Simdis (simulated distillation)

1832

Energy & Fuels 2004, 18, 1832-1840

Simulated Distillation Yield Curves in Heavy Crude
Oils: A Comparison of Precision between ASTM D-5307
and ASTM D-2892 Physical Distillation
Marcela Espinosa-Pena,* Yolanda Figueroa-Gomez, and Federico Jimenez-Cruz*
˜
´
´
Programa de Tratamiento de Crudo Maya, Instituto Mexicano del Petroleo (IMP), Eje Central
´
Lazaro Cardenas No. 152 Col. San Bartolo Atepehuacan C.P. 07750 Mexico D.F., Mexico
´
´
´
´
Received April 2, 2004. Revised Manuscript Received August 5, 2004

To develop an accurate and rapid evaluation of distillation yield curves of heavy crude oils,
simulated distillation by gas chromatography (SIMDIS GC) curves were performed for the first
time in Mexican Istmo and Maya crude oil samples. In this study, we found large uncertainties
using ASTM D-5307, and some improvements to the technique were applied as alternatives to
measure the assay distillation. These results were compared with the curves obtained from the
physical distillation method outlined in ASTM Method D-2892, showing good agreement. The
statistical analysis of the SIMDIS data is addressed as a good alternative for measuring these
heavy crude oils.

Introduction
Physical distillation is the major separation process
used in the petroleum industry. To ensure uniform
quality control in the refinery processes and in the final
petroleum products, it is essential to ascertain the
interval of the boiling point of crude petroleum and the
products thereof. Currently, the method used most
widely to determine the true boiling point (tBP) curves
is ASTM Method D-2892,1 which is a physical distillation with 15 theoretical plates with a relationship of
reflux of 5:1, followed by the application of ASTM
Method D-52362 for the heavier portion. The methods
based in the physical distillation, such as ASTM D-11603
and ASTM D-86,4 are described for one theoretical plate.
However, the inconveniences of these methods are the
excessively time-consuming analysis (∼48 h) and the
high level of operator intervention.5,6 In striking contrast, the simulated distillation by gas chromatography
(GC SIMDIS) method is a technique in which the
simulation of a distillation is involved.6-8 Simulated
distillation is the term used to designate the results
* Authors to whom correspondence should be addressed. E-mail
addresses: mespinos@imp.mx, jimenezf@imp.mx.
(1) ASTM Designation D-2892-03, 2003 Annual Book of ASTM
Standards; ASTM: Philadelphia, PA, 2003; Vol. 05.02.
(2) ASTM Designation D-5236-03. 2003 Annual Book of ASTM
(3) ASTM Designation D-1160. 2002 Annual Book of ASTM Standards; ASTM: Philadelphia, PA, 2002; Vol. 05.02.
(4) ASTM Designation D-86. 2002 Annual Book of ASTM Standards;
ASTM: Philadelphia, PA, 2002; Vol. 05.01.
(5) Previous work has been reported. For example, see: EspinosaPena, M.; Figueroa Gomez, Y.; Cano-Dominguez, J. L. Analytical
˜
´
Validation of Test Standard Simdis Method ASTM D 5307-97 for
Determination of Range Boiling Point of Crude Oil by Gas Chromatography. Presented at ACHEAMERICA 2002 in the 1st International
Congress on Process Technologies, Mexico City, March 18-20, 2002.
(6) Ceballo, C.; Murguia, E. Rev. Tec. INTEVEP 1983, 3, 35-45.
(7) Eggertsen, F. T.; Groennings, S.; Holst, J. J. Anal. Chem. 1960,
32, 904-909.
(8) Green, L. E.; Schmauch, L. J.; Worman, J. C. Anal. Chem. 1964,
36, 1512-1516.

obtained by chromatography of gases equivalent to those
calculated by physical distillation tBP curves; however,
SIMDIS reduces analysis time by offering the possibility
of automating the process.6 It also improves the accuracy and precision of the results.6,9 SIMDIS has
substantial advantages, in comparison to the methods
of physical distillation, not only for the simplicity of the
technique and management of the samples in small
quantity (0.2-0.5 µL), but for a minimum of contamination of the samples and accidents in the laboratory. Both
techniques are good to determine the distribution of
boiling-point intervals, for example, in gasoline and
distilled fractions of crude oils.9 In this context, ASTM
Method D-371010 corresponds to the simulated distillation for gasoline and ASTM Method D-288711 method
is used for fractions and products of petroleum such as
jet fuel, kerosene and diesel, light oils, and heavy gas
oils from coking and hydrotreatment. The methods used
for crude oils include ASTM Method D-530712 and
ASTM Method D-6352;13 both are currently used in
refining industry laboratories as a good alternative to
physical distillation. The difference between ASTM
Method D-5307 and ASTM Method D-6352 is that the
former has the possibility of calculating the residue
content (as a weight percentage) for samples with
nonvolatile material up to 538 °C. In addition, SIMDIS
techniques also have been developed in combination
with gas chromatography (GC)-mass spectroscopy,14
(9) Ceballo, C. D.; Bellet, A.; Aranguren, S.; Herrera, M. Rev. Tec.
INTEVEP 1987, 7, 81-83.
(12) ASTM Designation D-5307-97 . 2002 Annual Book of ASTM
Standards; ASTM: Philadelphia, PA, 2002; Vol. 05.02. (Reapproved
in 2002.)
(14) Roussis S. G.; Fitzgerald, P. Anal. Chem. 2000, 72, 1400-1409.

10.1021/ef049919k CCC: $27.50 © 2004 American Chemical Society
Published on Web 09/25/2004

Distillation Yield Curves in Heavy Crude Oils

GC-vacuum thermogravimetry,15 or high-performance
liquid chromatography (HPLC)-evaporative light scattering detector.16 The method of high temperature for
simulated distillation (HT SIMDIS), as described in
ASTM Method D-5307, have not been extensively
proven by the oil industry, because of the existence of
many problems in the preparation and nonhomogenization of the sample. These problems must be solved,
because, to obtain reliable results, a quantitative method
requires a rigorous and exact mass balance. In this
paper, we wish to describe a strategy for developing and
optimizing an appropriate methodology for the rapid
evaluation of distillation yield curves in Mexican crude
oils using GC SIMDIS described in ASTM Method
D-5307. In addition, an expeditious and improved
methodology for preparing heavy oil samples is described. Also, a comparison with the results of physical
distillation (ASTM Method D2892) tests was performed.5
Experimental Section
The samples of Istmo and Maya crude oil were supplied from
Pemex. Carbon disulfide (99.00%) was purchased from Aldrich
Chemical Company. A mixture of n-alkanes C5 through C98
(Polywax 655) was purchased from Analytical Control U.S.A.
A mixture of n-alkanes C14, C15, C16, and C17, which were
used as internal standards traceable to the National Institute
for Standards and Technology (NIST), was purchased from
Hewlett-Packard. A mixture of n-alkanes C5 through C44 was
used as a reference in the SIMDIS analysis, for comparison
and validation of the test.
The analyses were performed with a Hewlett-Packard model
HP 6890-II gas chromatograph that was equipped with a flame
ionization detector (FID) with an outlet diameter of 0.30 mm,
a liquid nitrogen cryogenic system, automatic injection for
eight vials, and software for calculation of the SIMDIS
methods. The column used was 5-6 m long, comprised of
stainless-steel capillary columns 0.53 mm in diameter, and
filled with methyl silicon, and the film thickness was 0.090.15 µm, respectively. The carrier gas was helium (99.999%
purity), with a flow of 20 mL/min and an inlet pressure of 80
psi. The injector and detector temperatures were each 430 °C.
The combustible gas for feeding the detector was hydrogen
(99.999% purity), with an inlet pressure of 60 psi and a flow
rate of 35 mL/min and air (99.999%, chromatographic grade)
with an inlet pressure of 80 psi and a flow rate of 350 mL/
min. The FID is highly sensitive (5 pg C/s) to hydrocarbons,
which allows for detection of the high-boiling-point components, such as heavy crude oil and their fractions. The detector
has a low sensitivity to carbon disulfide, which allows injection
of the dissolved crude oils into the chromatograph. Although
the FID is a mass-dependent detector, the analytic results are
comparable to the results of a physical distillation expressed
in terms of a volume percentage.
Conditioning of the Column. The column was conditioned without being connected to the detector, by purging with
helium at low temperature. The column outlet was covered
immediately with an appropriate seal. The flow of helium was
continued for 2-3 h at 430 °C. The oven was cooled at 100 °C,
and the seal was removed, to re-establish the helium flow in
the column. The equipment was programmed 2-3 times at
the operation conditions and the column was connected to the
detector. The equipment was stabilized at the required conditions. The oven was programmed to operate from 40 °C to 430
(15) Southern, T. G.; Iacchelli, A.; Cuthiell, D.; Selucky, M. L. Anal.
Chem. 1985, 57, 303-308.
(16) Padlo, D. M.; Kugler, E. L. Energy Fuels 1996, 10, 1031-1035.

Energy & Fuels, Vol. 18, No. 6, 2004 1833
°C and the injector was programmed to operate from 100 °C
to 430 °C, at a rate of 15 °C/min, and the detector was
programmed to operate from 50 °C to 430 °C, a rate of 10 °C
/min. The chromatogram was integrated over a period of 44
min, and the final temperature of the oven continued for 10
min to clean the system. The injector temperature was
maintained for 2 min.
Preparation of the Sample. The samples were previously
stored at a temperature of 0-5 °C for at least 4 h before
exposing them to the environment. To ensure homogeneity,
the heavy and viscous crude may require warming, as well as
stirring. The samples should be dried with anhydrous calcium
chloride or sodium sulfate by shaking the mixture of sample
and drying agent vigorously. According to ASTM Method
D-5307, the low-viscosity liquid samples can be analyzed
directly. The dried sample is removed from the desiccant using
a pipet and accurately weighted (0.15-0.20 g) in a 25 mL
volumetric flask and dissolved with 10 g of carbon disulfide.
The solution was weighed, and it had a concentration of ∼2%.
Two milliliters of this solution was withdrawn and poured into
a vial that had been weighed; this sample should be considered
as the sample without internal standard. The remainder of
the solution was weighed after this process and then a weighed
quantity of internal standard (20 µL, measured in a tared 100
µL syringe) was added to the remaining solution and mixed
by shaking. As done previously, 2 mL of this solution was
poured into a vial and should be considered as the sample with
internal standard.
Physical Distillation. This procedure was performed
according to ASTM Method D-2892. The water-free crude was
tested using columns of 15 theoretical plates under a relationship of reflux of 5:1; this method is known as the true boiling
point (tBP) assay. The distillation started under barometric
pressure (760 mm Hg) and is continued later under vacuum
conditions (5-100 mm Hg) at 370 °C. The boiling points are
converted to their equivalent value at 1 atm (AEBP). At this
point, the method was changed to the corresponding ASTM
Method D-5236 procedure, in which the distillation continued
at a pressure of 0.5 mm Hg until reaching a limit near the
AEBP (538 °C). Conversion charts for the conditions of AEBP
are included in the method.

Results and Discussion
For the purposes of this study, four analyses were
performed with two different crude oils from the two
following categories: Istmo crude (20-30 °API, 0.8932
g/cm3) and Maya crude (<20 °API, 0.9238 g/cm3). In
addition, two repeatability experiments and two reproducibility experiments for each operator were performed, according to the procedure described for ASTM
Method D-5307. The comparison between the two
analyses allows the percentage of the eluted sample to
be calculated, up to a temperature of 538 °C. Basically,
ASTM Method D-5307 is an extension of ASTM Method
D-2887, but the addition of a standard is not required.
By considering this stipulation, the strategy consisted
of performing an initial analysis for a calibration
mixture of C5 to C44 linear paraffins, under the same
conditions of the sample analysis under which all the
assignments were performed, by comparison with this
curve. Figure 1 shows a chromatogram with a boilingpoint (BP) distribution of the C5-C44 paraffin mixture,
as well as a plot of the calibration curve. At high
temperature, the samples should be eluted up to 430
°C, which is equivalent to atmospheric conditions.
Therefore, elution of the C44 paraffin, which has a BP
>538 °C, is conducted at 430 °C. Under these conditions,

1834

Energy & Fuels, Vol. 18, No. 6, 2004

Espinosa-Pena et al.
˜

Figure 1. Chromatogram (top) and calibration curve (bottom) for the mixture C5-C44.

no evidence of cracking has been visualized. In the
selected chromatographic conditions, the separation of

the corresponding peaks is good, which avoids saturation of the column. For the heavy crude oil, the sample



Table 1. Boiling Point Distribution in Reference Gas Oila
mass %

boiling point,
BP (°C)

mass %

boiling point,
BP (°C)

mass %

boiling point,
BP (°C)

mass %

boiling point,
BP (°C)

IBPb
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

199.0
334.5
374.5
389.0
397.5
403.5
408.0
412.0
415.0
418.0
420.5
422.5
424.5
426.5
428.0
429.5
431.0
432.5
434.0
435.0
436.5

21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41

437.5
439.0
440.0
441.0
442.0
443.0
444.0
445.0
446.0
446.5
447.5
448.5
449.5
450.5
451.0
452.0
452.5
453.5
454.0
455.0
456.0

42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62

456.5
457.5
458.5
459.0
460.0
461.0
461.5
462.5
463.0
463.5
464.5
465.0
466.0
467.0
467.5
468.5
469.0
469.5
470.5
471.0
472.0

63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83

473.0
473.5
474.5
475.0
476.0
477.0
477.5
478.5
479.0
480.0
481.0
481.5
482.5
483.5
484.5
485.5
486.5
487.0
488.0
489.5
490.5

mass %

boiling point,
BP (°C)

84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
FBPc

491.5
492.5
494.0
495.0
496.5
497.5
499.0
500.5
502.5
504.0
506.5
509.0
511.5
515.5
520.0
527.5
534.0

a Pertinent sample data: calibration method, external standard method; sample mass, 0.2184 g; solvent mass, 10.0860 g; mass of
internal standard, 0.0000 g; elution at start, 0.00; elution at end, <24.43; found recovery, 102.0%; and used recovery, 100.0%. b Initial
boiling point. c Final boiling point.

is not eluting completely in the chromatographic column, and, thus, area normalization cannot be applied.
The sample then must be analyzed in duplicate. In the
first run, the sample without an internal standard is
analyzed, whereas in a second run, the sample with an
internal standard is analyzed. The comparison between
two analyses allows calculation of the percentages of
sample that were eluted up to 538 °C. With these values,
these percentages are re-normalized from intervalcalculated BPs on the corresponding normalized curve
of distillation for the analysis of the sample without
internal standard.
For quality assurance, the reference gas oil that was
analyzed by physical distillation was also analyzed by
SIMDIS after and before each sequence of samples.
Results are reported in terms of mass percentage in
Table 1 and as the SIMDIS curve in Figure 2.
The BP distribution in Maya crude is described for a
mass fraction of 59.4 mass %, in which the initial boiling
point (IBP) was 36 °C and the final boiling point (FBP)
was 545 °C (see Table 2). The residue fraction is
estimated to be 40.6 mass %. In the Istmo crude, the
BP distribution is given for 80 mass % crude and 20
mass % residue. The corresponding chromatograms of
Maya crude with and without internal standard are
showed in Figure 3. In these chromatograms, the
quantitative calculations are illustrated and were performed using the re-normalization area method: the
chromatogram of the eluted sample is divided in three
segments, each of which represents the percentage of
total area and the total volume of the sample whose BP
interval corresponds to the assigned temperature and
the respective retention time. The first segment (denoted as A or B) corresponds to the total area of the
sample (crude with or without internal standard) that
is eluting up to 538 °C, and the second segment (denoted
as AIS or BIS) is the total area of the internal standard
in the chromatogram either with or without the internal
standard. The third segment (denoted as AI or BI)
describes the area of the noneluted sample after 538
°C. The chromatogram of the sample without internal

standard allows calculation of the relationship that
exists between the area of the second segment and the
sum of the areas of the first and third segments. For
practical purposes, the response factor in each integrated segment is considered to be 1.17 The response of
the detector is proportional to the distilled quantity for
each BP interval, and it is equivalent to the percentage
of this response, with respect to the total response of
the components in the analyzed mixture. Because of the
regularity of elution order, the retention times can be
correlated with BP temperatures, the graphic representation of which is a straight line (see Figure 1). The
empiric correlation between retention time and BP
temperature is established using a mixture of n-paraffin
that covers the expected BP interval. Although these
calculations can be performed automatically by the
SIMDIS software, they can be calculated empirically by
integrating the areas of each segment in both chromatograms.12
The usefulness of any method, in regard to its ability
to determine the tBP curves, is greatly dependent on
its ability to provide repeatable data. Therefore, it is a
fundamental requirement to obtain tBP curves with the
maximum level of repeatability possible. According to
ASTM Method D 5307-97 , the established repeatability
and reproducibility values in Maya and Istmo samples
are compared to the corresponding obtained values in
tBP. Table 3 presents this data as a temperature
fluctuation (twice the standard deviation), in terms of
degrees centigrade, observed for different intervals of
weight percent. Taking into account an average of four
determinations for two different operators, these values
are very satisfactory, in regard to mass percent and even
volume percent.
To describe the improvements of the SIMDIS method
in heavy Mexican crude oils over the physical distillation
method, a comparison of both methods was performed;
(17) Villanti, D. C.; Maynard, J. B.; Aryan, J. C.; Frayed, A. A. Yield
Correlation between Crude Assay Distillation and High-Temperature
Simulated Distillation (HTSD). Presented at the 1997 AIChE Spring
National Meeting Houston, TX, March 9-13, 1997.

1836


˜

Figure 2. Boiling-point distribution plot showing the simulated distillation (SIMDIS) curve for reference gas oil.
Table 2. Boiling Point Distribution in Maya Crude Oila
mass %

boiling point,
BP (°C)

mass %

boiling point,
BP (°C)

mass %

boiling point,
BP (°C)

mass %

boiling point,
BP (°C)

IBPb
1
2
3
4
5
6
7
8
9
10
11
12

<36.0
57.0
89.0
103.0
119.0
127.5
140.0
150.5
157.0
168.5
176.0
185.5
196.5

13
14
15
16
17
18
19
20
21
22
23
24
25

204.0
215.0
221.5
231.5
239.0
249.0
257.0
265.0
272.5
281.0
288.0
296.5
303.0

26
27
28
29
30
31
32
33
34
35
36
37
38

311.0
317.5
326.0
333.0
341.5
348.5
356.0
363.0
369.5
377.5
384.5
392.0
399.5

39
40
41
42
43
44
45
46
47
48
49
50
51

406.5
414.0
421.0
428.0
434.5
441.5
448.5
456.0
463.0
470.0
477.5
484.5
491.5

mass %

boiling point,
BP (°C)

52
53
54
55
56
57
58
59
59.4

498.5
505.5
512.0
518.0
524.0
530.5
536.5
542.5
545.0

a Pertinent sample data: calibration method, ASTM D 5307; sample mass, 0.0717 g; solvent mass, 5.9518 g; mass of internal standard,
0.0100 g; elution at start, 0.04; elution at end, <24.46; found recovery, 59.4%; and used recovery, 59.4%. b Initial boiling point.

this comparison showed good agreement, in terms of
either mass percent or volume percent (see Figures 4
and 5). These comparisons were evaluated by the
standard deviation parameter (σn-1). The value of this
feature, in terms of mass percent, for IBP to FBP of
Maya crude was in the range of 0.0-9.60 for physical
distillation and 0.0-6.71 for SIMDIS; for Istmo crude,
the σn-1 value was 0.0-6.92 for physical distillation and
0.0-0.25 for SIMDIS (see Table 4).
Determination of the volume percentage using the
SIMDIS method is highly desirable, because the majority of refinery operations are based on volume percentage rather than mass percentage. A plot of mass
percentage versus volume percentage is constructed for
the physical distillation results. The obtained curve
allowed interpolation between the mass and volume

percentage values from the SIMDIS method. Before
these values are correlated to determine the corresponding values for volume percentage in the SIMDIS
method (see Table 5), the standard deviation indicates
that the values are in good agreement. The best values
of σn-1 are observed for the SIMDIS method, in comparison to physical distillation. For Maya crude oil, in
terms of volume percentage, the σn-1 value from IBP to
FBP is 0.0 to 0.00 using the SIMDIS method, which
shows slight differences from IBP to FBP (σn-1 is 0.069
to 1.7). For Istmo crude oil, the σn-1 value for physical
distillation from IBP to FBP is 2.6 to 0.00, and the
SIMDIS method exhibits a σn-1 value of 1.8 to 1.8.
The SIMDIS results are dependent on the baseline
and the required correction for compensating the continuous partial loss of the stationary liquid phase,



Figure 3. Chromatograms of Maya crude with internal standard (top) and without an internal standard (bottom).

1838


˜

Table 3. Temperatures for Repeatability and Reproducibilitya
Repeatability (°C)
mass %
(0.5) IBP
5
10
20
30
40
50
60
70
80 FBP
residue

repeatability
3.7
4.7
6.9
6.8
7.6
9.3
10.6
11.8
17.6
24.8
2.6%

(°C)b

reproducibility

(°C)b

10.6
14.8
11.3
15.4
20.4
24.6
30.3
25.9
39.2
38.8
8.1%

a

Istmo crude
2.0
2.0
11.0
2.0
11.0
9.0
10.0
8.0
5.0
0.25
20%

Reproducibility (°C)

Maya crude

Istmo crude

2.0
2.0
10.0
10.0
10.0
15.0
19.0
18.0
0.25

21.5%

40%

Maya crude

2.0
2.0
5.0
8.0
9.0
8.0
8.0
8.0
4.0
0.25

2.0
2.0
5.0
5.2
4.8
5.2
15.4
0.25

41.5%

b

Average of four determinations of the temperature fluctuation and twice the standard deviation. Data obtained using ASTM Method
D-5307 .

Figure 4. Comparison between physical distillation and SIMDIS mass curves (top) and volume curves (bottom) in Maya crude.
Legend for mass curve: ([) physical distillation, (0) SIMDIS 1, and (4) SIMDIS 2. Legend for volume curve: ([) physical distillation
and (4) SIMDIS.

because of the high operation temperatures of the
chromatograph. The chromatograph has a specific device in place to subtract the baseline in each chromatogram electronically. The reproducibility and precision
of the results is achieved with automatic injection. Note
the possible evaporation of the solvent during the

manipulation: the previous registration of the weights
during the sample preparation for each vial diminishes
the systematic error.
The differences of statistical error, or the confidence
interval, between both physical and simulated distillation curves are reported in Table 6. The values for the



Figure 5. Comparison between physical distillation and SIMDIS mass curves (top) and volume curves (bottom) in Istmo crude.
Legend for mass curve: (9) physical distillation, (*) SIMDIS 1, and (b) SIMDIS 2. Legend for volume curve: ([) physical distillation
and (9) SIMDIS.
Table 4. Comparison between Physical Distillation and SIMDIS, on the Basis of Mass Percentage, for Maya and Istmo
Crude Oils
Maya Crude
Physical Distillation

SIMDIS

mass %

boiling point,
BP (°C)a

σb

0.5
5.0
10.0
20.0
30.0
40.0
50.0
55.0
58.0

37.5
115.0
160.0
250.0
320.0
400.0
476.0
516.0
538.5

0.00
3.60
3.05
4.04
3.21
4.16
5.03
4.04
9.60

a

Istmo Crude

boiling point, BP (°C)
mass %
(1)c
(2)d
0.5
5.0
10.0
20.0
30.0
40.0
50.0
55.0
58.0

36.0
100.5
155.0
249.0
329.0
405.0
479.0
514.0
533.0

36.0
100.5
157.0
254.0
334.5
412.5
488.5
523.0
542.5

SIMDIS

σb

mass %

boiling point,
BP (°C)a

σb

0.00
0.00
1.76
3.53
3.88
5.30
6.71
6.36
6.71

0
5
10
20
30
40
50
60
70
77

0.0
80.0
114.5
173.5
235.5
287.5
341.5
401.5
473.5
534.0

0.00
2.94
2.49
3.29
2.64
3.39
4.10
3.29
5.43
6.97

Average of four determinations. b Standard deviation. c Results for operator 1 in SIMDIS.

SIMDIS method are less than the corresponding values
for physical distillation. In SIMDIS, the confidence
intervals after 430-538 °C are greater for Maya crude,

d

boiling point, BP (°C)
mass %
(1)c
(2)d
0.5
5.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0

36.0
89.0
123.5
180.0
238.0
293.5
349.0
405.0
468.5
542.0

36.0
89.0
126.0
184.0
242.5
297.5
351.5
409.0
470.5
541.5

σb
0.00
0.00
1.25
2.00
2.25
2.00
2.00
2.00
1.00
0.25

Results for operator 2 in SIMDIS.

in comparison to Istmo crude. Heavy or very heavy
crude oils can be analyzed by following the improved
methodology described here.

1840


˜

Table 5. Comparison between Physical Distillation and SIMDIS, on the Basis of Volume Percentage, for Maya and
Istmo Crude Oils
Maya Crude

Istmo Crude


SIMDIS


SIMDIS

vol %

boiling point,
BP (°C)a

σb

vol %

boiling point,
BP (°C)a

σb

vol %

boiling point,
BP (°C)a

σb

vol %

boiling point,
BP (°C)a

σb

0.5
10.0
20.0
30.0
40.0
50.0
60.0
64.9

37.7
138.0
210.0
280.0
348.0
420.7
497.3
538.0

0.000
1.750
1.732
5.011
5.563
3.857
2.142
0.000

0.5
10.0
20.0
30.0
40.0
50.0
60.0
64.5

36.0
126.5
216.5
287.5
358.0
435.0
510.0
542.0

0.691
1.312
1.080
2.248
1.700
1.841
1.027
1.700

0.5
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
84.5

25.7
80.0
104.3
153.0
204.3
256.0
309.0
428.7
506.7
538.0

2.625
2.494
1.700
3.682
2.161
3.742
5.312
3.682
5.793
0.000

0.5
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
84.5

0.5
110.0
151.0
209.0
264.5
308.0
363.0
427.0
498.0
542.0

1.871
1.027
1.650
1.650
2.494
1.312
1.871
0.850
3.082
1.841

a

Average of four determinations. b Standard deviation.

Table 6. Comparison of Physical Distillation (ASTM D-2892) and SIMDIS (ASTM D-5307) in Maya and Istmo Crude Oils
Maya Crude
mass %

avg BP
(°C)a

confidence
rangea

0
10.7
20.8
31.5
41.0
58.3

37.67
166.66
254.33
334.67
406.67
538.00

(16.1
(6.6
(5.25
(2.49
(5.73
(0.00

Istmo Crude
SIMDIS GC

mass %

avg BP
(°C)a


confidence
rangea

Operator 1
46.5
(10.5
159.00
(8.5
249.50
(5.5
328
(1.0
403
(1.75
477
(4.0
538.5
(4.0

1
10
20
30
40
50
58.4

a

1
10
20
30
40
50
58.4

Operator 2
43.5
164.25
252.5
328.75
402
473.75
539.75

SIMDIS GC

mass %

avg BP
(°C)a

confidence
rangea

mass %

0.5
10.7
20.8
31.5
41.0
58.3
60.5
70.9
80.0

25.66
144.66
173.66
235.33
287.66
341.00
401.66
473.66
538.00

(2.62
(2.94
(3.30
(2.62
(3.40
(4.11
(3.30
(5.43
(0.00

0.5
10
20
30
40
50
60
70
80

Operator 2
36
123.50
180.00
239.50
295.00
349.25
407.25
469.50
545.00

(0.00
(1.25
(0.50
(2.25
(2.0
(2.0
(1.00
(0.25
(0.00

0.5
10
20
30
40
50
60
70
80

Operator 2
36
122.25
180.0
239.25
295.50
349.00
407.25
469.50
545.00

(0.00
(2.25
(0.50
(1.25
(1.75
(1.75
(1.25
(0.25
(0.00

(7.5
(9.25
(3.5
(0.25
(3.0
(5.25
(5.25

avg BP
(°C)a

confidence
rangea

Average of four determinations.

Conclusions
The true boiling point (tBP) curves that are obtained
by simulated distillation (SIMDIS) are characterized by
a greater level of confidence than those obtained by the
combination of two physical distillation methods, because they are obtained in a single continuous experiment with no additional correction to account for
pressure differences. The volume percentage plot is
characterized by a higher degree of scattering, perhaps
because of the error associated with the fluctuation of
the average density values for individual azeotropic-type
mixtures of compounds in the tBP curve.
A rapid and reliable SIMDIS method that was based
on ASTM Method D-5307-97 for two heavy Mexican
crude oils was assayed and analyzed. The improved
method for preparing the samples and the appropriate

consideration of quantifying the solvent evaporation
deserved special attention. Comparison between the
mass and volume percentage curves for this crude, as
determined by physical distillation and the SIMDIS
methods, showed good agreement. The precision of the
SIMDIS method for these samples at a final boiling
point (FBP) of 538 °C is better than (0.5 mass %. The
correlation between physical and simulated distillation
is, on average , <2 mass % for the interval of 10 °C.
The confidence interval is (2 mass % for Istmo crude
and (3 mass % for Maya crude.
Acknowledgment. The authors wish to acknowledge the financial support of IMP.
EF049919K

Simdis (simulated distillation)

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