Expired antihypertensive drugs as eco-friendly and efficient corrosion inhibitors for carbon steel in CO2 -saturated oilfield water: Experimental and theoretical approaches

In the process of oil and gas exploitation, it is crucial for the corrosion protection of carbon steel in oil and gas exploitation to develop highly efficient and eco-friendly corrosion inhibitors. Expired antihypertensive drugs (candesartan and valsartan) can be used as eco-friendly, low-cost and efficient green corrosion inhibitors. The corrosion inhibition performance and adsorption mechanisms of candesartan (CST) and valsartan (VST) for carbon steel in CO2-saturated oilfield water were investigated by weight loss tests, electrochemical measure-ments, surface analysis and theoretical calculations. The weight loss test results show that the corrosion inhi-bition efficiencies of 400 ppm (0.9 mM) VST and CST are 89.33 and 95.83% at 333 K, respectively. The polarization curves results indicate that VST and CST resist both anodic and cathodic reactions and function as mixed-inhibitors. The adsorption behavior of VST and CST follows the Langmuir adsorption model. Moreover, the adsorption modes of VST and CST involve physisorption and chemisorption. The results of theoretical cal-culations suggest that the adsorption of VST and CST on metal surface is mainly achieved by bonding N/O atoms to Fe atoms. Furthermore, the adsorbed films formed by CST and VST can inhibit the diffusion process of cor-rosive particles more effectively, thereby protecting the carbon steel from corrosion more efficiently. The results obtained from quantum chemical calculations and molecular dynamics simulations confirm the experimental findings and provide further insight into the mode of adsorption.