Naphthenic acid (CAS: 1338-24-5 ) (NAs)is the name for an unspecific mixture of several cyclopentyl and cyclohexyl carboxylic acids with molecular weight of 120 to well over 700 atomic mass units. The main fraction are carboxylic acids with a carbon backbone of 9 to 20 carbons. McKee et al. claim that "naphthenic acids (NAs) are primarily cycloaliphatic carboxylic acids with 10 to 16 carbons." Salts of naphthenic acids, which are naphthenates, are widely used as hydrophobic sources of metal ions in diverse applications.
Preparation and occurrence
They are obtained by oxidation of the naphtha fraction of the crude oil refining. The composition varies with the crude oil composition and the conditions during refining and oxidation. Naphthenic acids are present in crude oil. Fractions that are rich in naphthenic acids can cause corrosion damage to oil refinery equipment; the phenomenon of naphthenic acid corrosion (NAC) has therefore been well researched. Crude oils with a high content of naphthenic acids are often referred to as high total acid number (TAN) crude oils or high acid crude oil (HAC). Naphthenic acids are the major contaminant in water produced from the extraction of oil from Athabasca oil sands (AOL). Naphthenic acids have both acute and chronic toxicity to fish and other organisms.
In their oft-cited article published in Toxicological Sciences Rogers et al. stated that "naphthenic acids are the most significant environmental contaminants resulting from petroleum extraction from oil sands deposits." They found that "under worst-case exposure conditions, acute toxicity is unlikely in wild mammals exposed to naphthenic acids in AOS tailings pond water, but repeated exposure may have adverse health effects." Naphthenic acids are present in Athabasca oil sands (AOL) tailings pond water (TPW) at an estimated concentration of 81 mg/l. In their 2002 article cited over 100 times, Rogers et al. reported on a solvent-based laboratory bench procedure developed to "efficiently extract naphthenic acids from bulk volumes of Athabasca oil sands tailings pond water (TPW)."
Using Organization for Economic Cooperation and Development [OECD] protocols for testing toxicity, McKee et al. (2014) argued that based on their studies refined NAs when consumed orally were not acutely genotoxic to mammals. However, damage induced by NAs while transient in acute or discontinuous exposure, may be cumulative in repeated exposure.
Naphthenates are the salts of naphthenic acids. Analogous to the corresponding acetate, which are better defined but less useful, metal naphthenates are coordination complexes. They have the formula M(naphthenate)2 or are basic oxides with the formula M3O(naphthenate)6. The naphthenates are highly soluble in organic media, such as paints. They have industrial applications including synthetic detergents, lubricants, corrosion inhibitors, fuel and lubricating oil additives, wood preservatives, insecticides, fungicides, acaricides, wetting agents, thickening agent of napalm and oil drying agents used in painting and wood surface treatment. Industrially useful naphthenates include those of aluminium, magnesium, calcium, barium, cobalt, copper, lead, manganese, nickel, vanadium, and zinc.
- Richard H. McKee, Colin M. North, Paula Podhasky, Jeffrey H. Charlap, Adam Kuhl (February 2014). "Acute and Subchronic Mammalian Toxicity of Naphthenic Acids from Oil Sands Tailings". International Journal of Toxicology 33 (1): 347–355. doi:10.1177/1091581813504229.
- Angelo Nora, Alfred Szczepanek, Gunther Koenen, "Metallic Soaps" in Ullmann’s Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_361
- Walter E. Rudzinski, Leon Oehlers, and Yi Zhang (2002). "Tandem Mass Spectrometric Characterization of Commercial Naphthenic Acids and a Maya Crude Oil". Energy Fuels 16 (5): 1178–1185. doi:10.1021/ef020013t.
- Slavcheva E.; Shone B.; Turnbull A. (1999). "Review of naphthenic acid corrosion in oil refining". British Corrosion Journal 34 (2): 125–131. doi:10.1179/000705999101500761.
- "Article with details concerning naphthenic acid corrosion" (PDF).
- Allen, E. W. (2008). "Process water treatment in Canada’s oil sands industry: I. Target pollutants and treatment objectives" (PDF). Journal of Environmental Engineering and Science 7 (2): 123–138. doi:10.1139/S07-038.
- Vincent V. Rogers, Mark Wickstrom, Karsten Liber and Michael D. MacKinnon (2001). "Acute and Subchronic Mammalian Toxicity of Naphthenic Acids from Oil Sands Tailings". Toxicological Sciences 66 (2): 347–355. doi:10.1093/toxsci/66.2.347.
- Vincent V. Rogers, Karsten Liber, and Michael D. MacKinnon (August 2002). "Isolation and characterization of naphthenic acids from Athabasca oil sands tailings pond water". Chemosphere 48 (5): 519–527. doi:10.1016/S0045-6535(02)00133-9.
- Article concerning refining crude oil with a high content of naphthenic acids
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- Crude oils containing naphthenic acids in the Grangemouth refinery
- Overview of naphthenic acid corrosion
- Literature survey of naphthenic acid corrosion
- Removing naphthenic acids from the crude oil
- Presentation by Nalco on naphthenic acid corrosion
- Presentation by Baker Petrolite on naphthenic acid corrosion
- Presentation by ChevronTexaco on crude oils with a high content of naphthenic acids
- Information by Seth Laboratories on Naphthenic acid corrosion
- Details regarding Kuwaitian heavy crudes and naphthenic acid corrosion
- Article regarding naphthenic acid removal
- Article regarding naphthenic acid species
- Article abstract regarding molecular origins of heavy crude oil interfacial activity mainly caused by Naphthenic acids
- Article about processes to remove Naphthenic acids
- Article about stabilisation of water-in-oil emulsions by naphthenic acids
- Spectrometric Identification of Naphthenic Acids Isolated from Crude Oil
- Hydrogen flux and naphthenic acid corrosion