JPS6132359B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the production of lithium soap lubricating greases with high dropping points. Lithium soap greases are well known and have been used extensively for many years. The main advantages of lithium soap grease have been its high water resistance and its ease of dispersion in all types of lubricating oil bases. Although the lithium soaps used as thickeners for these greases can be made by reacting lithium hydroxide or other lithium bases with conventional high molecular weight fatty acids, lithium soaps of lithium hydroxystearate and related hydroxy fatty acids are preferred. were particularly useful because of their great mechanical stability. There are many applications for grease compositions where high dropping points are required, for example in the lubrication of bearings in electric train motors. The electric train motor is
Used to power modern diesel locomotives. The engine of a diesel locomotive generates direct current, which is then used to drive a train electric motor that is coupled directly to the drive shaft and wheel assembly of each chassis of the locomotive. single electric train motor
It could provide 200 horsepower, and this would constitute 1/10 or more of the locomotive's total electric power. The bearings on these locomotives can be used without any maintenance.
It is required to operate for a period of about a year, and such bearings reach temperatures as high as 250°C. Thus, in accordance with the present invention, a lithium soap grease having a dropping point in excess of 600% is prepared using a specific sequence of steps involving the separate formation of individual soaps.
Prepared from _C12 - _C24 hydroxy fatty acids and _C2 - _C12 dicarboxylic acids. Although the preparation of lithium soap greases from mixtures of monocarboxylic and dicarboxylic acids is known in the art, the present invention is disclosed in, for example, U.S. Pat.
Rather than by the use of esters of acids as taught in US Pat. Additionally, U.S. Patent No.
No. 2,940,930 teaches that high dropping point greases can be prepared from mixtures of monocarboxylic and dicarboxylic acids. However, in preparing the grease described in this patent, it was also necessary to include glycols. The presence of glycol is undesirable because it makes the grease susceptible to oxidation and makes the water resistance of the grease undesirably low for some applications. The present invention allows the production of greases from mixtures of hydroxy fatty acids and aliphatic dicarboxylic acids without the need to incorporate glycols. Of course, the total soap content of the greases of the present invention is sufficient to thicken the composition to a grease consistency, and this is typically about 2
to about 30% by weight, preferably about 5 to 20% by weight. The ratio of dicarboxylic acid to hydroxy fatty acid is within the range of about 0.2 to about 1.0 moles of dicarboxylic acid and preferably about 0.2 to 0.8 moles of dicarboxylic acid per mole of hydroxy fatty acid. The hydroxy fatty acids used in preparing the greases of this invention are about 12 to 24 or more usually about
It has 16 to 20 carbon atoms and is preferably a hydroxystearic acid such as 9-hydroxy, 10-hydroxy or 12-hydroxystearic acid, more preferably the latter. Also, 12−
An unsaturated form of hydroxystearic acid, 9-
Ricinoleic acid having a double bond at the 10 position can also be used. Other hydroxy fatty acids include 12-hydroxybehenic acid and 10-hydroxypalmitic acid. The dicarboxylic acids used in the greases of the invention have 2 to 12 carbon atoms, preferably 4 to 12 carbon atoms, and most preferably 6 to 10 carbon atoms. Such acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, pemeric acid, azelaic acid, dodecanedioic acid and sebacic acid. Particularly preferred are sebacic acid and azelaic acid. The lubricating oil base used in preparing the grease compositions of the present invention can be any of the commonly used mineral oils, synthetic hydrocarbon oils, or synthetic ester oils. Generally, these lubricating oils have a viscosity within the range of about 35 to 200 SUS at 210°.
The mineral lubricating oil base used in preparing the grease may be any commonly refined base oil derived from paraffinic, naphthenic and mixed base crude oils. Synthetic lubricating oils that can be used include esters of dibasic acids such as di-2-ethylhexyl sebacate, esters of glycols such as the C ₁₃ oxo acid diester of tetraethylene glycol, or 1 mole of sebacic acid and 2 moles of sebacic acid. and 2 moles of 2-ethylhexanoic acid. Other synthetic oils that can be used include alkylate residues from the alkylation of benzene with alkylbenzenes such as tetrapropylene or copolymers of ethylene and propylene;
Silicone oils such as ethyl phenyl polysiloxane, methyl polysiloxane etc., polyglycol oils such as those obtained by condensing butyl alcohol with propylene oxide, carbonate esters such as those obtained by reacting C ₈ oxo alcohol with ethyl carbonate to form half esters. Synthetic hydrocarbons such as the products obtained by forming and then reacting it with tetraethylene glycol and the like. Other suitable synthetic oils include:
Polyphenyl ethers include, for example, those having about 3 to 7 ether linkages and about 4 to 8 phenyl groups (column 3 of U.S. Pat. No. 3,424,678).
). In order to obtain a grease with an extremely high dropping point according to the invention, a mixture of lubricating oil and lithium soap of _C12 - _C24 hydroxy fatty acids is first prepared and then this mixture is added with _C2 - _C12 fatty acid dicarboxylic acids. and is converted to the dilithium soap under conditions that ensure the formation of a complex between the dicarboxylic acid lithium soap and the hydroxy fatty acid lithium soap. When an aliphatic dicarboxylic acid is being neutralized with a lithium base in the presence of a hydroxy fatty acid lithium soap, there are indications that two competing reactions are taking place. In one of these reactions, the dicarboxylic acid or its monolithium soap is incorporated into the crystal lattice of the hydroxy fatty acid lithium soap, thereby modifying its structure. The second competitive reaction is
The conversion of dicarboxylic acids to their dilithium soaps. Experiments have shown that it is only necessary to maintain conditions such that the first reaction occurs more rapidly than the second reaction in order to obtain the desired complex. The primary factors controlling the relative rate of the reaction include the reaction temperature and rate at which the lithium base is added to convert the dicarboxylic acid to its dilithium soap. Thus, in the case of neutralization of a dicarboxylic acid with an aqueous solution of lithium hydroxide, if the reaction is
If carried out at lower than 190〓, e.g. 175〓, the complexation reaction is relatively slow compared to the neutralization reaction, and to prepare a high dropping point grease the lithium hydroxide must be added very slowly, i.e. for a long time. It is necessary to add them in stages over a period of time. About 215〓 or more,
The complexation reaction is rapidly rapid, and especially when the mixture of lubricating oil and hydroxy fatty acid with lithium soap is dehydrated, lithium hydroxide is added at a rate rapid enough to interfere with the complexation reaction. This is virtually impossible. Preferred conditions for forming a complex include:
A reaction temperature of 175-240〓, more preferably 190-240〓, most preferably 210-230〓 is mentioned. Additionally, to promote complex formation, at least one of the following steps may be performed: (1) substantially dehydrating the hydroxy fatty acid lithium soap prior to converting the dicarboxylic acid to the dilithium soap;
(2) converting the dicarboxylic acid to its dilithium soap by stepwise addition of lithium base. Although lithium soaps of hydroxy fatty acids can be preformed and dispersed in the lubricating oil medium, the hydroxy fatty acids can be prepared at their location in the lubricating oil by neutralizing them with a lithium base (which is generally lithium hydroxide). It is generally more convenient to prepare the soap at Typical operations when preparing soaps in situ are approximately 1/1/2 of the total amount of lubricant base material that is ultimately intended to be incorporated into the final grease.
Pour 4 to about 1/2 of the oil into a grease pot and then add the hydroxy fatty acid. The mixture of fatty acids and oil is heated, for example at about 180 to 200 degrees centigrade, sufficient to produce a dissolving effect. A concentrated aqueous solution of lithium hydroxide is then added, usually in a slight excess of that required to neutralize the acid, and the temperature at this stage is usually about 200-210°C.
It is. The rate of addition of lithium hydroxide at this stage is not critical, but depending on the equipment at the grease plant, this may require from 30 minutes to about 2 hours. Although it is possible to carry out the addition of dicarboxylic acid and subsequent neutralization of the dilithium soap at this stage, it is necessary to ensure complexation of the two soaps with each other before causing complete neutralization of the dicarboxylic acid. Therefore, it is necessary to carry out the neutralization very slowly or in stages. Therefore,
When the hydroxy fatty acid lithium soap was manufactured in situ, the temperature of the lubricating oil and hydroxy fatty acid lithium soap mixture was first brought to about 250 to 300 °C before proceeding with the addition of the dicarboxylic acid and its conversion to the dilithium soap. It is preferred to increase the range to produce substantial dehydration of the mixture, ie, removal of 70-100% of the water. It has also been found that substantial dehydration at this stage promotes subsequent complexation reactions during dicarboxylic acid neutralization. After substantial dehydration, the mixture is cooled as quickly as possible, preferably to about 230-240°C, this cooling rate being primarily for time saving purposes. of course,
Cooling to a lower temperature is possible at this stage, but it is usually not necessary. Then,
adding the dicarboxylic acid and stirring the mixture briefly, e.g. 10 minutes, to create proper dispersion throughout the mixture;
A concentrated aqueous solution of lithium hydroxide is then added to convert the dicarboxylic acid to its dilithium soap. Typically, the amount of lithium hydroxide added at this stage is slightly in excess of the amount theoretically required to neutralize both acid groups of the dicarboxylic acid. During the addition of lithium hydroxide (which usually takes about 30 minutes to 2 hours), the temperature is normally maintained within the range of about 210-230°C, preferably about 220-230°C. Due to the cooling effect produced by the evaporation of water from the aqueous solution of lithium hydroxide as well as the water produced in the reaction, the
Maintaining a temperature of 230° is most automatic. After all of the lithium hydroxide has been added to complete neutralization of the dicarboxylic acid, the temperature of the grease mixture is increased to effect dehydration. Typically this is around 280-300
It is carried out at 〓. After dehydration of the grease mixture, it is preferred to further increase the temperature to about 380-400°C and maintain it at that level for about 10 minutes to 1 hour to ensure optimal soap dispersion and improved yield.
This temperature increase to 380-400° is done as quickly as possible to save time and minimize oxidation. The soap material is then cooled as quickly as possible, this cooling being assisted by incorporating the remaining amount of lubricating oil into the mixture. Mixing can continue until the grease reaches ambient temperature. When the temperature is reduced to about 150〓,
Other desired grease additives can be incorporated into the grease. If the grease is then passed through a conventional grease mill, the grease may be somewhat improved in yield and appearance. As a suitable grease mill,
Morehouse-mill, Charlotte and Gaulin homogenizers are mentioned. Although in most cases the lithium hydroxide used in forming either hydroxy fatty acid soaps or dicarboxylic acid soaps is most conveniently introduced into the grease kettle as a saturated aqueous solution, dry lithium hydroxide is used. It is also possible. However, the average grease production plant typically does not have adequate equipment to conveniently handle lithium hydroxide in that form. Typically, a slight excess of lithium hydroxide is used during each soap-forming step over that theoretically required for complete neutralization of the acid; this excess is expressed as sodium hydroxide. within the range of approximately 0.2-0.4% by weight of free alkali (ASTMD-
128). However, this is not a critical aspect of the invention. This is because by the method of the invention it is also possible to make high dropping point greases in which the soap may be very slightly on the acid side. It is to be understood that the formation of the hydroxy fatty acid soap should be performed prior to manufacturing the dicarboxylic acid soap. If this process were reversed, undesirable grease would result. EXAMPLES OF THE INVENTION Greases were prepared according to the invention in the following manner. 333 g of a base oil identified as LCT-20 base oil (which was a solvent refined and hydrofined naphthenic distillate with a viscosity of 315 SUS at 100 mm and a VI of 67) was charged to the grease kettle. is. Next, 70g (0.233
mol) of 12-hydroxystearic acid was dissolved under mild heating and then a concentrated aqueous solution containing 0.24 mol of lithium hydroxide was gradually added, during which time the temperature rose to 230°C. After the addition of lithium hydroxide, the temperature was rapidly raised to 300°C to substantially dehydrate the soap material. Then quickly stir the mixture to approx.
After cooling to 205〓, 24.13g (0.128mol)
of azelaic acid was added. After stirring the mixture for about 10 minutes, an aqueous solution containing 0.28 moles of lithium hydroxide was gradually added to saponify the azelaic acid, during which time the temperature rose to 230 °C. Addition of lithium hydroxide took approximately 45 minutes. When all of the lithium hydroxide was added, the temperature was raised to 300°C and held for 1 hour to complete dehydration.
The temperature was then rapidly raised to 390°C and held there for approximately 20 minutes. Thereafter, the soap mass was rapidly cooled and an additional 184 g of LCT-20 base oil and 316 g of paraffinic oil were added. These added oil portions were at ambient temperature, thus contributing to rapid cooling of the mixture. This paraffinic oil is derived from paraffinic distillate by phenolic extraction and solvent dewaxing to a pour point of 130〓 and a viscosity index of 75 and a
It had a viscosity of 155SVS. Grease is about 150〓
Stirring was continued until cooled to , at which time it was kneaded in a conventional grease mill and allowed to cool to room temperature. The final grease had a dropping point of 625〓 and a penetration of 266 ASTM units at 77〓. The yield of grease was 10.1%. As is well understood in the grease industry, the total weight of acid used, expressed as a percentage of the total weight of the final grease, is referred to as yield. Comparative Example In one case, a grease composition was prepared using a procedure according to the present invention, in which lithium hydroxystearate was formed in a base oil and then the mixture was treated with addition of azelaic acid followed by dicarboxylic acid. 300 before its conversion into dilithium soap
〓 produced virtually complete dehydration. In a comparative preparation, the soap material was not dehydrated at all before adding the azelaic acid and converting it to the dilithium soap. The proportions of each component were the same in the two cases and were as follows.

[Table] The preparation according to the invention was as follows. Pour base oil into the grease pot, and add approximately
12-Hydroxystearic acid was added to it after heating to 180°C. The base oil is the LCT listed above.
-20 base oil. Next, add 28.25 g of lithium hydroxide at about 180 to 200 μl of 12-hydroxystearic acid.
Neutralize with a hot saturated aqueous solution of
The mixture was dehydrated by heating for 1 hour. The mixture was then cooled to about 230°C and azelaic acid was added and stirred for several minutes. A second portion of lithium hydroxide (i.e., 31.5 g) was then added as a hot saturated aqueous solution while maintaining the temperature of the mixture at about 215-230°C. The grease was then dehydrated by heating to 300°, then the temperature was raised to 390° and held for about 30 minutes. At this stage, samples were taken to measure the latent heat of fusion by differential thermal analysis, a procedure well known in the art. 12-Hydroxystearic acid was neutralized with lithium hydroxide at 180-200°C in the same manner as above, but the resulting mixture of lithium hydroxystearate and oil was not subjected to a dehydration step, so a second A grease (comparative grease A) was prepared. Instead, the mixture was heated to about 210 °C, azelaic acid was added and stirred for 10 minutes, and a second portion of lithium hydroxide (31.5 g) was added as a hot saturated aqueous solution. After adding all of the lithium hydroxide,
The temperature of the grease mixture is raised to 300°C to produce virtually complete dehydration, and then the mixture is
Heat to 390° and hold it for 30 minutes as in the above preparation. At this stage, samples were taken to measure the latent heat of fusion by differential thermal analysis. The two greases prepared as described above were subjected to latent heat of fusion measurements and their dropping points were also determined. The results obtained are shown below.

[Table] From the above results, it can be seen that the grease prepared according to the present invention can be prepared without performing an intermediate dehydration step and without attempting to cause neutralization of azelaic acid in a stepwise manner to promote complex formation. It can be seen that it has a higher dropping point and lower latent heat of fusion than Grease A prepared. Another comparative Grease B was prepared using lithium hydroxystearate as the only grease thickener. This grease had the following ingredients:

Table: The procedure used to make this grease was essentially the same as the first step in the comparative preparation above. Briefly, 12-hydroxystearic acid was added to the hot base oil at about 180° and neutralized with a hot saturated aqueous solution of lithium hydroxide at about 180-200°. grease
After dehydration by heating to 300 ml, samples were taken for differential thermal analysis. The latent heat of fusion for Grease B was 7.83 calories/g. According to the above comparative example, in the case of the grease prepared according to the invention, an interaction takes place between 12-hydroxystearic acid and dilithium azelate, and dilithium azelate forms crystals of lithium 12-hydroxystearate. It has been shown that there are signs that the crystal structure has been modified and the latent heat of fusion has been lowered by becoming incorporated into the lattice. In the case of a lithium hydroxystearate-dilithium azelaate grease (Comparative Grease A) not made in accordance with the present invention, i.e. where conditions are not such as to promote complex formation, the latent heat of fusion is 6.79 cal/ g, which is only slightly lower than for Comparative Grease B, which contains only the lithium hydroxystearate thickener. Thus, it is clear here that dilithium azelaate did not affect the crystal lattice of lithium hydroxystearate. It should be understood that dilithium azelaate itself does not melt much above 500ⓓ, and thus the latent heat of fusion of dilithium azelaate is not relevant. The grease compositions of the present invention may also contain various other additives as will be understood by those skilled in the art. Such additives include, but are not limited to, antioxidants such as dye-phenyl-alpha-naphthylamine, rust inhibitor additives such as barium dinonylnaphthalene sulfonate, odor modifiers, tackifiers, polar Includes pressure additives and the like.

Claims (1)

[Claims] 1. Large proportion of lubricating oil and increasing proportion of grease (a)
_C12 ~ _C24 hydroxy fatty acid lithium soap and (b)
a combination of a C ₂ -C ₁₂ aliphatic dicarboxylic acid with a lithium soap, and 0.2 per mole of (a) above.
In the process of producing a high-drop lubricating grease in which ~1 mole of (b) is present, a mixture of a lubricating oil and a lithium soap of _C12 to _C24 hydroxy fatty acids is prepared, and to this mixture _C2 to
adding a C ₁₂ aliphatic dicarboxylic acid and then adding stepwise to the mixture sufficient lithium base to convert the dicarboxylic acid to its dilithium soap while heating the mixture to within the range of 175 to 240 °C; A method for producing a high dropping point lubricating grease, including each step of forming a complex between (a) and (b). 2 Large proportion of lubricating oil and grease with increasing proportion (a)
_C12 ~ _C24 hydroxy fatty acid lithium soap and (b)
a combination of a C ₂ -C ₁₂ aliphatic dicarboxylic acid with a lithium soap, and 0.2 per mole of (a) above.
A method for producing a high-drop point lubricating grease in which ~1 mole of (b) is present, in which a lithium base is added to a mixture of a lubricating oil and a _C12 - _C24 hydroxy fatty acid to form a lithium soap of the fatty acid in the lubricating oil. in situ, the resulting soap composition is substantially dehydrated, a _C2 to _C12 aliphatic dicarboxylic acid is added to the dehydrated soap composition, and the mixture is then reduced to within the range of 175 to 240 adding stepwise to said mixture with heating sufficient lithium base to convert said dicarboxylic acid to its dilithium soap, thereby forming a complex between (a) and (b); A method for producing high-drop point lubricating grease, including a process.