Ind. Eng. Chem. Res. 2009, 48, 1719–1726
1719
Optimization of Base Catalytic Methanolysis of Sunflower (Helianthus annuus) Seed Oil for Biodiesel Production by Using Response Surface Methodology Umer Rashid,† Farooq Anwar,*,† and Muhammad Arif‡ Department of Chemistry and Biochemistry and Department of Mathematics and Statistics, UniVersity of Agriculture, Faisalabad-38040, Pakistan
In the present work, the response surface methodology (RSM), based on a central composite rotatable design (CCRD), was used to determine the optimum conditions for the methanolysis of sunflower (Helianthus annuus) crude oil. Four process variables were evaluated at two levels (24 experimental design): the methanol/oil molar ratio (3:1-9:1), the catalyst concentration in relation to the oil mass (0.2-1.2 wt % KOH), the reaction temperature (35-65 °C), and the alcoholysis reaction time (10-120 min). Using RSM, a quadratic polynomial equation was obtained by multiple regression analysis for predicting the optimization of the transesterification reaction. The results indicated that the methanol-oil-molar ratio, catalyst concentration, and reaction temperature were the significant parameters affecting the yield of sunflower oil methyl esters (SOMEs/biodiesel). The optimum transesterification reaction conditions, established using RSM, which offered 97.8% SOME yield, were found to be 6.0:1.0 methanol-to-oil ratio, 0.70% catalyst concentration, 50 °C reaction temperature, and 65-min reaction time. The proposed process provided an average biodiesel yield of more than 91%. A linear relationship was constructed between the observed and predicted values of yield. The biodiesel produced in the present experiments was analyzed by gas chromatography (GC), which showed that it mainly contained four fatty acid methyl esters (linoleic, oleic, palmitic, and stearic acids). The nuclear magnetic resonance (1H NMR) spectrum of the SOMEs is also reported. The fuel properties of the SOMEs such as density, cetane number, kinematic viscosity, oxidative stability, lubricity, cloud point, pour point, cold filter plugging point, flash point, ash content, sulfur content, acid value, copper strip corrosion value, and higher heating value were determined and are discussed in light of biodiesel standards ASTM D6751 and EN 14214. 1. Introduction Sunflower (Helianthus annuus L.) is an oil seed crop of the Compositea (Asteracea) family and the genus Helianthus. It originated from North America, where it was traditionally cultivated by Native Americans. It is accounted one of the most widely cultivated oil crops in the world1,2 and the fifth most important source of edible oil after soybean, rapeseed, cottonseed, and peanut. Sunflowers are grown on ∼20 million hectares (ha) around the world. In Pakistan, sunflower is a domestically important oil seed crop and is grown on 379 204 ha, yielding 249 000 tons3 of oil. Sunflower seeds are widely used in the food and nutraceutical industries because of its high oil and protein contents and other valuable bioactive components. The most abundant fatty acids in sunflower oil are linoleic acid (64.9%), oleic (23.5%), palmitic (5.7%), and stearic (4.1%) acids, which together comprise about 98.2% of the total fatty acids.4-6 Sunflower oil also contains high levels of tocopherols (including vitamin E) and phytosterols.7 Worldwide energy usage continues to increase despite the ongoing depletion of accessible petroleum reserves. As a result, Pakistan and other energy-importing countries are exploring alternative domestic energy sources to reduce their dependence on imported fossil fuels and products. Vegetable oil fuel or biodiesel (BD) fuel [fatty acid methyl esters (FAMEs)] derived from animal fat, vegetable oil, or waste cooking oil is considered the preeminent candidate for diesel fuel replacement in diesel engines and can be used neat or in blends with petroleum diesel.8-10 At present, the most developed process for production * To whom correspondence should be addressed. E-mail: fqanwar@ yahoo.com. Fax: (92) 41 9200764. † Department of Chemistry and Biochemistry. ‡ Department of Mathematics and Statistics.
of biodiesel using transesterification reactions employs an alkali catalysis system. Transesterification process is the reaction of a triglyceride (vegetable oil/animal fat) with an alcohol to form esters and glycerin.11 The stoichiometric equation for the transesterification reaction requires 1 mol of triglyceride and 3 mol of alcohol to form 3 mol of methyl ester and 1 mol of glycerol in the presence of a strong base or acid.9 However, in practice, this is usually increased to 6:1 to raise the product yield. The main parameters affecting transesterification are the molar ratio of vegetable oil to alcohol, catalysts, reaction temperature and time, contents of free fatty acids, and water in the oils and fats.12,13 The recommended amount of alkali catalyst for transesterification is between 0.1% and 1.0% (w/w) of oils and fats. Generally, the reaction temperature is set at near the boiling point of alcohol. Alkali-catalyzed transesterification is much faster than acid-catalyzed transesterification and is most often used commercially because of its low cost.14 Some researchers have investigated the use of response surface methodology (RSM) for optimization of transesterifcation of vegetable oils using acid or base catalyst. Tiwari et al.15 used RSM to optimize the process parameters in pretreatment (esterification) and transesterification reactions for the reduction of free fatty acids of jatropha oil. In another study, Ghadge and Raheman16 applied the same method to reduce the free fatty acid content of Madhuca indica seed oil. Domingos et al.17 investigated the ethanolysis of Raphanus satiVus seed oil to optimize the process variables using response surface methodology. Response surface methodology has been applied to optimize transesterficitaion conditions for biodiesel production using jojoba oil and acid oil.18,19 Vicente et al.20 investigated the effects of temperature and catalyst concentration during transesterification of sunflower oil with methanol by using a
10.1021/ie801136h CCC: $40.75 2009 American Chemical Society Published on Web 01/12/2009
1720 Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 Table 1. Full-Factorial Central Composite Rotatable Design (CCRD) of Four Independent Variables in Natural Units along with the Observed Responses for Transesterification Process
run
methanol/ oil molar ratio
catalyst concentration (%)
reaction temperature (°C)
reaction time (min)
yield of biodiesel (wt %)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
4.5:1 7.5:1 4.5:1 7.5:1 4.5:1 7.5:1 4.5:1 7.5:1 4.5:1 7.5:1 4.5:1 7.5:1 4.5:1 7.5:1 4.5:1 7.5:1 3:1 9:1 6:1 6:1 6:1 6:1 6:1 6:1 6:1 6:1 6:1 6:1 6:1 6:1
0.45 0.45 0.95 0.95 0.45 0.45 0.95 0.95 0.45 0.45 0.95 0.95 0.45 0.45 0.95 0.95 0.7 0.7 0.2 1.2 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7
43 43 43 43 58 58 58 58 43 43 43 43 58 58 58 58 50 50 50 50 35 65 50 50 50 50 50 50 50 50
38 38 38 38 38 38 38 38 93 93 93 93 93 93 93 93 65 65 65 65 65 65 10 120 65 65 65 65 65 65
70.10 79.92 95.51 88.50 72.00 82.00 88.35 95.62 90.69 98.30 96.20 91.00 93.50 97.02 95.85 96.59 88.76 97.51 74.10 92.00 85.94 96.90 65.50 97.00 98.50 98.00 98.15 98.50 96.58 97.50
Table 3. Parameter Estimates Obtained by Least-Squares Fit and p Value for Their Significance model terms
estimated coefficient
sum of squares
F ratio
p value
intercept X1 X2 X3 X4 X12 X22 X32 X42 X1X2 X1X3 X1X4 X2X3 X2X4 X3X4
97.87 1.84 4.16 1.36 6.26 -0.81 -3.33 -1.25 -3.78 -2.20 1.02 -0.84 -0.02 -3.99 0.18
81.51 415.92 44.64 939.63 18.06 304.63 42.52 392.45 77.13 16.67 11.21 0.0068 254.80 0.49
8.83 45.05 4.83 101.77 1.96 32.99 4.61 42.50 8.35 1.81 1.21 0.00074 27.60 0.053
0.165 0.0095
