The oxidation stability of methyl esters derived from fresh rapeseed oil and waste frying oil, used as alternative biodiesel fuels, both distilled and undistilled, unstabilized and stabilized by pyrogallol and BHT, was studied by differential thermal analysis (DTA) under nonisothermal conditions at various heating rates and by the Rancimat test under isothermal conditions at 110°C. The results obtained by both techniques are compared. Both techniques show that oxidation stability increases considerably with the addition of antioxidants and that pyrogallol is very efficient. Distillation of the methyl esters prepared from rapeseed oil decreases their oxidation stability, obviously owing to the removal of natural antioxidants. The stability of methyl esters prepared from the waste frying oil is determined mainly by the history of the oil. From the DTA measurements, the kinetic parameters of an Arrhenius-like equation describing the temperature dependence of the oxidation induction period were obtained. The parameters enable one to assess the protective factor of antioxidants for temperatures outside the measuring region, estimate the residual stability, and model the process of biodiesel oxidation under nonisothermal conditions.

Properties of alkyl esters base on castor oilCastor oil is a non-traditional raw material for the preparation of methyl and ethyl esters of higher fatty acids as alternative fuels for diesel engines. Castor oil contains ricinoleic acid (12-hydroxy octadecene acid) with a major share of about 90%. The article presents the parameters of castor oil-based methyl esters (COME) and ethyl esters (COEE) defined by the standard EN 14 214. The densities of COME and COEE are higher than the limit defined by the standard EN 14 214. The viscosities are more than twice as high as the limit value. The cetane numbers are lower than defined by the standard EN 14 214. For the remaining parameters, COME and COEE meet, in principle, the standard EN 14 214. The presence of the free hydroxyl group has virtually no effect on the values of such parameters as carbon residue, filterability at low temperatures and oxidation stability, for which some influence was expected. The physicochemical parameters of the castor oil esters are discussed in comparison to the analogous esters of high-oleic sunflower oil, which contain about 80% of oleic acid. Both the methyl and ethyl esters of high-oleic sunflower oil meet the standard EN 14 214 in all prescribed parameters.

Fatty acid methyl esters (FAME) are considered to be promising and prospective alternative fuels for diesel engines. They can be produced from vegetable oils and animal fats by transesterification of triacylglycerols with methanol. This paper presents the results related to the stability of FAME from aging tests of FAME in the period of 7 months. The FAME were prepared from four oil types, which were finally treated, stabilized, and stored in a different way. The results show that lower ester content in freshly prepared FAME, having at the same time a good conversion, is related to degradation of the oil from which the FAME were prepared. The stabilities of FAME samples prepared from old oils and used frying oils are lower than the stability of FAME samples prepared from fresh oils. Insufficient conversion of FAME itself does not have negative influence on its stability. After final distillation treatment, FAME exhibits lower stability when compared with the sample treated in the standard way. However, they are very sensitive to the presence of an antioxidant; the addition of 0.04 wt % of pyrogallol ensures high FAME stability.

SummaryTh e article is devoted to the study of cold fl ow properties of neat esters of branched chain alcohols with fatty acids and blends of these esters with fossil diesel fuel. According to the determined CFPP values the infl uence of alcohol branching on the fuel fi lterability is negligible and was detected only in the case of 2-ethyl hexanol. Fossil fuel blending with fatty esters up to 10 % vol. does not substantially change the cold fl ow properties of fossil fuel. DSC cooling scan parameters should be employed to predict CFPP of blended diesel fuel.