Avaliação de antioxidantes naturais na estabilidade de biodiesel de soja.

Abstract

Biodiesel has advantages over petroleum diesel, such as renewability and biodegradability, but its low oxidative stability is a disadvantage, requiring the addition of antioxidants to inhibit the oxidative process. The objective of this work was to evaluate the efficiency of the natural extracts of passion fruit leaves and neem in the control of the oxidative process of soybean methyl biodiesel during 60 days of storage. The natural extracts were obtained from (Passiflora edulis) passion fruit leaves and (Azadirachta índica) neem by maceration, and using ethanol, acetone, ethanol/acetone (1:1) and ethanol / water (80:20) as the solvent. The antioxidant potential of the natural extracts was evaluated by determining the total phenolic content and by the DPPH•. method. High Performance Liquid Chromatography was used to identify and quantify the bioactive compounds present in the extracts. Soybean biodiesel was obtained by the transesterification reaction in the methyl route, using alkaline catalysis. The techniques used in the monitoring of the oxidative process of biodiesel were: acidity index, kinematic viscosity and Rancimat. Soybean biodiesel was also characterized by spectroscopic and thermogravimetric techniques. The extracts with the highest antioxidant activity were passion fruit extracts and neem obtained from the mixture of ethanol: acetone solvents. Through High Performance Liquid Chromatography were identified as major components present in the extracts of passion fruit and neem: 2.5 dihydroxybenzoic acid and flavonoid rutin. Samples of biodiesel without addition of extract and extracts of neem and passion fruit at 2000 ppm did not reach the minimum limit of oxidative stability specified in the Technical Regulation of the National Agency of Petroleum, Natural Gas and Biofuels. The sample of biodiesel added with neem extract at 3000 ppm presented acidity index, kinematic viscosity and oxidative stability (induction period of 8h) within the norm at time zero. However, oxidative stability did not remain within the norm during storage at 30 and 60 days.