Page 134 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

P2: IML/FFX
T1: IML
QC: IML/FFX
P1: IML/FFX
June 22, 2007
AT029-Manual-v7.cls
AT029-Manual
AT029-03
14:23
114 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
Example 3.9—It is assumed for the same fraction of Ex-
at 50 vol% vaporized may be used as the characterizing boil-
ample 3.8, the only information available is ASTM D 86 data: For narrow boiling range fractions, ASTM D 86 temperature --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
temperatures of 350.9, 380.9, 399.8, 428.2, and 457.6 K at 10, ing point for the whole mixture. However, for a wide boiling
30, 50, 70 and 90 vol% distilled, respectively. State how can range fraction if it is treated as a single pesudocomponent
you apply the proposed approach for wide boiling range frac- the MeABP should be calculated and used as the character-
tions to calculate the molecular weight of the fraction. izing parameter for T b in the correlations of Chapter 2. If
for a fraction TBP distillation data are available the average
Solution—Since distillation data are in terms of ASTM boiling point calculated through Eq. (3.37) with parameters
D 86, the first step is to convert ASTM to TBP through determined from TBP curve would be more appropriate than
Eq. (3.14). The second step is to determine the TBP distri- MeABP determined from ASTM D 86 curve for use as the
bution function through Eqs. (3.35) and (3.36). The third characterizing boiling point. For cases where only two points
step is to generate values of T at x = 0, 0.2, 0.4, 0.6, 0.8, and on the distillation curve are known the interpolated value at
0.99 from Eq. (3.35) and parameters determined from TBP 50% point may be used as the characterizing boiling point of
distillation curve. Since the specific gravity for this frac- the fraction.
tion is not known it may be estimated from Eq. (3.17) and For heavy fractions (M > 300) in which atmospheric dis-
constants in Table 3.4 for the ASTM D 86 data as follows: tillation data (ASTM D 86, SD, or TBP) are not available, if
SG = 0.08342 × (350.9) 0.10731 (399.8) 0.26288 = 0.756. The Wat- ASTM D 1160 distillation curve is available, it should be con-
son K is calculated as K W = (1.8 × 399.8) 1/3 /0.756 = 11.85. verted to ASTM D 86 or TBP through methods outlined in
Now we assume that K W is constant for the entire range of Section 3.2. In lieu of any distillation data, molecular weight
distillation curve and on this basis distribution of SG can be or viscosity may be used together with specific gravity to esti-
calculated through distribution of true boiling point. At every mate basic parameters from correlations proposed in Chap-
point that T is determined from Eq. (3.35) the specific grav- ter 2. If specific gravity is not available, refractive index or
ity can be calculated as SG = (1.8 × T) 1/3 /K W , where T is the carbon-to-hydrogen weight ratio (CH) may be used as the
temperature on the TBP curve. Once TBP temperatures and second characterization parameter.
SG are determined at x = 0, 0.2, 0.4, 0.6, 0.8, and 0.99 points,
molecular weight may be estimated from Eq. (2.50). Numer- 3.3.4 Method of Pseudocomponent
ical integration of Eq. (3.39) can be carried out similar to the (Defined Mixtures)
calculations made in Example 3.8 to estimate the molecular
weight. In this approach the result may be less accurate than A defined mixture is a mixture whose composition is known.
the result in Example 3.8, as ASTM distillation curve is used For a petroleum fraction if at least the PNA composition
as the only available data. is known it is called a defined fraction. Huang [11, 33] used
the pseudocompounds approach to estimate enthalpies of
Although the method outlined in this section improves narrow and defined petroleum fractions. This technique has
the accuracy of prediction of properties of wide boiling been also used to calculate other physical properties by
range fraction, generally for simplicity in calculations most other researchers [34, 35]. According to this method all com-
petroleum products are characterized by a single value of boil- pounds within each family are grouped together as a sin-
ing point, molecular weight, or carbon number regardless of gle pseudocomponent. An olefin-free fraction is modeled
their boiling range. The proposed method is mainly applied into three pseudocomponents from three homologous groups
to crude oils and C 7+ fraction of reservoir fluids with an ap- of n-alkanes (representing paraffins), n-alkylcyclopentanes
propriate splitting technique as is shown in the next chapter. or n-alkylcyclohexanes (representing naphthenes), and n-
However, as shown in the above example, for very wide boiling alkylbenzenes (representing aromatics) having the same boil-
range petroleum products the method presented in this sec- ing point as that of ASTM D 86 temperature at 50% point.
tion may significantly improve the accuracy of the estimated Physical properties of a mixture can be calculated from prop-
physical properties. erties of the model components by the following mixing rule:
(3.40) θ = x P θ P + x N θ N + x A θ A
3.3.3 Use of Bulk Parameters
(Undefined Mixtures) where θ is a physical property for the mixture and θ P , θ N , and
θ A are the values of θ for the model pseudocomponents from
An undefined petroleum fraction is a fraction whose com- the three groups. In this equation the composition presented
position (i.e., PNA) is not known. For such fractions infor- by x A , x N , and x A should be in mole fraction, but because the
mation on distillation data (boiling point), specific gravity, molecular weights of different hydrocarbon groups having
or other bulk properties such as viscosity, refractive index, the same boiling point are close to each other, the compo-
CH ratio, or molecular weight are needed. If the fraction is sition in weight or even volume fractions may also be used
considered narrow boiling range then it is assumed as a sin- with minor difference in the results. If the fraction contains
gle component and correlations suggested in Chapter 2 for olefinic compounds a fourth term for contribution of this
pure hydrocarbons may be applied directly to such fractions. group should be added to Eq. (3.40). Accuracy of Eq. (3.40)
All limitations for the methods suggested in Chapter 2 should can be increased if composition of paraffinic group is known
be considered when they are used for petroleum fractions. in terms of n-paraffins and isoparaffins. Then another pseudo-
As mentioned in Chapter 2, the correlations in terms of T b component contributing the isoparaffinic hydrocarbons may
and SG are the most accurate methods for the estimation of be added to the equation. Similarly, the aromatic part may be
various properties (molecular weight, critical constants, etc.). split into monoaromatics and polyaromatics provided their

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