Total acid number

The industry standard for this test is based on ASTM D 664. Normally expressed as Neutralization Number, this test predicts the acidity of an oil/distillate fraction. The sample normally dissolved in Toluene/IPAAVater is titrated with potassium hydroxide and the results are expressed as mg KOH per gram of sample. Crude Oils having high acid numbers are purchased cautiously due to possible corrosion problems in the refineries. Crudes typically have TAN values form 0.05-6.0 mg KOH/gm of sample. While whole crudes are outside the scope of this titration method, it is the only recognized method in the industry. 

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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. 

Total acid number (TAN) is a measure of the amount of acid or acid-like material in the oil sample. Because new oils contain additives that affect the TAN number, it is important to compare used oil samples with new, unused, oil of the same type. Regular analysis at specific intervals is important to this evaluation. 

Oil-related analysis encompasses a variety of physical and chemical tests such as viscosity, total acid number and particulate contamination. This is often extended to include the identification of wear debris, as an early warning of component failure, by either spectrographic... 

The oil analyses have shown that the TBN values of lubricating oils deplete completely while at the same time, the corrosion rate can be considerably reduced. The relationship between the solubilization of large quantities of acid, total base number (TBN), and total acid number (TAN) values with the rate of corrosion is still unresolved. TAN values are not a good prediction of corrosion, and the source of extra TBN is much more important in the neutralization of corrosive acids than the simple numerical value of TBN. The effect of hard-core RMs shows poor correlation between used oil sample TAN values and the potential for bearing corrosion (Denison, 1944 Kreuz, 1970). Where corrosion rates are reduced by treatment with hard-core reverse micelle detergent, and no significant reduction in TAN has occurred, corrosion protection must have occurred by a... 

The corrosive activity on copper/lead bearings for typical carboxylic acids, such as decanoic, lauric, palmitic, stearic, and oleic acids, as 1 % w/w solutions in a lubricating oil base stock with excess of hard-core RMs, measured by infrared spectroscopy, supports the observation for the corrosive activity of used lubricating oils. An increase in total acidic number (TAN) is generally either an indication of contamination with acidic combustion products or the result of oil oxidation. Corrosion of bearing metals by used lubricating oils requires the presence of both acids and peroxides and probably takes place by a two-step mechanism. In the first step, the peroxide reacts with the metal to form a metal... 

The oil deterioration mechanism, various deterioration indicators (viscosity change, total base number (TBN), total acid number (TAN), insolubles concentration, etc.) have been proposed and their respective detecting methods were reported. The oil deterioration component is divided into two general categories deterioration of the base oil and ingression of foreign matter. Ultimately, however, particles are considered to exist in engine oil in the form of insoluble elements. Fig. 6.1 shows the mechanism of the oil deterioration (Tomita et ah, 1995). 

The remaining useful life evaluation routine (RULER) is a useful monitoring program for used engine oils. The RULER system is based on a voltammetric method (Jefferies and Ameye, 1997 Kauffman, 1989 and 1994). The data allows the user to monitor the depletation of two additives ZDDP and the phenol/amineH+ antioxidant. The RULER results were compared to other standard analytical techniques, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), total base number (TBN), total acid number (TAN), and viscosity to determine any correlation between the techniques (Jefferies and Ameye, 1997 and 1998). The test concluded that the RULER instrument can... 

Table 6.3. Techniques and methods for the determination of total base number (TBN, mg KOH g 1 oil) and total acid number (TAN, mg KOH g 1 oil), (Fox et al., 1991)...

Table 6. 7. Results of the total base number TBN, total acid number TAN, lead content from the field and bench tests of diesel engine oil (Van Dam et al., 1997)...

Total base number and total acid number values have been determined for a set of oil samples (Pawlak et al., 1985), curves II and III of Fig. 6.8. The two values cross over at a value of TBN = 2, after which the TAN values increase sharply and become meaningful. TBN values decrease sharply after the crossing point. The oil is now acidic and corrosive. The implications of the curves in Fig. 6.8 taken together are that the presence of water in oil could be potentially more damaging for "well-used" oils in service than for a fresh oil. 

Wear experiments have been carried out on a three-roller-on-ring machine. Some characteristic correlations (ATAN) of the deteriorated engine oils used in the wear experiment are summarized in Table 6.9. An effect of deterioration of petrol engine oil on wear was that an increase in the total acid number of the deteriorated oil above an initial value had a definite correlation with wear of steel. 

Total acid number and total base number (fresh oil)... 

Used oil analysis. Used oil samples were analyzed for the following properties (Annual Book ASTM, 1985) viscosity ASTM D445, total base number ASTM D2896, total acid number ASTM D664, pentane insolubles ASTM D896, mass % zinc ASTM D811, mass % iron ASTM D811), "Active" zinc (differential infrared), carbonyl absorbance (differential infra-red). Over 250 samples were analyzed. 

Total acid number a measure of a lubricant s acidity. 

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. 

Emulsification with caustic is possible with oils that have a fairly high total acid number (TAN). Below about 1.5 mg KOH/gm oil, the oils either will not emulsify or will form water-in-oil emulsions. The rate of emulsification with caustic is much faster than emulsification with surfactant mixtures, which is a characteristic property for emulsions generated via the agent-in-oil procedure (1 ). 

Oils obtained from the Kern River field also emulsify readily with caustic at ambient temperatures however, heating to 43°C causes the emulsification to be more rapid. Water and sediment constitute 50% of the produced crude oil. Treated oil (generator feed) is also available in the field which contains only 2% water and, consequently, a higher TAN (total acid number) than the produced crude oil (see Table II). The treated Kern River oil forms an extremely stable 75% oil-in-water emulsion at an optimal 0.50% NaOH concentration. 

The total acid numbers (TAN) and the experimentally determined optimal NaOH concentrations for Kern River, Wilmington, and other viscous, asphaltic crude oils are given in Table III. 

Suspension A system containing solid particles dispersed in a liquid. TAN See Total Acid Number. 

Total Acid Number (TAN) A property of crude oil. The acid number expresses the amount of base (potassium hydroxide) that will react with a given amount of crude oil in a standardized titration procedure. A large acid number indicates a high concentration of acids in the oil, usually including natural surfactant precursors. 

Absolute porosity, definition, 220 Absolute viscosity, definition, 386 Acid number (total acid number, TAN), definition, 403 Adhesion, definition, 26-27 Adsorbed polymer layers, interaction with droplets, 62 Adsorption definition, 386... 

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