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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.

One of the conventional kraft pulp mills produce crude tall oil which is a mixture of free fatty acids, resin acids, sterols, terpenoid compounds, and many others. This study is devoted to the issue of direct transformation of crude tall oil in a mixture with straight-run atmospheric gas oil to liquid fuels using three different commercial hydrotreating catalysts. Diesel fuel production is an alternative to incineration of these materials. High catalytic activity was achieved for all tested catalysts in temperature range 360–380°C, under 5.5 MPa hydrogen pressure and ratio H2/feedstock 500–1000 l/l. Crude tall oil can be converted to diesel oil component via simultaneous refining with straight-run atmospheric gas oil on NiMo/Al2O3and NiW/Al2O3-zeolite catalysts. All tested catalysts had very good hydrodenitrogenation activity and high liquid yield were at tested conditions.

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