Synthesis of Ethylic Esters for Biodiesel Purposes Using Lipases Naturally Immobilized in a Fermented Solid Produced Using Rhizopus microsporus

We grew Rhizopus microsporus CPQBA 312-07 DRM in solid-state fermentation on a 1:1 mixture, by mass, of sugarcane bagasse and sunflower seed meal, to produce a fermented solid containing lipases (tricaprylin-hydrolyzing activity of 91 U g–1) and then used this fermented solid to catalyze the ethanolysis of corn oil. A 23 factorial design was used to optimize the reaction using n-heptane as the solvent. The best conversion was 91% at 48 h, obtained at 44 °C, with a molar ratio of ethanol/oil of 3:1 and the addition of 1.32 g of fermented solids/15 mL of reaction medium. Using these optimized conditions, we studied the effect of increasing the concentration of the reactants in the medium and even the use of a solvent-free system. In these systems, conversions were quite poor when the ethanol was added in a single aliquot at the start of the reaction. However, when the ethanol was added stepwise, with three equal aliquots added at 0, 24, and 48 h, promising conversions were obtained, including an ester yield of 51% at 72 h in the solvent-free medium. An improved fermented solid (tricaprylin-hydrolyzing activity of 183 U g–1) was then used to improve the production of ethylic esters in solvent-free medium, with an ester yield of 68% being obtained at 72 h. These results are promising and justify further optimization studies.