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Tech hology to I~fro~fth~e
GreaseMa king~Rrocess
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By Garetli Fish, P/iD CLS CLGS and Chris Hsu, PhD
Thc Lubrizol Corporation, Wick/life, Ohio, USA
Abstract
The process to manufacture grease is as important
to grease properties as are the base oil, thickener, and
the additives used to enhance performance. Grease
producers manufacture greases using a wide variety of
processes. This can be attributed to the availability of the
basic raw materials for grease making and differences
in the plant and equipment. Provided that the response
of each variable is known, grease making is a controlled
acid / base chemical reaction process. Grease makers
strive to optimize their process for each thickener type
based upon an understanding of the process variables.
This paper will discuss technologies that can enable
grease producers to improve and enhance their
grease making process. The technologies under
discussion are additives to: improve the grease yield
without compromising the general properties of the
grease; reduce oil bleed at both storage and elevated
temperatures; and enhance the dropping points of
lithium soap thickened greases. Also discussed are
methods to reliably manufacture high dropping point
lithium complex greases in a variety of base oils,
including vegetable oils and synthetic esters.
Introduction
The process to manufacture grease is as important to
grease properties as are the base oil, thickener, and the
additives used to enhance the performance properties
(1). Grease producers manufacture greases using a wide
variety of processes in a wide variety of equipment.
This can be attributed to the availability of the basic
raw materials for grease making and differences in the
plant and equipment. According to the EGLI REACH
Consortium (2) >30 types of lithium soap greases were
registered by grease makers both within the European
Union and by multi national lubricant companies. The
essentials of grease making have not changed since the
days of Klemgard (3). One or more fatty acids are reacted
with a slight excess of base or bases, to produce a salt
or salts and water. The water is stripped out and the
saponification reaction is finished by the application of
additional heat. For simple soaps it is typically desirable
to fully melt the simple soap followed by recrystallization
to achieve optimum properties, and for complex greases
that the reaction is driven to or as close to completion as
possible, as the more complete the reaction is the better
the thickening and typically, the higher the dropping
point.
Over the decades there have been numerous NLGI
papers and presentations on how to improve the
grease making process. Some focused on improved
manufacturing plant and equipment, such as Graham,
et. al. (4) and Krol (5); while other papers have covered
improved processing techniques for lithium greases such
as Polishuk (6) and more recently, Morgan et. al. (7).
20
VOLUME 79, NUMBER 4
One of the challenges outlined by Morgan was that it is
difficult to control both 1-step and 2-step reactions to
make high dropping point lithium complex greases.
Several papers have focused on components which can
be added to the grease manufacturing process to improve
the output. Nolan and Zeitz (8) outlined the use of
micronized lithium dispersions to improve the reactivity
of the lithium hydroxide and Lorimor (9) discussed
dropping point enhancers. Both of these topics will be
discussed and updated later in the paper.
What is clear from these papers and the authors’ own
experiences is grease makers will optimize their process
based on their own equipment. Grease makers strive to
optimize their process for each thickener type based on
understanding of the process variables. Provided that
the response of each variable is known, grease making
is a controlled acid I base chemical reaction process.
It is known that from a manufacturing perspective,
commodity charging of raw materials makes the process
easier to manage. If consistent, high quality fatty and
complexing acids are used, batch sizes can be defined
around a whole number of bags of acid into the cooking
vessel. High purity bases also need to be used along with
a post-saponification titration to confirm the desired
basicity has been achieved. If the acids and bases used
are not so consistent, commodity charging typically
results in a more variable grease output. Either from
supplier certificates or their own laboratory analyses, the
saponification numbers of the acids are used to make
adjustments to the charging. Many grease makers use
calculators to determine the amount of base needed
to neutralize the added acids and this improves the
consistency of grease batches.
market (10). This is a significant simplification of the
actual regional volumes, and to understand the need for
improved technology these volumes need to be looked
at regionally. In the mature market of North America,
lithium complex makes up almost 40% compared to 28%
for simple lithium soaps. By contrast, in India, simple
lithium soaps dominate the market approaching 85%
with complexes only at around 7%. As a developing
market, the Chinese market consists of 70% simple
lithium and 15% lithium complex thickeners. Europe and
Japan match the global average of simple lithium soap
greases but manufacture lower percentages of lithium
complex greases. In Europe, the difference is made up
largely by a higher market share of aluminum complex
greases, and in Japan the majority of high temperature
greases utilize urea thickeners.
Reviewing regional volumes it is clear that in North
America, the growing volume is lithium complex with
simple lithium embracing the commodity market. There
is a perceived need to improve the properties of lithium
complex greases in the following areas: water resistance;
oxidation stability and longer grease life; and improved
bleed. Oxidation stability and life improvements have
been previously presented (11) and polymer technologies
are available to improve water resistance (12). In
addition to these properties, dropping points above 280
are now common with some customers requesting
thickener systems that have consistently high dropping
points above 300 °C, trying to match the behavior of
calcium sulfonate greases. High quality, high temperature
thickeners in sensitive base oils are also required for the
growing demand in specialty fluids and for bio-based
greases.
Grease making equipment includes traditional open
kettles, autoclaves and other pressurized reactors and
continuous grease making units. For each of these types
of manufacturing, individual recipes are needed as well
as process control plans and procedures to ensure high
quality and consistent output.
Yield improver technologies offer a means to take cost
out of simple lithium grease production, by increasing
volume manufactured at a given consistency per unit of
soap. For markets such as India or China, technologies
to improve simple lithium greases are more important
today. For a few specialized applications, improved
lithium complex greases are also desired.
The largest volume of grease thickeners sold globally
are lithium soaps with around 58% based on simple
soaps and lithium complexes at around 19% of the global
This paper will discuss technologies that can enable
grease producers to improve and enhance their
grease making process. For simple lithium greases,
– 21 NLGI SPOKESMAN, SEPTEMBER/OCTOBER 2015
saponification aides are outlined which improve grease
yield without compromising the general properties of the
grease.
Additives to control bleed are also discussed. It was
previously shown (12) that the incorporation of polymers
into grease could reduce both storage bleed and that
which occurred in service up to 100 °C. One of the issues
with using polymers is that above 100 °C most of the
polymers employed start to lose their effectiveness and
other solutions are needed.
Technology to improve the dropping point of simple
lithium soap greases was previously outlined by Lorimor
(9). Two different approaches were illustrated which
worked in slightly different ways to enhance the dropping
points of lithium soap thickened greases. One ongoing
issue is it can be a challenge to consistently manufacture
high dropping point lithium complex greases. Both
one step and two step processes are used. The one step
process can be difficult to control, with batches often
giving good yields but with scatter in the resulting
dropping points. The two step process reliably will
produce dropping points of 260 to 280 °C, but based
on current targets of 280 to> 300 °C may not be good
enough, and other methods to reliably manufacture high
dropping point lithium complex greases in a variety of
base oils provide an alternative.
the grease making process. One of the features sought
by grease producers is the lowest possible soap content
to achieve the desired consistency grade. It has been
well documented that greases manufactured using
naphthenic base oils have lower soap contents compared
to those manufactured using paraffinic oils (1), but
typically grease quality naphthenic oils are higher cost
than paraffinic oils of the same viscosity class. Supply
of naphthenic oils is also an issue with only a limited
number of suppliers and in some developing markets,
quality naphthenic oils are difficult to obtain.
Improved yields can also be obtained by slow cooling
from top temperature to below 170 °C. This creates large
fibers that thicken the oil better but give higher oil bleed
and worse shear and roll stability, compared to grease
that has undergone a quench or partial quench.
Grease yield improvers are shown to reduce the amount
of soap necessary to achieve a penetration target when
using purely paraffinic oils. According to the NLGI
Grease Guide (1), yield is defined as “The amount of
grease (of a given consistency) that can be produced
from a specific amount of thickening agent.” To the non
grease chemistry professional, this definition is slightly
difficult to comprehend. An explanation is given in
table 1, with two greases with the same penetration, but
different soap contents. Grease B has a l5.4°o better yield
than grease A.
Yield Improvers
Based on the increasing commoditization of lithium
greases, cost becomes a very important consideration in
Grease
W60 Penetration
ISO VG 100 paraffinic base oil (%wt.)
Lithium 12-hydroxystearate soap (%wt.)
Normalized soap content
(100: iease/~i.i, soae)
Grease Yield Improvement (%)
Table 1 Grease.yield improvement
A
B
284
92.5
7-5
284
93.5
13.33
15.38
22
VOLUME 79, NUMBER 4
154
The first approach was to examine commercially
available polymers sold as yield improver additives.
The basic target was to reduce the amount of soap with
an additive or component added at a low treat level,
which would have a net treat cost lower than adding
additional soap. Reducing the soap content should also
improve the pumpability of the grease but give similar
These were incorporated into lithium soap greases at
the suggested treat rates and tested. The results for the
various polymers in group II oil are included in table
2. Based on the data in table 2, polymers can improve
shear and roll stability It was also desired to have no
effect on oil bleed and no negative effects on all other
grease properties. Based on current grease and patent
literature, there are two routes to improving yield.
grease yield based on reducing the soap content to
achieve the same level of worked penetration. Following
The first involves the use of polymers to increase the
unworked and worked penetration of the grease and the
a review of the data obtained they did not appear to
be the complete answer as the cost position was not
significantly improved over the grease without yield
second incorporates structure modifiers into the soap
matrix.
improver and some of the “no harms” data collected
suggested that the solution may have not been robust.
Grease
baseline
OCP1
OCP2
__________________________________
Polymer type
Treat rate (%wt.)
W60 penetration
Effect
Table 2 Effect of commercial polymer grease yield improver additives
Looking at general processing for greases, it was thought that better milling could be investigated as part
of the study. Three different milling techniques: triple roller with adjustable speeds and gaps, a colloidal
mill and a high pressure homogenizer were available. Two slightly different lithium complex soap greases
were milled using all three techniques and the milling quality compared in table 3.
Method
Grease
Property
Lithium
complex 1
Worked penetration
Lithium
complex 2
Worked penetration
Uniuilled
Dropping point(°C)
Dropping point(°C)
3-roller mill
Colloidal mill
High pressure
homogenizer
Lumpy not
tested
>308
Lumpy not
tested
227
235
245
>308
>308
>308
261
271
265
>308
>308
>308
>308
Table 3 Effect of milling on yield
Results from analyzing the data suggested that better milling and dispersing could bring improvements
to the yield. From this it was thought that adding a dispersant to the grease would improve the milling
process. Several commercial dispersants were tried at the same treat rate and all caused significant
softening of the grease compared to grease without dispersant. Some examples are shown in table 4.
Grease
H
I
Dispersant
Baseline
Dl
Treat rate
0
3.0
W60 Penetration
275
345
Effect
+70
Table 4 Effect of commercial dispersant additives on yield
J
K
L
D2
3.0
275
none
D3
3.0
350
+75
D4
3.0
>400
>+l25
From this, a few other compounds were tested, most of which did not work, but one candidate showed some
potential in initial trials. To further explore this, a series of four simple lithium 12-hydroxystearate greases were
made up in API group I paraffinic base oil, using an identical saponification process but with different soap
contents, ranging from 5.6 to 9.3%. These samples are plotted in figure 1, showing that for a similarly controlled
saponification in the same base oil, soap content follows worked penetration. Two greases were then made
up using the new yield improver treated at 1%. The first grease had a soap content of 5.5% but gave a worked
penetration of 285 and the second had a soap content of 7.5°o with a worked penetration of 252. This data is also
plotted on figure 1. There are two ways of looking at the data. The grease with 5.5% thickener and yield improver
reduced the penetration by approximately 30 points or the soap content by 2% and the grease with 7.5°o thickener
and yield improver reduced the penetration by approximately 30 points or the soap content by 2%.
340
0
I
• Withoutyield improver
315
A With yield improver
290
equivalent
265
equivalent
240
5
5.5
6
6.5
7
7.5
8
8.5
% Lithium 12-hydroxystearate
9.5
10
Figure 1. Grease yield improvement
Following on from this three series of greases were made up. The first repeated the initial experiments
in API group I oil; the second series investigated the behavior in group II oil; and the final series looked at
group III oils. Testing was carried out on the greases made with and without the yield improver in the three
families of oils to check for negative influences. This is typically called “No harms” testing. The test data for
the group I base oil (110 mm2/s at 40°C) grease is in Table 5, group II oil (115 mm2/s at 40°C) in table 6,
and group III oil (8 mm2/s at 100 °C) results are in table 7.
24
VOLUME 79, NUMBER 4
Sample identity
Method
38
39
40
Soap content (%)
7.5
7.5
5•5
With yield improver
No
Yes
Yes
Unworked penetration
286
260
296
284
252
285
317 (+33)
302 (+50)
334 (+49)
Worked penetration
D2 17
Worked penetration (100k)
Dropping point (°C)
D2265
194
216
212
Oil bleed at 100 °C (%)
D6184
4.4
1.3
3_S
D1264
D1831
48.1
24
28.8
40
10.9
36
D1478
3273
258
0.70
2710
254
0.56
2764
258
0.54
Waterwashout(%)
Roll stability change
LT torque at -20 °C (g-cm)
Starting
Running
4-Ball Wear scar diameter (mm)
Tables— Group I greases testing
Sample identity
D2266
Method
41
42
43
Soap content (%)
7.5
7.5
6.5
With yield improver
No
Yes
Yes
315 (+28)
323 (+49)
321 (+36)
775
863
719
Unworked penetration
Worked penetration
D2 17
Worked penetration (100k)
Dropping point (°C)
___________
Oil bleed at 100 °C (%)
____________
Water washout (%)
___________
D2265
D6184
D1264
Roll stability change
LT torque at -20 °C (g-cm)
Starting
Dl 831
__________
D1478
Runnin
4-Ball Wear scar diameter (mm)
Table 6
D2266
_________
Group II greases testing
25 NLGI SPOKESMAN, SEPTEMBER/OCTOBER 2015
Sample identity
Method
50
51
53
Soap content (%)
8.0
8.0
7.2
With yield improver
No
Yes
Yes
Unworked penetration
300
284
309
289
269
292
329 (+40)
329 (±60)
339 (±47)
Worked penetration
D217
Worked penetration (100k)
Dropping point (°C)
D2265
207
213
213
Oil bleed at 100°C (%)
D6184
4.8
2.6
4.1
Water washout (%)
Dl264
29.4
40.6
36.4
D1831
34
42
48
D1478
473
170
0.65
605
539
116
Rollstabilitycbange
LT torque at -20 °C (g-cm)
Starting
Running
4-Bail Wear scar diameter (Hun)
Table 7— Group ifi greases testing
D2266
117
0.58
0.59
Two larger scale kettle batches were manufactured in a pilot kettle. They used the same Group I base
oil as the greases reported in table 4 and identical 7.54°o soap. The grease with the yield improver was 28
penetration points stiffer than without it. Scanning electron micrographs of the grease structures were taken
to see if there was any difference between the structures of the grease with and without the yield improver.
As seen in figure 2, the grease with the yield improver has a much finer structure and is better dispersed
than the grease sample without the yield improver.
;sj-3. ‘~3~c
—
—
:308
>308
Dropping point (°C)
<220
Unworked penetration
<220
Worked penetration
Table 13 Comparison of lithium hydroxide dispersion and lithium hydroxide monohydrate powder
_________
29 NLGI SPOKESMAN, SEPTEMBER/OCTOBER 2015
A lithium complex grease using a 1-step process with
lithium hydroxide monohydrate powder provided
inconsistent results compared to making the grease using
the same base oil and acids with the lithium dispersion.
The data summarized in table 13 shows that the complex
grease made using the lithium hydroxide dispersion
gave higher dropping points than the complex grease
made using lithium hydroxide monohydrate powder
and a 2-step process. This outcome provides the grease
manufacturer with a tool to improve the dropping point
consistency of lithium complex greases and potentially
extract greater value from the complex grease process.
Sensitive base oils
Historically, it was only possible to use pre-formed
simple calcium or lithium soaps to thicken water
sensitive base oils. Preformed calcium anhydrous
(12-hydroxystearate) soaps will give grease dropping
points of 140 150 °C and those of pre-formed lithium
stearate or 12-hydroxystearate will give grease dropping
points of 180 to 200 °C, but these ranges are somewhat
dependent on the base oils, especially if exotic fluids with
significantly different polarities and solvencies compared
to mineral oils are used. At the NLGI Annual Meeting
in 2000, Polishuk (6) revisited using preformed soaps
and later Bessette (14) outlined how to use preformed
soaps “Dry Technology” to make greases with preformed
simple thickeners in a variety of different base oils.
Honary (15) outlined several manufacturing techniques
methods that could be used to develop greases in
temperature and water sensitive vegetable oils, including
—
Oil / fluid
Viscosity at4O°C (mm2/s)
Viscosity at 100°C (xnm2/s)
Viscosity Index
Acid Number
(mgKOH/geq.)
Copper conosion
(3 hours at 100°C)
Pour Point (°C)
PDSC oxidation induction
time (minutes)
the use of preformed soaps, soap concentrates, lithium
hydroxide dispersions and heating by microwave
technology. Honary explored the various issues with
the different ways of making grease in sensitive base
oils. Preformed soaps still have to be heated to melt the
soap and are not readily available as complexes. Soap
concentrates and the lithium hydroxide dispersions
worked well but introduced mineral oils or nonbiodegradable synthetic fluids into the grease. The
microwave heating technology was reported as being
able to drive the saponification reaction quickly and
heat the grease up to melting temperatures without
degradation. At the time, microwave heating technology
was chosen but later work showed that there were issues
with the microwave heating technology (16). Further
development of the anhydrous lithium hydroxide
dispersion technology showed that it could make
high quality lithium complex greases directly in water
sensitive base oils (17), and that the only viable option to
make high quality greases in sensitive base oils was to use
anhydrous lithium dispersions.
As part of the development of the technology, a series
of sensitive base oils was selected to see if the lithium
dispersion technology was capable of making high
quality lithium thickeners directly in the base fluid. The
properties of the five base fluids chosen soybean oil,
canola oil, high oleic sunflower oil, estolide and synthetic
diester are compared in table 14 along with those of a
600N API group I mineral oil, which was used as the
control.
Soybean
Canola
Sunflower
Estolide
Diester
600N
31.0
7.5
227
551.5
50.9
152
40.1
86
201
91.2
14.8
170
152.0
20.0
152
115.0
12.2
96
0.52
9.19
0.18
0.42
0.10
0.01
1A
2A
lB
1A
1A
1A
-10
-3
-12
-40
-30
-6
4.0
4.6
11.6
18.2
187.2
45.0
Table 14 comparative properties of the selected fluids
– 30 VOLUME 79, NUMBER 4
The anhydrous lithium hydroxide dispersion
technology, as outlined by Nolan and Zeitz (8), is ideally
suited to make grease in water and thermally sensitive
base oils. The small particle size (1400
-25°C (hPa)
modified
Table 15 Properties of the base greases manufactured
Canola
Estolide
Diester
600N
complex
284
312
>316
lB
1.4
complex
280
283
302
lB
0.3
complex
284
287
304
lB
2.1
complex
280
283
297
2A
2.1
2770
345
350
1270
—
31 NLGI SPOKESMAN, SEPTEMBER10 CTOBER 2015
Summary and Conclusions
This paper has shown that there are now several
technologies available to help the grease producer
manufacture cost effective lithium soap greases and high
quality lithium complex greases. The key technologies
outlined are: yield improvers for simple lithium greases;
bleed improvers for both simple and lithium complex
greases in a variety of different base oils; and enhancers
which can be used to improve the thermal stability and
dropping points of simple lithium greases
This paper also demonstrates that lithium complex
lubricating greases that utilize biobased synthetic esters
as base oils can be readily produced. The technology
has resulted in the development of environmentally
considerate higher performance lubricating greases.
Acknowledgements
The authors wish to acknowledge many co-workers and
departments within The Lubrizol Corporation for their
contributions to this work.
to Make Simple and Complex Lithium Greases’~
NLGI Spokesman (2007) Volume 71 pp17-24
(9)
Lorimor, J.J., “Improving the Heat Resistance of
Simple Lithium Soaps Using Borated Additives’~
77th NLGI Annual Meeting, Bonita Springs, FL,
14th June 2010
(10)
Grease Production Survey Report 2012, NLGI,
Kansas City, Missouri 64112 (wwwNLGI.org)
(11)
Ward, Jr., W. C., and Fish, G., “Development
of Greases with Extended Grease and Bearing
Life Using Pressure Differential Scanning
Calorimetry and Wheel Bearing Life Testing’
NLGI Spokesman (2010) Volume 74(5) pagesl427
(12)
Ward, Jr., W C., and Qureshi, F.S. “Influence of
components blended to a target base oil viscosity
on liquid phase and lithium grease properties”
NLGI Spokesman (2009) Volume 74 (1) pages
21-31
(13)
Waynick, J.A. “Polyurea Grease with Reduced
Oil Separation’~ US Patent 4,759,859, Jul. 26,
1988, USPTO
(14)
Bessette, P.A., “Manufacturing Grease Using Dry
Technology’~ NLGI Spokesman (2002) Volume
65(11) pages 14-17
(15)
Honary, L; “Market Opportunities in Biobased
Lubricating Greases’~ 76th NLGI Annual
Meeting Address 2009, Loews Ventana Canyon,
Tucson, AZ, June 15th 2009
(16)
Honary, L; “An Update on the Use of Microwaves
in Manufacturing Grease” paper #1302 80th
NLGI Annual Meeting Loews Ventana Canyon,
Tucson, AZ, June 16th 2013
(17)
Fish, G., Robinson. P, and McSkimming, N.
“Understanding Component Requirements for
Formulating High Performance Environmentally
Acceptable Greases” ASTM symposium on
Environmentally Considerate Lubricants,
December 9, 2013, Tampa, FL
References
(1)
NLGI Grease Guide, 5th Edition, NLGI 2006
(2)
ELGI Reach consortium presentation, 18th ELGI
Annual Meeting 2006, Prague, Czech Republic
(3)
Klemgard, E.N., “Lubricating Greases’~ (1927)
The Chemical Catalog Company, Inc.
(4)
Graham, D.S., Masters, K. and Scott, “Grease
Manufacturing Methods’~ NLGI Spokesman
(1992) Volume 56 page 363
(5)
Krol, R., “Planning, Design and Construction of
Specialty Lubricants Plant’~ NLGI Spokesman
(1993) Volume 57, page 490
(6)
Polishuk, A. T., “Lubricating Greases from
Preformed Soaps” NLGI Spokesman (2001)
Volume 65 (1) pages 12-15
(7)
Morgan, D., Kay, J.S. and Coe, C., “Critical
Variables in Lithium Complex Grease
Manufacturing” 80th NLGI Annual General
Meeting paper #1313, Tucson, Arizona, 2013
(8)
Nolan, S.J. and Zeitz, J.B. “Anhydrous Lithium
Hydroxide Dispersion: A New and Efficient Way