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Preparationandapplicationofbinaryacid-base
CaO-La2O3catalystforbiodieselproductio
ArticleinRenewableEnergy·February2015
DOI:10.1016/j.renene.2014.07.017
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Renewable Energy 74 (2015) 124e132
Contents lists available at ScienceDirect
Renewable Energy
journal homepage: www.elsevier.com/locate/renene
Preparation and application of binary acidebase CaOeLa2O3 catalyst
for biodiesel production
H.V. Lee a, *, J.C. Juan a, Y.H. Taufiq-Yap b
a
b
Nanotechnology & Catalysis Research Centre (NanoCat), Institute of Postgraduate Studies, University Malaya, 50603 Kuala Lumpur, Malaysia
Centre of Excellence for Catalysis Science and Technology, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 September 2013
Accepted 14 July 2014
Available online
A simple method was developed for biodiesel production from non-edible Jatropha oil which contains
high free fatty acid using a bifunctional acidebase catalyst. The acidebase catalyst comprising CaO and
La2O3 mixed metal oxides with various Ca/La atomic ratios were synthesized via co-precipitation
method. The effects of Ca/La compositions on the surface area, acidityebasicity and transesterification
activity were investigated. Integrated metalemetal oxide between Ca and La enhanced the catalytic
activity due to well dispersion of CaO on composite surface and thus, increased the surface acidic and
basic sites as compared to that of bulk CaO and La2O3 metal oxide. Furthermore, the transesterification
reactions resulted that the catalytic activity of CaOeLa2O3 series were increased with Ca/La atomic ratio
to 8.0, but the stability of binary system decreased by highly saturated of CaO on the catalyst surface at
Ca/La atomic ratio of 10.0. The highest biodiesel yield (98.76%) was achieved under transesterification
condition of 160 C, 3 h, 25 methanol/oil molar ratio and 3 wt.%. In addition, the stability of CaOeLa2O3
binary system was studied. In this study, CaeLa binary system is stable even after four cycles with
negligible leaching of Ca2þ ion in the reaction medium.
© 2014 Elsevier Ltd. All rights reserved.
Keywords:
Biodiesel
Transesterification
Jatropha oil
Acidebase catalyst
Co-precipitation
Heterogeneous catalyst
1. Introduction
Recently, the worldwide biodiesel production has grown
sharply. Biodiesel (fatty acid methyl esters, FAMEs) is a renewable,
biodegradable, non-toxicity and alternatives (or extender) for
transportation fuel (conventional petroleum based diesel fuel). The
physicochemical and fuel properties of biodiesel are grouped into
the same range as petroleum diesel. Thus, it can be applied to
compression-ignition diesel engines with little or no modification
[1,2].
Generally, biodiesel can be derived from natural and renewable
domestic source of triglycerides (vegetable oil). With the concern of
edible oil rivalry between food and fuel purpose, unpractical usage
of over-expensive materials in actual production of biodiesel
contributed to the shift of biodiesel feedstock from edible resources
to non-edible resources [3e6]. Jatropha Curcas oil, a potential
inedible source of biodiesel, has drawn the interesting of both
government and private sectors for biodiesel production, lately.
* Corresponding author. Tel.: þ60 3 7967 6954; fax: þ60 3 7957 6956.
E-mail addresses: [email protected], taufi[email protected] (H.V. Lee).
http://dx.doi.org/10.1016/j.renene.2014.07.017
0960-1481/© 2014 Elsevier Ltd. All rights reserved.
The current technologies for biodiesel production are based on
homogeneously catalyzed transesterification under basic conditions (NaOH or KOH). Non-edible jatropha oil consists of high free
fatty acids (FFAs) content, is cheaper in prices as compared to edible
oil due to its inferior nutritional value, low market demand and
high availability. The conventional basic catalysts (NaOH and KOH)
are sensitive to high content of FFAs, which led to formation of soap
and complicates the product separation as well as reduces the
biodiesel content. Numerous studies have been carried out by using
two step acidebase catalyzed reactions. The first acid catalyzed
treatment is used to reduce FFA to <1 wt.% via esterification followed by base catalyzed transesterification of treated oil to high
grade biodiesel. However, the main concerns are the high material
cost (excess methanol), post-treatment cost (multi-purification and
water washing) to remove homogeneous catalyst, additional
treatment to neutralize the pH for first and second processes.
Furthermore, the content of treated oil and final biodiesel product
were reduced during separation and washing step. Thus, the high
acid J. curcas oil is not feasible to be employed in conventional
approach for biodiesel production in view of its incompatibility to
the homogeneous catalysts [7,8].
To optimally exploit the high FFA content J. curcas oil in biodiesel
production, a new easy-to-operate heterogeneous catalytic system
H.V. Lee et al. / Renewable Energy 74 (2015) 124e132
which is capable of performing mild esterification and transesterification with minimal soap formation is highly desirable. Such
integrated solid catalyst furnish with bifunctional acidebase system where the Lewis acid sites involve to esterification reaction of
carboxylic acid with methanol and the conjugated basic sites activate the transesterification of triglyceride with methanol in onepot reaction. In contrast with two steps homogeneous acid and
base catalyze reactions, heterogeneous catalyst equipped with
acidebase properties may render many inherent advantages.
Previous research indicated that CaO, either from natural waste
shell or limestone or chemical Ca salt are widely used as an active
base catalyst for transesterification studies [9e14]. Conjugation
between CaO and metal oxides with different basicity/acidity is
able to enhance the basicity or provides acidebase active sites for
transesterification process. Currently, some of the heterogeneous
mixed metal oxides are reported to be active in transesterification
reaction because they are tolerance to high FFAs and water in
vegetable oil. Previously, we have successfully established that the
improvement of basicity and catalyst's stability by integrated CaO
with MgO or ZnO. The mixed metal oxide (CaOeMgO and
CaOeZnO) by ameliorate the basicity were highly active in transesterification of low grade jatropha oil. Furthermore, strong stability of these binary metal oxide system provide higher quality
biodiesel yield with less leaching of active metal ion, better reusability and highly tolerance to FFA as compare to pure CaO [15e17].
Recently, a bifunctional acidebase mixed metal oxide catalyst,
ZnOeLa2O3 which capable of catalyzing esterification and transesterification reaction simultaneously in a single step for unrefined
or waste oil with high water and FFAs content. The strong interaction between Zn and La species was induced by the presence of
both basic and acid active sites which found to simultaneously
catalyze the fatty acid esterification and oil transesterification reactions while minimizing oil and biodiesel hydrolysis. Approximately of 96% of biodiesel content was yielded at the high reaction
temperature (220 C) after 3 h of reaction even with crude palm oil,
crude soybean oil, waste cooking oil, food-grade soybean oil with
3% water and 5% oleic acid addition [18].
In this study, binary metal oxides comprised of CaO and La2O3
with adequate acidebase properties were synthesized via coprecipitation method. The potential materials use for catalyst
synthesis are Ca and La, it is anticipated that CaeO consist of
basicity that suitable for triglyceride transesterification whereby
La2þ render the acidic properties that preferable for esterification
of free fatty acid. The physicochemical properties and catalytic
activity of its bulk oxides and mixed metal oxides were studied.
The prepared binary oxide catalyst has been used in biodiesel
production via transesterification of non-edible jatropha oil with
methanol, to assess the technology's ability in order to meet
quality specification for biodiesel. Furthermore, the recyclability of
the catalysts has been investigated to determine its binary system
stability.
2. Experimental
2.1. Catalyst preparation
Catalysts with different Ca/La atomic ratios (0.5e10.0 atomic%)
were prepared using co-precipitation method. In a typical catalyst
preparation procedure, the required amount of Ca(NO3)2$4H2O and
La(NO3)3$6H2O was dissolved in deionized water. The two precursor solutions were mixed homogeneously and allowed to precipitate using a NaOH and Na2CO3 basic solutions at a constant pH of 10
and controlled by slow addition in metal salt mixture. The sample
was stirred for 24 h at 60 C. Finally, the precipitate formed was
then filtered, washed until the pH of the filtrate was 7 and dried at
125
100 C overnight. The sample was calcined at 950 C for 6 h after
drying based on the TGA analysis (Supplementary data). Thermal
activated catalysts were denoted as CL0.5, CL2, CL4, CL6, CL8 and
CL10 with incremental Ca/La atomic ratios of 0.5, 2.0, 4.0, 6.0, 8.0
and 10.0 atomic%, respectively.
For comparison, the bulk CaO was prepared using the same
procedure as above (co-precipitation method). The precursor for
the oxide was formed after the dropwise addition of precipitant
agent of Na2CO3 and NaOH solution into the aqueous solution of
Ca(NO3)2$4H2O at room temperature. The mixture was then under
vigorous stirring for 24 h at 60 C. The white solid was centrifuged
and washed with deionized water and dried at 100 C. The CaO
obtained after calcinations in air for 800 C for 6 h based on several
literature reviews [11,19].
2.2. Catalysts characterization
The powder X-ray diffraction (XRD) analysis was carried out
with a Shimadzu diffractometer model XRD6000. The diffractometer employed Cu-Ka radiation to generate diffraction patterns from
powder crystalline samples at ambient temperature. The Cu-Ka
radiation was generated by a Philips glass diffraction X-ray tube
(broad focus 2.7 kW type).
The total surface area of the catalysts was obtained using a
BrunauereEmmereTeller (BET) method with nitrogen adsorption
at 196 C. Analysis was conducted using a Thermo Finnigan
Sorptomatic 1900 series nitrogen adsorption/desorption analyzer.
Scanning electron microscopy with energy dispersive X-ray
spectroscopy (SEM-EDS) was used to obtain information about the
morphology and size of the samples. The morphology study of the
catalysts was carried out using a JEOL scanning electron microscope
model JSM-6400 while elemental chemical analysis done with the
EDS technique. Furthermore, bulk metal content present in the
catalysts was determined by using Inductive coupled plasmaAtomic emission spectrometer (ICP-AES), PerkinElmer Emission
Spectrometer Model Plasma 1000.
The basicity and the basic strength distribution of the catalysts
were studied by temperature-programmed desorption using CO2 as
probe molecule. TPD-CO2 experiment was performed using a
Thermo Finnigan TPDRO 1100 apparatus equipped with a thermal
conductivity detector. Catalysts (0.1 g) were pretreated under a
helium stream at 800 C for 30 min (10 C min1, 30 mL min1).
Then, the temperature was decreased to 50 C, and a flow of pure
CO2 (30 mL min1) was subsequently introduced into the reactor
for 1 h. The sample was flushed with helium at 50 C for 30 min
before the CO2 desorption analysis. The analysis of CO2 desorption
was then carried out between 100 and 1000 C under helium flow
(10 C min1, 30 mL min1) and detected by thermal conductivity
detector (TCD). The acidity of the catalyst was determined by using
ammonia (NH3) as a probe gas. The adsorption and desorption of
NH3 was followed the same steps as TPD-CO2 method. The amount
of basicity/acidity of the catalyst were determined by the shape of
the CO2/NH3 desorption peak from the data of area under the graph
that provided. The temperature of the peak maximum (Tmax) at
which the desorption of CO2/NH3 occurred used to study the
characteristic and basic/acid site distribution of the active sites for
the catalysts.
The chemical stability of the binary metal oxide catalyst was
investigated by analyzing the presence of free metal content in the
biodiesel product which could be attributed to the occurrence of
leaching. The biodiesel product from the reusability test was
analyzed without further purification step by atomic absorption
spectrometer (AAS-S Series; Thermo Scientific, San Jose, CA). The
concentration of Ca content (ppm) in biodiesel produced was
detected.
126
H.V. Lee et al. / Renewable Energy 74 (2015) 124e132
Table 1
Physicochemical properties and characteristic of J. curcas oil.
Properties (unit)
a
b
Specific gravity (g cm3)
Flash point ( C)
Viscosity at 40 C (cSt)
Sulphated ash (% mass)
Sulphur (% mass)
Cloud point ( C)
Copper corrosion
Cetane number
Water (% volume)
Free glycerin (% mass)
Total glycerin (% mass)
Phosphorus (% mass)
Distillation temperature ( C)
Oxidation stability (hours)
Saponification number (mg g1)
Free fatty acids % (Kg Kg1 100)
Acid number (mg KOH g1)
Heating value (calorific value)
(MJ kg1)
f
Fatty acid composition (%)
Palmitic acid (16:0)
Stearic acid (18:0)
Oleic acid (18:1)
Linoleic acid (18:2)
0.860e0.933
210e240
37.0e54.8 (at 30 C)
e
e
2
e
38.0e51.0
e
e
e
e
e
e
102.9e209.0
0.18e3.40
0.92e6.16
37.83e42.05
0.914
235
54.8
e
0e0.13
2
1
46.3
0.052
0.03
0.04
<0.004
Not under spec.
Min 6
c
186.48e193.32
d
9.0e12.0
e
16.03e22.85
e
Range
Range
oil is 9 wt.%. Transesterification was carried out in a BERGHOF
high-pressure laboratory reactor, which equipped with temperature controller, temperature probe, pressure gauge and stirrer
motor (Fig. 1). A certain amount of CaOeLa2O3 mixed metal oxides catalyst was added to the reaction mixture of 20.0 g of J.
curcas oil, along with the required amount of methanol. The
reactant mixture was then heated to a constant temperature
under maximum agitation. At the end of the experiment, the
catalyst was separated from the product using a centrifuge, and
the reaction mixture was then loaded into a rotary evaporator to
remove excess methanol.
The biodiesel product was analyzed with a gas chromatography
system (PerkinElmer Autosystem XL, USA) equipped with a flame
ionization detector (FID) and connected to an HP-Innowax capillary
column (30 m 0.25 mm 0.25 mm; J&W Scientific). The content
of methyl ester was calculated following the European regulated
procedure EN14103 [21].
2.4. Jatropha-based biodiesel quality evaluation
13.77
6.77
41.68
35.55
e
e
e
e
a
Information provided from Achten et al. 2008) [20].
Information provided by Biofuel Bionas Sdn. Bhd.
Saponification value testing by PORIM (1995) p3.1.
d
Free Fatty Acid content testing by PORIM (1995) p2.5.
e
Acid number testing by AOCS Cd 3d-63 (1997).
f
Other fatty acids (myristic, arachidic, behenic, lignoceric, palmitoleic, erucic and
linolenic acids) were presented in amounts of <1%.
b
c
The physico-chemical properties of biodiesels produced from
CaOeLa2O3 catalyzed transesterification reactions were analyzed
for standard specifications. The list of tests for biodiesel characterization are included density, viscosity, flash point, cloud point,
pour point, water content, sulphur content, acid value, iodine value
and analysis of methanol content. The following tests were carried
out in a MYCO2 green laboratory and the result was compared with
biodiesel standards of EN14121 and ASTM D6751 that available for
biodiesel fuel (Table 7).
3. Results and discussion
2.3. Catalytic activity
3.1. Physicochemical properties of CaOeLa2O3 catalysts
The catalytic activity was evaluated using transesterification of
crude J. curcas oil (JCO) (Bionas Sdn. Bhd.) with methanol (Aldrich,
99.5%). The physico-chemical properties of crude J. curcas oil were
shown in Table 1 [20]. The free fatty acid (FFA) content of jatropha
The XRD spectra of binary CaOeLa2O3 metal oxide, bulk CaO and
La2O3 are shown in Fig. 2. The series of CaOeLa2O3 with Ca/La
atomic ratio ranging from 0.5 to 10.0 which thermally pretreated
Fig. 1. Schematic diagram of high temperature reactor.
H.V. Lee et al. / Renewable Energy 74 (2015) 124e132
Fig. 2. XRD pattern for CaOeLa2O3 mixed metal oxides catalysts.
(950 C) showed the presence of individual CaO and La2O3 phases
in the mixed metal oxide. The diffraction patterns observed in
CaOeLa2O3 catalysts with Ca/La atomic ratio from 0.5 to 10.0
showed intense La2O3 phases and low intensity of Ca crystallite
peaks. Although Ca loading was continuously increased for every
catalyst synthesis, the corresponded XRD peaks for CaO were small.
This suggested that La3þ ions in the host lattice were partially
substituted by Ca2þ ions, which corroborated with Liu's study [22].
This is due to inhabitation of CaO crystal growth and vigorous
dispersion CaO crystal. The XRD pattern of CaOeLa2O3 with 8.0
atomic ratio (CL8.0) showed the most significant presence of CaO
crystal and La2O3 phases, which indicated that the saturated Ca2þ
ion in the host lattice of La2O3, and thus induced the formation of
free CaO phases on the composite surface [23]. For CL10.0, the intensities of CaO peaks was reduced together with crystallites phases of La2O3,which imply that some of the La3þ and excess of Ca2þ
do not precipitate completely during co-precipitation process.
The surface and bulk composition of Ca/La atomic ratio was
determined by EDS and ICP-AES analysis (Table 2). The results
showed that experimental surface atomic molar ratio of CaOeLa2O3
127
catalysts was lower than the intended ratio. This indicated that the
well dispersion of Ca content on the catalyst's surface. It is suggested that Ca atom was incorporated into the La species lattice and
render excess exposure of La on the catalyst surface [23]. This fact
was supported by ICP-AES analysis which the bulk Ca/La ratio was
higher than the surface Ca/La ratio. However, the bulk ratio was
found lower to those appointed metal ratio, indicating incomplete
precipitation of the metal ions by using coprecipitation method.
This condition was identical to Liu et al. (2007) and Sree et al.
(2009)'s studies [24,25]. As reported by Yan et al. (2010), although
binary oxides catalyst synthesized from co-precipitation method
show promise to obtain a high concentration of active catalytic
sites, it is apparent that a single precipitant agent cannot effectively
precipitate all metal ions in solution and sometimes will result in
un-precipitated Ca ion or La ion wash off during the preparation
process [23].
The crystallite size of binary oxide of CaOeLa2O3 catalysts was
calculated by the DebyeeScherrer equation based on the highest
intensity reflection peak of CaO and La2O3 (Table 2). The results
showed that the crystallite size for both CaO and La2O3 phase in the
mixed metal oxides with different ratio varied suggesting presence
of interaction between the Ca and La species which helped in Ca
dispersion. The series of CaOeLa2O3 catalysts have low specific
surface area ranges from 7.73 to 14.27 m2/g and the result was in
agreement with crystallite size of the catalysts. The big aggregation
concomitantly with large particle size resulted in low surface area
of the catalysts.
The basic sites and total basicity of heterogeneous catalyst
played main role as active centers for the transesterification reaction. The base strength and basicity of the catalysts was studied by
TPD-CO2. Fig. 3 shows the presence of main super basic strength
with CO2 desorption peak at the temperature range of >500 C.
According to several researchers [26e28], La2O3 contributed both
base and acid properties in the binary catalyst system. For metal
oxides (like La3þeO2), the surface lattice oxygen was attributed to
Lewis base sites (favor for transesterification) whereas the metal
ions are Lewis acid sites (favor for esterification). In this TPD-CO2
profile, the binary interaction between Ca and La species in binary
metal oxide induced the synergetic effect that further enhanced the
basicity and basic strength of CaOeLa2O3 compared to its single
oxides. The result indicated that mixed metal oxides rendered high
Table 2
Chemical composition and physicochemical properties of CaOeLa2O3 mixed metal
oxides catalysts.
Catalyst
Theoretical Experimental Experimental Crystallite
ratioa
surface ratiob atomic ratiob sizes (nm)c
Bulk oxide
CaO
e
La2O3
e
Mixed metal oxide
CaOeLa2O3 0.5
2
4
6
8
10
CaO
La2O3
SBET
(m2/g)d
e
e
e
e
40.2
e
e
41.94
0.16
1.15
2.78
4.30
6.39
4.06
0.47
1.84
3.03
5.56
7.56
5.89
e
59.80
35.03
49.44
63.07
41.37
40.32 14.27
56.53 10.93
69.03 11.12
45.16
8.98
53.87
7.73
37.43
8.77
9.5
2.20
a
Theoretical Ca/La atomic ratio of catalyst.
Experimental Ca/La atomic ratio in the synthesized catalyst determined by EDS
and ICP-AES.
c
Determined by using DebyeeScherrer equation.
d
BET surface area.
b
Fig. 3. TPD-CO2 for the CaO, La2O3 and series of CaOeLa2O3 mixed metal oxides
catalysts.
128
H.V. Lee et al. / Renewable Energy 74 (2015) 124e132
Table 3
The basic intensity for the series of CaOeLa2O3 mixed metal oxides
catalysts.
Catalyst
Bulk oxide
CaO
La2O3
Mixed metal oxide
CaOeLa2O3
0.5
2
4
6
8
10
a
Total basicity (mmol of CO2/g)a
290.42
179.86
549.92
663.67
737.75
2789.52
3198.74
2163.5
CO2 desorption peak for all catalysts at Tmax of >500 C.
amount of total basicity than that of CaO, which is 11 times larger
than pure oxide (290.42 mmol of CO2/g) [15] as compared with CL8
catalyst. Besides, the La3þ acts as an electron donor, enhancing the
interaction of reactant molecules with catalyst surface [29]. As
indicated in Table 3, the total basicity increased when the Ca/La
molar ratio was raised from 0.5 to 8.0 with exception for molar ratio
of 10.0.
The variation of surface morphology for the series of CaOeLa2O3
catalysts with different Ca/La atomic ratio was determined by SEM
analysis. The SEM micrographs showed the agglomerated particles
of cubic CaO structure and La2O3 with irregular shape structure
(Fig. 4A and B). In low Ca content such as CL0.5 (Fig. 4C), the
spherical structure was observed due to mainly formation of La2O3
phase with symmetrical particle size distribution. With the
increased of Ca/La loading from 4.0 to 8.0 atomic ratio, the particle
agglomeration occurred with the formation of merging structure of
CaO with La2O3. It was presence of non-uniform structures
(spherical or cubic) with different size of particles (Fig. .4D and E).
3.2. Catalytic test for transesterification process
Investigations were conducted on a series of calcium and
lanthanum oxides catalyst for biodiesel production. The optimum
transesterification condition was selected based on Response Surface Methodology (RSM) optimization tool that similar to our
previous study [30]: 160 C, methanol/oil molar ratio of 25, catalyst
loading of 3 wt.% in 3 h of reaction time. For CaOeLa2O3 catalyzed
transesterification, higher reaction temperature are needed to give
a satisfactory conversion as compared to that of several previous
mixed metal oxides studies (CaOeMgO and MgOeZnO) [16,31]. The
transesterification temperature (160 C) at moderate pressure able
to enhance oilemethanol miscibility (by reduce heterogeneous
phase separation) and increase rate of reaction, leading to a shorter
reaction time. Moreover, higher temperature minimizes the initial
mass transfer limitation in transesterification system. When the
reaction temperature reached 160 C, the vapor pressure of
Fig. 4. SEM micrographs for the for the CaO (A); La2O3(B); CL0.5 (C); CL4 (D); CL8 (E).
H.V. Lee et al. / Renewable Energy 74 (2015) 124e132
129
Table 4
Transesterification activities of for the bulk CaO, La2O3 and
series of CaOeLa2O3 mixed metal oxides catalysts for the
biodiesel synthesis.
Catalysts
Yield of FAME (%)
Metal oxide
a
CaO
b
La2O3
Mixed metal oxide (CaOeLa2O3)b
CL0.5
CL2
CL4
CL6
CL8
CL10
96
23
84
91
93
96
98
95
a
Transesterification condition: reaction temperature of
120 C, 3 h reaction time, 3 wt.% of catalyst and methanol/
oil ratio of 25:1.
b
Transesterification condition: reaction temperature of
160 C, 3 h reaction time, 3 wt.% of catalyst and methanol/
oil ratio of 25:1.
methanol is ~2.0 MPa, which will favor transesterification reaction
under this high pressure and temperature [32].
In the present study, the binary oxides catalyst showed a superior transesterification activity over pure calcium oxide (96%) or
pure lanthanum oxide (23%) catalysts. Although CaO is able to
render high transesterification activity at lower reaction temperature at 120 C, the stability of CaeO bonding system is weak, in
which Ca2þ easily to scrape away by FFAs under longer reaction
time or continuous batch reaction [33,34]. Among the CaOeLa2O3
catalysts with Ca/La ratio of 0.5e10.0 atomic %, CaOeLa2O3 with
atomic ratio of 8.0 rendered highest biodiesel yield of 99% (Table 4).
From the EDS and ICP results, the increment of Ca has significantly
influenced the basicity of the catalyst. It is interesting to observe
that the total basicity of CL6 (2789.52 mmol of CO2/g) is much higher
than that of CL4 (737.75 mmol of CO2/g), but the catalytic activity
does not increase as much than expected (3% increment). This is
because the surface area of CL6 (8.98 m2/g) is lower than that of CL4
(11.10 m2/g) although CL6 has higher amount of basicity. Therefore,
this has oppressed the catalytic activity of CL6 which supposed to
give much higher activity. It was same case for the reactivity of
CL10, the surface area of CL4 (11.12 m2/g) are slightly higher than
CL10 (8.77 m2/g), while basicity of CL10 (2163.50 mmol of CO2/g) has
reduced significantly as compared to CL8 (3198.74 mmol of CO2/g).
However the catalytic activity of CL10 (95%) is still much higher
Fig. 5. Correlation between the total basicity and FAME yield of the CaOeLa2O3 mixed
metal oxide catalysts.
than that of CL4 (93%). This indicated that the surface basic active
sites of catalyst still playing a priority role for the transesterification
reaction.
By coupling Ca and La into mixed metal oxide system, it is able to
increase stability of CaO and render acidebase properties for
simultaneous esterificationetransesterification reaction. The presence of mixed metal oxide system required higher temperature for
reaction as compared to CaO reaction temperature. This is because
acidity from La2O3 need higher temperature for acid catalyzed
esterification compared to base catalyzed transesterification [18].
The catalytic activity of CL8.0 were compared with several
similar studies [35e38], where CaOeLa2O3 catalyst were used to
study transesterification of vegetable oil (Table 5). From this summary, different types of catalyst synthesis methods (Solegel, coprecipitation and wet-impregnation support) and Ca:La ratio
were used to synthesize CaOeLa2O3 catalysts. The studies showing
that longer reaction time was required for these catalysts to catalyze the transesterification of oil with high FFA content. In our
study, higher reaction temperature (160 C) was capable to render
better yield of biodiesel within shorter reaction time.
The correlation between the effects of base strength and basicity
of the catalyst on the catalytic activity was studied. Fig. 5 shows the
catalytic trend of CaOeLa2O3 series with its basicity. The results
illustrated the catalytic trends were parallel to the variability of
total basicity. This study was in good agreement with previous
Table 5
Summary of studies for CaOeLa2O3 catalyzed transesterification reaction.
CaOeLa2O3 catalysts
Ca:La ratio
Synthesis method
Acidity/basicity
Transesterification conditions
Biodiesel yield
Ref.
CaOeLa2O3/
La2O3 support
CaOeLa2O3
3.08:1 (in %)
Basicitya
10.0 g of soybean oil, methanol:
oil ratio is 10:1, 0.8 g of catalyst, 3 h, 64 C.
10.0 g of soybean oil, Methanol/ethanol:
oil ratio is 5/5:1, 0.8 g catalyst, 0.5 h, 65 C
97.2%
[35]
2.68:1 (in %)
Impregnation
procedure
Solegel method
[36]
CaLa4
4:1 atomic
ratio (in %)
3:1 M ratio
Co-precipitation
method
Co-precipitation
Methyl Ester:Ethyl
Ester ratio is 3.4
Higher rate of
methanolys is
than ethanolysis
86.51%
[37]
94.3%
[38]
8:1 atomic
ratio (in %)
Co-precipitation
98.76%
Present Study
Ca3La1
CL8.0
a
b
c
d
Determined
Determined
Determined
Determined
by
by
by
by
titration method.
TPD-CO2 analysis.
Hammett indicator method.
TPD-NH3 method.
N/S
Basicityb
Basicityc
(Presence of Bronsted
and Lewis Bases)
Acidityd and basicityb
Jatropha oil (FFA: 20.16 wt.%), methanol:oil
ratio is 24:1, 4% of catalyst, 65 C, 6 h,
Food grade soybean (4% water and FFA 3.6%),
methanol:oil ratio is 20:1, 0.5 g of catalyst,
2 h, 58 C
Jatropha oil (FFA: 9 wt.%), methanol:oil ratio
is 25:1, 3 wt.% of catalyst, 160 C, 3 h.
130
H.V. Lee et al. / Renewable Energy 74 (2015) 124e132
(287.05 mmol of NH3/g) than individual La2O3 catalyst (186.72 mmol
of NH3/g). This is due to the presence of synergism effect between
CaO and La2O3. The unique cooperative action of acidebase sites
from CaeOeLa, CaeOeCaeO and LaeOeLaeO bonds render a
simultaneous esterificationetransesterification reaction for biodiesel production. This is in agreement with the studies above
(Table 4), where the presence of FFA in oil was esterifies into ester
products.
3.3. Reusability and leaching test
Fig. 6. TPD-NH3 for La2O3 and CL8 catalysts.
studies by Olutoye and Hameed (2009) [39], stating that the higher
basicity shall enhance the catalytic activity.
Other than basic active site of catalyst, it is anticipated that
catalytic activity of CaOeLa2O3 can be contributed by the acidity of
CaOeLa2O3 catalyst. Hence, an esterification reaction between oleic
acid with methanol was carried out by using CL8.0 catalyst. This
study was used to examine the capability of optimized CL8.0 to act
as acid catalyst and esterifies FFA in jatropha oil to methyl ester. In
this experiment, oleic acid (as a model compound of FFA) with
9 wt.% (similar to FFA content in jatropha oil) was reacted with
methanol at same transesterification condition (160 C, 3 h, 3 wt.%
of catalyst and methanol/oil molar ratio of 25). Oleic acid was
successfully converted to methyl oleate with around 95%, which
means that CL8.0 catalyst consisted acid sites for esterification
reaction.
In order to further affirm the presence of acid sites in CL8.0,
acidity of catalyst was analyzed by using TPD-NH3 technique. The
NH3-TPD profile (Fig. 6) showed that the catalysts (La2O3 and CL8.0)
had distinct desorption peak at Tmax of >500 C, indicating the
presence of strong acid sites for both catalysts. Once again, it proved
that binary system of CaOeLa2O3 rendered higher acidity
As shown in Fig. 7, the recyclability efficiency of the CaO and
CaOeLa2O3 (CL8.0) was investigated by performing the transesterification steps for several runs. The catalyst was reused for the
next consecutive run without any pre-treatment process such as
washing or thermal treatment. The catalytic activity of CaO
decreased sharply within 5 runs (from 96% reduced to 60%) [40].
This decrement was due to the fraction of bulk CaO that was
dissociate by FFA and dissolved in the methanolic solution.
Furthermore, the leaching of active Ca2þ from CaO will eventually
reduce the number of active sites and reactivity of the catalyst. In
case of CL8 reusability, the trend of transesterification activity
showed a marginal downward trend while maintaining FAME yield
at around 80% for first 3 runs. The results showed that significant
dropped of FAME yield for second run from 98.8 to 87.9% indicated
that free active Ca2þ ions in the binary system leached out during
the first reaction. Furthermore, the higher reaction temperature
(160 C) is a crucial factor to accelerate the leaching of Ca2þ. As a
result, the catalytic activity of second used catalyst was decrease as
the catalytic active sites was reduced.
In order to clarify the contribution of leached Ca2þ to the overall
biodiesel yield, following investigation test on CL8.0 catalyst was
performed. The fresh CL8.0 catalyst was first stirred with certain
amount of methanol (25:1 methanol to oil ratio) at usual transesterification condition (160 C and 3 h). Subsequently, the stirred
catalyst was then filtered out and the methanol filtrate was reacted
with fresh jatropha oil under the same reaction condition. It was
observed that 8% of FAME yield was obtained from the first run
(Table 6), which means that 8% from total of 98.76% of the FAME
yield was contributed by the presence of leached Ca2þ homogeneous catalyzed reaction. The second and third leaching experiment showed the decreased of FAME yield at 5 and 4%, respectively,
while the control experiment (without catalyst) renders 3% of
Fig. 7. Recyclability study for CaO and CL8 catalyst.
H.V. Lee et al. / Renewable Energy 74 (2015) 124e132
Table 6
Reusability and leaching tests profile.
Number of run
Reusability testb
(FAME yield %)
Leaching testb
(FAME yield %)
CL8 catalyst
Ca (ppm)c
Blank testa,b
1st run
2nd run
3rd run
e
98
88
82
3
8
5
4
e
26.31
11.97
11.93
a
Reaction between jatropha oil and methanol without catalyst.
Transesterification condition: reaction temperature of 160 C, 3 h reaction time,
3 wt.% of catalyst and methanol/oil ratio of 25:1.
c
Determine by AAS analysis.
b
131
standard EN14214. The fuel properties of Jatropha-based biodiesel
from CaOeLa2O3 catalyzed reaction was summarized in Table 7
along with a comparison to the recommended biodiesel international standards EN14121 and ASTM D6751. The physico-chemical
properties assessed includes, density, kinematic viscosity (40 C),
flash point, pour point, sulfated ash, acid value, iodine value and
moisture content. The results revealed comparable properties of
jatropha-based biodiesel with fossil diesel, which affirm the suitability of high acidity J. curcas oil to be a biodiesel feedstock if
bifunctional acidebase CaOeLa2O3 is use as transesterification
catalyst.
4. Conclusion
FAME yield. This give a clear indication that low content of soluble
Ca2þ species from CL8 binary system which only make a minor
contribution of homogeneous-type transesterification. This leaching test is in agreement with the reusability study where the overall
FAME yield was decreased sharply for 1st cycle while maintain at
>80% for next continuous cycles. The results for reusability and
leaching test were well correlated with the testing of Ca content in
biodiesel product by using AAS analysis. The concentration of
leached Ca2þ was found in high concentration (26 ppm) for firstrun biodiesel, while the second and third-run products rendered
lower Ca content in 12 and 12 ppm, respectively.
According to Xie and Huang (2006) [41], high loading of Ca
content in the binary system will generally lead to the formation of
free CaO phase coated on the surface of mixed metal oxides that do
not bind with in mixed oxide system. This amorphous material is
not stable and, thus can easily be flushed out with reactants.
Therefore it is very likely that the minor leaching during the initial
period is caused by the dissolution of amorphous materials, which
are not considered active centers for transesterification. Therefore
we can assume that the catalyst started to show high reusability
after flushing of amorphous materials from the catalyst.
3.4. Biodiesel quality evaluation
For biodiesel to be used in diesel engines, the fuel must meet
various specifications stated in biodiesel standard, mainly United
States biodiesel standard ASTM D6751 and European biodiesel
Table 7
Physicochemical properties of jatropha-based biodiesel.
Specification
Test method
EN14214
ASTM
D6751
Analysis
resulta
CaOeLa2O3
3
Density (kg/m )
Viscosity at 40 C
(mm2/s)
Flash point ( C)
Clould point (oC)
Pour point ( C)
Water content,
(% volume) mg/kg))
Sulphur content
(mg/kg)
Acid value
(mg KOH/g)
Iodine value
(g I2/100 g)
Methanol content
(% w/w)
EN 12185
ASTM D445
860e900
3.5e5.0
NS
1.0e6.0
890.7
3.9
ASTM D93
ASTM D2500
EN ISO 3016
ASTM D2709
120 min
N/S
N/S
0.050 max
130 min
N/S
N/S
0.050 max
162
2.0
6.0
0.048
AOCS Ca 17-01 10 max
15 max
MPOB official
method P2.5
MPOB official
method P3.2
EN 14110
0.5 max
0.8 max
N/D
(<10 mg/kg)
0.5
120 max
NS
88.7
0.2 max
NS
0.1
N/S: not specified. N/D: not detected, Min: minimum. Max: maximum, EN: European Standard. ASTM: American Standard Test Method, MPOB: Malaysian Palm Oil
Board, AOCS: American Oil Chemists' Society.
a
The physico-chemical properties of biodiesel were carried out in a MYCO2 green
laboratory.
The transesterification of non-edible jatropha oil with methanol
can be actively catalyzed using bifunctional acidebase CaOeLa2O3
catalysts. CaO is a suitable basic compound to be integrated with
La2O3 as a highly active and stable catalyst for biodiesel production.
Co-precipitation of La with Ca promoted the CaO dispersion and
thus, increased the surface acidic and basic sites rather than bulk
CaO and La2O3 metal oxide. The presence of acidity and basicity in
the active sites of CaOeLa2O3 was found to enhance the esterification and transesterification reaction of high FFA Jatropha oil. The
effect of Ca/La atomic ratio ranging from 0.5 to 10.0 towards the
transesterification activity was investigated. Among the series of
CaOeLa2O3 catalysts, Ca/La with 8.0 atomic ratio rendered the
highest biodiesel yield (98.76%) at the transesterification condition
of 160 C, 3 h, 25 methanol/oil molar ratio and 3 wt.%. The weak
reusability of the CaOeLa2O3 was influenced by the leaching of
active Ca2þ in the first run reaction. However, the catalyst's reusability was stable for the next 4 cycles with reduced of Ca2þ ion
leaching into the acid reaction medium. The leaching of the Ca2þ
was due to the partially soluble of free CaO that did not bind in the
binary system. This lead to the unfavorable neutralization of FFA
with base Ca2þ species and resulted in white layer Ca soap
formation.
Acknowledgment
The authors acknowledge the financial support of the National
Nanotechnology Directorate (NND) grant (Project Number:
5489200) and the financial support from Ministry of Higher Education Malaysia for Fundamental Research Grant Scheme (FRGS,
Project Number: FP054-2013B and FP056-2013B).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.renene.2014.07.017.
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