Correlation of structure and properties of groups I to III base oils

Abstract

The understanding of the relationship between molecular structure and viscosity–temperature behaviour of a lubricant system is a subject of considerable importance. The quantitative distribution and types of different classes of hydrocarbons such as aromatics, paraffins (normal and iso) and naphthenes determine the physico‐chemical behaviour of a lubricant system. The study of molecular structure and molecular alignment of hydrocarbons constituting a lubricant helps in the development of lubricating oil with desired physico‐chemical properties. The present study highlights the application of nuclear magnetic resonance spectroscopic technique for deriving detailed hydrocarbon structural features present in API groups II and III base oils produced through catalytic hydrocracking/isodewaxing processes. The viscosity–temperature and viscosity–pressure properties, such as viscosity index, pour point, elastohydrodynamic film thickness and cold cranking simulator viscosity, were determined. The structural features of these base oils such as various methyl branched structures of isoparaffins and branching index, which are characteristics of high performance molecules, were correlated with the above‐mentioned properties to explain their physico‐chemical properties, particularly low temperature properties. The molecular dynamics parameters such as diffusion coefficient and T1 relaxation times estimated from the nuclear magnetic resonance spectral studies have provided sufficient evidence for the dependence of these properties on these high performance molecules present in various types of methyl structures of isoparaffins of groups II and III base oils compared with conventional group I base oils. Results are explained on the basis of molecular structural differences of hydrocarbons present in these base oils and diffusion measurement studies. On the basis of the studies, molecular engineering concept for the designing of a high performance base oil molecule is proposed. Copyright © 2012 John Wiley & Sons, Ltd.

Correlation between the Molecular Structure and Viscosity Index of CTL Base Oils Based on Ridge Regression

“…This finding is in good agreement with previous studies that methyl branched chains in the center of carbon chains possess the ability to restrict molecular diffusion at high temperatures and thus exhibit high VI. 22 ACL also shows a similar correlation to VI in both base oils, with R 2 = 0.7597 in CTL base oil and R 2 = 0.6043 in mineral base oil. However, the positive effect of ACL on VI has been underestimated in some studies; 20 in mineral base oils, ACL does not only represent the length of carbon chains in normal and isoparaffinic chains but also represent part of the side chain that includes the linkage to the naphthenic hydrocarbons, so the ACL of mineral base oils is affected by the carbon content of naphthenic hydrocarbons, thus underestimating its positive effect.…”

“…In addition, the resonance signals of C#4 were stronger at 10–12, 14–15, 24–27, 32–34, and 36–40 ppm compared to that of M#4, which implies a higher content of branched structures. Based on the earlier study of peak assignments, 22 it was possible to distinguish specific branched structures, as shown in Figure 4 , where the relative content of the carbonaceous units was recorded by normalizing the total carbon integral area, based on which the molar fractions of the different branched structures were calculated by the contribution to the IP. The relative contents of specific carbon types and branched structures were calculated and are shown in Table 3 .…”

“…In addition, the correlation indicated that a decrease in ACL caused an increase in VI; however, this conclusion did not work for other studies. 21 , 22 Verdier et al 21 developed a correlation model for VI based on molecular structure data from 13 C NMR of 20 base oils and the correlation model was shown to predict the experimental data well with an R 2 of 0.9589. However, the significant correlation between molecular structures as input variables can make the regression model unstable.…”

Kriging Modeling to Predict Viscosity Index of Base Oils

“…Sharma et al 19,20 and Sarpal et. al 21 used a linear relationship to model VI of base oils from molecular parameters (different types of carbon contents, 13 C NMR peaks area corresponding to different branching structures). These works provided important information about the VI dependence on molecular structure of petroleum cuts, but due to the limited number of samples (6 to 8), model robustness can be questioned.…”

Molecular Dynamics of Synthetic-Based Lubricant System by Spectroscopic Techniques—Part 1

“…The structural parameters such as aromaticity, normalto-isoparaffin ratio, distribution of branched paraffins, that is, the position of methyl along the alkyl chain length, etc., are correlated statistically to predict or determine these properties (Sarpal,et al (8)). Because the diffusion of hydrocarbon molecules constituting a base stock depends on their relative proportion, the diffusion measurements and time relaxation parameters estimated by NMR technique are used to explain these properties (Sharma and Stipanovic (12); Sarpal,et al (8), (9), (21)). …”