Optimization of Base Catalytic Methanolysis of Sunflower (Helianthus annuus) Seed Oil for Biodiesel Production by Using Response Surface Methodology

Abstract

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.