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942) was used in order to study if the relatively high sulphur concentrations observed in the above mentioned samples had any effect in the oxidation stability of the greases produced with those oil blends. In this method the grease is oxidized in a pressurized vessel at a temperature of 99˚C. Pure oxygen is injected in the vessel to a pressure of 110psi, and the degree of oxidation is measured by seen how much oxygen is consumed after 100 hours. The reduction of pressure for greases A 2, B 2 and C 2 was of only 2psi. Here we have to remember that these were “naked” greases (i.e. not additives were added to them).
Water resistance The resistance to water was measured in the greases based on the blends A 3, B 3 and C 3. As it has been mentioned these blends were made with a residue based naphthenic oil with asphaltene molecules in its composition. These asphaltenes are high molecular weight hydrocarbons that could contribute to improve the water resistance of the greases. Water wash out (ASTM D 41264) and water spray off (ASTM D 4049) tests were done on the greases based on A 3, B 3, and C 3, in order to test this theory.
Table 5 shows how the water wash out values are relatively low, and are comparable with similar greases based only on paraffinic Group I oils (data not shown). However, the water spray off are lower than expected for naked greases, with no polymer in their composition.
At work at Nynas Grease laboratory, Nynas Technology Centre, Nynashamn, Sweden.
Conclusions Table 5. Water wash out and water spray off of the grease samples.
The base oil industry is going through significant changes that are already affecting the availability of widely used base oils, mainly paraffinic Group I. These changes are driving the lubricant industry to re-consider the raw materials they are using, and in many cases to reformulate their products. In the process of reformulation many factors have to be considered, such as the base oil availability and price, as well as its properties and how they adapt to the existing formulations. Blends of naphthenic and paraffinic base oils (Group II and III) have shown to be a good alternative to paraffinic Group I, as they provide two of the main properties that disappear with Group I oils, e.g. solvency and viscosity. In this article it has been discussed how not all naphthenic oils are the same, and that by carefully selecting the right naphthenic/paraffinic combination one can achieve more than just replacing Group I oils, actually one can also improve different properties of the grease going from water resistance, oxidation stability to the temperature range where the grease can be used. These improvements pave the way to more effective formulations, where savings in thickener content and additives could be made.
References 1. Bastardo-Zambrano, L. and M. Fathi-Najafi, Base oil blends to meet the new demands of the lubricant industry, in LUBE Magazine. 2013, UKLA: U.K. p. 22-27.
2. Persaud, M., Guide to Global Base oil refining, in Lubes’N’Greases. 2014: U.S.A.
3. Yeo, R. (2014) Outlook’13: Europe Group I base oils face another difficult year. ICIS News.
4. Gill, G. (2014) Total to Revamp Gonfreville Base Oil Plant. Lube report.
5. Gill, G. (2014) Shell to Pull Plug on Pernis Base Oil. Lube report.
6. Tocci, L. (2014) Major shift in Base Oil Landscape. Lube report. 7. Lynch, T.R., Process chemistry of lubricant base stocks. 1 ed. Chemical Industries, ed. J.G. Peight. Vol. 116. 2008, Boca Raton: CRC Press. 367.
8. Fathi-Najafi, M., When the going gets tough... A heavy specialty oil for grease formulations (Part II). NLGI Spokesman, 2014. 78(5).
Different properties, and appearance, some of the greases studied.
LINK
www.nynas.com/base-oils
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LUBE MAGAZINE NO.126 APRIL 2015
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