Accelerated oxidation of fresh and stored biodiesel samples obtained from castor and soybean oils using the petrooxy method

Abstract

In this study the accelerated oxidation of biodiesel obtained by transesterification of castor and soybean oil was evaluated for fresh samples and compared with the same samples after ca. one year of storage under controlled conditions. The oxidation kinetics of the samples was accelerated using the PetroOXY method at temperatures of 100, 120 and 140 °C and initial oxygen pressure of 700 kPa. Total acid number (TAN) of the samples at increasing accelerated oxidation times (up to 60 min) was used to follow the kinetics behavior for both castor and soybean biodiesel. A steep increase in total acid number of soybean biodiesel oxidized at 140 °C (reaching values up to 100 mg KOH/g) was observed. For biodiesel samples from castor oil, values of less than 20 mg KOH/g were reached under the same conditions. For castor biodiesel, kinematic viscosity and specific gravity were also evaluated with increasing accelerated oxidation times. Our results indicate that the oxidative stability after one year of storage for soybean biodiesel was more affected than for castor oil biodiesel.

Keywords:

• Oxidation kinetics
• biodiesel
• castor oil
• soybean oil
• petroOXY

Acknowledgements

The authors acknowledge financial and logistical support from CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), PRH-31/ANP (Programa de Recursos Humanos da Agência Nacional do Petróleo e Biocombustíveis) and PETROBRAS.