Wild melon: a novel non-edible feedstock for bioenergy
Wild melon: a novel non-edible feedstock for bioenergy
Maria Ameen 0 1 2
Muhammad Zafar 0 1 2
Mushtaq Ahmad 0 1 2
Anjuman Shaheen 0 1 2
Ghulam Yaseen 0 1 2
0 Department of Environmental Science , Female Campus , International Islamic University Islamabad , Islamabad , Pakistan
1 Biofuel Laboratory, Department of Plant Sciences, Quaid-i- Azam University , Islamabad , Pakistan
2 & Muhammad Zafar
In the present research work, a non-edible oil source Cucumis melo var. agrestis (wild melon) was systematically identified and studied for biodiesel production and its characterization. The extracted oil was 29.1% of total dry seed weight. The free fatty acid value of the oil was found to be 0.64%, and the single-step alkaline transesterification method was used for conversion of fatty acids into their respective methyl esters. The maximum conversion efficiency of fatty acids was obtained at 0.4 wt% NaOH (used as catalyst), 30% (methanol to oil, v/v) methanol amount, 60 C reaction temperature, 600-rpm agitation rate and 60-min reaction time. Under these optimal conditions, the conversion efficiency of fatty acid was 92%. However, in the case of KOH as catalyst, the highest conversion (85%) of fatty acids was obtained at 40% methanol to oil ratio, 1.28 wt% KOH, 60 C reaction temperature, 600-rpm agitation rate and 45 min of reaction time. Qualitatively, biodiesel was characterized through Fourier transform infrared spectroscopy (FTIR) and gas chromatography and mass spectroscopy (GC-MS). FTIR results demonstrated a strong peak at 1742 cm-1, showing carbonyl groups (C=O) of methyl esters. However, GC-MS results showed the presence of twelve methyl esters comprised of lauric acid, myristic acid, palmitic acid, non-decanoic acid, hexadecanoic acid, octadecadienoic acid and octadecynoic acid. The fuel properties were found to fall within the range recommended by the international biodiesel standard, i.e., American Society of Testing Materials (ASTM): flash point of 91 C, density of 0.873 kg/L, viscosity of 5.35 cSt, pour point of -13 C, cloud point of -10 C, total acid number of 0.242 mg KOH/g and sulfur content of 0.0043 wt%. The present work concluded the potential of wild melon seed oil as excellent non-edible source of bioenergy.
Cucumis melo var; agrestis Characterization Fuel properties
The ecological balance of natural resources has been
disrupted to alarming levels due to exponential growth of
human population and many other anthropogenic activities
(Eryilmaz and Yesilyurt 2016; Chang et al. 1996)
recent trends in urbanization and industrialization have not
only increased fuel consumption but also led to depletion
of finite fossil fuel resources (Ilkilic et al. 2011). The
increased rate of fossil fuel consumption has resulted in
increased carbon emissions, intensified local air pollution,
ozone depletion and acid precipitation as well as magnified
global warming up to alarming conditions
(Ahmad et al.
. Therefore, the search for eco-friendly, renewable
energy resources that may be substitutes for fossil fuels has
become indispensable for a sustainable future. In the
present scenario, biodiesel has a considerable attraction
because of its many favorable properties: non-flammable,
non-toxic, less pollutant emission, good lubricity and high
(Ahmad et al. 2011)
. Approximately, a 78%
reduction in overall CO2 has been observed in various
analyses of biodiesel because of its closed carbon cycle
(Ahmad et al. 2011)
. In addition to the high
biodegradability of biodiesel, its high rate of combustion efficiency
and low viscosity (measure of resistance of fluid to gradual
deformation by shear or tensile stress) are its other major
(Ahmad et al. 2007; Atabani et al. 2012)
many earlier studies, biodiesel had been synthesized from
edible resources. Nevertheless, the use of edible oils causes
insecurity of food supply (Ullah et al. 2015). To resolve
this issue, the exploration of non-edible sources of seed oils
for biodiesel synthesis has become indispensable
(Demirbas 2003; Murugesan et al. 2009)
. Among accessible
nonedible feedstocks, one of potential resources existing for
biodiesel production may be Cucumis melo var. agrestis
commonly known as wild melon, small gourd and wild
musk melon across the world. Wild melon is an annual
wild climber plant which grows up to 1.5 m. It is totally
different from water melon with many distinct
characteristics (Sahithi 2015). The stem is prostrate, branched
covered with scabrous hair; calyx 1.5 mm long; corolla
6–8 mm long, yellow; flower solitary; fruit ellipsoid,
round, with dark green stripes, 2.5–5 cm in diameter. It
grows in a wide range of habitats, found especially in arid
zones, but may grow in marsh landscapes, cypress heads,
creek beds, sand bars, fallow fields, pastures, alfalfa,
asparagus, rice, soybean and sugarcane fields, abandoned
home sites, vacant lots, railroad banks, roadsides, dumps
and medians, trash dumps and other disturbed areas
. This plant species can be grown on waste and
marshy lands where other crops do not grow easily. In fact,
it is a non-edible wild plant mostly infesting pearl millet,
sorghum, maize, cotton and range lands. However, in few
areas of Pakistan, its fruit is consumed as a vegetable, but
its seeds are totally non-edible. The seeds have
considerable oil content which can be used for the biodiesel
production. The fruit and seeds of wild melon are shown in
Figs. 1 and 2, respectively.
To the best of our knowledge, a comprehensive
literature review shows that no study has been done
systematically on biodiesel production from Cucumis melo var.
agrestis (wild melon). The aim and objectives of this study
were to determine the oil and free fatty acid (FFA) content
(%), to optimize various reaction variables of
transesterification for maximum biodiesel yield, to characterize
WMSO biodiesel by GC–MS and FTIR and to compare
fuel properties of synthesized biodiesel by ASTM methods.
2 Materials and methods
The present research was conducted in the Biodiesel
Laboratory, Department of Plant Sciences at Quaid-i-Azam
University, Islamabad. Seeds of Cucumis melo var. agrestis
were collected from wild habitats in Tehsil Talagang,
Chakwal district, Punjab, Pakistan. Oil from the seeds of
Cucumis melo var. agrestis (wild melon) was extracted
mechanically using an electric oil expeller and tested via a
chemical method using Soxhlet apparatus. The Soxhlet
apparatus and oil cake are shown in Figs. 3 and 4,
The extracted WMSO was filtered, and FFA content was
determined by aqueous acid–base titration. For this, two
types of titration including blank and sample titration were
carried out. For blank titration, 0.025 M KOH solution was
prepared by dissolving 0.14 g KOH in 100 mL of distilled
water, and the solution was loaded into a burette.
Meanwhile, phenolphthalein indicator was prepared by mixing
0.5 g phenolphthalein in ethanol (50%). Blank titration was
carried out using 10 mL of isopropyl alcohol in a conical
flask and 2 or 3 drops of phenolphthalein indicator, while
sample titration was carried out 1 mL of oil and 2–3 drops
of phenolphthalein. In order to calculate accuracy or
results, sample titration experiment was repeated twice and
mean was calculated of the used volume of KOH. The free
fatty acid number was calculated using readings of both
titrations using the following formula.
Acid number ¼ ðA
where A is the volume used in sample titration, B the
volume of KOH used in blank titration, C the amount of
catalyst in g/L, D the volume of oil used in sample titration.
Based on the result of titrations, biodiesel was
synthesized by a single-step method, i.e., alkali-catalyzed
transesterification by the following methods applied by
et al. (2015)
. During biodiesel synthesis from WMSO,
methoxide was prepared by adding various concentrations
of catalysts in methanol. Meanwhile, the oil was heated up
to 120 C and allowed to cool to 60 C. At this
temperature, methoxide was added to the oil. The reaction mixture
was stirred for 45 min at 600 rpm. The product obtained
was washed with distilled water resulting in a transparent
reddish yellow product, much less viscous than WMSO,
and it was considered as biodiesel by the following
methods applied by
Ullah et al. (2014)
. Various optimizations of
WMSO were performed by changing one reaction variable
while keeping all other operating parameters constant.
Tested variables include the methanol to oil ratio,
concentration of catalysts, reaction time and reaction
temperature. During optimizations, the methanol to oil ratio was
changed from 10% to 100% (v/v), the concentration of
NaOH and KOH changed from 0 to 2.0% (w/w of oil
taken), reaction temperature changed from 30 to 100 C,
and reaction time changed from 25 min to 2 h. Biodiesels
in different optimization reactions are shown in Fig. 5.
For chemical characterization of biodiesel and
confirmation of fatty acid methyl esters (FAMEs), GC–MS and
FTIR analyses and determination of ASTM fuel properties
were performed. For GC–MS, model GC-6860N directly
coupled with mass spectrometer, model MS-597MSD was
used. For FTIR spectroscopy, spectrometer Model Bruker
Tensor 27 with a range of 4000–400 cm-1 was used.
Studied fuel properties included color, density, flash point,
pour point, kinematic viscosity at 40 C, cloud point, sulfur
contents tested by methods of ASTM.
3 Results and discussion
In the present study, the total content of oil in wild melon
seeds was found to be approximately 29.1% and its total
FFA was found to be 0.64 mg KOH/g. To ascertain the
maximum biodiesel yield from WMSO, a range of
transesterification reactions was performed using NaOH and
KOH as catalyst. The effects of methanol to oil ratio,
catalyst concentration, reaction time and temperature were
studied in a series of reactions. The maximum yields of
FAMEs and their optimized conditions are discussed
3.1 Effect of methanol to oil ratio on biodiesel
In order to achieve the maximum yield of biodiesel,
various experiments were performed with the methanol to oil
ratio varying from 10% to 100% (v/v), while other constant
parameters were concentration of catalysts of 1.0 wt%,
reaction time of 45 min, stirring speed of 600 rpm and
reaction temperature of 60 C. In optimization with KOH,
the maximum yield (85%) of FAMEs was obtained with an
optimum methanol to oil ratio of 40% (v/v), while in
optimization with NaOH, a methanol to oil ratio of 30% (v/
v) yielded the maximum FAMEs of 92. Beyond this limit,
no significant effect of increasing the methanol to oil ratio
was observed on methyl ester yield. However, further any
increase in methanol to oil ratio resulted in difficulty in
separation of two layers, i.e., biodiesel and glycerol. The
results are shown in Fig. 6.
3.2 Effect of catalyst concentration on biodiesel
To optimize the concentration of catalysts, a number of
reactions were performed with varying amounts of NaOH
and KOH. For optimization with NaOH, 96% FAMEs yield
was obtained by the addition of 0.4 wt% catalyst where
other constant optimal conditions were as follows:
methanol to oil ratio of 30% (v/v), reaction temperature of 60 C,
reaction time of 45 min. For optimizations with KOH, in
series of reactions, maximum biodiesel yield (89%) was
obtained at the addition of 1.28 wt% catalyst, while other
constant reaction conditions were: methanol to oil ratio of
40% (v/v), reaction temperature of 60 C, reaction time of
45 min. The former catalyst was found to be more
favorable in the sense of quantified yield compared to the latter
one. The effect of catalyst concentration is shown in Fig. 7.
3.3 Effect of reaction temperature on biodiesel
To study the effect of reaction temperature on biodiesel
yield, a series of reactions were performed by keeping
constant all other parameters while changing temperature
during optimization reactions. In optimizations with
NaOH, a maximum (96%) of biodiesel yield was obtained
at 60 C by keeping other conditions constant. The
constant conditions were as follows: methanol to oil ratio of
30% (v/v), the catalyst concentration of 0.4 wt% and
reaction time of 45 min. On the other hand, in optimization
with KOH, optimized temperature was 60 C for a
maximum yield (89%) of biodiesel yield where constant
conditions were: methanol to oil ratio of 40% (v/v), catalyst
concentration of 1.28 wt% and reaction time of 45 min.
During optimization of reaction temperature, a serious of
reactions carried out showed that the reaction rate
increased with the temperature to a certain extent. In
results, the biodiesel yield increased proportionately with
the increase in reaction temperature up to 60 C. However,
the yield of biodiesel decreased significantly at temperature
higher than the boiling point of methanol (64.7 C) due to
emulsion formation. The effect of reaction temperature on
biodiesel yield is shown in Fig. 8.
3.4 Effect of reaction time on biodiesel yield
To study the effect of time on transesterification reactions
of WMSO, a series of reactions were performed with
NaOH as well as KOH. With NaOH, the maximum yield of
biodiesel was achieved at time of 60 min where other
constant conditions were methanol (30% of oil), catalyst
(0.4%) and temperature of 60 C. Meanwhile, with KOH,
the maximum yield of biodiesel was achieved at time of
45 min where other constant conditions were methanol
(40% of oil), catalyst (1.28%) and reaction temperature of
60 C. During both types of transesterification reactions,
the minimum time required for initiation of biodiesel yield
was 25 min, while below this no prominent phase
separation was observed. Hence, the biodiesel yield increased
proportionally from 25 to 60 min of time. In sense of time,
KOH, as a catalyst, showed suitability over NaOH for
biodiesel yield. The effect of reaction time on biodiesel
synthesis from WMSO is shown in Fig. 9.
3.5 Chemical characterization by FTIR and GC–
The synthesized biodiesel samples were characterized
chemically by FTIR and GC–MS techniques, and results
are shown in Figs. 10 and 11, respectively.
Fourier transform infrared spectroscopy (FTIR) is an
analytical technique that is used to analyze various
functional groups. In the present study, FTIR of biodiesel
samples showed a strong peak at 1743 cm-1 that indicates
the presence of methoxy ester carbonyl group. Based on the
observed peaks, various functional groups found in FAMEs
are shown in Table 1.
Gas chromatography and mass spectrometry (GC–MS)
is used for the determination of fatty acids in a sample. The
analyzed samples of biodiesel showed the diversity of fatty
acids being converted into methyl esters. The GC–MS
chromatogram of the synthesized biodiesel samples
showed the presence of a total of twelve fatty acid methyl
esters divided into saturated and unsaturated fatty acids.
Among saturated fatty acids, dodecanoic acid, lauric acid
(C12:0), methyl myristate and three hexadecanoic acid
methyl esters including palmitic acid (C16:0) and methyl
non-adecanoic acid were identified, while saturated fatty
acids including two linoleic acid methyl esters that were 9,
12 octadecadienoic acid and one linoleic acid isopropyl
ester were identified. Similarly, remaining methyl
eicos11-en-14-ynoate and 17-octadecynoic acid, methyl ester
has unsatisfied carbon valences in their chemical
composition as shown in Table 2.
3.6 Fuel properties
Fuel properties of biodiesel synthesized from WMSO were
determined by the methods of American Society of Testing
Materials (ASTM), and results are shown in Table 3. By
the ASTM D-93 method, the flash point of WMSO
biodiesel was found to be 91 C. The higher flash point of
biodiesel as compared to petro-diesel makes it safer to use,
transport and store
. The density of
WMSO biodiesel was found to be 0.873 kg/L according to
method ASTM D-1298. The density of biodiesel generally
Characteristic of peak
varies between strict limits of 0.86 and 0.90 g/cm3.
Kinematic viscosity of WMSO biodiesel was determined to be
5.35 cSt at 40 C, and it lies within the ASTM range of
1.9–6.0 cSt. The pour point or freezing point of biodiesel
was tested to be -13 C according to ASTM D-97 method.
The pour point of WMSO biodiesel is significantly lower
than petro-diesel, so it is better in cold regions. Moreover,
by the method ASTM D 6751, the pour point of WMSO
biodiesel was in the range of -15 to 16 C. According to
ASTM D-250 method, the cloud point of WMSO biodiesel
was found to be -10 C. Biodiesel is considered to be
environmentally biodegradable due to its negligible sulfur
content. Sulfur content was measured and found to be
0.00431 wt% according to ASTM D-4294. Total acid
number of the biodiesel was determined to be 0.242 mg
KOH/g according to ASTM D-974. This value is much less
than 0.8 and well within the range of standard ASTM
D-6751, i.e., \ 0.8. All the fuel properties of wild melon
biodiesel met the international standards for biofuel.
Wild melon seeds were studied systematically for
qualitative as well as quantitative biodiesel production using
different transesterification reactions.
• The total oil content in wild melon seeds was found to
be 29.1% (w/w), while its free fatty acid (FFA) content
found was 0.64%. Due to very low FFA content, the
conversion of triglycerides was carried out by a
singlestep alkali-catalyzed transesterification.
• In transesterification with NaOH, the highest
conversion rate of WMSO into biodiesel was 96%. It was
obtained using 30% methanol (v/v of oil), 0.4% catalyst
(wt/wt of oil), at a reaction temperature 60 C and
reaction time of 1 h, whereas in transesterification with
KOH, the maximum yield obtained was 89% where
other optimized constant conditions were 40%
methanol, 1.28 wt% catalyst, reaction temperature (60 C)
and 45 min of reaction time.
• GC–MS-analyzed results indicated the presence of
methyl esters including linoleic acid, palmitic acid,
lauric acid, tetradecanoic acid, isopropyl linolate,
octadecynoic acid. While methyl esters and
octadecadienoic acid methyl ester were the main components
found in biodiesel sample synthesized from WMSO, a
strong FTIR peak at 1743 cm-1 confirmed the
existence of a methoxy ester carbonyl group.
• The fuel properties of synthesized FAMEs were in full
agreement with ASTM standard D6751.
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