GB2319023A

GB2319023A - Ferrofluid to combat oil slicks

Info

Publication number: GB2319023A
Application number: GB9712192A
Authority: GB
Inventors: Tae Ok Kim; Hack Gi Shin; Jong Ho Suh; Won Goo Lee; Yoon Kyun Lee
Original assignee: LG Caltex Oil Corp
Current assignee: LG Caltex Oil Corp
Priority date: 1996-11-08
Filing date: 1997-06-11
Publication date: 1998-05-13
Also published as: GB9712192D0; KR19980034778A

Abstract

A ferrofluid for removing oil from a water surface is prepared by adsorbing surfactant pref. sodium oleate on the surfaces of magnetic particulates such as magnetite (Fe 3 O 4 ) particulates prepared from an acid waste solution; preparing a dispersion of said magnetic particulates by dispersing said magnetic particulates with the surfactant adsorbed into an organic solvent; pref. crude oil kerosene, cyclohexane etc. and adding an amphipathic non-ionic surfactant to said dispersion of the magnetic particulates. A preferred non-ionic surfactant is polyoxyethylene nonylphenyl ether. The ferrofluid has an improved power to disperse oil on a water surface. By using such ferrofluid and an oil slick drawing apparatus equipped with the permanent magnets, the oil can be selectively and effectively removed and recovered without adversely effecting the ecosystem of the sea.

Description

TITLE OF THE INVENTION A Ferrofluid For Removing Oil On A Water Surface, And Processes For Preparation And Use Thereof BACKGROUND OF THE INVENTION The present invention relates to a ferrofluid for removing oil on a water surface, a process for preparing the ferrofluid and a process for efficiently removing and recovering oil on a water surface using the ferrofluid. More specifically, the present invention relates to a ferrofluid for removing oil on a water surface (hereinafter, frequently referred to as an "oil slick"), which has an improved dispersive power of magnetic particulates for the oil on the water surface by adding an amphipathic non-ionic surfactant to the dispersion of the magnetic particulates such as magnetites. Also the present invention relates to a process for preparing the ferrofluid and a process for effectively removing and recovering the oil on a water surface using such ferrofluid and an oil slick drawing apparatus equipped with permanent magnets, which thus helps to protect the environment.

Recently, thin films having the thickness of about 1.5 mm or thin oil slicks have been frequently formed on the sea by the discharge of oil due to large accidents of ships and at various oil reservoirs. The films and oil slicks freely shift on the water surface because of winds, waves and tidal currents. Thus, the sea is polluted by the oil. As a result, the sea is deprived of dissolved oxygen since the supply of oxygen is blocked. As a result, sea organisms die or their growth is suppressed. Further, some of the toxic substances and carcinogens which are contained in oil are dissolved in water. The ecosystem is destroyed and thus the livelihood of fisherman, as well as the growth of aquatic organisms are threatened, so that it is necessary to, by all means and rapidly, control the pollution caused by oil that is discharged by accidents and the like.

Therefore in order to protect the environment and control effectively the pollution resulting from accidental oil discharge, and in order to reuse the oil recovered, the study of processes for effectively removing and recovering the oil discharged due to the accidents, etc. has been steadily progressing hitherto.

The conventional processes for removing oil on a water surface, particularly the sea, include physical methods, chemical methods, and microbiological methods.

The physical methods include a method using oil absorbing cloth, a method using skimmers and the like.

The former requires a great deal of oil absorbing cloth and the latter has the disadvantage that the work for removing the oil is interrupted by floating materials, (RTM) for example styrofoamA,wood, etc. and a great deal of sea water must be sucked in an apparatus at the same time. Thus a large unit for separation of oil and water and a great deal of time is required [see, Kempa J., "Cleaning up oil spills esp. on water or beaches by treatment with powdered and/or porous gypsum option in the presence of water", DE 4108089 (March 13, 1991); and Gerald M. Dickel, "Spill containment system", US 5,004,372 (April 2, 1992) and "Method, system, ship and collecting device for oil spill recovery", US 5,015,399 (May 14, 1991)].

The chemical methods include a method spreading emulsifiers. Here, the emulsifiers spread emulsify oil to disperse it in the sea water or to precipitate it to on the bottom of the sea. The oil thus dispersed or precipitated largely has an adverse effect on sea organisms since a long time is required for the dissociation thereof and the oil acts as a factor in generating red water.

The microbiological method is to propagate microorganisms (bacteria) having the ability to intake and dissociate oil and to remove the oil. This method has many practical problems since the disturbance of the ecosystem of the sea is caused by the rapid propagation and extinction of the bacteria. Also, a long time is required to remove the oil. Using the present technologies, the complete removal of the discharged oil is next to impossible even though a great deal of money is invested.

BRIEF SUMMARY OF THE INVENTION Thus, the present inventors have conducted extensive and intensive studies to provide a new practical process capable of effectively removing and recovering only oil on a water surface without adversely effecting the ecosystem of the sea and without being interrupted by floating materials. As a result, the present inventors have found that when using a ferrofluid having an improved oil dispersive power of magnetic particulates by adding amphipathic non-ionic surfactant to the dispersion of magnetic particulates such as magnetites, the ferrofluid only is selectively absorbed in an oil slick, the oil slick is magnetized and thus the oil slick magnetized shift toward magnets when a strong magnetic field is applied thereto. Thus, the oil slick can be selectively removed and recovered.

The present invention has been completed based on these novel findings.

Therefore, it is an object of the present invention to provide a high performance ferrofluid which can be used effectively for removing and recovering oil on a water surface.

It is a further object of the present invention to provide a process for preparing said ferrofluid.

It is an another object of the present invention to provide a process for simply and effectively removing and recovering oil on a water surface using said ferrofluid, which thus helps to protect the environment.

The said objects and other objects, features and advantages of the present invention will be more distinctly understood by referring to the following detailed description of the present invention.

Percentages are by weight unless otherwise stated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING Hereinafter, the present invention will be described in greater detail from the following detailed description taken in connection with the accompanying drawings in which: Fig. 1 is an FT-IR spectrum showing the effect of the addition of polyoxyethylenenonylphenylether on the dispersive power of a ferrofluid containing 8% of moisture; and Fig. 2 is an oil slick drawing apparatus used in a process for removing oil on a water surface according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Generally, in order to effectively remove oil on a water surface the following three (3) conditions should be satisfied: 1) only the oil is removed without the incorporation of water; 2) a method removing oil slicks must help to protect the environment of the sea and not have an adverse effect on the ecosystem of the sea; and 3) the removal process should not be interrupted by floating materials.

A first aspect of the present invention is to provide a ferrofluid which can be used effectively to remove and recover oil on a water surface while satisfying all the above conditions.

An oil dispersant ferrofluid of the present invention is prepared by a process comprising the following steps of: providing magnetic particulates; adsorbing surfactant on the surfaces of said magnetic particulates; preparing a dispersion of the magnetic particulates by dispersing said magnetic particulates with the surfactant adsorbed into an organic solvent; and adding an amphipathic surfactant to said dispersion of the magnetic particulates.

A ferrofluid of the present invention is a colloid type solution having an improved oil dispersive power of magnetic particulates by adding amphipathic non-ionic surfactant to the dispersion of the magnetic particulates, and characterized by the property that the liquid and solid does not separate even under gravity and a magnetic field, and the solution itself seems to be magnetized. It is preferred that the ferrofluid is not absorbed into the water but easily absorbed into oil only, is strongly magnetized and is not expensive.

The magnetic particulates which can be used to prepare a ferrofluid of the present invention include ferromagnetic particulates such as magnetite particulate, which can be prepared by the known method passing chlorine gas, an oxidant, through a FeCl2 solution which is discarded after acid washing in an iron and steel factory (see, Example 1 described later).

It is preferred that the ferromagnetic magnetite particulates have the particle size of about 100 A.

Such ferromagnetic magnetite (Fe3O4) particulates are made hydrophobic by coating and chemically adsorbing a surfactant to the surface thereof, wherein the surfactants which can be used include fatty acid salts such as sodium oleate. The amount of the surfactants adsorbed on the surface of the magnetic particulates is 10% to 20% by weight with respect to the magnetic particulates.

The magnetite particulates thus changed to be hydrophobic by chemical adsorption of surfactants on the surface thereof is then dispersed in an organic solvent in a concentration of 5% to 20% by weight, preferably 5% to 10% by weight. Since a ferrofluid is precipitated in the water if the specific gravity thereof is greater than that of the water depending on the type of organic solvents used, it is an important factor to select a solvent for the ferrofluid which is easily miscible with oil. The examples of the organic solvents which can be used in the present invention may be, for example, crude oil, kerosene, cyclohexane, etc., most preferably crude oil.

Since the power of the dispersion of the magnetite particulates thus prepared to disperse oil slick is largely affected by the moisture content of the dispersion, a drying process may be conducted to control the dispersive power. If the dispersion of the magnetic particulates has a moisture content of about 10%, the power of the magnetic particulates to disperse an oil slick is largely decreased to about 50%. On the other hand, if moisture is completely removed, the magnetite particulates coagulate, and thus creating the problem that a process for crushing them using ball mill, etc.

is required. Thus, costs are increased. Accordingly, it is preferred that the moisture content in the dispersion of the magnetic particulates is maintained to be less than or equal to 10% by weight, preferably 5% to 10% by weight.

A ferrofluid of the present invention is prepared by adding an amphipathic non-ionic surfactant to the dispersion of the magnetic particulates prepared as described in the above. According to the present invention, when a non-ionic surfactant is added to the dispersion of the magnetic particulates, the coagulation phenomena of the magnetic particulates does not occur since the complete removal of the moisture from the dispersion of the magnetic particulates is not required before adding the non-ionic surfactant to the dispersion. A process is not needed to crush the magnetic particulates and the cost of the manufacturing the dispersion is reduced. Also, the power of the ferrofluid to disperse an oil slick is increased due to the complete removal of the moisture in the ferrofluid and thereby the ferrofluid can be efficiently dispersed into an oil slick to be effectively removed and recovered.

The examples of the amphipathic non-ionic surfactants which can be used to prepare the ferrofluid of the present invention include polyoxyethylenenonylphenylether (n=4), polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tristearate, etc.

Especially preferred is polyoxyethylenenonylphenylether, which is a non-ionic surfactant having 4 polyoxyethylene groups and increases the dispersive power of a ferrofluid by blending the moisture with the oil when moisture is present in an organic solvent.

The reason why the power of the ferrofluid comprising the moisture according to the present invention to disperse an oil slick is increased by polyoxyethylenenonylphenylether which is an amphipathic surfactant is that a hydrophilic, polyoxyethylene group is oriented toward the water and a hydrophobic, nonylphenylether group is oriented toward the organic solvent to offset the action of the water. As identified in Figure 1, the FT-IR spectrum shows that the polyoxyethylenenonylphenylether also removes the moisture attached to the surface of magnetite particulates.

The FT-IR spectrum in Figure 1 shows the effect of adding polyoxyethylenenonylphenylether on the dispersive power of a ferrofluid containing 8% of moisture. In Figure 1, when polyoxyethylenenonylphenylether is not added, O-H stretching mode due to the adsorbed water appears in the vicinity of 3500 cm1 and overall the adsorption peak of oleate appears strongly. When 4% (0.4 g) and 6% (0.6 g) of polyoxyethylenenonylphenylether is added, O-H peak due to the adsorbed water does not appear and the adsorption peak of oleate appears weakly, compared to when polyoxyethylenenonylphenylether is not added. The fact that the adsorption peak of oleate appears strongly when polyoxyethylenenonylphenylether is not added shows that a water soluble dual adsorbing layer is not completely removed even though the pH of the ferrofluid suspension is adjusted to from 5 to 6 and therefore it is difficult to obtain a monomolecular adsorbing layer. The reason why the adsorption peak of oleate appears weakly as polyoxyethylenenonylphenylether is added is that the dispersive power of a ferrofluid is increased as the oleate dually adsorbed is effectively removed and thus the monomolecular adsorption layer consisting of hydrophobic substances only is formed on the surface of magnetite. Also, the peak of the adsorbed water appears again when 10% (1.0 g) of polyoxyethylenenonylphenylether is added based on the weight of the magnetite and this phenomena occurs since polyoxyethylenenonylphenylethers which are present in excess associate each other and the water is not effectively removed. When 12% (1.2 g) of polyoxyethylenenonylphenylether is added, the phenomena appears more distinctly (not shown). The phenomena shows that the ferrofluid in which 12% (1.2 g) of polyoxyethylenenonylphenylether is added is absorbed partially into the water as well as adsorbed into the oil.

Therefore, the amount of an amphipathic surfactant added to the dispersion of magnetic particulates must be varied according to the moisture content of the ferrofluid, and the amount must be increased as the moisture content of the ferrofluid is increased. On the other hand, to remove oil on a water surface, the ferrofluid is selectively absorbed to the oil only and thus the oil is magnetized only when the surface of the ferrofluid is completely hydrophobic. If too much nonionic surfactant is added, a part of the ferrofluid becomes hydrophilic so that it is adsorbed to even the water as well as the oil. Therefore, it is important that the non-ionic surfactant is added to the ferrofluid comprising about 10% of magnetite in an amount of about 4% to 8% by weight with respect to the magnetite. For example, in the case of the corresponding oil dispersant ferrofluid containing 5% moisture (magnetite content: 10%), it is preferred that the amount of the non-ionic surfactant added is 4% by weight (0.4 g) to 6% by weight (0.6 g) per 100 ml of the ferrofluid, most preferably 4% by weight (0.4 g) per 100 ml of the ferrofluid. In addition, in the case of the corresponding oil dispersant ferrofluid containing 8% moisture (magnetite content: 10%), it is preferred that the added amount of the non-ionic surfactant is 4% by weight (0.4 g) to 12% by weight (1.2 g) per 100 ml of the ferrofluid, most preferably 6% by weight (0.6 g) per 100 ml of the ferrofluid. If the amount of the non-ionic surfactant added is more than the above amount, the dispersive power of the ferrofluid to the oil slicks is increased but the oil cannot be completely removed because the non-ionic surfactant is dispersed into the water as well as the oil when the ferrofluid is spread on the water surface.

Also, according to the present invention, the process for removing and recovering oil on the water surface using the ferrofluid as described above is provided.

The process for removing and recovering oil on a water surface according to the present invention comprises the following steps of: spreading the ferrofluid according to the present invention on oil on a water surface to magnetize the oil, floating an oil slick drawing apparatus equipped with permanent magnets on said magnetized oil slick; and recovering said oil slick drawn by the permanent magnets by rotating said oil slick drawing apparatus.

In the process for removing and recovering the oil on the water surface according to the present invention, the ferrofluid to be spread on an oil slick is used in an amount of 2% to 10% by volume based on the volume of an oil slick.

Figure 2 shows an embodiment of an oil slick drawing apparatus used in the process for removing and recovering oil on a water surface according to the present invention. In Figure 2, the reference numeral A (RTh) represents permanent magnet (neoma)g)l, the reference numerals B and G represent teflon/plate and the reference numerals C, D, E and F represent soft magnetic metal having high magnetic permeability such as yoke, pure iron, silicon steel plate. Specifically, this apparatus can be manufactured by coating a nonmagnetic polymer complex, which is not corroded by the sea water and is not substantially wetted by the water, on the surface of a soft magnetic, metallic cylinder having high magnetic permeability and then interposing permanent magnets having nonuniform magnetic fields such (RTM) as a neomagland a suction pump for drawing a magnetized oil slick drawn by the permanent magnets in the cylinder.

The examples of the nonmagnetic polymer complexes coated on said soft magnetic, metallic cylinder include preferably glass fiber reinforced plastics (FRP) which are not corroded by the sea water and are not substantially wetted by water. The permanent magnets must be protected from the sea water and oil slick by sealing the polymer complex with a sealant after the permanent magnets are interposed in the cylinder. The cylinder type oil slick drawing apparatus equipped with the permanent magnets according to the present invention is rotated and also, if required, moved in an up-anddown motion according to the direction of the waves on the water surface.

Hereinafter, the present invention will be more specifically illustrated by the following examples but the scope thereof is not limited in any way to the examples.

Example 1: Preparation of Ferrofluid FeCl3 was prepared by passing chlorine gas which is an oxidant through a solution of FeCl2 discarded after acid washing in an iron and steel factory by a conventional method. Then, 0.5 M FeCl2and 0.5 M FeCl3 was mixed in the ratio of 1.15:2 to prepare a mixture, which was charged into a reaction vessel. 1 M NaOH solution was added to the produced mixture with aeration using nitrogen gas and then the mixture was warmed to 60 OC while maintaining the pH of 11. Thereafter, the mixture was oxidized for 10 minutes by aeration with air (1.5 liter/min) instead of nitrogen gas to obtain the magnetite particulates having the average particle size of about 100 and the saturated magnetic susceptibility of about 60 emu/g.

After washing the product 5 times with water, 12 g of sodium oleate was added to 40 g of the magnetite particulates to give a mixture and the mixture was subjected to an adsorption reaction at about 90 0C for about 30 minutes. Then the surface of magnetite was made hydrophobic by washing the product of adsorption reaction with water after adjusting pH to 5 using 1N HC1 to eliminate physical adsorbed layers. The magnetite was filtered and dried below 100 OC until a small amount of the moisture remained, and then the magnetite was dispersed in crude oil to prepare 400 ml of a crude oil dispersant ferrofluid comprising 10% of the magnetite.

In the procedure, the moisture included in the dispersion of the magnetite was measured using a Karl Fisher moisture measuring apparatus. The results showed an 8% moisture content. The dispersive power of the magnetite dispersion was low, at about 50%, due to the effect of the moisture. Accordingly, to improve the power of the magnetite dispersion to disperse an oil slick, polyoxyethylenenonylphenylether having 4 polyoxyethylene groups which is an amphipathic non-ionic surfactant was added subsequently to 100 ml of the dispersion of the magnetite as illustrated in the following Table 1. The change of the dispersive power depending on the amount of polyoxyethylenenonylphenylether added was examined. The result is shown in Table 1.

Table 1. Dispersive power of crude oil dispersant magnetite dispersion depending on the amount of nonionic surfactant added

Sample Solvent of Moisture The amount of Dispersive No. ferrofluid content non-ionic power (O/o) surfactant added O 1 0 50 2 0.2 80 3 0.4 92 Crude oil 8% 4 0.6 96 5 0.8 96 6 1.0 96 7 1 1.2 96 As previously described, in order to remove crude oil on a water surface, the surface of the ferrofluid should be completely hydrophobic so the ferrofluid is selectively absorbed into the oil only and the oil slick is magnetized. As shown in Table 1, when the ferrofluid was prepared by adding 0.6 g of non-ionic surfactant to 100 ml of the crude oil dispersant magnetite dispersion containing 8% of the moisture (sample 4), it was possible to prepare a ferrofluid having a 96% of the power to disperse an oil slick even though the crushing process of the magnetite was omitted. Also, it was shown that the dispersive power was not increased but constantly maintained even though the amount of nonionic surfactant added was increased to 1.2 g.

Therefore, in order to remove crude oil on a water surface using the ferrofluid according to the present invention, prepared by adding non-ionic surfactant to the dispersion of the magnetic particulates containing 8% of the moisture, it will be understood that polyoxyethylenenonylphenylether (n=4) in an amount of preferably 0.4 g to 1.2 g, especially 0.6 g per 100 ml of magnetite dispersion is most suitable.

Example 2 To a water bath having the dimension of length 180 cm x width 120 cm x height 60 cm, water was poured to about 2/3 of the water bath height, 1,000 ml of crude oil was spread on the surface thereof, and then a current was caused using a submarine pump. Then, 100 ml of the ferrofluid sample prepared in Example 1 was spread on the water surface on which the crude oil was spread. Separately, a soft magnetic FRP cylinder made from a silicone steel plate having the dimension of 160 cm (diameter) x 180 cm (length) and having a suction (RT) pump interposed was equipped with 36 neomag/permanent magnets having the dimension of 15 mm x 40 mm x 10 mm on the side surface thereof and was coated with a sealant to manufacture an oil slick drawing apparatus of the present invention. (Figure 2). The cylinder type oil slick drawing apparatus was floated on the water surface with the oil on which the ferrofluid spread, and was rotated in the direction of the current at the velocity of about 30 rpm. The crude oil drawn by the magnets was recovered using the suction pump interposed in the cylinder. 950 ml of the oil as well as about 10 ml of the water were recovered when this work was conducted for about 10 minutes. Thus, it was shown that the recovery rate of the oil by means of the process of the present invention was about 95%. Since the most of the residual oil is adsorbed on the wall of the water bath and the like, it can be understood that the recovery rate of the oil is practically more than 95%.

Example 3 To determine the amount of the ferrofluid added to the oil on the water surface, a water bath equipped with the 3,000 Gauss permanent magnets on the both sides thereof (100 mm x 100 mm x 300 mm) was charged with the water to about 2/3 of the height thereof, and 10 ml of crude oil was spread on the water surface. Sample 4 of the ferrofluid prepared in Example 1 was added to the water bath in the amount of 1%, 2%, 4%, 6%, 8%, 10% and 12% by volume with respect to the crude oil, respectively. After 1 minute without stirring, the removal rate of the crude oil was measured. The results are shown in Table 2.

Table 2.

The The amount of ferrofluid Removal rate of the crude added (ml) oil (%) 0.1 60 0.2 80 0.4 96 0.6 100 0.8 100 1.0 100 1.2 100 As shown in Table 2, when the ferrofluid was added in the amount of 1% by volume (0.1 ml) and 2% by volume (0.2 ml) with respect to the crude oil, the oil was not completely removed. When the ferrofluid was added in the amounts of 4%, 6%, 8%, 10% and 12% by volume, substantially all of the oil was removed. Therefore, to remove the crude oil spread on the water surface, the ferrofluid of the present invention must be added to the crude oil in an amount of 4% by volume or more. In this regard, it is shown that the removal rate of the oil slicks is not increased even though the amount of the ferrofluid added exceeds over 10% by volume.

As described in the above, an oil dispersant ferrofluid according to the present invention has an improved power to disperse oil on a water surface by adding an amphipathic non-ionic surfactant, and shortens the procedure for removing the oil since the complete removal of the moisture in the ferrofluid is not required, thereby lowering costs. Also, by using such ferrofluid and an oil slick drawing apparatus equipped with permanent magnets, oil can be selectively and effectively removed and recovered without adversely effecting the ecosystem of the sea. Also, the process is not interrupted by floating materials when the sea is polluted due to accidents involving the discharge of oil from ships, etc.

Claims

1. A process for preparing an oil dispersant ferrofluid for removing oil on a water surface comprising the steps of: providing magnetic particulates; adsorbing surfactant on the surfaces of said magnetic particulates; preparing a dispersion of the magnetic particulates by dispersing said magnetic particulates with the surfactant adsorbed thereon in an organic solvent; and adding an amphipathic non-ionic surfactant to said dispersion of magnetic particulates.

2. The process according to Claim 1, wherein said magnetic particulates are magnetite particulates prepared from an acid waste solution.

3. The process according to Claim 1, wherein said organic solvent is selected from the group consisting of crude oil, kerosene and cyclohexane.

4. The process according to Claim 1, wherein said nonionic surfactant is polyoxyethylenenonylphenylether.

5. The process according to Claim 4, wherein said nonionic surfactant is added to said dispersion in an amount of 0.4 to 1.2% by weight per 100 ml of the total ferrofluid.

6. An oil dispersant ferrofluid for removing oil on a water surface prepared by the process of any one of Claims 1 to 5.

7. A process for removing and recovering oil on a water surface, e.g., an oil slick, comprising the steps of: spreading the oil dispersant ferrofluid of Claim 6 on an oil slick to magnetize the oil slick; floating an oil slick drawing apparatus equipped with permanent magnets on the magnetized oil slick; and recovering the oil slick by rotating the oil slick drawing apparatus wherein said recovery is characterized in that the permanent magnets draw the magnetized oil slick.

8. The process according to Claim 7, wherein the oil dispersant ferrofluid is spread in an amount of 4% to 10% by volume with respect to the oil slick.

9. The process according to Claim 7, wherein said oil slick drawing apparatus comprises a soft magnetic, metallic cylinder having high magnetic permeability, the surface of which is coated with a nonmagnetic polymer complex, permanent magnets having nonuniform magnetic field and a suction pump.

10. The process according to Claim 7 or 9, wherein said oil slick drawing apparatus is further capable of upand-down motion according to the direction of the waves of the water surface.

11. An oil dispersant ferrofluid for removing oil from the surface of water, which comprises a dispersion of magnetic particulates in an organic solvent and additionally contains an amphipathic non-ionic surfactant.