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Petroleum Refining – Chapter 4: Characterization
4-1
Chapter 4 Characterization & properties estimation
of crude oil and petroleum products
Introduction
There is no analytical technique available to determine
(either quantitatively or quantitatively) all the tens of
thousands of chemical species in petroleum and its
fractions.
Only the low-boiling components C1-C5 can becompletely identified using gas chromatography analysis.
For the white fractions (e.g. Naphtha), only a limited
number of components can be completely identifiedusing PINA, PIONA, or Detailed HC GC analyzers
(Table 2.3 – 2.6).
To overcome this shortcoming, petroleum refiners resortto define (characterize) petroleum and its fractions usingglobal (bulk) properties.
This traditional way of oil characterization, though old, is
still being used today.
This type of characterization is used as basis for
assigning a price for crude oils and petroleum fractions
and in design of petroleum processes.
Sulfur content & API gravity have the greatest influence on the value of
crude oil, although N2 and metals content are increasing in importance.
The price of petroleum fractions is influence by other properties in
addition
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API Gravity (API)
A measure of crude oil density/specific gravity.
141.5API = 131.5sp.gr.
(4.1)
oil
water
(60 )
sp.gr. =(60 )
F
F
(4.2)
Light crude have lower density (sp.gr.)→ API is higher.
10 < API < 50(or less) (or more)
High API crude produces more distillates (valuable) thanit does residue (less valuable).
Distillation Range (Curve)
The boiling point range is an alternate method torepresent the composition of petroleum and its products.
It gives an indication of the quantities and qualities of the
various products present in crude oil (i.e. naphtha,kerosene, diesel, gas oil, residue, etc).
- Can be used to determine themost desirable processing
sequence to obtain therequired products.
- Can be used to determinewhether the crude is
suitable for asphalt orlube oil manufacture.
CrudeOil
GasesLPG
Naphtha
Kerosene
Diesel
Residue
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Types of distillation curves
1. TBP (True Boiling Point) distillation curve.
2. ASTM (D86/D1160) distillation curve.3. EFV (Equilibrium Flash Vaporization)
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TBP is the most useful.
- However, no standard test exists for measuring the
TBP.
- Most common TBP test is Hempel & D-285.
(Neither specifies # of stages or reflex ratio used).
- Trend is toward 15/5 distillation (D-2892) to stand
for TBP (assumed to be the same as TBP).
- An estimate of the composition of the butane and
lighter components is frequently added to the low- boiling end or the IBP of the TBP curve to
compensate for the loss during distillation.
ASTM is more common because it is simple to
determine in the laboratory. Kuwait refineries use ASTM
curve (Which is then converted to TBP curve).
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Example 4.1:
Estimate the true boiling point (TBP) distillation curve of the petroleum fraction having the following ASTM D86
distillation temperatures:
Vol % T (ºF)IBP -
5% -10% 400
30% 42050% 438
70% 46090% 485 → 490
95% -FBP -
Recovery = -
Solution:
Using Fig. 3A1.1 from the API technical Data Book
(1) Correct the ASTM D86 distillation temperatures above
475 ºF for cracking using Hadden equation.
Log D = – 1.587 + 0.00473 T
where, T & D are in ºF
For the 90% temp. → Log D = – 1.587 + 0.00473 (485) =
0.707
D = 5 ºF
The corrected 90% temp. becomes = 485 + 5 = 490 ºF
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(2) Find the atmospheric TBP mid (50%) temperature using
the mid temp of the ASTM D86 and the lower part ofFigure 3A1.1.
438 ºF on the x-axis → ∆T= 2 ºF on the y-axis
[correction]
Therefore, the TBP 50% T =ASTM 50% T + ∆T = 438+2= 440 ºF
(3) Find the temp for each segment of the TBP curve using
upper part of Figure 3A1.1.
Segment of
Curve (Vol
%)
ASTM ∆T (ºF)
[from table above]
TBP ∆T (ºF)
[Figure 3A1.1]
TBP (ºF) Vol %
0 to 10
10 to 3030 to 50
2018
3931
409 – 39 = 370440 – 31 = 409
IBP
10%30%
440 50%
50 to 70
70 to 90
90 to 100
22
30
33
40
440 + 33 = 473
473 + 40 = 513
70%
90%
FBP
Note: it is possible to convert TBP temperatures to ASTMD86 using Figure 3A2.1 from the API technical data
book, which involves a trial and error procedure.
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Petroleum Refining – Chapter 4: Characterization
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Crude oil analysis are reported in 2 parts,
1. D-86, atmospheric, (IBP up to 527 ºF end point 760
mmHg)
2. D-1160, vacuum, (392 to 572 ºF end point at 40 mmHg)
equivalent to 580 to 790 ºF at 1 atm.
- Vacuum Distillation is necessary to prevent excessive
pot ( وع ) temperatures, which cause cracking of the
crude oil.
- To combine the two results in one curve, the distillation
temperatures at 40 mmHg reported in the analysis must
be corrected to 760 mmHg pressure using Figure 3.6
from text.
The 572 ºF end point at 40 mmHg corresponds to 790 ºF at 760
mmHg.
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Figure 4.1: Boiling point distribution curve
Estimation of the TBP curve above 790 ºF can be obtained by
1. Extrapolating of probability graph (Figure 3.7 in text) to
1100ºF or higher FBP.
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4-12
Figure 4.2: Crude oil TBP Distillation Curve Probability Chart.
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Example 4.2: construction of the TBP & API Curves
Draw the TBP and API curves for the following crude assay
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Solution:
1. Results in the table are in TBP not ASTM so there is no need
for conversion.
2. On a graph paper, plot the sum percent (column 4) as your x-
axis and the cut temperature (column 2) as your y-axis untilyou reach the temperature 527 ºF (this is the atmospheric
distillation data).
3. To plot the vacuum distillation data on the same graph you
would need to correct the vacuum distillation temperatures(at 40 mmHg) to atmospheric pressure (i.e. convert from
D1160 to D86 test pressure) using the following equation,
T b (1atm) = 126.14 + 1.169 T b (40 mmHg)
then continue plotting the curve as above.
4. Plot all the data in step 1 and 2 above on the probabilitygraph extending the straight line to the FBP. Read the valuesof x (sum percent) and y (temperature) above 572 ºF and list
them in a table. Use the new values to continue the rest of
your distillation curve.
5. Plot on the same graph the API (column 6) versus cut mid%
calculated as follows;
Mid% cut 1 = 0.8/2 = 0.4 → API = 78.8
Mid% cut 2 = 0.8 + 1.0/2 = 1.3 → API = 75.1 Mid% cut 3 = 1.8 + 3.0/2 = 3.3 → API = 63.7
Mid% cut 4 = 4.8 + 3.4/2 = 6.5 → API = 55.9 etc.
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2. Better results are obtained when using the probability densityfunction shown below instead of Figure 4.2.
1/B
o
o
A 1T-T = ln
B 1-xT
(4.3)
Where x is the volume fraction distilled, T is the distillation
temperature, and To, A and B are constants determined byregression using the solver function in Microsoft Excel or any
curve fitting program. Once the constant are determined, the
function may be used in the above equation to construct therest of the boiling point diagram.
When applied to the crude in example 4.2 the following
values are obtained for the constantsTo = 30.788
A = 4986.5
B = 2.5131
Using these constants into the above equation, the followingTBP curve is predicted.
Hints: when applying the same to your own crude oil, use the
above values as initial guess. Also, add an absolute to theabove equation to avoid getting errors
1/B
o
o
A 1T-T = ln
B 1-xT
abs (4.4)
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vol % T (ºF) x T calculated abs diff
0.8 122 0.008 122 123.43632 1
1.8 167 0.018 167 158.976516 8
4.8 212 0.048 212 221.339965 9
8.2 257 0.082 257 268.288313 11
11.3 302 0.113 302 302.429928 0
15.2 347 0.152 347 339.126056 8
20.1 392 0.201 392 379.358772 13
26.9 437 0.269 437 428.88685 8
34.9 482 0.349 482 482.000019 0
53.1 584 0.531 584 596.320067 12
60.9 637 0.609 637 646.905867 10
67.1 690 0.671 690 689.704546 0
72.8 742 0.728 742 732.454459 10
79.7 795 0.797 795 791.401438 3
85 846 0.85 846 845.847377
90 911 0.9 911 911.151517
95 1008 0.95 1008 1008.33677
98 1118 0.98 1118 1117.85398
99.9 1394 0.999 1394 1393.84728
0
200
400
600
800
1000
1200
1400
1600
0 20 40 60 80 100
Vol. %
TBPTemperature(F)
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Petroleum Refining – Chapter 4: Characterization
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Characterization & Classification
Characterization Factors
Correlate between the yield and the aromaticity & paraffinicity of petroleum oils.
Several correlations exist,
1. UOP or Watson characterization factor (K w )
B
13
w@60 F
T =K (sp.gr.)
(4.5)
More commonly used.
TB is the normal boiling point of the pure compound orthe mean average boiling point of a petroleum fraction
in ºR [ºF+460].
Higher for lighter components and petroleum fractions
e.g. K w ≈ 12.1 (Naphtha), K w ≈ 11.9 (Diesel)
For petroleum fractions 10 < K w < 15
↑ ↑
contain containhighly highly
aromatic paraffinic
compounds compounds
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Copyright © 2001-2014 Dr. Tareq Albahri, Chemical Engineering Dept., Kuwait University, All rights reserved
4-18
For crude oil 10.5 < K w < 12.9↑ ↑
highly highly
naphthenic paraffiniccrude crude
For pure hydrocarbons
K w = 13 for paraffins.
K w = 12 for HC with equivalent chain and ringweights.
K w = 11 for pure naphthenes.
K w = 10 for pure aromatics.
2. US Bureau of Mines “Correlation Index”
B
@60 F= + 473.7 (sp.gr.) 456.8CIT
87,552 (4.6)
- TB & sp.gr. as above.
- Useful in evaluating individual fractions from oils (e.g.
naphtha, kerosene, diesel, etc.).
- The CI scale starts with 0 for straight-chain paraffins
and 100 for benzene.
0 → highly paraffinic
100 → highly naphthenic/aromatic
- CI values are not quantitative.
Low CI values→ high conc. of paraffins in the fraction.
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Higher CI values → high conc. of naphthenes &aromatics.
Example 4.3: Watson K for pure components
Calculate the Watson characterization factor and correlation index for n-
pentane.
Solution:For n-pentane, the boiling point is 97 ºF and sp.gr. is 0.63
Using equation (5.3) above
13
w
(97+460) = = 13.06K (0.63)
Using equation (5.4) above
= + 473.7 (0.63) 456.8 0CI87,552
(97+460)
Table 5.4: Comparison of K w and CI for pure components
Compound TB (ºF) Sp.gr. K w CI
n-Hexane
2-Methylpentane
CyclohexaneBenzene
Naphthalene
155.72
140.47
177.29176.18
884
0.664
0.658
0.78350.8845
1.176
12.8
12.8
11.09.7
8.16
0
0.7
51.799.8
199.2
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4-20
Classification of crude oil
- Paraffinic base
- Naphthenic base- Asphalt base
- Mixed base- Aromatic base (up to 80% in the far east)
These classifications convey the nature of the products to be
expected and the processing necessary.
US Bureau of Mines Classification
Based on the properties of the residue left from non-destructive atmospheric and vacuum distillation tests.
Fraction (1) from 482-527 ºF atm. distillation (760 mmHg)1.
Fraction (2) from 527-572 ºF vac. distillation (40 mmHg)2.
The gravity of these two fractions, obtained from Figure 3.8,
is used to classify crude as shown in table below.
ClassificationKey fractions, ºAPI
Fraction (1) Fraction (2)
ParaffinParaffin, Intermediate
Intermediate, Paraffin
Intermediate
Intermediate, Naphthene Naphthene, Intermediate
Naphthene
4040
33 – 40
33 – 40
33 – 4033
< 33
3020 – 30
30
20 – 30
2020 – 30
< 20
1&2 Both from TBP curve
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Crude Suitable for Asphalt Manufacture:
There are certain characteristics of crude oils that indicate if
they are possible sources of Asphalt.
Not 100% accurate as experimental tests.
A crude oil is usually suitable for asphalt manufacture if itmeats the three following criteria:
(1) The crude oil gravity < 35 ºAPI
(2) Contains a residue (MeABP=750ºF) with a Watson
characterization factor < 11.8.
(3) If (KW)550ºF – (KW)750ºF < 0.15
If > 0.15, the residue may contain too much
wax to meet most asphalt specifications.
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Copyright © 2001-2014 Dr. Tareq Albahri, Chemical Engineering Dept., Kuwait University, All rights reserved
4-22
Example 4.4:
Classify the following crude using the US bureau of mines classification
then specify whether it is suitable for asphalt manufacture. (See chapter 3)
Solution:
Figure. TBP and gravity-mid percent curves
Fraction (1) from 482-527 ºF atm. distillation (760 mmHg).
Fraction (2) from 527-572 ºF vac. distillation (40 mmHg)2.
The gravity of these two fractions, obtained from above figure, is used to
classify crude as shown in table below.
Fraction 1 → 33 ºAPI
Fraction 2 → 22 ºAPI
2 Equivalent to 740-790 ºF atm. distillation (760 mmHg).
0
200
400
600
800
1000
1200
0 20 40 60 80 100
Percent Distilled
Temperature(F
0
10
20
30
40
50
60
70
80
90
APIGravit
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From the table above, this crude would be classified as → Naphthene,
Intermediate
For the crude oil to be suitable for asphalt manufacture it should satisfy the
following
(1) API < 35 (specified in the data sheet for crude oil)
(2) (KW)550ºF – (KW)750ºF < 0.15
at 750 ºF → API = 25 → SG = 0.904
1/3
w
(750+460)K = 11.79
(0.904)
at 550 ºF → API = 32 → SG = 0.865
1/3
w
(550+460)K = 11.6
(0.865)
∆K w = 11.79 – 11.6 = 0.19 (> 0.15)
0
200
400
600
800
1000
1200
0 20 40 60 80 100
Percent Distilled
Temperature(F
0
10
20
30
40
50
60
70
80
90
APIGra
vit
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(3) Residue (MeABP = 750 ºF) (Kw < 11.8).
Calculate as above, only for the 790 ºF+ residue
The TBP curve for resid is first reconstructed as follows;
IBP is the final T reached by vac. distill. = 790 ºF
10 % T is 0.1(100-79) + 79 = 81.1%, T = 800 ºF
30 % T is 0.3(100-79) + 79 = 85.3%, T = 820 ºF
50 % T is 0.5(100-79) + 79 = 89.5%, T = 890 ºF
70 % T is 0.7(100-79) + 79 = 93.7%, T = 930 ºF
90 % T is 0.9(100-79) + 79 = 97.9%, T = 1030 ºF
FBP remains the same as before at about 1100 ºF
as an alternative, using computer program
(petrochem toolkit) API = 19 → MeABP = 860 ºF
Kw = 11.67 Ok
0
200
400
600
800
1000
1200
0 20 40 60 80 100
Percent Distilled
Temperature(F
0
10
20
30
40
50
60
70
80
90
APIGravit
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Copyright © 2001-2014 Dr. Tareq Albahri, Chemical Engineering Dept., Kuwait University, All rights reserved
4-26
Molal average boiling point
n
i bii=1
MABP =x T (4.8)
xi = mole fraction of component i.
T bi = normal boiling point of component i (ºF or R).
Weight average boiling point
n
wi bii=1
WABP = x T (4.9)
xwi = weight fraction of component i.
T bi = normal boiling point of component i (ºF or R).
Cubic average boiling point [R]
3
1/3
bi
n
vii=1
CABP = x T (4.10)
T bi = normal boiling point of component i (R only).
Mean average Boiling point
MABP + CABPMeABP =
2
(4.11)
Watson characterization factor
1/3
@60 Fw
(MeABP)K =
(sp.gr.) (4.12)
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- The Watson K is an approximate index of paraffinicity,with high values corresponding to high degrees of
saturation.
For multicomponent mixtures for which the composition isknown.
n
iwi
i=1
K = x K w (4.13)
Example 4.5:
Calculate the Watson characterization factor and the correlation index for
the following LPG mixture.
Vol %
C3 45
n-C4 50n-C5 5
Solution:
LPG is at high pressure, but the laboratory analysis for gas composition
are done at atmospheric pressure. This is close to ideal conditions and the
volume % is equal to the mole %.
mole % MW sp.gr. Boiling Point, ºF (ºR)C3 45 44 0.507 - 43.75 (416)
n-C4 50 58 0.584 31 (491)
n-C5 5 72 0.63 97 (557)
Average Sp.gr. = (0.45)(0.507)+(0.5)(0.584)+(0.05)(0.63) = 0.552
VABP = (0.45)(416)+(0.5)(491)+(0.05)(557) = 460.7 R
MABP = VABP (for ideal gas)
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C3 wt% = (0.45*44)/[(0.45*44)+(0.5*58)+(0.05*72)] = 37.8 wt%
C4 wt% = (0.5*58)/[(0.45*44)+(0.5*58)+(0.05*72)] = 55.3 wt%
C5 wt% = (0.05*72)/[(0.45*44)+(0.5*58)+(0.05*72)] = 6.9 wt%
WABP = (0.378)(416)+(0.553)(491)+(0.069)(557) = 467.3 ºR
31/3 1/3 1/3
CABP = 459.40.45(416) 0.5(491) 0.05(557)
R
MeABP = (MABP+CABP)/2 = (460.7+459.4)/2 = 460 R
Into equation (3) above1
3
w
(460) = = 13.9K (0.552)
orn
iwi
i=1
K = x K w = 0.378(14.7) + 0.553(13.5) + 0.069(13.03) = 13.92
Into equation (4) above
= + 473.7 (0.552) 456.8 5CI
87,552
(460)
Example 4.6: Watson K for petroleum fractions
For the following SR Naphtha,
69.1 ºAPI & ASTM D86 distillation3
Vol % T (ºF)
IBP 925% 11810% 128
30% 164
50% 198
70% 23090% 262
95% 272
3 D1160 can’t be used
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FBP 300Recovery = 98.8 vol.%
Calculate,
(1) The volumetric average boiling point, VABP(2) The weight average boiling point, WABP
(3) The molal average boiling point, MABP
(4) The cubic average boiling point, CABP
(5) The mean average boiling point, MeABP
(6) The Watson characterization factor, Kw
(7) The US bureau of mines correlation index, CI.
Solution:
No correction for temperature is required (since T < 475 ºF).
The volumetric average boiling point, VABP90
i
10
T
VABP5
i
10% 30% 50% 70% 90%
5
T T T T TVABP =
128+164+198+230+262 = = 196.45
ºF
Assuming ASTM curve is linear between 10 & 90%
90% 10% 262 128T TASTM slope = 1.67590 10 80
From Figure 2B1.1 API data book
For MABP → ∆T = -17 ºFFor CABP → ∆T = -3 ºF
For WABP → ∆T = +4 ºF For MeABP → ∆T = -10 ºF
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Using the corrections
MABP = 196.4 – 17 = 179.4 ºFCABP = 196.4 – 3 = 193.4 ºF
WABP = 196.4 + 4 = 200.4 ºFMeABP = 196.4 – 10 = 186.4 ºF
or = (179.4+193.4)/2 = 186.4 ºF
The Watson characterization factor, Kw
Sp.gr. = 141.5/(69.1+131.5) = 0.705
1/3 1/3
@60 Fw
(MeABP) (186.4+460)K = 12.3
(sp.gr.) (0.705) (mainly saturated)
The US bureau of mines correlation index, CI.
= + 473.7 (0.705) 456.8 0.7CI87,552
(186.4+460)
(paraffinic)
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Coordination Number (Hydrogen Deficiency) or “Z” Number
Cn H 2n+Z
As Z-number decreases, density increases.
Group Z
Paraffins
Olefins
NaphthenesAromatics
2
0
0-6
Examples of Z-values for Aromatic compounds
C6H6
Z = -6
C10H8
Z = -12
C14H10
Z = -18
C10H12Z = -8
C10H10Z = -10
C24H12Z = - 36
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Properties Estimation of Petroleum Fractions
1. Graphical Methods.
2. Correlations.
Example 4.7: Graphical Method
For the following SR Naphtha; 69.1 ºAPI & ASTM D86 distillationVol % T (ºF)
IBP 92
5% 118
10% 128
30% 164
50% 198
70% 230
90% 26295% 272
FBP 300
Recovery = 98.8 vol.%
Calculate the MW, aniline point, H/C ratio, the true and pseudocritical
temperatures and pressures.
Solution:
Previously calculated, the mean average boiling point,
MeABP = 186.4 ºF
Using Figure 2B2.1 from the API technical data book
The molecular weight, MW = 96
and the Watson characterization factor K W = 12.2(Compare to 12.3 calculated previously).
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The aniline point = 125 ºF.
H/C ratio = 5.5
MABP = 179.4 ºF → Figure 4A1.2 → T pc = 490 ºF.
WABP = 200.4 ºF → Figure 4A1.2 → Tc = 510 ºF.
MeABP = 186.4 ºF → Figure 4B1.2 → P pc = 440 psia.
Tc/T pc = (510+460)/(490+460) = 970/950 = 1.02
P pc = 440 & Tc/T pc = 1.02 → Figure 4B1.1 → Pc = 520 psia.
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Petroleum Refining – Chapter 4: Characterization
4-37
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Petroleum Refining – Chapter 4: Characterization
4-39
Liquid Viscosity
1. The absolute (or dynamic) viscosity.
Defined as the ratio of shear resistance to the shear velocitygradient.
This ratio is constant for Newtonian fluids.
Expressed in Pa.s (poise)
Commonly used unit is mPa.s (centipoise, cP)
2. The kinematic viscosity.
Defined as the ratio between the absolute viscosity and thedensity.
Expressed in mm2/s (centistokes, cSt)
The liquid dynamic viscosities at 100 ºF and 210 ºF are used
to characterize (heavy) petroleum fractions.
Viscosities can be estimated by the relation of Abbott et al.
2
100log 4.39371 1.94733 0.12769
W W K K
4 2 2
3.2629.10 1.18246.10W
A K A
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2 2(8.0325.10 1.24899 0.19768 )
( 26.786 2.6296 )
W
W
K A A
A K
(4.14)
210
4 2 3
2 2
log 0.463634 0.166532
5.13447.10 8.48995.10
(8.0325.10 1.24899 0.19768 )
( 26.786 2.6296 )
W
W
W
A
A K A
K A A
A K
(4.15)
whereK w = Watson characterization factor
A = API gravity
v100 = viscosity at 100 ºF [mm2/s]
v210 = viscosity at 210 ºF [mm2/s]log = common logarithm (base 10)
notes:
Should not be used if K w < 10 and A < 0.
Recommended for the following range;
0.5
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Petroleum Refining – Chapter 4: Characterization
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1. From the normal BP and standard specific gravity.
Riazi method: for light fractions
(sp.gr. < 0.97 & T b < 840 K).
M = 42.965 (T b1.26007 S4.98308)
[exp(2.097.10-4
T b – 7.78712 S + 2.08476.10-3
T b S)]
Lee-Kesler: for heavy petroleum fractions
(T b > 600 K & 60 < MW < 650).
7
2
12
2
3
12272.6 9486.4 (8.3741 5.9917 )
10 222.466 (1 0.77084 0.02058 ) 0.7465
10 17.3354 (1 0.80882 0.02226 ) 0.32284
b
b b
b b
M S T S
S S T T
S S T T
Where
M = Molecular weight [kg/kmol].
T b = Normal boiling point [K].
S = Standard specific gravity.
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2. From the viscosities at 210 ºF and 100 ºF and the standardspecific gravity (ave. error is 10%).
(1.1228 1.2435) (3.4758 3.038 ) 0.6665
100 210223.56 S S
M S
where
M = Molecular weight [kg/kmol].
v100 = viscosity at 100 ºF [mm2/s].
v210 = viscosity at 210 ºF [mm2/s].
S = Standard specific gravity.
Pseudo-Critical Constants for Petroleum Fractions.
To make use of the principle of corresponding states.
Use the method of Lee-Kesler (ave. error 10%)
1. Pseudo-Critical Temperature.
189.8 450.6 (0.4244 0.1174 )
(14,410 100,688 )
C b
b
T S T S
S
T
where,
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Petroleum Refining – Chapter 4: Characterization
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Tc = Pseudo-critical temperature [K].
T b = Normal boiling point [K].
S = Standard specific gravity.
2. Pseudo-Critical Pressure
3
2
7 2
2
10 3
2
0.0566ln 5.68925
4.12164 0.213426 10 0.436392
11.819 1.53015 10 4.75794
9.901 10 2.45055
C
b
b
b
P S
T S S
T
S S
T S
where,
Pc = Pseudo-critical pressure [bar].
ln = Napierian logarithm
T b = Normal boiling point [K].
S = Standard specific gravity.
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Copyright © 2001-2014 Dr. Tareq Albahri, Chemical Engineering Dept., Kuwait University, All rights reserved
4-44
Acentric Factor for Petroleum Fractions.
For T r < 0.8
2
7.904 0.1352 0.007465
1.408 0.1063 8.359
W W
W
br
br
K K
K T
T
b
br
c
T
T T
where
ω = acentric factor.
T br = reduced boiling point temperature.
K w = Watson characterization factor.
For T r > 0.8 (use Edmister's equation)
3
(log 1.0057)7 1 c x
P x
where b
c
T x
T
and
Pc = Pseudo-critical pressure [bar].
Tc = Pseudo-critical temperature [K].
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Petroleum Refining – Chapter 4: Characterization
4-45
log = common logarithm (base 10)
T b = Normal boiling point [K].
Specific Heat of Petroleum Fraction in the Ideal Gas State
5432325.2 FT ET DT CT BT A H gp
432 5432185.4 FT ET DT CT BC pgp
'8.1 T T
S K B
W
2846.029502.002972.035644.0
'24
05543.05524.19247.22
10C K K C
W W
S C
0694.50283.6
'
0844.06946.13
10 7
D
2
410.7.0885.0
1011
8.12
S S
K K W W
Kw = Watson characterization factor
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Copyright © 2001-2014 Dr. Tareq Albahri, Chemical Engineering Dept., Kuwait University, All rights reserved
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S = standard specific gravity
Flash Point
The API method (error 5°C)
T T
f
ln 1010
0034254.0
84947.2
02421.0
1
T10 = temperature at the 10% volume distilled point from ASTM
D86 [k].
Liquid EnthalpyHL = A1 7.259T A2 22 7.259T A3 33 7.259T
A1= 10-3
W
W
K K
4653582.1149)907.24722.23(26.1171
A2= 10-6
817.13086.56)82463.00.1( W K
A3= -10-9
3653.26757.9)82463.00.1( W K
Temperature (T)
Specific Gravity (SG)
Characterization Factor (Kw)
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Petroleum Refining – Chapter 4: Characterization
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Vapor enthalpy
266.5507.4 512.0
64.0 8.0
33
3
22
21
C
O
C
C
C C LV
RT
H H
MW
RT
T T B
T T BT T B H H
S
BW
B K 46.248
02.2953
1041
72.2944.356
S
BW W
B K K 46.25342.3016102 4)772.262.77(24.146
4
95.2487.569
103
B B
2
4
4 107.0885.00.10
0.10.18.12
S S
K K W W
B
HL Liquid Enthalpy of Petroleum Fractions
T Temperature
Tc Critical Temperature
R Gas Constant
MW Molecular Weight
ω Acentric Factor
S Specific Gravity
K W Watson Characterization Factor
(Ho- H)/RTC Pressure Effect on Enthalpy
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Copyright © 2001-2014 Dr. Tareq Albahri, Chemical Engineering Dept., Kuwait University, All rights reserved
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Hv Vapor Enthalpy of Petroleum Fractions
Calculation of Density by the Lee and Kesler Method
RT z
PM
V T
V V c
Vri
Di
Vri
Ci
Vri
Bi
Tr
Vri zi
T
d d D
T
c
T
ccC
T
b
T
b
T
bb B
ww
ww Z Z Z Z
Z Z w Z Z
l
l
rir
ri
ii
ri
ii
r
i
ii
r
i
r
i
ii
r
i
r
i
r
i
ii
23
224
52
21
3
321
3
4
2
321
12
1121
121
)exp()(
1Pr
)(
)('''5138.2
Pressure for Saturation
exp[ ( , )]m m s c r m
P P f T
0 0( , ) ln ln
mr m r m r T P P
6
0
6.09648ln 5.92714 1.28862ln 0.169347
m m
m
r r r
r
P T T
T
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Petroleum Refining – Chapter 4: Characterization
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1
615.6875ln 15.2518 13.4721ln 0.43577r m m
m
r r
r
P T T T
Pressure Correction for Density
1 ln1
s
s
B P C
B P
0.0861488 0.0344483m
C
4
1
a 1k
cm k
k
B P
1/ 3
1mr
T
Estimation of the pour point (page 172):
)333.031.0(
100
)474.0612.0(971.247.130 S S
EC v M S T
Estimation of the I nterfacial Tension of Petroleum fractions:
(page 167)
Kw
Tcf f
232.1]
15.2931[7.673
Thermal Conductivities of L iquids: (page 132)
T E l
4418.117.0
Influence of Pressure on the Viscosity of Liquids (Kouzel's
method):
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Copyright © 2001-2014 Dr. Tareq Albahri, Chemical Engineering Dept., Kuwait University, All rights reserved
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)4479.14829.5)((log 181.0 E Ms E Ps P Ms
M
Specific Heats for liquid Petroleum Fractions (Lee Kessler
1975) Page 121:
))410*508.5310*467.1(16734.03065.0)(055.035.0(185.4 S T S Kwl
Cp
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Petroleum Refining – Chapter 4: Characterization
Exercises
4.1. Repeat example 4.5 using another method by calculating K w for
pure components to find the same for the mixture.
4.2. Classify the crude oil handed out to you using the US bureau of
mines classification.
4.3. Is your crude oil suitable for asphalt or lube oil manufacture?
4.4. Draw the TBP and API curves for the crude oil assay handed out to
you. Use the probability density function to construct the heavier
portion of your TBP curve.
4.5. Estimate the MW, aniline point, and H/C ratio for the crude oil
handed out to you.