Activated carbon obtained from malt bagasse as a support in heterogeneous catalysis for biodiesel production

Two novel catalysts were prepared from malt bagasse, the main waste of brewery industry, and were employed in the synthesis of the ethylic biodiesel of soybean oil. Catalysts C1 and C2 were prepared by impregnation of KOH solution either on a previously calcined malt bagasse (C1) or on dried malt bagasse, followed by calcination (C2). Catalyst C1 presented 14.3% K+ w/w and specific surface area (SBET) of 2.495 m2 g−1, while these figures were 37.6% K+ w/w and 1.138 m2 g−1 for C2. Catalysts were further characterized by infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and lixiviation tests. A factorial design (23) was used to optimize the reaction time and the oil/ethanol molar ratio upon the biodiesel yield, being the reaction temperature (65 °C) and the catalyst amount (10% w/w catalyst/oil) fixed. Under optimum conditions, biodiesel yield was 91.8 ± 1.0% using C1, employing an 1:12 oil/ethanol molar ratio and 2 h of reaction time. Specific mass, cinematic viscosity and acidity index values of the biodiesel obtained in optimum conditions agree with the standards of the American Society for Testing and Materials (ASTM) and the European Standards (EN). Catalyst C1 was reused once, affording the biodiesel in 88.7% yield.