Page 68 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

T1: IML
QC: —/—
P2: —/—
P1: KVU/—
AT029-02
16:6
August 16, 2007
AT029-Manual-v7.cls
AT029-Manual
48 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
One should realize that Eq. (2.38) was developed based on
a two-parameter potential energy relation applicable to non- characterizing molecular energy and the molecular size. This
means that Eq. (2.31) can be expressed in terms of two pa-
polar compounds. For this reason, this equation cannot be rameters θ 1 and θ 2 :
used for systems containing polar compounds such as alco- b c
hol, water, or even some complex aromatic compounds that (2.39) θ = aθ θ
1 2
are considered polar. In fact constants a, b, and c given in However, one should realize that while these two parame-
Eq. (2.38) were obtained based on properties of hydrocar- ters are independent, they should represent molecular energy
bons with carbon number ranging from C 5 to C 20 . This is and molecular size. For example, the pairs such as (T b , M)
almost equivalent to the molecular weight range of 70–300. or (SG, I) cannot be used as the pair of input parameters
In fact molecular weight of n-C 20 is 282, but considering the (θ 1 , θ 2 ). Both SG and I represent size characteristics of
extrapolation power of Eq. (2.38) one can use this equation molecules and they are not a suitable characterization pair.
up to molecular weight of 300, which is roughly equivalent to In the development of a correlation to estimate the proper-
boiling point of 370 C (700 F). Moreover, experimental data ties of hydrocarbons, all compounds from various hydrocar-
◦
◦
on the critical properties of hydrocarbons above C 18 were not bon groups are considered. Properties of hydrocarbons vary
available at the time of development of Eq. (2.38). For heav- from one hydrocarbon type to another and from one carbon
ier hydrocarbons additional parameters are required as will number to another. Hydrocarbons and their properties can
be shown in Section 2.3.3 and Chapter 3. The lower limit for be tabulated as a matrix of four columns with many rows.
the hydrocarbon range is C 5 , because lighter compounds of Columns represent hydrocarbon families (paraffins, olefins,
C 1 –C 4 are mainly paraffinic and in the gaseous phase at nor- naphthenes, aromatics) while rows represent carbon num-
mal conditions. Equation (2.38) is mainly applied for unde- ber. Parameters such as T b , M, or kinematic viscosity at 38 C
◦
fined petroleum fractions that have average boiling points (100 F), ν 38(100) , vary in the vertical direction with carbon
◦
higher than the boiling point of C 5 as will be seen in Chapter number, while parameters such as SG, I, and CH vary signif-
3. Methods of calculation of properties of natural gases are icantly with hydrocarbon type. This analysis is clearly shown
discussed in Chapter 4. in Table 2.4 for C 8 in paraffin and aromatic groups and prop-
erties of C 7 and C 8 within the same group of paraffin family.
Example 2.3—Show that the molecular weight of hydrocar- As is clearly shown by relative changes in various properties,
bons, M, can be correlated with the boiling point, T b , and parameters SG, I, and CH clearly characterize hydrocarbon
specific gravity, SG, in the form of Eq. (2.38). type, while T b , M, and ν 38(100) are good parameters to charac-
terize the carbon number within the same family. Therefore,
Solution—It was already shown that molar volume at 20 C a correlating pair should be selected in a way that character-
◦
and 1 atm, V 20 , can be correlated to parameters A and B of a izes both the hydrocarbon group and the compound carbon
potential energy function through Eq. (2.32) as follows: V 20 = number. A list of properties that may be used as pairs of cor-
g 1 (A, B). In fact, parameter V 20 is similar in nature to the relating parameters (θ 1 , θ 2 ) in Eq. (2.39) are given below [29].
critical molar volume, V c , and can be correlated with T b and
b c
3
SG as Eq. (2.38): V 20 = aT SG . But V 20 = M/d 20 , where d 20 θ: T c (K), P c (bar), V c (cm /g), M, T b (K), SG, I (20 C), CH
◦
b
is the liquid density at 20 C and 1 atm and is considered a (θ 1 ,θ 2 ) (T b , SG), (T b , I), (T b , CH), (M, SG), (M, I), (M, CH),
◦
size parameter. Since T b is chosen as an energy parameter Pairs: (ν 38(100) , SG), (ν 38(100) ,I), (ν 38(100) , CH)
and SG is selected as a size parameter, then both d 20 and SG
represent the same parameter and can be combined with the
b
c
energy parameter as M = aT SG , which has the same form The accuracy of Eq. (2.39) was improved by modification of
b
of Eq. (2.38) for θ = M. its a parameter in the following form:
e
(2.40) θ = a exp[bθ 1 + cθ 2 + dθ 1 θ 2 ]θ θ f
1 2
2.3.2 Various Characterization Parameters
for Hydrocarbon Systems Values of constants a– f in Eq. (2.40) for various param-
eters of θ and pairs of (θ 1 , θ 2 ) listed above are given in
Riazi and Daubert [29] did further study on the expansion Table 2.5. It should be noted that the constants reported by
of the application of Eq. (2.38) by considering various in- Riazi–Daubert have a follow-up correction that was reported
put parameters. In fact instead of T b and SG we may con- later in the same volume [29]. These constants are obtained
sider any pair of parameters θ 1 and θ 2 , which are capable of from properties of hydrocarbons in the range of C 5 –C 20 in
TABLE 2.4—Comparison of properties of adjacent members of paraffin family and two families
of C 8 hydrocarbons.
Hydrocarbon group T b ,K M ν 38(100) , cSt SG I CH
Paraffin family
C 7 H 16 (n-heptane) 371.6 100.2 0.5214 0.6882 0.236 5.21
C 8 H 18 (n-octane) 398.8 114.2 0.6476 0.7070 0.241 5.30
% Difference in property +7.3 +14.2 +24.2 +2.7 +2.1 +1.7
Two Families (C 8 )
Paraffin (n-octane) 398.8 114.2 0.6476 0.7070 0.241 5.30
Aromatic (ethylbenzene) 409.4 106.2 0.6828 0.8744 0.292 9.53
% Difference in property +2.7 −7.0 5.4 +23.7 +21.2 +79.8
--`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---

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