Lube-Tech
The closure of Group I refineries has brought with it a deficit on the availability of high viscosity base oils. This deficit is having a major impact on the lubricant and grease industry since neither Group II nor Group III refineries can produce bright stocks. At the same time, there is a huge demand for lithium, which is used in the production of batteries for, among other things, mobile phones and vehicles.
This demand from the battery industry created a sudden price increase for lithium hydroxide during the last few years, and it is believed that prices will continue to increase as the world moves forward rapidly into the automobile’s electrification age.
The use of highly viscous naphthenic oils in lubricating grease formulations can be one of the solutions available for grease manufacturers today. Previous publications, e.g. [1], have indicated that the use of highly viscous naphthenic oils, and its blends with other base oils (mainly with paraffinic Group I, II and III oils), results in savings on soap consumption in most of the existing thickener systems, while keep the same grease performance.
The aim of this paper is to evaluate the performance of two-high viscosity naphthenic oils in lithium, lithium complex and bentonite (clay) greases. All these thickener systems, along with high viscosity base oil, can be used successfully in many applications, e.g., in the sugar mill industry. It is notable that high viscosity naphthenic oils will work excellently in most of the existing thickener systems such as aluminum complex.
The Base Oils Two highly viscous naphthenic base oils (BO1 and BO2), which were hydrotreated, were chosen for this study. Table 1 highlights some of the characteristics of these oils.
Table 1 shows some oil properties that directly connected to properties in greases that might be produced with these oils, mainly:
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.125 page 2
a) the higher values of VGC and CA as well as the lower aniline point suggest that BO2 has higher solvency power than BO1.
b) BO2 has significantly higher kinematic viscosity (> 60%) than BO1.
c) BO1 has lower pour point due its lower viscosity. d) the sulfur content of BO2 is almost three times higher than BO1, which may have some positive impact on some properties, e.g., oxidation stability.
Table 1: Typical characteristics of the two naphthenic oils.
The Greases In total, six greases (A, B, C, D, E and F) were prepared in a pilot plant using the two naphthenic oils. The thickeners were conventional lithium, lithium complex and organophilic clay. The acids were 12-hydroxystearate acid (12-HSA) and azelaic acid. It is well known that manufacturing process of Lithium, lithium complex and Bentonite greases are different. Thus, the greases have been produced according to the state of art, however, in the case of lithium and lithium complex greases 50 (wt.%) of the amount of base oil was used in the cooking stage and 50 (wt.%) during the cooling and finishing stages. For Bentonite greases, all oil was used at the beginning of the process.
Notable a) the process parameters for each type of grease were kept constant and b) no additives were added into the greases.
LUBE MAGAZINE NO.154 DECEMBER 2019 33
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