WO1993014034A1

WO1993014034A1 - Composition for oil removal

Info

Publication number: WO1993014034A1
Application number: PCT/GB1993/000036
Authority: WO
Inventors: Harry James Bradbury
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-01-08
Filing date: 1993-01-08
Publication date: 1993-07-22
Anticipated expiration: 1994-07-08
Also published as: AU3263293A

Abstract

There is disclosed a composition for removal of oil from oil-contaminated media, for example the sea. The composition comprises an oil-sorbant and a sealer-binder and the oil is retained within the composition. Optionally the composition may include a dense component so that the oil-sorbed composition can sink through a liquid medium, becoming a sediment and thus removing the polluting oil.

Description

COMPOSITION FOR OIL REMOVAL

The present invention relates to compositions for removal of oil, especially from oil-contaminated media, for example in oil slicks.

Oil spills on water and land are common environmental problems. Oil spills on water are normally dealt with by some combination of mechanical action (eg. skimmers and booms) and the use of surfactants to act as dispersing agents. In some cases, other materials have been used to sorb oils at the surface of the water. For example, silica beads (sometimes impregnated with agents which cause oxidation of hydrocarbons) have been used to sorb oils into a floating structural mat.

In the natural environment, current techniques of oil clearance have certain drawbacks. For instance, the use of mechanical means of removal of oils, especially crude oils, proves difficult in hostile or remote environments, and is an expensive process. In the case of surfactants, long-term damage to an ecosystem can occur through dispersion of hydrocarbons throughout the upper levels of a water column, and can lead to future coalescence of once dispersed slicks during their resurgence, itself leading to further environmental pollution. In relation to sorbants, most sorb oils at or near the surface of an oil slick, and prove ineffectual in tackling anything other than thin-film hydrocarbon slicks. Moreover, the effective sorbability of such materials can be impaired by water-wetting. In all such current techniques of oil spill clearance from a water medium, there is the inherent difficulty that treatment is a water surface phenomenon which often does not remove hydrocarbons from the water system swiftly and in a manner which arrests the flow of a slick and its attendant contamination of surface environments.

It has now been found that a composition comprising both an oil sorbant and a sealer-binder is able to remove oil from oil-contaminated media and retain the removed oil within the composition. Use of the composition according to the invention permits quick and easy oil-removal and minimises potential for environmental damage resulting from the continued presence of the oil.

In the context of the present invention, the term "oil" refers to any type of crude or refined oils which are, or are derived from, naturally occurring mineral oils or vegetable matter, or their synthetic equivalents.

The tem "sealer-binder" refers to a material which causes the sorbed oil to be sealed into or bound to the composition. Thus, oil sorbed by the composition of the invention is inhibited from leaching back into the surrounding medium.

It is a feature of the invention that the composition as disclosed herein is non-toxic to marine or freshwater life in both its unsorbed and oil-sorbed state when judged by standard tests.

Where oil is to be cleared from a liquid medium, for example the sea, the composition of the invention is able to rapidly sorb oils to create a hydrocarbon-soaked mass which may be harvested at or near the surface of a water within a short period after application if such harvesting is technically achievable or desirable. In the absence of such harvesting the reacted mass may be engineered to sink under gravity through the water, to create a non-toxic sediment at the base of the water column. By this action oil spills can be treated in a timely manner (restricting their ability to spread at or near the surface of the water column which would create thereby extensive environmental damage of surface waters, coastal environments, installations etc.) and in a manner so as to remove from the water column long- term, free oils which might otherwise escape to damage the ecosystems within or subjacent to a water mass, or the biomass which such ecosystems support.

Furthermore, the composition of the present invention may be developed to include structural porosity. Porosity is required for optimisation of the sorptive capacity of the product once granulated. Granulation is preferred in order to aid such sorbability, and to customise the product for ease of application, both ease of mechanical application and optimisation of surface action for such sorption. Structural porosity can be created by a number of mechanisms, but is conveniently provided by oleophilic wetting of the granules during preparation and the subsequent controlled drying to create void space. Care must be taken wherever possible to preclude the induction of fracture porosity during granule manufacture, since this type of structural porosity inhibits effective sorption of oils in a manner which also allows micro-encapsulation and sealing.

Where a fibrous sorbant is used internal porosity may be created whereby an internal void space is created by the fibrous structure of the sorbant and this may accommodate approximately 40% of the overall porosity requirements. Overall it is desirable that approximately 75% porosity be achieved within the fibrous composition if granulated, such porosity being provided in the two ways mentioned above.

The granules themselves may be variable in shape and size depending on the application, but should reflect wherever possible the need to optimise surface area for sorption of oil without creating a volume which might inhibit reaction time unduly by floating and soaking oils within a slick. Relatively small (preferably less than 5cm diameter granules) of quasi- spherical shape are convenient. The material density of the composition can be varied by adjustment of the relative volume proportions of the components, for example sawdust and cement (optionally with the inclusion of other minor ingredients as stated below) , and the effective density of the granules can be varied by adjustment of the structural porosity. With a granule density in the order of 0.2, maximum sorption of oil can lead to a reactant density which promotes sinking of the granule through the water column. However, variation of material and granule primary densities, adjustment of structural porosity and modification of void geometry and effective capillary dimension have proved effective in creating granules which remain buoyant even after reaction with oils. This application has merit in situations where harvesting of the reacted mass is required as opposed to the unattended oil removal to a sediment mass. Buoyant oil clearance materials are useful for manufacturing barrier devices to act as protective or remedial soak-structures to prevent spread of oils at or near the surface of a water column. In addition to the ability to modify the composition to form buoyant variants, adjustments can also be made to optimise the composition for marine (or other waters) conditions which are variable from place to place, and/or from time to time, in factors such as temperature and salinity, and variations in the different types of oils and their physico-chemical characteristics, such as viscosity.

The sorbant used in the composition must be able to rapidly and effectively remove crude or refined oils and silicon carbide (SiC) in any crystallographic form or variation is a suitable sorbant. Silicon carbide is commonly used as an industrial abrasive, and is normally produced through combustion of silica (often derived from sand) with carbon in a furnace at around 2000°C. With respect to treatment of water pollution, the structural and crystallographic state of the silicon carbide can be variable, but where possible, the chemistry should preclude possible furnace impurities such as iron oxide. The tolerable mean grain size of silicon carbide used in the water pollution product varies according to the type of hydrocarbon or other oils being treated, but normally falls within the range^' 50 to 450 microns. Metallurgical grade (or higher grade) silicon carbide normally processed to a mean grain diameter of less than 100 microns (but preferably less than 40 microns) has proved particularly effective in its sorbancy of crude oils of differing viscosities and chemical characteristics, as typified by crudes from the Brent field, Nigeria and the Urals.

Other synthetics of similar grain size, sorbancy and density could be used in substitution. Alternatives such as zirconium based sands and synthetics and fused and activated alumina have been used, although silicon carbide has proved more effective.

In addition to synthetics, certain natural materials have proved to be possible substitutes, although not as effective sorbants as silicon carbide. Of these, calcareous mudstones, marls and micrites from turbidite sequences have been utilised, the principal components of which have been carbonate-quartz assemblages at mineral grain sizes often less than 10 microns. For example mineralogical assemblages of siliceous and carbonaceous micritic limestone, being principally quartz, calcite and carbonaceous material in varying proportions (for example, 60% calcite, 30% quartz and 10% carbonaceous material) or its coarser grained equivalents such as calcareous siltstones, or calc-arenites are suitable sorbants. For convenience, this range of lithological variants (micrite, calcareous siltstone and calc-arenite) are combined into the term "micrite" for purposes of this document, a term which is used hereinafter. Variation may exist in the Ca, Mg and Fe composition of carbonate minerals which constitute micrite without detriment to its effectiveness.

The micrite will be in fine-grained, powdered form having undergone milling by a standard rock crushing and grinding process without prior physical or chemical separation of mineralogical components save for the selection of preferred rock types. During experimentation (as noted below) use has been made of the micrite prepared in this manner. However, use has also been made of powdered micrite created by selective drilling of hand samples of rock materials. The tolerable mean grain size range for the powdered micrite varies between 10 to 100 microns grain diameter for use with 'lighter' hydrocarbon fractions, whereas grain sizes up to 400 microns may be required for 'heavier' hydrocarbon fractions (it should be noted that the term "micrite" has no geological meaning at such coarse grain sizes, and is used here for simplicity of description) . The optimal grain size for micrite is dependent on the type of hydrocarbon.

The sorbant can constitute up to 60% of the composition but is often optimal at around 30%.

The sealer-binder may be, for example, mineralogical assemblages of dolomitic carbonate including Ca, Mg and Fe variants (hereinafter collectively termed "dolomite") , and, for certain treatments, siliceous dolomite including metamorphic equivalents of greenschist and amphiboloite facies metamorphic zones, which include calc-silicate mineral assemblages.

The dolomite will be in fine-grained, powdered form having undergone milling by a standard rock crushing and grinding process without prior physical or chemical separation of mineralogical components save for the selection of preferred rock types. Use has also been made of powdered dolomite created by selective drilling of hand samples of rock materials. The tolerable mean grain size range for the powdered dolomite can vary from 25 to 300 microns, and is preferably in the range 150 to 250 microns for heavier fractions. Powdered dolomitic carbonate at a mean grain size normally less than 100 microns (and preferably less than 40 microns) has proved effective in acting as a sealer-binder during migration of the material product/oil-reacted mass and in its settled state as a sediment.

The proportion of dolomite within the composition is variable dependent on the type of hydrocarbon or other oil. Generally, the dolomite proportion falls within the range 5 to 35%. Where calc-silicates are included in the formulation, the dolomite proportion can fall by up to 10%.

In other formulations, as considered below, different materials act as sealer-binders, and may substitute for dolomitic carbonate. Thus, as discussed below, in some embodiments cement may function as a sealer-binder.

The composition may further possess the ability to sink through a liquid contaminated medium thus removing the contaminating oil from the system affected. For this purpose the composition should be denser than the contaminated medium. Where the components, for example the sorbant or sealer-binder materials, are naturally dense the required effect will occur automatically. This is the case for silion carbide. However a dense carrier material may be added to the composition to achieve the required density.

The composition may also comprise an agent which act as a natural surface tension reducing agent which allows limited but controlled dispersion of oils during the period of sorption thus allowing increased opportunity for composition-oil interaction. In some compositions a component which also acts as a sorbent or sealer-binder may also cause surface tension release in the required manner. A suitable surface tension releasing agent is the feldspathic component of granitoid rocks (seπs foto) normally at a grain size less than 50 microns, which has proved effective in controlled dispersion of oil films, by progressive reduction of surface tension during break-up of the film on application. As defined here, granitic and granitoid rocks includes both igneous rocks such as granite and granodiorite and deformed and undeformed metamorphic mineralogical and chemical equivalents of feldspathic granites (eg. granitic gneiss, augen gneiss, blastomylonite or leucocratic migmatitic variants) . Also as defined here, granitic and granitoid rocks refers to textural variants such as pegmatities, microgranites and phenocrystic granites or granitoids as well as referring to textural variants of metamorphic and/or deformed equivalents such as porphyroblastic gneisses (especially containing feldspar porphyroblasts) and augen mylonites. It has proved convenient to mill feldspathic granitoids to a mean grain size of less than 100 microns for use without separation of the feldspathic component specifically.

The oil is preferably micro-encapsulated within the composition either during or following sorption. A combination of silicon carbide and powdered dolomitic carbonate is an example of material product able to micro-encapsulate the oil.

In one preferred aspect, the composition is able to promote degradation of the sorbed oil over a long-term period ie. over a period of years to produce dispersable, non-toxic components to add to the natural background sediment at the base of a water column, preferably over a time-frame greater than that during which it might be anticipated that anaerobic or aerobic natural (or induced) biological activity would degrade any encapsulated residual hydrocarbons which remain from the initial reaction. This can be achieved by including within the composition an energy supply or stimulus for oil-degrading micro-organisms. An example would be a sucrose-fructose-glucose and/or amino acid mixture.

One embodiment of the invention which has proved effective is an admixture of silicon carbide and dolomitic carbonate, blended together in a volume ratio whereby silicon carbide predominates. Inclusion of powdered granitoid assemblages, or their equivalent may reduce the volume of silicon carbide to less than 50% of the product mixture. The silicon carbide-dolomite +/- granitoid components are blended together after separate pre-preparation of milled grain-size fractions, or undergo coeval milling to an appropriate mean grain size after admixture. Whether or not this composition requires secondary treatment depends on the use to which the admixture is put. For example, to avoid the need for stratification of relatively less dense and more dense components in transit after manufacture, in storage, or during application, it has proved effective to granulate the formulated product prior to application, especially with a coating which is appropriately oleophilic and preferably hydrophobic.

In another embodiment of the present invention, the composition comprises sawdust derived by granulation of wood shavings to a powdered state (and preferably to a mean flake size less than 100 microns) as the sorbant. The sealer-binder is conveniently provided by Portland cement or its equivalent. The ratio of sawdust to cement volume is tolerated within the range allowing sawdust to comprise up to 80% of the material volume, depending on the needs for buoyancy. Sorbability and retentivity of encapsulated oils may be enhanced by the incorporation into the composition of up to approximately 15% by material volume of silicon carbide at a mean grain size of less than 100 microns (and preferably less than 40 microns) , or an equivalent of silicon carbide as discussed earlier.

The sorbability of the sawdust/cement composition is satisfied (probably by capillary action and adsorption) by the combined effects associated with the presence of sawdust itself and the overall porosity created in manufacture of granules. A nucleation site may be provided by the presence of sawdust/cement granules rather than by the individual components or combination of components in the dispersion of grains through an oil layer. A density carrier is formed by reaction between the sawdust/cement granules and the oil into which they are placed, or which interacts with such granules. The granules are able to float on water in the absence of oils, then to react with oils which themselves float on water and which come into contact with the granules, and, progressively sorb oils over a period which can be adjusted to suit the needs of the environmental situation faced (but normally ranging from a few minutes to a few hours) creating a reacted product, still in granular form, the new composite density of which induces settling of the granules through the water column and the creation of sediment. Therefore, the eventual settling of the reacted oil- soaked mass is promoted by density changes which occur through reaction between the granules and oil rather than deriving initially from the primary density of one or more components of the product mix (such as silicon carbide) . Thus, the sawdust/cement composition, suitably coated with a hydrophobing agent may be applied either to the surface of an oil slick or as a preventitive boom at the surface of a water column which will or might become contaminated with such an oil slick within the near future (within a period normally less than one calender month) . Barrier type devices which in part or in whole, use as their make-up mats or other geometries of granules essentially similar to the formulation defined here, are regarded as falling within - li ¬ the aegis of the present invention.

In this case, controlled dispersion is redundant since the granulated product is effective in breaking surface tension during downward migration of individual granules. Micro-encapsulation is accommodated in the first instance chiefly by the structural porosity of the engineered granules, and. is aided by secondary actions associated with sealer-binder effects. Both during settling and sedimentation (sensu bio), cement acts as an effective sealer-binder. Moreover, the inclusion of cement has further benefits in entombing any micro- encapsulated oils within the porosity of the granules, since, in marine waters, cement reacts with water within a short period of time (a maximum of a few days) to create a protective carapace of calcium carbonate which encrusts the sedimented granules (and thereby the granular mass) and prevents escape of oil components from the internal parts of the granules.

The long-term degradation of the two embodiments described above is built into the construction of the products. Individual grains are more likely to undergo early dispersion, and sawdust will undergo eventual water-softening with loss of structural integrity of the granules themselves.

It has proved beneficial to use a one to one relationship by volume of composition to oil for complete removal of the oil, although dependent on the thickness of the oil layer floating on the water medium, and the viscosity of the oil, lower volumes are also possible.

According to a further aspect, there is thus provided a composition according to the invention designed for oil clearance from solid substrates, including the surface of land and man-made surfaces. In most situations, the dominant requirements are those of sorbability, micro-encapsulation, sealing-binding, and possibly promoted oil degradation. A silicon carbide content in excess of 50% of the composition and at mean grain sizes of preferably less than 200 microns, allows rapid sorption of oils to produce a reacted material the consistency of which can be varied to a sludge or a solid granular mass dependent on the volume of product applied in relation to a fixed volume of oil, and according to need. In the case of semi-solid or solid masses so created, reacted materials may be mechanically excavated or otherwise removed from the solid substrate and used as solid fuel in some appropriately designed combustion device, which if controlled at temperatures less than 2000°C may be designed to recover and recycle silicon carbide for reuse. This feature of product recoverability and the development of soil fuel from the composition is a further feature of the invention.

Where an increased volume of composition is applied to a fixed volume of oil, the fla mability of the oils within the sorbed and reacted mass is reduced. Therefore, such a formulation has utility in all situations which require low-flammability in routine or emergency situations. In emergency situations, defense or environmental protection usage is possible. The compositions can be used for rapid immobilisation of oils spilt essentially on solid media, such as the emergency containment of oils within tankers, the oil from which might otherwise enter the environment inadvertently, or as precautionary measures which might be prudent prior to sluicing oils from the bilges of ships or in the deployment of protective barriers against oil spills or fires which could ensue.

The following, non-limiting, examples illustrate the composition of the invention. All percentages given are by volume.

Example 1

60% silicon carbide (45 μ mean grain size) and 25% dolomitic limestone (50 μm mean grain size) , 15% feldpathic microgranite (100 μm mean grain size) .

Experimental procedure and observations:

20 mis of Brent crude oil was poured onto the surface of a water column (20°C) in a one-litre measuring cylinder to create an oil layer approximately 6 mm thick. The water pollution produced was mixed into the correct composition from the individual components and 20 mis was applied to the surface of the oil through a sieve with a mesh size of 150 μm. The water pollution product was gradually taken into the oil layer to form a coagulated matrix on the surface of the water column, from which flakes detached and passed downward through the water and settled by gravity at the base of the cylinder. This coagulation and settling process took approximately 8 minutes. The sedimented flaked mass was stable and showed no signs of disintegration or release of the crude oil. The water was free of residual oil components.

Example 2

15% calcareous marl (50 μm) , 50% silicon carbide (50 μm) and 35% dolomitic limestone (100 μm) .

Experimental procedure and observations:

1 ml of automobile engine oil were applied to the surface of warm (30°C) , saline (20 g/1 NaCl) water to form a circular slick with a diameter of approximately 25 mm and a maximum thickness of approximately 1.5 mm. The product was mixed into the correct composition from the individual components and 0.8 mis was applied evenly across the surface of the slick through a sieve with a mesh size of 125 μm. The product gradually soaked into the oil, forming an amorphous matrix and encrusting the bottom and edges of the slick to retain the original surface shape, while bulging below at the lower water- oil interface. After approximately 5 minutes from addition of the water pollution product, the matrix sank rapidly as it contacted the lower oil-water interface, descending in an aggregated mass in a plughole effect to the base of the container. The sedimented matrix remained aggregated and stable, with no release of oil. The water was free of residual oil components.

Example 3

65% sawdust (50 μ ) , and 35% Portland cement (<50 μm)

Experimental procedure and observations:

Hardwood sawdust was milled and sorted to a mean flake size of approximately 50 μm, and physically mixed with dry Portland cement in the volume proportions given. Sufficient ethanol was then applied to the admixture to allow agglomeration to take place within the wetted medium, which was then placed in an appropriate mould which allowed creation of product granules with a mean diameter of approximately 1 cm, and slowly baked for approximately one hour at a mean temperature of approximately 80°C to volatilise the ethanol and leave structural porosity.

15 mis of Brent crude oil was poured onto the surface of a water column of warm (25°C) saline (32 g/1 NaCl) water in a glass tank to create an oil layer approximately 5 mm thick. 12 granules of the product was applied to the surface of the slick. After approximately 7 minutes, the first of the reacted granules began to sink through the water column, the last granule sinking within approximately 12 minutes from the start of the experiment. The sedimented granules formed a discrete unit at the base of the water column, and displayed no evidence of release or hydrocarbons into the water column. After approximately two days, a surface coating began to encrust the sedimented granules. Example 4

Water pollution product formulation:

25% granite (300 μm) , 60% silicon carbide (420 μm) and

15% dolomitic limestone (300 μm)

Experimental procedure and observations:

10 mis of Brent crude oil was poured onto the surface of a water column (20°C) in a one-litre measuring cylinder to create an oil layer approximately 3 mm thick. The water pollution product was mixed into the correct composition from the individual components and 20 mis was applied to the surface of the oil through a sieve with a mesh size of 350 μm. The water pollution product was gradually taken into the oil layer to form a coagulated matrix on the surface of the water columr from which flakes detached and passed downward thrc sύ the water and settled by gravity at the base of the cylinder. This coagulation and settling process tc approximately 30 minutes. The sedimented flaked mass was stable and showed no signs of disintegration or release of the crude oil. The water was free of residual oil components.

Example 5

Water pollution product formulation:

35% granitic gneiss (100 μm) 40% silicon carbide (50 μm) and 25% dolomitic limestone (100 μm)

Experimental procedure and observations:

4 drops of automobile engine oil were applied to the surface of warm (40°C) , saline (10 g/1 NaCl) water to form a circular slick with a diameter of approximately 15mm and a maximum thickness of approximately 1.5mm. The water pollution product was mixed into the correct composition from the individual components and 0.4 mis was applied evenly across the surface of the slick through a sieve with a mesh size of 125 μm. The product gradually soaked into the oil, forming an amorphous matrix and encrusting the bottom and edges of the slick to retain the original surface shape, while bulging below at the water-oil interface. After approximately 3 minutes from addition of the water pollution product, the matrix sunk rapidly as it contacted the lower oil-water interface, descending in an aggregated mass in a plughole effect to the base of the container. The sedimented matrix remained aggregated and stable, with no release of oil. The water was free of residual oil components.

Claims

Claims :

1. A composition which in use is able to remove oil from oil-contaminated media and retain it within the composition, said composition comprising

a) an oil-sorbant and . b) a sealer-binder.

2. A composition as claimed in claim 1 which in use has a density greater than the medium to which it has been applied.

3. A composition as claimed in either of claims 1 and

2 wherein the oil sorbed is micro-encapsulated by said composition.

4. A composition as claimed in any one of claims 1 to

3 comprising a nucleation site for oil sorption.

5. A composition as claimed in any one of claims 1 to

4 comprising a surface tension reducing agent for oil films.

6. A composition as claimed in any one of claims 1 to

5 comprising an oil degrading agent.

7. A composition as claimed in any one of claims 1 to

6 wherein said oil sorbant is selected from silicon carbide, zirconium based sand or synthetics, fused or activated alumina, calcareous mudstones, marls, micrites, or a mixture thereof.

8. A composition as claimed in claim 7 wherein silicon carbide, or a silicon carbide containing mixture, is said oil-sorbant.

9. A composition as claimed in any one of claims 1 to 6 wherein said oil-sorbant is sawdust.

10. A composition as claimed in any one of claims 5 to

9 wherein the feldspathic component of granitic rocks is said surface tension reducing agent.

11. A composition as claimed in any one of claims 1 to

10 wherein powdered dolomitic carbonate is said sealer- binder.

12. A composition as claimed in any one of claims 1 to 10 wherein cement is said sealer-binder.

13. A composition as claimed in any one of claims 1 to 12 in the form of granules provided with an oleophilic and/or hydrophobic coating.

14. A method of removing oil from an oil-contaminated medium, said method comprising administration of a composition as claimed in any one of claims 1 to 13 to said oil and, optionally, removing the oil-soaked composition once sorption is complete.

15. A method as claimed in claim 14 wherein said oil contaminated medium is sea water.

16. Use of silicon carbide as a sorbant for oil in the removal of oil from an oil-contaminated medium.