Viscosity Gravity Constant

The viscosity-gravity constant and the Universal Oil Prodncts characterization factor have been used to some extent as a means of classifying crnde oils. Both parameters are generally employed to give an indication of the paraffinic character of the crude oil, and both have been nsed, if a snbtle differentiation can be made, as a means of petroleum characterization rather than for petrolenm classification. 

Nevertheless, the viscosity-gravity constant (VGC) was one of the early indexes proposed to characterize (or classify) oil types  

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It is now common to use Viscosity Gravity Constant (VGC) as the criterion for choice of a processing oil. The VGC represents the overall average aromaticity of an oil independent of its molecular weight. 

Functions of properties such as the viscosity index or the viscosity gravity constant may be useful. However, the values of a function for a series of fractions of the same oil may be of approximately equal magnitude or may not be serial, as illustrated by the viscosity index (Table I). 

Point F represents the composition of the given feed stock. If we assign as desired end conditions a raffinate and extract viscosity-gravity-constant oF0.870 and 0.955, respectively (such values would represent a yield of 58.5% by weight), we can locate points Rn and E. Any addition of solvent to the feed stock must effect a composition which would fall on the line FA. Likewise, any mixture of final extract and raffinate layers must lie on the line r ei. An over-all materials balance requires that the solvent-feed mixture... 

Considerable data have been published and additional unpublished confirmatory data have been collected which indicate that for a given degree of refinement, measured by increased viscosity index or decreased viscosity gravity constant, the quality of refined oils produced by all popular solvent refining processes is so nearly equivalent that there is no clear-cut generalization possible which would favor one process over another. From the point of view of economy, two other considerations are important—namely, selectivity and... 

Ci = concentration of solute in first of two immiscible phases C2 = concentration of solute in second of two immiscible phases F = composition of feed to solvent extraction operation VGC = viscosity gravity constant... 

Figure 14.5. Representation of solvent extraction behavior in terms of certain properties rather than direct compositions [Dunstan et aL, Sci. Pet., 1825-1855 (1938)]. (a) Behavior of a naphthenic distillate of VGC = 0.874 with nitrobenzene at 10°C. The viscosity-gravity constant is low for paraffins and high for naphthenes, (b) Behavior of a kerosene with 95% ethanol at 17°C. The aniline point is low for aromatics and naphthenes and high for paraffins, (c) Behavior of a dewaxed crude oil with liquid propane at 70°F, with composition expressed in terms of specific gravity.

Type 104 oils are subclassified into types 104A and 104B for styrene-butadiene rubber greater than 0.820 (ASTM D 2501). and are naphthenic Type 104B oils have a VGC of 0.820 max., and are paraffinic. See aromatic, naphthene, paraffin. 

VGC (viscosity-gravity constant) an index of the chemical composition of crude oil defined by the general relation between specific gravity, sg, at 60°F and Saybolt Universal viscosity, SUV, at 100°F ... 

Correlative methods are also available for application to aviation fuels. Such methods include the use of viscosity-temperature charts (ASTM D-341), calculation of the cetane index (ASTM D-976, ASTM D-4737), calculation of the viscosity index (ASTM D-2270), calculation of the viscosity gravity constant (ASTM D-2501), calculation of the true vapor pressure (ASTM D-2889), and estimation of the heat of combustion (ASTM D-3338). 

The viscosity-gravity constant (ASTM D-2501) and the refractivity intercept (r) have been used for characterizing oils of widely different viscosity (ASTM D-2140). 

Viscosity-gravity constant see VGC (viscosity-gravity constant). 

Nevertheless, the viscosity-gravity constant is one of the indexes proposed to characterize oil types. For heavy oils, the low-temperature viscosity is difficult to measure. The viscosity-gravity constant for such type of petroleum is calculated by the formula... 

The viscosity-gravity constant is of particular value in indicating petroleum of a predominantly paraffinic or cyclic composition. The lower the index number, the more paraffinic the stock for example, naphthenic lubricating oil distillates... 

Refractivity intercept- Refractive index, density, viscosity Viscosity-gravity constant (in Saybolt seconds)... 

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