Demulsifying chemicals

Before distillation, crude oil salts and certain metals must be removed. The process of desalting is applied for this purpose. Desalting involves mixing the crude oil with water at a temperature of about 250°F (121.1°C) under enough pressure to prevent evaporation of both water and volatile crude oil components. The salts are dissolved and removed by the water. Oil/water emulsions often form which also contain salts. The emulsions can be broken by the use of high-voltage electrostatic coalescers or by the use of demulsifying chemicals. 

The bottle test is excellent for screening prospective demulsifier chemicals for plant use. However, it is less reliable when determining the quantity (dosage) of chemical required to treat a specific emulsion under plant conditions. (A rule of thumb that has been proposed (4) correlates 6-8 h in a bottle test with 24 h in the plant). For example, the bottle test may indicate... 

Demulsifier (Chemical) Any agent added to an emulsion that causes or enhances the rate of breaking of the emulsion (separation into its constituent liquid phases). Demulsifiers may act by any of a number of different mechanisms, which usually include enhancing the rate of droplet coalescence. 

Year Dosage (ppm) weight Successful demulsifier chemicals published... 

In the production of crude oil, the greatest part of the crude oil occurs as a water-in-oil emulsion. The composition of the continuous phase depends on the water/oil ratio, the natural emulsifier systems contained in the oil, and the origin of the emulsion. The natural emulsifiers contained in crude oils have a complex chemical structure, so that, to overcome their effect, petroleum-emulsion demulsifiers must be selectively developed. As new oil fields are developed, and as the production conditions change at older fields, there is a constant need for demulsifiers that lead to a rapid separation into water and oil, as well as minimal-residual water and salt mixtures. 

The emulsion must be separated by the addition of chemical demulsifiers before the crude oil can be accepted for transportation. The quality criteria for a delivered crude oil are the residual salt content and the water content. For the oil to have a pipeline quality, it is necessary to reduce the water content to less than approximately 1.0%. 

There are oil-soluble demulsifiers and water-soluble demulsifiers, the latter being widely used. Emulsions are variable in stability. This variability is largely dependent on oil type and degree of weathering. Emulsions that have a low stability will break easily with chemical emulsion breakers. Broken emulsions will form a foamlike material, called rag, which retains water that is not part of the stable emulsions. The most effective demulsifier must always be determined for the particular emulsion. 

Demulsifiers (specifically, oil spill demulsifiers) can be applied to oil spills in low concentrations. They prevent mousse formation for significant periods of time and cause a large reduction in oil-water interfacial tension. The best of these was found to prevent emulsification at dosages as low as 1 part inhibitor to 20,000 parts of fresh oil at 20° C [273]. At dosages of 1 1000, at temperatures higher than 10° C, the chemical also results in significant and rapid dispersion of the oil. For very low temperatures or highly weathered oil, the performance of the chemical falls off sharply. 

The performance of demulsifiers can be predicted by the relationship between the film pressure of the demulsifier and the normalized area and the solvent properties of the demulsifier [1632]. The surfactant activity of the demulsifier is dependent on the bulk phase behavior of the chemical when dispersed in the crude oil emulsions. This behavior can be monitored by determining the demulsifier pressure-area isotherms for adsorption at the crude oil-water interface. 

The chemicals used as demulsifiers can be classified according to their chemical structure and their applications. With the latter respect, a main division for water-in-oil and oil-in-water applications exists. Furthermore, the demulsifiers can be classified according to the oil type used. 

R. Varadaraj, D. W. Savage, and C. H. Brons. Chemical demulsifier for desalting heavy crude. Patent US 6168702, 2001. 

Although, many other methods (e.g. electrostatic separation, heating, centrifugation, etc.) may be used to separate the oil and water phases, chemical demulsification is the most inexpensive and widely used technique to resolve crude oil emulsions. The demulsifiers are oil-soluble water-dispersible non-ionic polymeric... 

The major problem in demulsifying crude oil emulsions is the extreme sensitivity to demulsifier composition. There have been attempts (2, 3) to correlate demulsifier effectiveness with some of the physical properties governing emulsion stability. However, our understanding in this area is still limited. Consequently, demulsifier selection has been traditionally based on a trial and error method with hundreds of chemicals in the field. 

Alkoxylated phenol formaldehyde resins are a well-known class of demulsifier, and the emulsion coalescence data in Table III confirm that Thin Film Spreading Agents, which belong to this class, can also function as chemical demulsifiers. When water in... 

Table III. Thin Film Spreading Agents Are a Well-Known Class of Chemical Demulsifier...

Two principal approaches for the demulsification of the loaded emulsion are chemical and physical treatments. Chemical treatment involves the addition of a demulsifier to the emulsion. This method seems to be very effective. However, the added demulsifier will change the properties of the membrane phase and thus inhibits its reuse. In addition, the recovery of the demulsifier by distillation is rather expensive. Therefore, chemical treatment is usually not suitable for breaking emulsion liquid membrane, although few examples of chemical demulsification have been reported for certain liquid membrane systems [88]. 

Some chemical additives such as corrosion inhibitors, wax crystal modifiers, detergents, and demulsifiers provide performance which is difficult to duplicate through refining without adversely affecting some other fuel property. Other additives such as metal chelators, fuel sweeteners, biocides, lubricity improvers, foam control agents and combustion enhancers can also be used to solve fuel performance problems. 

To break through this oil or surfactant layer and free the retained water, it is necessary to chemically disrupt the stability of this layer. Demulsifiers and dehazers can adsorb onto the protective film and subsequently interfere with the electrochemical forces which hold this outer layer together. 

Additive A chemical substance added to a product to impart or improve certain properties. Typical fuel additives include antioxidants, cetane improvers, corrosion inhibitors, demulsifiers, detergents, dyes, metal deactivators, octane improvers, and wax crystal modifiers. 

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