Production of a Biofuel that Keeps the Glycerin as Monoglycerides by Using Supported KF as Heterogeneous Catalyst

This study describes results obtained in the synthesis of a biofuel that integrates glycerol by applying a heterogeneous process where supported KF is employed as alkaline catalyst. Thus, the catalytic performance of KF supported at 10 wt %, on three different solid supports, Al2O3, ZnO and MgO, was investigated in the transesterification process of sunflower oil with methanol. In this respect, the standard experimental conditions employed in the heterogeneous methanolysis reactions were 12 mL of sunflower oil, 2.7 mL of methanol, 0.8 g of catalyst, at 65 ° C temperature during 1 hour. In all cases were obtained 100% conversion, with high selectivity values greater than 90%, as well as quite suitable viscosity values, 4.5 - 8.5 cSt. However, the best catalytic behavior was obtained by using Al2O3 as support. It has been also evaluated the influence of the catalyst weight by using variable amounts of KF/Al2O3 (0.2, 0.4, 0.6, 0.8, 1 g), as well the influence of the oil / methanol molar ratio (1/3, 1/4, 1/5, 1/6 and 1/7) with a fixed quantity of catalyst KF/Al2O3 (0.8 g) and operating at 65 °C of temperature during 1 hour. These three heterogeneous supported catalysts have resulted to be quite suitable to stop the transesterification of triglycerides (TG) with methanol in the second step, so that one molecule of TG generates two moles of fatty acid methyl esters (FAME) and one of MG, working under heterogeneous conditions, at atmospheric pressure, with oil / methanol molar ratio (1/5) and temperatures in the range of 50-65 °C. Thus, a new biofuel similar to conventional biodiesel applicable to diesel engines is obtained under sustainable experimental conditions, which avoiding glycerol production, not only minimizes waste generation but also maximizes efficiency of the process.