Naphthenic acids removal

Aqueous solutions of NaOH or KOH are very effective at removing a variety of compounds from fuel. Components removed by extracting or washing the fuel with either of these caustic solutions include mercaptans, phenols, hydrogen sulfide, and naphthenic acids. Removal of these compounds can improve the color, odor,... 

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. 

Interest in synthetic naphthenic acid has grown as the supply of natural product has fluctuated. Oxidation of naphthene-based hydrocarbons has been studied extensively (35—37), but no commercially viable processes are known. Extensive purification schemes must be employed to maximize naphthene content in the feedstock and remove hydroxy acids and nonacidic by-products from the oxidation product. Free-radical addition of carboxylic acids to olefins (38,39) and addition of unsaturated fatty acids to cycloparaffins (40) have also been studied but have not been commercialized. 

NAPFINING A process for removing naphthenic acids from petroleum fractions by extracting with aqueous alkali, using a bundle of hollow fibers. Developed by the Merichem Company, Houston, TX, and used in 19 plants in 1991. 

Naphthenic acids occur primarily in distillate and some heavy fuel fractions. Topically, caustic treatment effectively removes these compounds. However, even after caustic treatment, alkali salts of heavier naphthenic acids may still remain oil soluble. In fuel, these compounds can act as very effective emulsifying agents. Fuel haze and particulate contamination can be due to these acid salts. Caustic solutions of various strengths can be used to wash fuel. Usually 10 to 20 vol% of a 5% to 10% caustic wash solution is effective for most applications. 

Caustic wash fuel to remove naphthenic acids. Naphthenic acid salts are water-soluble. Care should be taken to ensure that emulsification does not result. 

During the processing of fuels and fuel components, solutions of sodium hydroxide or potassium hydroxide may be used. These caustic solutions can react with phenols, mercaptans, and naphthenic acids to form water-soluble salts. As a result, these undesirable components are removed from the fuel as the caustic separates from the fuel. Further water washing can be performed to clear the fuel of residual caustic and salts. 

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. 

The use of carboxylic acids for the removal of iron(III) from solutions of the rare-earth metals has been reported,38 but has not been described in detail. The stoichiometries of the extracted complexes of iron(III) have not been clearly established. The n-decanoic acid complex has been variously described as (FeA3)3 and Fe3A9 x(OH) (HA) 51 or [Fe(OH)A2]2 and [Fe(OH)2A-HA]2,57 the H-octanoic acid complex as (FeA3-H20)3,58 the naphthenic acid complex as FeA3,47 and that of Versatic 10 acid as [FeA3(HA)J>, or [Fe(OH)A2]3.59... 

Figure 35. Naphthenic acid concentrations and toxicity (Microtox 1C20) for (a) waters collected along the Athabasca River (from about 100 km upstream of Fort McMurray to the delta of Lake Athabasca), and (b) various waters at Syncrude s Mildred Lake Site. With time, the original toxicity and naphthenic acid levels in the fresh process waters (PW, SP) show a steady decrease when removed from fresh input of tailings (SS, 1, 3, and 5 years). Levels in the Athabasca River represent natural surface waters.

However, with ageing, the toxic response per unit of naphthenic acid decreases. From Fignre 38, the reduction in naphthenic acid content and of acnte toxicity with time for tailings waters, stored under aerobic conditions, is evident for an array of biota. Natural bioremediation processes are proceeding in the oil sands extraction waters, once they are removed from fresh input of process waters and maintained under aerobic conditions. This biodegradation process is the basis on which the both the wet and dry landscape reclamation options operate. With time, waters will be slowly released from the varions sinks (sand deposits, fine tails) in the end-lease landscape. If the rate of their release is less than the rate of the bioremediation processes, then the resulting waters should have the toxic components of the naphthenic acid group reduced to levels that will ensure the waters are neither acutely nor chronically toxic [136,142],... 

Sulfuric acid also removes or dissolves resinous or asphaltic substances that may be present because of poor fractionation, entrainment, or cracking. These materials tend to inhibit the crystallization of wax, and hence acid treatment often raises the pour point. Oxygen compounds, such as naphthenic acids and ketones, and substances such as alcohols mid aldehydes that are formed by high-temperature oxidation are dissolved by sulfuric acid, but when diluted with oil their removal is never complete. Nitrogen bases similar to quinoline or pyridine, which are produced in small quantities during distillation, are easily dissolved in dilute add. 

The effect of different imidazole derivatives and polar solvents were evaluated. The acid-removal rate was influenced by the 2-methylimidazole content, reagent/oil ratio, reaction time, and reaction temperature, all of which had a positive effect on the acid-removal rate. The reagent/oil ratio had a negative effect on the oil yield rate. High-purity naphthenic acids could be obtained in this process. 

Shi, L. J. Shen, B. X. Wang, G. Q. (2008). Removal of Naphthenic Acids from Beijiang Crude Oil by Forming Ionic Liquids. Energy Fuels, 22, 4177-4181, ISSN 0887-0624. 

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