The present invention relates to methods, uses and kits for removing aromatic compounds from a hydrocarbon fluid. In particular, the present invention relates to methods, uses and kits for removing polycyclic aromatic hydrocarbons, such as polynuclear aromatic hydrocarbons, from a hydrocarbon fluid. The methods, uses and kits may be used to prevent the build-up of soot and sludge in the lubricant system of an internal combustion engine.

Background of the Invention

Engine lubricating oils perform many functions. Some of the main functions include wear protection, engine cooling and contaminant dispersion. However, the build-up of both soot and sludge in the oil may hinder the oil in its function of these primary tasks.

Soot is widely believed to be an agglomeration of carbonaceous structures in engine lubricating oils, which may be graphitic in nature. These carbonaceous structures are believed to be polycyclic aromatic hydrocarbons (PAHs), i.e. molecules containing at least 2 aromatic rings which may or may not be fused together to form one, larger aromatic system. The molecule may also contain further functional groups such as alcohols, ketones and carboxylic acids, as well as various nitrogen containing functional groups, such as nitro groups.

PAHs may be formed during combustion processes in internal combustion engines in combustion regions which are locally rich in fuel. The PAHs may transfer into the lubricant via incorporation in blow-by gas travelling past the piston ring and liner region of the engine.

Soot is believed to develop in stages, starting with the nucleation of PAHs and leading to particles having a size of from 20 to 100 nm. These particles will typically contain about 1 million carbon atoms, and have a C:H ratio of from about 8:2 to about 9:1. These soot particles can then either grow from addition of further aromatic samples to a particle, defined as surface growth, or combine with other particles via agglomeration mechanisms. By further agglomeration, networks of soot particles can form which can immobilise sections of oil up to 25 μηι across.

The presence of soot in lubricants presents several challenges. Firstly, soot particles can be abrasive, and so undispersed soot may lead to large amounts of abrasive wear

within an engine, greatly decreasing engine lifetime. Secondly, soot may thicken the lubricant. This can lead to several problems such as oil starvation via blocking of engine oil filters (which are designed to remove metallic wear particles), or reduction in engine cooling via reduced oil flow. Soot-induced oil thickening can also lead to increased fuel consumption in an engine.

Sludge is defined as a viscous and gelatinous phase in an engine lubricating oil, widely believed to be a water-in-oil emulsion containing oxidised and nitrated partially burnt fuel, along with lubricant degradation products and polar lubricant additives. Several studies have shown the prevalence of water in engine sludge as well as the prevalence of nitrated species. Polycyclic aromatic hydrocarbons (PAHs) are believed to be implicated in the mechanism of sludge formation.

Development of engine sludge can be harmful for an engine for several reasons. Firstly, additives can be sequestered into the water phase, thereby depleting the oil of additives and leading to problems owing to reduced additive concentration and oil-drain interval. This problem may take several forms including increased wear, increased acid build-up and increased oil oxidation. Secondly, sludge can lead to the oil thickening, greatly increasing the fuel consumption of the vehicle. Thirdly, sludge can develop to such an extent that it blocks oil filters, leading to oil starvation throughout the engine, rendering the requirement for immediate engine maintenance. In addition, the prevalence of water in the sludge may lead to increased metal corrosion throughout the engine, decreasing the vehicle lifetime.

To reduce the negative impact of both soot and sludge, dispersants are added to engine lubricating oils. Dispersants are generally based on polyisobutene polyamines or polyisobutene succinic anhydride polyamines. However, the use of dispersants in an engine lubricant may have unwanted consequences. For instance, the dispersants may interact negatively with elastomer materials found in automotive engines. Moreover, the dispersants may greatly increase the viscosity of the engine lubricant, particularly the cold-temperature viscosity. This can impact the fuel efficiency of the engine.

Dispersants do not remove soot particles or sludge from lubricants. Instead, they mitigate many of the problems associated with both soot and sludge by stabilizing soot as smaller, dispersible particles with a reduced tendency to agglomerate. However, dispersants are only able to deal with a finite level of soot or sludge before they are

overwhelmed, enabling soot agglomeration and sludge formation to occur on a large scale with concomitant negative impacts. Moreover, the amount of dispersant that can be added to a lubricant is limited because of the unwanted effects that are mentioned above of elastomer incompatibility and lubricant thickening.

There is therefore a need for methods for controlling soot and sludge levels in a lubricating oil which does not rely on a physically active filter media or on the addition of further dispersants.

US 4,977,871 describes a method for removing polynuclear aromatics from used lubricating oils. The method involves the use of a sorbent, preferably activated carbon, to remove the polynuclear aromatics.

US 5,225,081 also describes a method for removing polynuclear aromatics from used lubricating oils. The method involves using a filter system which comprises a

thermoplastic binder such as nylon and a chemically active filter media, a physically active filter media, or a mixture thereof. The physically active filter media, as with US

4,977,871, is preferably activated carbon and is disclosed as suitable for removing polynuclear aromatics. The chemically active filter media may comprise strong bases such as magnesium oxide, sodium hydroxide, zinc oxide or mixtures thereof and are disclosed as suitable for removing soot.

Further use of activated carbon to remove polynuclear aromatics from used lubricating oils is disclosed in US 5,042,617.

Summary of the Invention

It has now been appreciated that particular solid-phase polymers may be used to sequester aromatic compounds, such as polycyclic aromatic hydrocarbons, from a lubricant and other hydrocarbon fluids.

Accordingly, the present invention provides a method for removing aromatic compounds from a hydrocarbon fluid, the method comprising contacting the hydrocarbon fluid with a solid-phase polymeric material, the solid-phase polymeric material comprising a cross-linked polymer containing aromatic groups.

Also provided is a method for preventing the build-up of soot or sludge in a system which comprises a lubricant, said method comprising adding a solid-phase polymeric material to the lubricant, the solid-phase polymeric material comprising a cross-linked polymer containing aromatic groups, and operating the system.

A kit comprising a lubricant composition and a solid-phase polymeric material, the solid-phase polymeric material comprising a cross-linked polymer containing aromatic groups, is also provided.

Uses of a solid-phase polymeric material, the solid-phase polymeric material comprising a cross-linked polymer containing aromatic groups, for removing aromatic compounds from a hydrocarbon fluid and for preventing the build-up of soot or sludge in a system which comprises a lubricant are also provided.

Also provided is a polymer bead comprising a solid-phase polymeric material, the solid-phase polymeric material comprising a cross-linked polymer, the cross-linked polymer comprising aromatic groups, wherein, on contacting a lubricant, the polymer bead removes aromatic compounds from the lubricant.

The invention will now be described by way of illustrative example only, and with reference to the accompanying drawings, in which:

Figure 1 is a plot showing percentage soot obtained by TGA against time for a number of reference lubricant compositions and lubricant compositions employing polymer beads;

Figure 2a is a transmission electron microscope (TEM) micrograph showing the surface of a polymer bead of composition A before exposure to soot in a lubricant system;

Figure 2b is a transmission electron microscope (TEM) micrograph showing the surface of a polymer bead of composition A after exposure to soot in a lubricant system;

Figure 3a is a transmission electron microscope (TEM) micrograph showing the surface of a polymer bead of composition B before exposure to soot in a lubricant system;

Figure 3b is a transmission electron microscope (TEM) micrograph showing the surface of a polymer bead of composition B after exposure to soot in a lubricant system;

Figure 4 is a transmission electron microscope (TEM) micrograph showing layers of carbon on the surface of a polymer bead of composition B after exposure to soot in a lubricant system;

Figure 5 is a scanning electron microscope (SEM) micrograph showing the surface and a highlighted region on the surface of a polymer bead of composition A before exposure to soot in a lubricant system;

Figure 6; is a scanning electron microscope (SEM) micrograph showing the surface of a polymer bead of composition B after exposure to soot in a lubricant system; and

Figure 7 is a scanning electron microscope (SEM) micrograph of the highlighted area in Figure 5 showing a magnified portion of the surface of the polymer.

Detailed Description of the Invention

Polymer

It has been appreciated that aromatic compounds may be removed from a hydrocarbon fluid using asolid-phase polymeric material comprising a cross-linked polymer containing aromatic groups. Thus, the polymeric material may be used to adsorb aromatic compounds from the liquid phase (for example from a hydrocarbon fluid such as a lubricant) to the solid phase (the polymeric material).

The solid-phase polymeric material is preferably in the form of polymer beads. The polymer beads will generally be spherical in shape, though a variety of shapes may be present such as ovoids. The polymeric material may also be used in other forms including sheets. Since the shape of the polymer bead may vary from an ideal sphere, each bead has an average diameter, that is a value corresponding to the average of the diameter taken at the broadest point of the bead. For an ideal sphere this diameter will be the same regardless of where it is measured. For a non-ideal sphere the maximum diameter may be used as the average diameter instead.

The polymer beads may have a mean average diameter of at least 0.1 μηι but less than 1500μηι, of from ΙΟμιη to ΙΟΟΟμιη or of from ΙΟΟμηι to 500μηι.

The mean average diameter of the polymer beads may be determined using scanning electron microscopy. For instance, the mean average diameter may be determined by sputter coating the polymer beads with gold, generating an image of the particles using scanning electron microscopy, e.g. using a Cambridge Instruments Stereoscan 90, and analysing the image to determine the mean average diameter using image analysis software, e.g. Image J.

A cross-linked polymer is a polymer in which chains are joined together to form a three-dimensional network. As a result of being cross-linked, the polymeric material will generally exhibit a degree of porosity, in their dry state and/or when used in a hydrocarbon fluid in which the three-dimensional polymer network may swell. In preferred

embodiments, the polymer is porous in its dry state.

Larger pore sizes are believed to be preferred for removing aromatic compounds in the form of larger particles, such as soot, while smaller pore sizes are believed to be preferred for removing molecular aromatic compounds.

The cross-linked polymer may have a specific surface area of from 50 to 3000 m2/g, from 200 to 1500 m2/g, or from 400 to 1500 m2/g.

The specific surface area of the cross-linked polymer may be measured using gas absorption techniques, e.g. according to ISO 9277: 2010. Preferably, the method is conducted using the vacuum technique for degassing (see section 6.1); direct determination of the saturation vapour pressure, po, using a nitrogen vapour pressure thermometer (see section 6.2); and the static volumetric method for assessing how much gas is adsorbed (see section 6.3, in particular 6.3.1).

The cross-linked polymer may have a mean pore size of from 0.1 to 100 nm, from 1 to 50 nm, or from 2 to 20 nm.

The mean pore size of the cross-linked polymer may be measured using mercury porosimetry and gas adsorption techniques, e.g. according to ISO 15901 - 2:2006 (for mesopores and macropores). Preferably, the method is conducted using the stepwise static method to obtain pore size data (see section 5.2); the vacuum technique for degassing (see section 8); the static volumetric method, within which the free space is measured with helium before the sample is immersed in liquid nitrogen (see sections 9.3.5, in particular 9.3.5.1 ; and 9.4.2, in particular 9.4.2.1); at least 20 points for the adsorption and desorption portions of the curve, and preferably 32 points for the adsorption portion and 23 points for the desorption portion (see section 9.3.8); reference isotherms according to the t-plot method for calculating the pore size distribution (see section 14.1); data from the adsorption branch for calculating pore volume and pore size distribution (see section 14.3, in particular 14.3.1); and the BJH method for calculating pore size distribution (see section 14.3.2). Other techniques for measuring the mean pore size of the cross-linked polymer include ISO 15901 - 3:2006 (for micropores).

It is generally understood in the art that micropores have a size of less than 2 nm in diameter, mesopores have a size of from 2 to 50 nm, and macropores have a size of greater than 50 nm (see e.g. IUPAC Gold Book, version 2.3.3). Therefore the crossed-linked polymers used may have mesopore pore sizes.

The cross-linked polymer may have a pore volume of from 0.01 to 5 cm3/g, from 0.05 to 1 cm3/g, from 0.1 to 0.5 cm3/g.

The pore volume of the cross-linked polymer may be measured using mercury porosimetry and gas adsorption techniques, e.g. according to ISO 15901 - 2:2006 (for mesopores and macropores, preferably conducted as outlined above) or ISO 15901 -3:2006 (for micropores).

In some embodiments, the polymeric material comprises a hyper cross-linked polymer. Hyper cross-linked polymers are obtainable by introducing cross-links into a polymer which is in a swollen state. Hyper cross-linking produces polymers with a high density of pores, and therefore a high specific surface area. For instance, whilst a cross-linked polymer prepared using standard techniques, such as by suspension polymerization, may have a specific surface area of up to about 1000 m2/g, a hyper cross-linked polymer may have a much greater specific surface area, for example of up to 3000 m2/g, or even higher.

The polymeric material may be obtained by a polymerization reaction between a monomer which comprises an aromatic group and a cross-linker.

Aromatic monomer

Without wishing to be bound by theory, it is believed that the aromatic group helps with attracting and binding aromatic compounds to the polymeric material.

The monomer which comprises an aromatic group is preferably a monomer which comprises a vinyl aromatic group.

In embodiments, the monomer which comprises an aromatic group is selected from a vinyl benzene, vinyl pyridine, vinyl pyrazine, vinyl imidazole, vinyl pyrazole, vinyl oxazole, vinyl thiophene, vinyl naphthalene, vinyl anthracene, vinyl phenanthrene, vinyl tetrazole and a vinyl boron nitride. Preferably, the monomer which comprises an aromatic group is selected from di vinyl benzene, vinyl pyridine and vinyl benzyl chloride. For instance, the monomer may be selected from 1,3- or 1,4-divinyl benzene (preferably 1,4-divinyl benzene), 4-vinyl pyridine and 4-vinyl benzyl chloride. Vinyl benzyl chloride is particularly suitable for use in hyper cross-linked polymers.

It will be appreciated that combinations of aromatic monomers may be used to prepare the cross-linked polymer.

The monomer which comprises an aromatic group may have a molar mass of less than 400 g/mol, less than 300 g/mol, or less than 200 g/mol. Generally, the monomer will have a molar mass of greater than 100 g/mol.

Cross-linker

The cross-linker is believed to be responsible for the formation of pores in the polymeric material.

Suitable cross-linkers are molecules which comprise at least two functional groups which can form bonds between two polymer strands, for example, two non-aromatic vinyl groups. A wide range of cross-linkers may be used. However, for ease of synthesis, it is generally preferred that the cross-linkers are water-insoluble.

Preferably, the cross-linker is selected from the group consisting of divinyl benzene and ethylene glycol-dimethacrylate. For instance, the cross-linker may be selected from 1,3- or 1,4 divinyl benzene (preferably 1,4-divinyl benzene) and ethylene glycol-dimethacrylate. Other suitable cross-linkers include , but are not limited to,

trimethylolpropane trimethacrylate (TRIM), pentaerythritol tetra-acrylate (PETRA), and acrylamide based cross-linkers. These cross-linkers are all suitable for use in hyper cross-linked polymeric materials.

Although the cross-linker and aromatic monomer may in some instances be the same (for example they may both be divinyl benzene), it is generally preferred that they are not the same.

The cross-linker may have a molar mass of greater than 70 g/mol and less than 500 g/mol. The molar mass may be between greater than 70 g/mol and less than 400 g/mol, or greater than 70 g/mol and less than 300 g/mol.

Preparation of the polymer

As mentioned above, the polymeric material may be obtained by a polymerization reaction between a monomer comprising an aromatic group and a cross-linker.

The polymeric material may be obtained using precipitation polymerization, suspension polymerization, or non-aqueous dispersion polymerization. Methods for preparing polymers are well-known to the skilled person.

The characteristics of the cross-linked polymer may be varied by making changes to the methods by which they are produced. For instance, smaller beads (nanoscale beads) are generally formed when emulsion polymerization preparation techniques are adopted.

Larger beads (micron to millimeter size beads) are generally formed using suspension polymerization. Even larger beads may be formed using ascension or sedimentation polymerization. Pore size and volume may be varied by changing the solvent system (the nature and amount of solvent) that is used in the polymer synthesis. Precipitation polymerization tends to give polymers with a relatively small (of the order of a few nanometers) pore size.

Cross-linked polymeric materials prepared by precipitation polymerization may be prepared by a method in which solutions of aromatic monomer and cross-linker and initiator are combined. The polymerization reaction gives a milky suspension of polymer particles.

Cross-linked polymeric materials prepared by non-aqueous dispersion

polymerization may be prepared by a method in which some of the aromatic monomer is dissolved in solvent in the presence of an initiator. After a period of time, the cross-linker and remaining aromatic monomer are added to the mixture.

Cross-linked polymeric materials prepared by suspension polymerization may be prepared by a method in which a non-aqueous phase containing the aromatic monomer and the cross-linker is added to, and maintained in the form of droplets in, an aqueous phase.

Hyper cross-linked polymeric materials may be prepared by a method in which a cross-linked polymer is formed, swollen, and hyper cross-linked. Thus, a hyper cross-linked polymer may be prepared by a method in which a cross-linked polymeric material(those obtained from any method disclosed above) is left to swell in a solvent. Suitable solvents include 1,2-dichloroethane for a highly swollen polymer and heptane for a less swollen polymer. A catalyst (for example a Friedel-Crafts catalyst such as ferric chloride) may then be added to the swollen polymer particles to produce the hyper cross-linked polymer. Any residual catalyst is preferably removed from the polymeric material by washing with a suitable solvent, with such solvents including but not limited to. polar solvents such as methanol, ethanol, dimethyl ether or diethyl ether. Partial hyper cross-linking may be carried out by using the catalyst in a small amount (less than 1 :2 molar ratio of catalyst to reactive groups, such as chloride groups, in the polymer). Alternatively exhaustive hyper cross-linking may be carried out by using the catalyst in a larger amount (at least a 1 : 1 molar ratio of catalyst to reactive groups, such as chloride groups, in the cross-linked polymer). Partial hyper cross-linking may followed by exhaustive hyper

cross-linking.

The polymer may be obtained by a polymerization reaction in which the monomer which comprises an aromatic group and the cross-linker are used in a ratio of from 500:1 to 1 :50 by weight. This ration may be from 300: 1 to 1 : 10, or from 200: 1 to 1 :2 by weight.

The aromatic monomer and the cross-linker may be used in a ratio of from 500: 1 to

20:1 by weight, or from 300:1 to 30:1 or from 200:1 to 50:1. These ratios are believed to enable a good degree of swelling during the preparation of a hyper cross-linked polymer. Alternatively, the aromatic monomer and the cross-linker may be used in a ratio of from 10:1 to 1 :50, or from 5:1 to 1:10, from 2:1 to 1:2 by weight. These ratios are believed to provide a good degree of porosity in polymeric materials which contain a non-hyper cross-linked polymer.

The aromatic monomer and the cross-linker preferably account for at least 80 %, by weight of the monomers used to obtain the polymeric material, sometimes at least 90% and on occasion at least 95% by weight.

Further functionality

The polymeric material may comprise further functionality, optionally in the form of a functional group grafted thereon.

For example, acid neutralization functionality may be added to the material by grafting a basic functional group thereon. Other functionality that may added to the polymeric material, for example by grafting of suitable functional groups thereon, includes anti-oxidancy.

The basic functional group preferably comprises an amine, such as an acyclic amine, an aromatic amine, or a N-containing heterocycle. Preferred basic functional groups comprise an acyclic amine.

Examples of acyclic amines include primary amines and secondary amines. Primary amines, such as alkyl ammonium carbonates, are generally preferred. Preferred examples of aromatic amines include diphenyldiamine and aniline. Preferred examples of N-containing heterocycles include imidazole, pyridine, pyrazine, pyrazole, oxazole, and piperidine groups.

Grafting of the functional groups

The functional groups may be grafted onto the polymer using known methods. For instance, the functional groups may be grafted onto the polymeric material by a

substitution reaction with leaving groups, for example, halogens, that are present in the polymer.

Aromatic compounds

The aromatic compounds preferably have low solubility in the hydrocarbon fluid. The aromatic compounds that are removed using the methods disclosed herein are preferably contaminants, that is components that are undesirable in the hydrocarbon fluid.

The aromatic compounds are preferably polycyclic aromatic hydrocarbons (PAHs), and more preferably polynuclear aromatic hydrocarbons (PNAs), which are polycyclic aromatic hydrocarbons containing fused aromatic rings. The PAHs and PNAs contain two or more aromatic rings, and preferably three or more aromatic rings.

In some embodiments, the methods of removing aromatic compounds from hydrocarbon liquids described above may be used to remove PAHs (and PNAs) in the form of non-aggregated PAHs, such as molecular PAHs, or aggregated PAHs, (say in the form of soot. Non-aggregated PAHs will typically have a size of from 1 to 500 nm. Aggregated PAHs will typically have a size of greater than 500 nm.

The method of the present invention may also be used to remove PAHs in the form of sludge.

Hydrocarbon fluid

The hydrocarbon fluid may be a lubricant or a fuel, and is preferably a lubricant. In preferred embodiments, the hydrocarbon fluid is for use in an internal combustion engine, e.g. a compression-ignition engine or a spark-ignition engine.

The lubricant may comprise a major amount of oil of lubricating viscosity and a minor amount of at least one lubricant additive. Major amount means greater than 50% and minor amount means less than 50 % by weight.

Base oil

In at least some examples the lubricant comprises base oil. Base oil comprises at least one base stock. The lubricant may comprise base oil in an amount of from greater than 50 % to about 99.5 % by weight, or from about 85% to about 95% by weight.

The base stocks may be be classified as Group I, II, III, IV and V base stocks according to API standard 1509, "ENGINE OIL LICENSING AND CERTIFICATION SYSTEM", 17th Edition, Annex E (October 2013 with Errata March 2015), as set out in Table 1.

Claims

A method of removing aromatic compounds from a lubricant, the method comprising contacting the hydrocarbon fluid with a solid-phase polymeric material, the solid-phase polymeric material comprising a cross-linked polymer, the cross-linked polymer comprising aromatic groups.

2. The method of Claim 1 , wherein the solid-phase polymeric material is obtainable by a polymerization reaction between a monomer, comprising an aromatic group, and a cross-linker.

3. The method of Claim 2, wherein the monomer comprising an aromatic group comprises a vinyl aromatic group.

4. The method of any of Claims 1 to 3, wherein the aromatic group is selected from a vinyl benzene group, a vinyl pyridine group, a vinyl pyrazine group, a vinyl imidazole group, a vinyl pyrazole group, a vinyl oxazole group, a vinyl thiophene group, a vinyl naphthalene group, a vinyl anthracene group, a vinyl phenanthrene group, a vinyl tetrazole group, a vinyl boron nitride group, and derivatives thereof.

5. The method of any of Claims 1 to 4, wherein the cross-linker is selected from divinyl benzene and ethylene glycol-dimethacrylate.

6. The method of any of Claims 1 to 5, wherein the solid-phase polymeric material comprises a hyper cross-linked polymer.

7. The method of any of Claims 1 to 6, wherein the solid-phase polymeric material is in the form of polymer beads.

8. The method of claim 7, wherein the polymeric material is in the form of polymer beads having a mean average diameter of from 0.1 to 1500 μιη.

9. The method of any of Claims 1 to 6, wherein the polymeric material is in the form of a sheet.

10. The method of any of Claims 1 to 9, wherein the cross-linked polymer has a specific surface area of from 50 to 3000 m2/g.

11. The method of any of Claims 1 to 9, wherein the cross-linked polymer contains mesopores.

12. The method of any of Claims 1 to 9, wherein the cross-linked polymer has a mean pore size of from 0.1 to 100 nm.

13. The method of any of Claims 1 to 9, wherein the cross-linked polymer has a pore volume of from 0.01 to 5 cm3/g.

14. The method of any of Claims 1 to 13, wherein the solid-phase polymeric material further comprises a functional group grafted thereon.

15, The method of Claim 15 wherein the functional group imparts anti-oxidancy.

16. The method of Claim 14, wherein the method comprises removing the lubricant from a lubricant system, contacting the lubricant with the solid-phase polymeric material, removing the solid-phase polymeric material from the lubricant, and reintroducing the lubricant into the lubricant system

17. The method of Claim 15, wherein the solid-phase polymeric material is present in a lubricant system in the form of a fluidized bed or contained in a sack, the sack being permeable to the lubricant.

18. The method of Claim 15, wherein the solid-phase polymer material is present on a filter within the lubricant system.

19. The method of any of Claims 1 to 18, wherein the aromatic compounds are polycyclic aromatic hydrocarbons.

20. The method of Claim 19, wherein the polycyclic aromatic hydrocarbons are polynuclear aromatic hydrocarbons.

21. A method for preventing the build-up of soot or sludge in a system which comprises a lubricant, said method comprising contacting a solid-phase polymeric material with the lubricant, the solid-phase polymeric material comprising a cross-linked polymer, the polymer containing aromatic groups, and operating the system.

22. A kit comprising a lubricant composition and a solid-phase polymeric material, the solid-phase polymeric material comprising a cross-linked polymer containing aromatic groups.

23. Use of a solid-phase polymeric material for removing aromatic compounds from a hydrocarbon fluid, the solid-phase polymeric material comprising a cross-linked polymer containing aromatic groups.

24. Use of a solid-phase polymeric material for preventing the build-up of soot or sludge in a system which comprises a lubricant, the solid-phase polymeric material comprising a cross-linked polymer containing aromatic groups.

25. Polymer bead or polymer sheet comprising a solid-phase polymeric material, the solid-phase polymeric material comprising a cross-linked polymer, the cross-linked polymer comprising aromatic groups, wherein, on contacting a lubricant, the polymer bead removes aromatic compounds from the lubricant.

26. The polymer bead or polymer sheet of Claim 25, wherein the solid-phase polymeric material is obtainable by a polymerization reaction between a monomer, comprising an aromatic group, and a cross-linker.

27. The polymer bead or polymer sheet of Claim 26, wherein the monomer comprising an aromatic group comprises a vinyl aromatic group.

28. The polymer bead or polymer sheet of any of Claims 25 to 27, wherein the aromatic group is selected from a vinyl benzene group, a vinyl pyridine group, a vinyl pyrazine group, a vinyl imidazole group, a vinyl pyrazole group, a vinyl oxazole group, a vinyl thiophene group, a vinyl naphthalene group, a vinyl anthracene group, a vinyl

phenanthrene group, a vinyl tetrazole group, a vinyl boron nitride group, and derivatives thereof.

29. The polymer bead or polymer sheet of any of Claims 25 to 28, wherein the cross-linker is selected from divinyl benzene and ethylene glycol-dimethacrylate.

30. The polymer bead or polymer sheet of any of Claims 25 to 28, wherein the solid-phase polymeric material comprises a hyper cross-linked polymer.

31. The polymer bead or polymer sheet of Claim 25, wherein the polymer beads have a mean average diameter of from 0.1 to 1500 μηι.

32. The polymer bead or polymer sheet of any of Claims 25 to 31 , wherein the cross-linked polymer has a specific surface area of from 50 to 3000 m7g.

33. The polymer bead or polymer sheet of any of Claims 25 to 31 , wherein the cross-linked polymer contains mesopores.

34. The polymer bead or polymer sheet of any of Claims 25 to 31 , wherein the cross-linked polymer has a mean pore size of from 0.1 to 100 nm.

35. The polymer bead or polymer sheet of any of Claims 25 to 31, wherein the cross-linked polymer has a pore volume of from 0.01 to 5 cm /g.

36. The polymer bead or polymer sheet of any of Claims 25 to 35, wherein the solid-phase polymeric material further comprises a functional group grafted thereon.

37. The polymer bead or polymer sheet of Claim 36, wherein the functional group imparts anti-oxidancy.

38. The polymer bead or polymer sheet of any of claims 25 to 37, wherein the aromatic compounds are polycyclic aromatic hydrocarbons.

39. The polymer bead or polymer sheet of Claim 38, wherein the polycyclic aromatic hydrocarbons are polynuclear aromatic hydrocarbons.