Naphthenic acids organic acidity

Naphthenic acids are viscous hquids, with phenohc and sulfur impurities present that are largely responsible for their characteristic odor. Their colors range from pale yeUow to dark amber. An odor develops upon storage of the refined acids. Naphthenic acids have wide boiling point ranges at high temperatures (250—350°C). They are completely soluble in organic solvents and oils but are insoluble (<50 mg/L) in water. Commercial naphthenic acids are available in... 

Naphthenic acid is a collective name for organic acids present in some but not all crude oils. In addition to true naphthenic acids (naphthenic carboxylic acids represented by the formula X-COOH in which X is a cycloparaffin radical), the total acidity of a crude may include various amounts of other organic acids and sometimes mineral acids. Thus the total neutralization number of a stock, which is a measure of its total acidity, includes (but does not necessaiily represent) the level of naphthenic acids present. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize one gram of stock as determined by titration using phenolphthalein as an indicator, or as determined by potentiometric titration. It may be as high as 10 mg KOH/gr. for some crudes. The neutralization number does not usually become important as a corrosion factor, however, unless it is at least 0.5 mg KOH/gm. 

Fuel oil Organic acids are thought to be responsible for corrosion of lead by fuel oil. Formerly, mercaptans were held to be the cause, but now it is believed that naphthenic acids are responsible. 

Most of the inhibitors in use are organic nitrogen compounds and these have been classified by Bregman as (a) aliphatic fatty acid derivatives, b) imidazolines, (c) quaternaries, (d) rosin derivatives (complex amine mixtures based on abietic acid) all of these will tend to have long-chain hydrocarbons, e.g. CigH, as part of the structure, (e) petroleum sulphonic acid salts of long-chain diamines (preferred to the diamines), (/) other salts of diamines and (g) fatty amides of aliphatic diamines. Actual compounds in use in classes (a) to d) include oleic and naphthenic acid salts of n-tallowpropylenediamine diamines RNH(CH2) NH2 in which R is a carbon chain of 8-22 atoms and x = 2-10 and reaction products of diamines with acids from the partial oxidation of liquid hydrocarbons. Attention has also been drawn to polyethoxylated compounds in which the water solubility can be controlled by the amount of ethylene oxide added to the molecule. 

Some crude oils contain certain organic compounds that are corrosive. In particular, these include naphthenic acids. Such crude oils cause problems in transportation, refining, and processing. The naphthenic acid content can be reduced simply with alcohol treatments, such as methanol, to form the corresponding ester. Hence, treatment temperatures will preferably be around 350° C. Pressures from about 100 to 300 kPa are typical and generally result from the system itself [1556]. 

Oxygen-containing impurities such as phenols and naphthenic acids can adversely affect water separation properties and initiate gum formation. No limit presently exists to control the amount of oxidized organic compounds found in jet fuel. However, tests for existent gums, neutralization number, and water separation indirectly limit the presence of oxygenated materials in jet fuel. 

Neutralization of naphthenic acids and other acidic compounds which may be present in fuel. Acidic organic compounds can react with other fuel components to initiate the formation of higher-molecular-weight, fuel insoluble deposits. 

The carboxylic acid group usually is attached to a naphthenic ring rather than an aromatic ring. These organic acids generally are known by the rather loose term naphthenic acids. These acids may be neutralized with common bases. For instance, the acid number of a crude oil is the number of milligrams of potassium hydroxide required to neutralize the... 

Organic acids (e.g., naphthenic acid) can cause severe corrosion above -450 F (230 C) (although attack has been seen as low as 340 F [170 C] in turbulent areas) if the neutralization number exceeds 2.0 mg of potassium hydroxide per gram (mg KOH/g). The naphthenic acid content is generally determined by... 

Before the growth of organic chemistry and techniques for sulfonating fats and oils, tanners emulsified oils for leather softeners with soap and protective colloids. These mixtures were prepared as water-in-oil emulsions, called mayonnaise in the trade and added to the water in the drum with the leather. They are still used but not nearly as frequently as sulf(on)ated oils. On the other hand, salts of naphthenic acid are used with hydrocarbon oils (e.g., 11) to make the reverse forms of these. 

Naphthenic Acids. Naphthenic acids are cycloparaffinic organic acids and usually are monocarboxylic. These acids occur in crude oils and normally are recovered with the straight run gasoline and distillate oil fractions in a topping unit. If these fractions are caustic scrubbed, the naphthenic acids are recovered as the sodium naphthenates (5). 

FIGURE 8.3-5 Fractional amonnt of extraction of trace levels of some metal cations from aqueous solution into organic solutions of naphthenic acid as a function of pH. From Ref. 18, with permission,... 

Corrosion-related issues regarding processing are handling organic acids [also referred to as naphthenic acid corrosion (NAC)] and sulfur species at high temperatures as well as water containing corrosives such as H2S, CO2, chlorides, and high levels of dissolved solids. 

The high-temperature crude corrosivity of distillation units is a major problem in the refining industry. The presence of naphthenic acid and sulfur compounds increases corrosion in the high-temperature parts of the distillation units and hence equipment failure became a critical safety and reliability issue. Most of the acids have the formula R(CH2) C00H, where R stands for the cyclopentane ring and n is greater than 12. In addition to R(CH2) COOH, a host of other acidic organic compounds are also present. 

At high temperatures, especially in furnaces and transfer lines, the presence of naphthenic acids may increase the severity of sulfidic corrosion. The presence of the organic acids may disrupt the sulfide film and fhereby promote sulfidic corrosion of the alloys that are normally expected to resist this form of attack. The alloys in question are 12 Cr and higher. In some cases, such as in side-cut piping, the sulfide film formed because of hydrogen sulfide is thoughl lo offer some degree of protection from NAC. 

Naphthenic acid corrosion Naphthenic acid pertains to a group of organic acids present in crude oil with the general chemical formula R (CH2) COOH, where R is one or more cyclopentane rings, and n is typically greater than 12. The ring structure can be tricyclic, tricyclic, or polycyclic. In addition, crude oil contains various other organic acids that contribute to acidity. These are often... 

Corrosion by naphthenic acid some organic acids, those having a naphthenic structure, together with iron, give rise to complex salts and, at temperatures between 200°C and dOO C, are particularly aggressive for carbon steels and low-alloy steels. 

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