Neutralizing Corrosion Inhibitors

Because corrosion is known to result from acid attack on metals, the removal or neutrahzation of acids is an obvious solution to the corrosion problem. In theory, any material sufficiently basic to neutralize the acid and raise the pH to the desired level should be satisfactory. In practice, the situation is complicated by other factors. 

This is illustrated by operation of the desalter, which is usually the first processing unit in the refinery proper. Its function is to reduce the content of bottom sediment and water (BS W) from the crude charge to the crude still. Water (generally brine) causes corrosion in units down-stream of the desalter as a result of decomposition of chlorides to hydrochloric acid at the elevated processing temperatures. Addition of alkali to the desalter reduces hydrolysis of calcium and magnesium chlorides and consequently results in less hydrochloric acid being formed in the crude still overheads, etc. 

Inexpensive neutralizers such as lime, calcium carbonate, and soda ash often may cause scaling problems due to precipitation of insoluble hydroxides and/or carbonates of Mg and Ca by reaction with these ions in water entrained from the desalter. Sodium hydroxide can be used in desalting, for which it is added in amounts approximating the chloride content of the desalter water. 

The first operating unit in a refinery after the desalter is the crude still, which effects a rough separation by boiling range of several refinery streams, such as naphtha, kerosene, diesel oil, etc. Distilled vapors are condensed at one or more points and products are taken off with the desired reflux 

Corrosion may be expected as soon as the dew point of the water is reached, so treatment chemicals must be added at or upstream of the points of initial condensation. For treatment of overhead streams, ammonia and other low molecular weight amines such as morpholine or cyclohexylamine, which are added either as undiluted liquids or vapors, or as aqueous solutions, are recommended. 

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Failure of sensitive filtration tests such as ASTM D-2276, Particulate Contamination in Aviation Fuel by Line Sampling, can be due to caustic neutralized corrosion inhibitor salts. Sodium or calcium salts of dimer-trimer fatty acid corrosion inhibitors are gel-like in character. Filtration of jet fuel containing gelled corrosion inhibitor will be impeded due to plugging of fuel filter media by the inhibitor gel. This slowdown of filtration can result in failure of jet fuel to pass this critical performance test. 

Test method ASTM D-2276, Particulate Contaminant in Aviation Fuel by Line Sampling, requires filtration of fuel through a 0.8-micron filter. Caustic neutralized corrosion inhibitor salts can block these filters and slow down the filtration of fuel enough to cause failure of this ASTM test. 

Fouling reactions occurring in the range of about 150 to 370 °C (300 to 700 °F) present problems, many of which are amenable to use of chemical anti-foulants. Above about 370 to 430 °C (700 to 800 °F), there is little experience to draw on in use of either film-forming or neutralizing corrosion inhibitors, or in the use of anti-foulants. 

Uses Pigment dispersant neutralizer corrosion inhibitor acid-salt catalyst pH buffer chemical and pharmaceutical intermediate solubilizer or emulsifier system component in personal care prods. raw material in hypoallergenic prods. Regulatory Approved in Japan (cosmetics)... 

Cyclohexylamine is miscible with water, with which it forms an azeotrope (55.8% H2O) at 96.4°C, making it especially suitable for low pressure steam systems in which it acts as a protective film-former in addition to being a neutralizing amine. Nearly two-thirds of 1989 U.S. production of 5000 —6000 t/yr cyclohexylamine serviced this appHcation (69). Carbon dioxide corrosion is inhibited by deposition of nonwettable film on metal (70). In high pressure systems CHA is chemically more stable than morpholine [110-91-8] (71). A primary amine, CHA does not directiy generate nitrosamine upon nitrite exposure as does morpholine. CHA is used for corrosion inhibitor radiator alcohol solutions, also in paper- and metal-coating industries for moisture and oxidation protection. 

Amine salts, especially acetate salts prepared by neutralization of a fatty amine with acetic acid, are useflil as flotation agents (collectors), corrosion inhibitors, and lubricants (3,8). Amine acetates are commercially available from a number of suppHers Akzo Chemicals Inc. (Armac) (73) Henkel Corporation (formerly General Mills) (Alamac) (74) Jetco Chemicals Inc. (The Procter Gamble Company) (fet Amine) (75) Sherex (Adogen) (76) and Tom ah Products (Exxon Chemical Company) (Tomah) (77). 

Petroleum Production and Refining. Specific polyamine derivatives are used in the petroleum production and refining industries as corrosion inhibitors, demulsifiers, neutralizers, and additives for certain operations. 

Carbon dioxide, from the decomposition in the boiler of temporary hardness salts present in some waters, causes corrosion of steel steam pipework and cast iron valves and traps. Corrosion inhibitors may be used, but the choice of inhibitor must take into account the other materials in the system. Neutralizing amines such as morpholine or cyclohexylamine are commonly used. 

The polarization characteristic of a corroding metal can be controlled by various additives to the solution, called corrosion inhibitors, which adsorb on the metal and lower the rates of the cathodic and/or anodic reaction. Inhibitors are used primarily for acidic electrolyte solutions, sometimes also for neutral solutions. Various organic compounds with -OH, -SH, -NHj, -COOH, and so on, as the functional groups are used as inhibitors. The effects of an organic inhibitor, tetradecylpiperidinium... 

The history of corrosion inhibitors and neutralizers and their invention, development, and application in the petroleum industry is documented by a review of Fisher [605]. Early corrosion inhibitor applications in each of the various segments of the industry, including oil wells, natural gas plants, refineries, and product pipelines, are reviewed. 

In another study, polyaspartic acid was examined as a corrosion inhibitor for steel as a function of pH and temperature [1629]. At low to neutral pH values, polyaspartic acid increases the corrosion rate of steel. At pH values above 10, polyaspartic acid is a reasonably robust corrosion inhibitor. 

A corrosion inhibitor with excellent film-forming and film-persistency characteristics is produced by first reacting Cig unsaturated fatty acids with maleic anhydride or fumaiic acid to produce the fatty acid Diels-Alder adduct or the fatty acid-ene reaction product [31]. This reaction product is further reacted in a condensation or hydrolyzation reaction with a polyalcohol to form an acid-anhydride ester corrosion inhibitor. The ester may be reacted with amines, metal hydroxides, metal oxides, ammonia, and combinations thereof to neutralize the ester. Surfactants may be added to tailor the inhibitor formulation to meet the specific needs of the user, that is, the corrosion inhibitor may be formulated to produce an oil-soluble, highly water-dispersible corrosion inhibitor or an oil-dispersible, water-soluble corrosion inhibitor. Suitable carrier solvents may be used as needed to disperse the corrosion inhibitor formulation. 

L. E. Fisher. Corrosion inhibitors and neutralizers Past, present and future. In Proceedings Volume. Annu NACE Corrosion Conf (Corrosion 93) (New Orleans, LA, 3/7-3/12), 1993. 

Uses Stabilizing rubber latex solvent for albumin, casein, shellac, and sulfur neutralizing oils in antifreeze as a corrosion inhibitor emulsifier adhesives textile lubricants fungicides manufacturing chelating agents such as EOT A (ethylenediaminetetraacetic acid) dimethylol-ethylene-urea resins organic synthesis. 

During the refining and processing of fuel, corrosion inhibitors, antifoulants, filmers, neutralizers, and other organic compounds may carry over into a finished product. These polar organics may attract and interact with water to tightly bind it into the fuel as an emulsion. The result is usually a cloudy, hazy fuel. These emulsions are often quite difficult to break. If the water present contains caustic, organic salts, or corrosion products, the emulsion may be quite stable. 

Caustic-resistant corrosion inhibitors have been developed to help overcome this neutralization concern. However, these products must often be used at higher concentrations than carboxylic acid based inhibitors. Also, some caustic-resistant inhibitors tend to emulsify with water later in the fuel distribution channel. 

Reaction Between an Amine-Based Filmer or Neutralizer and the Carboxylic Acid Based Corrosion Inhibitor... 

This problem is not common and is not expected. However, in a situation of gross overtreatment with an amine-based processing aid, interaction with a carboxylic acid based corrosion inhibitor is possible. In dilute solution within the fuel, it is unlikely that these compounds will react since only low levels, <5 ppm, of filmer or neutralizer will typically carry over into finished fuel. If the two do react, the product formed will provide corrosion protection, but not as effectively as the unreacted carboxylic acid based inhibitor. 

Current treatment solutions containing corrosive inorganic salts usually also contain corrosion inhibitors such as sodium dichromate or ammonium thiocyanate or are formulated to a more neutral pH (60). However, soluble-salt-treated wood in contact with metals should not be exposed to high relative humidities for prolonged periods. The treatment chemicals can attack and deteriorate metal fasteners. The corrosion products in turn deteriorate the wood. For example, under humid conditions, ammonium sulfate will attack the zinc and iron of galvanized punched-steel nail plates used in trusses (58). Alkaline and acidic areas are developed in the wood next to the attacked metal fastener, and cause degradation of the wood (58,63). 

Both neutralizers are injected in the fractionator overhead line in order to be present when the dew point of hydrochloric acid in solution is reached. It is important to use a quill to inject neutralizers or inhibitors because drip injection can cause dissolution of the protective scale on the inside of the pipe, which can result in corrosion and erosion in that area. Often, however, neutralization is not accomplished, and severe corrosion from hydrochloric acid still occurs at the dew point. The pH is controlled at the overhead receiver water draw because dew point pH measurement is not feasible. One method of controlling the dew point pH is to recycle water from the drum to the overhead line. This water buffers the condensate at the hydrochloric acid dew point and also provides water in which the ammonia can dissolve. 

The addition of various corrosion inhibitors to the epoxy encapsulant formulation to prevent corrosion was also evaluated (8). This procedure basically adds compounds or complexing agents to neutralize or "getter corrosion accelerating impurities or adds hydro-phobic agents to reduce the moisture permeation of the plastic. 

Corrosion inhibitors are commonly used to prevent corrosion. There are many hundreds of different inhibitors in commercial use. Some act by slowing the cathodic reaction and others inhibit the anodic reaction. Some are ionic and some are neutral. In choosing a suitable corrosion... 

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