Abstract
The applications of 5-hydroxytryptophan (5-HTP) now transcends food supplements to solving global oilfield problem caused by corrosion. Being an alkaloid, 5HTP is environmentally non-toxic and relatively inexpensive. Its potential as oilfield inhibitor of mild steel corrosion has been investigated at 30 °C to 60 °C using weight loss technigue simulated in both 2.0 M hydrochloric acid and 2.0 M sulphuric acid. The efficiency of inhibition increased with increase in concentration of 5-HTP and decreased with increase in temperature. High inhibition efficiencies up to 93.72 % and 90.23 % were obtained in hydrochloric acid and sulphuric acid respectively even at concentrations as low as 1.0 Ò 10−4 M 5-HTP at room temperature. The compound inhibits corrosion mainly by adsorption mechanism determined by fitting surface coverage data into some adsorption isotherms from where the nature of interactions in the adsorbed layer was predicted. The inhibition of mild steel corrosion by 5-HTP was best approximated by the Langmuir adsorption isotherm. Physical adsorption mechanism involving electrostatic interaction of charged molecules of the 5-HTP with charged metal is proposed. Stability of the inhibitor to high temperature was also elucidated using thermodynamic models. It was implied from results that 5-HTP is a stable inhibitor at temperatures up to 60 °C. The inhibitor protects the mild steel surface effectively from acid attack, with better protection obtained in HCl. The adsorption process was exothermic and spontaneous at the temperatures studied. 5-HTP would make an efficient corrosion inhibitor for oilfield operations.
