A Fresh Look at Lithium Complex Greases Part 1:

How Did We Get Here?

J. Andrew Waynick

August 26, 2020

 Overview of Presentation

• Review of the lithium complex grease literature

• Not exhaustive

• But representative

• Mountaintop flyover approach

• Primarily taken from patent literature, published research papers, NLGI Lubricating

Grease Guide, 6th Edition

• Provides foundation for Part 2 presentation

 Beginnings

• In 1942, five U.S. patents issued with Clarence E. Earle as inventor

• Defined simple lithium soap thickened greases for subsequent decades
• High temperature applicability limited, in part due to dropping point
• Dropping point (D.P.) typically about 200 C
• Shortly after the Earle patents issued, modifications to simple lithium soap greases
began to be developed
• The first ones did not increase D.P. , but did suggest directions in subsequent
development that led to today’s lithium complex greases
• A good discussion of these “pre-lithium complex” greases can be found in
“A Brief History of Lubricating Greases” by Arthur T. Polishuk, Chapter 12C
 U.S. Patent No. 2,898,296

• Issued August 4, 1959; Pattendon, et. al., only months after the Earle patents expired
• The first use of shorter chain dicarboxylic acids to produce higher dropping points
• Used di-esters of sebacic acid (C10) or adipic acid (C6)
• Longer chain monocarboxylic acid was stearic acid
• Stearic acid and diester of dicarboxylic acid in base oil reacted with LiOH(aq), heated to about
204 C, then cooled and finished
• Stearic/sebacic ratio = 2.1 (wt/wt)
• D. P. ranged from 248 C to >260 C
• When dicarboxylic acids used instead of esters: grainy product; D.P ~182 C
• Likely reason was that the esters and/or transient alcohols acting as coupling agent
• Enhanced “co-crystallization” of lithium stearate and di-lithium sebacate.
• Higher melting points of the di-lithium salts impart higher D.P. to a sufficiently co-crystallized
thickener structure
• True Werner coordination complex NOT formed! Term “complex” originally used as a marketing
tool, not as a chemically accurate term.
 Ehrlich, et.al., “The Development of Lithium Complex Greases”,
NLGI Spokesman, 44, 3, pp 97 – 100, June, 1980

• Reported that lithium complex grease development began in late 1959

• Initially used low molecular weight mono-carboxylic acids (formic, acetic) as
complexing acid candidates – without success
• Eventually used azelaic and sebacic acids – still with problems
• When di-esters of these acids were used, good results were obtained
• No record of this work can be found in the open literature before this 1980
Spokesman, 4-page paper
• Nonetheless, this paper continued to acknowledge the beneficial effect of using
esters in facilitating sufficiently co-crystallized lithium complex thickener twenty
years after the original documented work.
 U.S. Patent No. 2,940,930

• Issued June 14, 1960; Pattendon, et. al.

• Mixture of long chain fatty acid, shorter chain dicarboxylic acid, and polyhydric alcohol
heated to 148 C – 177 C for one to five hours to form complex acidic polyester mixture
• Typically stearic acid; adipic, sebacic, or azelaic acid; and ethylene glycol used
• Reaction mixture cooled, added to base oil, and reacted with LiOH(aq)
• Mixture heated again to as high as 204 C to fully form grease and dehydrate
• Alcoholic bi-products released if not remaining in final grease
• Stearic/azelaic ratio = 1.5 (wt/wt)
• D.P. ~ 260 C
• Required two heating and cooling cycles
• Once again, sufficiently co-crystallized lithium complex thickener likely facilitated by
ester and/or transient alcoholic moieties acting as coupling agents
 U.S. Patent No. 3,681,242

• Issued August 1, 1972; Gillani, et. al.

• Claimed presence of glycols in final grease deleterious to oxidation and water resistance
• 2-HSA and dicarboxylic acid (azelaic) dissolved in base oil at 82 C – 93 C
• LiOH(aq) slowly added and reacted
• During reaction, mixture heated to 204 C – 221 C to complete reaction and dehydrate
• Rapidly cool to about 104 C
• Heat again to about 177 C – 190 C
• Cool as rapidly as possible to at least 116 C and finish grease
• 12-HSA/azelaic ranged from 1.6 to 2.95 (wt/wt)
• D.P. as high as 282 C
• Avoided use of esters or glycols
• Required two heating and cooling cycles to achieve high D.P.
 U.S. Patent No. 3,791,973

• Issued February 12, 1974; Gillani, et. al.

• Claimed presence of glycols in final grease deleterious to oxidation and water resistance
• LiOH(aq) added to 12-HSA in base oil at 82 C – 93 C
• Heated to 149 C to fully react and form Li 12-HSt and dehydrate
• Cool to no lower than 96 C
• Add dicarboxylic acid (azelaic), add more LiOH(aq)
• Heat again to about 198 C to fully react
• Cool and finish grease
• 12-HSA/azelaic ranged from 2.0 to 3.2 (wt/wt)
• D.P. as high as 329 C
• Avoided use of esters or glycols
• Required two heating and cooling cycles to achieve high D.P.
 U.S. Patent No. 4,435,299

• Issued March 6, 1984; Carley, et. al.

• Avoided use of two heating/cooling cycles
• 12-HSA and di-carboxylic acid (azelaic) dissolved in initial base oil
• LiOH(aq) slowly metered into mixture at carefully controlled rate
• Mixture held below 100 C until reaction complete
• Heat to between 199 C and 204 C
• Rapidly quench to 190 C by base oil addition
• Cool and finish grease
• 12-HSA/azelaic was 2.6 (wt/wt) or lower
• D.P. >260 C
 Use of Stable LiOH Dispersion in Base Oil

• Developed as a convenient alternative to the use of LiOH(aq)

• Anhydrous
• Can be used to make simple lithium and lithium complex greases
• Reaction with acids proceeds rapidly allowing an earlier heating to top
temperature
• Heating to top temperature takes less time since no water from LiOH was
added (no latent heat of vaporization required)
• Only one heating/cooling cycle required
• Shown to allow reduction in process kettle residence time and associated
energy/manpower costs
• Yields at least as good as traditional methods that use LiOH(aq)
• Dropping points somewhat higher than when LiOH(aq) is used
• Allows simple lithium or lithium complex greases to be made in hydrolytically
unstable ester base oils, thus avoiding the use of pre-formed lithium soaps
 Borated Lithium Soap-Thickened Greases

• Boric acid, B(OH)3,has been used as an alternative to di-carboxylic acids as a

means to provide higher dropping point lithium soap-thickened greases

• Boric acid itself has been reacted in-situ during the lithium 12-HSt formation

reaction

• Alternatively, addition of various borated organic compounds have been used

• Representative examples of each are provided in the next slides

 U.S. Patent No. 3,758,407

• Issued September 11,1973; Harting

• Used long chain hydroxy-carboxylic acid (12-HSA), B(OH)3, LiOH

• Aqueous LiOH and B(OH)3 added to 12-HSA in base oil at about 82 C

• Mixed and heated to 199 C

• Additional base oil added; grease cooled and finished

• Optional second hydroxy hydrocarbyl acid could be used (salicylic acid)

• D.P. ranged from 251 C to >260 C

 U.S. Patent No. 4,376,060

• Issued March 8, 1983; Stadler

• Used long chain hydroxy-carboxylic acid (12-HSA), B(OH)3, LiOH

• Also used a poly-hydric alcohol to be present when LiOH was reacted with B(OH)3

• Poly-hydric alcohol preferably glycerol or cis-di-hydroxybenzene

• Aqueous LiOH and B(OH)3 added to 12-HSA in base oil at about 82 C in presence of alcohol

• Mixed and heated to 199 C

• Additional base oil added; grease cooled and finished

• D.P. ranged from 261 C to >315 C; without poly-hydric alcohol D.P. ranged from 218 C to 228
 Doner/Horodysky/Keller U.S. Patents
• At least 16 U.S. Patents issuing from April 15, 1986 to January 21, 1997
• Various families of organic compounds reacted with boric acid
• Compounds borated included epoxides, alcohols, catechols, Mannich bases,
alkoxylate alcohols, oxazolone, alkyoxylated amides, and amines
• Borated compounds added to Li 12-HSt base grease at typical temperatures for
grease additives
• Optional organic S/P compounds sometimes optionally used to provide further
increase in D.P.
• S/P compounds include ZDDP and/or mixtures of organic phosphates, phosphites,
and sulfurized olefins/sulfurized triacylglycerides
• D.P. has high as 327 C
 Insights Into How Borated Additives Work
• Doner, et. al. patents taught that overborating the organic substrate provided best
improvement in D.P.
• Likely due to formation of extended -(O-B-O)n- cross linkages between
12-hydroxystearate moieties – most likely the OH group
• Linkages may be present in finished grease, or possibly formed when grease is
sufficiently heated in actual use
• Several major additive companies now market borated esters, amines, etc. for their
ability to increase D.P. of lithium-based greases.
• Significant number of papers presented over the last 10+ years discussing the use
of such borated additives
• Some borated additives shown to improve oxidation stability and/or rust
protection
• Allows reduction or elimination of azelaic/sebacic acid
 Additional Approaches to Increasing Dropping Point of
Lithium 12-HSA Greases

• The earliest of the Doner, et. al. patents taught that combinations of borated
organic compounds with zinc dithiophosphates could synergistically increase D.P.

• Numerous other subsequent patents and research papers provided examples of this

• Other synergistic combinations comprising metal dithiophosphates and

dithiocarbamates have been suggested

• Diesters of terephthalic acid have been suggested

 Manufacturing Equipment Impact on Dropping Point

• Pressurized kettles allow small amount of solvent water to remain while

increasing reaction temperature, thereby increasing reaction rate and encouraging
more intimate association of Li 12-HSt and di-lithium azelate (sebacate)

• Contactors provide similar enhancements, but also provide a high speed impeller
and high speed cyclic mixing to further associate the two thickener components
during their initial formation, heating, and cooling

• Continuous manufacturing equipment can also provide similar benefits plus

lower overall manufacturing costs per pound of finished grease
 Conclusions
• Today’s lithium complex grease technology is the result of gradual
improvements in three areas:
ØChemistry
ØProcessing
ØEquipment
• These three areas did not improve separately; instead most improvements
involved a combination of two or all three.
• Three broad categories of lithium complex greases are:
ØLithium 12-HSA/di-lithium azelate (sebacate)
ØLithium 12-HSA enhanced with borated and/or other additives
ØA combination of the first two categories that reduces but does not
eliminate the dicarboxylic acid
§ Typically, in all reaction schemes, a source of LiOH is added to a source of the
thickener acid(s) (separately or together) in a portion of the base oil
§ An appropriate combination of mixing, heating, cooling, and usual finishing
methods result in the final grease