Development of a Gas-Phase Corrosion Inhibitor for Wet-Gas Carbon Dioxide Corrosion at 200°C

High-temperature applications remain a common challenge for organic chemistries because these chemistries might degrade under high temperatures. In this study, a corrosion inhibitor was developed for a gas compressor application at 200°C. The thermal stability, effect of various solvents, and interaction between the inhibitor molecule and the passive layer developed on C1018 carbon steel were compared experimentally. Corrosion models predicted that this passivating layer comprises primarily magnetite (Fe₃O₄), and surface scans showed that this passivating layer forms without the need for corrosion inhibitors. The surface scans also showed that naturally occurring defects developed in the passive-layer matrix. As a result, although the general corrosion is expected to be low, a corrosion inhibitor is needed to mitigate localized corrosion or pitting. This paper discusses the process used to screen various corrosion inhibitor chemistries for use at 200°C. The results show that a quaternary amine-based product provides the best results under these conditions.

Although organic corrosion inhibitors have been widely applied in the energy industry, many details regarding their protection mechanism remain unknown. For example, a corrosion inhibitor adsorbs on the clean steel/aqueous solution interface, driven by electrostatic interaction. With the corrosion product layer formed, how would the inhibitor adsorption interact with the corrosion product nucleation and precipitation? What is the effect of pre-corrosion in inhibitor testing?¹ How do the inhibitor molecule structure and properties interact with the aqueous solution and the metal surface? Which factor(s) should be considered the primary challenge in one application? While there are some proposed explanations related to high-temperature inhibition;^2,3,4 these studies are related more to new product development^5,6,7 than mechanistic studies.

Most corrosion inhibitor studies have concentrated on low temperatures (less than 70 °C).⁸ When explaining the effect of temperature on inhibitor performance, these studies have typically associated it with the adsorption mechanism. The inhibition efficiency of chemisorbed inhibitors increased with temperature, while that of physiosorbed inhibitors decreased with temperature.^9,10 Regarding imidazoline and its derivatives, in some studies, their performance increased at high temperatures,^11,12,13 while other studies have reported the opposite.^14,15,16,17 Because there are no lone pair or π electrons in quaternary ammonium salts (quat)-based inhibitors, a quat-based inhibitor could be anchored on a steel surface through physisorption only.¹⁸ If this temperature-effect theory is accurate, a quat-based inhibitor would not be a good candidate for high-temperature inhibition. Specifically, the performance of quat-based inhibitors reportedly decreased with a temperature increase at low temperatures (less than 70 °C), with few studies on the effect of high temperatures.^19,20 Pyrimidine, quinoline, and phosphate ester type corrosion inhibitors have been reported to be effective at high temperature applications of sour corrosion²¹ or refinery, although more mechanism studies should have been reported. Therefore, it is not yet fully understood how temperature affects inhibitor performance.