Cross-Reference to Related Applications

This Patent Application claims priority from Italian Patent Application No. 102022000019848 filed on September 27, 2022, the entire disclosure of which is incorporated herein by reference .

Technical Field

The present invention relates to a lubricant grease containing at least one or more spent bleaching earths as a main thickening agent and characterized by having a consistency belonging to at least one of the grades of the NLGI (National Lubricating Grease Institute) classification, for example an NLGI consistency of grade 0, 1, 2, 3 or also higher, with such a low tendency to lose weight as to guarantee the maintenance of said consistency along the service duration (mechanically stable grease along the service) .

In particular, the present invention concerns a lubricant grease as defined above, also provided with a high drop point, preferably >350 °C, such as to be classifiable as infusible grease, and with such good cold properties as to be employable up to -10 °C, with lubricating properties similar to those of the infusible bentonite greases conventionally used in the lubrication of mechanical moving members under high load conditions and possibly high temperature conditions (e.g. higher than 200°C), for example for lubrication of bearings, gears and mechanical parts operating at extremely high temperatures such as those, for example, of the processes in the cement factories and of the iron and steel industries, or of mechanical parts of agricultural machinery.

More particularly, the present invention concerns lubricant greases as defined above provided with improved performance characteristics compared to the bentonite grease such as, for example, substantial absence of weight increase due to water incorporation, while further showing low water washout values, preferably lower than 18% by weight, more preferably lower than 13%, even more preferably lower than 10%, thus reducing water penetration.

These latter properties make the lubricant greases of the invention particularly suitable for use as infusible greases in wet environments and/or in the presence of water, even at low temperatures.

Background

The aim of the lubrication with grease or oil is to reduce friction and wear between moving surfaces.

With respect to a lubricant oil, the grease has a lower pumpability and, given its nature, does not perform cooling function. However, the grease has considerable advantages that in some cases make it mandatory to choose it.

Generally, the greases are used in bearings with rotary elements, in the smooth bearings, in the gearboxes and in the open gears, where they perform an effective action of protection against wear and corrosion, thanks to their resistance to detachment from the lubricated surfaces, and also act as "sealants" so as to prevent the penetration of dirt and water: since a lubricant grease suitable for any operating condition does not exist, the choice of the most indicated type of grease must obviously be evaluated on a case-by-case basis.

The lubricant greases generally comprise a base oil (lubricating fluid or "stock base"), at least one main thickening agent and other optional additives that can impart certain characteristics to the finished product: they are typically subdivided based on their different consistency, for example according to the NLGI scale which can range from an NLGI grade 000 (very fluid grease) to an NLGI grade 6 (solid grease).

The main thickening agent in a lubricant grease is employed to form the reticular/crystalline structure in which the base oil is retained internally, like water in a sponge, and the greases are also identified based on the type of thickening agent employed, as well as based on the consistency, since such reticular/crystalline structure affects the performance properties of the grease.

The thickening agents most commonly used to date are the metal soaps such as, for example, lithium soap but other substances such as silica, polyurea and clays (bentonite) are also envisaged.

Of particular interest are the infusible lubricant greases known for their use in the lubrication at extremely high temperatures and/or under high load conditions as they have a very high drop point so as to avoid the dripping of the base oil at work temperatures.

Among the infusible greases mention can be made of those containing bentonite, also called bentonite greases: in them the base oil constitutes the predominant part of the grease formulation (at least 50% by weight) and the bentonite (which is a phyllosilicateA12O3-4S1O 2-4H2O consisting essentially of montmorillonite, calcium or sodium) reaches a maximum of 10-15% by weight of the total weight of the formulation.

The bentonite present in the bentonite greases is generally pre-treated and modified so that the sodium (and/or calcium) atoms of the starting montmorillonite are at least partly replaced by long chain secondary amino groups or by other organic cations (bentonite modified with organic cations), for example with dimethyldialkylammonium ions, to form a gel with the base oils.

In such bentonite greases there are very often included also fumed silica as a minority thickening agent in terms of percentage by weight with respect to the bentonite, and also polyisobutene is present as a possible polymer additive to increase the structural strength of the gel or as an additional base oil, since it belongs to Group V (GPV) of the API classification of the base oils of lubricants.

The bentonite greases however may show high values of water washout, e.g. higher than 18%, which make them sensitive to wet conditions and/or to the presence of water, if used.

The bleaching earths - which consist of inorganic absorbing material such as aluminosilicate minerals, i.e. bentonite - are known to be used, in an acid-activated form, as absorbent materials in pre-treatment systems (e.g. BLEACHING) of crude bio-charges such as vegetable oils, animal greases or derivatives thereof intended for the production of biofuels in biorefineries (Green Refinery processes).

The spent bleaching earths obtained from such processes of bio-charge pre-treatment contain not only inorganic absorbing material but also organic material constituted by the raw bio-charge remained absorbed on them and by the possibly impurities contained in the bio-charge. The above spent bleaching earths typically contain:

60-80% by weight of inorganic material consisting of the bleaching earths;

- 20-36% by weight of organic material mainly represented by the bio-charge (e.g. vegetable oil), in addition to the impurities remaining adsorbed on the earths;

0-4% by weight of moisture.

The disposal of said spent earths envisages to date recovering most of the oil remained adsorbed in the bleaching earths through extraction with solvent.

The spent bleaching earths can also be valorised as a co-feed of composting or biogas plants, where the organic part of the spent earths is transformed into biogas with disposal costs ranging between 180-250 €/ton.

However, these known processes of recovery or of valorisation of the spent bleaching earths are costly and in the case of the valorisation in composting/biogas plants the process does not involve a complete reuse of the spent earths, in contrast to an increasingly widespread circular economy need and in contrast to the growing need to reduce the landfill disposal of by-products in the industrial processes.

Summary

It is therefore highly desirable to find a method for the valorisation of spent bleaching earths that preferably does not require their treatment with solvent so as to have at least a saving of disposal costs.

It is also highly desirable to have infusible lubricant greases which show lower values of water washout with respect to the infusible greases actually available on the market, beside showing a combination of properties that are requested to the bentonite lubricating greases such as, for example, a low tendency to lose weight and to go out from the seat (evaluated, for example, by means of wheel bearing test), a high resistance in service (evaluated for example by means of the roll shell stability test).

The Applicant has now found that said spent bleaching earths can be valorised by using them as such in lubricant greases.

In fact, the Applicant has found that the spent bleaching earths coming from processes of purification of bio-charges, destined for the production of biofuels (green refinery), can be advantageously used as such as main thickening agent, even in high quantities, in the preparation of lubricant greases, in particular infusible greases, avoiding their disposal and the need to carry out an expensive pre-treatment with solvent before their disposal to remove the oil and/or impurities thereof.

The formulations of lubricant greases, preferably infusible greases, containing the aforesaid spent bleaching earths have also unexpectedly shown

- excellent capabilities of water washout resistance, with water washout values generally lower than 18% by weight, preferably lower than 13%, more preferably lower than 10%, and improved with respect to the bentonite greases;

- substantial absence of weight increase due to water incorporation;

- excellent rust-preventing properties with respect to the steel of the bearings (e.g. "Emcor" test for rust resistance of the steel);

- good cold characteristics (e.g. torque test, flow pressure test) at temperatures lower than 0 °C up to -10 °C, such as to make the lubricant greases object of the present invention a valid substitute of the bentonite grease known in the art, if not even an improved infusible lubricant grease.

A first object of the present invention therefore is a lubricant grease comprising

- at least one base oil ("lubricant base stock"), or mixtures of base oils,

- at least one first thickening agent,

- optionally a second thickening agent, preferably in smaller quantities than said first main thickening agent, and/or

- an optional polymer additive, possibly provided with water barrier properties, wherein

- said first thickening agent is one or more spent bleaching earths and is present in said grease in a quantity up to 80%-90% by weight relative to the total weight of the composition of grease,

- said at least one or more base oils are fossil oils, synthetic oils, oils of biological origin, renewable oils and/or biodegradable oils, preferably excluding UCO (Used Cooking Oil) oils, or combinations thereof,

- said lubricant grease having a consistency classified according to the NLGI scale and preferably being an infusible grease.

In the description of the present invention, unless otherwise specified, the values of the ranges include the extremes of the range.

In the description of the present invention, unless otherwise specified, the percentages (%) are to be understood by weight.

In the description of the present invention, the term "comprise" includes as a particular limiting case also its meaning as "consisting of".

In the description of the present invention, the term "consists essentially of" means that

- the composition or formulation necessarily includes the ingredients listed and that

- the composition or formulation is open to not listed ingredients which do not materially influence the basic properties and the innovative properties of the composition .

In the description of the present invention, unless otherwise specified, "part" and "parts" means part by weight and parts by weight, respectively.

In the present description the terms "thickener", "thickening agent" are used as synonyms and are intended to identify compounds, generally solid, designed to increase at least the consistency and/or viscosity of a composition containing them. In the present description first "thickening agent" is intended to identify the thickener or thickening agent that is present in the grease as the main thickening agent: preferably it is in a higher concentration than other possible thickening agents if present.

In the present description by "spent bleaching earths" it is intended to identify the bleaching earths at the end of their use in the raw bio-charge purification processes and which have not been subjected to any subsequent treatment of purification, recovery or removal of contaminants, e.g. oil.

Accordingly said spent bleaching earths contain both the typical inorganic absorbent material, i.e. bentonite, of the virgin bleaching earths (i.e. not spent) and the organic material remained absorbed on said bleaching earths, said organic material mainly comprising the bio-charge remained absorbed on the bleaching earths (i.e. edible oils, for example, vegetable oils, animal fats or their derivatives destined to the production of biofuels in biorefinery (green refinery process) and the possible impurities of the adsorbed raw bio-charge.

The spent bleaching earths which can be used in the grease according to the present invention can also be the spent bleaching earths that have undergone a subsequent solvent extraction treatment to recover the main part of the organic material, e.g. the oil remained absorbed on the bleaching earths. Such spent bleaching earths will be hereinafter indicated as "purified spent bleaching earths".

The non-purified spent bleaching earths generally contain 20-36% by weight of organic material mainly constituted of the bio-charge, e.g. vegetable oil, and also of other impurities which are present in the bio-charge remained adsorbed on said earths.

The purified spent bleaching earths contain lower amounts of the above organic material, generally lower than 20-36% by weight.

The presence of the organic material, intended as the overall material contained in the SBE that is neither inorganic material nor moisture, can be determined, for example, by means of XPS analysis, NMR or similar analysis known as capable to detect the elemental composition of the SBE and thus of the presence of carbon atoms as well.

It is to be understood that also any other methods known to the skilled in the art can be used to detect the presence of organic material, e.g. solvent extraction of the absorbed oil (Sohxlet), determination by subtraction of the moisture weight (measured by Karl Fischer titration) and the inorganic material weight (determined as the ashing residue to constant weight using a muffle furnace at 1000°C), without departing whereby from the scope of the present invention.

Illustrative but not limiting examples of non-purified spent bleaching earths are those coming from the pretreatment of palm oil or of other bio-charges such as, for example, castor oil, microbial oil but also animal oils and fats.

Other examples of vegetable oils or greases purified on bleaching earths may be sunflower, rapeseed, canola, palm, soybean, hemp, olive, flax, peanut, mustard, coconut oils or oils or greases contained in the pulp of pine trees ("tall oil"), or mixtures thereof. Examples of purified animal oils or greases on bleaching earths can be bacon, lard, tallow, milk fats, and mixtures thereof. Recycled oils or greases of the food industry, both of animal and vegetable origin, can also be used.

The vegetable oils or greases purified on bleaching earths can also be derived from plants selected by genetic manipulation .

Other examples of bio-charges subjected to purification treatments with bleaching earths can be the by-products obtained by extraction with solvent of the oil processing residues, such as for example "husk oil" derived from palm oil processing.

It is understood that the oils indicated above as biocharges are illustrative, but not limiting examples for the purposes of the present invention, of the organic component included in the spent bleaching earths usable in the greases of the present invention.

The spent bleaching earths exiting the bio-charge pre- treatment/purification processes generally contain bentonite as inorganic material: it is however understood that spent bleaching earths composed of other clay materials with high absorbing power other than bentonite can be used for the purposes of the present invention, without thereby departing from the scope of the present invention.

The typical composition of spent non-purified bleaching earths exiting bio-charge pre-treatment processes for biofuels can be exemplified, without limitation, as follows (% by weight relative to the total weight of non-purified bleaching earths):

• 80-60% by weight of bentonite (predominantly montmorillonite) as inorganic material;

• 20-36% by weight of organic material, predominantly represented for example by vegetable and/or animal oils and greases, C12+ hydrocarbons, phosphates, sulphates, metals and the like which have been adsorbed on the bleaching earths;

• 0-4% by weight of moisture.

It is understood that the aforesaid composition of nonpurified spent bleaching earths (SBE) is only indicative and is not limiting for the purposes of the present invention, neither in terms of percentages of the components nor in terms of the type of starting inorganic material and organic material adsorbed/retained in said bleaching earths.

It is also understood that for the purposes of the present invention, as the main thickening agent of the present lubricant grease it is possible to use the purified spent bleaching earths, i.e. the spent bleaching earths which have been subjected to one or more subsequent treatments of partial recovery and/or removal of the organic component e.g. oil extraction with solvent, and which therefore have an organic material content generally lower than 20% by weight (hereinafter referred to as purified spent bleaching earths), for example around 10-15% by weight, but also lower values, relative to the total weight of the purified bleaching earths.

In a preferred embodiment, the spent bleaching earths used as the main thickening agent of the grease of the present invention are those obtained at the end of the biocharge purification processes and which have not undergone one or more subsequent contaminant recovery or removal treatments, e.g. oil extraction with solvent (non-purifled spent bleaching earths).

What will be described hereinbelow with reference to the spent bleaching earths (hereinafter also referred to as SBEs for brevity's sake) is to be considered applicable both to the non-purified spent bleaching earths and to the purified spent bleaching earths, without thereby departing from the scope of the present invention.

The grain size of said SBEs (purified or non-purified) is not limiting for the purposes of the present invention and depends mainly on that of the starting virgin bleaching earths used in the bio-charge purification processes.

The starting virgin bleaching earths used in the biocharge purification processes may have a very variable surface area and/or a particle dimension distribution (e.g. in a range ranging from 0.8 pm to 2000 pm) but this is not binding for the purposes of the present invention.

As an example of the dimension range of the particles of the spent bleaching earth, the range ranging from 5 to 20 pm can be indicated.

In addition, the starting virgin bleaching earths may have a pH (evaluated in aqueous solution) that may range from 2 to 8.6 but this is not binding for the purposes of the present invention.

Also the spent bleaching earths (SBE) usable in the grease of the present invention, preferably in an infusible grease, may have an initial acid pH, evaluated by measuring the pH of an aqueous solution containing 10% by weight of said spent bleaching earths.

In one embodiment, the spent bleaching earths (SBE) useful in the grease of the present invention have an initial acid pH, which generally ranges from 2 to 6-6,3 (evaluated in aqueous solution, using 1 g of SBE dispersed in 10g of H2O, then measuring the pH of the resulting aqueous solution).

The pH of the aforesaid aqueous solution containing SBE can be, for example, variable from 2 to 9: in case of acid or basic pH it is advantageous to operate a neutralisation of the pH of the spent bleaching earths (SBE) to avoid that the acid or basic substances contained in the spent earths can form, in the presence of water, corrosive compounds for the metals that will come into contact with the lubricant grease containing said spent bleaching earths in accordance with the present invention.

In fact, the neutralisation of the SBEs with basic or acid substances, preferably inorganic substances, can be carried out before said SBEs are used in the formulation of the lubricating grease, e.g. before being mixed with the base oil, or during the preparation of the formulation of the lubricant grease of the invention, e.g. after having been mixed with the base oil, without thereby departing from the scope of the present invention.

As examples of basic substances employable for neutralising the acid pH of the SBEs mention can be made of calcium carbonate, propylene carbonate, calcium hydroxide, preferably calcium carbonate or calcium hydroxide.

In case the spent bleaching earths have a basic pH, for example with a pH around 9, it is preferable to neutralise them with strong acids, more preferably with strong acids in aqueous solution, for example HC1 solutions, so as to arrive at a pH around 6-7.5.

The concentration of strong acid in the above-mentioned aqueous solution of neutralisation of the SBEs is not binding for the purposes of the present invention and can be determined by the person skilled in the art without the need for specific teachings.

In one preferred embodiment, the spent bleaching earths which are initially acid are used in neutralized form in the lubricating grease of the present invention.

With the term "neutralized spent bleaching earths" it is herein intended to identify the spent bleaching earths which show a pH generally comprised within 6,5-7,5 (the pH being measured as the pH of an aqueous solution containing 10% by weight of said spent bleaching earths).

Particularly, the acid spent bleaching earths are preferably neutralised with calcium hydroxide when it is wished to prepare a lubricant grease containing one or more base oils of mineral type, preferably with an aqueous solution of Ca(OH)2.

In another embodiment, the acid spent bleaching earths are preferably neutralised with calcium carbonate, in aqueous solution, when it is wished to prepare a lubricant grease with one or more base oils of ester type.

Neutralisation of the spent bleaching earths is not a process that involves obtaining a bentonite modified with organic cations.

In one preferred embodiment, the spent bleaching earths, purified or non-purif led, are present in the lubricating grease of the present invention in neutralized form as regards the pH as above defined. In the lubricant grease of the present invention the content of spent bleaching earths may advantageously be at least 10% by weight relative to the total weight of the lubricant grease composition.

In one embodiment, the content of SBE may advantageously range from 10% to 80%-90% by weight relative to the total weight of the lubricant grease composition, the remaining portion to achieve 100% consisting only of one or more base oils as defined above, preferably excluding UCOs.

In another embodiment, the content of SBE ranges from 10% to 80%-90% by weight relative to the total weight of the lubricant grease composition, the remaining portion to achieve 100% consisting of one or more base oils as defined above, preferably excluding UCOs, and one or more additives chosen from

- a second thickening agent,

- a polymer additive, possibly provided with water barrier properties, and optionally one or more additives (additive package) chosen from

- rust-preventing additives,

- anti-wear additives,

- antioxidant additives,

- copper corrosion inhibitor and the like, e.g. extreme pressure additives such as, for example, graphite, as will be described in detail hereinbelow.

However, a total quantity of spent bleaching earth greater than 90% by weight or lower than 10% by weight relative to the total weight of the lubricant grease composition may be used to prepare a lubricant grease in accordance with the invention, without thereby departing from the scope of the present invention.

In another embodiment, the content of SBE may advantageously range from 20% to 80% by weight relative to the total weight of the lubricant grease composition, the portion to achieve 100% being capable of consisting only of one or more base oils as defined above or of one or more base oils as defined above and one or more additives as indicated above.

In another embodiment, the content of SBE can advantageously ranges from 20% up to amounts lower than 60% by weight with respect to the total weight of the lubricating grease composition, the remaining part to 100% being capable of consisting only of one or more base oils as defined above or of one or more base oils as defined above and one or more additives as indicated above.

Given the presence of impurities in the spent bleaching earths, it has been found unexpected that such spent bleaching earths can be used in the lubricant formulations of greases to form a gel without giving rise to negative phenomena such as, for example, reactions among the various ingredients (given the presence of metals in said SBEs), phase demixing (given the presence of residual bio-charge contained in said SBEs) or the like.

Brief Description of the Drawings

Figure 1 shows the different appearance of the consistency of the gel/paste of the invention compared to the starting SBEs which are presented as a non-powdery solid. Description of Embodiments

As mentioned above, the base oil employed in the lubricant grease of the present invention may be of different nature, in particular it may be chosen from the base oils of

- a fossil nature, for example a mineral oil (i.e. a mixture of hydrocarbons obtained starting from crude oil by means of a conventional refining process or by means of a medium hydrogenation process), of any viscometric cut (viscosity grade), for example a fluid cut (SN 125 ÷ 170 typically 150), a medium cut (SN 350 ÷ 600), a Brightstock (BS 150 ÷ 200) or mixtures thereof;

- of a synthetic nature, i.e. all types of base oils obtained by means of synthetic processes, for example by oligomerisation and hydrogenation of olefins, or polyol esters, such as for example PRIOLUBE 1965, PRIOLUBE 1963, or mixtures thereof;

- of a biological, renewable and/or biodegradable nature, for example palm oil, castor oil, microbial oil, or other oils indicated above for bio-charges preferably except for UCOs (WCO); polyalphaolefins functionalized with ester groups (PAO-esters) deriving from metathesis of vegetable oils; or

- combinations thereof.

The spent oils UCO (Used Cooking oil) are preferably excluded as base oils for the lubricant grease of the present invention as these spent oils generally have carbonaceous residues, high freeze temperatures, corrosive compounds such as FEA (free fatty acids) and decomposition temperatures above 300 °C, one or more of these characteristics representing an element of criticality both for obtaining a grease with a high drop point, i.e. greater than 350°C, and for the application of said grease containing UCO on the metallic surfaces, in particular steel surfaces, in view of the high continent of FFA which are corrosive for metals.

In the grease lubricant composition in accordance with the present invention when a second thickening agent is present, the UCOs are not present among the base oils forming the lubricant grease.

In addition, or as alternative to the above, when the base oil is UCO, the lubricating grease according to the present invention always includes the polymeric additive above defined.

As examples of mineral oil usable as base oil mention can be advantageously made of the mineral oils of API classification, preferably Group I (GPI), such as, for example, SN 500, BS 150,SN 150, BS 200 or mixtures thereof: the Group I oils advantageously allow the lubricant grease to achieve an NLGI class consistency of at least 1 but also higher.

As an alternative to the Group I mineral base oil, use can also be made of the API group II and/or group III mineral oils if it is wished to obtain a grease from mineral oils having a lower consistency according to the NLGI classification.

Examples of synthetic base oils employable in the lubricant greases of the present invention are the polyol esters (e.g. PRIOLUBE 1965, PRIOLUBE 1963) or mixtures thereof; polyalphaolefins (PAOs): generally said synthetic base oils belong to group IV of the API classification. As examples of base oil of renewable origin employable in the lubricant greases of the present invention mention can be made of palm oil, castor oil, microbial oil, polyalphaolefins functionalized with ester groups (Pao- esters) deriving from metathesis of vegetable oils, estolides.

It is also possible to use group V base oils such as for example polymethacrylate, polyisobutene, but generally in admixture with a Group I, II, III or IV base oil.

In a preferred embodiment, said at least one base oil employed in the lubricant grease of the present invention is a mineral base oil and/or an oil of renewable source, preferably a mineral base oil of Group I, or a mixture of mineral base oils, preferably of mineral base oils of Group I (GPI), more preferably a mixture of SN 500 and BS 150.

The viscosity of the base oil of the lubricant grease of the present invention is not binding for the purposes of the present invention, but the higher the viscosity and the higher the NLGI consistency of the lubricant grease obtainable will be.

Kinematic viscosity values of base oils suitable for forming lubricant greases ranges, for example, between 50 and 800 mm ² /s at 40 °C, preferably between 100 and 600 mm ² /s at 40 °C.

The lubricant grease of the present invention may therefore be composed

- of one or more SBEs (non-purified or purified) and of one or more base oils (two-component grease), preferably except for UCOs;

- or it may comprise in addition to SBE (purified or non- purified) and one or more base oils preferably except for UCOs, also one or more additives chosen from a second thickening agent, a polymer additive capable of improving the structural stability of the grease, possibly provided with water barrier properties, other additives conventional for lubricating greases such as rustpreventing additives, anti-wear additives, antioxidant additives, copper corrosion inhibitor and the like, e.g. extreme pressure anti-wear additives such as for example graphite, as indicated below in detail.

In one embodiment, the lubricant grease, preferably infusible grease, is formed by

- spent bleaching earths as defined above for 70-80% by weight, preferably around 75% -76% by weight relative to the total weight of the grease composition, and

- by one or more base oils as defined above, preferably except for UCOs, for the remaining portion to achieve 100% by weight.

In another embodiment, this above-defined grease composition provides that the above remaining portion to 100% is constituted of a mixture of one or more base oils with one or more additives, preferably with a combination of additives (additive package) chosen from rust-preventing additives, anti-wear additives, antioxidant additives, copper corrosion inhibitors, extreme pressure anti-wear additives and optional stabilizers.

As already mentioned, in the lubricant grease of the present invention containing SBE and base oils it is advantageously present - a polymer additive and/or

- a second thickening agent other than the spent bleaching earths.

In one embodiment, the grease according to the present invention comprises at least the polymeric additive as above defined.

In one preferred embodiment, in the lubricating grease containing SBE and base oils according to the present invention it is advantageously present said polymeric additive and said second thickening agent different from the spent bleaching earths.

The second thickening agent, hereinafter also defined as thickening agent or viscosity modifier, is chosen from those conventionally used in the lubricant greases, such as for example fumed silica, preferably hydrophobic fumed silica, i.e. modified on the surface with polydimethylsiloxane, without particular limitations in terms of surface area, average particle dimension and grain size distribution.

Fumed silica, thanks to its three-dimensional structure, has a thixotropic behaviour increasing the viscosity when used as a thickening agent.

The quantity of such second thickening agent depends on the viscosity and/or consistency to be obtained for the final grease, in particular for the infusible grease: generally, the quantity of the second thickening agent may range from 0.5% to 7% by weight, preferably from 1% to 5% by weight with respect to the total weight of the lubricant grease composition. In one embodiment, the amounts of said second thickening agent ranges from 1.5% to 3-4% by weight, relative to the total weight of the lubricant grease composition.

It is understood that quantities lower than 0.5% and greater than 7% of the second thickening agent may be employed without thereby departing from the scope of the present invention.

In one embodiment, the lubricant grease of the invention, preferably infusible grease, contains:

- 70-80% by weight, preferably 75-80% by weight, of spent bleaching earths as defined above;

10-30% by weight, preferably 18-25% by weight, of one or more base oils as defined above, except for UCOs, preferably one or more mineral oils;

0.5% to 7% by weight, preferably from 1.5 to 3-4% by weight, more preferably from 1.5 to 3% or from 3% to 4% by weight, of second thickening agent, preferably fumed silica, the quantities of the aforesaid components being chosen so that their sum is 100%.

If in the lubricant grease in accordance with the present invention one or more further additives are present, in addition to the indicated quantities of second thickening agent, the total content of SBE will generally be lower than 75% by weight, preferably lower than 60%: in such grease formulations furthermore the base oil or the mixture of base oils may advantageously range from 10% to 50% by weight, preferably from 15% to 30-35% by weight, relative to the total weight of the lubricant grease composition, and depends substantially on the grade of NLGI consistency to be achieved and on the total quantity of the further additives necessary for the grease formulation.

It is understood, however, that total quantities of base oil or of base oil mixture lower than 10% by weight relative to the total weight of the grease composition may be used in compositions in which one or more further additives are present in addition to the second thickening agent, without thereby departing from the scope of the present invention.

The one or more further additives, other than the second thickening agent, which can be used in the lubricant grease composition in accordance with the present invention, preferably in the infusible grease, are additives , which allow to achieve, if required, one or more conventional technical and performance specifications of the lubricant grease, including infusible greases, such as, for example:

- rust-preventing additives, in particular imidazolines, hemi esters of the succinic acid (e.g. carboxyimidazoline marketed by AFTON under the name HITEC 536);

- anti-wear additives, such as dithiocarbamates (e.g. methylene-bis-dialkyl-dithiocarbamate marketed by RHEINE CHEMIE under the name RC 6340), dithiophosphates (e.g. dithiophosphate marketed by CIBA under the name: IRGALUBE 353), phosphorothionates, amino phosphates;

- antioxidant additives, in particular substituted diphenyl amines (e.g. octylated/butylated diphenylamine marketed by BASF under the name IRGANOX L 57);

- polymer additives, possibly provided with water barrier properties, to increase the structural stability of the gel, such as for example polyisobutene, polymethylmethacrylate, generally of low molecular weight (Mn), for example around 1300 g/mol;

- stabilizers;

- copper corrosion inhibitor such as for example benzotriazole derivatives, (e.g. mixture of N,N-bis(2- ethylhexyl)-4-methyl-lh-benzotriazole-l-methylamine + N,N-bis (2-ethylhexyl)-5-methyl-lh-benzotriazole-l- methylamine, marketed by CIBA under the name IRGAMET 39; and the like, such as for example extreme pressure anti-wear additives, e.g. graphite.

Generally, the total content of further additives (other than the second thickening agent) in the lubricant grease is lower than or equal to 40% by weight, preferably lower than 35% by weight, relative to the weight of the total grease composition.

The quantity of each additive depends on the minimum quantity at which the specific performance for which the additive is used begins to take place: generally, quantities starting from 0.01% by weight, preferably from 0.1% by weight, of each additive relative to the weight of the total grease composition are to be considered minimum quantities, although larger quantities can be used without thereby departing from the scope of the present invention.

As already mentioned above, among the various additives usable in the lubricant grease, preferably infusible one, in accordance with the present invention compounds can be included that contribute to improving the structural stability of the grease such as polymer compounds, for example polyisobutene which is also advantageously provided with water barrier properties. Other usable polymer additives are those belonging to group V of the API base oils and can be for example polyalkylmethacrylates, in particular VISCOBASE 5-220 (Kinematic viscosity at 100 °C=460-500 cSt), marketed by EVONIK.

Generally, the quantity of polymer additive, possibly provided with water properties, preferably polyisobutene, may ranges between 1-35%, preferably between 7% and 35%, preferably between 10 and 32% by weight relative to the total weight of the lubricant grease composition.

In one alternative embodiment, the quantity of polymer additive, possibly provided with water properties, preferably polyisobutene, may ranges between 1% and 7%, preferably between 1,5 and 4% by weight with respect to the overall weight of the composition of the lubricating grease.

The maximum quantity of each further additive (other than SBE, second thickening agent and polymer additive) may be about 5% by weight relative to the total weight of the grease formulation, although this is not binding for the purposes of the present invention.

In a preferred embodiment, the lubricating grease comprises the spent bleaching earths as above defined, the base oil (or mixture of base oils) as above defined, fumed silica as second thickening and polyisobutene as polymeric additive.

In another preferred embodiment, the lubricant grease comprises the spent bleaching earths as defined above, the base oil (or mixture of base oils) as defined above, the second thickening agent, e.g. fumed silica, and the polymer additive, e.g. polyisobutene, in the following quantities - 50-55% by weight of spent bleaching earths;

10-22% by weight of base oil or of a mixture of base oils as defined above, except for UCOs;

1.5-4% by weight of second thickening agent, preferably fumed silica,

- 7-35% by weight, preferably 10-32% by weight, of polymer additive, preferably polyisobutene, the quantities of each one of the aforesaid components being capable of being chosen so that their sum is 100% of the total weight of the composition, or the remaining part to achieve 100% of the total weight of the composition being capable of being represented by one or more further conventional additives (additive package) for lubricant greases as indicated above chosen from rust-preventing additives, anti-wear additives, antioxidant additives, copper corrosion inhibitor, extreme pressure anti-wear additives and optionally stabilizers.

The lubricant grease of the present invention, preferably infusible grease, can therefore be formulated so as to have an NLGI consistency of class 0, or be formulated so as to have a greater consistency of class 1 or 2, but also higher for example 3, 4, by varying the concentrations of base oil, SBE, and of the other components (second thickening agent, polymer additive and other additives) without thereby departing from the scope of the present invention.

In a preferred embodiment, the lubricant grease is infusible and has a NLGI consistency of class greater than or equal to 1.

The lubricant grease of the present invention can therefore be formulated up to 80%-90% by weight with respect to its total weight from circular economy compounds with an important share of renewable material coming from the organic material present in the earths (about 30%), and from base oils of renewable origin for the remaining potential share to achieve 100%.

It has also been unexpected that the use of such spent bleaching earths results in a low water washout in the absence of additives known to confer water barrier properties, even in greases containing SBE as the sole thickening agent.

Some embodiments are infusible greases chosen from the following compositions (% by weight with respect to the overall weight of the composition of the lubricating grease): COMPOSITION A: from 10% to 80%-90% by weight of SBE, preferably from 70% to 80% by weight,more preferably from 75-80% by weight, relative to the total weight of the lubricant grease composition, the remaining portion to achieve 100% consisting only of one or more base oils as defined above, preferably mineral oils, except for UCOs.

COMPOSITION B:

- 70-80% by weight, preferably 75-80% by weight of spent bleaching earths;

10-30% by weight, preferably 18-25% by weight of one or more base oils as defined above, except for UCOs;

0.5% to 7% by weight, preferably from 1.5 to 3-4% by weight, of second thickening agent, preferably fumed silica, the quantities of the aforesaid components being chosen so that their sum is 100%.

COMPOSITION C:

- SBE < 75 % by weight, preferably < 60%; from 10% to 50% by weight of one or more base oils, preferably from 15% to 30-35% by weight,

0.5% to 7% by weight, preferably from 1.5 to 3-4% by weight, of second thickening agent, preferably fumed silica,

- < 35% by weight of one or more further additives chosen from polymer additives, rust-preventing additives, anti-wear additives, antioxidant additives, corrosion inhibitors, the quantities of the aforesaid components being chosen so that their sum is 100%.

COMPOSITION D:

- SBE < 75 % by weight, preferably 50-55 % by weight, from 10% to 50% by weight of one or more base oils as defined above, except for UCOs, preferably from 10% to 22% by weight,

0.5% to 7% by weight, preferably from 1.5 to 3-4% by weight, of second thickening agent, preferably fumed silica,

1-35% by weight, preferably 7-35% by weight, of polymer additive, preferably polyisobutene;

- < 35% by weight of one or more further additives (additive package) chosen from rust-preventing additives, anti-wear additives, antioxidant additives, corrosion inhibitors, extreme pressure anti-wear additives, the quantities of the aforesaid components being chosen so that their sum is 100%.

COMPOSITION E:

- 50-60% by weight of SBE,

- from 10% to 50% by weight of one or more base oils as defined above, except for UCOs, preferably from 10% to 35% by weight,

- from 1% to 4% by weight, of second thickening agent, preferably fumed silica,

- 1-5% by weight of polymer additive, preferably polyisobutene;

- < 35% by weight of one or more further additives (additive package, e.g. conventional additive package) chosen from rust-preventing additives, anti-wear additives, antioxidant additives, corrosion inhibitors, extreme pressure anti-wear additives, e.g. graphite, the quantities of the aforesaid components being chosen so that their sum is 100%.

The process to prepare the lubricant greases of the present invention, preferably infusible greases, comprises at least the following step of: mixing at least one or more spent bleaching earths as defined above with at least one or more base oils as defined above, preferably except for UCOs, at atmospheric pressure and at a temperature lower than or equal to 100 °C, preferably under ambient temperature conditions.

Mixing can take place in any apparatus provided with mixing and/or stirring devices suitable for mixing semisolid and extremely viscous products so as to obtain a workable mixture, such as apparatuses provided with mixing means with a high shear stress such as, for example, planetary mixing machines, propeller mixing machines, mixing machines provided with a twin-screw mixer, preferably a mixing machine provided with a twin-screw mixer.

Examples of stirring/mixing speeds can be speeds from 40 rpm up to 1200 rpm.

This preparation modalities which envisages a simple mixing, for example in a mixing machine, offers a great advantage over the preparation of the bentonite greases for which much more complex modes are envisaged: mixing temperatures higher than 100 °C and high work pressures, generally around 30 bar but also beyond, for example up to 200 bar, to carry out homogenisation.

The use of mixers with a twin-screw mixer has proved to be particularly advantageous as an infusible grease was obtained simply by using spent bleaching earths for 75-80% by weight of the lubricant grease, without resorting to a second thickening agent, such as fumed silica, conventionally used in the bentonite greases.

The greases of the invention thus obtained have unexpectedly also shown excellent properties of water washout resistance (even in the absence of additives also provided with water barrier properties, e.g. polyisobutene), infusibility and protection of the metals (e.g. copper, steel) against corrosion given by having passed the Emcor test (test on steel) in addition to the passing of the test on copper.

Moreover, the lubricant greases of the invention have shown a very high adhesiveness, generally higher than that of the known bentonite greases: high adhesiveness is in fact advantageous since it guarantees that the grease remains in the seat when it is subjected to the dynamic stresses during the operations.

In addition, a high adhesiveness allows to limit the centrifugation loss of grease which is typical in some applications, e.g. gearmotors.

In particular, the process of preparation is carried out advantageously by effecting, before the mixing step of SBE + base oil, a neutralization step of the pH of said spent bleaching earths.

More in particular, the preparation process advantageously takes place by preceding the SBE + base oils mixing step, with the following steps:

(1) optional homogenisation of the grain size of the spent bleached earths so as to make the grain size uniform, for example by means of a mill, in order to remove any nonhomogeneities, such as for example lumps, agglomerates or the like generated by the presence of water and bio-charge adsorbed on the spent bleaching earths;

(2) optional neutralisation of the pH of said spent bleaching earths by using basic or acid substances;

(3) loading of said spent bleaching earths into the mixing device, said spent bleaching earths being possibly previously homogenised and/or made uniform in terms of grain size, and/or optionally neutralised with basic or acid substances, where said loading can take place through the use, for example, of a conveyor auger;

(4) optional loading of one or more neutralising compounds into the mixing device if the spent earths loaded in step (3) have an acid pH, e.g. 5.5, or a basic pH, e.g. 9, for example by the addition of an aqueous solution containing 10-35% by weight of inorganic basic substance, e.g. Ca(OH)2, or of inorganic acid substance, and any removal of water if present.

Step (4) is preferably carried out when the SBEs have not previously undergone the neutralisation treatment of step (2): it is however understood that step (4) may be carried out even if step (2) has already been performed, without thereby departing from the scope of the present invention.

Next, it is proceeded with the step of adding one or more base oils under stirring and mixing SBE+ base oils, hereinafter referred to as step (5), at the end of which it is envisaged

- an optional subsequent addition step (step 5 bis) to add a second thickening agent, e.g. fumed silica, while the mixture of components is being stirred, until an homogenous mixture is obtained which has a cream-like look, or an homogeneous gel/paste is obtained, e.g. by continuing to stir for 4 hours; and

- an optional addition step (6) to add one or more further additives as indicated above, after having increased the work temperature in the mixing device compared to the preceding steps, preferably at least to 40 °C, more preferably to 60 °C, and while mixing until a mixture is obtained without granules which has a cream-like look or looks like a gel/paste, e.g. by continuing to stir for 1 hour.

The above steps (1) to (6) take place at atmospheric pressure. In addition, the above steps (1) to (5 bis) take place at ambient temperature.

In one embodiment, the step (1) of homogenising the grain size is advantageously carried out, even if there are visually no lumps, so as to be sure that the SBEs are uniform in terms of grain size before giving rise to the lubricant grease.

In another embodiment, the neutralisation step (2) and/or (4) is advantageously carried out to avoid possible corrosions to the production plant.

The advantages of the lubricant greases of the present invention obtained with the above-described process in accordance with the invention are manifold with respect to the known art.

A first advantage consists in the reuse of the spent bleached earths in far greater quantities than the quantity of bentonite used to produce lubricant greases (e.g. in percentage >>50%) unlike bentonite greases in which the percentage of use of bentonite is 8-10% max.

A second advantage is the reuse of the spent bleaching earths as such, without needing for posttreatment of the same, except for the possible neutralisation of their pH for reasons of corrosion of the materials of the plant.

Another advantage is the production process that is simple and simplified compared to that of the bentonite greases as it operates at atmospheric pressure, instead of under pressure, and at temperatures lower than 100 °C.

Furthermore, the process adopted in the present invention for the production of lubricant greases allows the improvement of some performance characteristics, for example the water washout, and an improved resistance to water penetration compared to the bentonite greases on account of the absence of weight increase due to water incorporation: these properties advantageously allow the use of the lubricant greases of the invention in humid environments and/or in the presence of water.

Some illustrative but not limiting examples of the present invention follow.

In the following examples the physical properties have been determined with the specified standard methods but it is understood that it is possible to measure the same physical properties with equivalent methods belonging to different norms/standards without thereby departing from the scope of the present invention.

EXAMPLES

Material

- PRIOLUBE™ 1965: polyol ester, marketed by Croda, and having a kinematic viscosity at 40 °C equal to 220 cSt;

- PRIOLUBE™ 1963: polyol ester, marketed by Croda, and having a kinematic viscosity at 40°C equal to 220 cSt;

- Fumed silica: CAB-O-SIL TS 720 by Cabot, surface modified with polydimethylsiloxane that makes it hydrophobic;

- PB 300 (thus indicated for brevity's sake): INDOPOL ® H-300 additive (POLYBUTENE H 300) having a molecular weight (Mn) of 1300, marketed by INEOS as a polymer additive (oligomer);

- BS 150: mineral base oil marketed by ENI SpA;

- SN 500:mineral base oil marketed by ENI SpA;

- Type 1 spent bleaching earths (coming from the ENI SpA plant in Venice for the bleaching treatment of palm oil) obtained from acid activated bentonite TONSIL 9194 FF marketed by Clariant: waste in the form of a non- powdery solid containing about 287 g/kg (28.7%) of animal and vegetable Oils and greases; C12+ heavy hydrocarbons: about 540 mg/kg; mineral oils: about 580 mg/kg; metals around 5 g/kg; phosphates and sulphates around 2.9 g/kg;

- Type 2 spent bleaching earths (sample coming from the ENI SpA plant in Gela for the treatment of bio-charges) obtained from acid activated bentonite TONSIL 9194 FF marketed by Clariant:waste in the form of a non-powdery solid and containing animal and vegetable Oils and greases, C12+ heavy hydrocarbons, metals, phosphates and sulphates in quantities similar to SBEs type 1 from the plant in Venice.

Characterisations/analysis method

- DROP POINT

It is the temperature at which a grease sample, if heated, starts flowing through an opening according to the method ASTM D566.

- CONSISTENCY after 60 double strokes (de)

It is the measurement of the stiffness of a grease and is evaluated by measuring the degree of penetration according to ASTM D217-21a (10' mm). The test measures in tenths of mm at which depth of a sample of grease a given cone sinks.

The consistency is classified according to a scale developed by NLGI (National Institute of Grease Lubrication) and reported hereinbelow: the greases for bearings are normally NLGI 1, 2 or 3, and the softer the grease, the lower the number.

- WATER WASHOUT

The measurement is made in accordance with the method ASTM D 1264: the test (Water washout) envisages coating a ball bearing placed in a housing with a grease. Thereafter, the bearing is rotated at 600 rpm and subjected to water jet at a temperature of 38 °C for one hour. At the end of the test, the bearing is dried in the stove for 16 hours and then weighed to check for any weight loss (% by weight) due to water washout of the grease.

COPPER CORROSION Evaluated by subjecting a sample of grease of the invention to the test according to ASTM D 4048.

- KINEMATIC VISCOSITY

Evaluated at 40°C according to the method ASTM D445.

EXAMPLE 1

Formation of an SBE gel/base oil and evaluation of the drop point

In order to evaluate the effective formation of a gel from the spent bleaching earths and to verify the formation of an infusible lubricant grease, it was proceeded with mixing a considerable quantity of a sample of spent bleaching earths with a base oil formed by a mixture of esters, PRIOLUBE 1965 and PRIOLUBE 1963, in relative quantities as reported in table 1.

Said base oil consisting of the mixture of esters has a kinematic viscosity at 40°C equal to 220 cSt.

The sample of spent bleaching earths (hereinafter referred to as type 1 spent earths) that comes from a bleaching treatment of a bio-charge consisting of palm oil, was mixed as such, at ambient temperatures and pressure, with the aforesaid base oil in the percentages indicated in Table 2.

The spent bleaching earths used (of type 1 - sample CER020304) show a pH equal to 3.2 evaluated in an aqueous solution containing 10% by weight of said spent earths.

Table 1 Table 2

The preparation of the gel was carried out according to the following procedure: to the type 1 spent bleaching earth, placed in a becker under a hood, addition is made of the base oil (mixture of ester bases) at ambient temperature and atmospheric pressure, under stirring starting from a speed of 40 rpm up to 1200 rpm for 1 hour.

The mixer used is a laboratory mechanical mixer, ICA® RW 16 BASIC.

A gel with an appearance as shown in Figure 1 was obtained, which was then subjected to the tests indicated in table 3 to measure its consistency and drop point.

Table 3

The drop point higher than 350°C and the consistency of the final composition belonging to the NLGI scale of the lubricant greases (grade 0, corresponding to a semi-fluid appearance) attest to the effective formation of a lubricant grease with a gel structure that retains the oil, given the high drop point. This means that the network formed by the spent bleaching earths is very resistant and prevents the outflow of the base oil retained inside it, in a way similar to what happens in infusible bentonite greases.

EXAMPLE 2

Preparation of infusible greases containing SBE and fumed silica

Using the same type 1 spent earths, three lubricant grease formulations (formulation 2, formulation 3 and formulation 5) were prepared in accordance with the present invention, the compositions of which are reported in table 4 .

The procedure followed for the preparation of the greases and the apparatus are the ones reported in example 1, except for the subsequent addition, after 1 hour of stirring, of the fumed silica keeping the composition under stirring .

Gels were obtained with an appearance as shown in Figure 1, which were then subjected to the tests indicated in table 4 to measure their consistency and the drop point.

Table 4

As can be noted from table 4, the addition of fumed silica allows the gel to harden, obtaining a "harder" grease, passing from a 0 consistency to a 1 consistency.

Then slightly increasing the quantity of spent earths SBE further increased the consistency.

In general, the greater the consistency of the grease and the greater the ability of the grease to remain in the bearing without generating excessive friction.

EXAMPLE 3

Preparation of infusible greases with neutralised spent earths

By repeating the procedure of example 2 and using the same type 1 spent earths and the same mixture of esters as the base oil, lubricant grease formulations containing basic substances were prepared.

Considering that the acid pH of the type 1 spent earths (having a pH equal to 3.2 in a 10% by weight aqueous solution of SBE) in the presence of water could favour the corrosion of the metals, three grease formulations were prepared by adding, with respect to example 2, different basic substances in aqueous solution, as reported in table 6, so as to have the neutralisation of the pH of the SBEs.

The addition of the basic substance, in the form of an aqueous solution, was carried out after the addition of base oil in the formulation. Subsequently, the water was removed from the product obtained by means of heating in the stove at 100 °C for 1 hour .

The basic substances, in 10% aqueous solution, which were added in the formulation are the following ones

-PROPLENCARBONATE (formulation 6)

-CALCIUM HYDROXIDE (formulation 7)

-CALCIUM CARBONATE (formulation 8)

Gels were obtained with an appearance as shown in Figure 1, which were then subjected to the tests indicated in table

5 to measure their consistency and the drop point.

Table 5

The pH of the formulation 8 is close to neutrality: the quantity of basic substance in the formulation is such that no worsening of the consistency and drop point characteristics of the grease is noted compared to formulation 5 which is not added with basic substances and has an acid pH.

EXAMPLE 4

Preparation of infusible greases using a base oil of mineral type, fumed silica and a polymer additive with water washout test

Example 2 was repeated using the same type of spent earths (type 1, Venice) except for using different base oils and for the addition of a further conventional polymer additive of polymer nature such as polyisobutene 300, indicated as PB 300 for brevity's sake.

A mixture of API Group I mineral base oils having substantially the same viscosity (at 40°C) as the mixture of ester base oils of examples 2 and 3 was used as the base oil .

The mixture of mineral base oils employed in this example has a kinematic viscosity at 40°C equal to 220 cSt (ASTM D455) and has the following composition

The preparation modalities of the various lubricating gels are identical to those employed in the previous examples 1-3 with the ester base oils.

In one of the formulations (formulation 16) it was proceeded with neutralising the spent bleaching earths before their formulation with the other components of the grease instead of during the formulation of the grease itself, using 3 g of Ca(0H)2 conveyed in a minimum quantity of water so as to bring the pH of the spent bleaching earths to neutrality when present at 10% in aqueous solution.

The spent earths employed in formulations 12, 13, 14 were not neutralised either during the formulation of the grease or prior to formulation.

Gels were obtained with an appearance as shown in Figure 1, which were then subjected to the tests indicated in table

6 to measure their consistency, drop point and the water washout.

Table 6

The above reported data show that the infusible greases in accordance with the present invention have excellent values of water washout resistance.

EXAMPLE 6

Preparation of infusible greases containing additives and a different type of neutralised spent bleaching earths (earths sample 2)

A sample of spent bleaching earths (SBE) coming from a different bleaching treatment plant than that indicated in example 1 (hereinafter referred to as type 2 spent earths), having a pH equal to 3.15 (measured in an aqueous solution containing 10% by weight of SBE) were pre-treated before being formulated with the other components of the lubricant grease, bringing the pH of the aqueous solution containing 10% by weight of SBE to the value of 7 by mixing with an aqueous solution of Calcium hydroxide at 33% by weight.

The final composition of the earths used is as follows

Employing the same mixing procedure described in the previous examples, the neutralised spent bleaching earths were then formulated with mineral base oils SN 500/BS 150 employed in the previous examples, and with additives (fumed silica and PB 300) already employed in the previous examples.

Mixing was carried out using in some cases a laboratory planetary mixer and in other cases mixing machines provided with a twin-screw mixer (ERWECA AR 402 200 g and Battagion 2 kg models).

Gels were obtained with an appearance as shown in Figure 1, which were then subjected to the tests indicated in table 7 to measure their consistency, drop point and the water washout.

Table 7 EXAMPLE 7

Infusible grease also containing a package of conventional additives

Formulation 19 of Example 6 was subsequently added with a standard package of additives widely used in the formulation of industrial lubricants, which comprises antioxidants, rust-preventing, anti-wear and copper corrosion inhibitor as defined hereinbelow.

The addition of the package of additives to formulation 19 was carried out using a twin-screw mixing machine.

The package of additives is composed as follows:

- Antioxidant: IRGANOX L 57 from BASF

(octylated/butylated diphenylamine);

- Rust-preventing: HITEC 536 from AFTON (carboxyimidazoline);

- Antioxidant/anti-wear: RC 6340 from RHEINE CHEMIE

(methylene bis-dialkyl-dithiocarbamate);

- Anti-wear extreme pressures: IRGALUBE 353

(dithiophosphate) and IRGALUBE 211 (triphenyl nonylate phosphorothionate) from CIBA;

- Copper corrosion inhibitor: IRGAMET 39 from CIBA (N,N- bis (2-ethylhexyl)-4-methyl-lh-benzotriazole-l- methylamine + N,N-bis (2-ethylhexyl)-5-methyl-lh- benzotriazole-l-methylamine) .

Table 8 reports the final composition (considered 100%) after the addition of the package of additives with the percentage of the components in the final grease. Tab1e 8

The grease thus obtained, with the appearance of a gel as shown in Figure 1, was characterized according to the typical analysis specifications for the lubricant greases whose results are reported in the following table 9.

Table 9 - Grease characterization formulation 19 a

As can be observed, the infusible grease obtained in accordance with the present invention has a combination of properties such as: - excellent resistance to water washout and absence of increase of weight due to water incorporation. The bentonite greases subjected to the test have a weight increase by about 20% due to water incorporation, a phenomenon not observable in the grease of the present invention as reported in the following table

Bentonite grease 1: product marketed by Eni under the name GREASE NF 2;

Bentonite grease 2:product marketed by Eni under the name GREASE 33 ED.

The increase of weight of the bentonite greases due to water incorporation could alter the chemical-physical and rheological characteristics of the grease, favouring corrosion phenomena and the oxidation of the grease itself.

- good rust-preventing response confirmed by the excellent result of the "Emcor" test in distilled water given by the merit value 1 which corresponds to a condition in which there are no more than three corrosion points and none of which has a diameter greater than 1 mm. The merit classes of the test are decreasing and range from 0 (no corrosion) to 5 (severe corrosion).

This is a particularly significant test developed by SKF to verify the ability of a grease to protect the bearing from rust formation: the more the grease has this property, the more the operating hours of a bearing will be.

- Good cold properties despite the presence of the polyisobutene polymer (at low temperatures its viscosity tends to increase and hinder the sliding of the grease) which attest to how the grease can be used at low temperatures up to -10 °C: this property is measured by the "torque test". A bearing, filled with grease, is cooled up to a given temperature at which the torque necessary for the rotation of the bearing is measured, overcoming the resistance of the grease. The results of the test are expressed by two numbers, one is the maximum value recorded at the beginning of the test, the other a continuous stationary torque once the continuous speed is reached. The higher these values, the lower the grease performance at the test temperature .

The test is passed when the starting torque <1000 mN.m, and/or operating torque <100 mN.m: at -10 °C the values obtained fall within the limits of the ISO 12924 grease specification, at -20 °C the operating torque is higher than the limit.

- The good cold properties of the grease in accordance with the present invention are also highlighted by the minimum operation temperature given by the values obtained with the "flow pressure" test, in which the pressure necessary to let a grease to flow at low temperatures is determined. The results obtained at 0 °C and at -10 °C are both below the limit reported by ISO 12924 indicated as <1400 hPa.

- Excellent resistance to processing attested by the "roll shell stability", in which the lubricant grease sample is placed in a cylinder containing a roller and rotated for 2 hours at 35 °C. The grease in question maintains the same initial consistency even after processing .

The loss in weight of grease from the bearings in operation was also evaluated by means of a "wheel bearing" test, which in any case gives an important indication of the tendency of the grease to exit from the seat. In this case the value obtained is good.

Finally, it is important to note that in general the addition of additives "softens the grease", and therefore if it is wished to obtain a grease of high consistency, for example NLGI 2, it is important to start from a gel (spent bleaching earths + base oil) of higher consistency.

EXAMPLE 8

Preparation of infusible greases with a higher content of type 2 spent earths and with base oils of different viscosity ISO VG

By repeating the procedure of example 6 (with the same type of twin-screw mixer), three infusible greases were prepared using the same type of neutralised spent earths but in higher percentages (75%) than in example 6, formulating them with three base oils with increasing viscosity formed by three different mixtures having different viscosities (ISO VG 320, ISO VG 220 and ISO VG 100), thus composed Gels were obtained with an appearance as shown in Figure 1, which were then subjected to the tests indicated in table 10 to measure their consistency, drop point, water washout and copper corrosion.

Table 10

As can be noted, with the same content of spent bleaching earths it is possible to achieve consistency and consequently higher NLGI classes if base oils or mixtures of base oils with increasing viscosity are used.

Furthermore, it is possible not to employ conventional additives to increase water resistance when employing high quantities of spent bleaching earth, for example greater than 50%, while at the same time achieving an NLGI grade greater than 1.

In particular, the grease in accordance with the invention of formulation 24 shows, in addition to infusibility and high content of spent bleaching earths, the following characteristics:

- high consistency

- high water washout resistance in the absence of additives; - excellent compatibility with copper (IB: the greater the number and the worse the merit, i.e. the corrosion resistance) despite not containing the specific corrosion inhibitor.