Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
1999-12-14
2001-02-27
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C210S925000, C510S365000
Reexamination Certificate
active
06194473
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an oil dispersant formulation and a process for dispersing spilled oil on water. More particularly, a formulation of chemical surfactants and inorganic salts results in a low toxicity dispersant which is effective at dispersing highly viscous oil at low concentrations in both salt and fresh water.
2. Description of the Related Art
One of the technologies used for oil spill response involves the use of chemical dispersants. The application of chemical dispersants is dependent on several factors: (1) weather conditions, (2) nature of the oil spilled, (3) area to be covered, (4) salinity of the water to be treated and (5) adequacy of equipment and supplies. Although it is highly desirable, it has not been possible to provide a single chemical dispersant formulation which will treat all oils under all conditions. For example, it is much more difficult to disperse a high-boiling viscous oil such a bunker oil as compared to a light crude oil. Furthermore, dispersant products which are effective in salt water often are substantially ineffective in fresh water.
A desirable property for chemical dispersants used to treat oil spills is that the surfactant formulation of the dispersant results in very low oil-water interfacial tension such that the oil is effectively dispersed as fine oil droplets in water without coalescing even at low dispersant to oil ratios. Also, the dispersant formulation should be of minimal toxicity so that it does not add to the environmental damage caused by the oil spill.
Various dispersant formulations have been advanced for treating oil spills. U.S. Pat. Nos. 5,618,468 and 5,728,320 disclose dispersant products which are highly effective for dispersing oil spills in salt water. In low salinity water, however, these dispersant products lose effectiveness and become ineffective in fresh water.
SUMMARY OF THE INVENTION
The present invention provides an improved dispersant formulation which is effective for dispersing spilled oil in both salt and fresh water.
The dispersant formulation comprises:
(a) a sorbitan monoester of a C
10
-C
20
aliphatic monocarboxylic acid;
(b) a polyoxyethylene adduct of a sorbitan monoester of a C
10
-C
20
aliphatic monocarboxylic acid, said adduct having from 6 to 30 ethyleneoxide units per mole of ester;
(c) an alkali metal salt of a dialkyl sulfosuccinate wherein the alkyl group is a branched chain radical containing 4 to 13 carbon atoms;
(d) a polyoxyethylene adduct of a sorbitan triester of a C
10
-C
20
aliphatic monocarboxylic acid having from 6 to 30 ethyleneoxide units per mole of triester or a polyoxyethylene adduct of a sorbitol hexaester of C
10
-C
20
aliphatic monocarboxylic acid, said having from 6 to 30 ethyleneoxide units per mole of hexaester;
(e) a glycol ether solvent selected from the group consisting of ethylene glycol ether, propylene glycol ether, dipropylene glycol ether and tripropylene glycol n-butyl ether; and
(f) an inorganic salt.
In another embodiment, the dispersant formulation comprises:
(a) a sorbitan monoester of a C
10
-C
20
aliphatic monocarboxylic acid;
(b) a polyoxyethylene adduct of a sorbitan monoester of a C
10
-C
20
aliphatic monocarboxylic acid, said adduct having from 6 to 30 ethyleneoxide units per mole of ester;
(c) an alkali salt of a dialkyl sulfosuccinate wherein the alkyl group is a branched chain radical containing 4 to 13 carbon atoms provided that the critical micelle concentration at 25° C. is greater than 0.05 g/100 ml;
(d) a polyoxyethylene adduct of a sorbitan triester of a C
10
-C
20
aliphatic monocarboxylic acid having from 6 to 30 ethyleneoxide units per mole of triester or a polyoxyethylene adduct of a sorbitol hexaester of C
10
-C
20
aliphatic monocarboxylic acid, said having from 6 to 30 ethyleneoxide units per mole of hexaester;
(e) a solvent comprising a paraffinic hydrocarbon and a glycol ether selected from the group consisting of ethylene glycol ether, propylene glycol ether, dipropylene glycol ether and tripropylene glycol ether.
(f) an inorganic salt containing a soluble divalent cation.
It has been found that the inorganic salts enhance the effectiveness of the dispersant formulation in fresh or low salinity water by reducing the tendency of low salinity water to extract surfactants before they can be effective in oil.
The improved process for dispersing an oil layer on water comprises contacting the oil layer on the water surface with the dispersant formulation described above.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the sorbitan esters of C
10
-C
20
aliphatic monocarboxylic acids (component (a)), the aliphatic radical is straight or branched chain and saturated or unsaturated. Preferred aliphatic monocarboxylic acids moieties are C
12
-C
18
straight chain saturated or monoethylenically unsaturated. Sorbitan esters are prepared by dehydrating sorbitol followed by reaction with aliphatic monocarboxylic acid, and are available commercially from ICI under the trade name Span®.
Polyoxyethylene adducts of sorbitan monoesters of C
10
-C
20
aliphatic monocarboxylic acids (component (b)) have from 6 to 30, preferably 15 to 22 ethyleneoxide units per mole of ester. Such polyoxyethylene adducts are prepared by reacting the sorbitan esters of aliphatic monocarboxylic acids described above with 1.2-ethylene oxide. These polyoxyethylene adducts are available commercially from ICI Inc. under the trade name Tween®.
The alkali metal salt of a dialkyl sulfosuccinate wherein the alkyl group is a C
4
-C
13
branched chain radical (component (c)) is an anionic surfactant. A preferred salt is sodium dioctyl sulfosuccinate commercially available from Mona Industries, Inc. under the trade name Monowet®. The critical micelle concentration for any given dialkyl sulfosuccinate is primarily a function of nature of the alkyl group on the sulfosuccinate. In the present dispersant formulation, the dialkyl sulfosuccinate surfactant has a critical micelle concentration at 25° C. of at least about 0.05 g/100 ml.
Polyoxyethylene adducts of sorbitan triesters or sorbitol hexaesters of C
10
-C
20
aliphatic monocarboxylic acids (component (d)) contain from 6 to 30, preferably 15 to 22 ethyleneoxide units per mole of triester or hexaester. The sorbitol adduct is prepared by reacting ethylene oxide with sorbitol followed by esterification and are commercially available.
The propylene or ethylene glycol ethers used as solvents in the present invention (component (e)) have a maximum solubility in water of 25 ml per 100 ml water at 25° C., preferably 10 ml per 100 ml water. Preferred solvents are dipropylene glycol n-butyl ether, propylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether and ethylene glycol phenyl ether, more preferably ethylene glycol n-butyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, and tripropylene glycol n-butyl ether, especially dipropylene glycol n-butyl ether. Glycol ethers are available commercially from Dow Chemical Co. under the trade name Dowanol®. Propylene and ethylene glycol monoethers possess favorable lipophilic properties for use in oil dispersant formulations and are also of low toxicity. From a toxicological standpoint, ethers which do not contain an aromatic moiety are preferred.
When the propylene or ethylene glycol ether solvents are combined with a paraffinic solvent, the solubility of the glycol ether solvents is of less importance, especially where the paraffinic solvent is the major component of the solvent package. It is feasible to use the propylene glycol ether or ethylene glycol ether with water, alcohol or glycol. Preferred paraffinic solvents are isoparaffinic solvents. Especially preferred are isoparaffinic solvents containing at least about 50 vol. % of isoparaffins. Such isoparaffinic solvents are available from Exxon Company, U.S.A. under the trade name ISOPAR®. The total amount of solvent is from 15 to 90 vol. % based on dispersant formulation, preferably from 30 to 80 vol. %. The amount o
Becker Kenneth William
Canevari Gerard Paul
Fiocco Robert John
George-Ares Anita
Lessard Richard Raymond
Brumlik Charles J.
Exxon Research and Engineering Company
Lovering Richard D.
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