Storage stabilities of fuel grade camelina, sunflower and rapeseed methyl esters.

Abstract

The storage stabilities of fuel grade camelina, sunflower and rapeseed methyl esters were evaluated in airtight and open containers. Commercial amounts (200 litres) of the methyl esters were stored in airtight drums and sampled regularly, and the effects of air exposure were evaluated from sixteen days laboratory-scale accelerated storage tests at 65oC. None of the methyl esters in airtight drums deteriorated during eighteen months of storage; composition, viscosities and free fatty acid levels remained unchanged. The accelerated storage test in open containers, however, indicated that exposure to air can cause rapid oxidation of each of the three methyl esters. However, oxidation can be delayed by the presence of tocopherols (natural antioxidants) in the methyl ester, and it can be further delayed by the presence of an unidentified carotenoid. The exceptional stability of rapeseed methyl ester seems to be due to a combination of relatively high levels of Μ-tocopherol and the unidentified carotenoid. The rates of oxidation (i.e. rate of increase of viscosity etc.) of sunflower and camelina methyl esters were about the same, but rapeseed methyl ester oxidised slower. The observed relative rates of oxidation could be predicted from the levels of reacting double bonds calculated from the oxidation data, but not from iodine numbers.