Crude oil acid number

The effect of these organic compounds on the corrosivity of the water phase is not well understood, but probably results from either direct chemical interaction with the metal surface in the manner of a chemical corrosion inhibitor, and/or their effect on wettability. An example of the effect of the crude oil acid number on crude oil wettability is given in Fig. 4 [i4]. The relative wettability of the crude oil and water phases determines whether the metal surfece will be oil wet or water wet, with significant effects on corrosion [77]. There is a great deal of scatter in these data, allowing determination of only a general trend. 

A series of experiments were conducted to determine the emulsion stability in caustic systems. Figures 6 and 7 show data for the kinetics of coalescence and hence emulsion stability for the crude oil from Huntington Beach (Lower Main Zone), California (oil gravity of 23°API and oil acid number of 0.65). Figure 6 shows data for a nonequilibrated system and for a very low concentration of NaOH (0.003%) and 1% NaCl. This emulsion is unstable. Figure 7 shows data for two different concentrations of... 

It also reduces adsorption of the (mostly anionic) surfactant on the reservoir rock, essentially by enhancing the negative surface charge. In some cases (alkaline-polymer floods), where there are high levels of saponifiable crude oil acids present in the crude oil (high acid number) added surfactant is not even required. The polymer is present to assist in mobility control and to ensure that the injected chemical slug remains intact and promotes the formation of an oil bank ahead of it. 

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. 

Raw material input to petroleum refineries is primarily crude oil however, petroleum refineries use and generate an enormous number of chemicals, many of which leave the facilities as discharges of air emissions, wastewater, or solid waste. Pollutants generated typically include VOCs, carbon monoxide (CO), sulfur oxides (SOJ, nitrogen oxides (NOJ, particulates, ammonia (NH3), hydrogen sulfide (HjS) metals, spent acids, and numerous toxic organic compounds. 

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. 

After bauxite treatment the product was fractionated to produce C3-C4 and naphtha (C5-204°C) fractions. The C3-C4 olefin-rich gas was oligomerized over a solid phosphoric acid (SPA) catalyst to produce an unhydrogenated polymer gasoline with a research octane number (RON) of 95 and MON of 82.21 The bauxite-treated FT motor gasoline (RON of 87, MON of 76) was mixed with the polymer gasoline and some natural gas condensates (and crude-oil-derived naphtha) to produce the final motor gasoline product. In this respect it is noteworthy that the Fe-HTFT-derived material was the high-octane-blend stock. 

The mineral-based oils are produced from heavy-end crude oil distillates. Distillate sneams may be treated in several ways, such as vacuum-, solvent-, acid-, or hydrotreated, to produce oils with commercial properties. Hydrocarbon types ranging from C15 to C50 are found in the various types of oils, with the heavier distillates having higher percentages of the higher-carbon-number compounds. 

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. 

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... 

Saponification, Resinous Substances.—Resin oils are not saponifiable, except for such part of the resinous substances as they may contain as impurities (especially in the crude oils) these combine with alkali and are detectable by the acid number see preceding paragraph) and by the saponification number, determined as in fatty oils see Vol. I, p. 375). 

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. 

A relationship between peroxide value and anisidine number that is used to measure the rancidity level of fats and oils. It is defined as (2 X PV) + AN. It reflects total oxidation to date. Considered an impurity. High levels of moisture in an oil can lead to deterioration in storage. Soap can be formed when moisture is present in the crude oil and reacts with the free fatty acids and a catalyst (alkali ion), or it can result from incomplete removal of soap from washed refined oil. 

Droplet size depends on a number of factors such as the type of oil, brine composition, interfacial properties of the oil-water system, surface-active agents present (added or naturally occurring), flow velocity, and nature of porous material. For the study of OAV emulsions, McAuliffe (9) varied emulsion droplet sizes and size distributions by increasing the sodium hydroxide concentration in the aqueous phase, as shown in Figure 10. Higher NaOH concentration neutralizes more of the surface-active acids in the crude oil and produces an emulsion that has droplets of smaller diameters and is also more stable. Emulsion droplet size distribution can also be varied by varying the concentration of a surfactant added to the crude oil, as shown in Figure 11. 

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