Abstract

The application of acid corrosion inhibitors is an absolute necessity to prevent damage to process equipment during acid cleaning operations. The use of organic acids and mineral acids that are not HCl has expanded because of environmental concerns and issues of compatibility with alloys such as stainless or duplex steel. Inhibitors which are used to protect the metals from corrosion by organic acids often contain a number of highly toxic compounds based on amine technology such as quaternary amines, amine ethoxylates, imidazolines and polyamides as well as sulfur compounds such as thiourea. Phosphate esters and organic boron compounds may also be used, which are not as acutely toxic as the amine compounds; however, in terms of ecological toxicity, it is easy to see that these do not make the green list. In addition, other additives used to formulate these inhibitors, such as nonyl phenol ethoxylates, are also toxic and have to be limited in their use. Several different organic acid inhibitors were tested which offer a non-toxic, low toxicity or green chemical profile. These were tested against several common organic acids used in industrial chemical cleaning, at a variety of temperatures and compared against the current top ranked organic acid inhibitor from our lab. Testing showed trends in the types of organic acid inhibitors that are effective as well the limits of their application.

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