Study of Thermal and Oxidative Stability of Cottonseed Biodiesel

Abstract

Biodiesel is a renewable fuel with excellent lubricity and biodegradability. However, its use may be compromised by factors that change its characteristics and occur during production, transportation and/or storage. Some of them are associated with biodiesel stability and can affect vehicle performance. The objective of this work was to analyze the main causes of cottonseed oil biodiesel instability due to the storage process, determining some physicochemical properties as kinematic viscosity, acidity index, refractive index, electrical conductivity as well as ester content, mass of precipitate formed and pH. The acidity and kinematic viscosity of biodiesel from cottonseed oil increase with storage time. The latter suggests the occurrence of a partial oxidation of biodiesel with formation of products that increase its viscosity. Gas chromatography results showed that even after thermo-oxidative treatment, biodiesel samples maintained the minimum ester content required by the ANP (Brazilian National Agency of Petroleum, Natural Gas and Biofuels) and unsaturated bonds tends to be preferentially oxidized over other carbon-carbon bonds. There was no significant influence of light exposure (storage in amber and transparent vials) on the ester content, refractive index and mass of precipitate formed. On the other hand, the latter was influenced by the heating time.