Oxidative stability of biodiesel from soybean oil fatty acid ethyl esters

Roseli Ap Ferrari,Ardalla Scabio,Vanessa Da Silva Oliveira

doi:10.1590/s0103-90162005000300014

Abstract

Biodiesel consists of long-chain fatty acid esters, derived from renewable sources such as vegetable oils, and its utilization is associated to the substitution of the diesel oil in engines. Depending on the raw material, biodiesel can contain more or less unsaturated fatty acids in its composition, which are susceptible to oxidation reactions accelerated by exposition to oxygen and high temperatures, being able to change into polymerized compounds. The objective of this work was to determine the oxidative stability of biodiesel produced by ethanolysis of neutralized, refined, soybean frying oil waste, and partially hydrogenated soybean frying oil waste. The evaluation was conducted by means of the Rancimat® equipment, at temperatures of 100 and 105ºC, with an air flow of 20 L h-1. The fatty acid composition was determined by GC and the iodine value was calculated. It was observed that even though the neutralized, refined and waste frying soybean oils presented close comparable iodine values, biodiesel presented different oxidative stabilities. The biodiesel from neutralized soybean oil presented greater stability, followed by the refined and the frying waste. Due to the natural antioxidants in its composition, the neutralized soybean oil promoted a larger oxidative stability of the produced biodiesel. During the deodorization process, the vegetable oils lose part of these antioxidants, therefore the biodiesel from refined soybean oil presented a reduced stability. The thermal process degrades the antioxidants, thus the biodiesel from frying waste oil resulted in lower stability, the same occuring with the biodiesel from partially hydrogenated waste oil, even though having lower iodine values than the other.

Highlights

There is an increasing interest in alternative energy sources since the major part of all energy consumed worldwide comes from petroleum, charcoal and natural gas
Biodiesel consists of long-chain fatty acid esters (Haas et al, 2001; Abreu et al, 2004) produced by transesterification reaction of vegetable oils with short chain alcohols (Noureddini et al, 1998; Encinar et al, 2002)
The objective of this work was to determine the oxidative stability of the ethyl esters manufactured by the transesterification of neutralized, refined, frying oil waste, and partially hydrogenated soybean frying oil waste

Summary

Introduction

There is an increasing interest in alternative energy sources since the major part of all energy consumed worldwide comes from petroleum, charcoal and natural gas. Mass and agricultural derived materials have been suggested as alternative energy sources and the use of biodiesel as fuel presentes a promising potential (AlWidyan & Al-Shyoukh, 2002; Mushrush et al, 2001b), being a market that grows rapidly (Harten, 2003) This is due to its great contribution to the environment (Bagley et al, 1998; Antolín et al, 2002) and to its role as a strategical source of renewable energy in substitution to diesel oil and other petroleum-based fuels (Wu et al, 1998; Cardone et al, 2002). One drawback of biodiesel is that it is more prone to oxidation than petroleum-based fuels and, in its advanced stages, this can cause acidity in the fuel and form insoluble gums and sediments that can plug fuel filters (Monyem & Van Gerpen, 2001)

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