International Journal of Biotechnology Research Vol. 1(8), pp. 120-127, September 2013
Available online at http://academeresearchjournals.org/journal/ijbr
ISSN 2328-3505 ©2013 Academe Research Journals
Full Length Research Paper
Evaluation of almond (Prunus amygdalus) seed oil as a
viable feedstock for biodiesel fuel
Ogunsuyi H. O.* and Daramola B. M.
Department of Chemistry, Federal University of Technology, Akure, Ondo State, Nigeria.
Accepted 5 September, 2013
Viability of almond (Prunus amygdalus) seed oil as a potential feedstock for biodiesel production was
reported. The oil content of the seed was extracted with n-hexane using Soxhlet extraction method. The
extracted oil was characterized to determine the key physical and chemical properties that mark the
suitability of the oil for biodiesel production. Values obtained for parameters such as density (0.98
3
g/cm ), flash point (220°C), acid value (40.14 mg/KOH/g) and kinematic viscosity (30 CSt at 40°C) for the
extracted oil were comparable with values reported for other non-edible oils such as Jatropha curcas,
Pongamina pinnata, Azadirachata indica and Simaroubia indica. The extracted seed oil was
transesterified using both homogeneous (NaOH) and heterogeneous (CaO and MgO) catalysts. The
yields of biodiesel obtained with homogeneous catalyst under optimum conditions such as 1500 rpm
agitation speed, 60°C reaction temperature, 5:1 methanol to oil ratio were relatively higher than the
yields obtained with heterogeneous catalyst under these same experimental conditions. Physicochemical properties of the biodiesel such as acid value (mgKOH/g), saponification value (mg/g), flash
-3
-1 -1
point (°C), fire point (°C), specific gravity (gm ), viscosity (Kgm S ), cloud point (°C) and centane
number were determined and found consistent with the standards set for ASTM D6751 and EN 14214. In
addition, remarkable variation was noticed in the flash point (298°C) and cetane number (62) of the
biodiesel when compared with those of petrol diesel which were 125°C and 49, respectively. Weight
percent composition of the biodiesel was 0.49 for diglycol diacetate, 43.04 for methyl oleate, 48.40 for
methyl palmitate and 8.07 for methyl stearate. The biodiesel profile of the seed-oil is comparable with
the high quality biodiesel produced with yellow oleander (Thevetia peruvian) seed oil. Hence, almond
seed oil is cheaper, cleaner and suitable feedstock for biodiesel fuel.
Key words: Almond seed-oil, catalysts, transesterification, biodiesel, petrol diesel.
INTRODUCTION
Global warming and other forms of pollution are few of
the consequences emanating from over dependence on
fossil fuels. Divesrse forms of alternative energy are
being exploited by researchers on daily basis to provide
substitutes that are environmentally friendly. Biodiesel is
categorised as one of the options that is very promising
by virtue of its remarkably lower carbon and sulfur
emissions compared with conventional petroleum-based
fuels. Basically, biodiesel fuels are generated from three
sources namely: edible sugars and starches, non-edible
plant materials, algae and other microbes. Generally,
these sources are renewable and generate fuels with
lower carbon emissions and lower sulfur compared with
conventional petroleum-based fuels that are characterized
by high carbon and sulfur emissions (EPA, 2002).
The general acceptability of biodiesel as a suitable
substitute lies in the possibility of being used either as
pure or in blends with conventional diesel fuel in
unmodified diesel engines, hence eliminating engine
exhaust pollutants. However, the relative simplicity of
biodiesel production can disguise the importance of
maintaining high quality standards for any fuel supplied to
a modern diesel engine. Bio-diesel is a promising
*Corresponding
author.
E-mail:
olayinkaogunsuyi@yahoo.com. Tel: 234 703 138 8288.
Int. J. Biotechnol. Res.
nontoxic and biodegradable renewable fuel that
comprised mono-alkyl esters of long chain fatty acids,
which are derived from vegetable oils or animal fat
(edible and non-edible) (Ma and Hanna, 1999; Haq et al.,
2008; Meher et al., 2005; Encinar et al., 1999; Noureddin
et al., 2005).
The most commonly used oils for the production of
biodiesel are soyabean, sunflower, palm kernel,
rapeseed, cotton seed and jattropha. However, there are
good numbers of seed-oils that are presently underutilized for biodiesel production among which are almond
(Prunus amygdalus). Essence of exploiting non-edible
seed oils for biodiesel does not limit to conserving the
edible counterparts for human consumption but also
providing a platform for economical production of
biodiesel with such resources that are readily available at
no cost.
EXPERIMENTAL
121
added and 1% H2SO4 by volume were also added. The
mixture was agitated at a very high speed at 60°C with
magnetic stirrer. The reaction time was achieved after 70
min, the mixture was then poured into a 250 mL
separating funnel, three layers were formed comprising
water at the bottom, oil sample at the middle while the
methanol was at the upper layer. The mixture was
carefully separated by removing the water first followed
by the oil and lastly, the methanol. The pretreated oil was
poured into a 250 mL beaker and placed inside the oven
set at 105°C until traces of water and methanol were
vaporized, consequent upon which the pretreated oil was
apparently suitable for the transesterification process.
Transesterification of the extracted oil sample
Transesterification of the extracted almond oil with
methanol was carried out in the presence of
homogeneous and heterogeneous catalysts to yield fatty
acid methyl ester (biodiesel).
Sample collection
Homogeneous transesterification
Almond seeds were collected from the premises of
Federal University of Technology Akure, Ondo State,
Nigeria.
Sample preparation
The seeds collected were manually dehulled and
carefully sorted to remove all the mesocarp. The seeds
were sundried for two days, oven dried for 2 h at the
temperature of 105°C and finely ground into flour using
blending machine.
Oil extraction of the seed flour
A total of 100 g of the prepared sample flour was
transferred into the soxhlet thimble which was carefully
fixed on a 500 mL capacity round bottom flask. 300 mL nhexane (b.p 40-60°C) was poured inside the flask and
heated on a thermostatically controlled heating mantle to
boiling point. The refluxing continued for four hours, until
the oil was observed to have been fully extracted.
Pretreatment of the oil sample
The almond seed oil could not be transesterified directly
due to its high Free Fatty Acid (FFA) value, hence the
pretreatment. The FFA value of the fat was reduced
below 1% using concentrated sulphuric acid as catalyst
and methanol prior to transesterification.
Procedure
About 10 mL of the extracted oil was measured into a
pre-dried flat bottom flask, then 60 mL of methanol was
Homogeneous transesterification was achieved using
sodium hydroxide (NaOH) as homogeneous catalyst. A
250 mL flat bottom flask was used as laboratory scale
reactor vessel and a hot plate assembled with magnetic
stirring device was used for heating and stirring
purposes.
Procedure: 10 mL of the oil was weighed inside the
reactor vessel, heated on the hot plate to heat the oil
adequately. Thereafter, 0.03 g of the alkali catalyst
(NaOH) was weighed and dissolved in 2 mL of methanol.
The mixture of the catalyst and methanol was poured
carefully inside the heated oil. The resulting mixture was
stirred and heated simultaneously at 60°C for a period of
90 min. The reaction mixture was allowed to cool, after
which it was transferred to the separating funnel and
allowed to stand for 24 h to achieve a good separation.
After the set time, two distinct layers appeared; the upper
layer consists of fatty acid methyl ester while the lower
layer was made up of glycerol, excess alcohol and the
catalyst. Each of the layers was carefully collected
through the tap and the methyl ester (biodiesel) layer was
washed with warm water about four times to remove
traces of alcohol and catalyst residues. The biodiesel
produced was dried in an oven set at 105°C for 2 h to
remove water molecules.
Heterogeneous transesterification
Transesterification of the pretreated oil of almond seeds
was performed with admixture of heterogeneous catalyst
of calcium oxide and magnesium oxide. The procedure
for homogeneous transesterification was adopted except
for the catalyst.
Ogunsuyi and Daramola
122
Physico-chemical properties of the derived biodiesel
The physico-chemical properties of the extracted oil were
determined and compared with the standard values of oil
suitable for biodiesel production. The parameters
considered include density, viscosity, flash point, fire
point, smoke point, acid value, free fatty acid peroxide
value, colour and iodine value; these were determined
according to ASTM standard method (D6751).
Biodiesel characterization using GCMS
Chemical components of the derived biodiesel were
characterized
with
Gas
Chromatography
Mass
Spectrometry, in order to correlate its composition with
those of petroleum-based diesel.
RESULTS AND DISCUSSION
Oil yield from the extraction process
The oil yield obtained from the almond seed using soxhlet
extraction was 47%. This showed that the oil content of
almond seed is relatively higher than other non-edible
seeds such as mangifera indica which contains 14.0%
(Nzikou et al., 2010). However, the oil content was
comparable with the oil content of Dacryodes edulis
which was 59% of its total seed as reported by Ogunsuyi
et al. (2013).
Physico-chemical properties of almond seed oil
Table 1 depicts the physico-chemical analysis performed
on the extracted oil of the almond seed. The oil indicated
a smoke point of 60.00°C and a flash point of 110.00°C
which were relatively lower than that of most of the nonedible seed oils commonly used for biodiesel. However,
the fire point of the seed oil was comparatively higher
than those of the other non-edible oils. The pH value of
the oil was 6.68; this implied that the oil was acidic in
nature. Refractive index which is related to the average
chain length and the degree of unsaturation was found to
be as low as 1.46, hence, the oil was a semi-solid at
room temperature. This observation was quite consistent
with the findings of Canakci and Gerpan (2001) who
asserted that refractive index increases as double chain
increases. The semi-solid nature of the almond oil
contributed to its lower iodine values of 12.46 mg/g. The
iodine value which is an index for assesing the ability of
an oil or fat to go rancid indicated that the oil contained
appreciable level of saturated bonds, hence, low ability to
undergo oxidative deterioration.
The acid value of almond seed oil was relatively high
(40.4 mgKOH/g) as compared to that of castor seed oil
which was 0.7 mgKOH/g. This showed that the acid value
of the seed oil is very high and may lead to the
neutralization of part of the catalyst present, thus
reducing the formation of the alkoxide and consequently
producing soaps within the reaction medium. Soap
formation would not only reduce mass transfer during
reaction but also increase the problem of phase
separation at the stage of product recovery.
Almond oil has significantly high viscosity of 302.39
CSt. The high viscosity of the oil reduces the fuel
atomization and increases the fuel spray penetration. The
bigger fuel spray is considered to be partially responsible
for the difficulties with deposits in the engine and
thickening of the oil. However, these effects can be
removed through the transesterification process, which
was evident in the drastic reduction in the viscosity of the
oil after being transesterified, which gave a value of 31.84
CSt.
Oil sample pretreatment
Oil sample pretreatment was carried out on the extracted
oil due to its high level of saturation and hence, could not
undergo direct transesterification. More also, the
pretreatment reduced the FFA contents of the extracted
oil. The FFA value of the fat was reduced below 1% using
concentrated sulphuric acid as catalyst and methanol
prior to the transesterification process.
The pretreatment process was noted to be effective, as
the free fatty acid of the almond seed oil significantly
reduced from 20.05 to 5.69 mg/KOH/g. The reduction in
FFA content actually made the seed oil suitable for
transesterification purpose.
Transesterification of the oil using homogeneous
catalyst (NaOH)
Transesterification process was conducted on the plant
seed oils to investigate the effects of parameters such as
catalyst concentration, methanol to oil ratio, agitation
speed and temperature on the yield of the biodiesel
produced.
Effect of catalyst concentration on biodiesel yield
The result of transesterification of the oil samples using
homogenous catalyst NaOH, at different catalyst
concentrations and their corresponding biodiesel yields is
as shown in Figure 1. As the catalyst concentration
increased from 0.020 to 0.182 g, the percentage yield
decreased from 59.90 to 19.70% which indicated that at
low catalyst concentration there was a higher yield of
biodiesel. This was attributed to the fact that at higher
concentration of the catalyst, saponification reaction was
likely to have set in thereby reducing the quantity of the
biodiesel. The soap particles formed emulsion with water,
which resulted into increased viscosity as reported by
Chettri and Watts (2008).
Effect of molar ratio of methanol to oil on biodiesel
yield
The effect of molar ratio of methanol to oil on the yield of
Int. J. Biotechnol. Res.
123
Table 1. Result of the Physico-chemical properties of the extracted oil.
Parameter
pH
o
Temperature ( C)
o
Flash point ( C)
o
Fire point ( C)
o
Smoke point ( C)
Refractive index
3
Density (g/cm )
Viscosity (CSt)
Acid value (mg/KOH/g)
Free fatty acid (mg/KOH/g)
Iodine value (mg/g)
Peroxide value (mg/KOH/g)
Colour
Saponification value
Almond oil
b
6.67 ± 0.01
e
28.80 ± 0.11
h
110.00 ± 1.15
j
220.00 ± 1.15
g
60.00 ± 0.00
a
1.46 ± 0.00
a
0.91 ± 0.01
k
302.39 ± 0.01
f
40.14 ± 0.01
d
20.05 ± 0.01
c
12.46 ± 0.01
2.25a ± 0.01
Yellow
i
151.55 ± 0.03
Each value is a mean of three replicate samples ± standard error of mean. Values followed by the
same letter(s) are not significantly difference (P>0.05) from each other by New Duncan’s Multiple
Range test.
Biodiesel yield (%)
70
Biodiesel yield (%)
60
50
40
30
20
10
0
0
0.05
0.1
0.15
0.2
Catalyst concentration (g)
Figure 1. Effect of catalyst concentration on the yield of almond seed oil biodiesel.
Figs 1: Effect of catalyst concentration on the yield of almond seed oil biodiesel
almond seed oil biodiesel is as depicted in Table 2. At 3:1
of methanol to oil ratio, 14.0 ml of biodiesel yield was
recovered. This increased to an optimum yield at ratio 5:1
of methanol/oil which gave 17.6 ml and thereafter
dropped below this value to 12.0 ml. Hence, the best
methanol to oil ratio was attained at 5:1 for the
transesterification process.
Effect of agitation speed
Agitation speed is an important factor in the
transesterification process since the speed affects the
equilibrium of the reaction. Figure 2 shows the various
biodiesel yields obtained at different speed between 500
and 1500 rpm at constant standard reaction conditions
(reaction time of 90 min, weight of catalyst concentration
of 0.03 and molar ratio of methanol/oil 5:1). It showed
that the stirring speed increased from 500 to 1500 rpm,
and the percentage yield also increased from 39.90 to
51.54% which was the highest stirring speed. This
implies that speed is directly proportional to the yield of
the biodiesel, that is, high stirring speed favours higher
yield of biodiesel. This result was in accordance with the
findings of Peterson et al. (1997) which showed that
agitation at a high speed during transesterification of
vegetable oils enhances the homogenization of the
Ogunsuyi and Daramola
124
Table 2. Yields of biodiesel at different ratio of methanol to oil.
Vol.of.oil (ml)
20
20
20
20
Vol. of methanol (ml)
60
80
100
120
Vol of H2SO4 (ml)
1
1
1
1
Methanol to oil ratio
3:1
4:1
5:1
6:1
Yield of biodiesel (ml)
14.0
16.0
17.6
12.0
60
Biodiesel yield (%)
50
40
Biodiesel yield
30
(%)
20
10
0
0
200
400
600
800
1000
1200
1400
1600
Speed (rpm)
Figure 2. Effect of agitation speed on the yield of almond oils.
reactants hence leading to higher yields.
Effect of temperature
The extracted oils was transesterified within the
temperature range of 50 and 70°C under standard
reaction conditions such as reaction time (90 min), weight
of catalyst concentration (0.03 g), molar ratio of
methanol/oil (5:1) and speed (1500 rpm). From Table 3, it
was noted that moderately high temperature such as
60°C was most suitable among the various temperatures
considered. At this optimum temperature of 60°C, the
yield of biodiesel produced with almond seed oil was
58.19%.
Transesterification of
heterogenous catalyst
almond
seed
oil
using
The result of transesterification of the oil samples using
heterogenous catalyst admixture of CaO and MgO at
different concentrations and their corresponding biodiesel
yields are shown subsequently.
Effect of concentration of admixture catalyst on
biodiesel yield
The concentration of the catalyst mixture used was in the
ratio of 1:1, 1:2, 1:3, 2:1 and 3:1 of CaO and MgO salts
respectively. The biodiesel yields obtained at different
ratios of the admixture catalyst of CaO and MgO are
shown in Figure 3. Considering the different ratios of the
two salts in admixture, it was noted that ratio 1:3 of CaO
and MgO gave the highest yield of 51.50% while the
lowest yield of 43.23% was noted at catalyst admixture
ratio of 2:1. Therefore, transesterification reaction using
almond seed oil was best at catalyst admixture ratio of
1:3.
Effect of agitation speed
The effect of agitation speed on yield of biodiesel is
shown in Figure 4. It can be seen that as the stirring
speed increases from 500 to 1500 rpm, the percentage
yields of biodiesel decreased from 54.82 to 51.50%. The
highest yield of the biodiesel (54.82%) was obtained at
the lowest stirring speed of 500 rpm.
Effect of temperature
The extracted oils were transesterified within the
temperature range of 50 and 70°C as shown in Figure 5
under optimum reaction conditions such as reaction time
(90 min), weight of catalyst concentration (0.04 g), molar
ratio of methanol/oil (5:1) and speed of 1500 rpm. It was
Int. J. Biotechnol. Res.
125
Table 3. Effect of temperature on the yield of almond oils biodiesel.
Vol. of oil (ml)
10
10
10
10
10
Catalyst conc. (g)
0.17
0.25
0.41
0.50
0.75
Temperature (°C)
50
55
60
65
70
Biodiesel yield (mL)
3,8
1.8
7.0
2.6
6.6
Biodiesel yield (%)
31.59
14.96
58.19
21.61
54.86
52
51
Biodiesel yield (%)
50
49
48
Biodiesel yield (%) 47
46
45
44
43
42
00:00
00:28
00:57
01:26
01:55
02:24
02:52
03:21
Ratio of Admixture catalyst
Figure 3. Effect of admixture catalyst concentration on the yield of almond oil biodiesel.
55
Biodiesel yield (%)
54.5
Biodiesel yield (%)
54
53.5
53
52.5
52
51.5
51
0
200
400
600
800
1000
1200
1400
1600
Speed (rpm)
Figure 4. Effect of agitation speed on the yield of almond oils biodiesel.
noted that moderately high temperature such as 50°C
was the most suitable temperature among the various
temperatures considered. At this temperature, 53.16%
yield of biodiesel was recovered and decreased to
49.83% at the highest temperature of 70°C. The
decrease in the yield can be attributed to loss of
Ogunsuyi and Daramola
126
53.5
Biodiesel yield (%)
53
52.5
52
Biodiesel yield
51.5
(%)
51
50.5
50
49.5
0
20
40
Temperature (oc)
60
80
Figure 5. Effect of temperature on the yield of almond oils biodiesel.
Table 4. Physico-chemical properties of the derived almond seed oil biodiesel.
Parameter
pH
o
Temperature ( C)
o
Flash point ( C)
o
Fire point ( C)
o
Smoke point ( C)
3
Density g/cm
Viscosity (CSt)
Acid Value (mg/KOH/g)
Free fatty ACID (mg/KOH/g)
Iodine Value (mg/g)
Colour
methanol during conversion. Since the boiling point of
methanol is 63.4°C, an increase in temperature above
this point will result into reduction in the quantity of
methanol needed for effective reaction as reported by
Haq et al. (2008). This suggested the exothermic nature
of the process.
Physico-chemical properties of the derived biodiesel
The various physico-chemical properties of the derived
biodiesel oil are presented in Table 4.
-3
The density of the seed oil biodiesel of 0.92 gcm was
-3
relatively higher than the standard value of 0.88gcm .
This implies that specific gravity of almond seed oil was
higher than the commonly used feed stock such as
jatropha for biodiesel production as reported by Belewu
et al. (2010).
The flash point of the biodiesel (200°C) is within the
Value
a
2.92 ± 0.01
c
28.93 ± 0.03
e
200.00 ± 5.77
f
240.00 ± 11.55
d
110.00 ± 2.89
a
0.92 ± 0.01
c
31.84 ± 0.01
ab
11.37 ± 0.01
a
5.69 ± 0.01
bc
22.33 ± 0.02
Light yellow
acceptable minimum percentage of 130°C as set by
American Standard Testing Materials (ASTM D6751biodiesel blend stock specification, B100 and ASTM
D975) for diesel fuel. Flash point helps to monitor the
safe handling and storage of fuel. The higher the flash
point the safer the fuel, vice versa. The flash point of the
biodiesel from almond seed oil is higher than that of fossil
diesel; therefore it could be said that the biodiesel is safer
to handle than fossil diesel.
The viscosity of biodiesel is relatively higher as
compared to that of fossil diesel, the implication is that
biodiesel will have more lubricating effect on engines,
since, this will reduce wears and tears in the engine.
Characterization of the derived biodiesel with Gas
Chromatography Mass Spectrometer (GCMS)
The chemical composition of almond oil was investigated
Int. J. Biotechnol. Res.
127
Table 5. Chemical compounds identified in almond oil biodiesel.
Sample
Almond oil biodiesel
Retention time (min)
10.16
15.59
17.29
17.44
using GCMS analysis. The presence of stearic, palmitic
and oleic fatty acids as the major components of
biodiesel oil was detected within the retention times
ranging between 3.0 and 23.0 min. They were found
consistent with previous works reported by Lima et al.
(2008). The compounds so identified in the oil samples
are as shown in Table 5.
The GCMS analysis for almond oil in Table 5 showed
that palmitic acid and oleic acid are the most abundant
and prominent fatty acid. Their retention times are 15.59
and 17.29 min while the % peak area are 43.04 and
48.40 respectively. These marked the suitability of the oil
for biodiesel production.
Conclusion
Biodiesel is a clean-burning diesel with chemical
structure of fatty acid alkali esters. The acid and base
catalysed tranesterification of oils and fats is currently the
most commonly adopted method of the various methods
available for producing biodiesel. This study has shown
that most of the evaluated properties examined for the
biodiesel conformed to ASTM and EN standard values.
It could be concluded from this study that the biodiesel
produced from almond (Prunus amygdalus) seed oil is
potentially suitable as alternative fuel to fossil diesel,
while the production and effective usage of the biodiesel
will help to reduce the cost of protecting the atmosphere
from the hazards associated with using fossil diesel and
hence boosts the economy of the country with standard
reaction conditions of reaction time (90 min), weight of
catalyst concentration (0.03 g), molar ratio of methanol/oil
(5:1), agitation speed (1500 rpm) and temperature
(60°C).
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