AU2015202299A1 - A method for the manufacture of lump-free lithium complex lubricating grease - Google Patents

Abstract

Abstract Provided herein is a method for the manufacture of a lithium complex lubricating grease that is substantially lump-free. Applying the inventive method it is possible to quantify the degree of turbulence or shear needed to achieve the grease quality required. The inventive method provides for efficiencies that are reproducible, quantifiable and cannot readily be achieved by applying repeated and random shear to conventional saponification products. (Figure 3) -3/4 3c FGb

Description

- 1 A METHOD FOR THE MANUFACTURE OF LUMP-FREE LITHIUM COMPLEX LUBRICATING GREASE Related Application 5 This application claims the benefit of Australian provisional patent application AU 2014902013, filed on 28 May 2014. The content of this provisional application is incorporated herein by reference in its entirety. Field of the Invention 10 The present invention relates to a method for the manufacture of a lithium complex lubricating grease that is substantially lump-free. The invention will be discussed hereinafter with reference to its potential use within the manufacture of lithium complex lubricating greases - and the advantages that may be gleaned from using such greases in industry. However, it will be 15 appreciated that the invention is not necessarily limited to these specific fields of use. Background of the Invention The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully 20 understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field. Most lubricating greases are mixtures of an oil and a soap. The soaps are 25 dispersed into and viscosify oils to form the stable gels that are commonly known as "greases". Greases are thereby semisolid lubricants. Grease generally consists of a soap crystallised within mineral, synthetic or vegetable oil. The characteristic feature of greases is that they possess a high initial viscosity which, upon the application of shear, drops to approximately the same viscosity as the base oil used in the grease (i.e., 30 thixotropy). Greases are thereby a type of shear-thinning or pseudo-plastic fluid. Greases are applied to mechanisms that can only be lubricated infrequently and where a lubricating oil would not stay in position. They also act as sealants to prevent -2 ingress of water and incompatible materials. The most widely used greases are those made with lithium soap. Lithium soap greases may be broadly classified into two distinct categories: non-complex and complex. Non-complex lithium grease has a drip or dropping temperature of 170 to 5 220 'C. Lithium complex grease has a drip or dropping temperature of greater than 230 'C, and usually greater than 250 'C. Lithium grease adheres particularly well to metal, is non-corrosive, may be used under heavy loads, resists moisture and exhibits good temperature tolerance. The combination of these properties lends to lithium grease being commonly used as 10 lubricant in household products such as electric garage doors, in moderate temperature industrial applications such as conveyor bearings, as well as in automotive applications such as CV joints. Lithium complex grease has similar use properties to non-complex lithium grease but can be used at higher temperatures. It is widely used in higher temperature industrial and automotive applications such as wheel bearings 15 on cars with disc brakes. The present invention relates specifically to lithium complex grease. Table 1: Comparative properties of lithium grease and lithium complex grease Property Li Grease Li Complex Grease Dropping point -195 0 C ~260 0 C Mechanical stability Good Very good Water resistance Good Very good Oil separation resistance Good Very good 20 In the manufacture of non-complex lithium lubricating greases, a soap is formed by the chemical reaction between lithium hydroxide and a fatty acid. The most commonly-used source of lithium is lithium hydroxide monohydrate, a solid in particulate form. The fatty acid is usually 12-hydroxy stearic acid or is sourced from 25 hydrogenated castor oil. The saponification reaction is usually carried out in an inert mineral oil carrier, with mechanical agitation to suspend the lithium hydroxide particles. It is conducted above the melting point of the acid, typically at 100 to 130 0 C, to ensure good contact -3 between the reactants, and it proceeds at the solid surface of each lithium hydroxide particle. The resulting soap has a melting point in the region of 165 to 180 0 C, meaning it is a solid at the reaction temperature. Depending on the shear environment at the particle surfaces caused by the 5 mechanical agitation, the soap product can build up on the particulate matter as the reaction proceeds and shield the remaining lithium hydroxide from the acid. The reaction can slow or even cease before the lithium hydroxide is consumed and many small particles can remain. These particles consist of a core of unreacted lithium hydroxide surrounded by a soft layer of soap. 10 Following the saponification step, the grease is taken up to a temperature of the order of 200 to 210 0 C, to dehydrate it. This temperature is above the melting point of the soap which runs off the residual lithium hydroxide solid particles, exposing them to the remaining acid. The reaction goes to completion and no particles remain. The finished grease is smooth and pumpable through fine filters. 15 In the manufacture of lithium complex grease 12-hydroxy stearic acid is again typically used but a second acid - a dicarboxylic acid, typically azelaic acid or sebacic acid - is included in the saponification reaction. In this case the resulting soap has a melting point of greater than 230 0 C. Hence it does not melt when the grease is dehydrated at 200 to 210 0 C. The residual particles, with their coatings of soft soap, 20 can remain. The grease is not smooth and can block fine filters when pumped. Such residual particles can be avoided in the manufacture of lithium complex grease if the shear environment is sufficiently intense. In this circumstance the reaction product is sheared off each particle and the reaction can proceed until the particles are consumed completely. 25 The majority of non-complex lithium soap-based grease is manufactured batch-wise in heated open kettles with counter-rotating stirrers and wall scrapers (see, Figure 1). Some manufacturers use pressurised vessels with mixing by a central impeller in a confining shroud (see, Figure 2). There are also some proprietary designs of manufacturing equipment, including continuous, non-batch processes. 30 In general, the shear conditions in the standard kettles with counter-rotating stirrers are not sufficiently intense to avoid the build-up of soap reaction product on lithium hydroxide particles of standard commercial size (c. 0.1 to 1 mm). It is -4 generally not possible to make lithium complex greases in these standard vessels without producing some residual small lumps in the final grease; these lumps are sometimes called "fleas". In contrast, shear conditions in the pressurised impeller-stirred vessels are 5 generally sufficient and residual particles are not a present at the end of the saponification step. Some manufacturers using standard kettles to manufacture lithium complex grease overcome the lump problem by either using very fine lithium hydroxide powder (c. < 0.1 mm diameter) or by first dissolving the powder in water. Both techniques 10 add significant raw material cost while the use of a solution also extends the batch manufacturing time as the excess water has to be boiled off. It will be broadly appreciated that the efficacy and desirability of any lubricant containing lumps/fleas of particulate matter is diminished by comparison with a corresponding smooth/lump-free lubricant. A grease with lumps tends to prematurely 15 block the filters in the centralized grease lubrication systems widely used in industry. Moreover, when the lubricant is applied in the context of working parts - for instance, wheel bearings - because this particulate matter has a refactory lithium hydroxide core it can grind or wear down the bearings, leading to shorter lifespan, and an increased risk of breakage/failure. 20 It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. Although the invention will be described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. 25 Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a section through a typical greasemaking vessel. It has counter 30 rotating stirrers (la), (lb), etc., and the primary function of the outside stirrer (1c) is to scrape the wall (1d) once a grease is formed, to assist with heat transfer from the outer jacket (le). The majority of non-complex lithium soap-based grease is manufactured -5 batch-wise in heated open kettles of this design. Figure 2 is a section through an alternative greasemaking vessel; this example depicts a pressurised vessel (2a) with mixing by a central impeller (2b) in a confining shroud (2c). This type of vessel is used for the saponification step and a finishing 5 vessel similar to the one shown in Figure 1 is also required. Both complex and non complex lithium grease can be made satisfactorily in such equipment. Figure 3 and Figure 4 relate to the implementation of preferred embodiments of the present invention and are described below. Figure 3 shows the greasemaking vessel of Figure 1, with the mixer driver (3c) operatively positioned within the vessel; 10 Figure 4 is a schematic showing another embodiment of the invention - in this case, the mixer (5) is positioned outside of the vessel (4). Definitions In describing and claiming the present invention, the following terminology 15 will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention 20 pertains. Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". 25 Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about". The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, "%" will mean "weight %", "ratio" will mean "weight ratio" and "parts" 30 will mean "weight parts". The water of crystallisation in the lithium hydroxide monohydrate does not participate chemically in the saponification reaction and is evaporated off.

-6 Accordingly, the names "lithium hydroxide" and "lithium hydroxide monohydrate" are used interchangeably throughout the ensuing description of the invention. The terms "predominantly" and "substantially" as used herein shall mean comprising more than 50% by weight, unless otherwise indicated. 5 The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., "1 to 5" includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). The terms "preferred" and "preferably" refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. 10 Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention. Summary of the Invention 15 The invention relates generally to a method for making lithium complex grease without residual lumps when using a standard kettle such as depicted in Figure 1. An area or zone of high shear and turbulence is created and used during the saponification stage, with a shear intensity sufficient to remove reaction product from unreacted particles of lithium hydroxide. The intensity is defined and quantified in terms of the 20 so-called "Kolmogorov scale" [see, Turbulence and Random Processes in Fluid Mechanics, Landahl MT, Cambridge University Press, 1992]. According to a first aspect of the present invention there is provided a method for the manufacture of substantially lump-free lithium complex lubricating grease, said method comprising a saponification step between lithium hydroxide and an acid or 25 acids within which a zone of predetermined shear intensity and turbulence is created such that the resultant lithium soap reaction product is removed from the surface of unreacted particles of lithium hydroxide, said unreacted lithium hydroxide thereby liberated for further saponification, said saponification thereby able to go to substantial completeness such that substantially all lithium hydroxide is saponified. 30 In an embodiment, the method is adapted to proceed within a standard greasemaking kettle. In another embodiment, the method is adapted to provide the turbulent zone -7 external to a standard greasemaking kettle. In all embodiments, the scale of the turbulence, f, when measured on the Kolmogorov scale of turbulent eddies, is less than the average particle size of the lithium hydroxide monohydrate by an order of at least 10 and preferably at least 20. 5 The zone of turbulence can be created by any appropriate mechanical device such as a rotor/stator mixer or a shear disc In a preferred embodiment, one or more periods of turbulence are initiated, thereby to successively actively remove lithium soap reaction product from the surface of unreacted particles of lithium hydroxide, thereby to facilitate the consumption of 10 substantially all lithium hydroxide particles. In an embodiment, the inventive method may employ a plurality of turbulent zones. Preferably, the plurality of zones provides for a reduction in the saponification reaction period. When introducing the zone of turbulence within-the-vessel the method further 15 comprises the step of lowering a rotor/stator mixing head into the vessel, operating the mixer for a predetermined time and then raising the mixing head out of the vessel. The depth to which the mixing head is lowered can be any workable depth at which the zone of turbulence can be generated. By way of non-limiting example, the zone of turbulence can be generated from a mixer head located at a level about 20% of the 20 liquid depth from the bottom of the vessel. When introducing the zone of turbulence outside-the-vessel, the inventive method comprises the action of an in-line rotor/stator mixer or similar device operatively associated with exit and entry ports within the vessel. In an embodiment, the exit port is substantially near the bottom of the vessel 25 and the entry port is substantially near the top, the in-line mixer being operatively connected therebetween. Preferably, the inventive method further comprises the step of providing means for pumping the saponification mixture, including substantially soap-covered lithium hydroxide particles, from the outlet port through the rotor/stator mixer, back to the 30 entry port. Preferably, the in-line rotor/stator operates at the saponification temperature, typically between about 100 and 130 0

C.

- 8 In all embodiments preferably the power input to the mixing zone will be sufficient to generate turbulence in the saponification mixture with a Kolmogorov length scale (f) less than one tenth the average particle size of the lithium hydroxide raw material (p), or smaller. 5 Preferably the relation between the power input (P) to the mixer, the volume (VM) of the mixer or mixing zone and the viscosity (v) and density (p) of the saponification mixture at the operating temperature will be such that (v3 VM p / P )O.25 is less than p/10 or smaller. Preferably, particles will spend a time in the high intensity mixing zone that is 10 not less than the Kolmogorov time scale (t,) for the turbulent eddies. Preferably, the relationship between the volumetric rate (Q) at which the saponification mixture passes through the turbulent zone and the volume of the zone will be such that VM / Q is greater than (v VM pIP )0-5. Preferably all or most particles will pass at least once through the high 15 intensity mixing zone. Preferably the relation between the rate at which the saponification mixture passes through the turbulent zone, the volumetric size of the saponification batch (VR) and the saponification time tR will be such that Q = 3 VR/ tR or greater. In an embodiment where the lithium hydroxide monohydrate has a particle size 20 range of 0.1 to 1.0 mm, the in-line mixer has a free volume within it of about 525 cm 3 ; the rotor a power of about 5 kW; and the fluid a viscosity of about 5 cSt; the calculated Kolmogorov length scale is about 0.011 mm, which is about one-fiftieth the size of the average lithium hydroxide monohydrate particle. In an embodiment, the in-line mixer has a free volume within it of about 525 25 cm 3 ; a rotor power of about 5 kW; a fluid viscosity of about 5 cSt; a fluid density of about 0.93 kg/Land a flow rate through it of 10 L/s. The calculated residence time in the mixer is 0.05 s which is greater than the calculated Kolmogorov time scale of 0.02 s. In an embodiment the saponification batch has a volume, of about 3500 L; the 30 saponification reaction time is about 20 minutes and the pumping rate through the turbulent zone is about 10 L/s. The calculated minimum pumping rate to ensure all or most particles pass through the turbulent zone is 9 L/s.

-9 According to a second aspect of the present invention there is provided substantially lump-free lithium complex lubricating grease, when manufactured by a method as defined according to the first aspect of the present invention. According to a third aspect of the present invention there is provided in a 5 method of manufacturing a lithium complex lubricating grease, an improvement residing in providing a zone of predetermined shear intensity and turbulence such that the lithium soap reaction product is removed from the surface of unreacted particles of lithium hydroxide, said unreacted lithium hydroxide thereby liberated for further saponification, said saponification thereby able to go to substantial completeness such 10 that substantially all lithium hydroxide is saponified, thereby to provide for substantially lump-free lithium complex lubricating grease. According to a fourth aspect of the present invention there is provided an apparatus for performing a method as defined according to the first aspect of the present invention, said apparatus comprising a standard saponification kettle/vessel 15 operatively associated with means for introducing a zone of predetermined shear intensity and turbulence such that lithium soap reaction product is able to be removed from the surface of unreacted particles of lithium hydroxide within said turbulent zone, said unreacted lithium hydroxide thereby liberated for further saponification, said saponification thereby able to go to substantial completeness such that 20 substantially all lithium hydroxide is saponified. In an embodiment, the means are operatively associated with the vessel either from within-the-vessel or outside-the-vessel (in-line). Preferably, the means is one or more rotor/stator mixers or similar device. In an embodiment, the rotor/stator mixer has a free volume within the mixer of 25 about 525 cm ; a rotor power of about 5 kW; a fluid viscosity of about 5 cSt; and a Kolmogorov length scale of about 0.011 mm. Turbulent flow contains eddies of different sizes, velocities and durations. Larger eddies are unstable and break up, transferring their energy to somewhat smaller eddies. These, in turn, break up and transfer their energy to even smaller eddies. This 30 energy cascade, in which energy is transferred to successively smaller eddies, continues until the "Reynolds number" is sufficiently small that the eddy motion is stable, and molecular viscosity is effective in dissipating the kinetic energy. The scale - 10 of these dissipative eddies is called the Kolmogorov scale and below this scale the fluid motion is non-turbulent. Kolmogorov derived the following relationship in respect of length scale, f: 5 f = (v 3 / c) 0.25 . where c is the rate of energy dissipation in the fluid; and v is the kinematic viscosity of the fluid. Kolmogorov further derived the related eddy velocity scale, u,: 10 u = (c v) 0.25 .... (2) The related Kolmogorov time scale t, is defined as: tq = Tl / uq 15 and from Equations (1) and (2): tq = (v / C ) 0.5 ....(3) 20 The typical particle size for commercial lithium hydroxide monohydrate is about 0.1 to 1 mm. Based on saponification studies of lithium complex grease in a 15 kg batch pilot plant and in a 2500 kg commercial-scale pressurised greasemaking vessel similar to Figure 2, it was found that, in order for there to be no residual particles, mixing or turbulence intensity should be of a level that results in the 25 Kolmogorov scale of the turbulent eddies, f, being of the order of 0.01 to 0.02 mm. This is a factor of 20 to 50 times smaller than the average lithium hydroxide monohydrate particle size. For comparison, in a typical lithium grease manufacturing vessel and batch, during the saponification step, f is of the order of 0.05 mm. The scale is too coarse by 30 a factor of about two to five to avoid residual lumps. In a commercial pressurised vessel with shrouded impeller, the scale is about 0.02 mm, which confirms that such equipment can potentially make lump-free lithium complex grease.

- 11 Two alternative methods have been tested for introducing a region with the appropriate Kolmogorov turbulence scale into the standard grease making process. One is located within the vessel and the other is outside. 5 a) Within-the-vessel method for manufacturing lump-free lithium complex grease A cross-section through a typical grease making vessel is shown in Figure 1. The prime function of the stirrer is to scrape the vessel wall once grease is formed, to assist with heat transfer from the outer jacket. The saponification reaction can proceed satisfactorily with just the inner stirrer in operation as viscosity is relatively low at this 10 stage of the process. A commercial, 6-tonne greasemaking vessel was used. With both stirrers turned off, an appropriately-sized and powered rotor/stator mixing head (3a) was lowered into the vessel to a level about 20% of the liquid depth from the bottom. The level was deliberately chosen so that the mixing head (3a) lay between two blades (3b) 15 of the inner stirrer (see, Figure 3). The size of the mixer was chosen so that its drive shaft (3c) was positioned outside the turning circle of the inner stirrer blades. The saponification reaction for lithium complex grease was run using standard commercial lithium hydroxide monohydrate powder, with both the rotor/stator mixer and the inner stirrer in operation but with the outer stirrer turned off. Once 20 saponification was complete the rotor/stator mixer was removed and the manufacturing process continued with both inner and outer stirrers in operation in the normal way. The trial was repeated with two rotor/stator mixers in place during saponification, located diametrically across the vessel and at different heights. 25 Both trials resulted in smooth, lump-free lithium complex grease. The reaction time was 10 to 15% shorter with the two mixing-head set up. b) Outside-the-vessel method for manufacturing lump-free lithium complex grease This trial employed the same 6-tonne commercial greasemaking vessel. The 30 vessel had an outlet at the bottom, feeding to a pump with a return line to the top of the vessel. An in-line rotor/stator mixer was installed in the return line. The saponification step was conducted in the kettle in the usual manner, with - 12 standard raw materials and with both the inner and outer stirrers operating. However, the pump/return line, complete with in-line mixer, was also in operation. Once saponification was completed, the pump and in-line mixer were turned off and the manufacturing process continued in the normal way. Lump-free lithium complex 5 grease was produced. Parameters for the in-line mixer at an operating temperature of 110 to 125 0 C were: Free volume within mixer 525 cm 3 Power to rotor 5 kW 10 Fluid viscosity 5 cSt From Equation 1, noting that e = P / VM, the calculated Kolmogorov length scale in the in-line mixer was 0.011 mm. 15 Flow rate through intense mixing zone A schematic of the proposed manufacturing method with external turbulent zone is shown in Figure 4. Relevant symbols are also shown. It is desirable that all particles pass through the mixing zone at least once. Referring to Figure 4, the probability that a given particle in the kettle will be pumped 20 through the external in-line mixer during the period of saponification tR is required to be at least 95%. If the kettle is assumed to be well mixed then it can be shown [see, Elements of Chemical Reactor Design and Operation, Kramers H. and Westerterp KR, Chapman and Hall Ltd. London, 1963] that in a period equal to three times the average residence time in the kettle, the probability that a given particle will leave through the 25 discharge to the pump is 95%. Referring to Figure 4, the mean residence time of the flow through the manufacturing kettle is VR / Q. Thus, to ensure a 95% chance, it is required that Q = 3 VR /tR or greater .... (4) 30 For the manufacturing trial with the external mixing zone, VR was 3500 L and tR was 20 min. From Equation (4), Q should be greater than 9 L/s; the actual pumping - 13 rate was 10 L/s. It is also desirable that all particles spend adequate time in the intense mixing zone. The time scale (t) of the Kolmogorov eddies can be calculated from the Kolmogorov length and velocity scales (see, Equations (1), (2) and (3), above). A 5 particle should spend this order of time in the mixing zone. Noting that the particle residence time in the zone is VM / Q then, to achieve this: VM =Q t or greater .... (5) 10 For the manufacturing trial with external mixing zone, Equation (5) indicates that the mixer size should be 0.2 L or larger for a pumping rate of 10 L/s; the actual size used was 0.525 L. As mixer size is increased the power input must also rise to maintain the desired eddy size and so there is an optimum. 15 Description of a Preferred Embodiment of the Invention With reference to Figure 4 of the accompanying drawings, the present invention will be described with reference to embodiment "b", as related above (i.e., the reaction vessel and the mixer are in an outside-the-vessel/in-line relationship). It 20 will be appreciated that actively pumping suspended soap-covered lithium hydroxide out of the bottom of the vessel; subjecting it to the required turbulence/shear in-line; and then pumping the separated and suspended lithium hydroxide and soap back into the top of the vessel provides for a continuous operation. Of course, however, the below-described method can also be effected on a batch-wise basis, if preferred. 25 The inventive method comprises associating a "standard" greasemaking kettle/vessel (4) with an in-line mixer (5) via a pump (6) and appropriate conduits (e.g., 10) therebetween so as to achieve a flow rate Q through the mixer volume VM. As described herein, the vessel (4) is a commercial, 6-tonne unit, having a heating jacket (not shown) and a reactor volume VR. The vessel (4) is equipped with an exit 30 port (7) near the bottom of the vessel and an entry port (8) near the top. The exit port (7) is associated with the in-line mixer (5) via an exit conduit (9); and the in-line mixer (5) is associated with the entry port (8) via an entry conduit (10).

- 14 To manufacture substantially lump-free lithium complex lubricating grease, the vessel (4) is loaded with approximately stoichiometric quantities of the reactants lithium hydroxide and a fatty acid such as 12-hydroxy stearic acid and a dicarboxylic acid such as azelaic acid. The operating temperature of the vessel (4) is about 100 to 5 about 130 0 C; and the reaction mixture may be agitated via the action of one or more impellers (11; not shown). Preferably, the impellers (11) are of a size such that upon rotation, they serve to actively remove reagents from the inner walls of the vessel (4). Under the reaction conditions employed, the acids react with the base, producing a fatty acid salt which is known as a soap. However, the lithium hydroxide 10 reactant is present as a solid; it typically has a particle size of c. 0.1 to 1 mm. It will be appreciated that as the saponification reaction proceeds at the particle surfaces, any unreacted lithium hydroxide particles are prone to become coated by these salts, which essentially shields the unreacted lithium hydroxide from any residual acid with which it would otherwise react. Despite unreacted acid and unreacted base remaining within 15 the reaction vessel (4), the saponification reaction is prone to essentially cease such that the acids and base can no longer be brought into intimate chemical contact with each other. Accordingly, the present invention relates to a method by which the coated, unreacted lithium hydroxide can be liberated from the fatty acid salt - and returned to 20 the reaction vessel for subsequent reaction with the acids. Either continually, or at predetermined intervals throughout the saponification reaction, the vessel contents are pumped, in a continuous operation, out of the exit port (7) by the pump (6), through the in-line mixer (5) via the exit conduit (9) and back to the vessel via conduit (10). Of course, the in-line mixer (5) is properly an in-line 25 mixer unit comprising one or more impellers operating in a relatively small free space within which the mixing/shear takes place. The in-line mixer (5) subjects those reactants to a high turbulence/high shear environment whereby the shear is of sufficient intensity to remove the fatty acid salt from the unreacted particles of lithium hydroxide; this effectively regenerates unreacted lithium hydroxide for continuous 30 reintroduction to the reaction vessel (4). Empirically, it is found that based on the Kolmogorov scale of turbulent eddies f, the shear should be such that it will produce turbulent eddies with a size or scale of the order of 0.01 to 0.02 mm for typical - 15 commercial lithium hydroxide particles of 0.1 to 1.0 mm. Once the uncoated/liberated lithium hydroxide has been returned to the vessel (4), it is then free to react with the fatty acids (when it may be coated again with the salt). The shear step, as described above, can be repeated indefinitely - although using 5 the conditions described above, it is found that a circulation period of three times the average residence saponification time tR of the circulating flow in the reaction vessel, in accordance with Equation (4), is generally sufficient to ensure that the saponification reaction proceeds to substantial completion with respect to the lithium hydroxide. 10 It will be appreciated that the consumption of substantially all the lithium hydroxide particles by the reactant acids provides for a lithium complex lubricating grease that is substantially lump-free ("flea-free"). Example 15 An exemplary inventive method for the production of substantially lump-free lithium complex lubricating grease when manufactured in a conventional grease making vessel is provided. In this example a single step, co-saponification of two acids is used. The invention can also be applied to a two or multi-step saponification process. 20 A conventional greasemaking kettle is used with a heating/cooling jacket and counter-rotating stirrers. The kettle has an outlet at the bottom with a shut-off valve. The outlet is connected via a pipe to a gear pump and by further pipe to an in-line rotor/stator mixer. A pipe runs from the outlet of the mixer back into the greasemaking kettle. 25 The batch raw materials used are listed in Table 2, below (quantities have been rounded to the nearest 5 kg). In this example, the bottom outlet valve of the kettle (see, e.g., Figure 4, feature (7)) is shut and all the materials are added. The counter rotating stirrers are turned on to suspend and mix the solid materials and the temperature is increased to 100 0 C. At this temperature, both of the acids melt and the 30 saponification reactions begin. Once saponification has commenced, the bottom valve is opened and the pump and in-line mixer are started. The reaction is allowed to run for 20 to 30 minutes, - 16 during which time the temperature is controlled to the range 110 to 130 0 C. Table 2: Batch raw materials used in inventive example Raw material Quantity (kg) Mineral oil 1555 12-hydroxy stearic acid 300 Azelaic acid 50 Lithium hydroxide monohydrate 70 Water 25 Total 2000 5 At the end of the saponification step, the pump and in-line mixer are stopped and the bottom valve is closed. The kettle contents are then heated to above 200 0 C to dehydrate the soap and the batch is finished in the normal way with the addition of more oil, homogenising or milling, and the addition of any performance additives. 10 Industrial Applicability The industrial applicability of the present invention is clear. Lithium complex lubricating greases are widely desired throughout many industries due to their lubricating qualities across a wide range of temperatures. However, the presence of 15 unreacted lithium hydroxide in lithium complex lubricating greases as lumps or "fleas" is undesirable both in consumer appeal - but also has a negative effect in respect of product efficacy. The presently-described invention provides a means for the efficient synthesis of substantially lump-free lithium complex lubricating greases when using a conventional greasemaking kettle. 20 Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (25)

1. A method for the manufacture of substantially lump-free lithium complex lubricating grease, said method comprising, in a reaction vessel, a 5 saponification step between lithium hydroxide monohydrate particles and appropriate fatty and dicarboxylic acids within which a zone of predetermined shear intensity and turbulence is created such that the resultant lithium soap reaction product is removed from the surface of unreacted particles of lithium hydroxide, said unreacted lithium hydroxide 10 thereby liberated for further saponification, said saponification thereby able to proceed to substantial completeness such that substantially all lithium hydroxide is consumed.

2. A method according to claim 1, wherein said vessel is a standard 15 greasemaking kettle.

3. A method according to claim 1 or claim 2, wherein the Kolmogorov length scale, f, of said turbulence is of the order of one-twentieth or less of the average lithium hydroxide particle size. 20

4. A method according to any one of the preceding claims, wherein said zone of turbulence can be introduced within-the-vessel or outside-the-vessel.

5. A method according to claim 4, wherein introducing said zone of 25 turbulence within-the-vessel comprises the step of lowering a rotor/stator mixing head or similar device into said vessel to a predetermined level within the vessel contents; and operating said mixing head, thereby to create said zone of turbulence. 30

6. A method according to claim 5, wherein one or more periods of turbulence are initiated, thereby to successively actively remove lithium soap reaction - 18 product from the surface of unreacted particles of lithium hydroxide, thereby to progressively facilitate the consumption of substantially all lithium hydroxide particles. 5

7. A method according to claim 5 or claim 6, employing a plurality of said rotor/stator mixing heads.

8. A method according to claim 7, wherein said plurality of rotor/stator mixing heads provides for a reduction in the saponification reaction 10 period.

9. A method according to claim 4, wherein introducing said zone of turbulence outside-the-vessel comprises the action of an in-line rotor/stator mixer or similar device operatively associated with exit and 15 entry ports within said vessel.

10. A method according to claim 9, wherein said exit port is substantially near the bottom of said vessel and said entry port is substantially near the top, said mixer being operatively connected therebetween. 20

11. A method according to claim 9 or claim 10, further comprising providing means for pumping in a continuous manner the vessel contents, including suspended substantially soap-covered lithium hydroxide particles, from said outlet port to said mixer; and following mixing at a predetermined 25 shear for a predetermined period, means for returning the resultant substantially liberated lithium hydroxide particles and soap, to said entry port of said vessel.

12. A method according to any one of claims 9 to 11, wherein said in-line 30 rotor/stator operates at between about 100 and about 130 0 C. - 19

13. A method according to any one of claims 9 to 12, wherein said in-line rotor/stator mixer has a free volume within the mixer of about 525 cm 3 ; a rotor power of about 5 kW; a fluid viscosity of about 5 cSt; and a Kolmogorov length scale of about 0.011 mm. 5

14. A method according to any one of claims 9 to 13, wherein if the saponification time is tR, the size of the grease batch at saponification is VR and the rate of pumping through the mixing zone is Q; then Q = 3 VR / tR or greater. 10

15. A method according to claim 14, wherein VR is about 3500 L; tR is about 20 minutes; and Q is at least about 9 L/s.

16. A method according to any one of claims 9 to 15, wherein a reacting 15 lithium hydroxide particle must spend adequate time in the zone of turbulence so as to remove lithium soap from its surface, said adequate time being at least the Kolmogorov time scale tq.

17. A method according to claim 16, wherein VM = Q tq or greater, wherein 20 VM is the mixer volume; and Q is the rate of pumping through the mixing zone.

18. A method according to claim 16, wherein VM is about 0.2 L or larger. 25

19. A method according to any one of the preceding claims, wherein the fatty acid is 12-hydroxy stearic acid and dicarboxylic acid is azelaic acid.

20. Substantially lump-free lithium complex lubricating grease, when manufactured by a method as defined according to any one of the 30 preceding claims. - 20

21. In a method of manufacturing a lithium complex lubricating grease by the saponification of lithium hydroxide monohydrate particles and appropriate fatty and dicarboxylic acids, an improvement consisting in providing one or more zones of predetermined shear intensity and turbulence such that 5 lithium soap reaction product is removed from the surface of unreacted particles of lithium hydroxide, said unreacted lithium hydroxide thereby liberated for further saponification, said saponification thereby able to go to substantial completion, thereby to provide for substantially lump-free lithium complex lubricating grease. 10

22. An apparatus for performing a method as defined according to any one of claims 1 to 19, said apparatus comprising a standard saponification kettle/vessel operatively associated with means for introducing one or more zones of predetermined shear intensity and turbulence such that 15 lithium soap reaction product is able to be removed from the surface of unreacted particles of lithium hydroxide within said turbulent zone/s, said unreacted lithium hydroxide thereby liberated for further saponification, said saponification thereby able to go to substantial completion such that substantially all lithium hydroxide is saponified. 20

23. An apparatus according to claim 22, wherein said means are operatively associated with said vessel either from within-the-vessel or outside-the vessel. 25

24. An apparatus according to claim 22 or claim 23, wherein said means is one or more rotor/stator mixers.

25. An apparatus according to any one of claims 22 to 24, wherein rotor/stator mixer has a free volume within the mixer of about 525 cm ; a rotor power 30 of about 5 kW; a fluid viscosity of about 5 cSt; and a Kolmogorov length scale of about 0.011 mm.