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8/3/2019 1033_1033_enpromer
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Mercosur Congress on Chemical Engineering
4th
Mercosur Congress on Process Systems Engineering
___________________________________
*Authors to whom correspondence should be addressed.
E-mail addresses: [email protected] and/or [email protected]
1
HEAVY PETROLEUM FRACTIONS CHARACTERIZATION: A NEW
APPROACH THROUGH MOLECULAR DISTILLATION
Batistella, C.B.1, Sbaite, P.
1, Wolf Maciel, M.R.
1, Maciel Filho, R.
1, Winter, A.
1, Gomes, A.
2, Medina, L.
2,
Kunert, R.21 Separation Process Development Laboratory, Faculty of Chemical Engineering,
State University of Campinas (UNICAMP), Brazil.2 CENPES/PETROBRAS, Brazil.
Abstract.Petroleum is evaluated mainly in function of its True Boiling Point (TBP). Through petroleumdistillation curve (TBP), it is possible to evaluate the yields of the products that will be obtained in the
refineries, as well as to establish operational strategies and process optimizations, as the cracking process.
The determination of TBP is well established for petroleum fractions that reach the TBP up to 565C through
ASTM. Even so, for higher temperatures, it does not exist, still, a standard methodology. On the other hand,
the molecular distillation presents great potential for the characterization of heavy oils. Its potential could be
verified in works of the group and it was demonstrated that this process presents short residence time, mild
and appropriate temperature conditions, which avoids, in the case of the petroleum, the thermal cracking,
permitting, thus, the determination of the true boiling points at values not reached so far. In this way,
methodologies were established for the determination of the TBP for the heavy fractions of petroleum above
565C, where it was possible to reach values up to 720C, representing a considerable progress in the
analysis system of the heavy petroleum fractions. Through falling film molecular distillator, experiments
were carried-out using heavy fractions of Brazilian petroleum, where operating temperatures were increased
systematically. With this information, aided to the process conditions of the molecular distillation and the
information of the physical characterizations of the materials being processed in the distillator, mathematical
models were developed in order to determine accurately and appropriately the true boiling points for each
studied heavy petroleum fraction. Finally, once obtained a better characterization of the Brazilian petroleum,
which is considered heavy, it will be possible to increase the operational yields in the refineries, besides
obtaining products of larger commercial interest.
Keywords: Heavy Petroleum, True Boiling Point, Molecular Distillator.
1. Introduction
Residues of petroleum distillation are referred as the bottom products of two types of distillation towers of
the refining processes. The term atmospheric residue describes the material at the bottom of the atmospheric
distillation tower which has an atmospheric equivalent temperature (AET) above 380 oC. The term vacuum
residue (also called heavy petroleum fractions) refers to the bottom of the vacuum distillation which has an
atmospheric equivalent temperature (AET) above 540oC (Madhusudan, 1998).
Molecular Distillation is a separation process, which uses high vacuum, operation at reduced temperatures,
low exposition of the material at the operating temperature and a small distance between the evaporator and the
condenser. It is a process in which vapor molecules escape from the evaporator in direction to the condenser,
where condensation occurs.
Then, it is necessary that the vapor molecules generated find a free path between the evaporator and the
condenser, the pressure be low and the condenser be separated from the evaporator by a smaller distance than
the mean free path of the evaporating molecules (Batistella and Wolf Maciel, 1998; Batistella et al., 2000;
Batistella et al., 2001a,b; Moraes et al., 2004).
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The short residence time of the liquid on the evaporating cylinder, of the order of a few seconds, is
guaranteed by distributing the liquid in the form of a thin film. The combination of a small distance between the
evaporator and the condenser (20-70 mm) with a high vacuum in the distillation gap, results in a specific masstransfer mechanism with evaporation outputs. Moreover, under these conditions, e.g., short residence time and
low temperature, distillation of heat sensitive materials is accompanied by only a negligible thermal
decomposition. Furthermore, the product flow rates are technologically viable (Batistella et al., 2000; Lutisan et
al., 2000). Since heavy petroleum fractions have high molecular weight and are easily cracked, the process
conditions above mentioned allow to apply this technique in petroleum characterization (Maciel Filho et al.,
2005).
Molecular Distillation is a multivariable process and, so, in order to obtain high performance operation, it is
important to define a suitable strategy focused on the product desired characteristics identifying the effect of
each process variable. Furthermore, the interactions among them should be understood and taken into account in
the process development.
According to the projections by the United States Energy Information Administration (EIA), the total world
demand for oil is expected to grow to 123 mmbpd (million barrels per day) by 2025. The Organization of
Petroleum Exporting Countries (OPEC) production is projected to be around 61 mmbpd by 2025, which is more
than twice its production in the year 2001. Production from non-OPEC countries is expected to show a steady
increase from ca. 47 mmbpd in 2002 to ca. 62 mmbpd by 2025.
On the other hand, the shrinking supplies in conventional light crude oils are, and will be, increasingly
forcing the petroleum industry towards upgrading heavier crude oils and residues Hence, with the growing
market demands for high-quality transportation fuels and middle-distillate products, the impetus for obtaining
high conversion from heavy oil and bitumen will be turning residue upgrading into priority research and
development target. Prior to be used as feedstock for conventional refining, bitumen is subjected to upgrading
for the removal of heteroelements and asphaltenes (Dehkissia et al., 2004).
The properties of natural petroleum and petroleum products make use of the True Boiling Point (TBP)
distillation analysis and it has been proved to be very useful for design and operation of refinery units. The TBP
distillation analysis has contributed to the petroleum science and technology, to the classification of petroleum,
to the development of petroleum property correlations and it has been used worldwide. However, when applied
to heavy petroleum fractions, difficulties are often encountered (Yang and Wang, 1999).
Usually, the evaluation of the TBP curve of heavy petroleum fractions has been carried out through ASTM
D2892 and D5236 methods, but values are limited to temperatures below 565oC. For higher temperatures, a well
established method does not exist, although this is a very important achievement, in order to improve the crude
oil processing.
On the other hand, large amounts of crudes processed in oil refineries are set aside as distillation residue. At
present, these residues are of relatively poor commercial value. More detailed structural characterizations are
necessary before to improve process routes to upgrade these materials, to lead them to have added values
(Suelves et al, 2003).
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Brazilian petroleum is becoming heavier, making more difficult the refining process. A new alternative to
obtain heavier petroleum residues was developed (Maciel Filho et al., 2005).
So, the objective of this work is to use the molecular distillation process to extend the TBP curve (above 565C), in order to use it for characterizing vacuum residue of heavy petroleum. This is of great importance for the
optimization of refining processes and environmental issues. Also, the ASTM D1160 will be adapted for high
vacuum for heavy petroleum application.
2. Experimental Procedure Using Falling Film Molecular Distillator
The falling film molecular distillator was used (Figure 1). The basic design of the falling film molecular
distillator unit is the Short Path Distillation unit: a vertical, double jacketed cylinder (evaporator) with a cooled
and centered internal condenser and a rotating roller wiper basket with an external drive. It, also, has a feeddevice with gear pump, rotating carousels that hold discharge sample collectors for distillate and residue (each
carousel consists of 6 collectors which can be positioned and moved by the operator without interrupting the
distillation process), a set of vacuum pumps with an in-line low temperature cold trap and 4 heating units.
A constantly rotating gear pump feeds the sample on a rotating distribution plate from a heatable feed
container. The centrifugal force distributes the material on the inner surface of the evaporator and the gravity
makes it to flow downward; the roller wiper system constantly redistributes it as a very thin film on the
evaporator internal surface. The volatile components of the feed material vaporize from this thin film and
condense on the cooled inner condenser. The most volatile of these vapors condenses on the cold trap and it is
collected. Distillate and residue are each one collected in reservoir cylinders assembled in the two carousels.
It is important to know some technical information about the unit: the size is approximately 221 m, the
feed flow rate capacity is 0.3 to 1.5 kg/h, the evaporator area is 0.048 m2, the evaporator diameter is 10 cm, the
high of the evaporator is 23 cm, the evaporator temperature ranged from 70 a 350oC, the condenser area is 0.065
m2, the condenser temperature ranged from -20 to 120
oC, the feed temperature ranged from 40 to 200
oC, the
residue temperature of exit ranged from 50 a 300oC.
In this work, each distillation experiment was conducted at a constant pressure (10 -3 mbar). Each step
produced one distillate cut and one residue cut. The molecular distillation temperatures (evaporator
temperatures) ranged from 235o
C to 340o
C (equivalent approximately to 591o
C and 720o
C atmospheric
equivalent temperature (AET), respectively): these converted values of molecular distillation temperatures to
atmospheric equivalent temperatures (AET) are obtained through ASTM D 1160 correlation (equations (1) and
(2)). The feed flow rate was 500 ml/h. All these variables were carefully monitored by the controllers present in
the assemble. The final temperature is a limitation of the equipment.
Several kinds of Brazilian vacuum residues were analyzed and here, only one case study is represented to
illustrate the extension of the TBP curve. In this case, a 565oC+ Brazilian vacuum residue (called here Alfa
fantasy name) was used and five distillate and residue fractions were produced through Molecular Distillation,
namely 235oC, 265
oC, 295
oC, 325
oC and 340
oC molecular distillation temperatures.
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Figure 1: The equipment of falling film molecular distillator
3. Extending the TBP Curve
The distillate and residue fractions were obtained from the Molecular Distillator and the temperature values
were converted to atmospheric equivalent temperature (AET) through ASTM D 1160 correlation.
The AET is calculated using the following equation
1.273
00051606.03861.01
1.748
+
=
AT
AAET
(1)
where:
AET = atmospheric equivalent temperature (oC);
A = value obtained from equation (2);
T = experimental temperature (K)
(2)
where:
P = experimental system pressure (mmHg).
P)}log76.95(129.2663/{)}Plog9774472.0(9991972.5{ =A
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3.1. The New Correlation for AET Calculation
A new correlation for AET calculation was developed (Sbaite et al., 2005). It is robust, of easy use andapplied to heavy oil.
The methodology used is based on two procedures, data training and simulated distillation, which allow to
convert the data from molecular distillation process to AET. Furthermore, it allows extending the True Boiling
Point (TBP) curve.
Figure 2 shows the procedure for the development of the new correlation.
The data obtained through the molecular distillation process, represented in Figure 2 as Molecular
Distillation Points are correlated in such way that they compose the TBP curve obtained by ASTM, represented
in the figure as Extension of the TBP curve.
Atmospheric residues 420oC + were distilled in the falling film molecular distillator. From 420oC to 540oC,
the temperatures obtained from the experiments are easily converted to AET using the conventional ASTM. This
step constitutes the so called Training range of the correlation.
For cuts of 540oC +, the following procedure were carried out: it was verified in which temperature the
evaporation started in the molecular distillator. This temperature represents the correspondent value of the AET.
This is the first point of the extended curve. The other points of this extended curve was obtained through the
use of simulated distillation technique, considering the distillate stream.
Figure 3 shows the chromatogram obtained, where it is important to verify the boiling point corresponding to
the final boiling point (FBP). This temperature is the last point of the extended curve.
Several heavy petroleum fractions were used in order to get enough information to be able to obtain an
expression with wider applicability and precision. It is important that the correlation has continuity in relation to
the TBP curve obtained by ASTM.
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Figure 2: ASTM, new correlation and extended TBP curves.
Figure 3: Chromatogram obtained from the distillate stream of the molecular distillation.
Training range of t he
correlation
Initial point of the
extension
Final point of the
extension
TBP curve obtained
through ASTM
0 10 20 30 40 50 60 70 80 90 100
% of Distillate
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
Temperature,
C
Petroleum Gamma
Extension ofthe TBP curve
Molecular Di stillationPoints
______ ASTM TBP Curve
_ _ _ _ Extended TBP Curve
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So, following the procedure described above, FRAMOL correlation was developed (Sbaite et al., 2005):
3624 1013.41064.11677.04.456 MDMDMD TTTAET +++=
(3)
where: AET= Atmospheric Equivalent Temperature, C
TMD = Molecular Distillator Operating Temperature, C
4. Results and Discussion for Alfa Petroleum
The distillation curve was determined, for ASTM D1160, from the temperature and the percentage ofdistillate obtained experimentally but, in this case, using molecular distillation (high vacuum). This is a new
procedure to build-up this curve. The relationship between the operating conditions from Molecular Distillation
and the data obtained from the atmospheric column (given by CENPES/PETROBRAS) generates the extension
of the TBP curve which was analyzed in this work.
Figure 4 shows the extension of the TBP curve of a Brazilian vacuum residue, called here Alfa (fantasy
name) obtained through the methodology developed in this work for the ASTM D1160 application.
It is possible to see that the extended TBP curve is in good agreement with the existing one, even with the
use of the ASTM D1160 correlation, that it is not the most appropriate to be used, because this correlation was
developed to conventional vacuum distillation. It is very important to say that, after developing and working
with this methodology, the new correlation (FRAMOL correlation) was developed and the results are shown in
Figure 5.
Figure 5 shows the TBP curve and its extension obtained with the FRAMOL correlation for the vacuum
residue Alfa. The extension of the curve reached approximately 700oC + and presents continuity and good
agreement with the ASTM curve. Comparing with Figure 4, it can be seen that the FRAMOL correlation
presents better performance than the ASTM D1160 using molecular distillation (high vacuum) for the extension
of the TBP.
Furthermore, it can be seen in Table 1, that the use of molecular distillation also enabled to obtain betterimprovement of the crude oil (gain of about 10% in distillate).
Table 1: Improvement obtained through Molecular Distillation in percentage of distillate accumulated.
Kind of Brazilian
petroleum
Percentage of Distillate
accumulated
Alfa 10
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0 10 20 30 40 50 60 70 80 90 100
% of Distillate
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
Temperature,
C
Petroleum Alfa
_____ AST M TBP curve fromexperimental data
_ _ _ _ ASTM 1160 through
molecular distillation
M olecular Distillation
Points
Extension of theTBP curve
Figure 4: Extension of the True Boiling Point curve for the vacuum residue Alfa (565oC+) through
Molecular Distillation considering ASTM D 1160 correlation.
0 10 20 30 40 50 60 70 80 90 100
% of distillate
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
Temperature,
C
Petroleum Alfa
____ ASTM TBP curve fromexperimental data
_ _ _ Framol Correlation
M olecular distillationPoints
Extension of theTBP curve
Figure 5: Extension of the True Boiling Point curve for the vacuum residue Alfa (565oC+) through
Molecular Distillation considering FRAMOL correlation.
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5. Conclusions
Regarding to the results obtained, it is possible to extend the TBP curve through Molecular Distillation
process with very good precision using the FRAMOL correlation and this is very important to define better
strategies and operating conditions for the petroleum processing, with better economical use of heavy petroleum,
as for example, in lighter components and asphalt, valuing this kind of petroleum due to its better
characterization.
The developments achieved in this work are very important since no standard methodology is available for
calculating the TBP extended curve, considering the large amount of availability of heavy petroleum today
encountered.
6. References
Batistella C.B. and Wolf Maciel, M.R.W. (1998). Recovery of Carotenoids from Palm Oil by Molecular Distillation.
Computers and Chemical Engineering,22, S53-S60.
Batistella, C.B.; Wolf Maciel, M. R.; Maciel Filho, R. (2000). Rigorous modeling and simulation of molecular distillators:
development of a simulator under conditions of non ideality of the vapor phase. Computers and Chemical Engineering,
24, 1309-1315.
Batistella, C. B., Moraes, E. B., Maciel Filho, R. and Wolf Maciel, M. R. (2001a). Molecular Distillation Process for
Recovering Biodiesel and Carotenoids from Palm Oil.Applied Biochemistry and Biotechnology.
Batistella, C. B., Moraes, E. B., Maciel Filho, R. and Wolf Maciel, M. R. (2001b). Molecular Distillation: Rigorous
Modeling and Simulation for Recovering Vitamin E from Vegetal Oils.Applied Biochemistry and Biotechnology.
Dehkissia, S., Larachi, F., Chornet, E. (2004). Catalytic (Mo) upgrading of Athabasca bitumen vacuum bottoms via two-step
hydrocracking and enhancement of Mo-heavy oil interaction.Fuel, 83, 1323-1331.
Lutisan, J, Micov, M., Cvengros J. (2000). Feed temperature influence on the efficiency of a molecular evaporator. Chemical
Engineering Journal, v. 78, 61-67.
Maciel Filho, R., Wolf Maciel, M.R., Sbaite, P., Vasconcelos, C.J.G., Batistella, C.B., Gomes, A., Medina, L. and Kunert, R.
(2005). Internal Report, Laboratory of Separation Process Development (LDPS), Laboratory of Optimization, Design and
Advanced Control (LOPCA), Faculty of Chemical Engineering, State University of Campinas (UNICAMP), Brazil.
Madhusudan, K.R. (1998). High-temperature simulated distillation CG analysis of petroleum resids and their products from
catalytic upgrading over Co-Mo/Al2O3 catalyst. Catalysis Today, v. 43, 187-202.
Moraes, E.B., Batistella, C.B., Torres Alvarez, M.E, Maciel Filho, R., Wolf Maciel, M.R. (2004). Evaluation of tocopherol
recovery through simulation of molecular distillation process.Applied Biochemistry and Biotechnology, 114, (1-3), 689-
712.
Sbaite, P., Batistella, C.B., Vasconcelos, C.J.G., Wolf Maciel, M.R., Maciel Filho, R., Medina, L., Gomes, A., Kunert, R.,
(2005). A new method to extend the true boiling point curve of Brazilian vacue residue thought molecular distillation.
Petroleum Science and Technology, accepted for publication.
Suelves, I., Islas, C. A., Milan, M., Galmes, C., Carter, J.F., Herod, A.A., Kandiyoti, R. (2003). Chromatographic separations
enabling the structural characterization of heavy petroleum residues.Fuel, v. 82, 1-14.Yang, G. E Wang, R.A. (1999). The supercritical fluid extractive fractionation and the characterization of heavy oils and
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petroleum residua. Journal of Petroleum Science and Engineering, v. 22, 47-52.
Acknowledgments
The authors are grateful to FINEP, PETROBRAS and CNPq for the financial support.