Bioethanol as the Sole Solvent for Vegetable Oil Extraction and Biodiesel Production

Abstract

Economic and environmental repercussions of oil reserves depletion have led to the implementation of programs promoting the use of alternative fuels such as ethanol and biodiesel. Brazil has great potential for the production of these fuels, as sugarcane and soybean are national major commodities. Biodiesel is produced mainly by transesterification, a process in which oils or fats react with short-chained alcohols in the presence of a catalyst. Hexane is used worldwide in the industrial solvent extraction. This solvent has considerably higher flammability, explosiveness and toxicity compared to ethanol. Since the 1980s, the Laboratory of Oils and Fats at ESALQ-USP Agricultural College has developed a line of research on ethanol oil extraction as a way to also explore the regional importance and availability of this feedstock. The product of soybean oil extraction with ethanol is a miscella (oil + solvent) that, after cooled down to less than 30 °C, separates into three phases: rich-in-alcohol miscella (poor miscella), rich-in-oil miscella (rich miscella) and gum (crude lecithin). The poor miscella, composed of approximately 91% ethanol, can be used as solvent in subsequent extractions. With the natural phase separation, poor miscella carries the majority of polar substances such as phospholipids (0.4%), water and free fatty acids (0.7%). It can be said that the poor miscella promotes a partial refining of the rich miscella. The latter contains 90% oil and 7.8% ethanol and is suitable for biodiesel production without the need for desolventization and refining steps, contributing to the energy recovery of the process. In addition, miscella’s oxidative stability in accelerated tests is three times higher than that of degummed oil. Meal produced from ethanol extraction also has a higher quality than hexane-extracted ones due to antinutritional compounds elimination. The economic and energy analyses of the ethanol process reveal that it requires adjustments to ensure higher efficiency. However, biodiesel from rich miscella via alkaline catalyst can be considered a promising alternative from several points of view, provided the whole process is executed in a single industrial plant using solely ethanol as the solvent extraction and acyl acceptor in the transesterification reaction.