Process for preparing a dispersion of lithium monohydrate in oil

Abstract

Process for preparing a dispersion of lithium monohydrate in oil. The present invention relates to a process for preparing a dispersion comprising particulate LiOH·H2O, said process comprising: - at least one step (E1) of forming a suspension (S1) comprising LiOH·H2O, at least one base oil, and at least one nonionic 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 grinding the homogenized suspension (S1) to form a dispersion comprising particulate LiOH·H2O. Figure for the abstract: none

Description

Title of the invention: Process for preparing a dispersion of lithium monohydrate in oil

[0001] The present invention relates to a process for preparing a dispersion of lithium hydroxide (or lithine) in oil, intended mainly for the manufacture of lubricating greases.

[0002] Lithium dispersions are used in the preparation of lubricating greases because of 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, it forms lithium soaps, essential components for the performance of lubricating greases, giving the grease high stability at extreme temperatures and good water resistance, making it suitable for industrial and automotive environments where these conditions are common.

[0003] These dispersions are crucial for the production of high-performance lubricating greases, as they allow lithium hydroxide to be conditioned in a stable manner and thus limit the handling of this salt by operators, since it is considered a dangerous and toxic product.

[0004] 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 (LiOH.H2O) is often preferred in formulations because it is more widely available, easier to handle, and provides similar properties.

[0005] However, the use of lithium monohydrate necessitates adjustments to the dispersion preparation process due to the water molecules contained in lithium hydroxide monohydrate. Therefore, the main challenge lies in removing this water to ensure a stable and efficient dispersion.

[0006] 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.

[0007] However, the dehydration steps are very energy-intensive because they require the application of a large amount of heat in order to eliminate water molecules present in the dispersal, particularly when dispersals are prepared on a large scale

[0008] There is therefore a need to provide a new, less energy-intensive process for preparing lithium dispersions.

[0009] There is therefore a need to provide a preparation process enabling the preparation of stable lithium dispersions with a reduced carbon footprint.

[0010] There is also a need to provide a process for preparing stable lithia 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 the formulation of lubricating grease.

[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] Thus, the present invention relates to a process for preparing a dispersion comprising particulate LiOH.H2O, said process comprising:

[0014] - at least one step (El) of suspension (SI) formation comprising LiOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function;

[0015] - at least one homogenization step (E2) of the suspension (SI) to obtain a homogenized suspension (SI);

[0016] - at least one step (E3) of grinding the homogenized suspension (SI) for to form a dispersion comprising particulate LiOH.H2O.

[0017] The inventors have discovered, surprisingly, that the introduction of a non-ionic surfactant comprising at least one carboxylic acid function with lithium hydroxide monohydrate (i.e. LiOH.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. Summary of the invention

[0018] The present invention relates to a method for preparing a dispersion comprising particulate LiOH.H2O, said method comprising:

[0019] - at least one step (El) of suspension (SI) formation comprising LiOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function;

[0020] - at least one homogenization step (E2) of the suspension (SI) to obtain a homogenized suspension (SI);

[0021] - at least one step (E3) of grinding the homogenized suspension (SI) for to form a dispersion comprising particulate LiOH.H2O.

[0022] According to one embodiment of the process of the invention, the non-ionic surfactant has the formula (I): O R--- OH

[0023] in which R represents an alkyl group, saturated or unsaturated, linear or branched, comprising from 8 to 23 carbon atoms and optionally comprising a terminal carboxylic acid function.

[0024] Preferably, the non-ionic surfactant is chosen from the group consisting of fatty acids, polyethoxylated fatty acids, and mixtures thereof.

[0025] 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.

[0026] According to one embodiment of the process of the invention, the non-ionic surfactant is chosen 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.

[0027] According to one embodiment of the process of the invention, the non-ionic surfactant is present in the suspension (SI) 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.

[0028] According to one embodiment of the process of the invention, the LiOH.H2O is present in the suspension (SI) 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.

[0029] According to one embodiment of the process of the invention, the mass ratio LiOH.H2 O : non-ionic surfactant in the suspension (SI) is from 2 to 140, preferably from 10 to 60, and even more preferably from 15 to 30.

[0030] 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.

[0031] 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.

[0032] The present invention also relates to a composition, preferably in dispersion form, comprising:

[0033] - from 1% to 5% by weight of at least one non-ionic surfactant having at least one carboxylic acid function;

[0034] - from 15% to 65% by weight of at least one base oil; and

[0035] - from 40% to 70% by weight of particulate LiOH.H2O, relative to the total weight of the composition,

[0036] said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0037] 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. Detailed description

[0038] As indicated above, the present invention relates to a process for preparing a dispersion comprising particulate LiOH.H2O, said process comprising:

[0039] - at least one step (El) of suspension (SI) formation comprising LiOH.H2O, at least one base oil and at least one non-ionic surfactant comprising at least one carboxylic acid function;

[0040] - at least one homogenization step (E2) of the suspension (SI) to obtain a homogenized suspension (SI);

[0041] - at least one step (E3) of grinding the homogenized suspension (SI) to to form a dispersion comprising particulate LiOH.H2O.

[0042] 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 LiOH.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.

[0043] For the purposes of this invention, "dispersion" means 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.

[0044] The difference between a dispersion according to the invention and a suspension lies in the average diameter of the particles present in them.

[0045] 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.

[0046] The average diameter of the particles was measured by optical microscopy, a method commonly used to observe the microstructure of materials.

[0047] 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.

[0048] 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.

[0049] Preferably, the dispersion prepared by the process according to the invention is a stable dispersion after 30 days of storage at room temperature.

[0050] By "organic medium" is meant an environment containing at least one oil or a mixture of oils in combination with one or more surfactants.

[0051] More specifically, the dispersion mentioned in the present invention refers to a dispersion of lithium hydroxide monohydrate particles in an oily medium.

[0052] As mentioned above, the process according to the invention includes a step (El) consisting of forming a suspension (Si) comprising LiOH.H2O, at least one base oil and at least one surfactant comprising at least one carboxylic acid function.

[0053] In the present invention, lithium monohydrate (LiOH.H2O) is in solid form and consists of lithium ions (Li+) and hydroxide ions (OH-), linked to a water molecule (H2O).

[0054] The base oil or oils may be chosen from mineral, synthetic or natural, animal or vegetable lubricating base oils known to those skilled in the art.

[0055] 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 ATIEL classification) (Table 1) or mixtures thereof.

[0056] [Tables 1] Saturates content Sulfur content Viscosity index (VI) Group I Mineral oils <90% > 0.03% 80 < VI < 120 Group II Hydrocracked oils >90% < 0.03% 80 < VI < 120 Group III Hydrocracked or hydroisomerized oils >90% < 0.03% >120 Group IV Polyalphaolefins (PAO) Group V Esters, PAGs and other bases not included in groups I to IV

[0057] 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.

[0058] Mixtures of synthetic and mineral oils can also be used.

[0059] The base oils of 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 mm².s⁻¹ according to ASTM D445. Their average molecular weight is generally between 250 g / mol and 3,000 g / mol according to ASTM D5296.

[0060] 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.

[0061] Naturally derived oils include vegetable oils such as soybean oil, linseed oil, canola oil, rapeseed oil, castor oil, cottonseed oil, sunflower oil or palm oil.

[0062] According to one embodiment, the base oil is chosen from synthetic oils, mineral oils and their mixtures.

[0063] According to another embodiment, the base oil is a mixture of at least one synthetic oil and at least one mineral oil.

[0064] 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.

[0065] Preferably, the base oil has a kinematic viscosity at 40°C, measured according to the ASTM D445 method, of between 75 mPa.s and 150 mPa.s, more preferably between 80 mPa.s and 120 mPa.s.

[0066] 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.

[0067] Generally, the base oil(s) are present in the suspension (SI) 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 (SI).

[0068] The surfactant used in step (El) is a non-ionic surfactant comprising at least one carboxylic acid function.

[0069] According to one embodiment, the non-ionic surfactant has the formula (I): O OH

[0070] in which R represents an alkyl group, saturated or unsaturated, linear or branched, comprising from 8 to 23 carbon atoms and optionally comprising a terminal carboxylic acid function.

[0071] According to a specific embodiment of the invention, the non-ionic surfactant has a chemical structure corresponding to formula (II): OO y-A-^ HO OH

[0072] in which is a linear or branched, saturated or unsaturated hydrocarbon chain comprising from 8 to 23 carbon atoms, preferably between 8 and 15 carbon atoms.

[0073] Preferably, the surfactant is chosen from azelaic acid, suberic acid, sebacic acid and mixtures thereof.

[0074] 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.

[0075] In other words, the surfactant is chosen from mono-, di- or tri- acids comprising between 8 and 24 carbon atoms.

[0076] Preferably, the surfactant is chosen from non-ionic compounds, more particularly from fatty acids, polyethoxylated fatty acids, and mixtures thereof.

[0077] The term “polyethoxylated fatty acids” refers to fatty acids having a carbon chain comprising 12 to 24 carbon atoms that have reacted with ethylene oxide to form polyethoxylated derivatives. Examples include polyethoxylated lauric acid and polyethoxylated stearic acid.

[0078] 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.

[0079] Preferably, the surfactant is chosen from stearic acid, hydroxystearic acid, oleic acid, 12-hydroxyoleic acid, riconoleic acid, palmitic acid, myristic acid, lignoceric acid, hydroxypalmitic acid and mixtures thereof.

[0080] According to a preferred embodiment, the surfactant is chosen from hydroxylated saturated fatty acids, more particularly chosen from hydroxystearic acid, hydroxypalmitic acid and their derivatives.

[0081] Preferably, the surfactant used in step (El) is chosen from hydroxystearic acid and its derivatives, more particularly the surfactant is 12-hydroxystearic acid (12HSA).

[0082] 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.

[0083] Preferably, the surfactant is chosen from azelaic acid, suberic acid, sebacic acid and mixtures thereof.

[0084] According to one embodiment of the invention, the non-ionic surfactant used in step (El) 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).

[0085] 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.

[0086] Preferably, the surfactant is present in the suspension (SI) 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.

[0087] Preferably, LiOH.H2O is present in the suspension (SI) 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.

[0088] Preferably, the mass ratio LiOH.H2O: non-ionic surfactant in the suspension (SI) is from 2 to 140, preferably from 10 to 60, and even more preferably from 15 to 30.

[0089] The LiOH.H2O introduced in step (El) is solid, preferably the LiOH.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 pmL.

[0090] The process according to the invention comprises at least one step (E2) of homogenizing the suspension (SI). This step is carried out after step (El).

[0091] 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.

[0092] Without wanting to be linked to any theory, these temperature ranges correspond to the melting temperatures of the surfactants used in step (El).

[0093] 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.

[0094] 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.

[0095] By a more stable dispersion, we mean a dispersion for which the sedimentation rate of particles is less than 1%.

[0096] By "sedimentation rate", in the context of the invention, we mean the quantity of dispersed particles settling at the bottom of the system.

[0097] The "sedimentation rate" as defined above can be measured by various measures known to those skilled in the art, such as dispersion transmittance measurements using a spectrophotometer, visual tests, or turbidity measurement tests.

[0098] 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.

[0099] 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.

[0100] By way of example, one can cite in particular 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. As another example, we can cite another 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.

[0101] Thus, the process according to the invention includes at least one step (E3) of grinding the suspension (SI) to form a dispersion comprising particulate LiOH.H2O.

[0102] By "particulate LiOH.H2O", for the purposes of the invention, means particles of LiOH.H2O having an average diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0103] Preferably the size of the particles of lithium monohydrate, 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.

[0104] Advantageously, the dispersion according to the invention has a particulate LiOH.H2O content after step (E3) ranging from 40% to 70% by weight, relative to the total weight of the dispersion.

[0105] The present invention also relates to a composition, preferably in the form of a dispersion, comprising:

[0106] - from 0.5% to 5% by weight of at least one non-ionic surfactant having at least one carboxylic acid function;

[0107] - from 15% to 65% by weight of at least one base oil; and

[0108] - from 40% to 70% by weight of particulate LiOH.H2O, relative to the total weight of the composition,

[0109] said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0110] Preferably, the composition according to the invention is a dispersion.

[0111] According to one embodiment, the non-ionic surfactant is present in the composition in a content ranging from 0.5% to 5% by weight, preferably from 2% to 3% by weight, relative to the total weight of the dispersion.

[0112] According to one embodiment, the base oil is present in the composition in a content ranging from 15% to 65% by weight, preferably from 20% to 50% by weight, and even more preferably from 30% to 45% by weight, relative to the total weight of the dispersion.

[0113] According to one embodiment, particulate LiOH.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.

[0114] Preferably, the composition according to the invention is a dispersion comprising:

[0115] - 2% to 3% by weight of at least one non-ionic surfactant having at least one carboxylic acid function;

[0116] - 30% to 45% by weight of at least one base oil; and

[0117] - from 50% to 65% by weight of particulate LiOH.H2O, relative to the total weight of the composition,

[0118] said particles having a diameter ranging from 30 pm to 60 pm, preferably ranging from 40 pm to 50 pm.

[0119] This dispersion can also be used for the preparation of lubricating greases.

[0120] The fat compositions prepared from the dispersion include:

[0121] - at least one base oil;

[0122] - at least one thickener selected from lithium salts of fatty acids;

[0123] - possibly one or more additives, said additives being different from the oils of base and different from thickeners.

[0124] The thickener as defined above is selected from lithium salts of fatty acids, in particular from lithium salts of mono-fatty acids or lithium salts of di-fatty acids, said mono-acids or di-acids preferably comprising from 8 to 28 carbon atoms.

[0125] The thickeners are obtained by reaction between a chain fatty acid and the lithium hydroxide monohydrate particles present in the dispersion described above. Specifically, the fatty acid reacts with the lithium hydroxide monohydrate present in the dispersion to thicken the composition, giving it the consistency of a lubricating grease.

[0126] Long chain fatty acids, typically comprising 10 to 28 carbon atoms, saturated or unsaturated, possibly hydroxylated, are preferred.

[0127] 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.

[0128] Lithium 12-hydroxystearate is the preferred thickener for the grease composition according to the invention.

[0129] Also, the fat composition includes:

[0130] - at least one base oil;

[0131] - at least one thickener being the product of the reaction between the hydroxide of lithium 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

[0132] - possibly one or more additives, said additives being different from the oils of base and different from thickeners.

[0133] The fat composition may include one or more additives, said additives being different from the base oils and different from the thickeners.

[0134] 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.

[0135] These additives may be introduced individually and / or in the form of a mixture.

[0136] The fat composition may include at least one antioxidant additive. The antioxidant additive can be chosen from among phenolic or amino type antioxidants.

[0137] Antioxidant additives may in particular be selected from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, and mixtures thereof.

[0138] 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 of the formula NR*R2R3 in which R1 represents an aliphatic or aromatic group, possibly substituted, R2 represents an aromatic group, possibly substituted, R3 represents a hydrogen atom, an alkyl group, an aryl group, or a group of 13 14 13 formula RS(O)ZR in which R represents an alkylene group or an alkenylene group, R14 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 cite diphenylamines, diphenylamines substituted by at least one alkyl group in C1-C12, N,N'-dialkyl-aryl-diamines and their mixtures.

[0139] 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.

[0140] According to one embodiment, the grease composition comprises at least one extreme-pressure additive.

[0141] According to one embodiment, the grease composition comprises 2 to 10% by weight of at least one extreme-pressure additive, relative to the total weight of the grease composition.

[0142] Preferably, the extreme-pressure additive is chosen from sulfur olefins, sulfur fatty acid esters, and mixtures thereof.

[0143] Sulfur-containing fatty acid esters can be obtained by sulfuring fatty acid esters. Said 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.

[0144] 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.

[0145] The fatty acids that can be used to form the sulfur-containing fatty acid esters are all fatty acids comprising from 6 to 24 carbon atoms, preferably from 14 to 22 carbon atoms, and more preferably from 16 to 20 carbon atoms. Fatty acids comprising 18 carbon atoms are the major fatty acids, that is to say, they are present at a mass concentration of at least 50% relative to the total mass of the sulfur-containing fatty acid ester.

[0146] 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.

[0147] Preferred monoesters of sulfur-containing fatty acids are Cl-C4 alkyl monoesters, such as methyl monoesters, ethyl monoesters, n-propyl monoesters, z-propyl monoesters, n-butyl monoesters, 5-butyl monoesters, and t-butyl monoesters. Preferably, the monoester is a methyl monoester. Preferably, the sulfur-containing fatty acid ester is a methyl ester of a sulfur-containing fatty acid.

[0148] 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.

[0149] As an example of sulfur fatty acid polyesters, pentaerythritol esters of sulfur fatty acids may be cited.

[0150] The present invention also relates to a method for preparing lubricating grease comprising the following steps:

[0151] - at least one step of forming a suspension comprising LiOH.H2O, at less a base oil and at least a non-ionic surfactant comprising at least one carboxylic acid function;

[0152] - at least one homogenization step of the suspension to obtain a homogenized suspension;

[0153] - at least one step of grinding the homogenized suspension to form a dispersion comprising particulate LiOH.H2O, and

[0154] - at least one step consisting of adding, to said dispersion comprising LiOH.H2 particulate matter, at least one base oil, at least one long-chain fatty acid, and water, to obtain a lubricating grease.

[0155] The present invention also relates to a method for preparing lubricating grease comprising the following steps:

[0156] - at least one step of forming a suspension comprising LiOH.H2O, at less a base oil and at least a non-ionic surfactant comprising at least one carboxylic acid function;

[0157] - at least one homogenization step of the suspension to obtain a homogenized suspension;

[0158] - at least one step of grinding the homogenized suspension to form a dispersion comprising particulate LiOH.H2O, and

[0159] - at least one step consisting of adding, to said dispersion comprising LiOH.H2 particulate matter, 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.

[0160] Lubricating greases are, for example, prepared according to a preparation process comprising:

[0161] a) at least one step consisting 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;

[0162] b) at least one step of evaporating water from the reaction mixture under stirring at a temperature between 80°C and 110°C;

[0163] c) at least one heating step of the reaction medium, in particular to a heating temperature of 130°C to 230°C.

[0164] d) at least one step of cooling the reaction medium to 80°C, and

[0165] e) a grinding step.

[0166] The dispersion of lithium hydroxide monohydrate in oil corresponds to the dispersion of lithium monohydrate prepared according to the process described above.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] 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.

[0174] The process also includes a step of cooling the reaction medium to 80°C. EXAMPLES 1. Materials

[0175] The examples were produced using the following raw materials:

[0176] 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 CAS reference 64742-52-5.

[0177] Base oil 2: Paraffin oil with a viscosity of 109 est. This oil is marketed by Exxon Mobil under the name Core 600 and CAS reference 64742-54-7.

[0178] 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.

[0179] Lithium hydroxide monohydrate: marketed by Livent under CAS ref 1310-66-3. The lithium has an average particle size of 500 pm.

[0180] Surfactant according to the invention: 12-hydroxystearic acid marketed by the company Oleo Chémie under the reference CAS 106-14-9. 2. Preparation of the dispersion

[0181] The dispersions according to the invention are prepared according to the following protocol.

[0182] 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.

[0183] The suspension obtained previously is subjected to homogenization for 30 minutes at a temperature of 90 °C. The set temperature is fixed at 90 °C so that the 12 HSA can melt and react with some of the lithium.

[0184] Finally, the suspension obtained after homogenization was ground using a Fryma mill, with the gap set at U2 revolution (i.e., 25 pm), yielding a dispersion with lithium hydroxide monohydrate particles with a particle size between 40 and 50 pm. The size of the lithium grains was determined by microscopic analysis.

[0185] The details of the dispersions are given in Table 2 below. The contents are given by mass, relative to the total mass of the dispersion.

[0186] [Tables2 Cl (according to the invention) C2 (according to the invention) C3 (according to the invention) Lithium hydroxide monohydrate 59% 59% 59% Base oil I 39% - - Base oil II - 39% - Base oil III - - 39% 12-HSA 2% 2% 2% 3. Results

[0187] 3.1. Evaluation of stability by visual measurement

[0188] In order 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 carried out on the dispersions at room temperature and at a temperature of 50°C.

[0189] These values ​​were subsequently related to the total height of dispersion contained in the sample. The results obtained are presented in Tables 3 and 4 below.

[0190] [Tables3] Dispersions at Room Temperature: 7 days, 15 days, 30 days; Cl 0%, 0%, 0%; C2 0%, 0%, 0%; C3 0%, 0%, 0%

[0191] [Tables4] Dispersions at 50°C: 7 days, 15 days, 30 days; Cl 0%, 0%, 0%; C2 0%, 0%, 0%; C3 0%, 0%, 0%

[0192] It is observed that the Cl, C2 and C3 dispersions according to the invention do not exhibit any oil release over 30 days at room temperature and when stored at 50°C. The dispersions according to the invention are stable.

[0193] 3.2. Evaluation of dispersion stability with the turbiscan

[0194] 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 (Xair = 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 stronger 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.

[0195] The results of the turbiscan showed no difference in transmittance between the top and bottom of the tank, thus confirming the stability of the dispersion after 30 days. Stability assessment with LUMifuge

[0196] - Comparative study of the dispersion instability index

[0197] The stability of the dispersions according to the invention was then evaluated by LUMifuge measurements. LUMifuge is an analytical device that allows the stability of several products to be classified. As with the Turbiscan, it analyzes the rays transmitted by a sample after exposure to near-infrared light beams. The specificity of LUMifuge lies in the centrifugation that the device subjects the samples to. Indeed, 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 allows for precise monitoring of the oil's phase shift and determination of its instability index over time.

[0198] Instability index measurements were performed three times for each dispersion and are reported in Table 5 below.

[0199] [Tables5] Instability index after 4 hours and 10 minutes Dispersion Measurement 1 Measurement 2 Measurement 3 Cl 0.047 0.07 0.056 C2 0.122 0.155 0.152 C3 0.203 0.2 0.175

[0200] The results show that the Cl dispersion obtained is by far the most stable, followed by the C2 dispersion. The C3 dispersion also has a satisfactory instability index of approximately 0.2, showing that the dispersions according to the invention are stable.

Claims

Demands

1. A process for preparing a dispersion comprising particulate LiOH.H2O, said process comprising: - at least one step (E1) of forming a suspension (SI) 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 (SI) to obtain a homogenized suspension (SI); - at least one step (E3) of grinding the homogenized suspension (SI) to form a dispersion comprising particulate LiOH.H2O.

2. A method according to claim 1, wherein the nonionic surfactant is of formula (I): O OH in which R represents an alkyl group, saturated or unsaturated, linear or branched, comprising from 8 to 23 carbon atoms and optionally comprising a terminal carboxylic acid function.

3. A method according to claim 1 or 2, wherein the non-ionic surfactant is selected from the group consisting of fatty acids, polyethoxylated fatty acids, and mixtures thereof.

4. A method according to any one of the preceding claims, 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.

5. A method according to claim 1, wherein 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.

6. A method according to any one of the preceding claims, wherein the non-ionic surfactant is present in the suspension (SI) 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.

7. A method according to any one of the preceding claims, wherein LiOH.H2O is present in the suspension (SI) 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.

8. A method according to any one of the preceding claims, wherein the mass ratio LiOH.H2O: non-ionic surfactant in the suspension (SI) is from 2 to 140, preferably from 10 to 60, and even more preferably from 15 to 30.

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

10. A method 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 is carried out for 30 minutes.

11. Composition, preferably in dispersion form, comprising: - 1% to 5% by weight of at least one non-ionic surfactant having at least one carboxylic acid function; - 15% to 65% by weight of at least one base oil; and - 40% to 70% by weight of particulate LiOH.H2O, relative to the total weight of the composition, said particles having a diameter of 30 pm to 60 pm, preferably 40 pm to 50 pm.

12. A process 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 process according to any one of claims 1 to 10.