Inhibition Behavior Of Inhibitors For Carbon Steel In A Supercritical CO₂/H₂O System

The corrosion behavior of N80 steel and the corrosion inhibition effect of various corrosion inhibitors in a supercritical CO2-H2O system was investigated using weight loss measurement,electrochemical test,and surface analysis etc.In the absence of inhibitor,the corrosion rate and the corrosion process have little change as the increase of CO2 partial pressure between non-supercritical or supercritical CO2 condition.In addition,the introduction of KI alone has no effect on the CO2 corrosion of carbon steel.Then,in the presence of imidazoline inhibitor,the corrosion rate of the carbon steel obvious decrease and surface becomes smoothly which compared to the blank sitiuation.Under non-supercritical CO2 conditions,the corrosion rate,corrosion current density Icorr,and the charge transfer resistance Rct have little change as the increase of CO2 partial pressure,whereas the corrosion rate evidently increases and the corrosion process greatly differs in case CO2 supercritical condition reached.The introduction of KI has little change on the CO2 corrosion of carbon steel under non-supercritical conditions,but it decreases the corrosion rate under supercritical CO2 condition greatly.The excess surface charge of carbon steel changes from negative to positive as the partial pressure of CO2 increases to supercritical condition value,thereby hindering the adsorption of imidazoline inhibitor,which in turn decreases inhibition efficiency.Two anionic inhibitor 1 auric acid and 2-mercaptobenzothiazole(MBTH)were introduced to further study the inhibition mechanism in a supercritical CO2-H2O system.It was found that no matter lauric acid or MBTH added,the corrosion rate and electrochemical parameters were little changed at the non-supercritical condition,in case the supercritical condition reached,the corrosion rate and Icorr decrease rapidly.The surface analysis results shown that the contact angle was significantly larger than that of the non-supercritical condition and the surface of the steel covered with a large amount of lauric acid in supercritical condition.In the presence of the MBTH,the surface of the steel smoothly under supercritical condition,whereas obvious pits could be observed at non-supercritical condition.XPS results show that the Fe-S peak intensity under supercritical conditions was stronger than non-supercritical condition,and the MBTH molecules could better adsorb on the surface of the carbon steel.