Effect of Oil-in-Water Emulsions on the Performance of Carbon Dioxide Corrosion Inhibitors

The effect of oil-in-water emulsions on the performance of four carbon dioxide (CO₂) corrosion inhibitors was studied in an impinging jet apparatus. Experimental conditions were 60°C to 90°C, pH 4.5 to 5, 1 bar CO₂, 100% to 90% water-cut, and 0.1 wt% to 1 wt% sodium chloride (NaCl). A refined, low-aromatic, white spirit product was used as the oil phase. The jet flow velocities were varied in the range from 0 to 12 m/s. Corresponding wall shear stresses were 0 to 350 Pa. Oil-in-water emulsions were formed by injecting small amounts of oil in the impinging jet stream. This created small amounts of emulsion (on the order of 1 vol% to 2 vol% oil) that broke down in a few hours. Surface active, amphiphilic inhibitor molecules have a high affinity for accumulation at the oil-water interface. The dispersed droplets may constitute a large surface area. When the surface area exceeds 1 m²/L (order of magnitude) the droplets may deplete a significant amount of corrosion inhibitor from the corrosive aqueous phase. This parasitic consumption of inhibitor may constitute a potential risk of inhibition failure and lead to increased inhibitor demand. The test results showed that the presence of emulsion reduced the performance substantially for two of the inhibitors. One product was slightly affected, whereas the protection offered by the fourth product was improved in the presence of the emulsion. The latter result was interpreted as a tendency of the oil droplets to form a thin oil film at the steel surface.