bottom ask equipped
with a water-cooled reux condenser and a magnetic stirrer. The
resulting white suspended slurry was continuously stirred at
600 rpm to facilitate sufficient contact between the reactants.
Then, the white paste precursor was formed by distilling most
of the methanol using a rotary evaporator under reduced pres-
sure and was then dried in a vacuum oven at 105 ꢀC for 1 h.
Henceforth, the catalysts are denoted as CMX, where X repre-
sents the reux time of 2, 4, 6, 8, 10 and 12 h, respectively.
Catalyst characterization
Thermogravimetric and differential thermal analysis (TG/DTA)
of the Ca(OCH3)2 catalysts was performed using a Mettler
Toledo thermogravimetric analyzer. The heating was carried out
in an air ow (100 ml minꢂ1) with a heating rate of 10 ꢀC minꢂ1
,
ꢀ
from 35 to 1000 C.
Powder X-ray diffraction analysis (XRD) was employed to
identify the crystallography of the Ca(OCH3)2 catalysts. The
analysis was carried out using a Shimadzu diffractometer model
XRD6000. The diffractometer employed CuKa radiation (2.7 kW
˚
and 30 mA) with wavelength (l) of 1.54 A to generate diffraction
patterns from powder crystalline samples at ambient tempera-
ture. The data were recorded over a 2q range of 5–40ꢀ with steps
of 0.02ꢀ and a count time of 1 s. Each sample was run for 35
minutes. The phases were identied using the power diffraction
le (PDF) database (JCPDS, International Centre for Diffraction
Data). The crystallite size of the catalysts can be calculated from
the line broadening or FWHM (full width at half maximum) of
the corresponding peaks (the most intense peaks), by using the
Debye–Scherrer equation15 as follows:
Experimental
Preparation and characterization of materials
0:89l
t ¼
(2)
bhkl cos qhkl
Crude Jatropha curcas L. oil (JCO) was purchased from Bionas where t is the crystallite size for (hkl) phase (nm), l is the X-ray
Sdn Bhd, Malaysia and was used without further treatment or wavelength of radiation for CuKa, bhkl is the full width at half
purication. CaO (R&M Chemicals, 99.0%), anhydrous meth- maximum (FWHM) at (hkl) peak in radians and qhkl is the
anol (Merck, 99.7%) were purchased from Fisher Scientic and diffraction angle for (hkl) phase.
used for methanolysis of CaO and transesterication of oil
The specic surface area, average pore size, total pore
reactions. Dichloromethane (Fisher Scientic, UK) was used as volume and pore size distribution of the Ca(OCH3)2 catalysts
solvent for FAME yield evaluation. Methyl heptadecanoate, were determined from the corresponding nitrogen adsorption–
C
18H36O2, was the internal standard for gas chromatography desorption isotherms at liquid nitrogen temperature (ꢂ196 ꢀC)
analysis. All the chemicals used in the present study were with
a Thermo Finnigan Sorptomatic 1900 series. The
analytical reagent grade.
isotherms were generated by dosing nitrogen onto the catalyst.
The fatty acid prole of crude JCO was identied and is Before the adsorption measurements, all the catalysts (0.5 g)
tabulated in Table 1. The average molecular weight (M) was were degassed for 8 h at 150 ꢀC under vacuum conditions until
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Table 1 Fatty acid composition of crude Jatropha curcas oil-based methyl esters (CJCOME) in comparison to other esters using GC-FID analysis
FAMEs
Carbon
CJCOMEa
POMEb
CiRMEc
SBMEd
SFOMEe
Lauric acid
12 : 0
14 : 0
16 : 0
16 : 1
18 : 0
18 : 1
—
—
20.2
1.1
7.2
39.8
—
31.2
0.3
0.2
27.6
72.4
0.9
1.5
41.9
—
2.7
40.8
—
11.9
0.3
—
47.0
53.0
—
—
26.9
—
4.6
25.6
1.2
37.7
3.8
0.2
31.7
68.3
—
—
—
—
Myristic acid
Palmitic acid
Palmitoleic acid
Stearic acid
12.5
—
5.2
23.5
—
48.8
10.0
—
17.7
82.3
46.0
—
4.0
40.0
—
10.0
—
—
Oleic acid
Asclepic acid
Linoleic acid
Linolenic acid
Arachidic acid
18 : 1 (n ꢂ 7)
18 : 2
18 : 3
20 : 0
P
f
50.0
50.0
SFA
P
g
USFA
CJCOME (crude Jatropha curcas oil methyl esters). b POME (palm oil methyl esters).21 CiRME (Citrus reticulate methyl esters).2 SBME (soybean
a
c
d
methyl esters).11 SFOME (sunower oil methyl esters).2 Total saturated fatty acid. g Total unsaturated fatty acid.
e
f
the pressure gradient reached an extremely low state. The total 900 rpm. The reaction proceeded at a controlled temperature,
surface area (SBET), total pore volume (cm3 gꢂ1) and average using a silicone oil bath to keep the temperature constant.
pore size (nm) of the catalysts were generated from adsorption– Typically, CMX (X ¼ 2–12) catalyst was suspended in the
desorption isotherms by using the Brunauer–Emmett–Teller required volume (n(methanol) : n(oil) ¼ 12 : 1) of methanol. The
(BET) method, whereas the pore size distribution was evaluated reaction temperature was controlled at 65 ꢀC by the silicone oil
from desorption branches by using the Barrett–Joyner–Halenda bath. Crude JCO (10 g) was added into the mixture under
(BJH) plot.
vigorous stirring in the presence of catalyst (2 wt%). Once the
Infrared spectra of the solid Ca(OCH3)2 catalysts were reaction had nished (1.5 h), the mixture was then cooled to
measured by using attenuated total reection-Fourier room temperature. Aer cooling, the catalyst was separated via
transform-infrared (ATR-FTIR) on a Perkin Elmer (PC) Spec- centrifugation and the residual methanol and glycerol of the by-
trum 100 FTIR spectrometer to identify the surface functional product were eliminated by washing with water. The trans-
groups presenting on the catalyst at room temperature. Each esteried oil was collected aer the separation process
spectrum was an average of 128 scans analyzed over the wave- mentioned above, and was dried with a rotary evaporator under
length scanning range of 650–4000 cmꢂ1 at a resolution of reduced pressure prior to analysis.
4 cmꢂ1
.
The morphological observations of the prepared Ca(OCH3)2
catalysts were made by eld emission scanning electron
microscopy (FESEM, JOEL, JSM-6700F) and transmission elec-
tron microscopy (TEM, Hitachi, H7100). For FESEM analysis,
the catalysts were coated with Au (gold) for avoiding the
induction of electric current using a sputter coater. Particle size
of the Ca(OCH3)2 catalysts was obtained by using TEM with an
accelerating voltage of 200 kV.
Analysis of fatty acid methyl esters
The yield of FAME produced was measured using gas chroma-
tography on a Shimazu GC-14C. A split type injector and a ame
ionization detector (FID) were connected to a polar BP-20
capillary column (30 m ꢁ 0.5 mm ꢁ 0.25 mm). The trans-
ꢀ
esteried oil was injected at 140 C with a split ratio of 1 : 30.
FAME was separated from the transesteried oil in the column
heated at 250 C, with the heating rate at 5 C minꢂ1. Methyl
heptadecanoate was used as an internal standard and
dichloromethane was used as the solvent. The FAME content
was determined in agreement with European regulated proce-
dure EN 14103.16 FAME content (%) was calculated using the
equations as following:
ꢀ
ꢀ
Methanolysis of triglycerides
Production of biodiesel by methanolysis of crude J. curcas-
derived oil, over Ca(OCH3)2 catalyst, was performed using a
100 ml two-neck round-bottom ask equipped with a water-
cooled reux condenser and with continuous stirring at
FAME yield (%) ¼ [(mFAME/MWFAME) ꢁ CFAME]/
[(mJCO/MWJCO) ꢁ 3] ꢁ 100%
(3)
where mFAME and mJCO are the mass of FAME produced and JCO,
respectively, and MWFAME and MWJCO are the average molecular
weights of FAME produced and JCO, respectively, which were
calculated according to the composition of fatty acids.
Additionally, CFAME is the FAME concentration and the
coefficient 3 accounts for the fact that each triglyceride mole-
cule yields three methyl ester molecules.
Scheme 2 Hydrothermal synthesis of calcium oxide with methanol.
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methyl esters (CiRME) > palm oil methyl esters (POME) >
Recyclability study of produced catalyst
sunower oil methyl esters (SFOME).
To study the catalyst lifetime and stability, used CM8 catalyst
was separated from the reaction mixture and reused in a
transesterication reaction without additional treatment. In
this case, crude JCO and methanol were added in the same
amount into each reaction system, and the reactions were per-
formed at the optimum conditions.
Catalyst characterization
In thermogravimetric analysis (TGA), the weight of the synthe-
sized catalyst was measured as a function of temperature while
it was subjected to a controlled heating programme. The
amount of weight loss provided a quantitative indication about
the composition of the catalyst. Additionally, the temperature of
thermal and oxidative degradation of the catalyst was also
measured using differential thermal analysis (DTA). The curve
showed the physical and chemical transitions of the sample by
measuring exothermic and endothermic effects.
Fig. 1 shows the TGA and DTA thermograms of the synthe-
sized Ca(OCH3)2 catalyst under air ow conditions. The TGA
curve remained constant from 35 ꢀC to 370 ꢀC. Ca(OCH3)2
catalyst began to decompose at about 370 ꢀC with a weight loss
of around 17%. This phenomenon was due to a chemical
reaction occurring. The DTA curve shows an exothermic peak
appearing between 370 and 460 ꢀC, which is consistent with the
peak in the TGA curve. The reaction at 430 ꢀC might be the
decomposition of Ca(OCH3)2 with oxygen to calcium carbonate
as shown in Scheme 3.
Results and discussion
Properties of crude Jatropha curcas L. oil
The crude JCO was found to contain 0.091% w/w of moisture.
Other analyses for the crude JCO were a density value of
0.9162 g cmꢂ3, a saponication value of 188.4 mKOH/moil
(mg gꢂ1) and an acid value of 13.6 mKOH/moil (mg gꢂ1). There-
fore, the average molecular weight of J. curcas oil was calculated
as 962.8 g molꢂ1. Moreover, the content of free fatty acids
presence in crude JCO is 6.8% w/w, which is in the higher range.
The gas chromatography results showed that the FAME
constituents present in J. curcas oil were methyl palmitate
(C16:0), methyl palmitoleate (C16:1), methyl stearate (C18:0),
methyl oleate (C18:1), methyl linoleate (C18:2) and methyl
arachidate (C20:0); unsaturated methyl esters were the most
prominent compounds.
The methyl ester composition of crude JCO is shown in
Table 1, which shows that it consisted of 72.4% unsaturated
fatty acids (USFA), whereas the level of saturated fatty acids
(SFA) was 27.6%. These results conform with the proles in the
literature.10 The GC data revealed the fatty acid proles of bio-
diesel fuels produced from other sources were comparable to
the major ester constituents derived from crude JCO. However,
crude JCO exhibited a high unsaturated/saturated lipid ratio,
with the sequence soybean methyl esters (SBME) > crude
Jatropha curcas oil methyl esters (CJCOME) > Citrus reticulate
Furthermore, the TGA curve showed evidence of thermal
decomposition of calcium carbonate, with the formation of
gaseous products above 600 ꢀC. A steep slope was observed
ꢀ
ꢀ
between 600 and 800 C in the TGA curve. At 720 C, the DTA
peak showed the endothermic transformation of CaCO3 to
stable CaO. The thermogravimetric analysis suggested that the
Scheme 3
Fig. 1 TGA and DTA thermograms of calcium methoxide catalyst.
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synthesized Ca(OCH3)2 catalyst is stable below 400 ꢀC. Thus, the 2 times smaller compared to pure metal oxide clusters. The
produced Ca(OCH3)2 catalyst is extremely stable during the results also showed that crystallite sizes of the catalysts were in
transesterication reaction.
The XRD patterns of all the catalysts are shown in Fig. 2. CaO FWHM with the increment of the crystallite size.
had very appreciable broad peaks at 2q of 32.1ꢀ and 37.2ꢀ (JPDS
The surface areas of all the catalysts are shown in Table 2.
agreement with the line width of the peak in which decrease of
le no. 00-037-1497). Ca(OCH3)2 was characterised with the The surface area of the catalysts was in agreement with XRD
presence of a peak at 2q of 10.8ꢀ (ref. 17) for CM2–CM12 cata- analysis which showed that smaller crystallite sizes gave
lysts. The insignicant three peaks at 2q of 17.8ꢀ, 28.6ꢀ, and higher surface areas, as demonstrated in Fig. 3. The BET
34.0ꢀ suggested the existence of calcium hydroxide (JCPDS le isotherm of the CM8 catalyst resembles the Type IV isotherms,
no.: 01-84-1264), which had probably appeared due to the with hysteresis loop of type H3 based on the IUPAC classi-
interaction of the catalyst with the water molecules formed as a cation.18,19 The measured surface area, total pore volume and
byproduct during the synthesis reaction.
average pore diameter were 30.5 m2 gꢂ1, 0.21 cm3 gꢂ1 and
The crystallite size and surface area of the catalysts are 31.97 nm, respectively. Therefore, this suggested that the
summarized in Table 2. As can be seen, the average crystallite catalyst is favourable for use in a liquid phase reaction since it
size for pure CaO catalyst was 66.3 nm. The CM2–CM12 cata- can provide a sufficiently large area of active sites in a stirrer-
lysts had crystallite sizes of 29.0, 31.1, 30.6, 27.5, 29.7 and 31.4 type reactor.20
nm, respectively. These results indicated that crystallite sizes of
The pore size distribution of the CM8 catalyst reveals that
the nal products were being reduced signicantly to become the surface is occupied by relatively small-size mesopore
structures in the range of 2 to 5 nm, as shown in Fig. 4. Mes-
oporous materials can serve as effective catalysts in trans-
esterication reactions for adsorbing large organic molecules,
due to their uniform pore structure and extremely high surface
area. Furthermore, a large part of the surface is fully occupied
by larger pore structures, with size between 6 and 100 nm. The
macropore structure of the particle catalyst provides rapid
mass transfer into the interstices of the catalyst and leads
reagent to the ultimate reaction sites. Consequently, high
surface area and porosity properties are important character-
istics of solid catalysts because they are closely related with the
catalytic activity.
The FTIR spectrum of the synthesized Ca(OCH3)2 catalysts at
room temperature are shown in Fig. 5, which indicates that the
important features appear in the –C–O stretching vibration of
primary alcohol (1070 cmꢂ1), –OH stretching vibration of
primary alcohol (3650 cmꢂ1), CH3 stretching vibrations (2800–
3000 cmꢂ1
)
and –C–H alkene bending (1465 cmꢂ1).20,21
Furthermore, the unusual peak that appeared at 3650 cmꢂ1
suggested the adsorption of water on the surface of all catalysts.
This peak indicates the existence of –OH functional groups
isolated on calcium cation.20 Since water was produced as a by-
product in the catalyst synthesis reaction, these isolated –OH
groups might have been produced from water, facilitated by the
Fig.
2 X-ray diffraction patterns of calcium oxide and calcium
methoxide catalysts. Ca(OCH3)2 was prepared with methanol reflux of
CaO at 65 ꢀC (under 50 ml minꢂ1 nitrogen flow conditions) for 2, 4, 6,
8, 10 and 12 hours, and is accordingly labeled as CM2, CM4, CM6,
CM8, CM10 and CM12. C, characteristic peak of calcium methoxide;
D, characteristic peak of calcium oxide; B, characteristic peak of
calcium hydroxide.
Table 2 Crystallite size, BET surface area, shape and particle size of calcium methoxide catalysts
Catalyst 2q (ꢀ)
FWHM Crystallite sizea (nm) SBETb (m2 gꢂ1
)
Shapec
Particle sized (nm)
CaO
37.4701 0.1510 66.3
10.8448 0.2784 29.0
10.8348 0.2597 31.1
10.8248 0.3074 30.6
10.8105 0.2941 27.5
10.8213 0.2721 29.7
9.2
Cubic crystal
137.02 ꢃ 11.30
CM2
CM4
CM6
CM8
CM10
16.2
18.3
20.5
30.5
28.8
Cubic crystal & irregular round 170.71 ꢃ 25.26e & 68.06 ꢃ 19.29
Cubic crystal & irregular round 120.07 ꢃ 23.32e & 34.74 ꢃ 3.26
Plate
Plate
Plate & round
267.10 ꢃ 35.10 (D) 72.46 ꢃ 22.34 (T)
391.77 ꢃ 65.34 (D) 111.38 ꢃ 13.12 (T)
530.41 ꢃ 21.69 (D) 157.38 ꢃ 5.69 (T) &
302.30 ꢃ 46.93
CM12
10.8223 0.2847 31.4
26.0
Irregular bulky round
366.52 ꢃ 24.82
a
b
c
d
Determined from XRD patterns using the Scherrer equation. BET surface area. Observed by SEM analysis. Measured by TEM technique.
unreacted CaO and (D): diameter and (T): thickness
e
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reduced to 120.07 ꢃ 23.32 nm (unreacted CaO) and 34.74 ꢃ 3.26
nm in diameter. The shapes of the CM2 and CM4 catalysts were
conrmed by FESEM, as shown in Fig. 7(c)–(f). These results are
consistent with the results obtained, corroborating the conclu-
sion from the XRD patterns about the existence of CaO and
Ca(OCH3)2 particles.
On the other hand, the TEM images in Fig. 6(g) and (h) show
that the CM6 catalyst was composed of bundles of particles of
biconvex-like structure (view from top of plate-like shape
particles). The average particle sizes of CM6 as determined from
the TEM images were a diameter of 267.10 ꢃ 35.10 nm and a
thickness of 72.46 ꢃ 22.34 nm. Furthermore, a small amount of
well arranged irregular plate-like shape particles is clearly
visible on the external surface of the catalyst observed in
Fig. 7(g) and (h). A minute amount of particles or patches also
coexisted. The close-up view of Fig. 7(g) and (h) shows a typical
plate-like structure with an overall size of about 70 nm in
length; and a few small particles attached on the assembled
plates formed rough surface particles. This result is consistent
with the result gained from morphological studies by the
FESEM technique.
Representative TEM images of the CM8 catalyst are dis-
played in Fig. 6(i) and (j). In the magnied TEM image in the
inset, rigid biconvex-like structure particles are sufficiently
revealed by the appearance of the clear edge (Fig. 6(j)). The
averages sizes of CM8 determined from TEM images (Fig. 6(i)
and (j)) were 391.77 ꢃ 65.34 nm in diameter and 111.38 ꢃ 13.12
nm in thickness, correspondingly. The primary particles of CM8
catalyst appeared to be formed of abundant clusters of thin
plates as shown in Fig. 7(i) and (j). Increasing the synthesis time
not only resulted in high quantities and uniform morphology,
but also enhanced the number of pores which are visible on the
surface of the catalyst. The pores and thin plate-like
morphology contributed to the high surface area of the cata-
lyst. The close-up view in the inset of Fig. 7(j) shows that the thin
plate particles possessed a smooth surface state and were about
100 nm in length, almost consistent with the FESEM
observations.
Fig. 3 Crystallite size and BET surface area of calcium methoxide
catalysts.
strong basic property of Ca(OCH3)2 catalyst, as shown in
Scheme 3.
The particle morphology of all the catalysts is summarized in
Table 2. It was found that the difference in synthesis time leads
to the different morphologies of Ca(OCH3)2 catalyst, as shown
in the TEM (Fig. 6) and FESEM (Fig. 7) images. Fig. 6(a) and (b)
show the TEM images of the parent and non-modied CaO as
the starting material. The TEM images of CaO show clusters of
well-developed cubic crystals. The particle sizes were measured
from the TEM image and the average particle sizes were 137.02
ꢃ 11.30 nm in diameter. The structure of commercial CaO
catalyst showed surface unevenness (Fig. 7(a) and (b)).
Fig. 6(c) and (d) show TEM images of the CM2 catalyst
synthesized over 2 hours, giving cubic crystals of unreacted CaO
and irregular round-shaped Ca(OCH3)2 that are 170.71 ꢃ 25.26
nm and 68.06 ꢃ 19.29 nm in diameter, respectively. Increasing
the synthesis time showed no signicant changes in
morphology for the CM4 catalyst (Fig. 6(e) and (f)). However, the
TEM images revealed that the average particle sizes were
Fig. 6(k) and (l) shows the TEM photos of the CM10 catalyst
consisting of aggregated biconvex-like structure particles
(530.41 ꢃ 21.69 nm in diameter and 157.38 ꢃ 5.69 nm in
thickness) and large aggregated round particles (302.30 ꢃ 46.93
nm in diameter). The higher crystallinity of CM10 was
conrmed by FESEM (Fig. 7(k) and (l)). The crystallites of the
CM10 catalyst were larger than those observed for the CM8
catalyst, which presented aggregates of variable morphology.
The micrograph of FESEM endorsed the crystallinity result of
XRD.
The TEM micrographs of the CM12 catalyst gave an irregular
shape of Ca(OCH3)2, for which the synthesis time was 12 hours.
The particle sizes were measured from the TEM image and the
average particle sizes were 366.52 ꢃ 24.82 nm in diameter, as
shown in Fig. 6(m) and (n). The FESEM micrographs of the
CM12 catalyst gave irregular bulky round-shape on the external
surface of the catalyst, as shown in Fig. 7(m) and (n). The CM12
catalyst with compact agglomeration was in agreement with the
TEM images.
Fig. 4 Pore size distribution of CM8 catalyst.
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Fig. 5 FTIR spectra of the calcium methoxide catalysts.
The results demonstrated that the synthesis time is the key noteworthy that the catalytic activity of synthesized Ca(OCH3)2
for controlling the morphology evolution of the cluster thin catalysts showed high transesterication activity in the range of
plate-like calcium methoxide architectures. The collapsing of 74–87% under conditions of: 2 wt% of catalyst, molar ratio of
the plate-like structure of calcium methoxide catalysts led to methanol/oil (12 : 1) and reaction time 2 h at 65 ꢀC. The FAME
the reduction of the total surface area of the catalysts. Notice yield was increased from CM2 to CM8, while the further incre-
that, from Table 2, the particle sizes measured between XRD ment of synthesis time from CM10 to CM12 resulted in small
and TEM show dissimilarity. The sizes obtained from TEM decreases in catalytic performance.
were greater than those obtained from the XRD measure-
The BET surface area of a catalyst is believed to be an
ment. This deviation is known to depend on the aspect ratio important factor which affects the catalytic activity.12,20,23 The
for nonplated shaped crystallites, apart from the contribu- correlation between surface area of catalysts and FAME yield is
tions to the FWHM by the microstrain in the crystallite.22 demonstrated in Fig. 8. The enhancement in FAME content
Despite this limitation, the agreement that is seen between from 74% to 87% while shiing from CM2 to CM8 might be
the sizes measured by these two techniques may be taken to due to the increase in the catalysts' surface area from 16.2 to
be good in terms of the conclusion drawn as to the shape and, 30.5 m2 gꢂ1. The further increment of synthesis time for CM10
to a limited extent, as to the approximate true size of these and CM12 led to a slight drop in surface area, giving areas of
crystallites.
28.8 and 26.0 m2 gꢂ1, respectively. The collapsing plate-like
structures in CM10 and CM12 tend to reduce the catalyst's
surface area. The lower catalyst surface with synthesis times
above 8 h is the reason for the decrease in catalyst activity. This
might be due to the diffusion limitation between the reactant
and the active sites which were located inside the pores of the
catalyst.
As shown in Fig. 8, the morphology of the CM2 and CM4
catalysts was revealed to be an irregular round shape, with a
surface area lower than that of the CM8 catalyst. However, their
catalytic activity was comparable. This was probably due to the
synergistic effect of the presence of CaO and Ca(OCH3)2 phases
in the CM2 and CM4 catalysts, which were observed from the
XRD prole (Fig. 2). The lower surface area of the CM2 and CM4
catalysts was contributed to by the CaO phases. Excessive CaO
phases caused lesser porosity on the catalyst surface, which
contributed to the reduction in surface area. On the other hand,
Transesterication reaction: correlation between biodiesel
yield and synthesis time, surface area and morphology of
catalysts
The transesterication reaction involved the cleavage of the
ester group RCOOꢂ, from triglycerides (TG), by an alcohol
moiety of methanol to produce new esters with the original
alcohol moiety exchanged with the reacting alcohol. Since there
are three ester groups in a TG molecule, the three fatty acid
moieties attached to a single alcohol moiety yielded interme-
diate formation of diglycerides (DG), monoglycerides (MG) and
glyceride (Gly). The consecutive-competitive steps of the trans-
esterication reaction between TG and methanol are shown in
Scheme 4.
Different synthesis times of bulk Ca(OCH3)2 catalysts on
transesterication of crude JCO are presented in Table 3. It is
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Fig. 6 TEM micrographs of calcium oxide and calcium methoxide Fig. 7 SEM micrographs of calcium oxide and calcium methoxide
catalysts: (a) & (b) CaO; (c) & (d) CM2; (e) & (f) CM4; (g) & (h) CM6; (i) & (j) catalysts: (a) & (b) CaO; (c) & (d) CM2; (e) & (f) CM4; (g) & (h) CM6, the
CM8; (k) & (l) CM10; (m) & (n) CM12.
insets are close-up views focused on one bunch of plate-like structure
particles; (i) & (j) CM8, the insert of (i) is an enlarged image focused on a
cluster of tiny plate and the inset of (j) is a magnified FESEM image of a
few cluster plates; (k) & (l) CM10; (m) & (n) CM12.
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Scheme 4 Stepwise consecutive transesterification reaction and formation of DG, MG and Gly.
the BET surface area of CM6 was 20.5 m2 gꢂ1, which raised the properties, as shown in Fig. 4. Mesoporous and macroporous
FAME yield to 81.2%. The presence of well arranged irregular materials can serve as effective catalysts in transesterication
plate-like shape particles in the catalyst provided more active reactions for adsorbing large organic molecules, due to uniform
surfaces for the transesterication reaction.
structure and extremely high surface area.12,20 Therefore, the
The CM8 catalyst exhibited much higher biodiesel produc- reactivity of a catalyst is directly correlated with the external
tion than that of the other catalysts, and a biodiesel yield of surface area of the catalyst.
87.1% was achieved at 2 h. There was only a pure Ca(OCH3)2
phase found at CM8 catalyst to be the highest surface area
which provide strong basic property toward the trans-
esterication reaction. The cluster thin plate-like architectures
of the CM8 catalyst showed mesoporous and macroporous
Recyclability study
Fig. 9 summarizes the experimental results of reusability
between Ca(OCH3)2 and CaO catalysts. Unlike the CaO catalyst,
Table 3 Transesterification activities of bulk CM2, CM4, CM6, CM8,
CM10 and CM12 catalysts with different synthesis times for biodiesel
productiona
Catalysts
Yield of FAME (%)
CM2
CM4
CM6
CM8
CM10
CM12
74
78
81
87
79
80
a
Fig. 8 Correlation between biodiesel yield with surface area of CM2,
CM4, CM6, CM8, CM10 and CM12 catalysts. Reaction conditions: oil ¼
10 g, catalyst dosage ¼ 2%, n(methanol) : n(oil) ¼ 12 : 1, reaction time
¼ 1.5 h, reaction temperature ¼ 65 ꢀC.
Transesterication
conditions:
catalyst
dosage
2%,
n(methanol) : n(JCO) ¼ 12 : 1, reaction time 2 h, reaction temperature
65 ꢀC.
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active sites participating in the reaction. Methanol and
triglyceride are adsorbed on the two neighboring free catalytic
sites, as indicated by step (a) and step (b). In step (a), the
surface Odꢂ extracts Hd+ and Cad+ adsorbs CH3Odꢂ from
methanol. Meanwhile, the adsorbed triglyceride forms a
surface intermediate between Odꢂ with the Cad+ on the surface
of the catalyst, as shown in step (b). The two neighboring
adsorbed species react with each other, in step (c), which
results in the formation of a fatty acid methyl ester and a
diglyceride. Using the stepwise consecutive and reversible
reaction, the diglyceride and monoglyceride react with meth-
anol on the surface of the catalyst to produce methyl esters and
glycerol in a similar fashion.
Fig.
9 Recyclability study of CM8 and CaO catalysts. Reaction
conditions: oil ¼ 10 g, catalyst dosage ¼ 2%, n(methanol) : n(oil) ¼
Conclusions
15 : 1, reaction time ¼ 1.5 h, reaction temperature ¼ 65 ꢀC.
Ca(OCH3)2 is a powerful heterogeneous catalyst for the
transesterication reaction of non-edible Jatropha curcas oil
for biodiesel production. Ca(OCH3)2 catalysts have three
types of morphologies: irregular round shape particles, a well
arrangement of plate-like structures with a rough surface and
the transesterication operation of Ca(OCH3)2 catalyst was
successively repeated 5 times and maintained sustained activity
ꢀ
to produce yields in excess of 86% biodiesel at 65 C. The only
a
cluster of tiny plate-like architectures with smooth
surfaces. Under optimum conditions of 65 ꢀC, 12 : 1 meth-
anol to oil molar ratio and 2% catalyst concentration, a
greater than 87% yield was achieved in 2 h. Ca(OCH3)2
catalyst can be separated easily from the reaction mixture
and reused to give consistent transesterication activity (ve
times reuse). This hydrothermal method is simple and the
steps to fabricate the Ca(OCH3)2 catalyst are easily per-
formed. The Ca(OCH3)2 catalyst produced can be used for
various application i.e. (i) transesterication of trimethylol-
propane for bio-lubricant production, (ii) ring-opening
polymerization of lactone and (iii) as an effective con-
solidants precursor material for polymerization.
slightly reduced in biodiesel yield was found during successive
cycles of use. Due to the lesser porosity and fewer active surface
basic sites of the CaO catalyst, the CaO catalyst was not suitable
for transesterication of crude JCO at short reaction times in
the presence of only low concentrations of catalyst.23
The proposed mechanism of the transesterication reaction
by the Ca(OCH3)2 catalyst with methanol and triglyceride
process is demonstrated in Scheme 5.
Firstly, when calcium methoxide is used as a solid base
catalyst, the catalysis mechanism could be assumed on the
basis that the catalytic reactions take place on the surface of
the catalyst, with Cad+ and Odꢂ being the two catalytically
Scheme 5 Reaction mechanism for the transesterification of triglyceride with methanol over the calcium methoxide catalyst, where R1, R2 and
3 represent the long-chain alkyl groups.
R
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