Page 144 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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124 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
TABLE 3.23—Comparison of VI, VGC, K W , and CI for several groups of oils [29].
Type of oil T1: IML VI 14:23 VGC K W CI
High VI distillate 100 0.800–0.805 12.2–12.5 <15
Medium VI distillate 80 0.830–0.840 11.8–12.0 15–50
Low VI distillate 0 0.865–0.890 11.0–11.5 >50
Solvent Extracts . . . 0.880–0.950 10.0–11.0 . . .
Recycle Stock . . . 0.900–0.950 10.0–11.0 . . .
Cracked Residues . . . 0.950–1.000 9.8–11.0 . . .
H versus kinematic viscosity of oil at 100 C(Y) when Y is less to calculate the VI. However, since kinematic viscosities are
◦
than 70 cSt are tabulated in the ASTM D 2270 method [4]. For given at 38 and 99 C, Eqs. (3.57) and (3.58) should be used. --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
◦
oils with values of Y greater than 70 cSt H must be calculated From the information given U = 1000 and Y = 100. Since Y
from the relation given below [5]. is greater than 75 cSt, Eq. (3.58) must be used to calculate
parameter H, which gives H = 3080.6. From Eqs. (3.55) and
2
(3.56) H = 0.1684Y + 11.85Y − 97
(3.57) we get N = 0.2443 and VI = 200.7. Since calculated VI is
If kinematic viscosities are available in English units at 37.8 greater than 100, the initial assumption is correct. Otherwise,
and 98.9 C (100 and 210 F), then Eqs. (3.54) and (3.56) should Eq. (3.51) must be used. Since the value of VI is quite high
◦
◦
be replaced with the following relations as given in the API- the oil is paraffinic as shown in Table 3.24. If ν 99(210) was less
TDB [2]: than 70 cSt then tables provided by ASTM [4] or API-TDB [2]
N
10 − 1 should be used to calculate parameters L and D.
(3.57) VI = + 100
0.0075
3.5.1.2 API (Riazi–Daubert) Methods
2
(3.58) H = 0.19176Y + 12.6559Y − 102.58 To develop a method for predicting the composition of olefin-
free petroleum fractions three equations are required to ob-
in which Eq. (3.58) must be used for fractions with kinematic tain fractions of paraffins (x P ), naphthenes (x N ), and aromat-
viscosity at 99 C (210 F) greater than 75 cSt [2]. ics (x A ). The first and most obvious equation is known from
◦
◦
Finally the correlation index (CI) defined by the U.S. Bureau the material balance:
of Mines is expressed by the following equation [7]:
48640 (3.60) x P + x N + x A = 1
(3.59) CI = + 473.7SG − 456.8
T b
Two other equations can be established by applying Eq. (3.40)
in which T b is the volume average boiling point (VABP) in for two parameters that can characterize hydrocarbon types
kelvin. Values of CI between 0 and 15 indicate a predomi- and are easily measurable. Analysis of various characteriza-
nantly paraffinic oil. A value of CI greater than 50 indicates a tion factors shown in Table 3.21 and Fig. 3.24 indicates that R i
predominance of aromatic compounds [7]. It has a tendency and VGC are the most suitable parameters to identify hydro-
to increase with increasing boiling point in a given crude oil. A carbon type. For example, if for a pure hydrocarbon R i = 1.04,
comparison between values of VI, VGC, K W , and CI for several it has to be a naphthenic hydrocarbon, it cannot be paraffinic
types of petroleum fractions and products is presented in Ta- or aromatic since only for the naphthenic group R i varies
ble 3.23. A complete comparison of various characterization from 1.03 to 1.046. Refractivity intercept has been related
parameters indicating composition of petroleum fractions for to the percent of naphthenic carbon atoms (%C N )as R i =
the three hydrocarbon groups is presented in Table 3.24. All 1.05–0.0002 %C N [7]. Riazi and Daubert [47] used both R i
parameters except R i , K W , and VI increase in the direction and VGC to develop a predictive method for the composition
from paraffinic to naphthenic and aromatic oils. of viscous petroleum fractions. Properties of pure hydrocar-
bons from the API RP-42 [56] have been used to calculate R i
Example 3.15—Calculate viscosity index of an oil having and VGC for a number of heavy hydrocarbons with molecu-
kinematic viscosities of 1000 and 100 cSt at 37.8 and 98.9 C lar weights greater than 200 as shown in Table 2.3 and Table
◦
(100 and 210 F), respectively. 3.21. Based on the values of R i and VGC for all hydrocarbons,
◦
average values of these parameters were determined for the
Solution—For this oil ν 99(210) > 70 cSt, thus we can use Eqs. three groups of paraffins, naphthenes, and aromatics. These
(3.51)–(3.57) for calculation of VI. Since the VI is not known average values for R i are as follows: 1.0482 (P), 1.0138 (N),
we assume it is greater than 100 and we use Eqs. (3.53)–(3.57) and 1.081 (A). Similar average values for VGC are 0.744 (P),
TABLE 3.24—Comparison of various characterization parameters for molecular type analysis.
Parameter Defined by Eq. (s) Paraffins Naphthenes Aromatics
R i (2.14) medium low high
VGC (2.15) or (2.16) low medium high
m (3.50) low medium high
SG (2.2) low medium high
I (2.3) (2.36) low medium high
CI (3.59) low medium high
K W (2.13) high medium low
VI (3.51)–(3.58) high medium low

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