Determination of the oxidative stability of biodiesel using near infrared emission spectroscopy

Oxidative stability is an important parameter for quality control of biodiesel samples. Autoxidation is the main cause of deterioration of this type of fuel, and yields hydroperoxides, peroxides and carboxylic acids as main products, in a similar way as in the raw materials employed for its manufacture (vegetable oils and animal fat). Usually, oxidative stability is determined by monitoring the formation of an autoxidation product until a significant change in its concentration can be detected. In this work, a near infrared emission (NIRES) method based on the hydroperoxide emission at 2900 nm (3450 cm−1) was evaluated for determining oxidative stability of biodiesel. A comparative study between the oxidative stability of biodiesel samples and their parent vegetable oils is also presented. Results show that the NIRES method provides oxidative stability values correlated to those obtained with the official Rancimat method (R2 = 0.88), and present equivalent precision. The photometer presents several advantages compared to the Rancimat method, including faster analysis, lower sample consumption and operational simplicity.