Crude naphthenic acids

The commercial production of naphthenic acid from petroleum is based on the formation of sodium naphthenate. Naphthenic acids are recovered by caustic extraction uf petroleum distillates rather than from crude petroleum. Crude naphthenic acid is obtained by acidulating the sodium naphthenate, and can be further refined to remove impurities. 

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MCPDEA. See m-Chlorophenyl diethanolamine MCPI. See 3-Chlorophenyl isocyanate MCPP 2-MCPP. See Mecoprop-P MCRS Crude Naphthenic Acid, MCRS High Purity Naphthenic Acid, MCRS Refined Naphthenic Acid, MCRS Semi-Refined Naphthenic Acid. See Naphthenic acid MCT 507, MCT 509, MCT 5071, MCT 5072, MCT 5075, MCT 5091, MCT 5096, MCT 5097. See Zinc phosphate MCT. See Monochlorotoluene M-C-Thin 45, M-C-Thin ASOL, M-C-Thin FWD, M-C-Thin . See Lecithin MD. See Manganese dioxide MD2M. See Decamethyltetrasiloxane MD3M. See Dodecamethylpentasiloxane... 

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In the crude, water is found partly in solution and partly in the form of a more-or-less stable emulsion this stability is due to the presence of asphaltenes or certain surfactant agents such as mercaptans or naphthenic acids. 

It is worthwhile to mention that the distribution of naphthenic acids is not uniform in a crude oil since a maximum value is observed in the fractions distilled between 400 and 450°C and whose average specific gravity is 0.950 (Figure 8.2). 

Oxygen compounds are present in some crude oils, and decompose to form naphthenic acids upon distillation. These may be highly corrosive. 

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. 

Where is naphthenic acid corrosion found Naphthenic acid corrosion occurs primarily in crude and vacuum distillation units, and less frequently in thermal and catalytic cracking operations. It usually occurs in furnace coils, transfer lines, vacuum columns and their overhead condensers, sidestream coolers, and pumps. 

Oxygen compounds in crude oils are more complex than the sulfur types. However, their presence in petroleum streams is not poisonous to processing catalysts. Many of the oxygen compounds found in crude oils are weakly acidic. They are carboxylic acids, cresylic acid, phenol, and naphthenic acid. Naphthenic acids are mainly cyclopentane and cyclohexane derivatives having a carboxyalkyl side chain. 

Naphthenic acids in the naphtha fraction have a special commercial importance and can be extracted by using dilute caustic solutions. The total acid content of most crudes is generally low, but may reach as much as 3%, as in some California crudes. 

Naphthenic acids and cresylic acid, which are extracted from certain crude oil fractions, are briefly reviewed at the end of the chapter. 

Naphthenic acids constitute about 50 wt% of the total acidic compounds in crude oils. Naphthenic-based crudes contain a higher percentage of naphthenic acids. Consequently, it is more economical to isolate these acids from naphthenic-based crudes. 

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]. 

To mitigate the effects of corrosion resulting from the presence of salts, it is advantageous to reduce the salt concentration to the range of 3 to 5 ppm. Typically, brine droplets in crude oil are stabilized by a mixture of surface-active components such as waxes, asphaltenes, resins, and naphthenic acids that are electrostatically bound to the droplets surface. Such components provide an interfacial film over the brine droplet, resulting in a diminished droplet coalescence. Adding water to the crude oil can decrease the concentration of the surface-active components on the surface of each droplet, because the number of droplets is increased without increasing component concentration. 

Naphthenic acids, complex carboxylic acids that are believed to have a cyclopentane ring or cyclohexane ring in the molecule, occur in petroleum. They seem to be of little consequence enviromnentally since thermal decarboxylation can occur during the distillation process. During this process, the temperature of the crude oil in the distillation column can reach as high as 395°C (740°F). Hence decarboxylation is possible (Speight and Francisco, 1990) ... 

The oxygen content of crude oil is typically low and is usually in the form of naphthenic acid compounds. Asphaltic crudes can contain significantly more of these acids than paraffinic crude oils. Also, the concentration of oxygen increases with the boiling point of the crude oil fraction. 

The naphthenic acids in crude oil are primarily monocarboxylic acids possessing an alkylated, cyclopentane single-ring structure. Fused ring, branched aliphatic and dicarboxylic acid compounds are also found in lower numbers. Most species contain 10 carbon atoms, but 20-carbon-atom species have been identified. 

Naphthenic Acids Acids derived from crude oil which are usually monocarboxylic, monocyclic, and completely saturated. Many are derivatives of cyclopentane and more complex alicyclic ring systems. 

Naphthenic acid from petroleum continues to be of interest as a material for making copper naphthenate and wood preservatives for use in greenhouses and the like. Naphthenic acids occur naturally to the highest extent in naphthenic crude oils, certain of which are stated to contain over 1% total naphthenic acid. As yet these meterials have not reached wide acceptance in agricultural pest control. 

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... 

NAPHTHENIC ACIDS. The term naphthenic acid, as commonly used in the petroleum industry, refers collectively to all of the carboxylic adds present m crude oil. Naphthenic adds are classified as monobasic carboxylic acids of the general formula RCOOH, where R represents the naphthene moiety consisting of cyclopentine and cyclohexane derivatives. Naphthenic adds are composed predominantly of alkyl-substituted cycloaliphatic carboxylic adds, with smaller amounts of acyclic aliphatic (paraffinic or fatty) acids. Aromatic, okfinic. hydroxy, and dibasic acids are considered to be minor components. Commercial naphthenic aads also contain varying amounts of unsaponifiable hydrocarbons, phenolic compounds, sulfur compounds, and water. The complex mixture of adds is derived from straight-run distillates of petroleum, mostly from kerosene and diesel fractions. See also Petroleum. 

Naphthenic acid corrosion has been a problem in petroleum-refining operations since the early 1990s. Refineries processing highly naphthenic crudes must use steel alloys 316 stainless steel is the material of choice. Conversely, naphthenic acid derivatives find use as corrosion inhibitors in oil-well and petroleum refinery applications. 

Nameplate capacities of naphthenic acid producers in North America are 9000 metric tons of crude and refined acid at Meridiem (Tuscaloosa, Ala.), and 3600 t of crude acid at Hewchem (Gulfport. Miss.). However, actual production capacity may vary widely as a result of the mix of feedstocks being processed. Naphthenic acid products are shipped in tank cars, tank trucks, and drums under DOT 9137/UN 3082 identifications numbers. 

Naphthenic acid corrosion is quite severe in vacuum and visbreaker towers. Crudes with total acid numbers over 2.0 mg KOH/g have corroded type 316 SS in the inlet areas. At times, type 317 (UNS S31700) SS, 904L (UNS N08904), or other corrosion resistant alloys are needed. Matching weld filler metal must be used. In one case, a type 310 (UNS S31000) SS weld filler metal was used on type 316 SS lining. While the strip lining was not attacked, the weld dissolved in one year. 

For naphthenic acid containing hydrocarbons (Table A-4) where the neutralization number of the feed exoeeds 2 mg of KOH/g in a crude unit or 0 5 mg of KOH/g In a vacuum unit, use type 316L (UNS S31603) SS (2.5% Mo minimum) above 450°F (23°C) regardless of sulfur content. For castings, 316 (CF8M) with 2.5% Mo minimum may be used provided the ferrite content is 8% minimum. 

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