Assessment of biodiesel stability under long-term storage and dynamic accelerated oxidation: a comparison approach

The biodiesel susceptibility to oxidation causes its qualitative deterioration and affects both its handling and long-term storage. This study aims to evaluate biodiesel (commercial-grade and fresh samples) oxidative degradation via combined extended storage studies and under dynamic laboratory-scale accelerated conditions. Biodiesel samples from various feedstocks (waste cooking oils, tallow oil, vegetable oils) with and without addition of a synthetic commercial antioxidant (Chimec HR 876 HFP, 500 mg/kg) were stored at ambient conditions for long-time periods (6 and 14 months), and/or submitted to accelerated aging. During the accelerated oxidation tests, the samples were exposed to an air flow rate of 100, 200 and 300 mL/min for 2, 4 and 6 h at 120 degrees C. The storage stability of biodiesels depended on the utilized feedstock, while the antioxidant addition rendered the storage of the samples from waste cooking oil and tallow oil for similar to 12 months. The biodiesels were intensively deteriorated when submitted to dynamic oxidation (at 120 degrees C with air flow rate of 300 mL/min for 6 h), as confirmed by the acidity and induction period. After 2 h of intense oxidation, the IP of the biodiesels decreased below EN 14214 limit, while after similar to 2-4 h, the TAN values exceeded the respective limit (with the exception of PME samples). These conditions could correspond to the biodiesel's quality deterioration after similar to 1-3 months of storage under the examined conditions, accounting the biodiesel type. Based on these results, the stability of biodiesel is associated with the aging conditions, its type and the antioxidant, as well. [GRAPHICS] .