Modeling the biodiesel production using the wheat straw ash as a catalyst

Wheat straw ash (WSA) was investigated as a new catalyst in biodiesel production from sunflower oil. The catalyst was characterized by temperature-programmed decomposition, X- ray powder diffraction, Hg porosimetry, N2 physisorption, and scanning electron microscopy - energy dispersive X-ray spectroscopy methods. The methanolysis reaction was tested in the temperature range of 55–65°C, the catalyst loading range 10–20 % of the oil weight, and the methanol-to-oil molar ratio range 18 : 1–24 : 1. The reaction conditions of the sunflower oil methanolysis over WSA were optimized by using the response surface methodology in combination with the historical experimental design. The optimum process conditions ensuring the highest fatty acid methyl esters (FAME) content of 98.6 % were the reaction temperature of 60.3°C, the catalyst loading of 11.6 % (based on the oil weight), the methanol-to-oil molar ratio of 18.3 :1, and the reaction time of 124 min. The values of the statistical criteria, such as coefficients of determination (R2 = 0.811, R2 = 0.789, R2 = 0.761) and the mean relative percent deviation (MRPD) value of 10.6 % (66 data) implied the acceptability and precision of the developed model. The FAME content after 4 h of reaction under the optimal conditions decreased to 37, 12, and 3 %, after the first, second, and third reuse, respectively