This work examines pressurized accelerated oxidation by a RapidOxy tester as an alternative method for determination of biodiesel oxidation stability. Sunflower oil-based biodiesel was synthesized and treated with antioxidants: tert-butylhydroquinone (TBHQ) - a synthetic antioxidant known for its powerful protective effect, and a mixture of bio-based antioxidant compounds extracted from vinery waste, VWEeth. The antioxidant potency of TBHQ was evaluated at varying temperatures (110 - 140 ?C) and concentrations (250 - 2,000 mg dm-3) by the RapidOxy method; assessment of selected results was performed by comparison with relevant data obtained by the standard Rancimat method. VWEeth was added in two high dosages to biodiesel (87,500 and 150,000 mg dm-3) and analyzed at 140 ?C by the RapidOxy method. Both antioxidants at all applied dosages showed beneficial effects on improving the oxidative stability of biodiesel, but not all of the achieved improvements reached the stability minimum identified by the EN14214 standard. The lowest addition of TBHQ seemed to have a similar effect as the tested dosages of VWEeth but these additions did not increase the induction period above the limit of 8 h; two-fold higher quantity of TBHQ was successful in this respect, increasing the initial oxidation stability by a factor of about 2, which was determined by both methods. The RapidOxy method proved to be a very fast method suitable for testing a large number of samples, which is particularly important for efficient testing of different types and doses of antioxidants.

This study evaluates six formulations in improving oxidation stability of different fatty acid methyl esters (MEs). Two MEs differed in the unsaturation levels as they were synthesized from different feedstocks: a blend of soybean and sunflower oils (SoSuME), and waste cooking oil (WCOME); they did not fulfill the requirements of the EN 14214 standard concerning the oxidation stability (~0.6 h) and some impurities. The third MEs (SoSuME-EN) were fully compliant with the standard. Five formulations were phenolic-based, containing single or mixed antioxidant compounds of different molecular structures; one was amine-based. Different dosages of the formulations were added to the ME samples (corresponding to the addition range ~50-48300 ppm). The MEs stability expressed as induction periods, IPs, determined by the Rancimat method, were used for calculation of stabilization factors, SFs, indicating the efficiency of the applied formulation. The formulation containing TBHQ was the most efficient concerning the lowest consumption rate and the highest SF achieved for the low quality ME. 2,2?-methylene-bis-(4-methyl-6-tert-butylphenol) was linked with higher antioxidant potency than amine-based formulation and the phenolic com-pounds with two bulky tert-butyl groups. Among 4 selected phenolic additives, BHT and 2,2?-methylene-bis-(4-methyl-6-tert-butylphenol) proved similar efficiency in SoSuME-EN (at ~500 ppm they produced SF~2), while it took twice of this amount for mixed butylphenols to achieve the same effect.