Investigation of the corrosion of stainless steel, copper and aluminium in sunflower biodiesel solution: Experimental and theoretical approaches

Abstract

The increase in energy has created a clear imbalance between the availability and usage of these resources, prompting the industry to resort to biofuels. The main objective of this study is to investigate the corrosion resistance of materials used as biofuel production reactors (stainless steel (SS), aluminium (Al), and copper (Cu)) during sunflower biodiesel production. The corrosion resistance of stainless steel, aluminium, and copper was investigated using electrochemical monitoring techniques such as open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). Throughout this work, spectroscopic methods, including Fourier transform infrared (FTIR), GS/MS, UV absorption, SEM/EDS, and X-ray diffraction (XRD), have been used to thoroughly examine the surfaces of the metals and the composition of the biodiesel after testing. All metals examined showed excellent corrosion resistance, attributed to the formation of such a passivation film on their surfaces, as shown by the EIS data. SEM/EDS analysis confirmed that the methyl esters had a slight impact on metal deterioration, with a modest corrosion rate and the formation of localized micro-pitting on the metal surface. The FAAS analysis also revealed the existence of a low concentration of metal ions released into the solution. Therefore, the correlation approach (DFT and molecular dynamics simulations (MDS)) was applied to support the experimental results that favoured aluminium as the base metal for biodiesel synthesis due to its low corrosion rate during the process.