Page 123 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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3. CHARACTERIZATION OF PETROLEUM FRACTIONS 103
SG
Distillation T 10 T1: IML TABLE 3.4—Correlation constants for Eq. (3.17). No. of AAD
T 50
type range, C range, C range a b c data points %
a◦
a◦
ASTM D 86 35–295 60–365 0.70–1.00 0.08342 0.10731 0.26288 120 2.2
TBP 10–295 55–320 0.67–0.97 0.10431 0.12550 0.20862 83 2.6
EFV 79–350 105–365 0.74–0.91 0.09138 −0.0153 0.36844 57 57
Source: Ref. [22].
a Temperatures are approximated to nearest 5.
used in a reverse form to predict SD from ASTM D 86, but this calculated ASTM and SG, the EFV temperatures can be es-
type of conversion is usually not desired as most predictive timated from Eq. (3.16) with constants given in Table 3.2.
methods use ASTM D 86 data while laboratories report SD EFV = 2.9747 (32 + 273) 0.8466 (0.7862) 0.4209 = 340.9 K =
data. Constants a, b, and c in Eq. (3.18) were obtained from 340.9 − 273 = 67.9 C. The calculated value is very close to the
◦
81 different samples and 567 data points and are given in actual value of 68.3 C (see Table 3.5). Similarly EFV values at
◦
Table 3.5 with the range of SD data at each percentage along other points are calculated and results are shown in Fig. 3.19.
the distillation curve. Predicted EFV curve from TBP are very close to the actual
Equation (3.18) and the method of Ford published by EFV curve. The AAD between predicted EFV and experimen-
ASTM, included in the earlier editions of API-TDB [21], were tal data is 2.6 K. It should be noted that if experimental ASTM
evaluated by some 570 data points and gave AAD of 5 and data and specific gravity were used, the predicted values of
5.5 C, respectively [22, 26]. Larger errors were observed at EFV would be even closer to the experimental values.
◦
the initial and final boiling points (0 and 100%) but excluding
these points the AAD reduces to about 3 C for conversions 3.2.2.2 Daubert’s Method
◦
within the range of 10–90% distilled. Daubert and his group developed a different set of equations
The procedures given in this section should be used with the to convert ASTM to TBP, SD to ASTM, and SD to TBP [23].
range of data specified in Tables 3.1–3.4. Use of these equa- These methods have been included in the sixth edition of API-
tions outside the specified ranges could cause large errors. TDB [2] and are given in this section. In these methods, first
Graphical forms of these equations for conversion of various conversion should be made at 50% point and then the differ-
distillation curves are given in Reference [22] as well as in the ence between two cut points are correlated in a form similar
fourth edition of the API-TDB-88 [2]. One of the advantages of to Eq. (3.14). In this method SD data can be converted di-
these equations is that they can be used in reversed form. This rectly to TBP without calculating ASTM as was needed in the
means one may estimate EFV from TBP data through conver- Riazi–Daubert method.
sion of TBP to ASTM by Eq. (3.15) and then using Eq. (3.16)
to estimate EFV from calculated ASTM curve. The example 3.2.2.2.1 ASTM and TBP Conversion—The following
below shows this conversion process. equation is used to convert an ASTM D 86 distillation at 50%
point temperature to a TBP distillation 50% point tempera-
Example 3.2—For a blend of naphtha–kerosene sample, ture.
ASTM, TBP, and EFV distillation curves are given in the API- 1.0258
TDB [2]. These data are represented in Table 3.6. Use the TBP(50%) = 255.4 + 0.8851[ASTM D 86(50%) − 255.4]
Riazi–Daubert methods to predict EFV curve from TBP curve. (3.20)
where ASTM (50%) and TBP (50%) are temperatures at 50%
Solution—TBP data are used as available input data. Equa- volume distilled in kelvin. Equation (3.20) can also be used
tion (3.15) should be used to estimate ASTM D 86 from TBP. in a reverse form to estimate ASTM from TBP. The following
For the initial point at 0%, the calculations are as follows. equation is used to determine the difference between two cut
ASTM D 86 = (1/0.9177) 1/1.0019 (10 + 273) 1/1.0019 = 305 K = points:
305 − 273 = 32 C. The actual data for the initial ASTM tem-
◦
perature is 35 C, which is close to the calculated value. (3.21) Y i = AX i B
◦
Now to estimate EFV from Eq. (3.16), specific gravity, is re- where
quired which is not given by the problem. SG can be esti- Y i = difference in TBP temperature between two cut
mated from Eq. (3.17) and constants given in Table 3.3 for
points, K (or C)
◦
the TBP. From Table 3.6, T 10 (TBP) = 71.1 and T 50 (TBP) = X i = observed difference in ASTM D 86 temperature be-
204.4 C. Using these values in Eq. (3.17) gives SG = 0.10431 ◦
◦
(71.1 + 273) 0.1255 (204.4 + 273) 0.20862 = 0.7862. Now from tween two cut points, K (or C)
A, B = constants varying for each cut point and are given
in Table 3.7
TABLE 3.5—Correlation constants for Eq. (3.18).
SD
Vol% a b c range, C TABLE 3.6—Data on various distillation curves
a◦
for a naphtha–kerosene blend [2].
0 5.1764 0.7445 0.2879 −20–200 Vol% ASTM D 86, TBP, EFV,
10 3.7452 0.7944 0.2671 25–230 distilled ◦ C ◦ C ◦ C
30 4.2749 0.7719 0.3450 35–255
50 1.8445 0.5425 0.7132 55–285 0 35.0 10.0 68.3
70 1.0751 0.9867 0.0486 65–305 10 79.4 71.1 107.2
90 1.0849 0.9834 0.0354 80–345 30 145.6 143.3 151.1
100 1.7991 0.9007 0.0625 95–405 50 201.7 204.4 182.2
Source: Ref. [22]. 70 235.6 250.6 207.2
a Temperatures are approximated to nearest 5. 90 270.6 291.7 228.3

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