Eco-friendly corrosion inhibitors based on Cashew nut shell liquid (CNSL) for acidizing fluids

Abstract The acidic fluids used in the acidification of oil wells can compromise metallic structures. As a consequence, corrosion inhibitors are needed to mitigate the corrosion process. Researches have been carried out on the use of eco-friendly corrosion inhibitors, which are obtained from low cost and sustainable source. In this work, Cashew nut shell liquid (CNSL), a by-product of the cashew nut industry, and the residue of its distillation (R) were evaluated as corrosion inhibitors for API P110 carbon steel in 15% HCl. The efficacy of eight organic formulations was assessed by mass loss, potentiodynamic polarization, linear polarization resistance and electrochemical impedance. CNSL and R were characterized by FTIR, 1 H NMR and TGA. The mass loss tests (298–353 K) revealed maximum efficiency of 99.47%, which was confirmed by electrochemical measurements. The formulations acted as mixed inhibitors. Molecular adsorption probably occurs through the oxygens and π electrons of the aromatic rings in agreement with DFT results. The formation of an inhibitor film was confirmed by SEM-EDX and FTIR. This study reveals the importance of sustainable assets, such as cashew nut residues, that when properly purified and formulated may exhibit high corrosion inhibition efficiency, even under aggressive conditions found in the offshore oil and gas industry. In addition, it represents a more noble application for a by-product in terms of value aggregation.