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Energy & Fuels 2000, 14, 112-116
African Pear Seed Oil: Potential Alternative Source to Diesel Oil V. I. E. Ajiwe* and A. E. Obika Department of Science Technology, Nnamdi Azikiwe University, P.M.B. 5025, Awka, Nigeria Received March 30, 1999. Revised Manuscript Received October 4, 1999
Diesel engines represent the most widely used machines in agriculture. The prices of diesel oil as fuel continue to increase because the sources of crude oil are diminishing. In addition, the exhaust gases from the combustion of fossil fuels in the engines pollute the environment. African pear seed (Dacryodes edulis) oil was tested to find out if it possesses physical and chemical properties enabling it to be used as fuel for diesel engines. Oil was extracted from the dried and crushed African pear seed by soxhlet extraction. The oil yield was 27%, and the oil had a light yellow color. The extracted oil and diesel oil were comparatively analyzed for fuel properties: relative density, refractive index, viscosity, water content, calorific value, ash content, and burning characteristics. Similarly, the seed sample was analyzed proximately for moisture, ash, protein, fat, carbohydrate, crude fiber, and energy content. Results showed that the African pear seed oil had fuel properties similar to those of diesel oil. This confirmed that African pear seed oil could be utilized as a substitute for diesel oil. Again, the proximate results showed that it had nutritional values and could be used for inclusion in animal feed formulation. It is suggested that the pear seed oil should be processed to serve as a substitute for diesel oil and that the defatted seed should be used for animal feed manufacture.
Introduction Oils are substances derived from plants and animals. In this paper, we discuss oils that are derived from seeds of annual plants. This is the largest source and includes such crops as soyabeans, cotton, peanuts, sunflowers, safflowers, flax, rapeseed, mustard, and other species. The fact that they are annuals allows for relatively rapid adjustment of the supply of their oils to meet changing market demands. They are adapted primarily to temperate environments. Oil from oil-bearing trees fall into two categoriessedible and inedible. Examples of edible oils include coconut, palm, and olive oils; an example of an inedible oil is tung oil, which is used for industrial purposes. In general the oil-bearing trees are adapted to a warm and tropical environment.1 Oils are generally liquid and are usually obtained by pressing the seed or fruit where they occur in great abundance. They are extracted either by crushing or by solvent extraction using a suitable solvent.2 These oils have several applications ranging from industrial uses (for manufacture of soap, paint, resins, polish, cosmetics, grease, wood varnish, etc.) to fuel utilization. Fuel is a material for producing heat or other forms of energy, e.g., wood, coal, oil, etc. Thirty years ago the term fuel was generally understood to refer only to those substances which on heating in air ignited and continued to burn with evolution of heat that could economi* Corresponding author. (1) Douglas, D. B.; Lark, P. C.; Stephen, R. C.; William, F. B. Crop Science and Food Production; Grey Division, McGraw-Hill Book Co.: New York, 1983; pp 232-233. (2) Bernedin, E. Batch and Continuous Solvent Extraction J. Am. Oil Chem. Soc. 1976, 33, 275-278.
cally be used to meet man’s needs of heat and power. The primary fuels included wood, peat, lignite, coals, oils, natural gas, and animal and vegetable wastes. On ignition these fuels combine with oxygen of the air with evolution of heat and production of carbon dioxide and water vapor.3 Today, the world relies largely on fossil fuel for the generation of energy to drive automobiles and machines. A recent informed survey has indicated that, at the present rate of energy consumption of the major sources of energy, at the end of 1986 there was sufficient oil remaining to last about 34 years, natural gas for some 58 years, and coal 219 years. Long before these reserves are finally exhausted, oil in particular will become scarce and inevitably more expensive.4 Hopefully, in what probably appears like a waste to wealth venture there is the possibility of converting waste seed from edible and inedible fruits into useful oils that can serve as fuel for use in diesel engine. Literature has shown that oils from peanut (Arachis hypogaea) sugarcane bagasse, rapeseed, and other seed oils taken in order has been researched by Quedraego et al.,5 Sood,6 Krepeka,7 Federal and Lander Government (1995), and Kalayasiri et al.9 for their physical and (3) Herman, F. M.; McDonald, J. J.; Standon, F. O.; Kirk-Othmer, A. Encyclopedia of Chemical Technology, 2nd ed.; Interscience Pub.: New York, London, Sydney, 1966; Vol. 10, pp 179-180. (4) Clark, G. H. Industrial and Marine Fuels Reference Book; Butterworths: Singapore, London, 1988; pp (4)3-21. (5) Quedraego, D.; Stepaoek, P.; Ottok, K. Possibilities to use bio fuels from peanut oil for diesel engines in the tropics and subtropics. Agri.sTrop.-Subtrop. 1995, 28, 41-57. (6) Sood, H. C. Yet another potential utilization of sugarcane bagasse - Manufacture of high class diesel. Chem. Eng.-World 1994, 29 (10), 177-181.
10.1021/ef990051l CCC: $19.00 © 2000 American Chemical Society Published on Web 12/14/1999
African Pear Seed Oil as Alternative to Diesel Oil
chemical properties enabling them to be used as alternative fuel oils in diesel engines.5-9 Research has also shown that suitable blends of some vegetable oils in the form of their methyl esters with diesel oil can be utilized as a substitute for diesel oil. These oils include rapeseed oil, tallow oil, soyabean oil, cottonseed oil, and other seed oils.10,11 The African pear (Dacryodes edulis) is found in many localities in Nigeria but extends to other countries such as Angola and Sao Tome. It can be cultivated in other African countries. It belongs to the family of Bueseraceae which are mainly shrubs and trees that yield resinous aromatic gum from their bark. The tree is 60 ft high and sometimes up to 5 ft in girth. The plant flowers between February and March. The flowers cluster at the end of the branches. It fruits in August, and the fruit is about 2.5 in. long and 1.5 in. diameter, hanging in clusters, at first pinkish, then blackens when ripe. The fruit, when roasted, softens and is used as food for garnishing maize. The fruit mesocarp contains 43.99% fat and 4.47% protein. The seed is often discarded and constitutes a big waste in towns and villages.12 The use of vegetable oils as a substitute for diesel fuel in engines is receiving increased attention. This potential energy source is renewable; it could reduce the risk of unavailability of fossil fuel (diesel), and could to a large extent reduce pollution effects resulting from the waste seed. It is on this basis that the African pear seed (D. edulis) is analyzed for the physical and chemical properties of its oil that will enable it to be used as a substitute for diesel oil as well as looking at the possibility of the use of the defatted seed as feed for animals. Experimental Sample Collection. The African pear seeds were picked randomly from the ground as waste and were washed and sundried for 3 to 4 days. They were reduced to powder in a mortar. The diesel oil used as a reference standard was purchased from a petro station in Awka, Nigeria. Oil was extracted from the pear seed by soxhlet extraction using petroleum ether (bp 60-80 °C), and the solvent was distilled off at 80 °C. The oil content was calculated from the ratio of mass of oil to the mass of crushed seed used for extraction. Free fatty acids (FFA) and non-fatty materials were separated from the crude oils by the method described by Wieldermann13 and the American Oil Chemists Society (AOCS) official method.14 (7) Krepeka, V. Optimization of Parameters of engine fuel systems with the use of methyl ester of rapeseed oil as fuel. Metod. Zavedeni Vysledku Vyzk. Zerned. Praxe 1995, 17, 32. (8) The Federal and Lander Governments (1995), Report on renewable raw materials. CAB Abstracts, 1996-7/97. (9) Kalayasiri, P.; Jeyashoke, N.; Krishang, Kura K. Survey of seed oils for use as diesel fuels. J. Am. Oil Chem. Soc. 1996, 73 (4), 471474. (10) Ali, V.; Eskridge, K. M.; Hanna, M. A. Testing of Alternative Diesel Fuel from Tallow and Soyabean Oil in Cummins N14-410 Diesel Engine. Bioresour. Technol. 1995, 53 (3) 242-254. (11) Xu, G.; Li, G.; Zhu, B.; Xu, G.; Xu, G. U.; Li, G. F.; Zhu, S. L. Studies on Cotton: diesel oil used as substitute fuel for the diesel engine. Trans. Chin. Soc. Agric. Eng. 1995, 11, (3) 139-144. (12) Keay, R. W. J.; Onochie, C. F. A.; Stanfield, D. P. Nigerian Trees; Onibonoje Press: Lagos, Nigeria, 1968; pp 251-253. (13) Wieldermann, L. M. Degumming, Refining and Bleaching of Soyabean Oil. J. Am. Oil Chem. Soc. 1981, 58, 159-165. (14) AOCS. Sampling and Analysis of Commercial Fats and Oils; Official Method of Analysis of American Oil Chemists Society, 1960; pp 801-855.
Energy & Fuels, Vol. 14, No. 1, 2000 113 Table 1. Calorific Value of Pear Seed Oil and Diesel Oil by Calculation from Percent Protein, CHO, Moisture, Ash, and Fat parameter
African pear seed diesel oil value
diesel oil value
ash % moisture % fat % protein % carbohydrate % calorific value
0.0232 4.7393 83.1190 8.7500 3.1597 795.711 Kcal
0.0682 5.2132 74.3711 7.0000 13.3475 750.7302 Kcal
Microelements and Other Fuel Properties of Pear Seed Oil and Diesel Oil The extracted oil and diesel oil were comparatively analyzed for their primary fuel properties such as relative density, refractive index, viscosity, water content, calorific value, ash content, trace elements, and burning characteristics. Similarly the defatted seed sample was analyzed proximately for moisture, ash, protein, carbohydrate, crude fiber, and energy. Relative density, calorific value, moisture, ash, and carbohydrate were determined by the methods outlined by Usoro et al.,15 Clark,4 Williams,16 Maynard,17 and Ajiwe,18 respectively.4,15-18 The refractive index was determined by the method outlined by Williard et al.,19 while kinematic viscosity was determined by the Institute of Petroleum Standards (IP).20 Crude fiber and crude protein were determined by the official methods of analysis of the AOAC,21 while the trace elements were determined by the methods described by Barrette and Copeland.22 The burning characteristics were determined by soaking a dried cotton thread with each of the oils, followed by ignition of the thread. The two oils burned with a sooty flame, but that of the pear seed oil burned with a very low sooty, flame. Results and Discussion The results of extraction and determination of physicochemical properties are given in Tables 1-4. Table 1 shows the calorific value of the seed oil and diesel, while Table 2 depicts the trace metal content of the oils. Table 3 gives the proximate values of the pear seed, while the fuel characteristics are displayed in Table 4. Discussion The oil obtained from African pear seed was light yellow in color. The percentage oil content of this seed compared favorably with the oil content of such seeds (15) Usoro, E. U.; Suyamsothy, E.; Sanni, G. A. Manual of Chemical Methods of Food Analysis; Bencox International Ltd, 1982; pp 1-35. (16) Williams, K. A. Oils, Fats and Fatty Foods, 4th ed.; American Elsevier Pub. Co. Inc.: London, 1966; pp 88-89. (17) Maynard, A. J. Methods in Food Analysis, Physical, Chemical and Instrumental Methods of Analysis, 2nd ed.; Academic Press: New York, San Francisco, London, 1976; pp 176-177. (18) Ajiwe, V. I. E. Analysis of Animal Feeding-Stuffs. M.S. Thesis, A.B.U., Zaria, Nigeria, 1983; pp 12-13. (19) Williard, H. H.; Merritt, L. L.; Dean, J. A. Instrumental Methods of Analysis, 4th ed.; Van Nostrand: New York, 1974; pp 420-423, 431433. (20) I. P. Standards for Petroleum and its Products, Part 1, 42nd ed.; London Institute of Petroleum Pub., 1983; pp 15, 71, 160, and 242. (21) AOAC. Official Methods of Analysis of the AOAC, 15th ed., 1980; pp 132-134. (22) Barrette, P.; Copeland, T. R. Trace Metal Monitoring by Atomic Absorption, Spectroscopy. In Monitoring Toxic substances; Sctinetzle, D., Ed.; American Chemical Society: Washington, DC, 1979.
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Table 2. Trace Metal Content of the Comparative Study of African Pear Seed Oil and Diesel Oil trace metals
African pear seed oil (mg/g)
diesel oil (mg/g)
potassium zinc magnesium copper calcium lead manganese iron
2.0000 1.41686 0.8879 N.D.a 6.01084 N.D.a N.D.a N.D.a
2.0000 0.6767 0.3859 N.D.a 2.4740 N.D.a N.D.a N.D.a
a
N.D. ) not detectable. Table 3. Proximate Values of African Pear Seed parameter
African pear seed
moisture % ash % protein % fat % crude fiber % carbohydrate % energy content kcal/kg
10.000 5.000 2.625 27.280 4.750 50.345 449.525
Table 4. Fuel Properties of African Pear Seed Oil and Diesel Oil parameter relative density at 15 °C/13 °C refractive index at 40 °C viscosity water content (%) ash content (%) burning characteristic calorific value gross calorific value (from density)
African pear seed oil
diesel oil
0.9483 1.4645 1.45 mm2/s 4.7320 0.0232 low sooty flame 795.711 Kcal 43.578 mj/kg
1.0111 1.4845 1.51 mm2/s 5.2132 0.0682 sooty flame 750.7302 Kcal 43.0264 mj/kg
as cotton (18.28%) and soyabean (14-25%) which are commercially extracted. The oil would be best extracted by solvent extraction method. The results obtained from the chemical analysis of the seed oil and its residue have shown that alternative diesel oil could be obtained from the African pear seed oil. Other results showed an estimate of the nutritional value of the pear seed without the oil (when defatted). Using petroleum diesel oil (bp 190-380 °C) as a standard which had physico-chemical results similar to those of African pear seed oil as shown in Tables 1, 2, and 4, it was obvious that the African pear seed oil had fuel properties similar to those of diesel. The ash content was in conformity with the ASTM (American Standard for Testing and Material) limiting requirement. This means that the seed oil contained low burnable material which mlkes it less likely to contribute to injector, fuel-pump, piston, and ring wear as confirmed by the fact that any solid ash-forming compounds remaining after filtration could cause severe abrasive wear in diesel engine fuel pumps and injectors as well as abrasive wear of piston rings and cylinder liners.4 The moisture or water content of the seed oil was calculated as 4.7783% by weight, which was very close to that of the diesel oil 5.2132% under the same condition. The low moisture content indicates little contamination. Moisture as a contaminant could cause corrosion in the fuel system especially if the moisture was salty, and it could also contribute to ash-forming constituents in diesel engine cylinders and gas turbines.
From the ASTM Standard specification, distillate fuels should not contain visible water while water contamination from external sources should not exceed 0.25% and preferably should be much lower. Residual fuels also could tolerate more water. Literature stipulated a lower moisture value, the result for both oils must have been associated with the humidity of the surrounding. The relative density of the seed oil was 0.9435 which was quite close to that of the diesel oil (1.0111). This similarity confirmed that diesel oil could be substituted with the pear seed oil. The low relative density of the pear seed oil indicated a good ignition property.4 Literature confirmed that a low relative density indicated a predominantly paraffinic fuel with good ignition properties when burned in diesel engines while high relative density indicated mainly aromatic or asphaltic fuel with poor combustion properties. The viscosities of both oils were quite close and showed that the pear oil was sufficiently viscous so that the real spray would penetrate across the combustion chamber and would become properly mixed with air. Too viscous a fuel would not break up and mix with air. Standard viscosities for most number 2 grade diesel fuels are within the range of 2-4.3 centistokes, while number 1 fuels ranged from 1.4-1.9 centistokes. The calorific values of both the seed oil and the diesel oil were very close; this confirmed that the pear oil would burn completely with a release of high energy which could be utilized to power a diesel engine just like diesel oil. Though not determined, cetane number often has a direct relation to viscosity and calorific value. From the discussions under viscosity and calorific values of both oils, their cetane number must be close. The structural relationship between diesel and pear seed oil (Figures 1 and 2) confirmed that their cetane number must be close. Fourier transform 1.r (Figures 1 and 2) showed that both diesel and pear seed oil had 0-H stretch at 3166 and 3008 cm-1, respectively; (free OH occurred at 3426 and 3404 cm-1 for diesel and pear); C-H stretch for alkene and aromatic bonds at same 2952 cm-1, C-H stretch for alkanes at 2855 and 2854 cm-1, respectively. Equally, both diesel and pear seed oil had CdO stretch for esters at 1746 and 1747 cm-1, respectively, but that of pear seed was more prominent, confirming that it was an ester. At 1461 cm-1 diesel oil had a prominent peak for CdC for aromatic compounds while that of pear seed occurred at 1457 cm-1, confirming the degree of unsaturation in the oil. Also, diesel and pear seed had C-O deformation for esters at 1167 and 1147 cm-1, respectively. It is equally worthy to note that cloud and pour point are only important when storage was being considered.4 The free fatty acid and acid value composition of the pear seed oil was very low, 1.68 ( 0.2 and 3.36 ( 0.4, respectively. These values confirmed its keeping quality and less corrosive activity in engines.23 The burning characteristics results also confirmed that the seed oil could be used as a substitute for diesel oil. Again, the trace metal values were low and would (23) Ajiwe, V. I. E.; Okeke, C. A.; Nnabuike, B.; Ogunleye, G. A.; Elebo, E. Applications of Oils Extracted from African Star Apple (Chrysophyllum africanum), Horse Eye Bean (Mucuna sloanei), and African Pear (Dacryodes edulis) Seeds. Bioresour. Technol. 1997, 59, 259-261.
African Pear Seed Oil as Alternative to Diesel Oil
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Figure 1. Diesel oil.
not contribute to pollution, corrosion of the engine, and subsequent engine damage.
The proximate analysis of the pear seed showed that the defatted seed was not a waste and could serve as
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Figure 2. African pear seed oil.
feed for farm animals when integrated into animal feed formulation because of its high nutritional value (see Table 3). The fact that the African pear seed was a waste and caused pollution of the environment called for its conversion to an alternative energy source. Since the African pear plants could easily adapt to new climatic conditions, could easily be propagated, and could live for very long periods,12 its adaptation as an alternative source for diesel would be an advantage. This would yield a new energy source which would be ozone layer depletion free.
Conclusion From the results and discussion, it is obvious that the African pear seed oil is a very important source of fuel for diesel engines. The percentage of oil content is quite high, and this suggests that the oil extraction on commercial scale is possible. Moreover, the utilization of the defatted pear seed as an animal feed would totally remove the seed as a waste. EF990051L
