Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-04-20
2001-01-09
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S800000, C435S281000
Reexamination Certificate
active
06171500
ABSTRACT:
The present invention is directed to a process for the breaking of an oil-water emulsion, by contacting the emulsion with a bacterial culture grown from hydrocarbons under non-sterile conditions, permitting oil and water layers to separate and then separating each of the layers. The oil-water emulsion may be an oil-in-water emulsion or a water-in-oil emulsion.
An emulsion is usually a mixture of minute globules of one liquid dispersed in a second non-miscible liquid. In the case of oil-water emulsions, the emulsion may be in the form of oil globules in a continuous water phase (oil-in-water) or, conversely, water globules in a continuous oil phase (water-in-oil). Two immiscible liquids will tend to form an emulsion as result of some type of physical or mechanical agitation of the two liquids if an emulsifying agent, which promotes emulsion formation, is present. Emulsifying agents found in water-petroleum oil emulsions include the asphaltene and resin components of the oil, oil-soluble organic acids or other chemicals originally present in the oil or which have been added to it.
In oil exploration and production, there is substantial need for processes to break crude oil:water emulsions with maximum oil recovery. As oil comes from the oil well, some water i.e. so-called produced water, from the formation is also recovered and the combined mixture of oil and water is pumped into a field tank. The oil and water phases tend to separate, with the oil phase rising to the top and the water phase being at the bottom. An oil and water emulsion usually forms at the interface between the phases.
Many such oil-water emulsions contain solids material. The solids may act as a mechanical barrier, and prevent coalescence of emulsion droplets. In the case of petroleum oil-water emulsions, the solids may consist of fine particles also known as clay fines.
The emulsion cannot be transferred to the pipeline. Typically, pipeline quality oil should contain less that one percent water and solids. Therefore, the emulsions are usually brought to a treater facility which aims to separate the emulsion into pipeline quality oil, which can be sold, and water and solids. Treater facilities aim to neutralize the properties of emulsifying agents or destroy them, thereby breaking the emulsion.
A combination of physical and chemical treatments may be used to break the emulsions e.g. centrifugation, heat, electrical treatment or use of chemicals. Chemicals used in the breaking of emulsions include soap, fatty acids and long chain alcohols. Chemical emulsion breakers when, for example added to a water-in-oil emulsion, make the droplets of water merge or coalesce. Larger droplets of water tend to settle out of oil faster than smaller droplets.
The emulsion may also be broken electrically or mechanically. Heat decreases emulsion viscosity, and increases the momentum of water and oil molecules increase in the mobility of the emulsion droplets causes the droplets to collide with each other more frequently which promotes rupturing of the emulsion, coalescence of the droplets and separation of the water and oil phases. The molecules of surfactant materials at the interfaces in an emulsion are arranged with polar ends facing the water phase and non-polar ends facing the oil phase. Electrical currents can cause these molecules to rearrange, thereby disrupting the emulsion.
Emulsion treaters used in commercial processing of crude oils are typically heat treaters or electrostatic treaters. However, even in these treaters a difficult-to-break emulsion layer, often referred to as slop oil emulsion, develops and accumulates in the treater and reduces treater capacity. One of the problems associated with use of heat and chemical-based methods to break emulsions is that the resulting slop oil emulsion tends to be more stable and more difficult to break. The stabilizing agent of slop oil emulsions is often a surface active material dissolved in one of the phases. Thus, degrading or modifying the stabilizing agent represents a key objective in attempting to break these emulsions. The volumes of slop oil emulsions may amount to one percent of oil produced.
Residual emulsion material, slop oil emulsions, is a waste material which either requires disposal or is accumulated on site. In some countries, emulsions which survive chemical, thermal or other treatment in the treater are dumped in oil pits or tanks or are transported in tankers to lagoons. Alternatively, these emulsions are disposed of by pumping into salt caverns or are sent to landfills.
Slop oil emulsions vary in their properties depending on the properties and viscosity of the oil, the geologic formation where the oil originated, the amount of water and solids, the salt content of the water, the nature of the solids material, and the chemical or physical treater process.
Bacteria have a variety of properties which give them potential for use in oil-water emulsion breaking processes. Bacteria can act in a number of ways to modify the forces stabilizing an emulsion. For instance, bacterial cells or their products may exhibit surfactant activity, may biotransform surface active agents into agents which have less surfactant activity, may degrade or transform oil components which are involved in emulsion formation or may modify the pH at the emulsion interface. These or other biological mechanisms may contribute to breaking an emulsion.
It is known to use single, pure bacterial cultures in the treatment of emulsions. For instance, (a)
Mycobacterium cuneatum, Mycobacterium petroleophilum
and some Psuedomonads cause coalescence of kerosene in water emulsions containing a surfactant; (b)
Nocardia amarae
, grown in a medium contained hexadecane, can de-emulsify oil-in-water emulsions that were prepared by mixing kerosene or various pure alkanes with a water-containing a surfactant; (c) acetoin, produced by
Bacillus subtilis
, promotes de-emulsification of a 1% oil in water emulsion containing Tween-80™ surfactant, and (d) pure cultures of
Nocardia amarae, Corynebacterium petrophilium
and
Torulopsis bombicola
de-emulsify oil-in-water and water-in-oil petroleum field emulsions. However, use of single pure bacterial cultures is a disadvantage from a commercial perspective, since preparation of the cultures requires use of sterilized fermenter and culture media which have high associated capital and operating costs.
U.S. Pat. No. 4,392,892 describes a process for separating hydrocarbons from particulate solids using a crude extract of microbially-produced glycolipids. U.S. Pat. No. 5,551,987 describes a process for treating of solid waste or mud contaminated with hydrocarbons which involves extracting the material with non-volatile organic solvent and contacting the oily extract with microbes which produce biosurfactants.
PCT/CA98/00108 filed Mar. 20, 1998 describes a mixed biological process for degradation of oil sludges, including refinery sludges, tank-bottoms, slop oil or treater emulsions and others. The method involves forming an oil-in-water emulsion in a reactor such that the reactor contains up to 50% by volume of hydrocarbons and where the hydrocarbon content in the reactor is reduced by at least 25%.
An improved process for the breaking of oil-water emulsions that may be operated In the field would be useful.
A biological process for the breaking or oil-water emulsions that may be used in the field has now been found.
Accordingly, one aspect of the present invention provides a process for breaking an oil-water emulsion comprising:
a) contacting the oil-water emulsion with a bacterial culture produced by growth in a liquid medium containing hydrocarbons under non-sterile conditions, said oil-water emulsion and bacterial culture being contacted under conditions that minimise degradation of said oil;
b) permitting the oil-water emulsion to form an oil layer and a water layer; and
c) separating each of the oil layer and the water layer so formed.
In a preferred embodiment of the process of the invention, solids are present in the emulsion and such solids are permit
Singh Ajay
Ward Owen P.
Libert & Associates
Petrozyme Technologies Inc.
Prince Fred
Simmons David A.
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