Page 138 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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118 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
TABLE 3.19—Comparison of various methods of predicting specific gravity of petroleum fractions of Table 3.17 (Example 3.12).
(1) Rule of thumb, (2) Use of d 20 , (3) Use of T b & n 20 , (4) Use of M & n 20 ,
SG = 1.005 d 20 Eq. (3.44) Eq. (2.59) for M < 300 Eq. (2.60) for M >300
No. M, exp SG, exp SG, calc AD% SG, calc AD% SG, calc AD% SG, calc AD%
1 233 0.9119 0.9127 0.09 0.9109 0.11 0.8838 3.09 0.8821 3.27
2 267 0.9605 0.9616 0.11 0.9591 0.15 0.9178 4.44 0.9164 4.59
3 325 0.8883 0.8889 0.07 0.8874 0.10 0.8865 0.20 0.8727 1.76
4 403 0.9046 0.9046 0.00 0.9029 0.19 0.9067 0.23 0.8867 1.98
5 523 0.8760 0.8794 0.39 0.8780 0.23 0.9062 3.45 0.8701 0.67
Total, AAD% 0.13 0.15 2.28 2.45
Method 3, which is recommended for light fractions, gives Kinematic viscosity of petroleum fractions can be esti-
better results for the specific gravity of heavy fractions. It mated from methods presented in Section 2.7 of the previous
should be noted that the boundary of 300 for light and heavy chapter. At reference temperatures of 37.8 and 98.9 C (100
◦
fractions is approximate and methods proposed for light frac- and 210 F), ν 38(100) and ν 99(210) can be determined from Eqs.
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tions can be used well above this boundary limit as shown in (2.128) and (2.129) or through Fig. 2.12 using API gravity and
Method 3. K W as the input parameters. In use of these equations atten-
Estimation of density is similar to estimation of specific tion should be paid to the limitations and to check if API and
gravity. When both T b and SG are available Eq. (2.113) is the K W are within the ranges specified for the method. To calcu-
most accurate method for estimation of density of petroleum late kinematic viscosity at any other temperature, Eq. (2.130)
fractions. This method gives AAD of 0.09% for the five frac- or Fig. 2.13 may be used. The procedure is best demonstrated
tions of Table 3.17 with higher errors for the last two fractions. through the following example.
This equation may be used safely up to molecular weight of
500 but for heavier fractions Eq. (3.44) or the rule of thumb Example 3.13—A petroleum fraction is produced through
should be used. Predicted value of density at 20 C from Eq. distillation of a Venezuelan crude oil and has the specific grav-
◦
(2.113) is not reliable if it is greater than the value of specific ity of 0.8309 and the following ASTM D 86 distillation data:
gravity used in the equation. The method of rule of thumb
with d = 0.995 SG gives an AAD of 0.13% and Eq. (3.44) gives vol% distilled 10 30 50 70 90
an AAD of 0.15%. ASTM D 86 temperature, F 423 428 433 442 455
◦
Refractive index is estimated from three different methods
Estimate kinematic viscosity of this fraction at 100 and 140 F
◦
and results are given in Table 3.20. In the first method, T b
and SG are used as the input parameters with Eq. (2.115) to (37.8 and 60 C). Compare the calculated values with the ex-
◦
estimate I and n is calculated from Eq. (2.114). In the sec- perimental values of 1.66 and 1.23 cSt [46].
ond method Eq. (2.116) is used with the same input data.
Equations (2.115) and (2.116) are both developed with data Solution—Kinematic viscosities at 100 and 210 F, ν 38(100) and
◦
on refractive index of pure hydrocarbons with M < 300. How- ν 99(210) , are calculated from Eqs. (2.128) and (2.129), respec-
ever, Eq. (2.116) in this range of application is more accurate tively. The API gravity is calculated from Eq. (2.4): API = 38.8. --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
than Eq. (2.115). But for heavier fractions as shown in Table To calculate K W from Eq. (2.13), MeABP is required. For this
3.20, Eq. (3.115) gives better result. This is due to the simple fraction since it is a narrow boiling range the MeABP is nearly
nature of Eq. (2.115) which allows its application to heavier the same as the mid boiling point or ASTM 50% temperature.
fractions. Equation (2.116) does not give very accurate refrac- However, since complete ASTM D 86 curve is available we use
tive index for fraction with molecular weights of 500 or above. Eqs. (3.6)–(3.12) to estimate this average boiling point. Cal-
Equation (2.117) in terms of M and SG is developed basically culated parameters are VABP = 435.6 F and SL = 0.4 F/vol%.
◦
◦
for heavy fractions and for this reason it does not give accu- From Eqs. (3.8) and (3.12) we get MeABP = 434 F (223.3 C).
◦
◦
rate results for fractions with molecular weights of less than As expected this temperature is very close to ASTM 50%
300. This method is particularly useful when boiling point is temperature of 433 F. From Eq. (2.13), K W = 11.59. Since
◦
not available but molecular weight is available or estimable. 0 < AP I < 80 and 10 < K W < 11, we can use Eqs. (2.128)
However, if boiling point is available, even for heavy fractions and (2.129) for calculation of kinematic viscosity and we
Eq. (2.115) gives more accurate results than does Eq. (2.117) get ν 38(100) = 1.8 , ν 99(210) = 0.82 cSt. To calculate viscosity at
as shown in Table 3.20. 140 F, ν 60(140) , we use Eqs. (2.130)–(2.132). From Eq. (2.131)
◦
TABLE 3.20—Comparison of various methods of predicting refractive index of petroleum fractions of Table 3.17
(Example 3.12).
(1) Use of T b & SG, (2) Use of T b & SG, (4) Use of M & SG,
Eq. (2.115) for M < 300 Eq. (2.116) for M < 300 Eq. (2.117) for M > 300
No. M, exp n 20 exp n 20 exp. AD% n 20 calc AD% n 20 calc AD%
1 233 1.5016 1.5122 0.70 1.5101 0.57 1.5179 1.08
2 267 1.5366 1.5411 0.29 1.5385 0.13 1.5595 1.49
3 325 1.4919 1.4960 0.28 1.4895 0.16 1.4970 0.34
4 403 1.5002 1.5050 0.32 1.4952 0.34 1.5063 0.41
5 523 1.4865 1.4864 0.01 1.4746 0.80 1.4846 0.13
Total, AAD% 0.32 0.40 0.69

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