Estudo do processo de interesterificação química de óleos vegetais, com foco na autointeresterificação do óleo de mamona, e avaliação do potencial uso de seus produtos de reação

Abstract

Oils and fats are important biomass sources with several industrial and technological applications, most often after modification processes. An example is the transesterification reaction of these materials, which can be influenced by the composition of the raw materials in terms of fatty acids (FAs). Thus, with the initial aim of comparing the reactions of mixtures of different sources of triacylglycerols (TAGs), but equivalent in terms of FA composition, in this work, studies on the transesterification of binary mixtures of castor (OM), soybean (OS) and coconut (OC) oils, in the presence of methanol and NaOH, before and after CH3OK-catalyzed chemical interesterification, were carried out. For cases in which OM is not present, studies have shown that random redistribution of fatty fragments in TAGs does not significantly affect the kinetic behavior of the transesterification reaction. On the other hand, binary mixtures containing OM, before and after interesterification, showed different kinetic behaviors. In other words, the kinetics of the transesterification reaction does not depend only on the FA composition of the oils used when utilizing OM as a source of TAGs, but also on how these FAs are organized in the acylglycerol molecules. From the results obtained, it was found that during interesterification of the mixtures containing this oil, parallel transesterification reaction occurs. It was confirmed that the hydroxyl group present on the 12th carbon of the ricinoleic portion of the OM acts as a transesterification agent under the interesterification conditions adopted in this work. In these cases, increases in viscosity in relation to physical mixtures containing OM (from 14 to 93%) and emergence of peaks of high retention times in high performance liquid chromatography (HPLC) determinations were observed. Carbon-13 nuclear magnetic resonance (13C NMR) analyzes confirmed that during the interesterification reaction in the presence of OM, acylglycerol estolides are formed, which explains the lower transesterification rates for interesterified mixtures. This is the first time that the production of estolides, FA-based ester oligomers with several industrial applications, has been reported under TAG interesterification conditions. Quantitative 13C NMR studies indicated high degrees of esterification (72- 97%) for the samples produced. In order to better understand the reaction process studied, the same reactions were carried out with neat OM. After OM interesterification (80-120 °C, 15-150 min), once again the formation of estolides was observed, as well as the formation of di- and monoacylglycerols, in addition to glycerol. There was also an increase in the degree of oligomerization and in the viscosity of the material obtained with the increase in reaction time and temperature. The sample with the highest kinematic viscosity at 40 °C showed an increase of 146% compared to OM. At 120 °C, the reaction demonstrated to follow second-order kinetics and a rate constant of 0.4984 L mol-1 min-1 , with relation to TAG concentration. The products derived from the chemical interesterification of OM showed potential for industrial application as lubricants and antifoams after investigation of their physicochemical properties (viscosity, pour point, flash point, ASTM color, thermo-oxidative stability, surface tension) and comparison with similar products reported in the literature or obtained commercially.