Coal liquids distillation tower corrosion. A mechanism of inhibition by strong base amines

Ionic chlorides cause severe corrosion of metallic construction materials during the distillation of coal derived liquids. Dicyclohexyl amine, a strong organic base, inhibits corrosion when added in an amount equivalent to the ionic chloride. Conductivity measurements show that inhibition is probably accomplished by reducing the chloride concentration of the solution, and thus the acidity, by the limited solubility of dicyclohexyl amine hydrochloride. The conductivity and corrosion rate increase linearly with increasing chloride concentration. Corrosion continues in a closed system until the corrosion product stoichiometry is approximately that of FeCl 2; at this composition the corrosion rate is low and is due to the presence of phenols in the coal liquid or model compound mixture. The corrosion and conductivity data, obtained with model compounds, closely resemble the results obtained with the more complex coal liquids.