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Pankaj Ajmera#, Sonja Richter*, Win Robbins*, Srdjan Nešić*
*Institute for Corrosion and Multiphase Technology, Department of Chemical Engineering, Ohio University, Athens, OH 45701, USA
# Currently at: Jacobs Engineering, 2920 Shadowbriar Dr. Houston, TX 77082 USA
The tendency of crude oil to inhibit corrosion has been observed in the field, but the mechanism of the inhibition has not been adequately explained. Furthermore, it is not known why some crude oils have good inhibition effect and others have poor inhibition effect. A Joint Industry Project (Water Wetting JIP) at Ohio University has been investigating the mechanism by which chemical compounds present in the crude oil inhibit corrosion and alter wettability. In addition to model surface active compounds, asphaltenes (heptane insolubles) have been considered as potential contributors to crude oil behavior. Asphaltenes extracted from an Arab Heavy crude oil have been tested using electrochemical methods (OCP, LPR and EIS) in a glass cell for corrosion rate measurements as well as a series of small scale tests, including contact angle and interfacial tension tests to assess wettability. It was found that asphaltenes form a strong protective layer on the carbon steel surface, which reduces the corrosion rate and makes the surface hydrophobic. Competitive inhibition study for asphaltene and acridine was conducted. Acridine, a pyridine analog, is a nitrogen-containing surface active compound that has been identified as having strong inhibitive effect on its own. A strong positive synergy between asphaltenes and acridine was found for both corrosion inhibition and wettability of the steel surface. It is proposed that acridine acts as a catalyst, allowing asphaltenes to disaggregate and be more active in adsorbing on the steel surface.
KEY WORDS: Asphaltenes, acridine,CO2 corrosion, carbon steel, wettability, inhibition
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