Monitoring Grease Production by Reaction Calorimetry and

Subscriber access provided by FLORIDA ATLANTIC UNIV

Article

Monitoring grease production by reaction calorimetry and thermoanalytical methods as an alternative to dropping point determination Luc Vincent, Sébastien Barale, Aurélie Sandeau, Reina Véronica Castillo, Nicole Genet, and Nicolas Sbirrazzuoli Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01920 • Publication Date (Web): 09 Sep 2017 Downloaded from http://pubs.acs.org on September 13, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Monitoring grease production by reaction calorimetry and thermoanalytical methods as an alternative to dropping point determination

Luc Vincent1, Sébastien Barale1, Aurélie Sandeau², Reina Véronica Castillo2, Nicole Genet2, Nicolas Sbirrazzuoli1,*

1

Université Côte d’Azur, Institut de Chimie de Nice, UMR CNRS 7272, 06100 Nice, France.

2

TOTAL, Centre de recherche de Solaize (CReS), Chemin du Canal, 69360 Solaize.

* [email protected]

1 ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 22

Abstract The present research work concerns the thermodynamic study of lithium grease production by reaction calorimetry. In addition, several thermoanalytical techniques such as DSC and rheology were employed to highlight grease thermal events. The results showed that the cooling rate mainly controls the crystallization of soap fibers and the formulation influences the reaction heat of saponification. The liquid fraction method (LFM) has been evaluated for both simple and complex lithium greases as a substitution technique to dropping point. For Lithium grease, the results showed a very good correlation between LFM data and standard dropping point measurements. On the other hand, the LFM method was not applicable to complex lithium soap for dropping point determination by DSC, while it was shown that shear strain sweep led to a good correlation with dropping point values.

Keywords: Lithium grease production; saponification; liquid fraction method; reaction calorimetry; thermal analysis; rheology.


Page 3 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1. Introduction The manufacturing of greases is known since the beginning of the XXth century, nonetheless it remains an empirical domain1. A good understanding of the grease thermal behavior during the cooking and cooling steps provides an accurate control of the process and an optimization of the production time. All the parameters of the grease fabrication process have an influence on the final properties of the grease. For example, the soap fibers size is controlled by the cooling rate and the fiber network give the mechanical properties of the grease. Process optimization requires investigations on the physical and the chemical events as functions of the temperature. Several techniques have been used to characterize physical properties of oil products such as Differential Scanning Calorimetry (DSC)2 or Pressure Differential Scanning Calorimetry (PDSC)3. Calorimetry is a technique which measures the heat flow variation versus time (at a given constant temperature) or versus temperature. In particular, reaction calorimetry (RC) can be an appropriate tool to study the influence of several parameters on grease production because the mixing system available is well adapted to grease production processes4,5. Compared to the DSC, the main advantage of reaction calorimetry is to dispose of mixing system. Thus, with these thermal techniques it is possible to follow the reaction during each step of the process. Users can obtain information on the reaction duration and enthalpy of phenomena like dehydration, saponification and melting of simple lithium soap. Finally, the adequate process can be selected when the grease that presents the optimal properties is obtained. This technique requires few matters and is transposable to any processes for simple greases. The aim of this study is to show the benefits provided by the use of reaction calorimetry in association with DSC and rheology for the industrial elaboration of lithium soap and complex


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 22

lithium soap and to better understand reactions taking place during the industrial process. In addition, new methods for substitution of dropping point technique will be proposed for both simple and complex lithium greases. 2. Experimental 2.1. Reaction calorimetry (RC) Reaction calorimetry measurements were performed with a C80 reaction calorimeter commercialized by Setaram. Measurements were made using the membrane mixing cell and PTFE membranes. The mixing was performed by a system developed in our laboratory and specifically designed for grease production. 2.2. Differential scanning calorimetry (DSC) DSC measurements were carried out on a Mettler-Toledo DSC 1 equipped with a FRS5 sensor and STAR© software for data analysis. Temperature and enthalpy calibrations were performed by using indium and zinc standards. Samples crucibles were filled with 8 mg of lithium soap and placed in 40 µL aluminum crucibles.

2.3. Dropping point determination (DP) The dropping point of a lubricating grease is the temperature at which it passes from a semisolid to a liquid state under specific test conditions. It is a measure of the cohesiveness of the oil and thickener of grease. Dropping point measurements have been performed at a heating rate of 2 K min-1 using a DP70 Dropping Point System commercialized by Mettler-Toledo.


Page 5 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

2.4. Rheology Rheological analyses were realized with a rotational rheometer (Kinexus Pro+ Malvern) at 25°C using plate-plate geometries (25 mm diameter, 0.5 mm gap). Strain sweep tests, at a frequency of 1 Hz, were previously performed on each sample to determine the linear viscoelastic region. All samples were stored at room temperature. Before each rheological test, grease samples were homogenized to erase the material aging.

2.5. Grease preparation Simple Lithium greases samples (LiS) were prepared in situ into the calorimeter through a saponification reaction between 12-hydroxystearic acid (12-HSA) and monohydrated lithium hydroxide (LiOH, H2O) within a naphthenic base oil medium. The formulation of the grease was defined in order to reach a specific NLGI grade of 2. The NLGI grade expresses a measure of the relative hardness of grease used for lubrication, as specified by the standard classification of lubricating grease established by the National Lubricating Grease Institute (NLGI). The reactants were introduced inside the calorimeter equipment with the following repartition between both parts of the calorimetric cell: the lithium hydroxide was placed in the upper part with 50 % of naphthenic base oil and 12-hydroxystearic acid was incorporated in the bottom part. Concerning complex lithium grease samples (LiX), the azelaic acid complexing agent was introduced in the same part as 12-HSA. Greases production processes are well-known since the beginning of XXth century1. A grease production requires typically two heating steps and one cooling step. An isothermal step can be added between both heating rates to optimize saponification reaction as shown on Fig. 1. Several parameters such as heating rate and isothermal duration can be adjusted to optimize grease fabrication. The thermal and mechanical performances of the grease are mainly related to the process. In this work, the process used is described by the following steps. The first 5 ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 22

heating step was performed at a heating rate of 1 K min-1 from 60 °C to 115 °C. During this first step, the melting phenomenon of 12-HSA is occurred. An isothermal step was then performed at 115 °C during 45 minutes. The saponification reaction was initiated by perforating the PTFE membrane to generate the mixing between 12-hydroxystearic acid and lithium hydroxide into naphthenic oil. The saponification occurs during the isothermal step at the temperature of 115 °C. The final step was composed of a heating rate at 1°C.min-1 from 115 °C to 215 °C. The cooling step was performed at a cooling rate of -1 °C.min-1 from 215 °C to room temperature, i.e. 20°C in this study.

3. Results / discussion 3.1. Obtention of simple lithium soap

An example of curves obtained during the LiS cooking step is reported in Fig.1. The first thermal event is an endothermic phenomenon characteristic of 12-HSA melting. The melting temperature measurement of 12-HSA (peak temperature at 81,1 ± 0.5°C (A), Tonset at 75,2 ± 0.5°C and Tendset at 85,0 ± 0.5°C, see Fig.1) was in agreement with literatures values (82 ± 1°C 6 ).


Page 7 of 22

210

150

Saponification

Exo

200 190

120

175°C

180 170

90

160

45 min.

150

60

140

Contacting reactants

30

130 120

115°C

110 0

•

C

B

Gap

100

•

90 80

81°C

-30

A -60 0

70 60

• 30

Temperature / °C

Heat Flow / mW

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

60

90

120

150

180

50 210

Time / min

Fig. 1. Heat Flow variation obtained by reaction calorimetry during the cooking step of simple lithium soap (red: temperature into the measuring cell).

After membrane perforation at 55 minutes (see. Fig.1), all products were mixed and an exothermic phenomenon was immediately recorded. C80 calorimeter has a high time constant (around 360s). Thus, to correct the measured thermal effect, a numerical treatment was applied using special software developed in our laboratory7. The exothermal event was related to the reaction between lithium hydroxide and 12-HSA as an acid-base reaction. The reaction starts immediately and generates water. Dehydration heat flow was masked by the high enthalpy of saponification. The duration of reaction was evaluated at 45 minutes (section in blue on the Fig.1). The gap observed between 55 min (C) and 100 min on the baseline was explained by the heat capacity (Cp) variation. The baseline level after the reaction was higher due to the heat capacity decreases during the reaction. The mixture was then heated to 7 ACS Paragon Plus Environment

Energy & Fuels

complete soap formation and dehydration. Melting point of lithium hydroxystearate was reported to be around 180°C. The value obtained on the thermogram of Fig. 1 is around 175°C (B), which is in good agreement with literature8. However the broad shape of the thermal event does not correspond to the thermal fingerprint of the melting of a pure compound. The experimental conditions were modified in order to better highlight the melting phenomenon: a cooling step was added after the isothermal step from 115 °C to 90°C followed by a heating to higher temperature (until 240°C) (see. Fig.2).

20 10 0

Heat flow / mW

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 22

-10 -20 -30 -40

Exo -50 -60 120

140

160

180

200

220

Temperature / °C

Fig. 2. Lithium soap melting during the grease cooking step (red LiS no cooling step, black LiS with cooling step)


Page 9 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

These modifications provided a sharper melting peak at higher temperature. In this case, the melting point of soap was determined more accurately and a value of 187,0°C ± 0.5°C was measured using the onset temperature of the melting peak (Tonset). Lithium Greases are composed of a soap fiber network whose morphology strongly impacts the final performances in particular thermal and mechanical stabilities9,10,11. The structure of the network can be controlled using appropriate heating and cooling rates during the processes. The combination of short and long fibers provides interesting properties1. The length of the fibers is controlled by the cooling rate. The faster is the cooling rate, the shorter are the fibers12. Indeed, the system has more time to crystallize and longer fibers are built when temperature decreases slowly. Enthalpy of crystallization is also modified with the cooling rate (Table 1). If the sample has more time to crystallize, the final sample crystallinity is higher, leading to a higher crystallization enthalpy and the shape of curves is substantially different as seen in Fig. 3. These effects are perfectly highlighted by calorimetric measurements (Table 1 and Fig. 3). The lower cooling rate provides a peak separation with at least two thermal events as observed at -0.3°C.min-1 with a shoulder at 157 °C and a peak at 168 °C .


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 22

Fig. 3. Influence of the cooling rate on the crystallization of lithium soap for LiS grease.


Page 11 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 1 Temperature and enthalpy of crystallization of the grease LiS as a function of cooling rate Ref Cooling rate Grease (°C.min-1) LiS 1 2 3

0.3 0.8 1.0

Peak Temperature Tpeak (°C) 170.4 ± 0.5 159.5 ± 0.5 158.2 ± 0.5

Onset Temperature Tonset (°C)

Endset Temperature Tendset (°C)

Enthalpy (J.g-1)

174.3 ± 0.5 164.1 ± 0.5 162.7 ± 0.5

162.0 ± 0.5 146.7 ± 0.5 151.4 ± 0.5

11 ± 1 7±1 7±1

3.2.Obtention of complex lithium soap The thermogram obtained with reaction calorimetry measurement during the cooking of complex lithium soap (LiX) is shown in Figure 4. The overall shape of the thermogram of the complex lithium soap is very similar to that obtained with lithium soap. The first thermal event occurring between 60°C and 85°C is attributed to the melting of 12 HSA. The second thermal event is the result of the convolution of several thermal effects. Indeed, two main reactions occur in parallel. Each acid react with lithium hydroxide to give soap and water. 12 HSA and one part of lithium hydroxide are reacting while azelaic acid is melting. The second part of lithium hydroxide reacts with liquid azelaic acid. These two reactions release water. Dehydration and saponification reactions are exothermic whereas melting of azelaic acid is an endothermic event. The overall thermal event mainly reflects the exothermic effects because their intensities are higher than the endothermic effect. The enthalpy of saponification is higher. The melting of lithium stearate is observed at around 175°C and the melting of lithium azelate is not visible below 200°C. Heat flow variation measured during complex lithium soap formation isn't so different from that of simple lithium soap though mechanism of reaction is different. At this stage it isn't possible to come to a conclusion about the complexation. The characterization of grease by dropping point measurement is necessary to confirm obtaining complex lithium soap.


Energy & Fuels

180

200

Exo

180 160 140

60

120 100

0

Temperature / °C

120 Heat Flow / mW

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 22

80 60

-60

40 0

30

60

90

120

150

180

Time / min

Fig. 4. Thermogram obtained with reaction calorimetry measurement during the cooking of complex lithium soap (LiX).

3.3.Grease characterization To ensure that grease produced in the calorimeter corresponds to grease targeted and to the industrial requirements, three tests are performed in industry. These tests are named: dropping point, NLGI grade evaluation and basicity test. For simple lithium soap samples (LiS) and complex lithium soap samples, the desired NLGI grade is the grade 2, the dropping point of these samples must be close to 180°C ± 7°C and 195°C ± 7°C respectively and the basis character have to be revealed by the test. If one or more tests do not correspond to the targeted values, this means that the synthesis of the greases was not correctly done. All results presented in this work were obtained on adequate greases.


Page 13 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

3.3.1.

Dropping point

The dropping point is measured with a standardized test given by procedures in ASTM standards D556 and D2265 13. The dropping point is defined as the temperature at which the grease goes from a semi-solid to a liquid state under specific test conditions. Because most of the physico-chemical transitions lead to heat exchanges, they can be measured by DSC with high accuracy. Thus, in the following the transition temperature measured by DSC was compared to dropping point determinated by ASTM D556. Mettler-Toledo society14 has used DSC to evaluate the dropping point of edible fat with success. The method applied is called liquid fraction method (LFM). In this study, this method was transposed to the evaluation of the dropping point of lithium greases. According to this method, the temperature of dropping point of edible fat corresponds to the temperature at 95% of conversion. All measurements have been conducted at a heating rate of 10 K min-1 between 20 and 320°C. Heat flow variation shows an endothermic event corresponding to lithium stearate melting (Fig. 5). The shape of the DSC curve is well defined in agreement with expected results14. Temperatures at 95% conversion of ten samples are compared to each dropping point values and summarized in Table 2.


Energy & Fuels

0 100

Exo -1

-2

60

-3

40

20

Extent of conversion

80

Heat flow / mW

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 22

-4 0 -5 160

170

180

190

200

210

220

T / °C

Fig. 5. Application of liquid fraction method to lithium soap. Measured heat flow (blue, left axis) and extent of conversion (red, right axis).

Table 2 95% melting temperature compared to ASTM dropping point for lithium grease (LiS) Sample Id lithium stearate

Temperature at 95% conversion by DSC (°C) precision given by the manufacturer ± 1°C

1 2 3 4 5 6 7 8 9 10

195 204 208 189 189 194 190 194 187 188

Dropping point ASTMD556 (°C) precision given by the manufacturer ± 7°C

198 202 206 187 189 191 188 194 188 187


Page 15 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

The values measured by DSC are in very good agreement with those obtained for dropping point using ASTM D556 method. In the case of dropping measurements, bleeding can occurs and the test has to be reproduced. With a DSC measurement the bleeding problem is removed and measurement duration is reduced. Because of the high sensitivity of the apparatus, DSC measurement allows dropping point determination with more precision. In addition, the measurement is easier and faster which is also an important advantage in regard to industrial applications. Thus the method of the liquid fraction seems easily transposable in the case of lithium soap.

Complex lithium soap has higher dropping point than lithium soap. Generally, complex lithium soap without additives has a dropping point near to 250°C. Heat flow measured by DSC shows several thermal events not present for lithium soap (Fig. 6). Thus the melting point of lithium stearate and the melting point of lithium azelate and lithium diazelate can be observed on thermogram. We first observe an endothermic peak at a temperature onset of 181 °C ± 1°C, that correspond to the melting of lithium stearate, followed by at least three melting points at 248°C, 269°C and 280°C respectively.


Energy & Fuels

0.00

100

Exo

80

60

-0.10

40 -0.15 20

Extent of conversion

-0.05

Heat flow / mW

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 22

-0.20 0 -0.25 50

100

150

200

250

300

T / °C

Fig. 6. Liquid Fraction Method (LFM) applied to complex lithium grease (LiX).

Temperature values taken at 95% conversion do not correspond to dropping point values (data not presented here). A better agreement between the two methods is obtained when an extent of conversion of 98% is used instead of 95% (Table 3), but it still exist a great difference between the values obtained from the two methods and no any correlation is observed.


Page 17 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 3 98% melting temperature obtained from DSC measurements compared to ASTM dropping point for complex lithium grease (LiX) Sample Id lithium stearate 1 2 3 4 5 6 7 8 9 10

Temperature at 98% conversion by DSC (°C)

Dropping point ASTMD556 (°C) precision given by the manufacturer ± 7°C

precision given by the manufacturer ± 1°C

280 280 272 278 288 258 280 279 270 252

262 257 284 290 287 270 295 282 292 269

This method cannot be used for complex lithium greases. This can be explained because dropping point of complex lithium soap is linked to the melting of a complex fiber network. This network is the result of several soaps formation. The structure of the fiber network confers mechanical properties to the grease and in particular its thermo-mechanical resistance. The mechanical properties can be characterized by rheological measurements15,16,17,18,19,20. The ASTM method is mainly related to the mechanical response of the sample. This explains why the values obtained are not directly correlated with the values obtained with DSC. Indeed, the calorimetric response reflects the temperature at which 95% of the melting enthalpy of the grease has been absorbed by the calorimeter. This temperature does not correspond necessarily to the temperature were the sample start to flow. In this context, we decided to investigate a potential link between rheological properties and dropping point. This measurement was performed on complex lithium soap (Fig. 7). Based on dropping point definition, the destruction of the fiber network induces the loss of grease mechanical resistance. In rheological analysis, the destructuration of a physical network structure can be highlighted during a shear strain sweep by a crossing between storage modulus (G’) and loss


Energy & Fuels

modulus (G’’). For gels systems, the intersection of G' and G” is used to detect gel-sol transition. As mentioned in earlier studies, the grease loses all its mechanical properties in the same way that it loses its mechanical stability when the dropping point is reached21. To check the validity of the proposed method, an exploratory study has been driven on several complex greases with various dropping points.

100000 G' storage modulus G" loss modulus

G' & G" / Pa.s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 22

10000

1000

100 0.1

1

10

100

1000

Shear Strain / %

Fig. 7. Shear strain sweep of complex lithium soap LiX at 25°C using plate-plate geometries (25 mm diameter, 0.5 mm gap) at a frequency of 1 Hz. For each complex lithium grease, the dropping point has been measured by a DP700 Dropping point system and the crossing point (S) between loss modulus and storage modulus have by determined by rheology. The percentage of shear strain, observed at the crossing point (S), increases with the dropping point temperature. A representation of the relation between the dropping point and the crossing point S is shown in Fig. 8. Moreover, the shear strain obtained at the flowing point seems strongly correlated to the dropping point


Page 19 of 22

temperature as shown in Fig. 8. In the case of complex lithium grease obtained by the same process the dropping point could be estimated using rheological measurements. Table 4 Flowing point of a complex lithium soap Reference of the grease LiX with is dropping temperature (°C) LiX298 – 298 °C LIX296 – 296°C LIX292 – 292 °C LiX290 – 290 °C LiX282 – 282°C

Shear strain values of flowing point (%) 48 46 39 34 21

50

Shear strain values of flowing point / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

45

40

35

30

25

20 280

285

290

295

300

Dropping temperature / °C

Fig. 8. Shear strain values of flowing point vs. dropping temperature for complex lithium soap LiX.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 22

4. Conclusion The present work reveals that reaction calorimetry can be considered as an interesting technique to understand thermal events during grease fabrication and predict their final properties before industrial scale production. Accuracy of temperature events measurements can be exploited to extract reliable data and transpose them to industrial process. Melting point can be determined with high accuracy. The dropping point temperature which is the key property of lithium soap can be determined with high accuracy using the liquid fraction method (LFM) by DSC. This method allows obtaining faster results and can be used to overcome oil leakage observed in ASTM method. Unfortunately, LFM method is not applicable in the case of complex lithium greases due to their particular network. To overcome this, we investigate a promising method based on rheological characterization of the network destructuration obtained by shear strain sweep and its correlation with dropping point temperature.

5. Acknowledgements The authors gratefully acknowledge TOTAL Company for the fruitful collaboration and the financial support.


Page 21 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

References

(1) Boner C.J., Manufacture and application of lubricating greases. National Lubricating Grease Institute, library of congress catalog card number. Original edition 1954 ; reprint 1983, 54-11031. (2) Santos J.C.O., Garcia dos Santos I.M., Souza A.G., Sobrinho E.V., Fernandes Jr V.J., Silva A.J.N. Thermoanalytical and rheological characterization of automotive mineral lubricants after thermal degradation. Fuel 2004, 83, 2393-2399. (3) Zhou J., Xiong Y., Liu X. Evaluation of the oxidation stability of biodiesel stabilized with antioxidants using the Rancimat and PDSC methods, Fuel 2017, 188, 61-68. (4) Drabik J., Trzos M., Ilowska J., Bereska B. Complex greases produced in calorimetric reactor. Part I. Optimization of process parameters with respect of the grease quality, Przem. Chem 2013, 92, 10, 1846-1849. (5) Ilowska J., Szwach I., Bereska B., Gniady J., Szmatola M., Semeniuk I., Drabik J., Kozdrach R. Complex greases produced in calorimetric reactor. Part 2. Effect of process parameters on properties of the greases, Przem. Chem 2013, 92, 10, 1850-1852. (6) Lide D.R., Frederikse H.P.R., CRC handbook of chemist and physics. Boca Raton, FL: CRC Press. 1993; 3465. (7) Barale S., Vincent L., Sauder G., Sbirrazzuoli N. Deconvolution of calorimeter response from electrical signals for extracting kinetic data, Thermochimica Acta 2015, 615, 30–37. (8) Delgado M.A., Sanchez M. C., Valencia C., Franco J. M., Gallegos C., Relationship among microstructure, rheology and processing of a lithium lubricating grease, Chemical Engineering Research and Design, 2005, 83(A9): 1085–1092. (9) Podlennykh L., V., Ishchuk L.P. Influence of cooling rate and soap concentration on isothermal crystallization temperature of lithium greases, Plenum Publishing Corporation 1987; 50, 9. (10) Vold M.J., Colloidal structure in lithium stearate grease, J. Phys. Chem. 1956, 60(4) 439442. (11) Bondi A.A., Proceedings of the Third World Petroleum Congress The Hague, E.J. Brill; First edition, 1951. (12) Martín-Alfonso J.E., Valencia C., Sánchez M.C., Franco J.M., Gallegos C. Influence of some processing variables on the rheological properties of lithium lubricating greases modified with recycled polymers, Int. J. Materials and Product Technology 2012, 43(1-4), 184-200. (13) ASTM D556, Test Method for Dropping Point of Lubricating Grease and ASTM D2265, Standard Test Method for Dropping Point of Lubricating Grease Over Wide Temperature Range, ASTM International, West Conshohocken, PA, 2010, www.astm.org (consulted on 10/28/2016). (14) Mettler-Toledo, Thermal analysis Usercom n°11, 2000, www.mt.com (consulted on 10/28/2016). (15) Franco J.M., Delgado M.A., Valencia C., Sánchez M.C., Gallegos C. Mixing rheometry for studying the manufacture of lubricating greases, Chem. Eng. Sci. 2005, 60, 2409 – 2418. (16) Delgado M.A., Valencia C., Sanchez M.C., Franco J.M., Gallegos C. Influence of Soap Concentration and Oil Viscosity on the Rheology and Microstructure of Lubricating Greases, Ind. Eng. Chem. Res. 2006, 45, 1902-1910. (17) Martın-Alfonso J.E., Moreno G., Valencia C., Sanchez M.C., Franco J.M., Gallegos C. Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating greases modified with virgin LDPE, J. Ind. Eng. Chem. 2009, 15, 687–693.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 22

(18) Delgado M.A., Valencia C., Sanchez M.C., Franco J.M., Gallegos C. Thermorheological behaviour of a lithium lubricating grease, Tribol. Lett. 2006, 23(1), 47-54. (19) Delgado M.A., Franco J.M., Valencia C., Kuhn E., Gallegos C., Transient shear flow of model lithium lubricating greases, Mech Time-Depend Mater 2009, 13, 63–80. (20) Yonggang M., Jie Z.A. Rheological model for lithium lubricating grease, Tribology International 1998, 31(10), 67-70. (21) Agernas O., Tengberg T., Development of two methods to evaluate lubricating greases using a rheometer, Chambers, Göteborg, Sweden 2011.


Monitoring Grease Production by Reaction Calorimetry and

Recommend Documents