Base Stock Composition

The antioxidant performance of ZnDTP is influenced not only by the base stock composition but also by the dispersants and detergents, demonstrated by Fig. 4.7. The deleterious effect of the dispersant on the oxidation stability of the ZnDTP-containing lubricant is clearly enhanced by calcium detergents [100] and, to a larger extent, magnesium detergents [39], In summary, the additive interaction pattern is influenced by the type of dispersant and detergent, by the base stock composition and by the concentration ratio of the additives used in a formulation [101],... 

Viscosity gravity constant This is an indicator of base stock composition and solvency that is calculated from the density and viscosity according to ASTM D2501 it usually has a value between 0.8 and 1.0. High values indicate higher solvency and therefore greater naphthenic or aromatic content. This is usually of interest for naphthenic stocks. See Chapter 4 for further details. 

A number of papers have looked at the development of relationships between base stock composition as measured by NMR and either physi-cal/chemical properties or their performance.22 27 Most of this work has been focused on group II and III base stocks, with less or little attention paid to solvent extracted ones. These have all relied on various techniques to simplify the spectra and the assignments of peaks and make peak integration more reliable. These have many acronyms,23 for example, GASPE (gates spin echo), PCSE (proton coupled spin echo), INEPT (insensitive nuclei enhancement by polarization transfer), DEPT (distortionless enhancement by polarization), QUAT (quaternary-only carbon spectra), 2D COSY (two-dimensional homo-nuclear spectroscopy), and HETCOR (heteronuclear shift correlated spectroscopy)]. Table 4.10 provides an example of some of the chemical shift data generated26 and employed in this type of work, and Adhvaryu et al.25 were able to develop the correlations between base stock properties and carbon types in Table 4.11, whose main features correspond to intuition (e.g., the values of API and aniline points are both decreased by aromatic carbon and increased by the... 

The most valuable assessment of a base stock is how it performs in use as a formulated product and how well it meets the expectations of the formulator and the customer. The answer to this in the real world is complex, since many factors (application, specific conditions of use, price, availability, etc.) are involved. There are a number of standardized tests that provide comparative information under controlled conditions. For the most part, these tests employ inhibited base stock samples (i.e., those containing antioxidants). Perhaps most importantly, these tests are evaluations of the base stock s response to antioxidants, which is the result the formulator really wants and needs. These tests have also been used successfully to provide scientific information on the effects of base stock composition. This approach, coupled with advances in analytical technology, has been particularly successful when applied to the developing field of hydrocracked base stocks, which began in the 1970s. These stocks differ from solvent refined ones in having only very low levels of aromatics, sulfur, and nitrogen, so the focus was much more on hydrocarbon composition itself. 

Source D. W. Murray, J. M. MacDonald, A. M. White, and P. G. Wright, The Effect of Base Stock Composition on Lubricant Oxidation Performance, Petroleum Review February 36 10 (1982). With permission. 

Source A. S. Galiano-Roth and N. M. Page, Effect of Hydroprocessing on Lubricant Base Stock Composition and Product Performance, Lubrication Engineering 50(8) 659-664 (1993). With permission. 

Examples of both solvent refined and hydrocracked-hydrofinished finished base stock compositions are shown in Table 8.2,3 where it can be seen that hydrocracked oils have exceptionally low levels of sulfur and aromatics compared to those obtained by solvent refining. 

Early chapters provide a background to some of the physical properties that base stocks are expected to meet, the chemical and physical means by which they are distinguished, and the relationships between structure and physical properties. The viscosity index property is a key measure of viscosity response to temperature and deserves the attention of the full chapter (Chapter 3) that it receives. Methodology to determine both petroleum and base stock composition would require several books to outline. I have chosen to restrict this subject in Chapter 4 to a number of older methods which are still applicable but I have also included some discussion of NMR methods which increasingly will play a vital role. Since oxidation during use is probably the biggest hurdle that lubricants face, Chapter 5 provides a summary of the most significant work on the oxidation of base stocks and those oxidation studies on formulated products that reflect information on base stock composition and the process. 

Galiano-Roth, N., and Page, M. (1994). Effect of hydroprocessing on lubricant base stock composition and product p>erformance. Lubrication Engineering. 50(8) 659 -664. Holder, G. A., and Winkler, J. (1965). Wax crystallization from distillate fuels. Part III. Effect of wax compwsition on response to pour depressant and further development of the mechanism of pour depression. /. Inst. Pet. 51(499) 243- 252. 

Figure 4. Hydrocracking impact on base stock composition...

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