Protection of low carbon steel in mineral acid solutions by alkylphenyl-substituted imidazolines

Alkylphenyl imidazolines with phenyl (PHI), 4-methylphenyl (TI) and 4-isopropoxyphenyl (IPRI) substituents were synthesized and their properties in slowing down the corrosion of 08PS low-carbon steel have been studied in 2 M HCl, 2 M H2SO4 and 2 M H3PO4 (t=25–95°C). It has been demonstrated that for the protection of steel in mineral acid solutions, it is promising to employ not individual alkylphenyl-substituted imidazolines, but rather a combination of corrosion inhibitors containing them. Additives of 5 mM alkylphenyl-substituted imidazolines slow down the corrosion of steel in 2 M HCl (t=25–60°C). At higher temperatures, it is recommended to use a mixture of alkylphenyl-substituted imidazoline (5 mM)+ hexamethylenetetramine (HMT, 25 mM). The addition of TI (5 mM)+HMT (25 mM) in 2 M HCl (t≤95°C) ensures a corrosion rate of steel (k) no higher than 8.7 g/(m2·h). In 2 M H2SO4 (t=25–80°C) and 2 M H3PO4 (t=25–95°C), a significant reduction in the corrosion rate of 08PS steel is achieved by adding 5 mM of alkylphenyl-substituted imidazoline and 0.5 mM of KNCS. The maximum values of k are observed in the presence of these compositions based on PHI, TI and IPRI in 2 M H2SO4 (t≤80°C) are 2.4, 1.5 and 1.8 g/(m2·h), and in 2 M H3PO4 (t≤95°C) – 2.3, 1.3 and 0.99 g/(m2·h), respectively.