Salts In crude

The presence of salts in crude oils has several disadvantages ... 

Caustic that is added downstream of the crude oil desalter. Caustic is injected downstream of the desalter to control overhead corrosion. Natural chloride salts in crude decompose to HCl at typical unit temperatures. Caustic reacts with these salts to form sodium chloride. Sodium chloride is thermally stable at the temperature found in the crude and vacuum unit heaters. This results in sodium chloride being present in either atmospheric or vacuum resids. Most refiners discontinue caustic injection when they process residue to the FCC unit. It can still be present in purchased feedstocks, however. 

Salt in crude oil must be removed before the oil undergoes processing in a refinery. The crude oil is fed to a washing unit where freshwater feed to the unit mixes with the oil and dissolves a portion of the salt contained in the oil. The oil (containing some salt but no water), being less dense than the water, can be removed at the top of the washer. The spent wash water (containing salt but no oil) is removed at the bottom of the washer. If the spent wash water contains 15% salt and the crude contains 5% salt, determine the concentration of salt in the washed oil product if the ratio of crude oil (with salt) to water used is 4 1. 

Salt in crude oil may be deleterious in several ways. Even in small concentrations, salts will accumulate in stills, heaters, and exchangers, leading to fouling that requires expensive cleanup. More importantly, during flash vaporization of crude oil certain metallic salts can be hydrolyzed to hydrochloric acid according to the following reactions ... 

Thus knowledge of the content of salt in crude oil is important in deciding whether and to what extent the crude oil needs desalting. 

Oil plants handle saline water, known as "formation water" and containing about 20% of salts, together with the product. This is an undesirable phenomenon which compels diversion of the well jet from the main stream to be refined. As a rule, 5-10 wells feed each gas-oil separation unit, intended to remove gas from the oil in three or four stages. It would be uneconomic to place one analyser in each well stream, so that analysers are placed only in the unloading line of each gas-oil separation unit. The analysers typically used here are salt-in-crude analysers and densitometers for low and high concentrations, respectively, of water in the oil. 

Only the MgCl2 and CaCl2 salts in crude oil decompose to HCI at temperatures above 350 F. This HCI is very hydroscopic. That is, the first drop of water that condenses in the overhead condensers will absorb all the HCI it contacts. This leads to a very low localized pH. The operators see the effect of the hydroscopic nature of HCI as extremely accelerated localized corrosion at the inlets to the overhead crude condensers. 

Chlorides are routinely introduced into refinery streams primarily from two sources salt in crude oil (most crude unit desalters are less than 95% efficient), and chlorides intentionally added to naphtha reformer reactors to promote catalyst activity. Although the amount of chlorides in a particular stream may be small, it is possible for the chlorides to concentrate at certain points. A reclaimer for an amine system is one such example. A rough guide to the time-temperature-concentration relationship to initiate cracking in Type 304 stainless is shown in Figure 22-3. 

The desalter should remove 90+% of the salts in crude. If it does not, check the desalter temperature (usually 270+°F). Steam condensate should be used for wash water. Is the proper dosage of desalter chemical being injected Is the voltage up to design ... 

In most production wells, chloride salts are found either dissolved in water that is emulsified in crude oU or as suspended solids. Salts also originate from brines injected for secondary recovery or from seawater ballast in marine tankers. Typically, the salts in crude oils consist of 75% sodium chloride, 15% magnesium chloride, and 10% calcium chloride. When crude oils are charged to crude distillation units and heated to temperatures above approximately 120 °C, hydrogen chloride is evolved from magnesium and calcium chloride, whUe sodium chloride is essentiaUy stable up to roughly 750 °C. 

The salt content is routinely determined by comparing the conductivity of a solution of crude oil in a polar solvent to that of a series of standard salt solutions in the same solvent [ASTM Test Method D3230, Salts in Crude Oil (Electrometric... 

This test method covers the determination of salts in crude oil. 

This test method has been extensively tested in a number of laboratories and found to give results comparable to those from other procedures for determining salt in crude oils. Exact precision data have not been derived because of inability to obtain stable, homogeneous, and representative samples for cooperative testing. 

Water, Sediment, and Salt Contents in Crude Oils... 

To obtain the free acid, dissolve the potassium salt in 50 ml. of cold water, filter the solution if a small undissolved residue remains, and then boil the clear solution gently whilst dilute sulphuric acid is added until the separation of the acid is complete. Cool the solution and filter off the pale orange-coloured crystals of the benzilic acid wash the crystals on the filter with some hot distilled water, drain well, and then dry in a desiccator. Yield of crude acid, 4 g. Recrystallise from benzene (about 50 ml.) to which a small quantity of animal charcoal has been added, filtering the boiling solution through a preheated funnel fitted w ith a fluted filter-paper, as the benzilic acid readily crystallises as the solution cools alternatively, recrystallise from much hot water. The benzilic acid is obtained as colourless crystals, m.p. 150°. 

Hot corrosion is a rapid form of attack that is generally associated with alkali metal contaminants, such as sodium and potassium, reacting with sulfur in the fuel to form molten sulfates. The presence of only a few parts per million (ppm) of such contaminants in the fuel, or equivalent in the air, is sufficient to cause this corrosion. Sodium can be introduced in a number of ways, such as salt water in liquid fuel, through the turbine air inlet at sites near salt water or other contaminated areas, or as contaminants in water/steam injections. Besides the alkali metals such as sodium and potassium, other chemical elements can influence or cause corrosion on bucketing. Notable in this connection are vanadium, primarily found in crude and residual oils. 

Base V, CjgHj or 26O2N2. This substance is present in small quantity (about 1-5 per cent.) in crude aphylline hydrochloride and when the base is liberated into ether from this salt, the solution deposits Base V on standing. It is sparingly soluble in ether or light petroleum, readily in benzene or alcohol and crystallises from benzene-light petroleum in colourless tablets, m.p. 137° (dec.). 

The crude product (48.4 grams, 80.9% yield) was recrystallized from an absolute ethanol-ethyl acetate solvent system by suspending the salt in boiling anhydrous ethyl acetate and just enough absolute ethanol was gradually added to effect solution after which the solu-... 

Metals in the forms of inorganic salts or organometallic compounds are present in the crude mixture in trace amounts. The ratio of the different constituents in crude oils, however, vary appreciably from one reservoir to another. 

Many metals occur in crude oils. Some of the more abundant are sodium, calcium, magnesium, aluminium, iron, vanadium, and nickel. They are present either as inorganic salts, such as sodium and magnesium chlorides, or in the form of organometallic compounds, such as those of nickel and vanadium (as in porphyrins). Calcium and magnesium can form salts or soaps with carboxylic acids. These compounds act as emulsifiers, and their presence is undesirable. 

Although metals in crudes are found in trace amounts, their presence is harmful and should be removed. When crude oil is processed, sodium and magnesium chlorides produce hydrochloric acid, which is very corrosive. Desalting crude oils is a necessary step to reduce these salts. 

Or S W. Basic sediment and water. The paraffin, sediments, and salt water impurities in crude and oil fuels that need to be removed prior to further processing or use. 

To a slurry of 33.5-33.9 g. of the pure (-)-amine (-)-DAG salt in 130 ml. of water is added 56 ml. of aqueous 2AT sodium hydroxide, and the resulting oily suspension is extracted with four 80-ml. portions of ether. The combined ether extracts are washed with 50 ml. of water and dried over anhydrous magnesium sulfate. After filtration and removal of the ether on a rotary evaporator, the crude base is distilled under reduced pressure through a 20-cm. Vigreux column (Note 8). This operation affords 10.9-11.7 g. (85-90% yield, based on the amount of the salt used) of the pure ()-amine as a colorless liquid, b.p. 156-157° (11mm.), n2i d 1.6211-1.6212, df 1.056, [a]2D5 -80.1° (neat), [oc]2d3 -60.4° (c 10.0%, methanol), [a] -59.3° (c 0.65%, methanol) (Notes 9 and 10). 

The sodium and potassium salts of glutaconaldehyde are soluble only in polar solvents such as water, dimethyl sulfoxide, N,N-dimethylformamide, pyridine, and methanol. However, the stable tetrabutylammonium salt is soluble in relatively nonpolar solvents such as chloroform and ethyl acetate. It may be prepared from the potassium salt in the following manner. In a 1-1. Erlenmeyer flask equipped with a magnetic stirring bar are placed a solution of 13.6g. (0.1 mole) of crude glutaconaldehyde potassium salt in 200 ml. of water and a solution of 33.9 g. (0.1 mole) of tetrabutyl-ammonium hydrogen sulfate in 200 ml. of ice-cold water, the pH of wliich was adjusted to 10 by adding aqueous 2M sodium hydroxide. 

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