Energy & Fuels 2006, 20, 2249-2252
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Synthesis of Alkyl Esters from Three Unconventional Sudanese Oils for Their Use as Biodiesel A. Mariod,*,† S. Klupsch,‡ I. H. Hussein,§ and B. Ondruschka‡ Food Science and Technology Department, College of Agricultural Studies, Sudan UniVersity of Science and Technology, Post Office Box 71, Khartoum North, Sudan, Institute for Technical Chemistry and EnVironmental Chemistry, Friedrich-Schiller UniVersity, Lessingstrasse 12, 07743 Jena, Germany, and National Oil Processing Research Institute (NOPRI), UniVersity of Gezira, Post Office Box 20, Wad Madani, Sudan ReceiVed January 26, 2006. ReVised Manuscript ReceiVed May 20, 2006
Biodiesel is a renewable, biodegradable, and nontoxic fuel that can be derived from vegetable oils by transesterification. In this study, Sclerocarya birrea oil (SCO), melon bug oil (MBO), and sorghum bug oil (SBO), three long-term stable oils from Sudan, were transesterified using methanol or ethanol in the presence of sulfuric acid; the obtained biodiesel characteristics were studied in accordance with the DIN EN 14214 specifications for biodiesel. Most of the biodiesel characteristics met the DIN specifications (water content, iodine number, phosphorus content). The kinematic viscosity values of all samples were higher than those of biodiesel standard limits. Concerning the oxidative stability, only SCO has an induction period higher than the required limit. It was possible to prepare the methyl and ethyl esters catalyzed by H2SO4 from the three unconventional Sudanese oils. Under the described transesterification conditions, SCO seems more suitable for biodiesel than MBO and SBO.
Introduction Sclerocarya birrea subsp. Caffera, family Anacardiaceae, is a Savannah tree. The seed encloses 2-3 soft white edible kernels (nuts), which are rich in oil and protein.1,2 In the literature, only a few reports dealing with the seed oil of S. birrea are available.3-6 Aspongubus Viduatus (melon bug), order Hemiptera, is a bug of 20 mm height, widely distributed in Sudan and considered the main pest of watermelon. The oil is used in cooking (during famine and shortage of food) and some medicinal applications, e.g., skin-lesion remedy. Elobied Agricultural Research Station (North Kordofan state of Sudan) designed a handpicking program for melon bug adults in four different areas of the state, for two seasons. During these seasons, a total of 15 tons of * To whom correspondence should be addressed: Food Science and Technology Department, College of Agricultural Studies, Sudan University of Science and Technology, Post Office Box 71, Khartoum North, Sudan. Telephone: +249-(0)-185-311082. Fax: +249-(0)-185-311896. E-mail:
[email protected]. † Sudan University of Science and Technology. ‡ Friedrich-Schiller University. § University of Gezira. (1) FAO Food and Nutrition, paper number 42. Traditional Food Plants, U.N., Rome, Italy, 1988. (2) Mizrahi, Y.; Nerd, A. New crops as a possible solution for the trouble Israeli export market. In Progress in New Crops; J. Janick, J., Ed.; ASHS Press: Alexandria, VA, 1996; pp 37-45. (3) Salama, R. B. The seed oil of Sclerocarya birrea. Sudan J. Food Sci. Technol. 1973, 5, 4-6. (4) Ogbobe, O. Physico-chemical composition and characterization of the seed, and seed oil of Sclerocarya birrea. Plant Foods Hum. Nutr. 1992, 42, 201-206. (5) Mariod, A. A.; Matthau¨s, B.; Eichner, K. Fatty acid, tocopherol and sterol composition as well as oxidative stability of three unusual Sudanese oils. J. Food Lipids 2004, 11, 179-189. (6) Mariod, A. A.; Ali, A. O.; Elhussein, S. A.; Hussien, I. H. A Reinvestigation of physicochemical characteristics and fatty acid composition of Sclerocarya birrea (Homeid) kernel oil. Sudan J. Sci. Technol. 2005, 6, 178-183.
melon bug adults were collected in the first season and 226 tons were collected in the second one.7 In an integrated management program, the plant protection department of North Kordofan state, Sudan, together with the World Food Program (WFP), proposed to collect more than 1400 tons of adult bugs in 3 million feddans of watermelon in the state for the 2005/ 2006 season.8 The bug contain 45% oil, which contained 46.5, 3.4, and 44.2% oleic, linoleic, and palmetic acids, respectively (Table 1), with a low amount of tocopherol of 0.3 mg/100 g and a high oxidative stability of 38 h in the Rancimat test at 120 °C.5 Agonoscelis pubescens (sorghum bug) belongs to the order Hemiptera (family Pentatomidae), commonly known in Sudan as Dura andat. In some areas of Sudan, the collected bugs were extracted and the obtained oil was used for cooking and some medicinal uses. The oil content of sorghum bug was 60%, with 40.9, 34.5, and 12.1% of oleic, linoleic, and palmetic acids, respectively (Table 1), and the oil contains 34.0 mg/100 g tocopherols.5 More than 350 oil-bearing crops have been identified, among which mainly sunflower, safflower, soybean, cottonseed, rapeseed, palm, and peanut oils are considered to be potential alternative fuels for diesel engines. In fact, vegetable oils used as fuel create several problems that have been identified; i.e., the high viscosity and high molecular weight cause poor fuel atomization (which leads to incomplete combustion) and low volatility.9 The transesterification of vegetable oils constitutes an efficient method to provide a fuel with chemical properties that are similar to those of diesel fuel. The proportion of reagents thus (7) Bashir, Y. G. A.; Ali, M. K.; Ali, K. M. IPM options for the control of field watermelon pests in Western Sudan; a paper presented in the 67th meeting of the Pests and Diseases Committee; Agricultural Research Corporation (ARC): Medani, Sudan, July, 2002. (8) Alsudani daily newspaper. Vol. 2o, number 143 31.03.2006.
10.1021/ef060039a CCC: $33.50 © 2006 American Chemical Society Published on Web 09/06/2006
2250 Energy & Fuels, Vol. 20, No. 5, 2006
Mariod et al.
Table 1. Chemical and Physical Properties of Unconventional Sudanese Oilsa SCOb (%)c
fatty acid 16:0d 16:1 n - 7 17:0 18:0 18:1 n - 9 18:2 n - 6 SAFA MUFA PUFA ratio of UFA/SAFA other parameters free fatty acids (%) peroxide value (mequiv of O2/kg) kinematic viscosity at 40 °C (mm2/s) water content (%) induction period at 120 °C (h)
MBOb
SBOb
30.9 ( 0.3 10.7 ( 0.2 2.4 ( 0.1 3.5 ( 0.1 46.6 ( 0.3 3.9 ( 0.1 37.4 57.5 3.9 1.6
12.2 ( 0.2 1.0 ( 0.1 0.1 ( 0.2 7.3 ( 0.2 40.9 ( 0.2 34.5 ( 0.2 20.8 42.2 35.6 3.7
2.1 ( 0.1 0.8 ( 0.04
3.0 ( 0.1 2.1 ( 0.2
10.5 ( 0.1 5.1 ( 0.2
25 ( 0.5
35 ( 0.1
27 ( 0.1
0.25 ( 0.01 43 ( 0.6
0.22 ( 0.02 38 ( 0.4
0.30 ( 0.01 5.1 ( 0.3
14.2 ( 0.2 0.2 ( 0.2 0.1 ( 0.1 8.8 ( 0.2 67.3 ( 0.3 5.9 ( 0.1 25.2 67.5 6.1 2.9
a Mariod, A. A.; B. Matthau ¨ s, B.; Eichner, K. J. Food Lipids 2004, 11, 179-189. b Data are reported as mean values of triple determinations ( standard deviation (SD). SCO (S. birrea), MBO (melon bug), and SBO (sorghum bug) are codes for the different oils. SAFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; UFA, sum of MUFA and PUFA. c Other fatty acids (12:0, 14:0, 18:3, 20: 0, 22:0, and 24:0) were present in an amount of
