10329 The Role of Asphaltenes in Inhibiting CO2 Corrosion and Altering the Wettability of the Steel Surface

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Product Number: 51300-10329-SG

ISBN: 10329 2010 CP

Author: Pankaj Ajmera, Win Robbins, Sonja Richter and Srdjan Nesic

Publication Date: 2010

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Asphaltenes (heptane insolubles) from a variety of crude oils have been previously identified as contributors to inhibition of internal corrosion of mild steel pipelines. However, the mechanism of inhibition is unknown. To explore the mechanism, CO₂ corrosion rates and wettability (oil/water contact angles) have been measured using Arab Heavy crude oil and its asphaltenes. Inhibition of CO₂ corrosion rates for carbon steel was measured by electrochemical methods in a glass cell; wettability was assessed using contact angle measurements in a multiphase goniometer. The phase behavior of asphaltenes in corrosion and wetting was evaluated in the crude, toluene or heptol (70:30 mixture of heptane and toluene). To evaluate the strength of the asphaltene interactions, tests were repeated on solutions containing mixtures of asphaltenes with acridine (previously identified as surface active using these tests). Inhibition on steel exposed to hydrocarbon phases increased with concentration of asphaltenes in toluene. Inhibition by asphaltenes in toluene appears to be more effective than in the whole crude. At 5% in toluene asphaltenes form a strong protective layer on the carbon steel surface, which reduces the corrosion rate and makes the surface hydrophobic. Heptol appears to have little effect on the wetting. However, in heptol, inhibition begins at lower asphaltene concentrations and is nearly complete at 5%.

KEY WORDS: Asphaltenes, acridine,CO₂ corrosion, carbon steel, wettability, inhibition