Combination of Fractional Factorial and Doehlert Experimental Designs in Biodiesel Production: Ethanolysis of Raphanus sativus L. var. oleiferus Stokes Oil Catalyzed by Sodium Ethoxide

Fodder radish-Raphanus sativus L. var. oleiferus Stokes-oil has been regarded as an interesting option to produce biodiesel, because the oil cannot be used for human consumption, the seeds have high oil content, and the cost of production is low. Furthermore, the plant has been used for green fertilization during the interval between harvests of other crops, due to its rapid development as well as its great ability to recycle nutrients. The content of free fatty acids in the crude oil is less than 0.5%, which makes it appropriate for basic catalyzed synthesis. However, basic catalyzed synthesis is very sensitive to the presence of water in the reaction environment. This study proposes the optimization of biodiesel synthesis using sodium ethoxide (sodium ethylate) as a catalyst, with the purpose of minimizing water formation during reaction, increase efficiency, and thus carry out transesterification in a single step. Ethanol was used instead of the methylic route, aiming at the production of an entirely renewable and environmentally preferable fuel. The experiments were proposed and carried out using a combination of fractional factorial design and Doehlert design, in order to allow an extensive study of the process variables with a minimum of experiments. Very intense levels of agitation and high temperatures proved to be inadequate to reach an effective reaction. At optimum conditions the ester content reached approximately 97.9%, which along with several other physical chemistry assays confirm the good quality of the product and that the synthesis of fodder radish crude oil can be performed in a single step efficiently.