Inhibition of steel by alkylamine ethoxylate in petroleum production

Abstract

The corrosion of low carbon steel in mixtures of oil and water with various oil/water ratios has been studied using weight loss and potentiodynamic polarisation measurements. The inhibiting behaviour of some alkyl amine ethoxylate derivatives having an average of 14-14.3 moles ethylene oxide per mole and different chain lengths has been investigated. These included: ethoxylated hexyl amine, C₆H₁₃NH(CH₂CH₂O)₁₄-H; ethoxylated decyl amine, C_{6 0}H₁₃NH(CH₂CH₂O)₁₄-H; and ethoxylated tetradecyl amine, C₁₄H₂₉NH(CH₂CH₂O)₁₄-H. The inhibitors were used at concentrations corresponding to 40-100 ppm of the water content in the environment and the effects of storage time at temperatures of 30, 50, and 70 °C were investigated. The inhibitors provided satisfactory corrosion inhibition which decreased with increasing temperature. The adsorption of the inhibitors on the carbon steel surface was found to obey the Langmiur adsorption isotherm. Thermodynamic activation parameters such as the activation energy E°, enthalpy ΔH°, entropy ΔS°, and free energy of activation ΔG° for the dissolution of carbon steel were calculated. The inhibition efficiency was observed to increase with increasing chain length of the alkyl amine group. The tetradecyl amine ethoxylate, which has the longest chain, was the most efficient inhibitor.