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Advances in Materials Physics and Chemistry, 2012, 2, 138-141
doi:10.4236/ampc.2012.24B036 Published Online December 2012 (http://www.SciRP.org/journal/ampc)
Biodiesel Production from Rubber Seed Oil Using A
Limestone Based Catalyst
Jolius Gimbun1,2, Shahid Ali1, Chitra Chara n Suri C haran Kanw al1, Liyana Amer Shah1,
Nurul Hidayah Muhamad Ghazali1, Chin Kui Cheng1,2, Said Nurdin1
1Faculty of Chemical Engineering and Natural Resources, Universiti Malaysia Pahang, Gambang, Pahang, Malaysia
2Centre of Excellence for Advanced Research in Fluid Flow (CARIFF), Universiti Malaysia Pahang, Gambang, Pahang, Malaysia
This paper presents the potential of limestone based catalyst for transesterification of high free fatty acid (FFA) rubber seed oil
(RSO). Pre-calcinated limestone known as clinker was activated using methanol and transesterification was performed under reflux
with constant stirring. Mineral composition of the catalyst was analysed using x-ray fluorescence (XRF) with in build x-ray diffrac-
tion (XRD). The rubber seed oil was obtained using both microwave and soxhlet extraction using hexane as solvent. FFA content and
fatty acid methyl ester content were determined using gas chromatography mass spectrometry (GC-MS). The results showed an effi-
cient conversion (up to 96.9%) of high FFA rubber seed oil to biodiesel. The results suggest that the catalyst employed in this work is
not negatively affected by moisture and free fatty acids and can be recycled very easily without significant loss in its activity. The
highest conversion of 96.9% was achieved from catalyst activated at 700°C, with catalyst loading of 5 wt. %; methanol to oil molar
ratio of 5:1; reaction temperature of 65°C and reaction time of 4 hours. The biodiesel produced in this work is within the limits of
specification described by American standard test method (ASTM D6751).
Keywords: Biodiesel; Microwave Extraction; Cement Clinker; Rubberseed Oil
Biodiesel has been touted as a viable alternative to the traditional
petroleum-derived fuels due to environmental concern and
sustainability issue. There are several sources of vegetable oil
suitable for production of biodiesel such as palm oil, jatropha,
soy bean and some selected species of forest seeds. Recently,
the European Union is critical to the biofuel production using
edible oils such as palm oil, corn, soy bean and maize, which
are also consumed as food. These open a new avenue of
producing a biodiesel using a non-food source crop such as the
seed of the rubber tree (HeveaBrasiliensis). Malaysia has an
estimated acreage of 1,021,540 hectares of rubber plantation in
2009  producing an estimated average of more than 120
thousand tons of rubber seeds annually and this project aims to
utilize these unused seeds to produce biodiesel. The rubber seed
contain approximately about 40% kernel with 20-25% moisture.
The dried kernel contains 40-50% of oil  which translates to
a potential production over 20 million litres of oil per year. The
rubber seed oil has a high free fatty acid content, which mean
the use of alkaline catalysts such as sodium hydroxide to
produce biodiesel is unfavorable  because of the formation
of relatively large amounts of soaps, leading to product loss and
difficulty in the separation and purification of the biodiesel
produced . Thus, this work aims to overcome this issue by
using a limestone based heterogeneous catalyst.
Heterogeneous base catalysts have advantages of being re-
usable, noncorrosive, show greater tolerance to water and free
fatty acids (FFAs) in feedstock, improve biodiesel yield and
purity, have a simpler purification process for glycerol and are
easy to separate from the biodiesel product [4-7]. Calcium ox-
ide (CaO) is one of the most common used heterogeneous base
catalysts for the transesterification of vegetable oil. Producing
biodiesel using CaO as a solid base catalyst has many advan-
tages, such as higher activity, mild reaction conditions, reusable
and low cost [4-7]. Liu et al.  shows that CaO powder can
give about 95% conversion of soybean oil to biodiesel in pre-
sent of excess methanol (12:1) at temperature of 60 °C and
reaction time of 3 hours. Hsiao et al.  achieved 96.6% of
conversion of soybean oil to biodiesel using a microwave as-
sisted transesterification with 3% wt. of nanopowderCaO cata-
lyst, methanol/oil ratio of 7:1, reaction temperature of 65°C and
residence time of 1 hour. Use of nanopowderedCaO has several
drawbacks because the nanopowder is not readily available and
hence require a high energy to manufacture, furthermore, cata-
lyst recovery or separation will be challenging for nanoparticle.
This work aims to prepare a cheaper catalyst from limestone
that is easy to recover apart from providing an efficient conver-
sion of vegetable oil to biodiesel.
2. Materials and Methods
Chemicals were obtained from various sources namely Merck
Malaysia (dried methanol 99.9%, KOH pellets, hexane HPLC
grade), John Kollin Chemicals (ethanol, 99.9%), R&M chemi-
cals (diethyl ether), and Sigma-Aldrich (fuller earth, phenol-
phthalein, methyl heptadecanoate GC grade, n-hexane, ace-
Copyright © 2012 SciRes. AMPC
J. GIMBUN ET AL. 139
2.2. Rubber Seeds
The Rubber seeds were collected during maturation period from
the rubber tree plantation area located near KampungPandan,
Kuantan, Pahang, Malaysia. They were washed to remove dirt
and stored at 4°C until extraction. Rubber seeds were first
de-shelled and dried at 60°C for 3 hours. The dried seeds were
finely crushed using Waring Commercial Lab Blender and then
subjected to drying in an oven at 45°C overnight.
2.3. Soxhlet Extraction (SE)
Hundreds grams of ground seeds were subjected to a total ex-
traction time of 4 hours at 60°C and 250 ml of n-hexane was
used as a solvent. After the extraction was completed oil–sol-
vent mixture was subjected to evaporation process under vac-
uum (BUCHI® Rotavapor R-200) at 60°C to evaporate the
solvent and recover the extracted oil.
2.4. Microwave Assisted Extraction (MAE)
250 g of crushed seed was put into a glass jar and the oil was
extracted with 500 ml of n-hexane for 30 minutes at 64°C and
power of 200W using the Milestone Micro synth ATC-FO 300.
The n-hexane was then separated from the crude rubber seed oil
using a rotary evaporator.
2.5. Analysis of Rubber Seed Oil and Biodiesel
The extracted RSO and biodiesel was being analyzed for its lipid
and ester content respectively. Standard ASTM D6751 methods
were being used to find, acid value (ASTM D664), calorific value
(ASTM D240), kinematic viscosity (ASTM D445), moisture
content (ASTM D2709), flash point (ASTM D93), specific
gravity (ASTM D287) and cetane number (ASTM D613).
2.6. Catalyst Activation
The limestone based cement intermediate called clincker was
obtained from Pahang Cement atKuantan Malaysia. Detail chemi-
cal composition of the clinker obtained from X-ray florescence
with in-build XRD (ARL 8660S) is shown in Table 2 which
indicates a significant CaO content (66.6%) useful for trans-
esterification process. Clinker was crushed and ground to re-
duce the particle size around 200 μm to ensure a large surface
area per unit mass. The catalyst activation was performed by
soaking with methanol followed by calcination at 700°C for 7
hours in the furnace (Carbolite, CWF1215).
2.7. RSO and Biodiesel Composition Analysis
Oil and FAME composition of seed oil was determined using
gas chromatography mass spectroscopy (GC-MS) according to
ASTM D6584. Samples from the extraction and biodiesel pro-
duction process were taken and dissolved in HPLC grade hex-
ane before being injected into the GC-MS. Tri-acylglycerides
(TAG) analysis was performed on Agilent 7890A GC System
Table 1. Clinker analysis with XRF-XRD.
Element CaO SiO2 Al2O3 Fe2O3 MgOSO3 K2O Na2O P2O5TiO2
Wt. % 66.61 21.92 6.33 4.00 0.73 0.46 0.92 0.12 0.03 0.30
equipped with Agilent 7683B Series Injector, 5975C Inert MSD
and a DB-1 column (30 m × 0.25 mm × 0.25 μm films), with a
temperature range of 60 – 340°C, while the FAME produced
were analyzed on HP-5 column (30 m × 0.25 mm × 0.25 μm)
with a temperature range of 60°C to 325°C. Identification of the
peaks was performed by comparing retention times with those
of library standards analyzed under the same conditions. FAME
and fatty acid composition was determined as in Table 3. The
most abundant fatty acids in RSO were linoleic, stearic, and
palmitic acids. While the FAME is mainly of methyl linolelai-
date and methyl vaccinate.
2.8. Transesterification and Purification of Rubber
The catalyst of various amount ranged from 3 to 7 wt% was
dispersed in methanol at temperature ranged from 50 to 70°C
for a period of time prior to contact with the preheated feed-
stock, providing a robust transesterification catalyst system.
Transesterification were performed at various residence time
ranged from 0.5 to 4 hours with aid of agitation. Water soluble
methanol and glycerol were removed by washing intensely with
water. The biodiesel produced was filtered to remove the cata-
lyst and residual methanol was vacuum evaporated. Fuller earth
was used to reduce the moisture content of the product. Eppen-
dorf 5810R centrifuge was used to remove the fuller earth,
residual catalyst and glycerol followed by analysis of its prop-
erties according to ASTM D6751 standard. All experiments
were repeated three times, and the value reported in this paper
was the average value.
Table 2. FAME and Fatty Acid composition of RSO.
Properties This work Ramadhas et al. 
Fatty acid composition (%)
Palmitic acid C16:0 10.29 10.2
Stearic acid C18:0 8.68 8.7
Oleic acid C18:1 20.07 24.6
Linoleic acid C18:2 58.5 39.6
Linolenic acid C18:3 0.8 16.3
FAME content (%)
Methyl palmitate 7.7
Methyl stearate 3.9
Methyl linolelaidate 43.2
Methyl vaccenate 45.1
Specific gravity 0.92 0.91
Calorific value (MJ/kg) 38.96 37.5
Acid value (mg KOH/g) 35.14 34
Table 3. Properties of Methyl Esters from Rubber Seed Oil.
Properties ASTMLimits This work
et al. 
Calorific value (MJ/Kg)D240-- 39.37 36.5
40°C (mm2/s) D4451.9 - 6.0 4.64 5.81
Flash point (°C) D93 > 130 154.6 130
Specific Gravity D2870.82 - 0.9 0.87 0.87
Acid value (mg KOH/g)D664< 0.50 0.07 0.8
Cetane number D613> 47 66.2 43
Copyright © 2012 SciRes. AMPC
J. GIMBUN ET AL.
3. Results and Discussions
3.1. Compar ison of Soxhlet and Microwave Asis sted
Comparison of extraction efficiency of rubber seed oil using
soxhlet and microwave extraction is presented in Figure 1. The
results suggest that microwave extraction is better than the
conventional soxhlet method because the yield of oil extracted
is much higher at 40% compared to the soxhlet at 36%. Fur-
thermore, microwave extraction is much faster at 15 minutes
compared to about 6 hours for the soxhlet method. This is due
to microwave heating which interact selectively with the free
solvent molecules present in the homogenized solution; this
leads to localized heating, and the temperature increases rapidly.
Thus, such systems undergo a dramatic expansion, with subse-
quent rupture of cell walls, allowing the oil to flow outwards
from the inside of finely crushed seeds . In contrast the sox-
hlet extraction is diffusion driven where the solvent diffuses
into the matrix and extracts the components by solubilization,
hence a slow process. The yield of oil recovered from rubber
seed in this work is in agreement with earlier work by Ramad-
has et al. . The MAE method is more efficient in terms of
yield and time consumption for the extraction process. There-
fore, microwave extraction method will be used for the re-
mainder of this work.
3.2. Influence of Methanol to Oil Molar Ratio
Theoretically the stoichiometry of transesterification reactions
requires 3 mole of alcohol for every mole of triglyceride in
order to produce 3 mole of methyl ester and 1 mole of glycerol
as by product. However, it is not always possible to achieve an
optimum transesterification using a 3:1 ratio since yield of
glycerol and conversion is not always perfect.Results in Figure
2 shows the increasing trend of conversion rate with the
methanol/oil molar ratio ranging from 2:1 to 4:1, but afterwards
shows a slight decline in conversion rate with the methanol/oil
molar ratio going from 5:1 to 6:1. At first, excess methanol
increases the solubility of the by-product (glycerol)  which
then may initiate the reversible reaction to reduce the conver-
sion. The optimum methanol/oil molar ratio was observed at
4:1. Excess methanol can be removed easily by washing with-
water, and its residual may be removed using rotary evaporator.
Figure 1. Comparison of soxhlet and microwave assisted extraction.
3.3. Influence of Catalyst Loading
Figure 3 shows the conversion of RSO to biodiesel increases
when the amount of catalyst increased from 2.0 to 6.0 wt.%
with the methanol to oil ratio of 4:1, but decreased when the
amount of catalyst exceeded 6.0 wt.%.This is due to reversible
nature of the transesterification process  whereby the catalyst
concentration levels greater than 6% may have favored the
backward reaction. The results suggest that optimum catalyst
loading for RSO transesterification is 6 wt.% with conversion
3.4. Influence of Temperature
Generally, as the reaction temperature increases, the rate of
reaction increases as they are affected by temperature through
the Arrhenius equation. Figure 4 shows the conversion in-
creases from 65.4% to 96.9%when the temperature increased
Figure 2. Effect of methanol to oil ratio (4 wt.% catalyst, 55°C).
Figure 3. Effect of catalyst loading (Temperature 55°C, Metha-
Figure 4. Effect of temperature to (methanol:oil 4:1, catalyst load-
ing 5% wt.).
Copyright © 2012 SciRes. AMPC
J. GIMBUN ET AL.
Copyright © 2012 SciRes. AMPC
Figure 5. Catalyst recycability study.
from 40°C to 65°C. Higher temperature improves the efficiency
of transesterification, which in turn enhances the RSO conver-
sion. However, increasing the temperature above 65°C does not
significantly affect the RSO conversion; in fact conversion
reduces slightly to 95.8% when temperature increases to 70°C.
This is due to methanol evaporation at temperature higher than
64.7°C (methanol boiling point) and hence oil to methanol ratio
cannot be maintained to achieve a desirable reaction. Opti-
mumtemperature for RSO transesterification with limestone
based catalyst is around 65°C.
3.5. Catalyst Recycability
The most important advantage of using heterogeneous material
as catalysts is the ability to recycle and reuse. The catalyst was
collected for reuse using a filter paper and washed with acetone
to remove the impurities of the mixture at the end of the reac-
tion. The catalyst was reused up to 5 times for rubber seed oil
transesterification with some reduction (about 5% per cycle) in
conversion at the 3rd, 4th and 5thcycle as shown in Figure 5. The
catalyst in this work has a comparable reuse efficiency as the
metal based catalyst, e.g. hydrotalcite particles with Mg/Al
used by Deng et al.  for transesterification of Jatropha oil.
The decline may be attributed to entrapment of glycerol on its
active surface. In comparison with the recyclability of other
solid metal based catalysts , the cement clinker catalysts
showed an unprecedented stability and recyclability for bio-
3.6. Properties of Methyl Esters from Rubber Seed Oil
The fuel properties of FAME produced in this work is com-
pared with Ramadhas et al. , who studied rubber seed oil
transesterification using a homogeneous catalyst (NaOH). This
work is a single step method which involved only the trans-
esterification process unlike the two-step method employed by
Ramadhas et al. . As shown in Table 1, all the properties are
within the biodiesel specification described by ASTM D6751.
The calorific value of in this work seems to be slightly higher
than the previous work by Ramadhas et al. ; furthermore, the
kinematic viscosity and acid value are very much lower in
comparison. The cetane number of 66.2 for biodiesel produced
in this work is better than the previous work  and compliance
to the ASTM standard. The good biodiesel property in this
work is attributed to extensive the purification step undertaken
to the FAME which include among other washing, centrifuga-
tion and bleaching.
Microwave assisted extractionis more efficient in terms of yield
and time consumption as it can achieve a maximum extraction
within 4 minutes, which cannot be achieved through conven-
tional soxhlet method even after 6 hours. The limestone based
catalyst derived from cement clinker showed an efficient con-
version (up to 96.9%) of high FFA rubber seed oil to biodiesel.
The results suggest that the catalyst employed in this work is
not negatively affected by moisture and free fatty acids and can
be recycled very easily without a significant loss in its activity.
The biodiesel produced in this work is within the limits of
specification described by ASTM D6751.
ShahidAli thanks Universiti Malaysia Pahangfor the GRS100348
funding. We thank Ministry of Higher Education Malaysia for
the MTUN COE grant RDU121216.
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