Preparation of high dropping point lithium complex soap grease

A high temperature multipurpose grease is prepared from the lithium soap of a C.sub.12 to C.sub.24 hydroxy fatty acid, (e.g. 12-hydroxy stearic acid) and a dilithium soap of a C.sub.4 to C.sub.12 dicarboxylic acid, (e.g. dilithium azelate) wherein the acid mole ratios range from 3:1 to 0.5:1 respectively under carefully controlled processing conditions including controlled alkali addition and one step heating.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is concerned with the preparation of a lithium complex soap 
grease having a high dropping point. Lithium soap greases have been known 
and widely used for many years. The principal advantages of a lithium soap 
grease have included high water resistance and ease of dispersion of the 
soap in all types of lubricating oil base stocks. While the lithium soaps 
used as thickening agents for these greases can be prepared by reaction of 
lithium hydroxide or other lithium base with conventional high molecular 
weight fatty acids, lithium 12-hydroxy stearic acid and the lithium soaps 
of related hydroxy fatty acids have been particularly useful because of 
their great mechanical stability. 
There are many fields of application of grease compositions where a high 
dropping point is required, as for example in the lubrication of 
automotive disc brake wheel bearings. Such disc brakes are used in modern 
locomotives. 
The prior art discloses batch processes for preparing high dropping point 
lithium complex soap greases. One known process requires separate 
saponification steps for the monocarboxylic fatty acid and for the 
dicarboxylic fatty acid components. In another process, the monocarboxylic 
acid and dicarboxylic acid components are saponified together but this 
process requires at least two distinct heating steps following the 
saponification step in order to complete grease formation. 
Improved complex soap process for preparing high dropping point lithium 
greases, having fewer steps would be commerically advantageous and 
desirable. 
An object of this invention is to provide a process for preparing lithium 
complex soap greases which will provide substantial advantages in 
convenience and economy over known methods. 
2. Description of the Prior Art 
U.S. Pat. No. 3,681,242 discloses a batch process for preparing a high 
dropping point lithium complex soap grease which includes two distinct 
heating stages after saponification. The lithium soap is prepared from a 
mixture of C.sub.12 to C.sub.24 hydroxy fatty acid and a C.sub.4 to 
C.sub.12 dicarboxylic acid. 
U.S. Pat. No. 3,791,973 discloses a batch process for preparing a high 
dropping point lithium complex soap grease by a particular sequence of 
steps which includes the separate formation of the lithium soaps of a 
C.sub.12 to C.sub.24 hydroxy fatty acid and of a C.sub.4 to C.sub.12 
aliphatic dicarboxylic acid. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a lithium complex soap grease 
having a dropping point in excess of 500.degree. F. is prepared by a 
process which comprises the steps of: (1) dissolving from 3 to 0.5 moles 
of a C.sub.12 to C.sub.24 hydroxy fatty acid per one mole of a C.sub.4 to 
C.sub.12 aliphatic dicarboxylic acid in a lubricating oil to form an 
oil-acid mixture, in which the amount of oil employed comprises from about 
30 to 50 weight percent of the total amount of oil employed in the 
finished composition, (2) adjusting the oil and acid mixture to a 
temperature of below about the boiling temperature of the water; (3) 
adding at a controlled rate of less than about 0.30 lbs./minute per 100 
lb. batch of finished grease composition, a concentrated aqueous solution 
of 8-10 weight percent lithium hydroxide in an amount slightly in excess 
of that required to neutralize the acids; (4) maintaining the reaction 
conditions for a period of time sufficient to obtain substantially 
complete saponification between the fatty acids and lithium hydroxide; (5) 
dehydrating the mixture of the lubricating oil and lithium complex soap; 
(6) heating the mixture until it is uniformly at a temperature from about 
390.degree. F. to about 430.degree. F.; (7) rapidly cooling the mixture to 
about 375.degree. F. or below by quenching it with additional lubricating 
oil and finally (8) incorporating the remainder of the lubricating oil 
into said grease composition. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention is concerned with a process for the preparation of a lithium 
complex soap grease having a dropping point above 500.degree. F. The 
thickener system of the grease is a combination of a lithium soap of a 
C.sub.12 to C.sub.24 hydroxy fatty acid and a lithium soap of a C.sub.4 to 
C.sub.12 aliphatic dicarboxylic acid. The key sequence of steps included 
in this invention is: 
(1) Dissolving from 3 to 0.5 moles of a C.sub.12 to C.sub.24 hydroxy fatty 
acid per one mole of a C.sub.4 to C.sub.12 aliphatic dicarboxylic acid by 
stirring the acids into about 30 to 50 weight percent of the total amount 
of base oil to be used in the finished grease; 
(2) Adjusting the temperature of the oil and acid mixture to below about 
the boiling temperature of the water; 
(3) Adding slowly at a controlled rate of less than 0.30 lbs./minute per 
100 lb. of finished grease product, a concentrated aqueous solution of 
approximately 8-10 weight percent of lithium hydroxide usually in an 
amount slightly in excess of that required to neutralize the acids. 
(4) Maintaining the reaction conditions for a period of time sufficient to 
obtain at least substantially complete saponification between the fatty 
acids and the lithium hydroxide; 
(5) Dehydrating the mixture of lubricating oil and lithium complex soap; 
(6) Heating the mixture until it is uniformly at a temperature from about 
390.degree. F. to about 430.degree. F.; 
(7) Rapidly cooling the mixture to about 375.degree. F. or below by 
quenching it with approximately 5 to 25 weight percent of the total amount 
of lubricating oil employed in the finished composition; 
(8) Incorporating the remainder of the lubricating oil into the said grease 
composition. 
The hydroxy fatty acid employed in preparing the grease of this invention 
will have from about 12 to 24, or more usually about 16 to 20, carbon 
atoms, and will preferably be a hydroxy-stearic acid, e.g. 9-hydroxy, 
10-hydroxy, or 12-hydroxy, stearic acid, most preferably 12-hydroxy 
stearic acid. Other acids which can also be used include: ricinoleic acid, 
12-hydroxy tetradecanoic acid, 10-hydroxy tetradecenoic acid, 12-hydroxy 
hexadecanoic acid, 8-hydroxy hexadecenoic acid, 12-hydroxy icosanic acid 
and 16-hydroxy icosanic acid. 
The dicarboxylic acid used in the greases of this invention will have from 
4 to 12 carbon atoms, preferably 6 to 10 carbon atoms. Such acids include 
succinic, glutaric, adipic, suberic, pimelic, azelaic, dodecanedioic, and 
sebacic acids. Azelaic acid is preferred. 
The proportion of hydroxy fatty acid to dicarboxylic acid will be in the 
range of about 3:1 to 0.5:1 moles respectively with a preferred mole ratio 
range of about 2:1 to 0.5:1 and a most preferred mole ratio of about 1.6:1 
moles respectively. 
The lubricating oils forming the major constituent of these greases may be 
any oils of lubricating characteristics which are suitable for use in 
lubricating greases generally. Mineral lubricating oil base stocks used in 
preparing the greases can be any conventionally refined base stocks 
derived from paraffinic, naphthenic and mixed base crudes. Such oils 
include particularly the conventional mineral lubricating oils having 
Saybolt Universal viscosities in the range from about 35 seconds to about 
300 seconds at 210.degree. F., which may be either naphthenic or 
paraffinic in type or blends of different oils. When a blend of 
lubricating oils is employed to make the grease composition, the oils may 
be blended separately prior to use in the grease making process or they 
may be blended as used in the grease making process as done in Example I. 
The latter procedure permits use of an oil in the initial stage of the 
grease preparation in which the fatty acids dissolve more readily, and is 
also more convenient where blended oils are not readily available. The 
preferred mineral oils are those having Saybolt Universal viscosities in 
the range from about 60 seconds to about 80 seconds at 210.degree. F., 
which may be blends of lighter and heavier oils in the lubricating oil 
viscosity range. 
Synthetic lubricating oils, which may be preferred for obtaining greases 
having special properties required for certain types of lubricating 
service, include oils prepared by cracking and polymerizing products of 
the Fischer Tropsch process and the like, as well as other synthetic 
oleaginous compounds such as diesters, polyesters, polyethers, etc., 
having viscosities within the lubricating oil viscosity range. Examples of 
suitable diesters include the aliphatic dicarboxylic acid diesters, such 
as di-2-ethylhexyl sebacate, di(secondary amyl) sebacate, di-2-ethylhexyl 
azelate, di-iso-octyladipate, etc. Other synthetic oils that can be used 
include synthetic hydrocarbons such as alkyl benzenes, e.g. alkylate 
bottoms from the alkylation of benzene with tetrapropylene, or the 
copolymers of ethylene and propylene; silicon oils, e.g. ethyl phenyl 
polysiloxanes, methyl polysiloxanes, etc.; polyglycol oils, e.g. those 
obtained by condensing butyl alcohol with propylene oxide; carbonate 
esters, e.g. the product of reacting C.sub.8 oxo alcohol with ethyl 
carbonate to form a half ester followed by reaction of the latter with 
tetraethylene glycol, etc. 
The total soap content of the grease of the present invention will be in 
the range of from about 2 to 30 weight percent and preferably from about 5 
to 20 weight percent and most preferably about 10-14 weight percent. 
According to the present invention a C.sub.12 to C.sub.24 hydroxy fatty 
acid and a C.sub.4 to C.sub.12 aliphatic dicarboxylic acid are dissolved 
by stirring and heating into about from 20 to 50 weight percent and 
preferably in about 40 weight percent of the total amount of a suitable 
base oil to be used in preparing the grease. Preferably the hydroxy fatty 
acid has 16 to 20 carbon atoms and the dicarboxylic acid has from 6 to 10 
carbon atoms, with the most preferred acids being 12-hydroxy stearic acid 
and azelaic acid respectively. The mole ratio range of hydroxy fatty acid 
to dicarboxylic acid is approximately 3:1 to about 0.5:1 and preferably 
2:1 to 0.5:1 with approximately 8:5 moles respectively being the most 
preferred mole ratio. When azelaic acid is employed usually the 
temperature necessary for dissolution of the acids is from about 
240.degree. F. to about 250.degree. F. The temperature of the oil and acid 
mixture is then brought to below the boiling temperature of water, 
preferably to about 200.degree. to 210.degree. F., range, and a 
concentrated aqueous solution of approximately 8 to 10 weight percent and 
preferably 9.4 weight percent of lithium hydroxide is added at a 
controlled rate. This rate is usually below about 0.30 lbs./minute per 100 
lbs. of finished grease product and preferably from about 0.05 to about 
0.25 lbs./minute per 100 lbs. of finished grease product with the most 
preferred rate being about 0.15 lbs./minute per 100 lbs. of finished 
grease product. The rate of alkali addition is a critical feature of this 
invention and it is important that it be carefully controlled. The amount 
of lithium hydroxide solution added is usually an amount slightly in 
excess of that required to neutralize the acids. While the alkali is being 
added the mixture may be slowly circulated at a rate of 1 lb/min for every 
2 to 10 lbs of mixture in the kettle giving 1 kettle volume turnover every 
2 to 10 minutes and preferably at a rate of 1 lb/min for every 2 to 5 lbs 
of mixture in the kettle which gives 1 kettle volume turnover every 2 to 5 
minutes. Most preferably the circulation rate is 1 lb/min for 
approximately every 3 lbs of mixture in the kettle giving 1 kettle volume 
turnover approximately every 3 minutes. After the alkali addition is 
complete, the mixture is maintained at a temperature below the boiling 
temperature of water, i.e. 212.degree. F. and preferably at from 
200.degree. F. to 210.degree. F., until saponification is substantially 
complete which may take from about 15 to about 45 minutes and more likely 
about 30 minutes. Following saponification the oil and lithium soap 
mixture are dehydrated. This is a accomplished by heating the mixture to 
from about 220.degree. to about 250.degree. F. After dehydration the 
temperature is further raised until the mixture is uniformly at from about 
390.degree. F. to about 430.degree. F. The minimum heating time is usually 
15 to 30 minutes and frequently an hour or more. The mixture is then 
rapidly cooled to below about 375.degree. F. by quenching it with 
additional oil i.e. approximately 5 to 25 percent and preferably 5-10 
percent of the total amount of lubricating oil employed in the finished 
grease composition. The mixture may be further cooled by an external 
cooling means such as an insulating jacket or heat exchanger. The 
remainder of the base oil and any desired additives may be incorporated 
into the mixture as it cools. Upon completion of the oil addition, the 
mixture may be milled. Although milling is not necessary for the 
preparation of a satisfactory grease according to the process of this 
invention, it improves the consistency of the grease and therefore greases 
made according to the process of this invention are usually milled. 
The nature of this invention and the manner in which it is practiced will 
be better understood when reference is made to the following examples 
which include preferred embodiments.

EXAMPLE 1 
A grease kettle was charged with 34.90 lbs. of a deasphalted, solvent 
refined and dewaxed paraffin base residual oil having a viscosity of 160 
SUS at 210.degree. F., 7.85 lbs. 12-hydroxystearic acid, and 3.77 lbs. 
azelaic acid. The mixture was heated with stirring to 250.degree. F. to 
dissolve the acids. After cooling to 200.degree.-210.degree. F., 17.76 
lbs. concentrated aqueous lithium hydroxide solution containing 1.67 lbs. 
lithium hydroxide was added at 0.15 lb./minute while slowly circulating 
the mixture at a rate of 1 lb/min for every 3 lbs of batch giving 1 kettle 
volume turnover approximately every 3 minutes. After completion of the 
lithium hydroxide addition, the mixture was held at 
200.degree.-210.degree. F. for 30 minutes to complete saponification. 
Next, the mixture was heated to bring about dehydration, and then heating 
was continued until a temperature of 410.degree.-420.degree. F. was 
reached. After holding the mixture at 410.degree.-420.degree. F. for 30 
minutes, it was quenched with 7.0 lbs. initial batch of base oil and 
further cooled by an external means to 325.degree. F., when 46 lbs. of 
additional oil (a 1.7:1 ratio blend of the oil used in the initial charge 
of the batch and a solvent refined and dewaxed paraffin base distillate 
oil with a viscosity of 180 SUS at 100.degree. F.) was added to the batch 
at 0.3 lb./minute. Upon completion of oil addition, the mixture was milled 
using a conventional Charlotte mill. 
The following data was obtained for the grease prepared by the above 
procedure: 
Dropping Point, .degree.F.: 500+ck 500+ 
Worked Penetration at 77.degree. F.: 266 
Soap, Wt % (Calculated): 12.0 
The following examples show that the high dropping point is not obtained if 
the rate of alkali addition is too fast or if all of the alkali is added 
at one time. 
COMATIVE EXAMPLE 1 
Example 1 was repeated except that the aqueous lithium hydroxide was added 
at the rate of 0.50 lb./minute. The prepared grease gave the following 
data: 
Dropping Point, .degree.F.: 484 
Worked Penetration at 77.degree. F.: 282 
Soap, Wt % (Calculated): 12.0 
COMATIVE EXAMPLE 2 
Example 1 was again repeated except that the aqueous lithium hydroxide was 
added all at once. The data obtained from that batch is as follows: 
Dropping Point, .degree.F.: 435 
Worked Penetration at 77.degree. F.: 285 
Soap, Wt % (Calculated): 12.0 
Various other additives may be incorporated into the grease composition of 
this invention, as is understood by those skilled in this art. Such 
additives include, but are not limited to, dyes, antioxidants such as 
phenyl-alphanaphthylamine, rust inhibitors such as barium dinonyl 
naphthalene sulfonate, odor modifiers, tackiness agents, extreme pressure 
agents, and the like.