Acids naphthenic

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. 

The production of naphthenic acids from middle distillates occurs by extraction with 7-10% caustic solution. 

The formed sodium salts, which are soluble in the lower aqueous layer, are separated from the hydrocarbon layer and treated with a mineral acid to spring out the acids. The free acids are then dried and distilled. 

Using strong caustic solutions for the extraction may create separation problems because naphthenic acid salts are emulsifying agents. Properties of two naphthenic acid types are shown in Table 4-4.  

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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). 

The majority of acids contained in the diesel cuts are cyclic and come from cyclopentane or cyclohexane. They are better known as naphthenic acids / ... 

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

Naphthazarin dyes Naphthenate Naphthenate esters Naphthenates, metallic Naphthenes Naphthenic acid Naphthenic acids... 

Two undesirable aspects of FCC naphtha quaUty are that it may contain unacceptably high amounts of foul smelling mercaptans, and that its thermal stabiUty may be too low. Mercaptans are usually found in the light FCC naphtha and may be removed or converted to sulfides and disulfides by a sweetening process such as Merox, developed by UOP. Thermal stabiUty is improved in sweetening processes through removal of cresyUc and naphthenic acids. It may be further improved by clay treating and by addition of oxidation inhibitors such as phenylene diamine. 

Copper quinolinolate (oxine copper) is the chelate of divalent copper and 8-hydroxyquinoline and shares most of its market with copper naphthenate, which is a complex copper salt of mixed naphthenic acids. The principal uses are in wood treatments and some military textiles, where the green color is not objectionable. Copper naphthenate has an odor but is cheaper than oxine. Both copper naphthenate and 2inc naphthenate have performed well in environment tests, with exposure to soil above-ground, as well as concrete (33). 

The term naphthenic acid, as commonly used in the petroleum industry, refers collectively to all of the carboxyUc acids present in cmde oil. Naphthenic acids [1338-24-5] are classified as monobasic carboxyUc acids of the general formula RCOOH, where R represents the naphthene moiety consisting of cyclopentane and cyclohexane derivatives. Naphthenic acids are composed predorninandy of aLkyl-substituted cycloaUphatic carboxyUc acids, with smaller amounts of acycHc aUphatic (paraffinic or fatty) acids. Aromatic, olefinic, hydroxy, and dibasic acids are considered to be minor components. Commercial naphthenic acids also contain varying amounts of unsaponifiable hydrocarbons, phenoHc compounds, sulfur compounds, and water. The complex mixture of acids is derived from straight-mn distillates of petroleum, mosdy from kerosene and diesel fractions (see Petroleum). 

Naphthenic acids have been the topic of numerous studies extending over many years. Originally recovered from the petroleum distillates to minimise corrosion of refinery equipment, they have found wide use as articles of commerce in metal naphthenates and other derivatives. A comprehensive overview of the uses of naphthenic acid and its derivatives can be found in References 1 and 2. A review of the extensive research on carboxyUc acids in petroleum conducted up to 1955 is available (3), as is a more recent review of purification, identification, and uses of naphthenic acid (4). 

The name naphthenic acid is derived from the early discovery of monobasic carboxyUc acids in petroleum, with these acids being based on a saturated single-ring stmcture. The low molecular weight naphthenic acids contain alkylated cyclopentane carboxyUc acids, with smaller amounts of cyclohexane derivatives occurring. The carboxyl group is usually attached to a side chain rather than direcdy attached to the cycloalkane. The simplest naphthenic acid is cyclopentane acetic acid [1123-00-8] (1, n = 1). 

Naphthenic acids are lepiesented by a general formula where n indicates the carbon number and specifies a homologous series. The ... 

Fig. 1. Typical naphthenic acid stmctures, where R = alkyl. For the acychc case z = 0 and the stmcture is simply R—COOH.

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 corrosion has been a problem ia petroleum-refining operations siace the early 1900s. Naphthenic acid corrosion data have been reported for various materials of constmction (16), and correlations have been found relating corrosion rates to temperature and total acid number (17). Refineries processing highly naphthenic cmdes must use steel alloys 316 stainless steel [11107-04-3] is the material of choice. Conversely, naphthenic acid derivatives find use as corrosion inhibitors ia oil-weU and petroleum refinery appHcations. 

Naphthenic acids are normal constituents of nearly all cmde oils, but not all cmdes contain sufficient quantities of usable acids to make recovery an economic process. Heavy cmdes from geologically young formations have the highest acid content, and paraffinic cmdes usually have low acid content. 

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