Application of Psidium guajava']java L. leaf extract as a green corrosion inhibitor in biodiesel: Biofilm formation and encrustation

In this paper guava leaf extract was used as antioxidant additive to biodiesel in order to verify its corrosive properties. The study of the copper exposed to soybean oil biodiesel was carried out at room temperature for 2520 h and at 60 degrees C for 1440 h. Scanning Electron Microscopy/ Dispersive Energy Spectroscopy (SEM/EDS) and X-ray Diffraction (XRD) results show less wear and oxidation of the copper plates immersed in biodiesel with the additive indicating that it is better protected from corrosive processes presenting an efficiency of inhibition (Ei) of 55.37 % and 21.11 % at room temperature and 60 degrees C, respectively. At room temperature the effect of using the additive is observed with the naked eye and confirmed by the SEM in which it is verified that the specimen was less attacked compared to neat biodiesel. However at 60 degrees C the use of the additive showed a significant improvement in the vaporization of biodiesel in the region that was not exposed to the fuel. These behaviors result in less formation of corrosion products on the surface of the copper that was exposed to additive biodiesel according to XRD analysis. The observed positive results are justified due to the physisorption of antioxidant compounds found in the additive on the metallic surface with formation of a protective biofilm on the metal surface.