••,
Critical Variables in Litbium
Complex Grease Manulacturing
‘I
1
•S
I
Presented at the
By
80th NLGI Annual General Meeting
Tucson, Arizona
15th— 18th June 2013
David Morgan STRATCO, Inc.
John S. Kay, P.E., CLGS STRATCO, Inc.
Chuck R. Coe, CLGS, CLS Grease
Technology Solutions, LLC
Abstra~
Lithium complex greases represent a high performance
grease type with specialized applications, and these
greases are steadily growing in widespread markets.
Several options are available to the grease manufacturer
regarding raw materials and manufacturing methods.
The selection of the complexing agent has economic
ramifications and also performance and procedural
considerations. Due to the differences in reactivity of the
complexing agents, there may be optimum temperature
profiles for each material. A lab scale STRATCO0
Contactor~ reactor is used to make lithium complex
greases using two common complexing agents, namely
azelaic acid and sebacic acid. This type of reactor is
used in order to have better control of the temperature
profile during the process. Holding the base oil and
soap concentrations constant, the temperature profiles
are varied and the physical properties are analyzed and
compared to establish optimum reaction conditions.
Introduction
Greases made from Lithium possess many desirable
properties, such as good water resistance, high
temperature properties, shear resistance and pumpability
as compared to other alkali metal based greases. Lithium
complex grease is a great all-purpose lubricant because
of its uses over a wide range of temperatures. According
to a recent NLGI Production Survey, approximately 75
percent of the grease sold worldwide is based on either
simple lithium soap or lithium complex thickener [1].
–
–
–
Lithium complex grease continues to slowly displace
simple lithium grease because of its higher dropping
point. This makes lithium complex ideal for higher
temperature applications.
Lithium complex grease has a higher dropping
point because of the presence of a complexing agent.
Lithium complex grease is made with two molecules:
the co-crystallization of a lithium soap molecule and
a lithium dibasic salt molecule [2]. These dibasic salts
are made by the saponification of a dicarboxylic acid
with lithium hydroxide. Dicarboxylic acids have an
acid functional group on both ends of the short-chain
carbon molecule. Typical complexing agents are: azelaic
acid, sebacic acid, adipic acid and sometimes boric
acid [2]. Of these, azelaic acid and sebacic acid are the
most widely used. The fluctuating raw material cost of
these two chemicals can be a deciding factor on which
complexing agent is used by a manufacturer. Due to
the differences in reactivity of these two materials, it is
important to recognize the differences in manufacturing
processes inherent in each.
The general consensus, based on experience, regarding
the strategy of reacting lithium complex greases is
the need for allowing the initial simple saponification
reaction to precede the reaction of the complexing
agent. This is generally accomplished by maintaining
the ingredients at a lower temperature range for a
period of time to allow the simple reaction to be
8VOLUME 78, NUMBER 5
NLGI
completed, followed by the elevation to the final reaction
temperature. As with most grease manufacturing
practices, procedures vary from manufacturer to
manufacturer. The use of conventional kettles for the
reaction stage involves some inherent limitations of
heating rates due to the heating surface available and
the limited heat transfer rate associated with this type of
vessel. The use of the pressure rated Contactor reactor
allows faster heating and improved temperature control
due to its greater heating surface and higher heating and
cooling rates. The goal of this study is to determine the
optimum heating profile and manufacturing practice
using the Contactor reactor in order to achieve desirable
properties with the limited residence time in the reactor.
This will allow the manufacturer to manufacture produce
this high performance product in the shortest time
for a quicker turnover and the minimum lead time for
their customer’s product. Differences in manufacturing
procedures include heating rates, holding times, the
employment of a quench stage before transfer to the
finishing kettle, and the consideration of a one-step
versus two-step procedure.
The use of a quench stage in the Contactor reactor
offers decidedly different conditions when compared to
quenching, or cooling, in the finishing kettle, namely:
(1) the quenching can be accomplished much quicker
in the Contactor reactor and (2) the crystallized fibers
will experience a higher shear in the Contactor reactor,
resulting in a moderate milling effect. There is certainly a
processing time advantage in having the base grease start
at a lower temperature in the finishing kettle.
The strategy of a one-step versus two-step procedure
represents a compromise between minimizing the
manufacturing time and ensuring that the complexing
reaction does not interfere with the simple reaction.
The one-step method is characterized by the addition
of all ingredients at the beginning of the reaction stage
while the two-step method involves the addition of the
complexing agent only after the simple reaction has
been completed. Regarding the two-step method, the
authors are aware of two different practices employed
with the Contactor reactor: (1) cooling the Contactor
reactor product after the simple reaction is completed
and introducing the complexing agent for the balance
of the reaction process in the Contactor reactor and
(2) transferring the simple base grease and adding the
complexing agent in the finishing kettle. This study
will employ the former practice in order to minimize
manufacturing time.
In summary, the key issues addressed in this study
include:
Identifying the optimum intermediate temperature
target representing the upper limit of the range of the
simple reaction
• Establishing the minimum time required in the simple
reaction region
o Establishing the minimum time required for the
complex reaction
o Determining the effects of quenching in the Contactor
reactor
o Verifying the need for a two-step process
o
Equipment and Procedures
Lithium complex grease batches were produced in the
laboratory of Stratco, Inc. in Scottsdale, Arizona using a
lab scale Stratco~ Contactor” reactor. Critical variables
such as heating rates, intermediate temperatures, reaction
times and quenching techniques were studied through
analysis of the batch properties. Properties evaluated
were dropping point and penetration, including
unworked, worked and 10,000 stroke. The dropping
point was indicative of the quality of the complexing
reaction while the penetrations were used to evaluate
yield efficiency and mechanical stability.
In order to simplify the comparisons, a single, simple
base oil was used, which was not specifically selected to
optimize yield or dropping point. It was also decided to
use the same soap content (11%) and not to use additives
to avoid synergistic effects on the complexing agents.
The equipment usedfor this project included the
following:
STRATCO® Model VJS 8-12.5-17.2 Contactor’~
reactor
o Groen Model NSP Double-Motion kettle
• Viking Model H32 gear pump
o Cuno Auto-Klean filter (0.005 in. spacing)
Chemicolloid Labs Model G-5 mill
o
-9
NLGI SPOKESMAN, NOVEMBER/DECEMBER 2014
NLGJJ
Figure 1 provides a picture of the equipment configuration.
Figure 1. Equipment Arrangement
The general procedure was to perform the
reaction phase in the Contactor reactor and then
manually transfer the product to the finishing
kettle. The procedures varied in the reaction phase
with the different raw materials. The product,
once transferred to the kettle, was recirculated
by-passing the mill and filter to facilitate cooling.
A portion of the base oil was withheld from the
contactor and added to the kettle for cooling and
dilution. When suitably cooled, the circulation
was stopped, the mill set at 5 microns and
energized and milling performed prior to drawing
samples. All the batches throughout this study
were quenched with a portion of base oil in the
kettle and milled at 5 microns when the product dropped to 100°C for 10 minutes before taking
samples.
The base oil used was a Group II 500 Neutral paraffinic oil. The other raw materials supplied
were standard grade materials that are used in the grease industry. As mentioned previously, the
additives were left out of the greases for this project to avoid synergistic effects with the chemically
different complexing agents. The raw materials used were 12-hydroxystearic acid, lithium hydroxide
monohydrate, azelaic acid and sebacic acid.
All batches started at 80°C after the initial ingredients were added and melted. They were then
heated to an intermediate temperature over a specified period of time, then heated to 204°C to
complete the complexing reaction, although one batch was allowed to reach 2 10°C. For the twostep method the batch was cooled from the intermediate temperature to below boiling temperature
to add the complexing agent, then heated to 204°C. Although the water of reaction was vented to
control the pressure at 5.5 bar, the residual water/steam was allowed to remain for the addition of the
complexing agent in the two-step process in order to utilize the pressure when reheating to maintain
flow and assist in the discharge. Several batches were allowed to cool (quench) in the Contactor
reactor following the reactions, while the other batches were discharged and transferred immediately
to the finishing kettle at the maximum reaction temperature. Several of the sebacic acid trials were
performed as a two-step process while all the others were a single step process. Quenching in the
lab scale Contactor reactor was accomplished by cooling the thermal oil in the vessel jackets. In
commercial operations, quenching is typically accomplished with the addition of base oil.
The variables manipulated were: heating rates between the beginning, intermediate and final
temperatures, the intermediate temperature itself, as well as holding times at different temperatures.
Charts 1 and 2 illustrate the test design and variable conditions for the two complexing agents.
– 10 VOLUME 78, NUMBER 5
NLGI
Chart 1. Testing design conditions for azelaic acid
Batch Number
1
2
3
4
5
6
7
8
80°C
80°C
80°C
80°C
80°C
80°C
80°C
80°C
60
35
60
47
35
60
25
25
150°C
150°C
150°C
150°C
150°C
150°C
130°C
130°C
Hold Time
0
0
0
0
0
0
35
10
Ramp Time
35
30
60
30
65
30
50
50
204°C
204°C
204°C
204°C
204°C
204°C
204°C
204°C
Hold Time
0
0
60
0
0
0
0
0
Quench in Contactor Time
0
0
0
0
0
25
25
25
Starting Temperature
Ramp Time (mm)
Intermediate Temperature
Final Temperature
Chart 2. Testing design conditionsfor Sebacic Acid Highlighted batches used the two-step process
–
Batch Number
Starting Temperature
Ramp Time (mm)
9
10
11
12
13
14
15
16
17
18
19
20
80°C
80°C
80°C
80°C
80°C
80°C
80°C
80°C
80°C
80°C
80°C
80°C
60
35
60
60
60
25
25
15
15
15
25
20
Intermediate Temperature 150°C 150°C 150°C 150°C 135°C 130°C 130°C 130°C 121°C 121°C 130°C 130°C
Hold Time
0
0
0
0
0
35
35
45
15
15
35
10
Ramp Time
60
35
35
35
35
65
65
50
50
50
65
65
Final Temperature
204°C 204°C 204°C 204°C 204°C 210°C 204°C 204°C 204°C 204°C 204°C 204°C
HoldTime
60
0
0
0
0
0
0
0
0
0
0
0
Quench in Contactor Time
0
0
0
25
25
0
0
0
0
25
25
0
Experimental Results and Data
The greases were made in the Contactor reactor starting with the azelaic acid complexing agent then moving
on to the sebacic acid complexing agent. Data recorded included product temperature, thermal oil supply
temperature, vessel pressure and motor amperage versus time. Motor amperage remained steady throughout
testing. Time vs. Temperature plots were generated for all batches, which are shown in Graphs 1 through 5.
-11NLGI SPOKESMAN, NOVEMBER/DECEMBER 2014
Graph 1: Li~Complex Greases with Azelaic Acid
Comp~exing Agent not Quenched in the Contactor
220
1:
c~ 160
ci)
140
0
20
40
60
80
100
120
140
160
180
Time in Minutes
batch 1
batch 2
batch 3
batch 4
batch 5
Graph 2: Li~Complex Greases with Sebacic Acid
Complexing Agent I Step Process Non~Quenched in
Contactor
220
210
200
LI
190
w 180
170
160
150
ci) 140
130
120
ci)
0~ 110
aj 100
90
80
70
60
~-
0
10
20
30 40
50
60
70
80
90 100 110 120 130 140 150 160 170 180 190 200
Time in Minutes
Batch 9
~Batch 10
Batch 11
–
12-
VOLUME 78, NUMBER 5
Batch 16
—Batch 17
Graph 3: Li~Complex Greases with Azelaic Acid
Complexing Agent Quenched hi Contactor
220
200
U
a)
w 180
a)
~ 160
C-
w 140
-)
~ 120
a)
ci
2 100
a)
I-
80
60
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
Time in Minutes
batch 6
batch 7
batch 8
Graph 4: Li~Complex Greases with Sebacic Acid
Complexing Agent Quenched in Contactor
220
210
200
190
180
~ 170
160
150
CI)
140
130
120
~11o
100
90
80
70
60
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140 150 160 170 180
Time in Minutes
~Batch 12
Batch 13
Batch 18
Batch 19
– 13 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2014
150
Graph 5: Li-Comp~ex Greases with Sebacic Ac~d
Comp~exing Agent 2 Part Process
220
200
L)
180
1~~
~ 160
a)
140
~ 120
a)
Q.
100
I-
80
60
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140 150 160 170 180
Time in Minutes
Batch 14
Batch 15
Batch 19
Batch 20
The grease batches were tested for unworked penetration, 60 stroke penetration, as well as 10,000 stroke
penetration. These tests were performed in accordance with Cone Penetration ASTM D 217. Dropping
points were also determined using standardized test ASTM D 2265, °C. Charts 3 and 4 show the results of the
aforementioned tests. Chart 5 summarizes total residence time in the Contactor reactor for all test batches,
including charging time.
Chart 3. Test resultsfor azelaic acid complexing agent
Batch
Unworked
Penetration
60 Strokes
Penetration
10,000 Strokes
Penetration
1
2
3
4
5
6
7
8
287
318
294
322
294
279
274
268
292
329
313
318
304
286
279
278
339
381
349
377
338
309
304
364
– 14 VOLUME 78, NUMBER 5
Difference Dropping
6Ovs 10K Point°C
47
52
36
59
34
23
25
86
250
232
250
226
257
262
263
243
NLGI
Chart 4. Test resultsfor sebacic acid complexing agent Highlighted Batches used the two-step process
–
Batch
Unworked
Penetration
605trokes
Penetration
10,000Strokes
Penetration
9
10
11
12
13
14
15
16
17
18
19
20
309
301
278
267
281
271
273
280
278
273
268
279
311
298
294
262
265
272
262
280
280
263
265
273
351
378
381
383
379
284
279
295
302
338
280
281
Difference Dropping
6Ovs 10K Point°C
40
80
87
121
114
12
17
15
22
75
15
8
211
212
235
232
223
263
265
246
251
218
258
272
Chart 5. Total residence time in Contactor reactor
Batch
Hours
Minutes
Batch
Hours
Minute~
1
2
3
4
5
6
7
8
9
10
1
1
3
1
1
2
2
1
3
1
30
10
0
15
40
0
15
45
0
15
11
12
13
14
15
16
17
18
19
20
1
2
2
2
2
1
1
1
2
1
40
0
0
30
21
50
25
55
40
55
– 15 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2014
NLGI
Analysis and Conclusions
For the azelaic acid trials, the initial intermediate
temperature selected was 150°C based on previous
experience. The first trial ramped the temperature to the
intermediate target over 60 minutes, then rapidly heating
to 204°C over 35 minutes and transferred immediately
without a quench to the finishing kettle. This resulted in
a reasonable DP of 250°C, bearing in mind that this was
not additized and the base oil not optimized. The next
trial reduced the intermediate ramp time to 35 minutes,
which resulted in a lower DP and lower yield. The third
trial replicated the first except for increasing the final
ramp time to 60 minutes. This resulted in no change in
the DP, although a slight reduction in yield and greater
spread between penetrations. The fourth trial replicated
the first trial except reducing the intermediate ramp time
by approximately 15 minutes; this had negative effects
worse than the second trial. The fifth trial allowed a 35
minute intermediate ramp time and 65 minute final ramp
time with a comparable overall residence time. This
resulted in a marginal increase in DP at close to 260°C
with a slight reduction in yield compared to trial 1.
The last three trials included a quench stage in the
Contactor reactor. Trial #6 replicated the first trial but
included a quench to 182°C over a 25 minute span.
This resulted in a DP of over 260°C and a much better
yield. The next two trials explored a lower intermediate
temperature of 130°C. The seventh batch had a lower
intermediate ramp time, but included a hold at the
intermediate temperature resulting in holding it at this
lower range for 60 minutes, similar to trial #6. However,
the final ramp time was slightly longer. This resulted
in slight improvements in all test properties. The last
trial for azelaic acid reduced the intermediate residence
time to 35 minutes, which resulted in a marked negative
impact to DP.
sealed and heated. This is certainly very desirable in
simplifying the manufacturing process and minimizing
the manufacturing time. Quenching in the Contactor
reactor also saves time in finishing. The trials also suggest
that allowing approximately 60 minutes in the lower
intermediate range produces better dropping points.
The study demonstrates that a good dropping point can
be achieved with a reaction residence time for azelate
complex grease of approximately two hours.
The sebacic acid trials demonstrated a distinctly
different reaction profile. In order to achieve a dropping
point of 260°C, a two-step procedure was required. The
base oil, lithium hydroxide and 12-hydroxystearic acid
are placed in the Contactor reactor first, sealed and
heated to the intermediate temperature. The contents
are then cooled to below 100°C with jacket cooling and
the sebacic acid is then added to the Contactor reactor
and heated to 204°C. Final quenching in the Contactor
reactor had a negative impact on the physical properties
of the grease. Batches 14, 15 and 20 had the highest
dropping points without the final quenching and were all
two-step procedures. As with the azelaic acid, these trials
also demonstrated achieving optimum dropping points
with reaction stage residence times of approximately two
hours, even with the two-step procedure implemented.
The complexing agent chosen for production could be
due to monetary reasons, production reasons or both.
Azelaic acid and sebacic acid can both make good lithium
complex greases with excellent dropping points (over
260°C) having good yield and mechanical stability as
shown by the data. The study clearly demonstrates that
these two complexing agents require distinctly different
reaction procedures. Further optimization is likely
possible with the fully formulated greases to consider the
synergistic effects of base oils and additives, which could
provide higher dropping points and better yields.
The azelaic acid trials showed that a quench in the
Contactor reactor yields positive effects for dropping
point. These were all one-step procedures, meaning
that all the contents were added to the Contactor
reactor at the beginning of the reaction stage and then
– 16 VOLUME 78, NUMBER 5
NLGI
Acknowledgements:
The authors would like to thank John Lorimor CLS/CLGS of Axel Americas,
LLC, Buck Evans of Sea-Land Chemical, Co. and Aaron Read of North American
Lubricants, Co. for supplying all the raw materials and base oil for this project.
References:
Turner, D., “Grease Selection: Lithium vs. Lithium Complex”
Machinery Lubrication, January 2011
Polishuk, A.T., A Brief History of Lubricating Greases, 1998.
CaN for Papers
—
NLG~ 82~ Annu& Meeting
A call is hereby issued for technical papers for presentation at the NLGI 82~’ Annual
Meeting, which will be held at the Coeur d’Alene Resort, Coeur d’Alene, Idaho, USA from
June 6th-9th, 2015. You do not need to be an NLGI member in order to present a technical
paper at our Annual Meeting.
The NLGI 82n,d Annual Meeting theme is: Digging into Grease Lubrication’, Therefore,
papers related to grease applications, environmental concerns, performance or testing for
mining equipment are of special interest and will be given priority. How can greases
contribute to cost savings, improved performance and efficiency in mine operations?
Some lubricating products used in mines are: Heavy duty and EP greases, wire-rope
lubricants, open gear lubes and penetrating oils/greases.
Papers covering any other phase of grease chemistry, grease formulation or grease
manufacturing technology are also welcomed.
Technical papers approved for presentation at the Annual Meeting may be published in the
NLGI Spokesman after evaluation by the NLGI Editorial Review Committee.
Commercial Papers: NLGI will also accept up to 5 papers of a commercial nature.
Presentation of commercial papers will be on Tuesday afternoon during the NLGI Annual
Meeting and will not conflict with any other presentations or events. Commercial papers will
be accepted on a first come, first served basis. (A fee of $500 will be charged for all
commercial papers accepted for presentation.)
You may download the Author Information and Author Instructions forms for your technical
presentation, as well as the Commercial Presentation Application form, on our website:
htt~s://www. nI~i .org/caII-for-pa~ers/
If you are interested in submitting a technical or commercial paper for presentation, please
send your name, contact information and abstract to:
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Summit, MO 64063 USA
Phone 816/524-2500 FAX 816/524-2504 Email mariIyn~~nlqi.org
– 17 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2014