Implications of waste cooking oil biodiesel on carbon steel alloy in automobiles: Corrosion degradation

Abstract

The need to minimise metal degradation and dissolution in biodiesel (BD) fuels used in the transportation sector is nowadays becoming a challenging task that, if not properly attended to, can lead to human safety issues, environmental concerns, and vehicular failures in automobile systems. Metal degradation by BD fuel is a major issue of great concern to the scientific community, and this has resulted in intense research globally. Sustainable use of waste cooking oil (WCO) BD (WCOBD), which has a lower carbon footprint, and its implication on corrosion degradation in the transportation industry in terms of detailed applications of UV–Vis, FTIR, and SEM techniques to elucidate the corrosion behaviour of metallic components in the BD at various durations (0, 28, 42, and 56 days), temperature (25 °C), and atmospheric pressure (760 mmHg) are investigated in this study. The fuel properties of the produced WCOBD were within acceptable standard limits: viscosity of 4.785 mm²/s; density of 0.886 g/cm³; acid value of 0.120; flash point of 172.4 °C; fire point of 136 °C; cloud point of -4.2 °C; and pour point of -7.8 °C. The major fatty acid group responsible for the metal degradation was C18, with a high degree of unsaturation, having 90.63 % of the total constituent of the BD. UV–Vis analysis after the various immersion periods revealed two peaks at wavelengths of 928.3 and 1033.76 nm, which were formed during the esterification and transesterification reactions of the free fatty acid from the WCO and thus responsible for the metal degradation at the various immersion periods. FTIR spectra exhibited characteristics of double peaks around 2918 and 2842 cm^-1 wavelengths, with other peaks equally observed as being present in the BD. These peaks represented CO, CO, CH, CC, and (CH₂)_n functional groups as expected from free fatty acids in BD. SEM morphology revealed randomly distributed uneven structures, which were attributed to the formation of protective corrosion products and their physical adsorption on the metal surface. Thus, this study contributes to a deeper understanding of the corrosiveness of WCOBD to carbon steel, elucidates techniques to ascertain the degree and form of corrosion on the metal surface during storage and transportation of the BD in vehicular systems, and reveals the potential inherent in the use of un-inhibited WCOBD in real-world automotive applications.