Tinospora cordifolia stem extract as an antioxidant additive for enhanced stability of Karanja biodiesel

Oxidative stability of biodiesel is an important fuel quality parameter that not only affects the composition of the fuel but also affects the performance of the engine and tailpipe emissions. The fatty acid profiling of Karanja oil used in this study revealed the presence of ≈69% unsaturated components and the Karanja biodiesel (2.49 h) failed to meet the ASTM D6751 (3 h) and EN 14214 (6 h) specification for oxidation induction period. The utility of T. cordifolia stem extract as an antioxidant additive for Karanja biodiesel has been investigated in this work. The extraction experiments were optimised in terms of solvent composition, extraction time and extraction temperature using response surface based Box-Behnken designing approach. Characterisation of the stem extract revealed high total phenolic content with excellent radical scavenging activity. The extract was reasonably soluble in biodiesel, and it was able to extend the oxidation induction period of biodiesel. The ASTM D6751 and EN 14214 specifications were met at a loading of 100 and 600 ppm respectively. The findings of the study indicate that the T. cordifolia stem extract can serve as a cheap, environment-friendly and non-toxic alternative of synthetic antioxidants.