|Content Type||Conference Paper|
|Title||Development and Testing of a Low-Toxicity Acid Corrosion Inhibitor for Industrial Cleaning Applications|
|Authors||Wayne W. Frenier, HydroChem Industrial Services|
|Source||CORROSION 96, March 24 - 29, 1996 , Denver, Co|
|Copyright||1996. NACE International|
|Keywords||Acetylenic alcohol, inhibitor, hydrochloric acid, quaternary ammonium salt|
A low toxicity corrosion inhibitor for use in hydrochloric acid cleaning formulations has been developed. This formulation does not contains formaldehyde. It contains cinnamaldehyde, quaternary nitrogen salts, and a nonionic surfactant, none of which are currently known or suspected to be carcinogens. In laboratory tests, corrosion protection values were equivalent to those provided by current commercial acid inhibitors. Field tests using the low toxicity inhibitor have been conducted.
Chemical cleaning processes use reactive chemicals to from industrial equipment. This category includes process units power generating utility and industrial boilers. The water sides dissolve and remove fouling deposits such as heat exchangers as well as of these types of equipment become fouled with corrosion products (iron oxides and copper) and dissolved water scales that frequently yield calcium carbonate and silica deposits. Aqueous solutions of hydrochloric acid with concentrations that range from 5% (wt/wt) to about 15°have been used in the cleaning services for many years. Since these solvents also may be corrosive to the construction materials (usually carbon steels), corrosion inhibitors are added to the acid prior to its introduction into the unit to be cleaned. Many different types of chemicals have been proposed as corrosion inhibitors for the hydrochloric acid solutions. See reviews by Cizek and Frenier. Many commercial acid inhibitors used in chemical cleaning services have been based on the Mannich condensation reactions introduced by Saukaitis, Gardner, Mansfield, and Monroe.
Equation 1 shows the generic Mannich reaction.
This process uses formaldehyde, an amine and a ketone to produce a Mannich base. Since this reaction rarely goes to completion, some formaldehyde will remain in the reaction product that is formulated as the commercial inhibitor. Formaldehyde has been shown to be an animal carcinogen and appears on the OSHA Specifically Regulated Substance List and the National Toxicity Program Source List 9C (compilation of carcinogens); therefore, it is desirable to remove this substance from inhibitor formulations.
In addition to a condensation reaction product, commercial acid inhibitor formulations frequently contain acetylenic alcohols7 such as propargyl alcohol, hexynol or ethyloctynol (see Figure 1 for chemical structures). While these materials can produce excellent corrosion inhibitor packages, many acetylenic alcohols are quite toxic to mammals (Table 1) and the lower alcohols (propargyl alcohol and hexynol) are readily adsorbed through the skin. For these reasons, there is a growing necessity for producing corrosion inhibitors that are less toxic than current formulations.
Frenier has described formulations of áâ-unsaturated aldehydes with surfactants that have been shown to be effective corrosion inhibitors for steel in hydrochloric acid. Based on this technology, the aromatic compound t-cinnamaldehyde, has been proposed as an ingredient in low toxicity inhibitor formulations?. According to Growcock, this aldehyde adsorbs onto the surface of the steel and then forms a low molecular weight polymer film that enhances the corrosion protection. This current report will describe the development of an inhibitor formulation based on cinnamaldehyde that is suitable for use in industrial cleaning formulations containing hydrochloric acid or hydrochloric acid containing ammonium bifluoride (ABF). The report also will describe corrosion testing results, scale dissolution tests and results of field applications of the inhibited acid formulations containing the low toxicity corrosion inhibitor. The goal of the project was to produce a pro
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