292
The Chemistry and Technology of Petroleum
Application to oils with a relatively high naphthene ring content is presumed not to cause serious
errors. Although the presence of foreign elements influences its accuracy unfavorably, the method is
applicable to samples containing sulfur up to 2%, oxygen up to 0.5%, and nitrogen up to 0.5%.
11.2.1.5 Dispersion–Refraction Method
This method is analogous to the direct method, but the hydrogenation and the examination of the
hydrogenated product are replaced by the determination of specific dispersion, bromine number
(ASTM D1159; IP 129; IP 130), and specific refraction (Lorentz-Lorenz) of the original fraction.
The analytic results obtained by the dispersion–refraction method are similar to those derived from
the direct method, except olefin double bonds, and are also measured. The method is based on data
derived from pure hydrocarbons having fewer than 18 carbon atoms per molecule and requires
the following determinations; carbon and hydrogen content, refractive index, density, dispersion,
molecular weight, and bromine number.
Calculation of the structural parameters is fairly involved, and the accuracy of the method does
not seem to be very high. However, it should be remembered that the method can be used on
materials derived from cracking processes as determination of the olefin content is provided for by
inclusion of the bromine number.
11.2.1.6 Density–Temperature Coefficient Method
For the analysis of paraffin–naphthene mixtures with a density below 0.861, it is assumed that in
the density–density temperature coefficient diagram the portion of the intercept (at constant density)
between the paraffin and naphthene line is divided by the sample point into parts proportional to
paraffin and naphthene content. In this way the following equation for mixtures of paraffins and
naphthenes in the regions below 0.861 density was derived:
Wt.% rings = [190.0d − 217.9 − l0 5 dd/dt]/(0.593d − 0.249)
where
d is the density at 20°C (68°F) (Chapter 10)
dd/dt is the change in density per degree change in temperature
For mixtures having a density above 0.861, a compromise was reached between the condensed
and noncondensed naphthenes, assuming an equal distribution of these two types. The sample point
was assumed to divide the line between the limiting paraffin point and a point on the naphthene
ring line above 0.861 into parts proportional to paraffin and naphthene content, and for this region
the following formula was derived:
Wt. rings = [102.8d − 142.8 − 10 5 dd/dt]/0.262
Simplification of the experimental procedure could be achieved by deriving the density coefficient
from the molecular weight, which in turn can be estimated from other physical properties, such as
the density and mid-boiling point, or viscosity at 38°C (100°F) and 99°C (210°F). However, since
−10 5 dd/dt = 53.5 + 3360/M
If d < 0.861,
Wt.% rings = [190.0d − 164.4 + 3360/M](0.593d − 0.249)
If d > 0.861,
Wt.% rings = (102.8d − 89.3 + 3360M)/0.262
The Chemistry and Technology of Petroleum
Application to oils with a relatively high naphthene ring content is presumed not to cause serious
errors. Although the presence of foreign elements influences its accuracy unfavorably, the method is
applicable to samples containing sulfur up to 2%, oxygen up to 0.5%, and nitrogen up to 0.5%.
11.2.1.5 Dispersion–Refraction Method
This method is analogous to the direct method, but the hydrogenation and the examination of the
hydrogenated product are replaced by the determination of specific dispersion, bromine number
(ASTM D1159; IP 129; IP 130), and specific refraction (Lorentz-Lorenz) of the original fraction.
The analytic results obtained by the dispersion–refraction method are similar to those derived from
the direct method, except olefin double bonds, and are also measured. The method is based on data
derived from pure hydrocarbons having fewer than 18 carbon atoms per molecule and requires
the following determinations; carbon and hydrogen content, refractive index, density, dispersion,
molecular weight, and bromine number.
Calculation of the structural parameters is fairly involved, and the accuracy of the method does
not seem to be very high. However, it should be remembered that the method can be used on
materials derived from cracking processes as determination of the olefin content is provided for by
inclusion of the bromine number.
11.2.1.6 Density–Temperature Coefficient Method
For the analysis of paraffin–naphthene mixtures with a density below 0.861, it is assumed that in
the density–density temperature coefficient diagram the portion of the intercept (at constant density)
between the paraffin and naphthene line is divided by the sample point into parts proportional to
paraffin and naphthene content. In this way the following equation for mixtures of paraffins and
naphthenes in the regions below 0.861 density was derived:
Wt.% rings = [190.0d − 217.9 − l0 5 dd/dt]/(0.593d − 0.249)
where
d is the density at 20°C (68°F) (Chapter 10)
dd/dt is the change in density per degree change in temperature
For mixtures having a density above 0.861, a compromise was reached between the condensed
and noncondensed naphthenes, assuming an equal distribution of these two types. The sample point
was assumed to divide the line between the limiting paraffin point and a point on the naphthene
ring line above 0.861 into parts proportional to paraffin and naphthene content, and for this region
the following formula was derived:
Wt. rings = [102.8d − 142.8 − 10 5 dd/dt]/0.262
Simplification of the experimental procedure could be achieved by deriving the density coefficient
from the molecular weight, which in turn can be estimated from other physical properties, such as
the density and mid-boiling point, or viscosity at 38°C (100°F) and 99°C (210°F). However, since
−10 5 dd/dt = 53.5 + 3360/M
If d < 0.861,
Wt.% rings = [190.0d − 164.4 + 3360/M](0.593d − 0.249)
If d > 0.861,
Wt.% rings = (102.8d − 89.3 + 3360M)/0.262