Synthesis and characterization of novel ethyl levulinate coupled N-phenyl-p-phenylenediamine multifunctional additive: oxidation stability and lubricity improver in biodiesel

Abstract

ABSTRACT Biodiesel is an emerging solution to petrodiesel owing to its high flash point, low toxicity, biodegradability, and less greenhouse gas (GHG) emissions. It is still a problem for end-users due to poor oxidation stability and cold flow properties. However, biodiesel can be used as a lubricity improver in petrodiesel, but high dosages of biodiesel may be cost-intensive. Multifunctional additives can provide a robust solution to the said challenge. We report herein the Schiff base ethyl levulinate coupled with N-phenyl-p-phenylenediamine (EL-NPPD) as multifunctional additive, viz. antioxidant and lubricity enhancer for the biodiesel. The additive was synthesized in two steps: ethyl levulinate (EL) production followed by imine formation. The final product was characterized using thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) spectroscopy. The antioxidant properties of the synthesized additive were checked in terms of induction time using Rancimat as per EN14112 methods. At the 1000 ppm concentration, the induction period value of 7.94 ± 0.6 was observed. Further, as the concentration increased, induction time got increased. Furthermore, the antioxidant potential was checked with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition-based method in which different concentrations of additive ranging from 1000 to 5000 ppm were used against commercial antioxidants. As concentration increased to 4000 ppm, % inhibition values got increased by 15%, which showed better antioxidant activity of EL-NPPD. Similarly, the lubricity tests were performed using the HFRR test in which additive ranging from 1000 to 2000 ppm was used, and the average wear scar diameter (AWSD) was significantly reduced from 258 ± 11 to 248 ± 10, i.e. around 5% reduction than neat biodiesel sample.