Abstract
Eco-friendly compound, 5-hydroxytryptophan (5-HTP), was investigated as acid corrosion inhibitor for X80 steel for the first time. Aqueous hydrochloric acid was used to simulate the well acidizing fluid. The efficiency of 5-HTP was determined using Weight Loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques. Inhibition efficiency obtained decreased from 95.6% and 75.2% in 1M and 15% HCl respectively at 30°C to 79.0% and 42.3% in the respective acid solutions at 90°C. Blending 5-HTP with potassium iodide and glutathione optimized the efficiency to values above 80% in both acid solutions at 90°C. The inhibitor was spontaneously physically adsorbed on the steel surface as best approximated by Langmuir adsorption model. Adsorption was also exothermic with resultant decrease in entropy of the bulk solution. Increase in 5-HTP concentrations decreased the double layer capacitance and increased charge transfer resistance. Tafel polarization study shows that 5-HTP behaves as mixed type inhibitor with anodic predominance. Other techniques like SEM/EDS, FTIR, UV-Vis and quantum chemical studies were also employed and results indicate possibility of formation of protective film between 5-HTP and X80 surface facilitated by O, N and CC functionalities.
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