Production of sunflower oil methyl esters by optimized alkali-catalyzed methanolysis
Introduction
Biodiesel, defined as the simple monoalkyl esters of fatty acids derived from vegetable oil, animal fat, or waste oils, is an interesting and environmentally friendly alternative to conventional diesel fuel (CDF) for combustion in compression-ignition (diesel) engines. Biodiesel is produced by transesterification of a triglyceride with methanol in the presence of catalyst to produce fatty acid methyl esters (FAME) and glycerol. Transesterification employing alkali catalysis and short-chain alcohols provides a high level of conversion. The main parameters affecting the transesterification reaction are molar ratio of vegetable oil to alcohol, catalyst type and amount, reaction time and temperature, and the contents of free fatty acids (FFAs) and water in substrate oil [1]. A number of alkaline catalysts are in practice for transesterification of triglycerides, such as NaOH, KOH, sodium and potassium alkoxides, and carbonates [2]. For alkali-catalyzed transesterifications, the triglyceride must contain relatively low levels of FFAs and the alcohol used is essentially anhydrous. Otherwise, unwanted soap formation and ester hydrolysis may occur [1], [3], [4]. In cases where triglycerides contain high levels of FFAs, acid catalysis may be necessary to avoid pretreatment [5]. Methanol is normally the alcohol of choice for biodiesel production because it is inexpensive and affords a high level of conversion [2].
Sunflower (Helianthus annuus L.), a member of the Compositea family is an important oilseed crop worldwide, yielding approximately 45–50% oil (dehulled seed mass basis). In Pakistan, sunflower, considered as a non-conventional oilseed crop is generally grown in two seasons, spring and summer. In wide range climatic conditions of Pakistan, sunflower crop fits well in the local intercropping systems and could be successfully grown in spring and fall thus yielding two crops in 1 year [6]. A huge potential exists to increase the domestic production of sunflower in Pakistan. Recently, serious efforts have been made to encourage the local production of this crop. As a result, the sunflower acreage has increased from 107,717 ha in 2002–03 to 379,204 ha in 2006–07. The current sunflower seed and oil production in Pakistan is 656,000 and 249,000 tons, respectively [7].
Sunflower oil, widely used in foods for cooking and frying purposes, is also gaining attention as a feedstock for biodiesel production. Antolin in 2002 [8] reported the transesterification of sunflower oil with methanol, examining the effects of alcohol, catalyst amount, and reaction temperature. The following optimized conditions were obtained: alcohol:oil molar ratio of 9:1; 0.28% (w/w) KOH catalyst; and 70 °C reaction temperature. There is no previously reported sufficient data on optimization of conditions for the methanolysis of sunflower oil. Therefore, the main objectives of the present work were to optimize the type and concentration of catalyst, molar ratio of alcohol to oil, and reaction temperature for the transesterification of sunflower oil. The resultant sunflower oil methyl esters (SOME) were characterized and a number of important fuel properties were determined and compared.
Section snippets
Materials and methods
Sunflower (H. annuus) seeds (variety viz. FH-330), harvested by mid of November 2006 were procured from Ayub Agricultural Research Institute (AARI), Faisalabad, Pakistan. The seeds stored in storage room of AARI at ambient and collected after about 1 month of the harvest were not further stored prior to extraction in the experimental lab. Pure standards of FAME were obtained from Sigma Chemical Company (St. Louis, MO). All other chemicals and reagents were analytical reagent grade and purchased
Reaction temperature
The transesterification of sunflower oil was carried out at 30, 45, and 60 °C in order to evaluate the effect of reaction temperature on SOME production. The constant reaction time of 120 min, 1.0% (w/w) of NaOCH3 catalyst, methanol:oil molar ratio of 6:1, and agitation intensity of 600 rpm were maintained with the temperature variations for the production of SOME. The transesterification was proceeded to more than 80% completion after 10 min, regardless of the temperature variations. As indicated
Conclusion
Results of present study demonstrated that the optimum conditions elucidated for the methanolysis of sunflower oil were: 6:1 molar ratio of sunflower oil to methanol, 60 °C reaction temperature, and 1.00% (w/w) NaOH catalyst. The optimized conditions provided SOME in high yield (97.1%). The fuel properties of SOME measured were also within prescribed ASTM D 6751 specifications, thus indicating that SOME is acceptable as a substitute for other common biodiesel and petrodiesel fuels for combustion
Disclaimer
Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.
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