Coal Tar Base Fractions as Pickling Inhibitors in Hydrochloric and Sulphuric Acid Solutions

Abstract

Four coal-tar-base fractions were found to be effective in preventing the dissolution of low-carbon steel and in limiting the absorption of hydrogen by steel during pickling in 2 N- and 4 N-hydrochloric acid at 100° and 150°F. The crude quinoline bases and distilled quinoline bases were also effective inhibitors in 2 N-sulphuric acid solutions at 100°F, but at 200°F these same fractions afforded no better than 78% inhibition when tested at 0·25 vol.-%.

Previous investigations have shown that NaCl, NaBr and NaI are moderately effective inhibitors in 2 N-sulphuric acid at 200°F. In the presence of coal-tar bases, these and other inorganic halides display a remarkable synergistic effect. When used at relatively low halide concentrations, the inhibitor properties of the mixtures are much better than those of the halides or tar bases used alone in sulphuric acid. The superior performances of the tar-base fractions in HCl may be associated with the fact that HCl is a halogen acid. Moreover, the tar base–halide mixtures studied, in addition to being superior in limiting the dissolution of steel, were more effective than many commercial inhibitors in limiting hydrogen absorpiion by during pickling at 200°F.

Although the other tar-base fractions can be used as inhibitors with proper halide additions, the crude and distilled quinoline bases were effective when used with NaCl and, therefore, such formulations would be of relatively low cost. Inhibitor formulaiions for use in H₂SO₄ solutions up to 10 N in concentration have been evaluated.