INTRODUCTION:

Due to the depletion of the world’s petroleum reserves and the increasing environmental concerns, there is a great demand for alternative sources of petroleum-based fuel, including diesel and gasoline fuels. Indiscriminate extraction and increased consumption of fossil fuels have led to the reduction of the underground-based carbon resources (Ramadhas et al., 2004). Biofuels are produced from renewable sources and they do not add to the stock of total carbon-dioxide in the atmosphere. These plant forms, typically, remove carbon-dioxide (the major green house gas) from the atmosphere and give up the same amount when burnt within a few years. Hence, biofuels are considered to be “CO₂ neutral” (Ramadhas et al., 2004). The primary goals of National Energy policy are to increase the energy supplies using a more mix of domestic resources and to reduce our dependency on imported oil or petroleum. As a domestic renewable energy source, biomass offers an alternative to conventional energy sources and supplements national energy security, economic growth and environmental benefits (Ma and Hanna, 1999).

Biodiesel, a clean renewable fuel, has recently been considered as the best alternative for a diesel fuel substitution because it can be used in any compression ignition engine without the need for modification (Xu and Wu, 2003). Chemically, biodiesel is a mixture of methyl esters with long-chain fatty acids and is typically made from nontoxic, biological resources such as vegetable oils (Azcan and Danisman, 2008), animal fats (Saraf and Thomas, 2007), or even used cooking oils (UFO) (Issariyakul et al., 2008). Vegetable oils are promising feedstocks for biodiesel production since they are renewable in nature, can be produced on a large scale, and are environmentally friendly (Patil and Deng, 2009). Vegetable oils include edible and non-edible oils. More than 95% of biodiesel production feedstocks come from edible oils since they are mainly produced in many regions and the properties of biodiesel produced from these oils are much suitable to be used as diesel fuel substitute (Gui et al., 2008). However, it may cause some problems such as the competition with the edible oil market, which increases both the cost of edible oils and biodiesel (Kansedo et al., 2009). On this note, the food-fuel debate over conventional vegetable oils has rekindled research interest in exploring lesser known and minor oil crops (Solomon et al., 2010).

Fluted pumpkin (Telfairia occidentalis Hook. F) is a member of the family Cucurbitaceae. It is a cotyledonous plant with about 90 genera and more than 700 species which are distributed all over the warm parts of the world (Purseglove, 1997). It is an important leaf and seed vegetable indigenous to Southeastern Nigeria and found throughout the former forest areas from Sierra Leone to Angola and up to Uganda in East Africa (Purseglove, 1997).

The crop is grown across the low land humid tropics of West Africa. It is partially drought resistant and is tolerant to a wide range of soils (Okoli and Nyanayo, 1988). The fluted pumpkins are planted solely from seed often close to fences and walls so that the shoots have a support to climb against. In other cases, they are planted in mounds measuring approximately 75–90cm. They are planted both in the wet and dry season and are usually harvested 120–150 days after sowing (Okoli and Nyanayo, 1988).

The seeds are used as propagating materials, eaten roasted, boiled or ground to paste as soup thickener. The fruit case and pulp of Telfairia occidentalis which constitute 64% of whole fresh fruit weight can be used as feedstuff for livestock and the protein content of the pulp (1.0%) has been used for the production of marmalade (Egbekun et al., 1998). The crop is primarily grown as a leafy vegetable and is used for human consumption and animal fodder. The seeds are either roasted or ground for other food preparations. Good cooking oil can be extracted from the seeds. It has been suggested that the oil could be used for soap production. Telfairia provides an appreciable cash income to small farm families (Akoroda, 1990). Activated carbon produced from fluted pumpkin seed can be utilized for the removal of lead II ion (Pb²⁺) from simulated wastewater (Ejikeme et al., 2007). Other works on fluted pumpkin seed include: Dietary incorporation of boiled fluted pumpkin (Telfairia occidentalis Hook F) seeds 1: Growth and toxicity in rats (Ejike et al., 2010), Chemical composition and potential of some underutilized tropical biomass. I: fluted pumpkin (Telfairia occidentalis) (Esuoso et al., 1998). In this work, fluted pumpkin seed oil was studied, for the first time, as a potential feedstock for biodiesel production.

MATERIALS AND METHODS:

Collection and Processing of Sample:

The fluted pumpkin (T. occidentalis) fruit pulps were obtained from Enugu Ezike, Enugu State of Nigeria and were identified by Mr. Ozioko of Biodiversity Centre, Nsukka. The fruit pulps were broken and the seeds removed. The seeds were cleaned by washing first with distilled water and then with normal saline (0.9%w/v NaCl solution) to clean up and remove possible mycotoxins. This was followed by the dehulling of the wet seeds with a knife after which the dehulled seeds were dried in an oven at 40⁰C for approximately 72 hours. The low temperature was necessary so as to prevent the evaporation of volatile constituents in the fluted pumpkin seeds. The seeds were then broken into smaller bits, ground with a warring blender into coarse particles and ready for oil extraction.

Extraction of Oil from the Fluted Pumpkin Seed:

This was done by soxhlet extraction method. The ground fluted pumpkin seeds (100g) were properly packed into the thimble of the soxhlet extractor, and n-hexane (300ml) was poured into the round bottom flask of the soxhlet extractor. The complete soxhlet extractor (i.e. with its condenser) was then mounted on a heating mantle which had its temperature guage set at 80⁰C. At this temperature, the extractor set up was left to stand for 6 hours. The percentage (%) yield of the fluted pumpkin seed oil was determined after triplicate run and the mean value reported.

Physico-chemical Analysis of the Fluted Pumpkin Seed Oil:

The physico-chemical properties of the oil were then determined using the method of AOAC, 1975. These properties include kinematic viscosity, relative density, acid value, iodine value, peroxide value, saponification value. The colour was determined visually. All the chemicals used were of analytical reagent grades.

Production of Biodiesel from the Fluted Pumpkin Seed Oil:

The Freedman method, 1984 was used. Biodiesel (fatty acid methyl esters or simply FAME) was produced from the fluted pumpkin seed oil using the classical method. Methanol containing 1% sodium hydroxide (NaOH) was prepared by dissolving NaOH (1g) in a small volume of methanol and made up to 100ml mark. This solution was then mixed with the fluted pumpkin seed oil in the mole ratio of 6:1 (v/v) and refluxed at 60^oC for 1 hour. The refluxed mixture was poured into a 250ml separating funnel and separation carried out. First, a bilayer was introduced by adding petroleum-ether (100ml, 150ml, 200ml), into the refluxed mixture, which extracted the biodiesel that floated above the glycerol layer. Secondly, the bilayer was further improved by the addition of distilled water (50ml), which increased the glycerol phase. This glycerol phase (denser than the biodiesel) was run-off from the separating funnel and the biodiesel phase washed with saturated sodium hydrogen carbonate (NaHCO₃) using 100ml, 150ml and 200ml respectively. After washing, the biodiesel was dried over anhydrous sodium sulphate to remove water contaminants. The dried biodiesel was then placed in a hot-air oven (at 50⁰C) to remove petroleum-ether used in the downstream processing of the biodiesel.

Physico-chemical Properties of the Biodiesel:

The physical and chemical properties of the biodiesel were determined using the same methods applied for the characterization of the parent oil (fluted pumpkin seed oil) except for additional physical (fuel) properties which include flash point, cetane number and heat of combustion. Flash point and heat of combustion were determined according to relevant biodiesel test methods. The cetane number of fluted pumpkin seed oil methyl esters was evaluated via the use of empirical formula in the literature (Ramos et al. 2009) as shown below:

CN = X_ME (wt %) x CN_ME

Where, CN, is the cetane number of the biodiesel, X_ME is the weight percentage of each methyl ester (Oluba et al., 2008), and CN_ME is the cetane number of individual methyl ester (Moser, 2009).

RESULTS:

Results of the extractions of the oil from the fluted pumpkin (T. occidentalis Hook F) seeds showed average yield of 46.20±0.20 % (Table 1), an oil content higher than that of linseed (33.33%), soybean (18.35%) and palm kernel (44.6%) (Akbar et al., 2009).

Table 1. Fluted pumpkin seed oil compared with other feedstock

Feedstock	Oil Yield (%)
Fluted pumpkin seed	46.20 ± 0.20
Linseed	33.33*
Soybean seed	18.35*
Palm kernel	44.60 *

*Akbar et al. (2009)

The physical properties of the oil showed a yellow colour (Table 2) with kinematic viscosity and relative density of 24.20mm²/s and 0.908, respectively. The kinematic viscosity value was found to be lower when compared to that of neem oil (44.00mm²/s; Sekhar et al., 2009) and coconut oil (43.30mm²/s; Alamu et al., 2010), but higher than that of Jatropha curcas oil (17.00mm²/s; Wilson, 2010).

Table 2: Physico-chemical Properties of Fluted Pumpkin Seed Oil

Parameter	Fluted pumpkin seed oil
Colour	Yellow
Kinematic viscosity (mm²/s)	24.20 ± 0.20
Relative density	0.908 ± 0.002
Acid value (mgKOH/g)	0.44 ± 0.11
Iodine Value (mg I₂/g)	104.78 ± 1.22
Saponification value (mgKOH/g)	151.48 ± 1.40
Peroxide Value (meq/1000g )	0.22 ± 0.00

The acid value of the oil was 0.44mgKOH/g, a value relatively lower than most conventional biodiesel feedstock such as soybean oil (2.67mg KOH g^-1), rapeseed oil (2.88mg KOH g^-1) (Jordanov et al., 2007), sunflower oil (7.4mgKOHg^-1) and palm oil (3.8mgKOHg^-1; Christian, 2006). The value was also lower than that reported by Esuoso et al. (1998) for the same oil (fluted pumpkin seed oil) having a value of 3.05mgKOHg^-1. The acid value thus, was lower than the limit recommended for virgin and non-virgin edible oils by the Codex Standards (<4.0mgKOHg^-1 acid value). This suggests relatively higher alkyl ester yield on transesterification, and also minimal side reaction (saponification reaction). This also entails no pre-treatment of the oil prior to transesterification since the free fatty acid content was very minimal. The iodine value of the oil was found to be 104.78 mgI₂/g, a value indicative of a high content of unsaturated fatty acids and susceptibility to autoxidation in contrast to palm oil (50-55 mgI₂/g) (Knothe, 2002). The peroxide and saponification values were 0.22 mEq/Kg and 151.48 mgKOH/g. The low peroxide value suggest little/minimal peroxidative rancidity of the oil due to proper handling and storage of the fluted pumpkin seeds before extraction and also, a much less effect of heat on the oil during extraction since heat favours oxidation of fatty acids thereby increasing the formation of peroxides (Oluba et al., 2008). The peroxide value was lower than that reported by Esuoso et al., (1998), having a peroxide value of 3.02±0.07mEqKg^-1. The saponification value, though high, was found to be lower than that of palm oil (190-209mgKOHg^-1; Knothe, 2002) and that reported by Esuoso et al. (1998) with a saponification value of 166mgKOHg^-1. This shows that the oil has potentials for industrial applications.

Transesterification of the oil extracts were done using methanol which gave fatty acid methyl esters’ (FAMEs; products of methanolysis) yield of 90%, a value higher than sunflower methyl ester (88% yield) but lower than that of canola methyl ester (93.5 yield) and rape seed methyl ester (94% yield) produced with the same base catalyst and under the same reaction conditions (Table 3).

Table 3: Fluted Pumpkin seed oil methyl ester yield compared with other feedstocks

Feedstock methyl esters	Yield (wt. %)
Fluted Pumpkin	90.00 ± 1.00
Beniseed	74.00*
Jatropha seed	76.54*
Tobacco seed	83.31*
Soybean	84.90**
Sunflower	88.00**
Canola	93.5†
Rapeseed	94.50**

*Allen et al. (1999); **El-Diwani et al. (2009); †(Leung and Guo, 2006)

Table 4: Physico-chemical properties of the fluted pumpkin seed oil methyl esters.

Parameter	Fluted Pumpkin seed oil methyl esters
Colour	Yellow
Relative density	0.872 ± 0.000
Kinematic viscosity (mm²/s) @ 40°C	2.50 ± 0.20
Acid value (mg KOH/g)	0.22 ± 0.00
Iodine value (mg I₂/g)	102.33 ± 4.39
Flash point (°C)	138 ± 1.20
Cetane number	64.079
Heat of combustion (KJ/g)	35.30 ± 0.30

The physico-chemical properties of the fluted pumpkin seed oil biodiesel are shown in Table 4. The results of the physical characterizations of the FPSO biodiesel show that the biodiesel was yellowish in colour, with similar relative densities with, and lower kinematic viscosities than those of petro diesel and some conventional biodiesels. The relative density obtained (0.872) was found to be within the limits of EN 14214 (0.860 – 0.900) biodiesel fuel standard. The kinematic viscosity of the biodiesel (2.5mm²/s at 40°C) was found to be lower than those of jatropha oil biodiesel (4.8mm²/s), rape seed oil biodiesel (6.17 mm²/s), canola oil biodiesel (4.892 mm²/s), (Peterson et al., 1990) and was found to be within limits of ASTM D6751 (1.9 – 6.0 mm²/s) biodiesel fuel standard. Hence, the lower kinematic viscosity value of the FPSO biodiesel when compared to other conventional biodiesels shows its improved flow quality through pipelines, injector nozzles and for atomization of fuel cylinder (Rolia and Choo, 2007).

This also can account possibly, for improved low-temperature operability of FPSO biodiesel when compared to other conventional biodiesels. The flash point of the FPSO biodiesels (138°C) was found to be above the minimum value (120°C) of the EN 14214 biodiesel fuel standard. The flash point of FPSO biodiesel was higher than that of jatropha oil biodiesel (135°C) but lower than that of palm kernel oil biodiesel (167°C), (Alamu et al., 2008). The value was also higher than that of neem seed oil biodiesel (120°C) and more importantly, extremely higher than that of petro diesel (54°C). This relatively higher flash point value of FPSO biodiesels is of prime importance for storage and transportation of the fuel (Moser, 2009). The heat of combustion of the FPSO biodiesel (35.3MJ/Kg) was lower than that of petro diesel (45MJ/Kg), soybean oil biodiesel (38.1MJ/Kg; DeOliveira et al., 2006) but slightly higher than that of neem seed oil biodiesel (35.2 MJ/Kg; Sekhar et al., 2009). The lower value of heat of combustion FPSO biodiesel, and in general, conventional biodiesels when compared to that of petro diesel was as a result of higher oxygen content and lower carbon-to-hydrogen ratio in the former than in the later. However, these factors account for the improved lubricity properties of biodiesels when compared to petro diesel. The FPSO biodiesel had empirically calculated cetane number of 64.079 which is well above the minimum value of the ASTM D6751 (40 minimum) and EN 14214 (51 minimum) international biodiesel fuel standards. Cetane number is one of the primary indicators of a good diesel fuel quality and is related to the ignition delay time a fuel experiences once injected into a diesel engine combustion chamber (Moser, 2009). The cetane number of FPSO biodiesel was found to be higher than some conventional biodiesels such as soybean oil biodiesel (49; Ramos et al., 2009), sunflower oil biodiesel (55; Rashid et al., 2009). Thus, the higher cetane number of FPSO biodiesel when compared to petro diesel and other conventional biodiesels suggests a shorter ignition delay time of FPSO biodiesel.

The chemical characterizations of the FPSO biodiesel gave acid value of 0.22 mgKOH/g, a value far below the upper limits of the ASTM D6751 (0.5mgKOH/g maximum) and EN 14214 (0.5mgKOH/g maximum) biodiesel fuel standards. The acid value was equally lower than that of sunflower oil biodiesel (0.40mgKOH/g maximum) and jatropha oil biodiesel (0.4mgKOH/g maximum), (Wilson, 2010). The lower acid values of FPSO biodiesel when compared to other conventional biodiesels indicate that the fuel is relatively purer, with little or no water contaminant which might bring about the hydrolysis of biodiesels resulting in the release of more free fatty acids. The peroxide value of the FPSO biodiesel was found to be 0.20±0.10 mEq/Kg. This relatively low peroxide value of the FPSO biodiesel indicates little peroxidative rancidity of the biodiesel as a result of proper handling/storage of the fuels. Lastly, the iodine values of the FPSO biodiesel (102.33 mgI₂/g) was found to be within the limits of EN 14214 (120mgI₂/g maximum) biodiesel fuel standard. The value was appreciably high, indicating the preponderance of unsaturated fatty acid methyl esters in the biodiesel, thus accounting for the fluidity of biodiesel high in unsaturated fatty acid alkyl esters than those high in saturated fatty acid alkyl esters, such as biodiesel made from animal fats. The iodine value of FPSO biodiesel was comparable to that of jatropha oil biodiesel (101mgI₂/g; Tamalanpundi et al., 2008). Table 5 compares numerically the fuel properties of fluted pumpkin seed oil with that of petro diesel and other conventional biodiesel fuels.

CONCLUSION:

Fluted pumpkin (Telfairia occidenatlis Hook F.) seed oil biodiesel, as evidenced by this work, had shown quite appreciable relatedness and suitability when compared to conventional biodiesels and petro diesel. The percentage oil yield and biodiesel yield were comparable to, and in some cases, higher than those of some conventional biodiesel feedstocks and biodiesels. Some of the fuel properties investigated had shown, to a reasonable extent, that quality biodiesel can be produced from the oil-rich fluted pumpkin seeds which are locally available and abundant in our tropical region, Nigeria. Hence, by improving fluted pumpkin cultivation more than its present state via mechanization and genetic engineering therefore, can facilitate the incorporation of fluted pumpkin seed as an additional feedstock for biodiesel production.

FURTHER STUDY:

The influence of increasing alkyl ester head groups on the fuel properties of the fluted pumpkin seed oil biodiesel is currently on-going, and this certainly will add to its possible use eventually as a biodiesel.

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Received on 15.06.2011 Modified on 16.08.2011

Asian J. Research Chem. 4(10): Oct., 2011; Page 1582-1586

Parameters	Limits		Petrodiesel*	SOB †	SUOB**	FPSOB
Parameters	ASTM D6751	EN 14214	Petrodiesel*	SOB †	SUOB**	FPSOB
Relative density	-	0.86 – 0.90	0.86	0.89	0.88	0.87 ± 0.00
Kinematic viscosity; 40°C (mm²/s)	1.9 6.0	3.5 – 5.0	4.1	4.2	4.85	2.50 ± 0.20
Acid value (mg KOH/g)	0.5max.	0.5max.	-	0.14	0.40	0.22 ± 0.00
Iodine value (mg I₂/g)	-	120max.	-	-	-	102.33± 4.39
Flash point (°C)	130min	120min	54	171	168	138 ± 1.20
Cetane number	47min	51min	42.0	49	55	64.079
Heat of combustion (KJ/g)	-	-	45.5	38.10	45.5	35.30 ± 0.30