Integrated production of biodiesel and bioethanol from sweet potato

Abstract

In the present study, the production of sweet potato bioethanol was conducted at a small industrial plant in Brazil and integrated in biodiesel production through ethanolysis. The specific objectives were: (i) monitor bioethanol production at a small industrial plant, considering production yield; (ii) study the ethanolysis of sunflower oil using sweet potato bioethanol with different grades (98, 99 and 99.4 degrees GL), with focus on biodiesel yield and purity. Bioethanol was produced under the following conditions: Sweet potato dilution in water (1:1 in wt.%); enzymatic hydrolysis with alpha-amylase (90 degrees C) and glucoamylase (60 degrees C) enzymes (700 mL/t); and, fermentation (30 degrees C) with saccharomyces cerevisiae (3.3 kg/t). Ethanolysis was performed as follows: 6:1 ethanol:oil molar ratio; 1.0 wt% NaOH; 45 degrees C; 1 h. The average yield of bioethanol was 161.4 L/t, corresponding to 10 598 L/ha. Biodiesel synthesis using bioethanol of different grades showed that both the yield and purity of the product increased with the grade of the ethanol used, with values ranging from 63 to 83 wt%, and 50 to 94 wt% for yield and purity, respectively. Results show that a high alcohol grade is required to make viable integrated production of biodiesel and bioethanol.