Effect of Thio-Chemicals Molecular Structure for Corrosion Inhibition in CO2 Corrosive Environments

Abstract

Abstract Carbon dioxide often exists in oil and gas fields, and CO2 flooding is also increasingly used to enhance oil recovery. CO2 is highly corrosive to steel in oilfield fluid. The effective and economical method for controlling corrosion is the addition of corrosion inhibitors for carbon steel materials. Small thio-compounds have been found effective to enhance corrosion inhibition of imidazoline inhibitors. In this study, several small thio-derivatives inhibitor including mercaptoethanol (ME), thiourea (TU), and mercaptoacetic acid (TGA) and 2-mercaptobenzimidazole (MBI) were compared to inhibit the CO2 corrosion. They were used as synergists to enhance corrosion inhibition of oleic imidazoline (OIM) for carbon steel at 60 °C in CO2-saturated brine. The corrosion inhibition was investigated by weight loss and electrochemical methods. The surface was characterized by scanning electron microscopy (SEM). The mechanism of corrosion inhibition was studied by quantum chemical calculations. The results show that the MBI with the aromatic group gave the best corrosion inhibition than that of ME, TGA, and TU. The surface characterization showed no pitting and localized corrosion at 10 ppm of inhibitor. The model of interaction is proposed that OIM is protonated and coupled with MBI by electrostatic attraction to co-adsorb on the carbon steel surface. MBI adsorbs on Fe by a bidentate binding-N-S-bridge connection, which effectively prevents the corrosion of carbon steel in the CO2 environment. The research provides a structure-properties relationship of thio-chemicals to develop more effective corrosion inhibitors.