WO2020160802A1

WO2020160802A1 - Polymer-modified metal oxides, manufacturing process thereof and their use for obtaining mineral oil

Info

Publication number: WO2020160802A1
Application number: PCT/EP2019/080322
Authority: WO
Inventors: Maximilian CORNELIUS; Ulrich Fischer; Manfred Braum
Original assignee: Evonik Operations Gmbh
Priority date: 2019-02-08
Filing date: 2019-11-06
Publication date: 2020-08-13

Abstract

Polymer-modified metal oxides, manufacturing process thereof and their use for obtaining mineral oil The invention relates to polymer-metal oxide particles, comprising metal oxide bonded to polymers, comprising functional silane (meth)acrylate units of formula (I) or (Ia) and polyether (meth)acrylate units of formula (II); manufacturing process thereof, aqueous dispersions comprising such particles and their use e.g. for obtaining mineral oil.

Description

Polymer-modified metal oxides, manufacturing process thereof and their use for obtaining mineral oil

The invention relates to polymer-modified metal oxides, manufacturing process thereof, aqueous dispersions comprising such particles and their use for obtaining mineral oil. Since the discovery of new mineral oil reservoirs is becoming increasingly difficult and the development of the old sources is becoming ever more expensive, ways of increasing the yield from reservoirs already in production are being sought. These include the optimization of primary and secondary oil recovery methods, for example, flooding with water, gas injection etc. The so-called enhanced oil recovery methods (EOR, also known as tertiary oil recovery) including thermal recovery, gas injection and chemical injection, can be used to extract an additional oil after the primary and secondary recovery methods have already been applied. EOR methods can help to achieve the yield of crude oil of 30 to 60 percent or even more of the original amount of oil in the reservoir compared to 20 to 40 percent extracted using primary and secondary recovery methods. Use of chemicals during the secondary oil recovery, but also chemical injection methods of EOR are among the most promising methods for increasing crude oil yields. However, the environmental aspects of pumping large amounts of chemicals into oil wells must be considered.

Formulations containing metal oxide nanoparticles, e.g. those of silicon dioxide are environmentally benign and therefore very promising for the use in oil recovery methods such as EOR methods.

WO 2014020061 A1 describes a method of producing mineral oil in which a shear thickening formulation of polyethylene oxide, water and particular hydrophobic silica particles is used. This formulation exhibits thickening at moderate shear rates and thinning at high shear rates. This is said to enable simpler introduction of the formulation into the mineral oil deposit. However, the formulation described has limited stability in solutions having a high salt concentration, for instance seawater, which is usually used in water flooding and EOR methods.

US2015075798 describes a method of producing mineral oil, in which a dispersion comprising hydrophobically modified polyacrylamide particles (HMPAM) and particles of a silica, for example a fumed silica, is used. The combination of particles is said to be more effective than a dispersion containing either only HMPAM or only silica.

Abbas Roustaei et al. report in Egyptian Journal of Petroleum (2013) 22, 427-433 on the capability of silica particles to alter the wettability of the reservoir rock and reduce the interfacial tension between crude oil and brine phases. Fumed silica AEROSIL® R 816 was used, which is obtained by surface-modifying of hydrophilic fumed silica with hexadecylsilane. Fluids, comprising 1-4 g/L of AEROSIL® R 816 in ethanol were prepared by sonication. These ethanol dispersions turn milky upon mixing with water, suggesting possible phase separation and challenges associated with pressure increase in long-term oil recovery processes.

US 2003220204 discloses a method of recovering oil comprising the step of injecting a foamable fluid, the fluid comprising surface-modified nanoparticles. The nanoparticles are selected from the group consisting of silica, titania, alumina, zirconia, vanadia, ceria, iron oxide, antimony oxide, tin oxide, alumina/silica, and combinations thereof. The

nanoparticles can be surface-modified to obtain a non-polar or a polar surface-modified nanoparticle. Suitable surface-modifying substrates are silanes selected from the group consisting of alkylchlorosilanes, alkoxysilanes, trialkoxyarylsilanes, silane functional (meth)acrylates and polydialkylsiloxanes.

WO 2017071985 A1 describes a fluid, comprising surface-modified aluminium-silicon mixed oxide particles and a method of obtaining mineral oil using this fluid. The surface modification of such particles consists of functional silane groups Si-(CH₂)_n-Y_m-R comprising ethylenoxy moieties Y = (OChhChhj_o with o = 5-15. Such surface modification results from the reaction of metal oxides with the corresponding organo silanes comprising ethylenoxy moieties Y. The described fluid is shown to be stable in seawater under elevated temperatures and not to cause an increase of pressure when in contact with the permeable formation comprising the mineral oil. Organosilanes used for surface treatment of particles in WO 2017071985 A1 are relatively difficult to synthesize and therefore are quite expensive. If the optimization of surface-treatment of metal oxide particles is required in order to synthesize tailor-made products, this is only possible by synthesizing of new organosilanes, which is rather inconvenient.

The problem addressed by the present invention is that of providing metal oxide particles suitable for processes of mineral oil recovery such as enhanced oil recovery methods, especially in offshore facilities. Such particles and aqueous dispersions on their basis must therefore be stable in seawater. A further problem to be solved by the present invention is that of providing metal oxide particles cost-efficiently and with a high degree of possible variations of surface treatment.

The invention provides polymer-metal oxide particle, comprising at least one metal oxide bonded to one or more polymers, each polymer comprising: a) units derived from one or more compounds of formula (I) or (la)

wherein R = H or CH3,

0 < h < 2

Si(A)h(X)3-h is a silane functional group

A is H or a branched or unbranched C1 to C4 alkyl residue,

B is a branched or unbranched, aliphatic, aromatic or mixed aliphatic-aromatic C1 to C30 hydrocarbon group,

X is selected from H, Cl or a group OY , wherein Y is H or a C1 to C30 branched or unbranched alkyl-, alkenyl-, aryl-, or aralkyl- group, branched or unbranched C2 to C30 alkylether-group or branched or unbranched C2 to C30 alkylpolyether-group or a mixture thereof,

and

b) units derived from one or more compounds of formula (II)

wherein R¹ = H or CH3

each of R², R³, R⁴ and R⁵ independently is H or a branched or unbranched C1 to C6 alkyl group

3 < n < 1000

R⁶ is H, branched or unbranched C1 to C30 alkyl group, wherein the weight ratio of the metal oxide particle to the one or more polymers bonded to the metal oxide particle is in the range of 1 : 0.03 to 1 : 1.80.

US 20130005881 A1 discloses a hybrid organic-inorganic nanocomposite dispersion, wherein silica nanoparticles are covalently bonded to organic polymers. Such organic- inorganic nanocomposites can be produced among other things, by the following steps: a) surface treating silica nanoparticles with a silane monomer bearing an ethylenically unsaturated organic moiety and b) reacting organic monomers, e.g. alkyl acrylates with surface-treated silica nanoparticles. No (meth)acrylic monomers according to formula (II) are disclosed.

KR 100795508 describes preparation of nanocomposites, in which nanoparticles are bonded to a main chain of a vinyl-based polymer by co-polymerization of a silane-based acrylic monomer, e.g. methacryloxypropyl trimethoxysilane, acryl-based compound, e.g. alkyl methacrylate in the presence of colloidal silica. No acryl-based compounds according to formula (II) are disclosed. The nanocomposites described in KR 100795508 can be used for preparation of thermoplastic nanocomposite resin compositions.

WO 2018019783 A1 discloses polymeric-inorganic nanoparticles comprising inorganic nanoparticles covalently bonded to polymers prepared from at least one (meth)acrylate monomer with a silane functional group and at least one alkyl (meth)acrylate with an alkyl group containing from 1 to 40 carbon atoms. Such hydrophobic nanoparticles can be incorporated in lubricant oil formulations and be used for reducing friction and wear as well as for reducing the pour point of lubricant compositions. Neither polymeric-inorganic nanoparticles, which would be water-compatible, nor the polymer units according to formula (II) of the present invention, are disclosed in WO 2018019783 A1.

US 20110311826 A1 discloses coating compositions comprising a copolymer prepared from a reaction mixture comprising (a) an ethylenically unsaturated hydrolysable silane;

(b) an ethylenically unsaturated polyoxyalkylene; (c) an ethylenically unsaturated fluorinated polyether and (d) an initiator. Examples 4-10 of this application show the reaction of a silicone sol-gel hardcoat with a solid content of 13-16 wt% S1O2 with copolymers comprising a polyoxoethylene methacrylate (PEG-Mar), trimethoxysilane substituted methacrylate (Si-Mar) and a perfluorinated polyether methacrylate monomers. The weight ratio of the metal oxide (Sol-gel) to polymer is 98.5 : 1.5 (1 : 0.015) to 98 : 2 (1 :0.020).

US 20070275042 A1 discloses a curable composition comprising (a) 1-20 parts by weight of a surface modified nanoparticle component having ethylenically unsaturated groups with the average particle size of less than 20 nm and (b) 80-99 parts by weight of a monomer component comprising a monofunctional poly(alkylene oxide) free-radically polymerizable macromonomer having a poly(alkylene oxide) moiety. Examples 1 , 3 and 4 of this application describe the preparation of colloidal silica particles surface modified by sequential treatment with PEO/PPO silane, methacryloxypropyl trimethoxysilane (Silquest A-174) and methoxypolyethylene glycol acrylate (M-PEG 400 A or M-PEG 300 A). The weight ratio of the metal oxide (S1O2) to polymerformed from methacryloxypropyl trimethoxysilane and methoxypolyethylene glycol acrylate is in the range 1 : (2.1-2.2).

In the course of extensive experimentation, it was surprisingly found that it is the metal oxide/polymer weight ratio of 1 : 0.03 to 1 : 1.8 that gives the polymer-metal oxide particles of the present invention their beneficial properties, particularly in aqueous dispersions applicable for obtaining mineral oil. Thus, if less than 3 wt% polymer in respect to the used metal oxide is applied, i.e. the weight ratio metal oxide/polymer is 1 : < 0.03, the resulting polymer-metal oxide particles tend to agglomerate and form unstable aqueous dispersions. Moreover, the stability of such dispersions in seawater declines dramatically. If more than 180 wt% polymer in respect to the used metal oxide is applied, i.e. the weight ratio metal oxide/polymer is 1 : > 1.8, much larger polymer-metal oxide particles result, which leads to considerable increase in viscosity of aqueous dispersions of such polymer-metal oxide particles. Large size of polymer-metal oxide particles and high viscosity of aqueous dispersions thereof precludes the use of such dispersions for obtaining mineral oil, as in this application any blockade of the pores of the rocks comprising mineral oil would be undesirable. Moreover, the higher content of the polymer would result in increasing overall cost of such polymer-metal oxide particles.

Polymer

The polymer-metal oxide particle according to the present invention may comprise units derived from one or more compounds of formula (I)

wherein R = H or CH3, preferably CH3

0 < h < 2, preferably h = 0 or h =1 , most preferably h = 0,

Si(A)h(X)3-h is a silane functional group

A is H or a branched or unbranched C1 to C4 alkyl residue, preferably methyl, ethyl, n-propyl or iso-propyl, most preferably A = H or CH3. B is a branched or unbranched, aliphatic, aromatic or mixed aliphatic-aromatic C1 to C30 hydrocarbon group, preferably C1 to C10 hydrocarbon group, more preferably B = -(CH2)m-, wherein m = 1-6,

X is selected from H, Cl or a group OY , wherein Y is H or a C1 to C30, preferably C1 to C10, more preferably C1 to C7 branched or unbranched alkyl-, alkenyl-, aryl-, or aralkyl- group, branched or unbranched C2 to C30, preferably C2 to C10, more preferably C2 to C6 alkylether-group or branched or unbranched C2 to C30, preferably C2 to C10, more preferably C2 to C6 alkylpolyether-group or a mixture thereof, Most preferably is X = Cl, OCHs or OCH2CH₃.

The compound of formula (I) is most preferably selected from 3-(triethoxysilyl)propyl methacrylate, 3-(trimethoxysilyl)propyl methacrylate and 3-(trichlorosilyl)propyl methacrylate.

The polymer-metal oxide particle according to the present invention may comprise units derived from one or more compounds a of formula (la)

wherein R = H or CH₃, preferably CH₃

B is a branched or unbranched, aliphatic, aromatic or mixed aliphatic-aromatic C1 to C30 hydrocarbon group, preferably C1 to C10 hydrocarbon group, more preferably B = -(CH2)m-, wherein m = 1-6,

In the context of the present invention, a“hydrocarbon group” B is a group consisting of atoms C (carbon) and H (hydrogen), which is derived from the corresponding

hydrocarbons, such as e.g. alkanes, cycloalkanes, alkenes, alkynes or aromatic hydrocarbons by a formal removal of two hydrogen atoms. The compound of formula (la) is most preferably selected from

(dichlorosilanediyl)bis(propane-3,1-diyl) bis(2-methylacrylate) (la, R = CH₃, B = -(CH₂)₃-, X = Cl), (dimethoxysilanediyl)bis(propane-3,1-diyl) bis(2-methylacrylate) (la, R = CH₃, B = -(CH2)3-, X = OCH3) and (diethoxysilanediyl)bis(propane-3,1-diyl) bis(2-methylacrylate) (la, R = CH₃, B = -(CH₂)₃-, X = 0C₂H₅).

The polymer-metal oxide particle according to the present invention comprises units derived from one or more compounds of formula (II)

wherein R¹ = H or CH3, preferably CH3.

each of R², R³, R⁴ and R⁵ independently is H or a branched or unbranched C1 to C6, preferably C1 to C4 alkyl group, preferably methyl, ethyl, n-propyl or iso-propyl, most preferably each of R², R³, R⁴ and R⁵ is H or CH3.

3 < n < 1000, preferably 4 < n < 500, more preferably 5 < n < 200, most preferably 5 < n < 100,

R⁶ is H, branched or unbranched C1 to C30, preferably C1 to C10, more preferably C1 to C6 alkyl group. Most preferably R⁶ = CH3.

Most preferably, in the compound of formula (II) each of R², R³, R⁴ and R⁵ = H and R⁶ = CH3 and compound of formula (II) is an acrylate or methacrylate ester of poly(ethylene glycol) methyl ether (MPEG). Such MPEGs can usually have a number average molecular weight of 500 to 10.000 g/mol.

The polymer-metal oxide particle according to the present invention comprises one or more polymers, wherein each polymer may comprise:

a) 0.1 to 50 % by weight, more preferably 1.0 to 40 % by weight, even more preferably 5.0 to 30 % by weight of units derived from one or more compounds of formula (I) or (la), based on the total weight of the polymer, and

b) 50 to 99.9 % by weight, more preferably 60 to 99 % by weight, even more preferably 70 to 95 % by weight of units derived from one or more compounds of formula (II), based on the total weight of the polymer.

The polymer-metal oxide particle of the invention comprises one or more polymers, wherein each polymer may further comprise: 0 to 49.9 % by weight, more preferably 1.0 to 40 % by weight, even more preferably 5.0 to 30 % by weight of units derived from one or more alkyl (meth)acrylate monomers of formula (III), based on the total weight of the polymer,

where R⁷ is hydrogen or methyl, R⁸ means a linear, branched or cyclic alkyl residue with 1 to 30 carbon atoms.

In one embodiment of the invention, in compound of the formula (III), R⁷ is hydrogen or methyl, R⁸ means a linear, branched or cyclic alkyl residue with 1 to 8 carbon atoms, preferably 1 to 5, more preferably 1 to 3 carbon atoms. Examples of such monomers according to formula (III) are, among others, (meth)acrylates which are derived from saturated alcohols such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate and hexyl (meth)acrylate; cycloalkyl (meth)acrylates, like cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, 2-tert-butylheptyl (meth)acrylate, n-octyl (meth)acrylate and 3-isopropylheptyl (meth)acrylate,. Preferably, the polymer comprises units being derived from methyl methacrylate.

In another embodiment of the invention, in compound of the formula (III), R⁷ is hydrogen or methyl, R⁸ means a linear, branched or cyclic alkyl residue with 9 to 15 carbon atoms, more preferably a linear, branched or cyclic alkyl residue with 12 to 15 carbon atoms, even more preferably a linear, branched or cyclic alkyl residue with 12 to 14 carbon atoms. Examples of such monomers according to formula (III) are, among others, (meth)acrylates that are derived from saturated alcohols, such as nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate, n-dodecyl (meth)acrylate, 2-methyldodecyl (meth)acrylate, tridecyl (meth)acrylate, 5-methyltridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, pentadecyl (meth)acrylate; (meth)acrylates which derive from unsaturated alcohols, for example oleyl (meth)acrylate; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate having a ring substituent, like tert-butylcyclohexyl (meth)acrylate and trimethylcyclohexyl (meth)acrylate, bornyl (meth)acrylate and isobornyl (meth)acrylate.

In still another embodiment of the invention, in compound of the formula (III), R⁷ is hydrogen or methyl, R⁸ means a linear, branched or cyclic alkyl residue with 16 to 30 carbon atoms, more preferably with 16 to 20 carbon atoms. Examples of such monomers according to formula (III) are, among others, (meth)acrylates which are derived from saturated alcohols, such as hexadecyl (meth)acrylate, 2-methylhexadecyl (meth)acrylate, heptadecyl (meth)acrylate, 5-isopropylheptadecyl (meth)acrylate, 4-tert-butyloctadecyl (meth)acrylate, 5-ethyloctadecyl (meth)acrylate, 3-isopropyloctadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, cetyleicosyl (meth)acrylate, stearyleicosyl (meth)acrylate, docosyl (meth)acrylate, behenyl (meth)acrylate and/or eicosyltetratriacontyl (meth)acrylate; cycloalkyl (meth)acrylates such as 2,4,5-tri-t-butyl-3-vinylcyclohexyl (meth)acrylate, 2,3,4,5-tetra-t-butylcyclohexyl (meth)acrylate.

The compound of formula (III) may also be a hydroxyalkyl (meth)acrylate like 3-hydroxypropyl (meth)acrylate, 3,4-dihydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2 hydroxypropyl (meth)acrylate, 2,5-dimethyl-1 ,6-hexanediol (meth)acrylate, 1 ,10-decanediol (meth)acrylate. The polymer-metal oxide particle of the invention comprises one or more polymers, wherein each polymer may further comprise:

0 to 20 % by weight, more preferably 0.5 to 15 % by weight, more preferably 1.0 to 10 % by weight of units derived from one or more (meth)acrylamide monomers of formula (IV), based on the total weight of the polymer,

where R⁹ is hydrogen or methyl, each of R¹⁰ and R¹¹ independently means hydrogen or a linear, branched or cyclic alkyl residue with 1 to 30, more preferably 1 to 10, carbon atoms, optionally with further substituents.

Specific examples of compounds of formula (IV) are aminoalkyl (meth)acrylamides like N-(3-dimethyl-aminopropyl)methacrylamide, 3-diethylaminopentyl (meth)acrylate, 3-dibutyl-aminohexadecyl (meth)acrylate.

The polymer-metal oxide particle according to the invention comprises one or more polymers, which preferably have a weight average molecular weight of 500 g/mol to 200.000 g/mol, more preferably of 1.000 g/mol to 100.000 g/mol, even more preferably of

5.000 g/mol to 80.000 g/mol. The polymer weight average molecular weight can be measured by gel permeation chromatography (GPC) calibrated using polymethyl methacrylate) standards and with tetrahydrofuran (THF) used as eluent. The polymer used for preparation of polymer-metal oxide particle of the invention preferably does not contain any fluorine. Thus, preferably, no fluorine-containing monomers are employed for the preparation of the polymers used for preparation of polymer-metal oxide particle of the invention. Metal oxide particle

The term “metal oxide” used in the present invention refers to chemical compounds formed by at least one metal, e.g. Al, Ti, Fe, Zr, Ce or one metalloid, e.g. B, Si, Ge, Sb with oxygen. The polymer-metal oxide particle according to the invention can comprise metal oxides of the following elements: Y(yttrium), Ti (titanium), Zr (zirconium), V (vanadium), Cr (chromium), Mo (molybdenium), W (tungsten), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu (copper), Zn (zink), Al (aluminium), B (boron), Si (silicon), Sn (tin), Pb (lead). Apart from the individual metal or metalloid oxides, the metal oxides of the present invention may also include doped or mixed oxides, core-shell oxides and other types of oxides comprising two or more different metals or metalloids. Most preferably, the metal oxide particle referred to in the present invention is selected from S1O2, AI2O3, T1O2, doped, mixed oxides or core-shell metal oxides of at least two elements selected from Si, Al and Ti.

It is preferable when fumed metal oxide particles, i.e. the metal oxide particles obtained from pyrogenic processes, are employed in polymer-metal oxide particles of the present invention. In these processes, metal compounds are reacted in a flame generated by the reaction of hydrogen and oxygen. The thus obtained powders are referred to as “pyrogenic” or“fumed” metal oxides. The reaction initially forms highly disperse primary particles, which in the further course of reaction coalesce to form aggregates. The aggregate dimensions of these powders are generally in the range of 0.2 - 1 pm. Said powders may be partially destructed and converted into the nm range particles

advantageous for the present invention by suitable grinding.

The metal oxide particle is preferably selected from fumed silica (S1O₂), fumed alumina (AI₂O₃), fumed titanium dioxide (T1O₂), doped, mixed oxides or core-shell fumed metal oxides of at least two elements selected from Si, Al and Ti.

It is possible to employ the fumed mixed metal oxides, for example silicon-aluminum mixed oxide disclosed in EP-A-995718 in the present invention. Said mixed metal oxide is obtained by reacting a vaporous silicon dioxide precursor and an aluminum chloride solution in a flame. The fine distribution of aluminum chloride in the aerosol and during the genesis of the oxide in the gas phase results in substantially homogeneous incorporation of the aluminum. Commercially available fumed mixed silicon-aluminum oxide powders are AEROSIL ^® MOX 80 having a BET surface area of 60-100 m²/g and an aluminum oxide content of 0.3 - 1.3% by weight and AEROSIL^® MOX 170 having a BET surface area of 140 - 200 m²/g and an aluminium oxide content of 0.3 - 1.3% by weight, both from Evonik Resource Efficiency GmbH.

It is also possible to employ other types of metal oxides, such as precipitated metal oxides or metal oxide sols, for example precipitated silica, precipitated alumina, precipitated titanium dioxide, silica sol, alumina sol or titanium dioxide sol.

Metal oxide produced by precipitation (precipitated metal oxide) is formed, for example, during the reaction of water glass solution (water-soluble sodium silicate) with mineral acid. A colloidal silicon dioxide (silica sol) can also be produced in the solution from sodium silicate, which provides dispersions with very small particle sizes and very good dispersion stability.

The metal oxide particle preferably has a number median particle diameter dso of 5 - 300 nm, more preferably 10 - 250 nm, even more preferably 20-150 nm. The number median particle diameter can be determined with dynamic light scattering method (DLS) in an aqueous dispersion. The metal oxide particles may be in the form of isolated individual particles and/or in the form of aggregated particles. In the case of aggregated particles, the number median particle diameter refers to the dimension of the aggregate.

The BET surface area of the metal oxide is preferably 40 - 500 m²/g, particularly preferably 80 - 300 m²/g. The BET surface area can be determined according to DIN 9277:2014 by nitrogen adsorption according to Brunauer-Emmett-Teller procedure.

Polymer-metal oxide particle

The polymer-metal oxide particle preferably has a number median particle diameter dso of 5 - 400 nm, more preferably 5 - 300 nm, even more preferably 10-150 nm. The number median particle diameter may be determined with dynamic light scattering method (DLS) in an aqueous dispersion. The metal oxide particles may be in the form of isolated individual particles and/or in the form of aggregated particles. In the case of aggregated particles, the number median particle diameter refers to the dimension of the aggregate.

The weight ratio of the metal oxide particle to the one or more polymers bonded to the metal oxide particle is preferably in the range of from 1 : 0.03 to 1 : 1.7, more preferably from 1 : 0.03 to 1 : 1.6, more preferably from 1 : 0.03 to 1 : 1.5, more preferably from 1 : 0.04 to 1 : 1.4, more preferably from 1 : 0.04 to 1 :1.3, more preferably from 1 : 0.05 to 1 : 1.2, more preferably from 1 : 0.05 to 1 : 1.1 , more preferably from 1 : 0.05 to 1 : 1.0, more preferably from 1 : 0.07 to 1 : 0.9, more preferably from 1 : 0.08 to 1 : 0.8, more preferably from 1 : 0.09 to 1 : 0.7. Carbon content of polymer-metal oxide particle of the invention may be from 1 to 25 % by weight, more preferably from 2 to 20 % by weight, even more preferably from 3 to 15 % by weight. The carbon content can be determined by elemental analysis.

Process for producing polymer-metal oxide particle

Present invention further provides a process for producing the polymer-metal oxide particle of the invention, comprising the following steps:

(i) preparing a polymer by polymerizing a monomer composition comprising at least one compound of formula (I) or (la) and one compound of formula (II),

(ii) bonding the polymer prepared in step (I) with the metal oxide particle.

Step (i)

The preparation of the silane-containing polymer, comprising units derived of a silane monomer of formula (I) or (la), units derived of monomers of formula (II) and optionally units derived of monomers of formula (III) and (IV) can be performed in a manner well- known in the art. Thus, these polymers can be obtained in particular by free-radical polymerization and related processes, for example ATRP (=Atom Transfer Radical Polymerization), RAFT (=Reversible Addition Fragmentation Chain Transfer) or NMP processes (nitroxide-mediated polymerization). More preferably, the silane-containing polymers of the invention are prepared by free-radical polymerization.

Customary free-radical polymerization is described, inter alia, in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Chapter“Polyacrylates”. In general, a polymerization initiator is used for this purpose. The usable initiators include the azo initiators widely known in the technical field, such as 2,2’-azo-bis-isobutyronitrile (AIBN), or peroxy compounds such as tert-butyl-hydroperoxide, mixtures of two or more of such or other compounds, able to form free radicals.

Furthermore, chain transfer agents can be used. It is well known in the art that a good way to control the molecular weight of a polymer chain is to use chain transfer agents during the polymerization synthesis. Common chain transfer agents are organic compounds comprising SH groups such as n-butyl mercaptan, n-octyl mercaptan, dodecyl mercaptan, tert-dodecyl mercaptan, dodecyl mercaptan, butylthiol glycolate, and octylthiol glycolate. Use of chain transfer agents leads to the polymer chain with one terminal end comprising the chain transfer agent. Therefore, it is possible to use chain transfer agent with functional groups so that one chain end comprises this group. According to a particular embodiment of the invention, the silane-containing polymer comprises a terminal polymer chain end derived from silane-containing chain transfer agent or is obtainable by a polymerization process using a silane-containing chain transfer agent. For example, 3-(trimethoxysilyl)-1-propanethiol HS(CH2)3Si(OCH3)3, may be used as a chain transfer agent, and the resulting polymer will have a terminal chain end with -S(CH2)3Si(OCH3)3. Thus in a particular embodiment, the present invention relates to a silane-containing polymer as described above with all the characteristics and preferences indicated above applying to the polymer and having a terminal polymer chain end with -S(CH2)3Si(OCH3)3. Especially, the monomer mixture used to prepare the silane-containing polymer in the process of the present invention may comprise 1 to 15% by weight, preferably 2 to 10% by weight and more preferable 4 to 8% by weight initiator based on the total weight of the monomer composition. The amount of chain transfer agents can be used in an amount of 0 to 2% by weight, preferably 0.01 to 1 % by weight and more preferably 0.02 to 0.3% by weight based on the total weight of the monomer composition.

The polymerization may be carried out at standard pressure, reduced pressure or elevated pressure. The polymerization temperature is not critical. Conventionally the polymerization temperature may be in the range of 0 °C to 200 °C, preferably 0 °C to 130 °C, and more preferably 60 °C to 120 °C. Higher temperatures are especially preferred in free radical polymerizations using high amounts of initiators.

The polymerization may be carried out with or without solvent. The term solvent is to be understood here in a broad sense. The polymerization is preferably carried out without a solvent or in a polar solvent, like water or alcohol.

Step (i) of the process according to the invention is preferably carried out in such manner, that monomer conversion of more than 98% is achieved.

Step (ii)

In step (ii) of the inventive process, silane-containing polymers formed in the first step, are bonded to the metal oxide particles. For the purposes of the present invention, the term “bonded” refers to the connection by means of covalent type of bonds, which are created by silanization of the surface of metal oxide particles with functional silane groups of organosilanes. The term“bonded” is used in the present invention as an analog of the term“covalently bonded”. Thus, the free hydroxyl-groups present on the surface of metal oxides ^*M-OH react with such organosilanes to form covalent bonds ^*M-0-Si.

According to the present invention, the term“one or more” polymers means that one metal oxide particle may be bonded to one polymer or to several polymers. When many polymers are bonded to the same particle, then the polymers may be prepared with the same monomer composition, or be different polymers prepared with different monomer compositions.

According to the present invention, a polymer-metal oxide particle is the result of one metal oxide particle, being bonded to at least one polymer, said polymer preferably having at least two of its silane functional groups of monomer units of formula (I) or (la) being covalently bonded to the one particle.

According to a preferred embodiment of the invention, the process step (ii) is performed by mixing at high speed greater than 4000 RPM, and optionally conducting an ultrasonic treatment.

Optionally ultrasonic treatment is conducted simultaneously during the step (ii), or subsequently after step (ii). Using an ultrasonic treatment allows to deagglomerate any large particle agglomerates from the raw metal oxide powder, allowing all metal oxide particles to get well dispersed.

Step (ii) of the inventive process can be carried out at temperatures ranging from room temperature to 150 °C depending on the solvent and monomer composition.

Preferably, step (ii) of the process according to the invention is carried out in water. Thus, polymer, synthesized in in step (i) is reacted with an aqueous dispersion comprising metal oxide particle resulting in bonding of in step (i) formed polymer to metal oxide particle. Both cationic and anionic aqueous dispersions of metal oxides can be used for producing polymer-metal oxide particle of the invention. The aqueous dispersion of the metal oxide preferably has a pH of from 5 to 12, more preferably from 7 to 11 , even more preferably from 8 to 10.

Numerous methods of dispersing are available to those skilled in the art. To produce finely divided aqueous dispersions of metal oxide, apparatuses such as for example ultrasound probes, ball mills, stirred ball mills, rotor/stator machines, planetary kneaders/mixers or high-energy mills or combinations thereof are available. Thus, for example a preliminary metal oxide dispersion may be prepared using a rotor/stator system, which in a

subsequent step is subjected to further milling by means of a high-energy mill. This combination makes it possible, for example, to produce extra fine aqueous dispersions of metal oxides having a particle diameter of 200 nm or less. In the case of a high-energy mill, a preliminary dispersion under high pressure is divided into two or more streams, which are then decompressed through a nozzle and impinge exactly on one another.

After carrying out step (ii) of the process according to the invention, the solvents and/or the silanyzation reaction products can be at least partially removed from the mixture, for example under reduced pressure. When polymers having alkoxysilane groups are employed in step (ii), the reaction product is an alcohol, for example methanol or ethanol.

Aqueous dispersion comprising polymer-metal oxide particle

Present invention further provides aqueous dispersion comprising the metal oxide particle of the invention. The aqueous dispersion according to the invention preferably comprises 1 to 40 % by weight, more preferably 5 to 30 % by weight, even more preferably 10 to 25 % by weight, of the polymer-metal oxide particles.

The aqueous dispersion according to the present invention preferably has a median particle diameter dso of 30 - 300 nm, more preferably 40 - 250 nm, more preferably 50-150 nm. The median particle diameter can be determined with the methods for the determination of particle size distributions in dispersions, known to those skilled in the art, e.g. with dynamic light scattering method (DLS).

The aqueous dispersion of the invention preferably has a pH of from 5 to 12, more preferably from 7 to 1 1 , even more preferably from 8 to 10.

The aqueous dispersion of the invention may also contain small proportions of alcohol, such as methanol, ethanol, propanol or butanol, in addition to water. The proportion of alcohol is generally less than 10% by weight, preferably 3 - 7% by weight, in each case based on the mass of the dispersion.

The aqueous dispersion according to the invention may comprise small amounts, preferably less than 100 ppm, of customary dispersants. However, the presence of dispersants is not desired in the context of the present invention. The stabilizing effect of the aqueous dispersion according to the invention derives solely from the polymer- modified metal oxide powder. Therefore, particularly preferably, the dispersion of the invention contains no additional dispersants.

The aqueous dispersions according to the invention are generally seawater-stable. For the purposes of the present invention, the term“seawater-stable” refers to stability, that is, essentially no sedimentation, of a 0.5 weight per cent aqueous dispersion in a reference solution simulating sea water for at least 1 month at a temperature of 25°C. The seawater stability is tested in a reference solution which is obtained by adding sufficient fully demineralized water at 23°C to a mixture of 28.500 g of NaCI, 0.220 g of NaHCC>3, 4.066 g of Na2SC>4, 1.625 g of CaCh x 2 H2O, 3.162 g of MgCh x 6 H2O, 0.024 g of SrCh x 6 H2O and 0.721 g of KCI to give 1000 ml. of solution.

The use of polymer-metal oxide particle

The polymer-metal oxide particle or the aqueous dispersion according to the invention can be used as a constituent of pharmaceutical preparations, cosmetic preparations, water- based paints and coatings, of cleaning products, of dishwashing detergents, of coating slips in the paper industry, of water-based lubricants, of heat transfer fluids in battery systems or other electrical equipment, and for obtaining mineral oil, for example via enhanced oil recovery methods. The polymer-metal oxide particle or the aqueous dispersion of the present invention may be a constituent of a heat transfer fluid, especially for electrical equipment. Such heat transfer fluids, particularly cooling liquids should have a high specific heat capacity and should in particular be suitable for use in thermal management systems for high power batteries. The inventive polymer-metal oxide particle or the aqueous dispersion may be used in heat transfer fluid for electrical equipment like electric batteries, electric motors, electric transformers, electric power converters, electric capacitors, fluid-filled

transmission lines, fluid-filled power cables, and computers. The examples of such heat transfer fluids are given in patent applications WO 20131 15925 A1 and

WO 2014106556 A1.

The polymer-metal oxide particle or the aqueous dispersion according to the present invention may be a constituent of water-based lubricants. Such water-based lubricants can be used particularly in drive elements, for example such as chains, gears, roller bearings, and plain bearings or seals on rotating shafts. Water-based lubricants can meet the increasingly stringent requirements on the lubricant compositions, in particular with respect to environmental protection and carbon dioxide emissions. Some examples of such water-based lubricants are given e.g. in DE 102009039626 A1.

The polymer-metal oxide particle or the aqueous dispersion of the present invention are particularly suitable for obtaining mineral oil, for example via enhanced oil recovery methods. Obtaining of mineral oil using the polymer-metal oxide particle or the aqueous dispersion according to the invention can be conducted by introducing the fluid comprising seawater and the polymer-metal oxide particle into a mineral oil deposit having a temperature of 10-200°C, preferably 20-150°C, more preferably 40-100°C.

Experimental Part

General procedure for the preparation of the polymers

All the reactions were carried out without using solvents, the resulting products therefore contained 100% polymers (solids content = 100%).

In a 1000 ml. vessel with a paddle agitator, the monomers were homogeneously mixed. After that, substances which control the molecular weight of the resulting polymers and the initiator were added and thoroughly mixed again. The resulting mixture was pumped in a 2000 ml. double jacket vessel under nitrogen atmosphere and is heated to 90 °C under stirring. The feed rate was determined by the reaction temperature, which was kept at 90 °C constantly. After addition of the whole amount of monomer mixture, additional initiator was added in order to complete the polymerization at 90 °C. After complete addition of the initiator and completed polymerization i.e. after 60 minutes stirring at 90 °C the product was cooled to room temperature (22 °C).

The overall yield of the polymers obtained was in the range between 500 - 1000 g.

Weight-average molecular weight (Mw) of the synthesized polymers was determined by gel permeation chromatography (GPC) calibrated using poly(methyl-methacrylate) standards and with tetrahydrofuran (THF) used as eluent.

Polymer 1 : MPEG 500 MA: MEMO (90 : 10 wt% : wt%), Mw = 12.000 g/mol

In this example a mixture containing 90 wt.% of MPEG 500 MA (polyethylenglycol- methylether methacrylate, molecular weight of PEG: 500 g/mol, manufacturer: Evonik Performance Materials GmbH) and 10 wt.% of Dynasylan^® MEMO (3-methacryloxypropyl trimethoxysilane, manufacturer: Evonik Resource Efficiency GmbH) were used for polymerization. Dodecylmercaptane (1.95 wt% relating to the mixture of monomers) and 2-ethylhexyl thioglycolate (1.95 wt% relating to the mixture of monomers) were used as chain transfer agents (CTA). To this mixture 1 wt.% (relating to the mixture of monomers) of tert-butylperoxy-2-ethylhexanoate was added under stirring. This mixture was fed within 3.5 h into the reaction vessel at 90 °C. After complete addition, another 0.95 wt% (relating to the mixture of monomers) of tert-butylperoxy-2-ethylhexanoate were added under stirring. This mixture was kept at 90 °C for additional 60 minutes. After cooling to room temperature (22 °C), the product was collected in a vessel and stored under inert gas atmosphere. The weight average molecular weight of the resulting polymer was

Mw = 12.000 g/mol.

Polymer 2: MPEG 500 MA: MEMO (90:10 wt%:wt%), Mw = 65.000 g/mol

In this example a mixture containing 90 wt.% of MPEG 500 MA (polyethylenglycol- methylether methacrylate, molecular weight of PEG: 500 g/mol, manufacturer: Evonik Performance Materials GmbH) and 10 wt.% of Dynasylan^® MEMO (3-methacryloxypropyl trimethoxysilane, manufacturer: Evonik Resource Efficiency GmbH) were used for polymerization. Dodecylmercaptane (1.95 wt% relating to the mixture of monomers) and 2-ethylhexyl thioglycolate (1.0 wt% relating to the mixture of monomers) was used as a chain transfer agent (CTA). To this mixture 1 wt.% of tert-butylperoxy-2-ethylhexanoate (relating to the mixture of monomers) was added under stirring. This mixture was fed within 3.5 h into the reaction vessel at 90 °C. After complete addition, another 0.95 wt% (relating to the mixture of monomers) of tert-butylperoxy-2-ethylhexanoate were added under stirring. This mixture was kept at 90 °C for additional 60 minutes. After cooling to room temperature, the product was collected in a vessel and stored under inert gas atmosphere. The weight average molecular weight of the resulting polymer was

Mw = 65.000 g/mol.

Polymer 3: MPEG 500 MA: MEMO: dimethylaminopropyl methacrylamide (86:10:4, wt% : wt% :wt%), Mw = 12000 g/mol

In this example a mixture containing 86 wt.% MPEG 500 MA (polyethylenglycol- methylether methacrylate, molecular weight of PEG: 500 g/mol, manufacturer: Evonik Performance Materials GmbH), 10 wt.% Dynasylan^® MEMO (manufacturer: Evonik Resource Efficiency GmbH) and 4 wt.% of dimethylaminopropyl methacrylamide

(manufacturer: Evonik Performance Materials GmbH) were used for polymerization. Dodecylmercaptane (1.95 wt% relating to the mixture of monomers) and 2-ethylhexyl thioglycolate (1.95 wt% relating to the mixture of monomers) were used as chain transfer agents (CTA). To this mixture 1 wt.% (relating to the mixture of monomers) of tert- butylperoxy-2-ethylhexanoate was added under stirring. This mixture was fed within 3.5 h into reaction vessel at 90 °C. After complete addition, another 0.95 wt% (relating to the mixture of monomers) of tert-butylperoxy-2-ethylhexanoate were added under stirring.

This mixture was kept at 90 °C for additional 60 minutes. After cooling to room

temperature, the product was collected in a vessel and stored under inert gas

atmosphere. The weight average molecular weight of the resulting polymer was

Mw = 12.000 g/mol.

Polymer 4: MPEG 950 MA : MEMO(90:10 wt% : wt%), Mw = 16.000 g/mol

In this example a mixture of 90 wt.% MPEG 950 MA (polyethylenglycol-methylether- methacrylate, molecular weight of PEG: 950 g/mol, manufacturer Evonik Performance Materials GmbH) and 10 wt.% of Dynasylan^® MEMO (manufacturer: Evonik Resource

Efficiency GmbH) were used for polymerization. Dodecylmercaptane (1.95 wt% relating to the mixture of monomers) and 2-ethylhexyl thioglycolate (1.95 wt% relating to the mixture of monomers) were used as chain transfer agents (CTA). To this mixture 1 wt.% (relating to the mixture of monomers) of tert-butylperoxy-2-ethylhexanoate was added under stirring. This mixture was fed within 3.5 h into the reaction vessel at 90 °C. After complete addition another 0.95 wt% (relating to the mixture of monomers) of tert-butylperoxy-2- ethylhexanoate were added under stirring. This mixture was kept at 90 °C for additional 60 minutes. After cooling to room temperature, the product was collected in a vessel and stored under inert gas atmosphere. The weight average molecular weight of the resulting polymer was Mw = 16.000 g/mol. Dispersion A

A 100 L stainless steel vessel was charged with 37 kg of water. Subsequently, under shear conditions (intensive mixing with Ystral Conti-TDS 3 at 3000 rpm, stator slots: 4 mm ring and 1 mm ring, rotor/stator separation about 1 mm), 10 kg of AEROSIL^® MOX 170 (fumed silica-alumina mixed oxide, Al content ca. 1 wt%, BET = 170 m²/g, manufacturer Evonik Resource Efficiency GmbH) were first sucked in. The remaining 5 kg of

AEROSIL® MOX 170 were sucked in stepwise in amounts of about 1 kg each time. After the end of the addition, shearing was continued at 3000 rpm for 30 min. By addition of 23 kg water, the solid content was adjusted to 20 wt.%. The resulting pH was in the range between 3-4. In order to grind fractions of coarse particles still remaining, this preliminary dispersion was passed through the Sugino Ultimaizer HJP-25050 high-energy mill at a pressure of 2500 bar with diamond nozzles of diameter 0.25 mm in two runs and subjected to further intensive grinding in this way. The concentration of the resulting AEROSIL® MOX 170 dispersion is 20% by weight. The average particle diameter dso was determined to be 112 nm by static light scattering method (LA- 950, Horiba Ltd., Japan).

Dispersion B

A 100 L stainless steel vessel was charged with 37 kg of water. Subsequently, under shear conditions (intensive mixing with Ystral Conti-TDS 3 at 3000 rpm, stator slots: 4 mm ring and 1 mm ring, rotor/stator separation about 1 mm), 10 kg of AEROSIL^® 200 (fumed silica with BET = 200 m²/g, manufacturer Evonik Resource Efficiency GmbH) were first sucked in. The remaining 5 kg of AEROSIL^® 200 were soaked in stepwise in amounts of about 1 kg each time. After the end of the addition, shearing was continued at 3000 rpm for 30 min. By addition of 23 kg water, the solid content was adjusted to 20 wt.%. The pH was adjusted to 9-10 by addition of a 25 wt.% ammonia solution, the particle size was in the range of ca. 130 nm as determined by static light scattering method (LA- 950, Horiba Ltd., Japan). Commercially available dispersions

The colloidal silica dispersions C and D were obtained from CWK Chemiewerk Bad Kostritz GmbH. The following two grades were used:

Dispersion C: Kostrosol K 1530: cationic colloidal silica dispersion, pH ca. 4.1 , specific BET surface area ca. 190 m²/g, dso particle size ca. 15 nm, solids content 30 wt.%.

Dispersion D: Kostrosol 0515: anionic colloidal silica dispersion, pH ca. 10.1 , specific BET surface area ca. 450 m²/g, dso particle size ca. 5 nm, solids content 15 wt.%.

Preparation of the mixtures containing polymer-functionalized metal oxide particles (nanofluids)

Example 1 : Dispersion A + Polymer 2

10 g of Polymer 2 were dissolved in 90 g of demineralized water under stirring. In a separate flask, 100 g of metal oxide dispersion (Dispersion A) were stirred and heated to 55 °C. To that fluid, 20 g of the dissolved polymer solution were added. The pH was adjusted to 9 by addition of 25 wt.% aqueous ammonia solution. The reaction mixture was stirred for 1 h at 55 °C and was afterwards cooled to room temperature (22 °C). The particle size dso was 218 nm as determined by dynamic light scattering. Example 2: Dispersion A + Polymer 3

10 g of Polymer 3 were dissolved in 90 g demineralized water under stirring. In a separate flask 100 g of metal oxide dispersion (Dispersion A) were stirred and heated to 55 °C. To that fluid, 20 g of the dissolved polymer solution were added. The pH was adjusted to 9 by addition of 25 wt.% aqueous ammonia solution. The reaction mixture was stirred for 1 h at 55 °C and was afterwards cooled to room temperature (22 °C). The particle size dso was

145 nm as determined by dynamic light scattering.

Example 3: Dispersion B + Polymer 4

10 g of Polymer 4 were dissolved in 90 g demineralized water under stirring. In a separate flask 100 g of metal oxide dispersion (Dispersion B) were stirred and heated to 55 °C. To that fluid, 40 g of the dissolved polymer solution were added. The pH was adjusted to 9 by addition of 25 wt.% aqueous ammonia solution. The reaction mixture was stirred for 1 h at 55 °C and was afterwards cooled to room temperature. The particle size dso was 229 nm as determined by dynamic light scattering. Example 4: Dispersion C + Polymer 1

10 g of Polymer 1 were dissolved in 90 g demineralized water under stirring. In a separate flask, 100 g of metal oxide dispersion (Dispersion C) were stirred and heated to 55 °C. To that fluid, 90 g of the dissolved polymer solution were added. The pH was adjusted to 9 by addition of 25 wt.% aqueous ammonia solution. The reaction mixture was stirred for 1 h at 55 °C and was afterwards cooled to room temperature. The particle size dso was 107 nm as determined by dynamic light scattering.

Example 5: Dispersion D + Polymer 1

10 g of Polymer 1 were dissolved in 90 g demineralized water under stirring. In a separate flask 100 g of metal oxide dispersion (Dispersion D) were stirred and heated to 55 °C. To that fluid 45 g of the dissolved polymer solution were added. The pH was adjusted to 9 by addition of 25 wt.% aqueous ammonia solution. The reaction mixture was stirred for 1 h at 55 °C and was afterwards cooled to room temperature. The particle size dso was 32 nm as determined by dynamic light scattering.

Example 6: Dispersion D + Polymer 1 (acidic pH)

10 g of Polymer 1 were dissolved in 90 g demineralized water under stirring. In a separate flask 100 g of metal oxide dispersion (Dispersion D) were stirred and heated to 55 °C. To that fluid 20 g of the dissolved polymer solution were added. The pH was adjusted to 4 by addition of concentrated acetic acid. The reaction mixture was stirred for 1 h at 55 °C and was afterwards cooled to room temperature. The particle size dso was 193 nm as determined by dynamic light scattering.

Comparative example 1

A hydrophobic polymer from WO2018019783 Polymer 1 (P1 ) was used for particle modification of metal oxide material (Dispersion A). 10 g of the polymer were added to 90 g of demineralized water under stirring. The polymer could not be dissolved at room temperature and a phase separation occurred. Even under heating the mixture to 55 °C the polymer was not dissolved. 10 g of this non-dissolved polymer/water mixture were added to 100 g of Dispersion A under stirring at 55 °C. The fluids did not form a homogeneous phase, particle modification could not be achieved. Preparation of synthetic sea water

Synthetic sea water (SSW) was prepared under laboratory conditions with a composition to mimic that from the North sea: 28.500 g of NaCI, 0.220 g of NaHCC>3, 4.066 g of Na₂S0₄, 1.625 g of CaCI₂ x 2 H₂0, 3.162 g of MgCI₂ x 6 H₂0, 0.024 g of SrCI₂ x 6 H₂0 and 0.721 g of KCI were dissolved in 900 g of deionized water (Dl water) and the solution made up to 1 liter with Dl water.

The prepared sea water had a density of 1.024 g/cm³ and viscosity of 1.025 cP at 21 5°C. The amount of total dissolved salts (TDS) in the SSW was approximately 35000 ppm.

Synthetic sea water stability test

99.5 g of the synthetic sea water solution were initially charged into a 125 mL wide necked bottle made of NALGENE® FEP (tetrafluoroethylene-hexafluoropropylene copolymer; Thermo Scientific), 0.5 g of the dispersion under test was added and the mixture was homogenized by shaking. The mixture was stored at 25°C or at 50 °C and the occurrence of a precipitate was visually monitored. If no precipitate was formed after a specified time, the dispersion was considered to be“sea water-stable”. The results of these tests are summarized in Table 1 :

Table 1 : Synthetic sea water stability test

As it can be seen from Table 1 , all the tested mixtures containing polymer-functionalized metal oxide particles were stable in sea water at 25 °C, whereas at 50 °C all the mixtures except for the one from Example 6 were stable.

Crude oil

The degassed crude oil used for core flooding experiments was characterized by

Saturates, Aromates, Resins and Asphaltenes (SARA Analysis). The used oil has the following composition in wt.% (normalized): Table 2: composition of the crude oil used

Preparation of core for core flooding experiments

The materials used throughout core-flooding tests included Berea sandstone core plugs, fluids, and core-flooding rig. The experiments were conducted to determine oil recovery factor. All experiments were performed at room temperature.

The following core preparation procedure was employed:

1. Core Cleaning: All core impurities were removed by continuous extraction of the cores in Soxhlet apparatus with methanol for approximately 8 hours. The next step was to dry them at 60 °C for 2-3 days, to retain the clay’s intrinsic structure within the pore space.

2. Porosity and Permeability: Petrophysical properties were measured using two methods.

Porosity was measured via Helium Porosimeter and weight difference between the dried and SYNTHETIC SEA WATER saturated core. Air permeameter and core-flooding techniques were employed to determine the permeability of the dried and saturated cores, respectively.

3. Core Saturation: The cores were placed in a beaker and vacuumed at 100 mbar for 2 hours before allowing seawater to enter the core to establish 100% saturation. The system was let under the same 100 mbar vacuum pump pressure for additional 2-3 hours. Then, the cores were removed and submerged in the same seawater for 10 days at ambient temperature, to attain ionic equilibrium with the rock constituents.

4. Establishing Irreducible Water Saturation (S_Wir): The crude oil was pumped to displace synthetic seawater in a confined core plug in the core holder.

Rock Core-Flooding Rig

Figure 1 shows a schematic diagram of the core-flooding rig with the main components labelled:

1 : Cylinder filled with hydrocarbon fluid (4)

2: Injection pump

3: Swagelock valve

4: Hydrocarbon fluid (Exxsol D60)

5: Piston used to separate fluids 6: Crude oil

7: Seawater

8: Nanofluid

9: Differential pressure gauge

10: Bypass valve

1 1 : Core holder

12: Sleeve pressure

13: Core plug

14: Check valve

15: Back Pressure Regulator (BPR)

To aid flowing the fluids (6-8) through the core plug (13), the rig utilizes injection pump (2) with three accumulators containing the designated fluids (crude oil (6), SYNTHETIC SEA WATER (7) and nanofluid (8)) mounted vertically inside the convection oven, a Hassler core-holder (11 ) type with a Viton sleeve, and the pressure regulators connected at the inlet and outlet of the core holder. The Back Pressure Regulator (BPR, 15) was not used. The flowing fluids are transported by PTFE tubes with inner diameter of 1/16 inches. The Swagelok fittings and valves were used to direct the fluids. All the equipment carrying the fluids were placed inside the temperature controlled oven.

General Core-Flooding Procedure

The text below outlines an unsteady-state core-flooding procedure adopted to evaluate the effect of the newly formulated metal oxide dispersions on oil recovery.

1. Nanofluid-Flooding as Secondary Oil Recovery

• A 100% seawater saturated core was loaded in the core-holder and flowed with seawater to replace the soaking seawater for 1-2 pore volumes (PVs).

• Crude Oil Injection: Crude oil was injected at different flow-rates, 0.5, 1.5 and 3.0 ml/min until oil production occurred. This procedure was conducted for 5 to 8.5 PVs. The flow- rate was sequentially increased to reduce zones of end-effects. This also included shifting the core injection end to even fluid distribution.

· Nanofluid-Flooding: Nanofluid was injected at 0.2 ml/min until no oil production. Oil production was collected for every 1/4 PV injected after the dead volume was produced. Then, oil recovery factor and pressure recorded as function of PV injected. All core-flooding experiments were performed using two nearly identical cores plugs to determine experimental repeatability. Additional studies were conducted on nanofluid flooded cores (at S_or ). That is, one core was soaked in the injected nanofluid at 40 °C for 10 days to simulate prolonged interaction between the nanoparticles and the rock system, the other core was immediately submitted to the wettability assessment.

Secondary Nanofluid-Flooding in Water-wet Cores

Core plugs with 3.75 cm diameter and length of 4.5 cm were used for tests. The water permeability and porosity ranged from 247 to 304 mD and 16.0 to 18.3%, respectively. The oil in place and residual water saturation achieved after primary oil drainage ranged from 5.4 to 6.7 ml. and S_wir from 19.6% to 39.9% of total PV.

Results

Table 3: Results of secondary core flooding experiments

Oil recovery factor at the end of secondary water flooding in water-wet cores

As it can be seen from the results summarized in Table 3, dispersions according to the invention (Examples 1-5) provided significantly higher oil recovery factors than pure synthetic sea water. Thus, the average oil recovery factors varied from 47.6% to 54.5% of Original Oil in Place (OOIP) for Examples 1-5 compared with 39.7% for reference water- flooding.

Claims

1 . Polymer-metal oxide particle, comprising at least one metal oxide bonded to one or more polymers, each polymer comprising:

a) units derived from one or more compounds of formula (I) or (la)

wherein R = H or CH₃

0 < h < 2

Si(A)h(X)3-h is a silane functional group

A is H or a branched or unbranched C1 to C4 alkyl residue,

X is selected from H, Cl or a group OY, wherein Y is H or a C1 to C30 branched or unbranched alkyl-, alkenyl-, aryl-, or aralkyl- group, branched or unbranched C2 to C30 alkylether-group or branched or unbranched C2 to C30

alkylpolyether-group or a mixture thereof,

and

b) units derived from one or more compounds of formula (II)

wherein R¹ = H or CH₃

each of R², R³, R⁴ and R⁵ independently is H or a branched or unbranched C1 to C6 alkyl group 3 < n < 1000

R⁶ is H, branched or unbranched C1 to C30 alkyl group,

wherein the weight ratio of the metal oxide particle to the one or more polymers bonded to the metal oxide particle is in the range of 1 : 0.03 to 1 : 1.8.

2. The polymer-metal oxide particle according to claim 1 , wherein the compound of formula (I) is selected from 3-(triethoxysilyl)propyl methacrylate,

3-(trimethoxysilyl)propyl methacrylate and 3-(trichlorosilyl)propyl methacrylate.

3. The polymer-metal oxide particle according to either of claims 1 to 2, wherein in the compound of formula (II) R², R³, R⁴ and R⁵ = H and R⁶ = CH₃.

4. The polymer-metal oxide particle according to either of claims 1 to 3, wherein in the compound of formula (II) 5 < n < 100.

5. The polymer-metal oxide particle according to either of claims 1 to 4, wherein each polymer comprises:

a) 0.1 to 50 % by weight of units derived from one or more compounds of formula (I) or (la), based on the total weight of the polymer, and

b) 50 to 99.9 % by weight of units derived from one or more compounds of formula (II), based on the total weight of the polymer.

6. The polymer-metal oxide particle according to either of claims 1 to 5, wherein each polymer comprises:

0 to 49.9 % by weight, of units derived from one or more alkyl (meth)acrylate monomers of formula (III), based on the total weight of the polymer,

7. The polymer-metal oxide particle according to according to either of claims 1 to 6, wherein each polymer comprises:

0 to 20 % by weight, of units derived from one or more (meth)acrylamide monomers of formula (IV), based on the total weight of the polymer, where R⁹ is hydrogen or methyl, each of R¹⁰ and R¹¹ independently means hydrogen or a linear, branched or cyclic alkyl residue with 1 to 30 carbon atoms, optionally with further substituents.

8. The polymer-metal oxide particle according to either of claims 1 to 7, wherein each polymer has a weight average molecular weight of 1.000 g/mol to 100.000 g/mol.

9. The polymer-metal oxide particle according to either of claims 1 to 8, wherein the metal oxide particle is selected from S1O2, AI2O3, T1O2, doped or mixed oxides, core shell metal oxides of at least two elements selected from Si, Al and Ti.

10. The polymer-metal oxide particle according to either of claims 1 to 9, wherein the weight ratio between the metal oxide particle and the one or more polymers bonded to the metal oxide particle is in the range of 1 :0.04 to 1 :1.4.

1 1. Process for producing the polymer-metal oxide particle as defined in either of claims 1 to 10, comprising the following steps:

(i) preparing a polymer as defined in either of claims 1 to 10 by polymerizing a monomer composition comprising at least one compound a of formula (I) and compound b of formula (II),

(ii) bonding the polymer prepared in step (I) with the metal oxide particle.

12. Aqueous dispersion comprising the metal oxide particle according to either of claims 1 to 10.

13. Aqueous dispersion according to claim 12, comprising 5 to 30 %, by weight, of the polymer-metal oxide particles.

14. Aqueous dispersion according to claim 12 or 13, wherein the pH of the dispersion is from 5 to 12.

15. Use of the polymer-metal oxide particle according to one of claims 1 to 10 or of the aqueous dispersion according to one of claims 12 to 14 as a constituent of pharmaceutical preparations, cosmetic preparations, water-based paints and coatings, of cleaning products, of dishwashing detergents, of coating slips in the paper industry, of water-based lubricants, of heat transfer fluids in battery systems or other electrical equipment, and for obtaining mineral oil.