Avaliação do uso de óleo de soja degomado e etanol supercrítico em processo contínuo não catalítico para a produção de biodiesel

Abstract

Biodiesel is an alternative fuel that is renewable, non-toxic and biodegradable, has lower contaminants contents and produces a lower amount of pollutants. Nowadays, biodiesel is usually produced from the transesterification of vegetable oils with short chain alcohol using a homogeneous catalyst. However, some non-conventional methods can be an interesting alternative to obtain this fuel, such as to perform the reaction without catalyst under alcohol supercritical conditions. This route has the advantages of promoting a better contact between the reagents leading to good conversions, having an easier purification and the ability of accepting lower quality oils, with higher water and free fatty acids contents. Methanol is the alcohol used in the majority of the studies since it presents a higher reactivity than ethanol and presents lower cost. On the other hand ethanol is more environmental friendly since it is considered a renewable compound and is easily available in the market, especially in Brazil. Therefore, the objective of this study was to investigate the production of biodiesel from degummed soybean oil using ethanol in supercritical conditions. The experiments were conducted in a continuous reactor and the process parameters investigated were temperature (250-340 oC), residence time (11 to 50 min.) and alcohol-to-oil molar ratio (9:1 to 51:1), at pressure of 200 bar. The effect of each parameter, as well as, of the interactions among them in the conversion of fatty acid ethylic esters was evaluated using design of experiments (DOE). The results showed that the reactions of degummed soybean oil with ethanol led to esters yields up to 65% (340 oC, 39 min and alcohol-to-oil molar ratio 30:1). These values are inferior when compared to the ones obtain with refined soybean oil probably due to the presence of several impurities in degummed soy bean oil such as pigments, antioxidants, phospholipid, etc. Despite of this lower yield, the use of degummed soy bean oil can still be a good alternative since this is a lower cost raw material and non-edible.