Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

solution would be nickel-copper Alloy 400 or the nickel- based molybdenum-chromium-iron alloy. The use of Alloy 400 is contingent again on the removal of oxidizing species from the aqueous systems; residual chlorine, air or other oxidants, can greatly increase the rate of attack. For the reaction area in chloroacetic acid production equipment, where chlorine is reacted with acetic acid, glass- lined steels, TEFLON-lined, or other fluorocarbon plastic- lined equipment is often used. HASTELLOY alloy C-276 appears to be acceptable for many of these ex- posures, but the conventional process utilizes lined equip- ment for the reaction area. Other metals such as tantalum or titanium may also be used if available. Trichloroacetic acid is perhaps even more corrosive than monochloroacetic acid. Glass-lined equipment, titanium, HASTELLOY alloy B-2, DURICHLOR and certain other specific alloys selected after extensive testing may be used for handling the material at lower temperatures. None of the chloroacetic acids should be stored or processed in any quantity without a thorough understanding of the corrosive nature of these materials and the judicious choice of the materials of construction for tankage or process equipment. Although the nickel-based alloys are prime candidates for use in these solutions once the free chlorine is removed, all alloys may show evidence of pitting or crevice corrosion in the halogenated acids, and a thorough exploration of corrosion resistance of the various alloys in a specific stream should be conducted. 6. Amino Acids The aminocarboxylic acids are an important group of chemicals used for the preparation of drugs, agricultural chemicals and as precursors for numerous other organic compounds. As a group, the compounds are not exces- sively corrosive. The basic material glycine (aminoacetic acid) provides essentially the same corrosive charac- teristics as acetic acid at the lower temperatures and is less corrosive than its counterpart at the higher temperatures. As the molecule is lengthened, the amino acids become less corrosive, and those above approximately four car- bons in length can be considered as inhibitors in aqueous

systems at moderate temperatures. The decomposition products of such acids at the higher temperatures can present unique corrosion problems that should be avoided. This is particularly true when nickel or copper-containing alloys are used. Discoloration of the amino acid can occur when using nickel or copper alloys at temperatures above ambient temperatures. The austenitic stainless steels are most satisfactory for handling the amino acids. No problem with their use is usually anticipated until temperatures above the boiling point of the aqueous systems are encountered. Some of the acids not normally encountered, such as cyanuric acid, can be corrosive in streams and should be identified as a potential corrodent when choosing materials of construc- tion for applications involving amine solutions. 7. Sulfoacetic Acid Sulfoacetic acid characterizes one of those organic acids containing a sulfur atom. The material is not particularly corrosive once it is prepared and has the general charac- teristics of acetic acid itself. If the preparation is made by the addition of a strong sulfuric acid solution to acetic anhydride, the process conditions are too severe for use of the austenitic stainless steels. HASTELLOY alloys B-2 and C-276 are apparently acceptable for this step based upon service experience. Once the product is prepared, the austenitic stainless steels are almost always excellent for handling the acid up to 100 ºC (212 ºF).

INCOLOY alloy 825 tanks for the storage of monochloracetic acid resin solution. This alloy was required to maintain product purity.

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