Chemistry: electrical and wave energy – Processes and products – Electrical
Reexamination Certificate
1999-02-26
2001-05-08
Metzmaier, Daniel S. (Department: 1712)
Chemistry: electrical and wave energy
Processes and products
Electrical
C204S569000, C210S708000, C210S748080, C516S183000, C208S188000
Reexamination Certificate
active
06228239
ABSTRACT:
FIELD OF THE INVENTION
The invention is related to chemical demulsifier formulations useful in desalting heavy or waxy crude oils. The invention is also related to methods for mixing crude oil and chemical demulsifier formulations.
BACKGROUND
Crude oil contains varying amounts of inorganic salts. The presence of such salts presents difficulties during crude oil processing such as corrosion of the oil processing equipment. In order 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 by weight of the crude oil. This concentration corresponds to approximately 2 pounds of inorganic salts per 1,000 barrels of crude oil.
Among the crude oil desalting methods in use today, electrostatic desalting is frequently used with crudes containing 0.5 to 2% water. Wash water is added until the crude's water content is in the range of 4 to 8 vol. %, and a chemical emulsion breaker is added so that the oil and the aqueous phases can be separated and diverted for storage or further processing. As used herein, a crude oil emulsion is a mixture of crude oil and a dispersed aqueous phase, which may be in the form of droplets stabilized by naturally occurring surface active compounds in the crude oil. Additionally, inorganic fines such as clay particles can contribute to emulsion stabilization. Dispersing added wash water into the crude increases both the average droplet number density and the droplet surface area available for binding the surface active components. Increasing droplet surface area results in a reduction in droplet coverage by the surface active components; this results in a decrease in emulsion stability and an increase in droplet coalescence.
In electrostatic separation, brine droplets in the mixture of crude oil, wash water, and chemical emulsion breaker coalesce in between electrodes located in the oil phase. The coalesced aqueous droplets then settle below the oleaginous crude oil phase. The separation may occur in a separator where an effluent brine may be removed. Treated crude containing 3-5 ppm inorganic salts is removed from the upper part of the separator. Intermediate between the oil phase and the brine phase is an undesirable “rag” layer comprising a complex mixture of oil-in-water emulsion, water-in-oil emulsion, and solids. The rag layer remains in the desalter vessel or it may be removed therefrom for storage or further processing.
Electrostatic desalting may undesirably require adding a substantial amount of wash water to the crude prior to desalting. Frequently, water must be purchased for this purpose. Another difficulty in electrostatic desalting results from the quantity and quality of effluent brine, which itself may require further processing before discharge.
Other problems associated with electrostatic desalting include crude incompatibility and the formation of undesirable emulsions. For example, electrostatic desalting becomes more difficult as a crude's concentration of asphaltenes, resins, waxes, and napthenic acids (typically found in “heavy” or “waxy” crudes) increases. Rag layers at the water-oil phase boundary also result in processing difficulties that become more serious as the emulsion becomes more stable, the rag layer increases in volume, or both.
Consequently, there is a need for a crude oil desalting method that limits the formation of undesirable emulsions, is effective with heavy and waxy crudes, that minimizes the quantity of water added prior to crude treatment, and that minimizes the quantity of effluent brine.
SUMMARY OF THE INVENTION
In one embodiment, the invention is a crude oil desalting process comprising:
(a) adding to the crude oil a chemical demulsifier formulation, the chemical demulsifier formulation being present in an amount ranging from about 1 ppm to about 1,000 ppm based on the weight of the crude oil;
(b) adding wash water to the crude oil and chemical demulsifier formulation in an amount ranging from about 0.5 vol. % to about 3.0 vol. %, provided that no wash water is added when the concentration of the brine in the crude oil is greater than about 3.0 vol. % , all vol. % being based on the total volume of the crude oil; and
(c) separating the brine from the crude oil and chemical demulsifier formulation.
In another embodiment, the invention is a method for removing a brine of salt and water from a crude oil, the method comprising:
(a) mixing the crude oil under opposed-flow conditions at a temperature ranging from about 20° C. to 150° C., for a time ranging from about 1 minute to about 50 hours, and at a viscosity ranging from about 1 cP to about 250 cP in order to coalesce the brine droplets, and then
(b) separating the brine from the crude oil.
DETAILED DESCRIPTION OF THE INVENTION
The invention is based on the discovery that brine droplet coalescence in crude oil can be enhanced by adding chemical emulsion breakers to the crude oil emulsion, subjecting the crude oil and brine to opposed-flow mixing, or both. 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 highly elastic collisions between droplets during processing, resulting in diminished droplet coalescence.
While the invention can be practiced with any crude oil containing a brine, it is preferably practiced with heavy or waxy crude oils. Heavy or waxy crude oils have one or more of the following characteristics:
(a) The crude oil has an API gravity ranging from about 5 to about 30.
(b) The crude oil has a high naphthenic acid concentration, characterized by a high “TAN” number (the TAN number represents the number of milliequivalents of potassium hydroxide required to neutralize 1 gram of crude oil).
(c) The fraction of the crude oil insoluble in n-heptane ranges from about 0.5 wt. % to about 15 wt. %.
Adding water to the crude 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. It has been discovered that the amount of added water needed for desalting may be minimized by adding a chemical emulsion-breaker to the crude that is capable of displacing the surface active components from the brine droplets and then subjecting the crude oil to controlled mixing.
Chemical emulsion-breakers useful in the invention have a hydrophobic tail group and a hydrophilic head group. Preferably, the emulsion breaker has the formula:
x ranges from 1 to 5, y ranges from 0 to 2, and R is an alkyl group having 4 to 9 carbon atoms, and n ranges from 3 to 9.
Preferably, the chemical emulsion-breaker is used in combination with a delivery solvent. Delivery solvents useful in the practice of this invention include a high aromaticity solvent such as toluene, xylene, and high aromatic condensates such as heavy aromatic naphtha in combination with an oxygenated solvent such as diethylene monobutyl ether or benzyl alcohol. The preferred formulation comprises about 10 wt. % to about 60 wt. % chemical emulsion breaker, about 35 wt. % to about 75 wt. % diethylene glycol mono butyl ether, and about 5 wt. % to about 15 wt. % heavy aromatic naphtha. Particularly preferred is a formulation of 45% chemical emulsion-breaker, 50 wt. % diethylene glycol mono butyl ether, and 5 wt. % heavy aromatic naphtha (“HAN”).
An effective amount of the chemical emulsion-breaker-delivery solvent formulation (“chemical demulsifier formulation”) is combined with the crude oil. An effective amount of the formulation is the amount necessary to displace the surface active component from the brine droplets and render the brine droplets more amenable to coalescence. The effective amount ranges from about 1 ppm to about 1,000 ppm based on the weight of the crude oil, with about 20 to about 40 ppm being preferred.
In a preferred embodiment, a c
Brons Cornelius Hendrick
Hemrajani Ramesh R.
Manalastas Pacifico V.
Sartori Guido
Savage David W.
Exxon Research and Engineering Company
Hughes Gerard J.
Metzmaier Daniel S.
Scuorzo Linda M.
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