Page 90 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

P2: —/—
T1: IML
QC: —/—
P1: KVU/—
AT029-Manual-v7.cls
16:6
AT029-02
AT029-Manual
August 16, 2007
70 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
correlation for n-alkanes is
estimation of reference kinematic viscosities and are also in-
cluded in the API-TDB [2]:
(2.126) T MP = 374.5 + 0.02617M − 20172/M
log ν 38(100) =
where T MP is in kelvin. For naphthenes, aromatics, and 2
isoparaffins the melting point temperature may be esti- 4.39371 − 1.94733K W + 0.12769K W −2
−4
2
mated from the following relation given by Pan–Firrozabadi– + 3.2629 × 10 2 API − 1.18246 × 10 K W API −2 2
W
Fotland [63]. + 0.171617K + 10.9943(API) + 9.50663 × 10 (API) − 0.860218K W (API)
(API) + 50.3642 −4.78231K W
(2.127) T M(iP,N,A) = 333.45 − 419 exp(−0.00855M) (2.128)
where T M is in kelvin. Subscripts iP, N, and A indicate iso- log ν 99(210) =
paraffins, naphthenes, and aromatics, respectively. − 0.463634 − 0.166532(API) + 5.13447
−4
2
× 10 (API) − 8.48995 × 10 −3 K W API
Example 2.10—Estimate the freezing point of n-hexa- 8.0325 × 10 −2 K W + 1.24899(API) + 0.19768(API) 2
triacontane (C 36 H 74 ) from Eqs. (2.123) and (2.126) and com- +
pare with the actual value of 348.19 K [20]. Also draw a graph (2.129) (API) + 26.786 − 2.6296K W --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
of predicted T M from Eqs. (2.123) to (2.127) for hydrocarbons
from C 7 to C 40 for the three homologous hydrocarbon groups K W and API are defined by Eqs. (2.13) and (2.4). In these
2
from paraffins, naphthenes, and aromatics based on the above relations the kinematic viscosities are in cSt (mm /s). These
correlations are also shown by a nomograph in Fig. 2.12. The
two methods and compare with actual values given up to C 20
given in Table 2.2. above relations cannot be applied to heavy oils and should
be used with special care when K W < 10 or K W > 12.5 and
API < 0 or API > 80. Average error for these equations is in
Solution—For n-C 36 , we have M = 36 × 12.011 + 74 × 1.008 =
the range of 15–20%. They are best applicable for the viscos-
508.98 and T M = 348.19 K. From Eq. (2.123), T M = 397 −
2
exp(6.5096 − 0.14187 × 508.98 0.47 ) = 349.78 K. The percent ity ranges of 0.5 <ν 38(100) < 20 mm /s and 0.3 <ν 99(210) < 40
2
absolute relative deviation (%AD) is 0.2%. Using Eq. (2.126), mm /s [8]. There are some other methods available in the lit-
T M = 348.19 K with %AD of 0.24%. A complete evaluation is erature for the estimation of kinematic viscosities at 38 and
demonstrated in Fig. 2.11. On an overall basis for n-alkanes 99 C. For example Twu [81] proposed two correlations for the
◦
Eq. (2.126) is more accurate than Eq. (2.123) while for naph- kinematic viscosities of n-alkanes from C 1 to C 100 in a similar
thenes and aromatics, Eqs. (2.124) and (2.125) are more ac- fashion as his correlations for the critical properties discussed
curate than Eq. (2.127). in Section 2.5.1. Errors of ±100% are common for prediction
of viscosities of typical oils through this method [17].
Once kinematic viscosities at two temperatures are known,
2.7 PREDICTION OF KINEMATIC ASTM charts (ASTM D 341-93) may be used to obtain viscos-
VISCOSITY AT 38 AND 99 C ity at other temperatures. The ASTM chart is an empirical
◦◦
relation between kinematic viscosity and temperature and it
Detailed prediction of the viscosities of petroleum fractions is given in Fig. 2.13 [68]. In using this chart two points whose
will be discussed in Chapter 8. However, kinematic viscos- their viscosity and temperature are known are located and
ity defined by Eq. (2.12) is a characterization parameter a straight line should connect these two points. At any other
needed to calculate parameters such as VGC (Section 2.1.17), temperature viscosity can be read from the chart. Estimated
which will be used in Chapter 3 to determine the compo- values are more accurate within a smaller temperature range.
sition of petroleum fractions. Kinematic viscosity at two This graph can be represented by the following correlation
reference temperatures of 100 F (37.78 ≈ 38 C) and 210 F [8]:
◦
◦
◦
(98.89 ≈ 99 C) are generally used as basic characterization (2.130) log[log(ν T + 0.7 + c T )] = A 1 + B 1 log T
◦
parameters and are designated by ν 38(100) and ν 99(210) , respec-
tively. For simplicity in writing, the reference temperatures of where ν T is in cSt, T is the absolute temperature in kelvin,
100 and 210 F are presented as 38 and 99 C rather than accu- and log is the logarithm to base 10. Parameter c T varies with
◦
◦
rate values of 37.78 and 98.89. Kinematic viscosity decreases value of ν T as follows [8]:
2
with temperature and for highly viscous oils values of ν 99(210) 0.085(ν T − 1.5) 2 if ν T < 1.5 cSt [mm /s]
are reported rather than ν 38(100) . The temperature dependency (2.131) c T =
2
of viscosity is discussed in Chapter 8 and as will be seen, the 0.0 if ν T ≥ 1.5 cSt [mm /s]
viscosity of petroleum fractions is one of the most complex If the reference temperatures are 100 and 210 F (38 and
◦
physical properties to predict, especially for very heavy frac- 99 C), then A 1 and B 1 are given by the following relations:
◦
tions and multiring aromatic/naphthenic compounds. Heavy
oils with API gravities less than 10 could have kinematic vis- A 1 = 12.8356 × (2.57059D 1 − 2.49268D 2)
cosities of several millions cSt at 99 C (210 F). These viscos- B 1 = 12.8356 (D 2 − D 1)
◦
◦
ity values would be almost impossible to predict from bulk (2.132)
properties such as boiling point and specific gravity. How- D 1 = log[log(ν 38(100) + 0.7 + c 38(100) )]
ever, there are some relations proposed in the literature for D 2 = log[log(ν 99(210) + 0.7 + c 99(210) )]
the estimation of these kinematic viscosities from T b and SG
or their equivalent parameters K W and API gravity. Relations Various forms of Eq. (2.130) are given in other sources
developed by Abbott et al. [80] are commonly used for the [2, 11, 17]. Errors arising from use of Eq. (2.130) are better or
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