Page 142 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

T1: IML
P2: IML/FFX
P1: IML/FFX
QC: IML/FFX
June 22, 2007
14:23
AT029-Manual
AT029-03
AT029-Manual-v7.cls
122 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
is defined by Eq. (2.36). Paraffinic oils have low I values while
aromatics have high I values. Carbon-to-hydrogen weight
ratio defined in Section 2.1.18 is also a useful parameter
that indicates degree of hydrocarbon saturation and its value
increases from paraffinic to naphthenic and aromatic oils.
Methods of prediction of CH was discussed in Section 2.6.3.
Application of the hydrogen-to-carbon ratio in characteriza-
tion of different types of petroleum products is demonstrated
by Fryback [54]. An extensive analysis and comparison of
various characterization parameters useful for prediction of
the composition of petroleum fractions is presented by Ri-
azi and Daubert [36,47]. Comparison of parameters R i , VGC,
K W , and I is presented in Table 3.21 and Fig. 3.24. From this
analysis it is clear that parameters R i and VHC best separate
hydrocarbon types, while parameters K W and I show large
variations for aromatic and naphthenic compounds making
them less suitable for prediction of composition of petroleum
fractions.
Another very useful parameter that not only separates
paraffins and aromatics but also identifies various hydrocar-
bon types is defined through molecular weight and refractive
index as [36]:
(3.50) m = M(n − 1.475)
where n is the refractive index at 20 C. Parameter m was de-
◦
fined based on the observation that refractive index varies lin-
early with 1/M with slope of m for each hydrocarbon group
[55]. Values of parameter mfor different hydrocarbon groups
calculated from Eq. (3.50) are given in Table 3.22.
As shown in Table 3.22, paraffins have low m values while
aromatics have high m values. In addition, paraffinic and
naphthenic oils have negative m values while aromatic oils
have positive m values. Parameter m nicely identifies vari-
ous aromatic types and its value increases as the number of
rings increases in an aromatic compound. A pure hydrocar-
bon whose m value is calculated as −9 has to be paraffinic,
it cannot be naphthenic or aromatic. This parameter is par-
ticularly useful in characterizing various aromatic types in
aromatic-rich fractions such as coal liquids or heavy residues.
FIG. 3.23—Estimation of VGC from kinematic viscosity and Besides the parameters introduced above there are a num-
specific gravity [4]. ber of other parameters that have been defined for the purpose
of characterizing hydrocarbon type. Among these parameters
Aromatic oils have low K W values while paraffinic oils have viscosity index (VI) and correlation index (CI) are worth defin-
high K W values. Kurtz and Ward in 1935 [52] defined refrac- ing. The viscosity index was introduced in 1929 by Dean and
tivity intercept, R i , in terms of refractive index (n) and density Davis and uses the variation of viscosity with temperature
(d)at20 C, which is presented by Eq. (2.14). The definition as an indication of composition of viscous fractions. It is an
◦
is based on this observation that a plot of refractive index empirical number indicating variation of viscosity of oil with
against density for any homologous hydrocarbon group is lin- temperature. A low VI value indicates large variation of vis-
ear. R i is high for aromatics and low for naphthenic stocks. cosity with temperature that is a characteristic of aromatic
The most recent characterization parameter was introduced oils. Similarly, paraffinic hydrocarbons have high VI values.
in 1977 by Huang [53] in terms of refractive index and it The method is described under ASTM D 2270-64 [4] and in

TABLE 3.21—Values of characterization factors.
Value Range
Hydrocarbon type M R i VGC K I
Paraffin 337–535 1.048–1.05 0.74–0.75 13.1–1.35 0.26–0.273
Naphthene 248–429 1.03–1.046 0.89–0.94 10.5–13.2 0.278–0.308
Aromatic 180–395 1.07–1.105 0.95–1.13 9.5–12.53 0.298–0.362
Taken with Permission from Ref. [47].

--`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---

Copyright ASTM International
Provided by IHS Markit under license with ASTM Licensee=International Dealers Demo/2222333001, User=Anggiansah, Erick
No reproduction or networking permitted without license from IHS Not for Resale, 08/26/2021 21:56:35 MDT