Evaluation of the Fluid Dynamic Properties and Kinetic Study by Pressurized Differential Scanning Calorimetry (PDSC) of Ethanolic Biodiesel Derived from Used Frying Oil / Avaliação das Propriedades Fluído-dinâmicas e Estudo Cinético por Calorimetria Exploratória Diferencial Pressurizada (PDSC) de Biodiesel Etílico Derivado de óleo de fritura usado

Raul Rosenhaim

The present work aimed at investigating the biodiesel issuing from the transesterification of used frying oil with ethanol, via alkaline catalysis. Such investigation covers its thermo-oxidative stability during heating (thermal analysis and rheological properties) as well the kinetic profiles of the samples in the best oxidative induction time by the technique of Pressurized Differential Scanning Calorimetry (PDSC). The behavior of such biodiesel, as part of binary blends with fossil diesel at the proportions of 3, 5, 10, 25, 50, 75 and 100%, was also studied. The biodiesel synthesis used the ethanol route and was carried out under the following conditions: oil/alcohol molar ratio of 1:6 (m/m), 1 % de KOH, temperature of 32 C, washing with 0.1M HCl and hot water. The reaction yield, determined by means of a mass balance aided by the technique of gas chromatography coupled to mass spectrometry, was of 90.56% and the ester content was of 99.56%. According to the physicochemical analyses, all the specifications for the biodiesel and blends met the requirements from Technical Regulation # 7 from the Brazilian National Agency of Petroleum, Natural Gas and Biofuels, with the exceptions of the odixative induction time (1.72 h) and kinematic viscosity (6.10 mm2s-1), which displayed values outside the limits established by the standard. In the thermal study, the thermogravimetric curves showed that the biodiesel blends in diesel are more volatile than the biodiesel derived from used frying oil (B100), whereas at lower concentrations (3, 5, 10 and 25%) are similar to fossil diesel. At higher concentrations (50 and 75%) the blends presented lower volatility and higher thermal stability in relation to fossil diesel and thus, biodiesel and its more concentrated blends showed higher safety in relation to transport, storage, handling and utilization. The study of the fluid dynamic properties of biodiesel and its blends showed that all the samples behave as Newtonian fluids at the studied (10, 25 and 40 C) temperatures. Also the results of cloud point, pour point and cold filter plugging point showed that the behavior of the blends with 3, 5 and 10% are similar to fossil diesel, therefore at these concentrations biodiesel acts as a lubricity additive to fossil diesel. The study by Pressurized Differential Scanning Calorimetry (PDSC) in the dynamic mode and the Rancimat technique revealed that the best antioxidant for the storage of biodiesel is BHT at the concentration of 2500 ppm. The determination of the kinetic parameters by the isothermal PDSC technique allowed determining the theoretical value of the shelf life of used frying oil biodiesel with 2500 ppm of the antioxidant BHT. Therefore, used frying oil biodiesel and its blends B3, B5, B10, B25, B50 and B75 may be used as an alternative source of biofuels.

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