Produção e avaliação de biodieseis de óleos de soja oriundos de diferentes processos

Abstract

In this work, biodiesels were produced from soybean oil obtained through different processes, namely: purified soybean oil purchased from the local market, cold-pressed soybean oil, solvent-extracted soybean oil, and residual soybean oil from household culinary use. Volumetric analyses of the acidity of the oil samples were conducted, and all samples were found to be in compliance. To produce biodiesels, the oils were transesterified with sodium methoxide and purified by contact with the ion exchange resin AMBERLITE™ B10DRY. Mid-infrared spectroscopy was applied to quantify the reaction yield based on the free glycerol content present in the samples, and all produced biodiesels met the parameters of current legislation after the purification step, with a conversion rate above 96.5%. Biodiesel samples were characterized by gas chromatography coupled with mass spectrometry to evaluate the levels of methyl esters of fatty acids present, and the levels were close to those found in the literature. Nuclear magnetic resonance was used to calculate the reaction yield based on the methyl esters of fatty acids, and all produced biodiesels showed conversion values close to 100%. Inductively coupled plasma optical emission spectrometry was applied to quantify the metals and phosphorus present in the samples. The results demonstrated that the levels of these compounds were generally above the permitted values in current legislation. Among the evaluated parameters, all biodiesel samples showed good results, indicating only the need for some process adjustments, such as the addition of biodiesel washing steps to reduce metal and phosphorus levels. Biodiesel produced from cold-pressed soybean oil proved to be very promising, as it is made using crude oil without the need for potentially costly purification processes. It also allows for the reuse of generated soybean meal, for example, as a feed ingredient for animal production, unlike the meal obtained from solvent extraction. Additionally, it does not require parameter adjustment steps that may be necessary for residual oils, such as those with elevated acidity due to prior use.