Method for preparing a dispersion of monohydrated lithium hydroxide in oil

Abstract

The present invention relates to a method for preparing a dispersion comprising particulate LiOH.H2O, said method comprising: - at least one step (E1) of forming a suspension (S1) comprising LiOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function; - at least one step (E2) of homogenizing the suspension (S1) to obtain a homogenized suspension (S1); - at least one step (E3) of milling the homogenized suspension (S1) to form a dispersion comprising particulate LiOH.H2O.

Description

[0001] PROCESS FOR PREPARING A DISPERSION OF LITHINE MONOHYDRATE IN OIL

[0002] The present invention relates to a process for preparing a dispersion of lithium hydroxide (or lithia) in oil, intended mainly for the manufacture of lubricating greases.

[0003] Lithium dispersions are used in the preparation of lubricating greases due to their excellent mechanical and thermal properties, essential for demanding applications. Lithium hydroxide (or lithium) acts as a thickening agent and, when it reacts with fatty acids, forms lithium soaps, key components for the performance of lubricating greases. These soaps impart high stability at extreme temperatures and good water resistance, making the grease suitable for industrial and automotive environments where such conditions are common.

[0004] These dispersions are crucial for the production of high-performance lubricating greases, as they allow for the stable conditioning of lithium hydroxide and thus limit the handling of this salt by operators, as it is considered a dangerous and toxic product.

[0005] However, the high cost of lithium hydroxide presents an economic challenge in the production of these greases, making them more expensive than other alternatives. To reduce costs while maintaining performance, lithium hydroxide monohydrate (UOH.H2O) is often preferred in formulations because it is more widely available, easier to handle, and provides similar properties.

[0006] The use of lithium monohydrate, however, necessitates adjustments to the dispersion preparation process due to the water molecules present in lithium hydroxide monohydrate. Therefore, the primary challenge lies in removing this water to ensure a stable and effective dispersion.

[0007] Patent EP 2 087 080 B1 describes a process for preparing lithium hydroxide dispersions, particularly in monohydrate form, in an organic medium such as oil. This process further includes a dehydration step, which removes water from the lithium hydroxide, thereby improving the reactivity and effectiveness of the prepared dispersions.

[0008] However, the dehydration steps are very energy-intensive because they require the application of a large amount of heat to remove the water molecules present in the dispersion, especially when the dispersions are prepared on a large scale. Therefore, there is a need to provide a new, less energy-intensive process for preparing lithium dispersions.

[0009] Therefore, there is a need to provide a preparation process that allows for the preparation of stable lithium dispersions with a reduced carbon footprint.

[0010] There is also a need to provide a process for preparing stable lithium monohydrate dispersions with improved mechanical and thermal properties.

[0011] The present invention aims to provide a less energy-intensive process for preparing stable and efficient lithium dispersions for lubricating grease formulation.

[0012] The present invention also aims to provide stable dispersions of lithium monohydrate with improved mechanical and thermal properties for the formulation of lubricating grease.

[0013] The present invention also aims to provide a less energy-intensive process for preparing stable and high-performance lubricating greases.

[0014] Thus, the present invention relates to a method for preparing a grease comprising:

[0015] - at least one step (E1) of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant of formula

[0016] (I): in which R represents an alkyl group, possibly substituted, linear or branched, comprising from 8 to 23 carbon atoms and possibly comprising a terminal carboxylic acid function;

[0017] - at least one step (E2) of homogenizing the suspension (S1) to obtain a homogenized suspension (S1);

[0018] - at least one step (E3) of grinding the homogenized suspension (S1) to form a dispersion comprising particulate UOH.H2O (S2); and

[0019] - at least one step (E4) consisting of adding, to said dispersion comprising particulate UOH.H2O (S2), at least one base oil, at least one mono- or di-acid comprising 8 to 28 carbon atoms, and water, to obtain said grease. The present invention also relates to a process for preparing a dispersion comprising particulate UOH.H2O, said process comprising:

[0020] - at least one step (E1) of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function;

[0021] - at least one step (E2) of homogenizing the suspension (S1) to obtain a homogenized suspension (S1);

[0022] - at least one step (E3) of grinding the homogenized suspension (S1) to form a dispersion comprising particulate UOH.H2O.

[0023] The inventors surprisingly discovered that the introduction of a non-ionic surfactant comprising at least one carboxylic acid function with lithium hydroxide monohydrate (i.e. UOH.H2O) further enabled the formation of a stable lithium monohydrate dispersion, no longer requiring the removal of water present in the dispersion, and therefore it was possible to avoid implementing a very energy-intensive evaporation step.

[0024] It has also been found that the use of this specific surfactant makes it possible to obtain a high-performance and stable grease, also without the need for water removal, thus resulting in a substantial gain in energy consumption.

[0025] Summary of the invention

[0026] The present invention relates to a method for preparing a dispersion comprising particulate UOH.H2O, said method comprising:

[0027] - at least one step (E1) of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function;

[0028] - at least one step (E2) of homogenizing the suspension (S1) to obtain a homogenized suspension (S1);

[0029] - at least one step (E3) of grinding the homogenized suspension (S1) to form a dispersion comprising particulate UOH.H2O.

[0030] According to one embodiment of the process of the invention, the non-ionic surfactant has the formula (I): in which R represents an alkyl group, possibly substituted, saturated or unsaturated, linear or branched, comprising from 8 to 23 carbon atoms and possibly including a terminal carboxylic acid function.

[0031] Preferably, the non-ionic surfactant is chosen from the group consisting of fatty acids, polyethoxylated fatty acids, and mixtures thereof.

[0032] In particular, the non-ionic surfactant is chosen from saturated or unsaturated fatty acids, hydroxylated or non-hydroxylated, having between 12 and 24 carbon atoms, preferably between 16 and 22 carbon atoms.

[0033] According to one embodiment of the process of the invention, the non-ionic surfactant is selected from the group consisting of stearic acid, hydroxystearic acid, oleic acid, 12-hydroxyoleic acid, riconoleic acid, palmitic acid, myristic acid, lignoceric acid, hydroxypalmitic acid and mixtures thereof.

[0034] According to one embodiment of the process of the invention, the non-ionic surfactant is present in the suspension (S1) in a content ranging from 1% by weight to 5% by weight, preferably ranging from 2% by weight to 3% by weight, relative to the total weight of said suspension.

[0035] According to one embodiment of the process of the invention, UOH.H2O is present in the suspension (S1) in a content ranging from 10% to 70% by weight, preferably ranging from 30% to 60% by weight, relative to the total weight of said suspension.

[0036] According to one embodiment of the process of the invention, the mass ratio UOH.H2O: non-ionic surfactant in the suspension (S1) is from 2 to 140, preferably from 10 to 60, and even more preferably from 15 to 30.

[0037] According to one embodiment of the process of the invention, step (E2) is carried out at a temperature ranging from 80°C to 110°C, preferably ranging from 82°C to 100°C, and even more preferably ranging from 85°C to 95°C.

[0038] According to one embodiment of the process of the invention, step (E2) is carried out for a period of 25 minutes to 40 minutes, and preferably the step is carried out for 30 minutes.

[0039] The present invention also relates to a composition, preferably in dispersion form, comprising:

[0040] - 1% to 5% by weight of at least one non-ionic surfactant having at least one carboxylic acid function;

[0041] - 15% to 65% by weight of at least one base oil; and

[0042] - 40% to 70% by weight of particulate UOH.H2O, relative to the total weight of the composition, said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0043] The present invention also relates to a method for preparing a lubricating grease comprising at least one step of introducing into a reactor at least one base oil, at least one long-chain fatty acid, at least one dispersion of lithium hydroxide monohydrate in oil and water to form a reaction mixture, characterized in that said dispersion is obtained by the method as defined above.

[0044] As mentioned above, the process for preparing a grease according to the invention comprises the following steps:

[0045] - at least one step (E1) of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant of formula

[0046] (I): in which R represents an alkyl group, possibly substituted, linear or branched, comprising from 8 to 23 carbon atoms and possibly comprising a terminal carboxylic acid function;

[0047] - at least one step (E2) of homogenizing the suspension (S1) to obtain a homogenized suspension (S1);

[0048] - at least one step (E3) of grinding the homogenized suspension (S1) to form a dispersion comprising particulate UOH.H2O (S2); and

[0049] - at least one step (E4) consisting of adding to said dispersion comprising particulate UOH.H2O (S2), at least one base oil, at least one mono- or di-acid comprising 8 to 28 carbon atoms, and water, to obtain said grease.

[0050] In particular, step (E4) consists of introducing into a reactor at least one base oil, at least one monoacid or diacid comprising 8 to 28 carbon atoms, at least the particulate UOH.H2O dispersion (S2) in oil and water, to form a reaction mixture.

[0051] Preferably, the fat preparation process according to the invention does not include a step of dehydrating the particulate UOH.H2O dispersion (S2).

[0052] According to one embodiment of the fat preparation process according to the invention, the non-ionic surfactant is selected from saturated or unsaturated fatty acids, hydroxylated or non-hydroxylated, having between 12 and 24 carbon atoms, preferably between 16 and 22 carbon atoms. Preferably, the non-ionic surfactant is selected from the group consisting of stearic acid, hydroxystearic acid, 12-hydroxystearic acid, oleic acid, 12-hydroxyoleic acid, ricinoleic acid, palmitic acid, myristic acid, lignoceric acid, hydroxypalmitic acid, and mixtures thereof.

[0053] Preferably, the non-ionic surfactant corresponds to formula (II): in which A is a hydrocarbon chain, possibly substituted, linear or branched, saturated or unsaturated, comprising from 8 to 23 carbon atoms, preferably from 8 to 15 carbon atoms.

[0054] Preferably, the non-ionic surfactant is chosen from azelaic acid, suberic acid, sebacic acid and mixtures thereof.

[0055] According to one embodiment of the grease preparation process according to the invention, the non-ionic surfactant is present in the suspension (S1) in a content ranging from 0.3% by weight to 5% by weight, preferably ranging from 2% by weight to 3% by weight, relative to the total weight of said suspension.

[0056] According to one embodiment of the grease preparation process according to the invention, UOH.H2O is present in the suspension (S1) in a content ranging from 10% to 70% by weight, preferably ranging from 30% to 60% by weight, relative to the total weight of said suspension.

[0057] According to one embodiment of the grease preparation process according to the invention, the mass ratio UOH.H2O 0: non-ionic surfactant in the suspension (S1) is from 2 to 140, preferably from 10 to 60, and even more preferably from 15 to 30.

[0058] According to one embodiment of the grease preparation process according to the invention, step (E2) is carried out at a temperature ranging from 80°C to 110°C, preferably ranging from 82°C to 100°C, and even more preferably ranging from 85°C to 95°C.

[0059] According to one embodiment of the fat preparation process according to the invention, step (E2) is carried out for a period of 25 to 40 minutes, and preferably the step is carried out for 30 minutes.

[0060] The present invention also relates to a composition comprising:

[0061] - 1% to 5% by weight of at least one non-ionic surfactant as defined above, in particular of formula (I) or formula (II);

[0062] - 15% to 65% by weight of at least one base oil; and

[0063] - 40% to 70% by weight of particulate UOH.H2O, relative to the total weight of the composition, said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0064] Detailed description

[0065] As mentioned above, the present invention relates to a process for preparing a dispersion comprising particulate UOH.H2O, said process comprising:

[0066] - at least one step (E1) of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function;

[0067] - at least one step (E2) of homogenizing the suspension (S1) to obtain a homogenized suspension (S1);

[0068] - at least one step (E3) of grinding the homogenized suspension (S1) to form a dispersion comprising particulate UOH.H2O.

[0069] For the purposes of this invention, "suspension" means a mixture of at least one compound in solid form with a liquid organic medium. In the context of this invention, the compound in solid form consists of UOH.H2O particles having an average diameter ranging from 100 pm to 700 pm, preferably from 300 pm to 600 pm, and even more preferably from 400 pm to 500 pm.

[0070] For the purposes of this invention, "dispersion" refers to a system in which solid particles are uniformly dispersed in an organic liquid medium, thereby creating a homogeneous and stable mixture. This system is used to improve the distribution of components in various products, such as paints, cosmetics, and greases, and can influence the physical and chemical properties of the final product.

[0071] The difference between a dispersion according to the invention and a suspension lies in the average diameter of the particles present in them.

[0072] Preferably the lithium hydroxide monohydrate particles present in the dispersion have an average diameter ranging from 30 pm to 80 pm, preferably ranging from 40 pm to 60 pm.

[0073] The average diameter of the particles was measured by optical microscopy, a method commonly used to observe the microstructure of materials.

[0074] For the purposes of this invention, "stable dispersion" means a dispersion in which less than 1% by weight of the solid particles separate from the dispersion after 30 days, when the dispersion is maintained at room temperature or at 50°C without agitation.

[0075] Preferably, the dispersion prepared by the process according to the invention is a stable dispersion after 30 days of storage at a temperature of 50°C. Preferably, the dispersion prepared by the process according to the invention is a stable dispersion after 30 days of storage at room temperature.

[0076] By "organic medium" we mean an environment containing at least one oil or a mixture of oils in combination with one or more surfactants.

[0077] More specifically, the dispersion mentioned in the present invention refers to a dispersion of lithium hydroxide monohydrate particles in an oily medium.

[0078] As mentioned above, the process according to the invention includes a step (E1) consisting of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one surfactant comprising at least one carboxylic acid function.

[0079] In the present invention, lithium monohydrate (UOH.H2O) is in solid form and consists of lithium ions (Li + ) and hydroxide ions (OH“), linked to a water molecule (H2O).

[0080] The base oil(s) may be chosen from among the mineral, synthetic or natural, animal or vegetable lubricating base oils known to those skilled in the art.

[0081] The base oils used in the process according to the invention can be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATI EL classification) (Table 1) or mixtures thereof.

[0082] [Table 1] Mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalpha removal, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

[0083] Mixtures of synthetic and mineral oils can also be used.

[0084] The base oils for the lubricating compositions according to the invention can also be selected from synthetic oils, such as certain esters of carboxylic acids and alcohols, and from polyalphaolefins. Polyalphaolefins used as base oils are, for example, obtained from monomers comprising 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100 °C is between 1.5 and 15 mm 2 . s -1according to ASTM D445. Their average molecular mass is generally between 250 g / mol and 3000 g / mol according to ASTM D5296.

[0085] According to one embodiment, the base oil can be chosen from oils of natural origin such as, for example, oils of vegetable or animal origin.

[0086] Naturally derived oils include vegetable oils such as soybean oil, linseed oil, canola oil, rapeseed oil, castor oil, cottonseed oil, sunflower oil, and palm oil.

[0087] According to one embodiment, the base oil is chosen from synthetic oils, mineral oils and mixtures thereof.

[0088] According to another embodiment, the base oil is a mixture of at least one synthetic oil and at least one mineral oil.

[0089] Advantageously, the base oil is chosen from mineral oils, preferably the base oil is chosen from naphthenic mineral base oils, paraffinic mineral base oils and mixtures thereof.

[0090] Preferably, the base oil has a kinematic viscosity at 40°C, measured according to the ASTM D445 method, between 75 mPa.s and 150 mPa.s, more preferably between 80 mPa.s and 120 mPa.s.

[0091] Preferably, the base oil has a flash point measured according to the ASTM D92 method between 200°C and 250°C, preferably between 215°C and 235°C.

[0092] Generally, the base oil(s) are present in the suspension (S1) in a content ranging from 15% to 75% by weight, preferably from 30% to 60% by weight, relative to the total weight of the suspension (S1).

[0093] The surfactant used in step (E1) is a non-ionic surfactant comprising at least one carboxylic acid function. In one embodiment, the non-ionic surfactant has the formula (I): in which R represents an alkyl group, possibly substituted, saturated or unsaturated, linear or branched, comprising from 8 to 23 carbon atoms and possibly including a terminal carboxylic acid function.

[0094] According to the invention, the term "alkyl" designates a saturated, linear or branched, optionally substituted, hydrocarbon aliphatic group comprising, unless otherwise stated, from 8 to 23 carbon atoms.

[0095] Preferably, R is a saturated alkyl group, possibly substituted, linear or branched, comprising 8 to 23 carbon atoms and possibly including a terminal carboxylic acid function.

[0096] Preferably, R is a saturated, unsubstituted, linear or branched alkyl group comprising 8 to 23 carbon atoms and a terminal carboxylic acid function. According to this embodiment, R corresponds to a radical of the formula HOOC-Ai-, in which Ai is a hydrocarbon aliphatic alkylene radical comprising 8 to 23 carbon atoms.

[0097] In the context of the present invention, "alkylene" radicals represent radicals (also called alkylides) derived from alkanes from which both terminal hydrogen atoms have been removed. The term "alkylene" here designates a divalent radical corresponding to an alkyl radical in which one of the terminal hydrogen atoms has been removed. Such a radical corresponds to a C radical n H2n, where n represents the number of carbon atoms.

[0098] According to one embodiment, in formula (I), R represents a formula group -C nH2n-COOH, where n is an integer from 8 to 23.

[0099] In one embodiment, R is a saturated, unsubstituted, linear or branched alkyl group comprising 8 to 23 carbon atoms. In this embodiment, in formula (I), R represents a group of formula -C n H2n+i, where n is an integer from 8 to 23.

[0100] According to one embodiment, in formula (I), R is a saturated alkyl group, substituted by at least one linear or branched hydroxyl group, comprising from 8 to 23 carbon atoms. According to this embodiment, at least one of the carbon atoms of the alkyl group is substituted by an OH group. According to one embodiment of the invention, the nonionic surfactant has a chemical structure corresponding to formula (II): in which A is a hydrocarbon chain, possibly substituted, linear or branched, saturated or unsaturated, comprising from 8 to 23 carbon atoms, preferably from 8 to 15 carbon atoms.

[0101] Preferably, in formula (II), chain A is an unsubstituted, saturated hydrocarbon chain comprising only carbon and hydrogen atoms.

[0102] Preferably, chain A is an alkylene radical as defined above, comprising 8 to 23 carbon atoms.

[0103] According to the fat preparation process according to the invention, the surfactant is not a (poly)ethoxylated fatty acid.

[0104] Preferably, the surfactant is chosen from azelaic acid, suberic acid, sebacic acid and mixtures thereof.

[0105] Preferably, the surfactant according to the invention is a compound having at least one acid function and having a hydrocarbon chain containing between 8 and 24 carbon atoms.

[0106] In other words, the surfactant is chosen from mono-, di- or tri-acids comprising between 8 and 24 carbon atoms.

[0107] Preferably, the surfactant is chosen from non-ionic compounds, particularly fatty acids, polyethoxylated fatty acids, and mixtures thereof. "Polyethoxylated fatty acids" refers to fatty acids with a carbon chain of 12 to 24 carbon atoms that have reacted with ethylene oxide to form polyethoxylated derivatives. Examples include polyethoxylated lauric acid and polyethoxylated stearic acid.

[0108] Advantageously, the surfactant is chosen from saturated or unsaturated fatty acids, hydroxylated or non-hydroxylated, having between 12 and 24 carbon atoms, preferably between 16 and 22 carbon atoms.

[0109] Preferably, the surfactant is selected from stearic acid, hydroxystearic acid, oleic acid, 12-hydroxyoleic acid, riconoleic acid, palmitic acid, myristic acid, lignoceric acid, hydroxypalmitic acid, and mixtures thereof. In a preferred embodiment, the surfactant is selected from hydroxylated saturated fatty acids, more particularly from hydroxystearic acid, hydroxypalmitic acid, and their derivatives.

[0110] Preferably, the surfactant used in step (E1) is chosen from hydroxystearic acid and its derivatives, more particularly the surfactant is 12-hydroxystearic acid (12HSA).

[0111] According to one embodiment, the surfactant according to the invention can be chosen from saturated or unsaturated diacids, hydroxylated or non-hydroxylated, having between 8 and 24 carbon atoms, preferably having between 8 and 14 carbon atoms.

[0112] Preferably, the surfactant is chosen from azelaic acid, suberic acid, sebacic acid and mixtures thereof.

[0113] According to one embodiment of the invention, the non-ionic surfactant used in step (E1) is a mixture of at least one surfactant selected from fatty acids, polyethoxylated fatty acids, and mixtures thereof, and at least one acid of formula (II).

[0114] Advantageously, the surfactant is a mixture of at least one acid selected from the group consisting of stearic acid, hydroxystearic acid, oleic acid, 12-hydroxyoleic acid, riconoleic acid, palmitic acid, myristic acid, lignoceric acid, hydroxypalmitic acid and mixtures thereof, and another acid selected from the group consisting of azelaic acid, suberic acid, sebacic acid and mixtures thereof.

[0115] Preferably, the surfactant is present in the suspension (S1) in a content ranging from 0.5% by weight to 5% by weight, preferably ranging from 1% by weight to 3% by weight relative to the total weight of the suspension.

[0116] Preferably, the surfactant is present in the suspension (S1) in a content ranging from 0.5% by weight to 2% by total weight of the suspension.

[0117] Preferably, UOH.H2O is present in the suspension (S1) in a content ranging from 10% to 70% by weight, preferably ranging from 30% to 60% by weight, relative to the total weight of the suspension.

[0118] Preferably, the mass ratio of UOH.H2O to non-ionic surfactant in the suspension (S1) is from 2 to 140, preferably from 10 to 60, and even more preferably from 15 to 30.

[0119] The UOH.H2O introduced in step (E1) is solid; preferably, the UOH.H2O introduced is in the form of particles having an average diameter ranging from 100 pm to 700 pm, preferably ranging from 150 pm to 500 pm. The process according to the invention comprises at least one step (E2) of homogenizing the suspension (S1). This step is carried out after step (E1).

[0120] Preferably, step (E2) in the process according to the invention is carried out at a temperature ranging from 80°C to 110°C, preferably ranging from 82°C to 100°C and even more preferably ranging from 85°C to 95°C.

[0121] Without wanting to be linked to any theory, these temperature ranges correspond to the melting temperatures of the surfactants used in step (E1).

[0122] Advantageously, step (E2) is carried out in a period of time ranging from 25 minutes to 40 minutes, and preferably step (E2) is carried out for 30 minutes.

[0123] Without intending to be bound by any particular theory, the inventors discovered that homogenizing the suspension over this time interval results in a more stable dispersion. Indeed, the surfactant according to the invention reacts with a portion of the lithium monohydrate, forming a viscous mixture that traps the lithium monohydrate particles, thus preventing their sedimentation.

[0124] A more stable dispersion is defined as a dispersion in which the sedimentation rate of particles is less than 1%.

[0125] For the purposes of this invention, "sedimentation rate" refers to the quantity of dispersed particles that settle at the bottom of the system.

[0126] The "sedimentation rate" as defined above can be measured by various methods known to those skilled in the art, such as dispersion transmittance measurements using a spectrophotometer, visual tests, or turbidity measurement tests.

[0127] According to the invention, the suspension obtained following step (E2) can be transformed into a dispersion by grinding in order to reduce the size of the solid particles of lithium hydroxide monohydrate and to disperse the particles obtained in an organic medium.

[0128] The grinding of the suspension can be carried out using various types of mills, such as media mills, grinding wheels, ball mills, roller mills, attrition mills, disintegrators, microfluidizers, jet mills, ultrasonic mills, and / or homogenizers. Mills may include bead mills, sand mills, pebble mills, and / or bead mills. The media used in media mills (e.g., balls) have an average diameter of approximately 0.3 to 2.5 mm.

[0129] As an example, one can cite ball mills using balls with an average diameter of between approximately 1.5 and 2.5 mm, and in some cases between approximately 1.8 and 2.2 mm, with a preference for approximately 2 mm. Another example is a ball mill using balls with an average diameter of between approximately 0.3 and 0.8 mm, preferably between approximately 0.4 and 0.7 mm, and even more preferably approximately 0.5 mm.

[0130] Thus, the process according to the invention includes at least one step (E3) of grinding the suspension (S1) to form a dispersion comprising particulate UOH.H2O.

[0131] By "particulate UOH.H2O", we mean, in the sense of the invention, UOH.H2O particles having an average diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0132] Preferably, the size of the lithia monohydrate particles present in the dispersion following step (E3) has an average diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0133] Advantageously, the dispersion according to the invention has a particulate UOH.H2O content after step (E3) ranging from 40% to 70% by weight, relative to the total weight of the dispersion.

[0134] Advantageously, the process according to the invention does not include a dehydration step.

[0135] Advantageously, the process according to the invention does not include a dehydration step of the homogenized suspension (S1).

[0136] The present invention also relates to a composition, preferably in dispersion form, comprising:

[0137] - from 0.5% to 5% by weight of at least one non-ionic surfactant having at least one carboxylic acid function;

[0138] - 15% to 65% by weight of at least one base oil; and

[0139] - 40% to 70% by weight of particulate UOH.H2O, relative to the total weight of the composition, said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0140] Preferably, in the aforementioned composition, the non-ionic surfactant is as defined above. According to one embodiment, in the composition, the non-ionic surfactant conforms to one of the aforementioned formulas (I) or (II).

[0141] Preferably, the composition according to the invention is a dispersion.

[0142] In one embodiment, the non-ionic surfactant is present in the composition at a concentration of 0.5% to 5% by weight, preferably 2% to 3% by weight, relative to the total weight of the dispersion. In another embodiment, the base oil is present in the composition at a concentration of 15% to 65% by weight, preferably 20% to 50% by weight, and even more preferably 30% to 45% by weight, relative to the total weight of the dispersion.

[0143] According to one embodiment, particulate UOH.H2O is present in the composition in a content ranging from 40% to 70% by weight, preferably from 20% to 50% by weight, and even more preferably from 50% to 65% by weight, relative to the total weight of the dispersion.

[0144] Preferably, the composition according to the invention is a dispersion comprising:

[0145] - 2% to 3% by weight of at least one non-ionic surfactant having at least one carboxylic acid function;

[0146] - 30% to 45% by weight of at least one base oil; and

[0147] - 50% to 65% by weight of particulate UOH.H2O, relative to the total weight of the composition, said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0148] This dispersion can also be used for the preparation of lubricating greases.

[0149] In this application, the terms "grease" or "grease composition" or "lubricating grease" are used interchangeably to refer to the product obtained at the end of the process of the invention, comprising the aforementioned steps (E1) to (E4).

[0150] The grease compositions prepared from the dispersion include:

[0151] - at least one base oil;

[0152] - at least one thickener chosen from among the lithium salts of fatty acids;

[0153] - possibly one or more additives, said additives being different from the base oils and different from the thickeners.

[0154] The base oil is specifically as defined above.

[0155] Preferably, the base oil is a mineral oil or a mixture of base oils comprising at least one mineral oil.

[0156] Preferably, the base oil is a mineral oil or a mixture of base oils comprising at least one Group I oil.

[0157] According to one embodiment, the aforementioned fat compositions comprise, as a base oil, at least one mineral oil; preferably, they comprise several base oils, including at least one mineral oil (or a Group I oil). The thickener as defined above is selected from lithium salts of fatty acids, in particular from lithium salts of mono- or di-fatty acids, said mono- or di-acids preferably comprising from 8 to 28 carbon atoms.

[0158] Thickeners are obtained by a reaction between a chain fatty acid and the lithium hydroxide monohydrate particles present in the previously described dispersion. Specifically, the fatty acid reacts with the lithium hydroxide monohydrate in the dispersion to thicken the composition, giving it the consistency of a lubricating grease.

[0159] Long-chain fatty acids are preferred, typically comprising 10 to 28 carbon atoms, saturated or unsaturated, possibly hydroxylated.

[0160] Long-chain fatty acids (typically comprising 10 to 28 carbon atoms) include, for example, capric, lauric, myristic, palmitic, stearic, arachidic, behenic, oleic, linoleic, and erucic acids, and their hydroxylated derivatives. 12-Hydroxystearic acid is the preferred derivative.

[0161] Lithium 12-hydroxystearate is the preferred thickener for the fat composition according to the invention.

[0162] Also, the fat composition includes:

[0163] - at least one base oil;

[0164] - at least one thickener being the product of the reaction between lithium hydroxide monohydrate present in the dispersion and at least one long-chain fatty acid, typically comprising 10 to 28 carbon atoms, saturated or unsaturated, possibly hydroxylated; and

[0165] - possibly one or more additives, said additives being different from the base oils and different from the thickeners.

[0166] The fat composition may include one or more additives, said additives being different from the base oils and different from the thickeners.

[0167] According to one embodiment, the additional additive(s) are chosen from extreme-pressure additives, antioxidant additives, anti-corrosion additives, metal passivating additives, and mixtures thereof.

[0168] These additives can be introduced individually and / or in the form of a mixture.

[0169] The fat composition may include at least one antioxidant additive. The antioxidant additive may be selected from phenolic or amino-type antioxidants. Specifically, antioxidant additives may be selected from sterically hindered phenols, sterically hindered phenol esters, and sterically hindered phenols containing a thioether bridge, and mixtures thereof.

[0170] Amino compounds are another class of antioxidant additives that can be used, possibly in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example, aromatic amines with the formula NR 1 R 2 R 3 in which R 1 represents an aliphatic group or an aromatic group, possibly substituted, R 2 represents an aromatic group, possibly substituted, R 3represents a hydrogen atom, an alkyl group, an aryl group, or a group with the formula R 13 S(O) Z R 14 in which R 13 represents an alkylene group or an alkenylene group, R 14 represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2. Among the amine-type antioxidants, we can mention diphenylamines, diphenylamines substituted by at least one alkyl group at C1-C12, N,N'-dialkyl-aryl-diamines and their mixtures.

[0171] The fat composition according to the invention may comprise from 0.05% to 5% by weight, preferably from 0.1% to 4% by weight or from 0.2% to 2% by weight of antioxidant agent, relative to the total weight of the composition.

[0172] According to one embodiment, the grease composition includes at least one extreme-pressure additive.

[0173] According to one embodiment, the fat composition comprises 2% to 10% by weight of at least one extreme-pressure additive, relative to the total weight of the fat composition.

[0174] Preferably, the extreme-pressure additive is chosen from sulfur olefins, sulfur fatty acid esters, and mixtures thereof.

[0175] Sulfur-containing fatty acid esters can be obtained by sulfurizing fatty acid esters. These fatty acid esters are obtained by reaction between one or more fatty acids and alcohols of all kinds, or by transesterification between one or more fatty acid esters and alcohols of all kinds.

[0176] By ester of sulfur fatty acid, we mean an ester of at least one sulfur fatty acid, it being understood that it is most often an ester of a mixture of sulfur fatty acids.

[0177] The fatty acids that can be used to form sulfur-containing fatty acid esters are all fatty acids comprising 6 to 24 carbon atoms, preferably 14 to 22 carbon atoms, and more preferably 16 to 20 carbon atoms. Fatty acids comprising 18 carbon atoms are the major fatty acids, meaning they are present at a mass concentration of at least 50% of the total mass of the sulfur-containing fatty acid ester.

[0178] Sulfur fatty acid esters may be sulfur fatty acid monoesters, sulfur fatty acid diesters, sulfur fatty acid triesters or sulfur fatty acid polyesters taken alone or in mixture.

[0179] Preferred monoesters of sulfur-containing fatty acids are C1-C4 alkyl monoesters, such as methyl monoesters, ethyl monoesters, n-propyl monoesters, β-propyl monoesters, n-butyl monoesters, s-butyl monoesters, and t-butyl monoesters. Preferably, the monoester is a methyl monoester. Preferably, the ester of sulfur-containing fatty acids is a methyl ester of sulfur-containing fatty acids.

[0180] As an example of sulfur fatty acid triesters, we can cite sulfur fatty acid triglycerides which will be completely or partially esterified and will therefore possibly include, in addition to triesters, diesters and / or monoesters.

[0181] Examples of sulfur-containing fatty acid polyesters include pentaerythritol esters of sulfur-containing fatty acids.

[0182] The present invention also relates to a method for preparing lubricating grease comprising the following steps:

[0183] - at least one step of forming a suspension comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function;

[0184] - at least one homogenization step of the suspension to obtain a homogenized suspension;

[0185] - at least one step of grinding the homogenized suspension to form a dispersion comprising particulate UOH.H2O, and

[0186] - at least one step consisting of adding, to said dispersion comprising particulate UOH.H2O, at least one base oil, at least one long-chain fatty acid, and water, to obtain a lubricating grease.

[0187] The present invention also relates to a method for preparing lubricating grease comprising the following steps:

[0188] - at least one step of forming a suspension comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function; - at least one step of homogenizing the suspension to obtain a homogenized suspension;

[0189] - at least one step of grinding the homogenized suspension to form a dispersion comprising particulate UOH.H2O, and

[0190] - at least one step consisting of adding, to said dispersion comprising particulate UOH.H2O, at least one base oil, at least one monoacid or diacid preferably comprising 8 to 28 carbon atoms, and water, to obtain a lubricating grease.

[0191] The fat preparation process according to the invention is in particular as defined above, in particular by the implementation of steps (E1) to (E4).

[0192] The grease preparation process according to the invention therefore includes the implementation of the process for preparing a dispersion according to the invention and as defined above, followed by the implementation of step (E4) as mentioned above.

[0193] According to one embodiment, the fat preparation process according to the invention does not include a dehydration step. According to this embodiment, no water removal step is implemented.

[0194] Advantageously, the grease preparation process according to the invention does not include a dehydration step of the homogenized suspension (S1). Preferably, the nonionic surfactant used in the grease preparation process according to the invention is as defined above, in particular as that used for the dispersion preparation process of the invention.

[0195] According to one embodiment, in the fat preparation process according to the invention, the non-ionic surfactant is selected from saturated or unsaturated fatty acids, hydroxylated or non-hydroxylated, having between 12 and 24 carbon atoms, preferably between 16 and 22 carbon atoms.

[0196] According to one embodiment, in the grease preparation process according to the invention, the non-ionic surfactant corresponds to one of the formulas (I) and / or (II) as defined above.

[0197] Lubricating greases are, for example, prepared according to a preparation process comprising: a) at least one step of introducing into a reactor at least one base oil, at least one monoacid or diacid preferably comprising 8 to 28 carbon atoms, at least one dispersion of lithium hydroxide monohydrate in oil as defined above and water to form a reaction mixture; b) at least one step of evaporating the water from the reaction mixture under stirring at a temperature between 80°C and 110°C; c) at least one step of heating the reaction medium, in particular to a heating temperature between 130°C and 230°C; d) at least one step of cooling the reaction medium to 80°C; and e) a grinding step.

[0198] The dispersion of lithium hydroxide monohydrate in oil corresponds to the dispersion of lithium monohydrate prepared according to the process described above.

[0199] Preferably, the fatty acid is introduced in step a) in a content ranging from 2% to 20% by weight, preferably from 6% to 15% by weight and even more preferably from 8% by weight to 12% by weight, relative to the total weight of the reaction mixture.

[0200] Preferably, the base oil is introduced in step a) in a content ranging from 60% to 98% by weight and even more preferably from 70% by weight to 90% by weight, relative to the total weight of the reaction mixture.

[0201] Advantageously, the water is introduced in step a) at a content of less than 3% by weight, preferably less than 2% by weight, relative to the total weight of the reaction mixture.

[0202] The use of a dispersion of lithium monohydrate in oil according to the invention in the preparation process makes it possible to reduce the amount of water introduced into the reaction mixture and to reduce the amount of water to evaporate in said reaction mixture.

[0203] Preferably, the dispersion of lithium hydroxide monohydrate in oil is introduced in step a) in a content ranging from 1% to 5% by weight and even more preferably from 2% by weight to 3% by weight, relative to the total weight of the reaction mixture.

[0204] The preparation process includes a step b) of evaporating the water from the reaction mixture under stirring at a temperature between 80°C and 110°C, preferably between 85°C and 105°C.

[0205] The process includes a step c) of heating the reaction mixture which is carried out at a temperature between 130 °C and 230 °C, preferably between 140 °C and 220 °C.

[0206] The process also includes a step of cooling the reaction medium to 80°C. EXAMPLES

[0207] Example 1: Preparation of dispersions according to the invention

[0208] 1. Materials

[0209] The examples were created using the following raw materials:

[0210] Base oil 1: Naphthenic oil with a viscosity of 117 est. This oil is marketed by the company ERGON under the name Hygold 600 and the reference CAS 64742-52-5 (group I).

[0211] Base oil 2: Paraffinic oil with a viscosity of 109 est. This oil is marketed by Exxon Mobil under the name Core 600 and the CAS reference 64742-54-7 (group II).

[0212] Base oil 3: Paraffinic oil with a viscosity of 87 est. This oil is marketed by Saudi Aramco Base Oil under the name Prima 500 and CAS reference 64742-54-7 (group III).

[0213] Lithium hydroxide monohydrate: marketed by the company Livent under the reference CAS 1310-66-3. The lithium has an average particle size of 500 µm.

[0214] Surfactant according to the invention: 12-hydroxystearic acid marketed by the company Oleo Chémie under the reference CAS 106-14-9.

[0215] 2. Preparation of the dispersion

[0216] The dispersions according to the invention are prepared according to the following protocol.

[0217] A suspension was prepared by mixing the base oil, lithium monohydrate, and 12-hydroxystearic acid (12HSA). This mixture contains 59% lithium monohydrate, 2% 12HSA, and 39% base oil.

[0218] The previously obtained suspension is homogenized for 30 minutes at a temperature of 90°C. The set temperature is 90°C so that the 12 HSA can melt and react with some of the lithium.

[0219] Finally, the suspension obtained after homogenization was ground using a Fryma mill, with the gap set at 1 revolution (25 µm), resulting in a dispersion with lithium hydroxide monohydrate particles ranging in size from 40 to 50 µm. The lithium particle size was determined by microscopic analysis. Details of the dispersions are given in Table 2 below. The concentrations are given as a percentage of the total mass of the dispersion.

[0220] Table 2

[0221] 3. Results

[0222] 3.1. Evaluation of stability by visual measurement

[0223] To assess the stability of the dispersions, the height of oil released onto the surface of the different samples was measured over time. This assessment was performed on the dispersions at room temperature and at a temperature of 50°C.

[0224] These values ​​were subsequently related to the total height of dispersion contained in the sample. A phase shift value above 5% is unacceptable and indicates instability in the dispersion.

[0225] The results obtained are presented in tables 3 and 4 below.

[0226] Table 3

[0227] Table 4

[0228] It is observed that the dispersions C1, C2 and C3 according to the invention exhibit minimal oil release, below the acceptable value of 5% over 30 days at room temperature and when stored at 50°C. The dispersions according to the invention are stable.

[0229] 3.2. Evaluation of dispersion stability using the turbiscan

[0230] The stability of the dispersions according to the invention was evaluated by transmittance measurements. The analysis is based on multiple light scattering. The device directs a pulsed LED light source emitting in the near-infrared (Δair = 880 nm) onto the sample. The backscattered and transmitted rays are captured by different sensors. Thus, if sedimentation occurs, the transmission and backscattering of light will not be the same at all heights of the sample. For example, if an oil layer is observed on the surface, the oil / light interactions will produce a higher transmission than if the infrared rays passed through a medium concentrated in lithium. The Turbiscan therefore makes it possible to determine whether a sample is stable at time T.

[0231] The Turbiscan results showed no difference in transmittance between the top and bottom of the tank, thus confirming the stability of the dispersion after 30 days. Stability evaluation with LUMifuge

[0232] Comparative study of the dispersion instability index

[0233] The stability of the dispersions according to the invention was then evaluated using LUMifuge measurements. LUMifuge is an analytical device that allows for the classification of the stability of various products. Similar to the Turbiscan, it analyzes the rays transmitted by a sample after exposure to near-infrared light beams. The unique feature of LUMifuge lies in the centrifugation it applies to the samples. Each dispersion to be analyzed is placed in a rotating compartment. The samples are subjected to a centrifugal force induced by the rapid rotation. This force simulates increased gravity, causing suspended particles to fall. The phase shift rate can therefore increase significantly. This device makes it possible to precisely monitor the phase shift of the oil and determine its instability index over time.

[0234] Instability index measurements were performed three times for each dispersion and are reported in Table 5 below.

[0235] Table 5

[0236] The results show that dispersion C1 is by far the most stable, followed by dispersion C2. Dispersion C3 also has a satisfactory instability index of approximately 0.2, demonstrating that the dispersions according to the invention are stable. Example 2: Preparation of additional dispersions according to the invention

[0237] 1. Materials

[0238] The following raw materials were used:

[0239] Base oils 1, 2 and 3: base oils from groups I, II and III respectively, identical to those used in example 1.

[0240] Lithium hydroxide monohydrate: marketed by the company Livent under the reference CAS 1310-66-3. The lithium has an average particle size of 500 µm.

[0241] Surfactants according to the invention:

[0242] - 12-Hydroxystearic acid, marketed by the company Oleo Chémie under the reference CAS 106-14-9 (same as example 1);

[0243] - Azelaic acid marketed by Emery Oleochemicals LLC under the reference CAS 23-99-9

[0244] - Palmitic acid marketed by Sigma-Aldrich under the reference CAS 57-10-3

[0245] 2. Preparation of the dispersion

[0246] The dispersions according to the invention are prepared according to the same protocol as that detailed in example 1.

[0247] The details of the dispersions are given in Table 6 below. The concentrations are given by mass, relative to the total mass of the dispersion.

[0248] Table 6 3. Results - Evaluation of stability by visual measurement

[0249] The dispersions in Table 6 (C4 to C8 compositions) are evaluated according to the protocol as described above in Example 1.

[0250] The results obtained are presented in tables 7 and 8 below.

[0251] Table 7

[0252] Table 8

[0253] It is observed that dispersions C4, C5, C6, C7, and C8 according to the invention exhibit minimal oil release below the acceptable value of 5% over 30 days at room temperature and when stored at 50°C. The dispersions according to the invention are stable. Example 3: Preparation of fats according to the invention

[0254] 1. Preparation of fats

[0255] The fats according to the invention are prepared according to the following protocol.

[0256] A grease was prepared by mixing, in a reactor, the base oil, a dispersion according to the invention (defined above), a thickener (here 12-HSA) and water.

[0257] Agitation at 150 rpm is maintained in the reactor during mixing.

[0258] The mixture is first heated to 90°C, then the grease is gradually heated to 120°C. The temperature is then increased to 205°C. The reaction mixture is then cooled to 80°C. Finally, the mixture is cooled to ambient temperature by the gradual addition of the remaining base oil.

[0259] Finally, the fat obtained after homogenization was ground using a Fryma grinder, with the gap set to 3 turns (i.e., 150 pm), in order to ensure optimal homogenization of the fat.

[0260] The breakdown of fats is given in Table 9 below. The amounts are given by mass, relative to the total mass of fat:

[0261] Table 9 2. Evaluation of fat stability by measurements of consistency and dropping point

[0262] To ensure the conformity of the properties of the synthesized fats, a characterization is carried out to measure the consistency and dropping point of the fats.

[0263] The consistency of a grease is essential for it to remain in the bearing without generating excessive friction. It is classified according to the NLGI (National Lubricating Grease Institute) scale. The optimal grade is NLGI 2. The consistency test measures the penetration depth of a cone into the grease, expressed in tenths of a millimeter. Two types of measurements exist: P0, which corresponds to the initial penetrability without prior work, and P60, which corresponds to the penetrability after 60 cycles of simulated mechanical work. These penetrability measurements are performed with a cone penetrometer.

[0264] The table below shows the grade / consistency correspondence according to the NLGI scale:

[0265] The dropping point is the temperature at which a heated grease begins to flow through a standardized orifice under the influence of gravity. This measurement determines the grease's thermal resistance: it indicates the threshold beyond which the lubricant's structure degrades and loses its ability to remain in place. The dropping point is therefore a crucial criterion for evaluating a grease's stability at high temperatures, particularly in demanding mechanical environments. For simple lithium greases, the specification states that the dropping point must be above 190°C.

[0266] The results obtained are shown in Table 10 below. Table 10

[0267] The results reveal that the G1, G2, G3 and G4 greases have PO and P60 penetration values ​​corresponding to an NLGI grade 2. The dropping point temperatures of the different synthesized greases are those expected in the case of simple lithium greases.

[0268] These various results show that the fats synthesized according to the process of the invention are stable.

Claims

DEMANDS 1. A process for preparing a fat comprising the following steps: - at least one step (E1) of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant of formula (I): in which R represents an alkyl group, possibly substituted, linear or branched, comprising from 8 to 23 carbon atoms and possibly comprising a terminal carboxylic acid function; - at least one step (E2) of homogenizing the suspension (S1) to obtain a homogenized suspension (S1); - at least one step (E3) of grinding the homogenized suspension (S1) to form a dispersion comprising particulate UOH.H2O (S2); and - at least one step (E4) consisting of adding to said dispersion comprising particulate UOH.H2O (S2), at least one base oil, at least one mono- or di-acid comprising 8 to 28 carbon atoms, and water, to obtain said grease.

2. A process for preparing a grease according to claim 1, not comprising a step of dehydrating the particulate UOH.H2O dispersion (S2).

3. A method for preparing a fat according to claim 1 or 2, wherein the non-ionic surfactant is selected from saturated or unsaturated fatty acids, hydroxylated or non-hydroxylated, having between 12 and 24 carbon atoms, preferably between 16 and 22 carbon atoms.

4. A method for preparing a grease according to any one of the preceding claims, wherein the non-ionic surfactant is selected from the group consisting of stearic acid, hydroxystearic acid, 12-hydroxystearic acid, oleic acid, 12-hydroxyoleic acid, ricinoleic acid, palmitic acid, myristic acid, lignoceric acid, hydroxypalmitic acid and mixtures thereof.

5. A process for preparing a grease according to any one of claims 1 to 3, wherein the non-ionic surfactant corresponds to formula (II): in which A is a hydrocarbon chain, possibly substituted, linear or branched, saturated or unsaturated, comprising from 8 to 23 carbon atoms, preferably between 8 and 15 carbon atoms.

6. A method for preparing a grease according to any one of claims 1 to 3 or 5, wherein the non-ionic surfactant is selected from azelaic acid, suberic acid, sebacic acid and mixtures thereof.

7. A method for preparing a grease according to any one of the preceding claims, wherein the non-ionic surfactant is present in the suspension (S1) in a content ranging from 0.3% by weight to 5% by weight, preferably ranging from 0.5% by weight to 2% by weight, relative to the total weight of said suspension.

8. A process for preparing a grease according to any one of the preceding claims, wherein the UOH.H2O is present in the suspension (S1) in a content ranging from 10% to 70% by weight, preferably ranging from 30% to 60% by weight, relative to the total weight of said suspension.

9. A process for preparing a grease according to any one of the preceding claims, wherein the mass ratio UOH.H2O: non-ionic surfactant in the suspension (S1) is from 2 to 140, preferably from 10 to 60, and even more preferably from 15 to 30.

10. A process for preparing a grease according to any one of the preceding claims, wherein step (E2) is carried out at a temperature from 80°C to 110°C, preferably from 82°C to 100°C, and even more preferably from 85°C to 95°C.

11. A method for preparing a grease according to any one of the preceding claims, wherein step (E2) is carried out for a period of 25 minutes to 40 minutes, and preferably step (E2) is carried out for 30 minutes.

12. A process for preparing a dispersion comprising particulate UOH.H2O, said process comprising: - at least one step (E1) of forming a suspension (S1) comprising UOH.H2O, at least one base oil and at least one non-ionic surfactant of formula (I): in which R represents an alkyl group, possibly substituted, linear or branched, comprising from 8 to 23 carbon atoms, and possibly comprising a terminal carboxylic acid function; - at least one homogenization step (E2) of the suspension (S1) to obtain a homogenized suspension (S1); and - at least one step (E3) of grinding the homogenized suspension (S1) to form a dispersion comprising particulate UOH.H2O.

13. A method for preparing a dispersion comprising particulate UOH.H2O according to claim 12, wherein the non-ionic surfactant used in step (E1) is as defined in any one of claims 2 to 5.

14. Composition, preferably in dispersion form, comprising: - from 1% to 5% by weight of at least one non-ionic surfactant as defined in any one of claims 1 or 3 to 6; - 15% to 65% by weight of at least one base oil; and - 40% to 70% by weight of particulate UOH.H2O, relative to the total weight of the composition, said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

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