Commercial fatty acid ethoxylates as corrosion inhibitors for steel in pickling acids

Abstract

Corrosion inhibitors have been prepared by ethoxylation of four commercially available unsaturated fatty acid mixtures: tall oil, soya bean oil, cotton seed oil, and linseed oil. The compounds obtained have the general formula R–COO–(CH₂CH₂O)_n–H, where R is mainly a mixture of C₁₇H₂₉, C₁₇H₃₁, and C₁₇H₃₃ and n equals 20 ethylene oxide moles per mole of fatty acid. They have almost the same hydrophilic-lipophilic balance (HLB), which governs most of their surface activities, but differ in their fatty acid composition. The synthesised compounds provide satisfactory inhibition of steel in hydrochloric acid at temperatures up to 80°C. The ethoxylate of linseed oil is the most efficient inhibitor on account of its high content of linolenic acid, which has three double bonds. Polarisation measurements indicate that the additives act as mixed type inhibitors.