Oleic Acid Transfer from Oil to Water as a Perspective of Water-Dispersible Corrosion Inhibitor

Oil-soluble and water-dispersible corrosion inhibitors are used to mitigate corrosion in pipelines. The performance of corrosion inhibitors has been described mainly in terms of the adsorption of surfactants on metal surfaces. However, the partition of the surfactant from oil to water and its dispersion in water should also significantly affect the corrosion inhibition mechanism of pipelines operating in metal-oil-water systems. Based on this perspective, we investigate the oil droplet dispersion process in the presence of a surfactant. This study examines the mechanism by which oleic acid (OA), a water-insoluble fatty acid, transfers from a decane (C10) solution to the aqueous phase to exert its corrosion inhibition effect. Corrosion rates were evaluated using the linear polarization resistance method. Measurements included interfacial tension, total organic carbon (TOC) in the aqueous phase, zeta potential, and particle size. Corrosion inhibition was observed only when OA was dissolved in C10 and under agitation conditions. As OA concentration increased, the interfacial tension between C10 and water decreased, and TOC in the aqueous phase increased, indicating enhanced oil droplet dispersion, although the average droplet size remained relatively constant at approximately 1.27 μm. The dispersed droplets exhibited a negative zeta potential (average −65.4 mV), suggesting the adsorption of OA anions onto their surfaces. This suggests that stirring breaks C10 droplets into smaller particles, from which OA is released from the droplet interior and adsorbs onto the metal surface, forming a hydrophobic film, and thereby exhibits corrosion inhibition. The upper limit of the droplet size is determined by Stokes' law, while the lower limit is governed by the OA concentration in C10.