NO129282B - - Google Patents

Description

Application of sorbitan monoacylate and polyoxyalkylene

sorbitan monoacylate for dispersing oil on water.

The present invention relates to the use of improved

biodegradable oil slick dispersing compounds.

Water pollution caused by oil spills in water, resulting in the formation of unsightly oil stains, is a well-known issue. Such oil slicks or films are not only undesirable from an aesthetic point of view, but also because continuous oil films represent a barrier to oxygen transfer from the atmosphere for the entertainment of marine life, and furthermore the oil slicks are a danger to bird life while polluting coastal strips. Contamination of water with oil is sometimes negligently caused by the discharge of ballast water from oil tanks or from offshore drilling facilities. Although depletion

Cf. at 85c-l

of oil in the water in such situations is often unintentional and sought to be avoided, nevertheless problems arise.

Different techniques have been put forward to solve the oil pollution problem. One solution involves the use of strong detergents to emulsify the oil with the water. However, the use of such strong detergents or surfactants has resulted in serious damage to marine life.

In the present invention, it has been found that intact continuous oil films or oil stains can be quickly dispersed by bringing them into contact with a dispersing system consisting of a sorbitan monoacylate, a polyalkylene oxide derivative of a sorbitan monoacylate, and mixtures thereof. The dispersing system preferably exhibits a hydrophilic lipophilic equilibrium number of approx. 14.0. The dispersion system can be used on oil stains either alone or in conjunction with a polar diluent. Highly desirable results - are achieved by spraying the dispersing system directly and as uniformly as possible onto the surface of the oil spot using approximately 1 part by weight of dispersant per 10 to 100 parts by weight of oil, if possible followed by agitation of the contaminated area to help disperse the oil film. The active components of the dispersion system, namely the sorbitan derivatives, are non-toxic to marine life and are easily biodegradable.

The drawing shows a series of curves that illustrate the effect

to the dispersing system used according to the invention compared to other dispersing materials.

The sorbitan products used in the formation of the oily stain-dispersing system are prepared, in the case of sorbitan monoacylates, by reacting a long-chain saturated or unsaturated hydrocarbon fatty acid with a mixture of polyalcohols formed by dehydration of sorbitol, and in the case of polyoxyalkylene sorbitan monoacylates, by reaction of the sorbitan monoacylethanes with a 1,2-alkylene oxide, such as ethylene oxide or propylene oxide. The dehydration of sorbitol to the intermediate sorbitan compounds takes place as follows:

Products A, B and C above are all formed during the dehydration reaction. Sorbitan monoacylates are obtained by reacting compounds A, B and C or mixtures thereof with a fatty acid in the following manner:

As can be seen from equation II, the esterification reaction comprising a long-chain monocarboxylic acid is rather specific since only certain 0 of the available hydroxyl groups in the sorbitan compound participate in the esterification reaction. The term "sorbitan monoacylates" used is meant to denote the compounds D, E and F alone or in a mixture.

Polyoxyalkylene sorbitan monoacylates are formed by bringing sorbitan monoacylates (compounds D, E or F, or mixtures thereof) into contact with a 1,2-alkylene oxide so that one or more of the remaining hydroxyl groups in the sorbitan monoacylate react to form compounds containing one or more polyoxyalkylene groups . When ethylene oxide is used, the resulting polyoxyethylene groups have the structural formula (CH2CH2O)nH. When propylene oxide is used, the polyoxypropylene groups have the structural formula:

Since the polyoxyethylene and polyoxypropylene radicals are polymer products, a compound with "n" ethylene oxide units or "m" propylene oxide units actually contains a wide range of groups where the numerical average is either n or m. The term "polyoxyalkylene orbital monoacylate" is intended to include the polyoxyalkylene derivatives of compounds D, E and F and their mixtures.

According to the invention, a mixture of a sorbitan mono-

acylate with the formula:

and a polyoxyalkylene sorbitan monoacylate of the formula: where Y is a sorbitan radical, R is a monovalent alkyl or alkenyl radical of 8-20 carbon atoms and preferably 12-18 carbon atoms, and R' is a radical of the general formula and selected from the group which

where n is 6-30, preferably 15-22 and m is 5-1^, the dispersant having an HLB number of from 13.5 to 1^.5" and which optionally contains a solvent which comprises 70-90 wt. % of the total solvent/dispersant mixture, for dispersing oil stains on water.

The group Y can be a monocyclic or bicyclic sorbitan radical (a sorbitan radical which is defined as the compounds A, B, C or mixtures thereof, with the hydrogen atoms in one or more of the hydroxyl groups in the compounds removed). It should be understood that the polyoxyethylene or polyoxypropylene radicals may be present on one or more of the available hydroxyl radicals in the cyclic compounds and that the values for n, and m as indicated above represent the average number of polyoxyethylene or polyoxypropylene groups present in the compound and not that the relevant groups exist in a polymer chain. Representative examples of suitable monocarboxylic acids which can be used in the production of either sorbitan monoacylate or polyoxyalkylene sorbitan monoacylate include: decanoic acid, dodecanoic acid, hypogaeic acid, oleic acid, elaidic acid, pelargonic acid, capric acid, undecyl acid, lauric acid, tri-decoic acid, myristic acid, palmitic acid, margaric acid, stearic acid, nondecyl acid , arachidic acid, and the like.

The dispersion mixtures used consist of either sorbitan monoacylates, polyoxyalkylene sorbitan monoacylates or mixtures thereof. These compounds are used in the dispersion system in such a way that the hydrophilic-lipophilic equilibrium number (HLB) of the dispersion system varies between 13.5 and 14.5, preferably approx. 14.0. For the purpose of the present invention, the hydrophilic-lipophilic equilibrium number is determined according to the following equation:

The HLB number is determined by dividing the molecular weight of the hydrophilic compounds used in the synthesis of a given compound by the molecular weight of this compound and multiplying the result by 20. In situations where several materials are used in the dispersion system, the HLB number for the entire system is the sum of The HLB figures for the individual components multiplied by the weight percentage of the special components in the entire dispersing system. The HLB number for the lauric acid ester of compound A from equation I is determined, e.g. by dividing the molecular weight of the sorbitan compound, (the hydrophilic part of the molecule) namely compound A, which has a molecular weight of 164 by the molecular weight of sorbitan monolaurate (compound D) which is 346 and multiplying the result by 20. Thus the HLB number for compound D is from equation II, where R is the alkyl part of the lauric acid material, 9*5 • As is clear from the method used when calculating the HLB value, the HLB number for any given compound can be increased by adding polyoxyethylene or polyoxypropylene radicals to the compound or by reducing the molecular weight of the alkene or alkenyl part of the monoacid used in the synthesis of the initial sorbitan monoacylate. The active ingredients in the active dispersing system can be applied directly to the continuous oil stain to produce dispersion, but it is however desirable that the active ingredients are used in conjunction with a solvent. If solvents are used, these make up from 70 to 90 percent by weight of the total mixture. Suitable solvents include: water, ^ 2~^ 10 alkyl alcohols such as ethariol, isopropanol, n-pentanol, 2-ethylhexanol, etc., aromatic- and alkyl-substituted aromatic hydrocarbons, such as benzene, toluene, ethylbenzyl neo-pentylbenzene, heavy aromatic naphtha -refinery effluent, xylene, etc. Water and lower alkanols are preferred as solvents because they do not create a marine toxic problem. ;Usually from 1 to 10 parts by weight of the total dispersing system, i.e. active ingredients plus any solvent used, is used per 100 parts by weight, oil. Dispersion of oil stains can be achieved by spraying the entire dispersing mixture directly onto the oil stain. The dispersing system actually works at the oil-water interface and by careful application of the dispersing system to the film, rapid breakdown and dispersion of the film results. It is desirable that the dispersant be applied to the oil stain using a small diameter hose and fitted with a spray nozzle to provide a uniform, fine jet for effective distribution. The dispersion system is preferably applied from a work vessel as opposed to applying the material from a remote tanker or wharf. For extensive application, mechanical modifications of this arrangement may be appropriate. The dispersant can e.g. is applied more efficiently over a larger area by means of a simple pipe distributor to which several spray nozzles are attached. This application device can be mounted on the side or in the bow of the work vessel to increase the applied area at each passing of the vessel. After applying the dispersing system to the oil film, vigorous stirring is recommended, e.g. achieved with a water hose with a high feed rate or with a powerful propeller, although such agitation is not essential for an effective use of the dispersant. Oil slick formation can mainly be avoided by using the present dispersing mixtures by introducing the dispersing agent into lines or pipes which possibly contain oil-water mixtures for feeding this mixture to the main drainage water facility. ;Example in ;A number of experiments were carried out to demonstrate the effectiveness of the dispersants of the present invention compared to other commercially available dispersants. In each of these trials, 2 cm^ of a mixture consisting of 10 parts by weight of South Louisiana crude oil and 1 part by weight of the dispersant was mixed with 100 crn^ of freshwater and the whole was shaken vigorously for 5 minutes using a mechanical shaker. These mixtures were then poured into colorimeter cells for measurement of turbidity as determined by light transmission measurements. The basis for the experiments lies in the fact that the decrease in light transmission in relation to time is a measure of the dispersion's stability, as the most stable dispersion lets through less light, which thus indicates a more efficient dispersion system. The dispersion system according to the present invention consisted of 9% by weight of sorbitan monooleate ("SPAN 80") and 91% by weight of a 20 mol polyoxyethylene adduct of sorbitan monooleate ("TWEEN 80"). The system had an HLB value of 14.O. The activity of the mixture according to the invention was compared with two commercially available oil stain dispersing systems namely "Biocleanosol" and "Polycomplex A-ll", and two other dispersing systems consisting of commercially available emulsifiers. The commercially available emulsifier systems called B and D in fig. 1, consists of the following components: mixture B consisted of 50% by weight of heavy aromatic naphtha (HAN), 10% by weight of a tertiary amine formed by the condensation of 15 mol of ethylene oxide with 1 mol of a primary stearic acid amine ("Armour Ethomeen S/15") and 40% by weight of an alkylaryl polyether alcohol ("Rohm & Haas Triton X-45")• Mixture B has an HLB value of 10.6. Mixture D consisted of 50% by weight HAN, 10% by weight "Armour Ethomeen S/15" and 40% by weight "Renex 697<*> (a polyoxyalkylene alkyl aryl ether). Mixture D had an HLB value of 9-8. The control experiment was identical to the other experiments -ments with the exception that a dispersant was not present.

As can be seen from fig. 1 was the dispersing system which

falls within the limits of the present invention, significantly superior to the other emulsifiers and to the commercially available materials sold as oDjsfleck dispersants.

The curves in fig. 1 illustrates that the oil-water dispersion that is formed

using the mixture according to the present invention, was much more unaffected with respect to separation than any of the other sub-

searched materials.

Example 2

The effectiveness of the other dispersant systems

according to the invention was also tested in real cases. During offshore drilling operations, the oil obtained is sometimes contaminated with sea water. The water and oil are separated using typical decantation methods and the water, which contains smaller amounts of oil, is emptied into the lake. Due to the fact that the decanting operation is not fully

constantly effective, oil stains develop as a result of the discharge of oil into the lake water. At the trial, a dispersing system was created. consist-

end of 52 parts by weight of water, 20 parts by weight of isopropanol and 28 parts by weight of the mixture according to example 1 with an HLB value of 14, used. In the experiment, the dispersing system was injected into the oily water in the discharge line which carried the water from the separation container to the lake. The oily water discharge comprised 298,000 liters per day and the oily water contained approximately 1,000 parts of oil per million parts of water. The dispersing system was injected into the discharge line in a quantity of 30 liters per day, the dispersing system being used in a quantity of approx. 10 parts dispersant per 100 parts oil by weight. By using this technique, the oil stain that nor-

painted surrounding the turret completely removed. The -biodegradable-

heat and non-toxicity of the present dispersing systems were demonstrated using the classic Warburg Respirometer tests and with biological assay tests using live tropical fish.

Claims (1)

Use of a mixture of a sorbitan monoacylate with the formula: and a polyoxyalkylene sorbitan monoacylate of the formula: where Y is a sorbitan radical, R is a monovalent alkyl or alkenyl radical with 8-20 carbon atoms, and R' is a radical with the general formula and selected from the group consisting of: where n is 6-30 and m is 5-14>, the dispersant having an HLB number of from 13.5 to 14.5, and which optionally contains a solvent which comprises 70-90 percent by weight of the total solvent/dispersant mixture, for dispersion of oil stains on water.