| Summary: | <p><em>Economic and environmental reasons show a trend towards replacing fossil fuels with biofuels such as those from triglycerides. Biodiesel can be obtained from vegetable oils and animal fat through several processes such as transesterification, esterification, usually with methanol, ethanol or through pyrolysis, all of them in the presence of an acid or basis catalyst. The use of solid catalysts in biodiesel production has the following advantages: easy recovery and reuse, thus decreasing process costs and amount of waste generated.<sup>1</sup> Some of the problems in the use of solid catalysts are: low concentration of active sites, microporosity, and leaching of active sites.<sup>2 </sup>Studies aiming at developing methodologies involving hydrated niobium oxide as catalyst in biodiesel production have been carried out by our research group.<sup>3,4</sup> Parameters such as the use of assistant solvent to increase the boiling point of the mixture (toluene, ethylene glycol, and DMSO), pre-thermal treatment (calcinations) and catalyst molar concentration were initially assessed in esterification, oleic acid, and methanol reactions. From these studies we could observe that high temperatures and excessive alcohol favor esterification reactions. The best reaction conditions were then used as models and employed in transesterification reactions of soybean oil. DMSO (Dimethyl sulfoxide) was the solvent used to increase the reaction medium temperature without evaporating all the methanol. Transesterification reactions were carried out with soybean oil (0.5 g), methanol (0.85 g), DMSO (2.50 ml), and hydrated niobium oxide as catalyst in ratios of 20% and 100% (in relation to oil mass). Catalyst was employed without pretreatment and after pretreatment at 115 °C, 300 °C, and 500 °C. The reactions occurred at 170 °C, under reflux for 48 hours. A reaction without a catalyst was also carried out. </em><em>All the reactions have shown conversion using CCD and they have been determined by <sup>1</sup>H NMR spectroscopy.</em></p>
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