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Investigation of Relationships between Petroleum Properties and Their Impact on Crude Oil Compatibility Dicho Stratiev,*,† Ivelina Shishkova,† Angel Nedelchev,† Kiril Kirilov,† Ekaterina Nikolaychuk,† Atanas Ivanov,† Ilshat Sharafutdinov,† Anife Veli,‡ Magdalena Mitkova,‡ Tanya Tsaneva,‡ Nedyalka Petkova,§ Ron Sharpe,§ Dobromir Yordanov,‡ Zlatozvet Belchev,‡ Svetoslav Nenov,∥ Nikolay Rudnev,⊥ Vassia Atanassova,# Evdokia Sotirova,‡ Sotir Sotirov,‡ and Krassimir Atanassov‡,# †

LUKOIL Neftohim Burgas, 8104 Burgas, Bulgaria University Assen Zlatarov, 8010 Burgas, Bulgaria § Energy Services Division, Nalco Company, Naperville, Illinois 60563, United States ∥ University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria ⊥ Ufa State Petroleum Technical University, Ufa, Russia 450080 # Department of Bioinformatics and Mathematical Modelling, Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, 105 Academic Georgi Bontchev Street, 1113 Sofia, Bulgaria ‡

ABSTRACT: Twenty-two crude oils around the world, from which 19 are processed in the LUKOIL Neftohim Burgas (LNB) refinery, were characterized in the LNB research laboratory by measuring 67 properties. These 22 crude oils included light low sulfur, light sulfur, intermediate low sulfur, intermediate sulfur, intermediate high sulfur, heavy high sulfur, and extra heavy extra high sulfur crudes. A new mathematical approachthe intercriteria analysiswas employed to study the relations between the petroleum properties. It was found that the petroleum properties, density, and sulfur content, along with the crude oil simulated distillation, seem to be capable of providing the same information as that from the full assay of a crude oil. Crude oils containing insoluble asphaltenes (self-incompatible oils) were found to have a high content of low aromaticity naphtha and kerosene. It was found that the asphaltene solubility correlated with the asphaltene hydrogen content. The oil solubility power was found to correlate with the oil saturate content. The oil colloidal stability seems to be controlled by the following rule: “like dissolves like”. The higher the aromaticity of the asphaltenes, the higher the aromaticity of the oil is required to keep the asphaltenes in solution. The processing of blends of oils which are incompatible or nearly incompatible may deteriorate the performance of the dewatering and desalting in the refinery, which consequently may damage the equipment due to accelerated corrosion, entailed by salt deposition. The processing of blends of oils, which are incompatible, not always can be related to an increased fouling. determinant for the profitability of an oil company.4,5 The quality of crude oil is known as the single variable that has the biggest impact on refinery performance. The quality and value of a crude oil depend on its true boiling point (TBP) curve, and the quality of crude oil fractions as feeds for refinery units such as reformer, hydrotreaters, FCC (fluid catalytic cracking), and VGO (vacuum gas oil) hydrocracking units, as well as bottom of the barrel conversion units such as visbreaker, coker, and hydrocracker. The quality of crude oil is also affected by the presence of naphtenic acids, sediments, and impurities such as various salts.6,7 Another factor that has an influence on the relative value of a crude oil as a feedstock for a refinery is its compatibility with the other crudes processed in that refinery.8,9 Incompatible crude oils can impair desalter performance and consequently increase corrosion rate and fouling.7,10 Their processing in the refinery can significantly deteriorate refinery economics due to the appearance of unplanned shut down for cleaning and repairing of damaged equipment. This underlines the crucial role of the

1. INTRODUCTION Petroleum refining is a section of the industrial chemistry which provides modern technology the energy that drives it. Although other forms of energy, such as coal, natural gas, and nuclear energy, and recently renewable sources, have made their bid to overtake petroleum, the liquid state of petroleum gives it a great edge. As a result, it can be easily stored and transported in a concentrated form of chemical energy that is relatively safe.1 The fuels produced by petroleum refining are still the main choice for driving our vehicles: automobiles, trucks, airplanes, ships, and trains. The byproducts of petroleum refining provide the petrochemical building block materials: plastics, synthetic fibers, and synthetic elastomers. Petroleum refining business has faced many challenges lately. They concern low and volatile margins, strict environmental legislation, and tough product specifications. As a result, several dozens of refineries worldwide could not survive in these heavy conditions and were shut down.2 Oil refining management is increasingly faced with the often competing requirements to increase margins while maintaining high levels of reliability and on-stream availability.3 Crude oil cost, accounting for around 80% of the refinery expenditures, is the single most important © 2015 American Chemical Society

Received: August 10, 2015 Revised: October 26, 2015 Published: November 16, 2015 7836

DOI: 10.1021/acs.energyfuels.5b01822 Energy Fuels 2015, 29, 7836−7854

Article

Energy & Fuels

Figure 1. Variation of salt content in the raw and desalted crude oil in one of the LUKOIL Neftohim Burgas crude distillation units for a period of 5 years.

the LNB refinery was increased (after the second half of 2013). A laboratory investigation of the influence of the presence of relatively high asphaltenic material such as fuel oil in the Urals crude oil (the typical crude mainly processed in the LNB refinery) in the amount of 5% of the crude oil revealed that the crude oil dewatering cannot be performed at all. This laboratory study was performed to evaluate the effect of mixing of fuel oil with crude oil because the crude oil is transported from the marine terminal to the refinery by a pipeline. The same pipeline is used to transport the fuel oil from the refinery to the marine terminal. As a result, some quantity of mixed crude oil with fuel oil is processed in the refinery crude distillation units. Figure 2 presents the impact of the presence of fuel oil in the blend Urals crude oil (95%)−fuel oil (5%) on the efficiency of dewatering.

process of crude oil selection for achievement of good margins, reliable operation, and high on-stream factor. Pavlovic has shown that crude oil properties, such as API gravity and sulfur content are the accurate indicators for the evaluation of crude oil.11 Swafford and McCarthy have shown that certain petroleum properties (gravity, sulfur content, and simulated distillation) are sufficient to predict the majority of other petroleum properties by using the advanced nonlinear statistics.12 Their statistical model is the engine behind it, Spiral Crude Manager’s ability to update existing assays or create new ones. This model seems to be a valuable tool for the refinery engineers who deal with the crude oil selection. However, Swafford and McCarthy in their study mentioned nothing about crude oil compatibility12 and whether there is a relationship between properties, which characterize oil compatibility and other petroleum properties. LUKOIL Neftohim Burgas (LNB), the only refinery operating these days in Bulgaria, has processed 19 different crude oils for a period of 5 years (between 2010 and 2015). During their processing some upsets in desalting and dewatering operations were registered. Figure 1 is an illustration of wide variation of salts content in the raw and the desalted crude oil. As a result, once the LNB high pressure middle distillate hydrotreater was unexpectedly shut down due to excessive formation of solids in one of its heat exchangers, the consequence was poor desalter performance for that period.13 An expensive compabloc plate heat exchanger that utilizes the heat of vapors from the main rectification column from one of the LNB crude distillation units was damaged every year for a period of three consecutive years due to corrosion entailed by the presence of high salt content in the desalted crude oil. The poor performance of desalter was registered when the amount of alternative crudes processed in

Figure 2. Impact of presence of fuel oil in amount of 5% in Urals crude oil on efficiency of desalting. 7837


Article

Energy & Fuels Table 1 (a) Bulk Properties of the Crude Oils and the Fuel Oil Sample under Study no.

crude oil

d20 4

sulfur, wt %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

crude oil-1 crude oil-2 crude oil-3 REBCO Basrah crude oil-6 Boscan Okwibome Oryx Val’d Agri SLCO crude oil-12 Azeri light crude oil-14 Bonga El Bouri Aseng Arabian medium Ras Gharib Caspian heavy Caspian heavy + REBCO heavy Kazakh crude fuel oil

0.8052 0.8485 0.8633 0.8675 0.8716 0.8488 0.9926 0.8641 0.9122 0.8255 0.8469 0.8466 0.8459 0.8173 0.8716 0.895 0.8707 0.8684 0.9222 0.9304 0.9034 0.8741 1.0150

0.63 0.80 2.63 1.29 2.84 0.21 5.40 0.20 4.21 1.94 0.59 0.61 0.16 0.22 0.25 1.81 0.26 2.24 3.44 1.86 1.61 0.40 2.90

toluene equiv, vol %

heptane dilution test, ml

>100 0 >100 0 >100 0 25 7 25 6 >100 0 15 11 0 >25 33 4.5 15 4 30 5 >100 0 0 >25 >100 0 0 10 30 5 15 8.5 25 6 25 8 10 12 22 9 25 8 60 3 (b) Other Measured Fuel Oil Properties

insolubility no.

solubility blending no.

P-value

15.3 15.7 −73.4 36.9 34.4 −25.7 27.0 0.0 41.1 18.6 39.3 26.4 0.0 20.7 0.0 38.6 24.5 34.5 38.3 20.7 36.6 39.3 68.0

15.3 15.7 −73.4 88.5 75.6 −25.7 86.4 41.0 78.0 33.5 78.6 26.4 36.6 20.7 40.5 77.3 66.3 75.9 99.6 70.2 102.4 102.3 109.0

1.00 1.00 1.00 2.40 2.20 1.00 3.20 1.90 1.80 2.00 1.00 1.00 2.00 2.70 2.20 2.60 3.40 2.80 2.60 1.60

SARA, wt % S-value

Sa

So

saturate, wt %

1.49

0.4970

0.75

23.59

IBP 229 °C

5 wt % 322 °C

10 wt % 371 °C

30 wt % 504 °C

aromatic, wt %

resin, wt %

51.2807 11.00 Simulated Distillation, °C/(wt %) 50 wt % 70 wt % 572 °C 631 °C

asphaltene, wt % 14.20 90 wt % 694 °C

95 wt % 717 °C

FBP 910 °C

fractionated under vacuum from 1 to 0.2 mmHg in a Potstill Euro Dist System according to ASTM D-5236 requirements. Besides TBP analysis of the investigated crude oils, their distillation characteristics were also analyzed by gas chromatographic simulated distillation according to ASTM D-7169 requirements. The densities of the crude oils and their fractions at 20 °C were analyzed according to ASTM D-4052. The sulfur contents in the crude oils and their fractions were analyzed according to ASTM D-4294. The contents of paraffinic, naphthenic, and aromatic portions in the light and heavy naphtha fractions of the investigated crude oils were estimated by the method of Riazi and Daubert.15 The contents of saturate and aromatic compounds in kerosene and diesel fractions of the studied crude oils were determined by ASTM D-5134. The contents of saturate and aromatic compounds in vacuum gas oil fractions of the studied crude oils were determined by the method described in ref 16. The contents of saturates and mononuclear aromatics (MNA) in the vacuum gas oils were determined by the method described in ref 17. The polynuclear aromatic (PNA) content in the VGO was obtained by the difference 100 − (saturates + MNA), %. SARA (saturates, aromatics, resins, and asphaltenes) analysis of the vacuum residual fractions from the investigated crude oils was performed in accordance with the procedure described in ref 16. Specific viscosity of the vacuum residual fractions was measured according to ASTM D-1665 (Engler specific viscosity of tar products) at 120 °C. The conversion of specific viscosity in kinematic viscosity was performed according to the equation18

These data clearly indicate the role of the quality of the hydrocarbon material that is a subject of desalting and dewatering. Crude oil incompatibility is known as a reason for desalter operation upsets and increased equipment fouling.14 In order to understand the relationship between crude oil compatibility test results and the other petroleum properties, 22 crude oils from different parts of the world, 19 of which have been processed in the LNB refinery, were characterized in the LUKOIL Neftohim Burgas Research Laboratory. These 22 crude oils include light low sulfur, light sulfur, intermediate low sulfur, intermediate sulfur, intermediate high sulfur, heavy high sulfur, and extra heavy high sulfur crudes. For the purpose of this study, we decided to apply the intercriteria analysis. The aim of this work is to discuss the relationship between the petroleum properties and their impact on crude oil compatibility.

2. EXPERIMENTAL SECTION Twenty-two crude oils originating from Russia, Kazakhstan, Turkmenistan, Libya, Egypt, Venezuela, Nigeria, Equatorial Guinea, Saudi Arabia, Iraq, and Italy were investigated in this work. Nineteen of them were processed in the LNB refinery, and three of them were considered for possible future processing in the refinery. The crude oils were fractionated ina true boiling point (TBP) Euro Dist System from ROFA Deutschland GmbH, designed to perform according to ASTM D-2892 requirements at pressure drop from 760 to 2 mmHg. Its fractionation column is equipped inside with packing, equivalent to 15 theoretical plates, and the condenser provides the standard’s mandatory reflux ratio of 5:1. The atmospheric residue from the TBP column was

(1)

ν = 7.41E

where ν = kinematic viscosity, mm /s; and E = Engler specific viscosity, °E. The metal content Ni + V in the vacuum residual fractions was measured in accordance with the ASTM D-5863 method. 2

7838


7839

crude oil-1 crude oil-2 crude oil-3 REBCO Basrah crude oil-6 Boscan Okwibome Oryx Val’d Agri SLCO crude oil-12 Azeri light crude oil-14 Bonga El Bouri Aseng Arabian medium Ras Gharib Caspian heavy Caspian heavy + REBCO heavy Kazakh crude

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

22

crude oil

no.

5.82

16.53 9.32 10.12 7.03 8.22 8.41 1.26 7.19 5.55 12.52 9.03 7.28 6.21 10.99 7.60 5.45 5.88 7.80 3.98 0.00 5.27

0.7034

0.6826

0.6768 0.6990 0.6738 0.6874 0.6830 0.6980 0.7247 0.7120 0.6861 0.6822 0.6907 0.7099 0.7101 0.6905 0.7113 0.6971 0.7182 0.6863 0.6943

0.03

0.07 0.02 0.04 0.11 0.04 0.02 0.13 0.07 0.00 0.10 0.01 0.02 0.01 0.03 0.01 0.01 0.08 0.09 0.06 0.02 0.02 5.96

16.80 13.40 12.37 8.79 11.43 11.67 2.26 10.58 8.85 15.63 10.62 10.77 10.57 12.91 10.40 9.27 9.06 10.32 6.48 2.24 5.95 0.7620

0.7587 0.7650 0.7538 0.7622 0.7277 0.7629 0.7525 0.7630 0.7519 0.7562 0.7561 0.7671 0.7666 0.7566 0.7851 0.7678 0.7824 0.7566 0.7617 0.8042 0.7776

d20 4

0.02

0.25 0.04 0.09 0.20 0.09 0.02 0.64 0.08 0.06 0.13 0.02 0.09 0.02 0.05 0.03 0.02 0.10 0.13 0.35 0.12 0.10

sulfur, wt %

yield, wt % of crude

sulfur, wt %


d20 4

heavy naphta (110−180 °C)

light naphta (IBP−110 °C)

5.82

13.08 12.76 8.56 9.00 7.71 10.64 3.58 11.16 7.51 11.51 9.83 11.39 10.57 10.15 10.79 8.36 9.47 10.35 7.27 5.41 7.21


0.8038

0.8010 0.8055 0.7941 0.8057 0.7942 0.8042 0.8244 0.8180 0.7935 0.7941 0.7849 0.8048 0.8043 0.7909 0.8337 0.8108 0.8262 0.7964 0.8125 0.8367 0.8198

d20 4

0.06

0.27 0.11 0.24 0.29 0.30 0.03 2.29 0.10 0.33 0.29 0.06 0.15 0.03 0.06 0.07 0.15 0.16 0.26 1.02 0.26 0.25

sulfur, wt %

kerosene (180−240 °C)

19.00

23.21 25.40 19.68 24.49 19.88 22.50 11.86 34.90 16.20 22.73 22.63 25.43 26.71 22.74 33.42 19.14 23.66 19.96 14.41 23.67 20.15


0.8466

0.8384 0.8527 0.8548 0.8534 0.8518 0.8443 0.8911 0.8769 0.8524 0.8579 0.8523 0.8465 0.8430 0.8252 0.8782 0.8598 0.8579 0.8511 0.8597 0.8742 0.8602

d20 4

0.21

0.63 0.64 1.78 0.90 1.83 0.11 3.83 0.19 1.94 1.91 0.35 0.48 0.09 0.18 0.22 1.21 0.27 1.47 2.31 0.92 0.88

sulfur, wt %

diesel (240−360 °C)

Table 2. TBP Yields, Density, and Sulfur Content of the Wide Fractions from the Crude Oils under Study

39.05

19.96 23.64 24.80 28.27 24.69 28.43 31.50 29.19 24.47 21.64 29.08 29.21 30.27 28.60 27.07 30.94 38.15 25.68 26.65 34.32 29.77


0.8995

0.8970 0.8766 0.9286 0.9304 0.9225 0.8879 0.9525 0.9310 0.9320 0.9430 0.9197 0.8860 0.9009 0.8622 0.9418 0.9134 0.8885 0.9186 0.9385 0.9190 0.9272

d20 4

0.35

0.95 1.37 3.18 1.53 3.25 0.23 4.73 0.29 3.80 3.29 0.80 0.74 0.19 0.26 0.37 1.95 0.32 2.64 2.95 1.62 1.51

sulfur, wt %

vacuum gas oil (360−540 °C)

23.35

9.27 14.57 23.49 24.42 27.07 17.35 49.50 6.86 37.42 14.97 17.81 14.92 14.67 13.61 9.74 25.84 13.75 24.89 40.21 34.36 30.65


0.9637

0.9805 0.9964 1.0447 1.0007 1.0377 0.9620 1.0636 0.9979 1.0840 1.0011 0.9999 0.9785 0.9727 0.9534 0.9947 1.0356 0.9890 1.0100 1.0540 1.0227 1.0100

d20 4

0.91

2.10 2.10 6.30 2.80 6.06 0.63 6.65 0.49 7.92 6.41 1.56 1.69 0.45 0.67 0.73 3.40 0.59 5.00 5.50 3.31 3.01

sulfur, wt %

vacuum resid (540 °C+)

Energy & Fuels Article


Article

Energy & Fuels

Table 3. Chemical Properties of the Light Oil and Heavy Oil TBP Wide Fractions Separated from the Crude Oils under Study (a) Light Oil TBP light naphta (IBP−110 °C)

heavy naphta (110−180 °C)

kerosene (180−240 °C)

diesel (240−360 °C)

no.

crude oil

P

N

sat

A

P

N

sat

A

P

N

sat.

ARO

kero CI

sat

ARO

cetane index

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

crude oil-1 crude oil-2 crude oil-3 REBCO Basrah crude oil-6 Boscan Okwibome Oryx Val’d Agri SLCO crude oil-12 Azeri light crude oil-14 Bonga El Bouri Aseng Arabian medium Ras Gharib Caspian heavy Caspian heavy + REBCO heavy Kazakh crude

75.5 70.0 76.4 72.8 73.9 70.1 63.5 66.7 73.3 74.2 72.0 67.2 67.1 72.1 66.8 70.3 65.3 73.1 71.0

16.0 17.1 14.5 16.9 16.1 17.6 19.3 18.2 15.7 15.8 16.8 18.4 18.9 16.6 18.9 17.6 18.2 16.5 17.9

91.5 87.1 90.9 89.6 90.1 87.7 82.8 84.9 89.0 89.9 88.8 85.5 85.9 88.7 85.6 87.9 83.5 89.6 88.9

8.5 12.9 9.1 10.4 9.9 12.3 17.2 15.1 11.0 10.1 11.2 14.5 14.1 11.3 14.4 12.1 16.5 10.4 11.1

74.0

16.8

90.7

9.3

54.2 52.8 55.4 53.4 61.9 53.3 55.7 53.2 56.0 54.9 54.9 52.2 52.3 54.8 47.9 52.0 48.6 54.8 53.4 43.2 49.7

25.9 25.5 25.8 25.9 25.1 25.8 25.4 25.7 25.0 25.4 25.9 26.1 25.9 25.8 26.2 26.0 26.1 25.7 26.1 26.9 26.1

80.1 78.3 81.3 79.3 87.0 79.0 81.1 78.9 81.1 80.3 80.7 78.3 78.3 80.5 74.1 78.0 74.6 80.5 79.6 70.1 75.8

19.9 21.7 18.7 20.7 13.0 21.0 18.9 21.1 18.9 19.7 19.3 21.7 21.7 19.5 25.9 22.0 25.4 19.5 20.4 29.9 24.2

43.0 42.1 44.7 42.0 44.8 42.4 37.1 39.2 45.0 44.8 47.1 42.2 42.5 45.6 35.5 40.8 37.2 44.2 40.1 34.7 38.7

29.9 29.3 30.1 29.4 29.7 29.5 29.1 28.6 29.5 29.6 29.9 29.6 29.1 29.6 28.3 29.3 28.7 29.9 29.7 28.4 28.9

72.9 71.4 74.8 71.4 74.5 71.9 66.3 67.9 74.5 74.4 77.0 71.8 71.5 75.3 63.9 70.1 65.9 74.0 69.8 63.1 67.5

10.4 20.8 5.2 20.9 9.8 17.0 35.9 36.7 13.0 11.4 18.8 15.7 24.7 8.6 16.9 22.2 38.1 9.3 19.0 32.5 26.7

51.5 46.4 54.0 46.4 51.8 48.3 39.0 38.6 50.2 51.0 47.4 48.9 44.5 52.4 48.3 45.7 37.9 52.0 47.3 40.6 43.5

78.3 69.6 69.2 69.2 69.5 73.6 53.3 56.2 68.0 66.2 69.1 72.6 73.6 81.8 56.9 65.1 64.5 70.8 67.1 60.5 66.3

21.7 30.4 30.8 30.8 30.5 26.4 46.7 43.8 32.0 33.8 30.9 27.4 26.4 18.2 43.1 34.9 35.5 29.2 32.9 39.5 33.7

57.6 52.0 51.7 51.8 52.0 54.6 41.6 43.5 51.0 49.9 51.7 53.9 54.6 59.7 43.9 49.1 48.7 52.7 50.4 46.2 49.9

68.7

18.8

87.4

12.6

53.4

26.3

79.7

20.3

42.6

29.2

71.7

20.9

46.4

69.8

30.2

52.1

22

(b) Heavy Oil TBP vacuum gas oil (360−540 °C)

vacuum resid (540 °C+)

no.

crude oil

sat

ARO

PNA

gasoline precursors

sat

arom

resins

asphalt

CCR

VIS

S-value

Sa

So

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

crude oil -1 crude oil-2 crude oil-3 REBCO Basrah crude oil-6 Boscan Okwibome Oryx Val’d Agri SLCO crude oil-12 Azeri light crude oil-14 Bonga El Bouri Aseng Arabian medium Ras Gharib Caspian heavy Caspian heavy + REBCO heavy Kazakh crude

61.4 71.4 47.7 47.0 50.2 65.7 38.9 46.8 46.4 42.2 51.4 66.6 59.6 79.0 42.7 54.0 65.4 51.8

38.6 28.6 52.3 53.0 49.8 34.3 61.1 53.2 53.6 57.8 48.6 33.4 40.4 21.0 57.3 46.0 34.6 48.2

21.9 15.2 32.8 33.4 30.7 19.1 41.0 33.8 34.0 37.8 29.9 18.4 23.4 10.3 37.4 27.7 19.3 29.5

78.1 84.8 67.2 66.6 69.3 80.9 59.0 66.2 66.0 62.2 70.1 81.6 76.6 89.7 62.6 72.3 80.7 70.5

45.5 35.6 26.3 29.8 26.3 50.0 15.1 31.7 19.3 25.09 47.0 33.5 45.4 41.7 26.4 26.7 22.7 32.6

40.8 42.0 49.7 52.9 54.2 36.6 44.5 56.0 44.1 61.0 42.9 47.6 39.3 49.5 59.0 43.2 58.5 55.5

10.3 16.0 11.3 9.3 7.2 8.3 5.3 10.5 5.7 8.8 4.5 11.3 13.2 7.4 13.9 12.6 15.2 7.5

3.4 6.4 12.8 8.0 12.3 5.1 35.2 1.7 30.9 5.2 5.6 7.6 2.1 1.3 0.7 17.5 3.7 4.5

16.0 18.5 22.3 18.3 23.2 13.6 27.8 12.9 29.4 20.4 15.0 15.1 11.5 11.7 12.8 25.5 14.2 17.1

23 36 121 48 128 13 1028 9 564 80 24 25 19 15 36 139 28 95

2.387 2.869 2.495 3.749 2.967 2.934 2.995

0.556 0.721 0.776 0.939 0.762 0.649 0.993 0.990 0.845 0.933 0.748 0.799 0.660 0.581

2.989

0.767 0.749 0.689 0.749 0.743 0.779 0.668 1.000 0.622 1.000 0.771 0.707 1.000 0.769 1.000 0.693 1.000 0.722

43.9 51.6 48.3

56.1 48.4 51.7

36.2 29.6 32.3

63.8 70.4 67.7

19.7 31.4 32.1

44.7 50.0 48.5

9.6 10.1 10.3

26.0 8.5 9.1

25.1 19.0 18.7

430 121 74

2.530 3.290 3.240

60.2

39.8

22.9

77.1

48.6

40.9

8.0

2.6

10.9

17

4.264

19 20 21 22

Analysis of vacuum residual fraction colloidal stability expressed by the S-value (intrinsic stability), Sa (peptisability or ability of the asphaltenes to remain in colloidal dispersion), and So (peptizing power of oil is the “aromatic” equivalent of the oil) was performed in accordance with a modification to ASTM D-7157−05 as described in ref 19.

2.237 3.263 2.724 2.519 2.797

V, ppm

Ni, ppm

0.859 0.960 0.831

120 70 143 227 165 22 2078 1 255 19 116 43 19 37 6 80 13 143

35 33 54 76 43 23 186 18 102 25 46 37 21 33 14 74 23 40

0.671 0.765 0.760

0.832 0.773 0.780

248 382 305

178 109 93

0.840

0.680

65

21

Toluene equivalence, heptane dilution test, insolubility number, and solubility blending numbers of the 22 crude oils under investigation were determined according to the procedures described in ref 1. Tables 1 and 2 summarize the bulk properties of the crude oils under study. Sections a and b of Table 3 summarize data of properties of the 7840


Article

Energy & Fuels Table 4. High Temperature Simulated Distillation (ASTM D-7169) of the Crude Oils under Studya temperature, °C no.

crude

0.5 wt %

5 wt %

10 wt %

20 wt %

30 wt %

40 wt %

50 wt %

60 wt %

70 wt %

80 wt %

90 wt %

95 wt %

99.5 wt %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 17 18 19 20 21 22

crude oil-1 crude oil-2 crude oil-3 REBCO Basrah crude oil-6 Boscan Okwibome Oryx Val’d Agri SLCO crude oil-12 Azeri light crude oil-14 El Bouri Aseng Arabian medium Ras Gharib Caspian heavy Caspian heavy + REBCO heavy Kazakh crude

69 70 57 52 69 68 103 85 36 34 36 71 34 69 69 68 62 67 123 38 72

109 125 115 114 125 114 232 130 118 90 100 125 108 103 133 125 115 142 215 142 161

134 158 150 151 158 151 291 168 161 117 142 161 149 136 173 165 150 195 252 204 211

177 214 216 219 224 220 375 229 236 164 209 219 213 197 243 239 213 276 308 284 271

216 260 283 274 284 276 440 260 303 209 263 265 261 252 299 289 269 344 357 339 322

255 302 342 326 342 328 502 295 369 253 313 307 302 302 350 330 325 407 401 378 371

296 348 394 379 398 378 566 328 433 304 361 350 349 347 401 380 380 462 442 413 418

338 397 443 430 454 420 614 364 500 358 411 397 399 394 448 421 435 522 491 447 464

387 447 499 487 517 461 640 406 574 419 461 442 444 440 503 451 497 584 554 494 524

445 509 568 558 590 524 663 443 635 484 525 500 505 501 569 494 570 636 617 558 596

531 594 645 639 657 607 696 507 673 588 610 593 592 596 644 569 647 679 667 638 657

602 650 686 680 696 658 718 576 701 652 661 653 651 654 686 626 687 708 700 683 694

716 777 847 823 866 771 910 698 846 779 762 784 776 787 840 719 845 893 862 836 839

a

Values for Bonga (No. 15) were not determined.

Table 5. High Temperature Simulated Distillation (ASTM D-7169) of the Crude Oils under Study (Wide Faction Yields)a yield, wt %

a

no.

crude

IBP−110 °C

110−180 °C

180−240 °C

240−360 °C

360−540 °C

540 °C−FBP

1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 17 18 19 20 21 22

crude oil-1 crude oil-2 crude oil-3 REBCO Basrah crude oil-6 Boscan Okwibome Oryx Val’d Agri SLCO crude oil-12 Azeri light crude oil-14 El Bouri Aseng Arabian medium Ras Gharib Caspian heavy Caspian heavy + REBCO heavy Kazakh crude

5.25 3.86 5.08 4.83 3.87 5.18 1.19 3.18 4.71 8.49 6.22 3.52 5.25 6.05 3.37 5.34 4.70 3.29 0.00 3.17 1.22

15.13 9.39 8.01 8.54 8.33 7.78 1.72 8.41 6.83 14.70 8.99 9.18 9.33 10.32 6.95 6.40 9.25 4.90 1.81 4.52 5.37

15.71 11.67 9.41 10.02 9.71 9.71 2.70 12.52 7.96 13.67 10.42 11.66 11.22 11.69 8.94 8.64 10.39 6.32 6.31 6.52 8.08

28.99 27.48 22.69 23.64 22.52 25.05 10.78 34.34 19.62 24.58 24.56 27.85 26.60 25.95 23.28 25.96 23.18 17.92 22.73 21.59 22.99

25.05 32.19 31.50 30.93 29.77 34.41 33.37 35.76 29.49 23.60 31.28 32.80 32.09 29.91 33.63 40.48 29.07 32.09 38.57 41.81 35.44

10.00 15.41 23.31 22.03 25.80 17.86 50.24 5.80 31.39 14.96 18.54 15.09 15.52 16.08 23.82 13.18 23.41 35.49 30.57 22.39 26.89

Values for Bonga (No. 15) were not determined.

wide fractions: light naphtha (IBP−110 °C), heavy naphtha (110− 180 °C), kerosene (180−240 °C), diesel (240−360 °C), vacuum gas oil (360−540 °C), and vacuum residue (540 °C+). Tables 4 and 5 present data of simulated distillation characteristics of the crude oils.

are classified in condensate (API > 45°; specific gravity < 0.8017), light crude oils (API = 34−45°; specific gravity = 0.8017−0.855), medium crude oils (API = 22−33°; specific gravity = 0.8600−0.9220), heavy crude oils (10° < API < 22°; specific gravity > 0.9220 < 1.000), and extra heavy crude oils (API < 10°; specific gravity > 1.000).20,21 Based on sulfur content, crude oils are classified in low sulfur (S < 0.5 wt %), sulfur (1.5% > S > 0.5%), high sulfur (3.1 wt % > S > 1.5 wt %), and extra high sulfur (S > 3.1 wt %).22

3. RESULTS AND DISCUSSION 3.1. Relationships between Petroleum Properties. The crude oils are typically classified based on their specific gravity (density) and sulfur content. Depending on specific gravity, they 7841


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with the membersip function. More formally the IFS itself is formally denoted by

The data in Tables 1 and 2 indicate that all possible crude oils around the world are included in this study. The relative density d20 4 of the studied crude oils varies between 0.8052 and 0.9926, the sulfur content varies between 0.20 and 5.4 wt %. The light naphtha (IBP−110 °C) content varies between 0 and 16.5 wt %; the heavy naphtha (110−180 °C) content varies between 2.2 and 16.8 wt %; the kerosene (180−240 °C) content varies between 3.6 and 13.1 wt %; the diesel (240−360 °C) content varies between 11.9 and 26.7 wt %; the vacuum gas oil (360−540 °C) content varies between 20 and 39.1 wt %; and the vacuum residue (>540 °C) content varies between 9.3 and 49.5 wt %. The data in Table 3a,b show that the hydrocarbon composition of the fractions obtained from the different crude oils differentiates. In the light naphthas, the aromatic portion varies between 8.5 and 17.2%; in the heavy naphthas it varies between 13 and 25.9%. In the middle distillate fractions (kerosene and diesel) aromatic hydrocarbon content varies between 9.3 and 36.7% for the kerosene fractions and respectively between 21.7 and 46.7% for the diesel fractions. The total aromatic content in the vacuum gas oil fractions varies between 21 and 61.1%, and the polynuclear aromatic (PNA) content varies between 15.2 and 41.0%. The content of the most aromatic and polar fraction in the vacuum residual fractions asphaltenesvaries between 1.3 and 35.2%. The density and Conradson carbon content in the vacuum residual fractions, which are known to be related to residue aromatic content23,24 for the investigated crude oil vacuum residual fractions, vary between 0.9637 and 1.0840 for the density and between 10.9 and 29.4% for the Conradson carbon content. In order to investigate the relationships between the different petroleum properties, the novel approach of InterCriteria Analysis (ICrA)25 was employed. The ICrA approach is specifically designed for data sets comprising evaluations or measurements of multiple objects against multiple criteria. In the initial formulation of the method, the aim was to detect dependences between the criteria in order to eliminate future evaluations/measurements against some of the criteria, which exhibit high enough dependences with others. This might be the desire, when some of the criteria are for some reason deemed unfavorable: for instance, they come at a higher cost than other criteria or are harder, more expensive, and/or more timeconsuming to measure or evaluate. Elimination or reduction of these unfavorable criteria from future evaluations or measurements may be desirable from a business point of view in order to the reduce cost, time, or complexity of the process. The method has been under development for the past 2 years and has not yet obtained wide popularity. It differs from the well-known method of correlation analysis, as follows: while in correlation analysis we are interested in the numerical values of the parameters, and the differences between them, here we only render an account of the relations between these numerical values. The building blocks of the presented ICrA for decision support are the two concepts of intuitionistic fuzziness and index matrices. Intuitionistic fuzzy sets defined by Atanassov26−29 are one of the most popular and well-investigated extensions of the concept of fuzzy sets, defined by Zadeh. Besides the traditional function of membership μA(x) defined in fuzzy sets to evaluate the membership of an element x to the set A with a real number in the [0; 1]-interval, in intuitionistic fuzzy sets (IFSs), a second function has been introduced, νA(x) defining respectively the nonmembership of the element x to the set A, which may coexist

A = {⟨x , μA(x), νA(x)⟩|x ∈ E}

and the following conditions hold: 0 ≤ μA(x) ≤ 1,

0 ≤ νA(x) ≤ 1

0 ≤ μA(x) + νA(x) ≤ 1

Multiple relations, operations, and modal and topological operators have been defined over IFS, showing that IFSs are a nontrivial extension of the concept of fuzzy sets. The second concept, on which the proposed method is based, is the concept of index matrix, a matrix which features two index sets. The basics of the theory behind the index matrices is described in ref 30 and recently developed further on in ref 31. In the ICrA approach, the raw data for processing are put within an index matrix M of m rows {O1, ..., Om} and n columns {C1, ..., Cn}, where for every p, q (1 ≤ p ≤ m, 1 ≤ q ≤ n), Op is an evaluated object, Cq is a evaluation criterion, and eOpCq is the evaluation of the pth object against the qth criterion, defined as a real number or another object that is comparable according to relation R with all the rest elements of the index matrix M.

From the aforementioned requirement for comparability, it follows that for each i, j, k it holds the relation R(eOiCk,eOjCk). The relation R has dual relation R̅ , which is true in the cases when relation R is false, and vice versa. For the needs of our decision making method, pairwise comparisons between every two different criteria are made along all evaluated objects. During the comparison, it is maintained one counter of the number of times when the relation R holds and another counter for the dual relation. Let Sμk,l be the number of cases in which the relations R(eOiCk,eOjCk) and R(eOiCl,eOjCl) are simultaneously satisfied. Let also Sνk,l be the number of cases in which the relations R(eOiCk,eOjCk) and its dual R̅ (eOiCl,eOjCl) are simultaneously satisfied. As the total number of pairwise comparisons between the object is m(m − 1)/2, it is seen that there hold the following inequalities: 0 ≤ Skμ, l + Skν, l ≤

m(m − 1) 2

For every k, l, such that 1 ≤ k ≤ l ≤ m, and for m ≥ 2 two numbers are defined: μC , C = 2 k

l

Skμ, l m(m − 1)

,

νCk , Cl = 2

Skν, l m(m − 1)

The pair, constructed from these two numbers, plays the role of the intuitionistic fuzzy evaluation of the relations that can be 7842


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Table 6. Statistically Meaningful Relations between the Bulk Crude Oil Properties Density and Sulfur Content and the Other Petroleum Properties for the 22 Studied Crude Oils positive consonance

d20 4

sulfur, wt %

negative consonance

d20 4

sulfur, wt %

VRO yield, wt % AR yield, wt % kero sulfur, wt % diesel sulfur, wt % VGO sulfur, wt % VRO sulfur, wt % diesel d20 4 VGO d20 4 VRO d20 4 VGO ARO, wt % VGO PNA, wt % VRO asphaltenes, wt % VRO CCR, wt % VRO VIS, mm2/s asphaltenes in crude, wt % VRO res + VRO ARO in crude, wt % PNA from VGO in crude, wt % res + VRO aro + VGO PNA in crude, wt % VRO V, ppm VRO Ni, ppm VRO Ni + V, ppm 540 °C−FBP yield (SD)

0.8524 0.8905 − − − − 0.7667

0.805

light naphtha yield, wt % heavy naphtha yield, wt % kerosene yield, wt % diesel yield, wt % VRO Sa VGO saturates, wt % IBP−110 °C yield (SD), wt % 110−180 °C yield (SD), wt % 180−240 °C yield (SD), wt % 240−360 °C yield (SD), wt %

0.1286 0.1524 0.1524 0.2476 − − 0.2143 0.1190 0.1048 0.1905

− − − − 0.162 0.267 0.395 0.367 0.314 0.190

0.7762 − − − − 0.7476 0.7714 0.8143 0.7857 0.8333 0.7429 0.7333 0.7571 0.8238

0.852 0.957 0.952 0.938 0.790 0.824 0.733 0.733 0.848 0.905 0.919 0.867 0.852 − 0.786 0.824 0.800 0.824 0.776

established between any two criteria Ck and Cl. In this way, the index matrix M that relates evaluated objects with evaluating criteria can be transformed to another index matrix M* that gives the relations among the criteria:

detailed in ref 34. The values of positive consonance with μ = 0.75 ÷ 1.00 means a statistically meaningful positive relation, where the strong positive consonance exhibits values of μ = 0.95 ÷ 1.00 and the weak positive consonance exhibits values of μ = 0.75 ÷ 0.85. Respectively, the values of negative consonance with μ = 0.00 ÷ 0.25 means a statistically meaningful negative relation, where the strong negative consonance exhibits values of μ = 0.00 ÷ 0.05 and the weak negative consonance exhibits values of μ = 0.15 ÷ 0.25,.34 As evident from the data in Table 6, there are statistically meaningful relations between the bulk crude oil property density and the yields of petroleum fractions light (strong negative consonance, μ = 0.129), heavy naphtha (negative consonance, μ = 0.152), kerosene (negative consonance, μ = 0.152), atmospheric (positive consonance, μ = 0.890), and vacuum residue (positive consonance μ = 0.890). These relationships were quantified by the following equations:

From practical considerations, it has been more flexible to work with two index matrices Mμ and Mν, rather than with the index matrix M* of IF pairs. The final step of the algorithm is to determine the degrees of dependence between the criteria. We call these dependences between the criteria “positive consonance”, “negative consonance”, or “dissonance”. Let α, β ∈ [0; 1] be the threshold values, against which we compare the values of μCk,Cl and νCk, Cl. We call these criteria Ck and Cl are in (a) (α, β)-positive consonance, if μCk,Cl > α and νCk,Cl < β; (b) (α, β)-negative consonance, if μCk,Cl < β and νCk,Cl > α; and (c) (α, β)-dissonance, otherwise. The approach is completely data driven, and each new application would require taking specific threshold values α, β that will yield reliable results. Various applications and suggested approaches to defining the thresholds have been discussed in a series of publications, available in ref 32. Here, the ICrA approach finds application over data from the measurement of 22 samples of different crude oils, against 67 criteria (crude oil properties). As a result of running the data through the ICA software application,33 which has been currently under development, the statistically meaningful positive and negative consonances have been detected for the main bulk crude oil properties: density and sulfur content (Table 6). The meanings of the values of positive and negative consonance are

4 LNyield = 71.656 − 73.737d 20

R2 = 0.7471

(2)

4 HNyield = 77.224 − 77.245d 20

R2 = 0.7834

(3)

R2 = 0.7419

(4)

4 keroyield = 52.565 − 49.695d 20 4 AR yield = 275.57d 20 − 189.98

R2 = 0.8254

(5)

4 VROyield = 231.48d 20 − 179.8

R2 = 0.7709

(6)

The data in Table 6 also show that the crude oil density has a statistically meaningful weak relation with the petroleum properties: density of diesel (weak positive consonance, μ = 0.767); density of VRO (weak positive consonance, μ = 0.776); the content of asphaltenes in crude oil (weak positive consonance μ = 0.771). The crude oil density has also statistically meaningful weak relations with the VRO viscosity (weak positive consonance, μ = 0.748) and VRO metal content (weak positive consonance, μ = 0.757). The relations between 7843


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Figure 3. Relation between crude oil density and VRO metals content (a, eq 8); between crude oil sulfur content and VRO viscosity (b, eq 14); between crude oil asphaltene content and VRO viscosity (c, eq 17).

viscosity. It is quantified by

crude oil density and VRO viscosity, and VRO metal content are quantified by

νVRO = 16.017(COA)2 + 148.59COA + 142.19

4 2 4 νVRO = 293046(d 20 ) − 489079d 20 + 204188 2

R2 = 0.9913

(7)

R = 0.8241

Equations 2−16 confirm the high importance of the crude oil bulk properties density and sulfur content. They allow the refiner to obtain valuable information about the potential of any crude as a refinery feedstock. Figure 3 graphically illustrates the strong relation between the crude oil density and the VRO metals content, and that between the crude oil sulfur content and the VRO kinematic viscosity. Metals are known as an irreversible catalyst poison for the residue catalytic upgrading processes.35−38 Therefore, information about their content in the vacuum residual fraction is of great importance. The VRO viscosity has been shown recently to be the factor that controls the viscosity of the unconverted residual oil during the VRO thermal conversion,39 and as such its value has a considerable impact on the refinery economics. In Figure 3, the graphical dependence of VRO viscosity on crude oil asphaltene content is also given. Some equations derived in this work (eqs 9−12) were tested for their predictability with 11 crude oils not included in the starting database of 22 crude oils. These 11 crude oils were arbitrarily chosen from those available in the LUKOIL Neftohim Burgas refinery crude assays. They were analyzed in different laboratories. Table 7 presents data of the densities and sulfur

4 3 4 2 metals VRO = 562786(d 20 ) − 1411016(d 20 ) 4 + 1179088d 20 − 328285

R2 = 0.9719

(8)

It is evident from the data in Table 6 that the bulk crude oil property sulfur has statistically meaningful relations with the petroleum properties: diesel sulfur (strong positive consonance, μ = 0.957), VGO sulfur (strong positive consonance, μ = 0.952), VRO sulfur (positive consonance, μ = 0.938), VRO asphaltene content (positive consonance, μ = 0.848), VRO Conradson carbon content (positive consonance, μ = 0.905), VRO viscosity (positive consonance, μ = 0.919), and the content of asphaltenes in the crude oil (positive consonance, μ = 0.867). These relations are quantified by diesel sul = 0.6447COS VGOsul = 1.001COS

VROsul = 1.8015COS

R2 = 0.9272 R2 = 0.9014

VROasphalt = 6.0616COS + 0.2777

(9) (10)

R2 = 0.8032

(11)

R2 = 0.8378

Table 7. Sulfur Content, Density, and VRO Asphaltenes Content of 11 Crude Oils Not Included in the Original Data Base of 22 Crude Oils

(12)

VROCCR = 3.435COS + 12.885

R2 = 0.8369 (13)

νVRO = 337.07(COS)2 − 478.42COS + 296.29 R2 = 0.9769

(14)

COA = 0.6286(COS)2 − 01519COS + 0.4828 R2 = 0.9261

(17)

(15)

The VRO yield of crude oil can be predicted from information on crude oil density and sulfur content by the regression presented by

no.

crude oil

density at 20 °C, g/cm3

total sulfur, wt %

VRO C7 asphaltenes, wt %

1 2 3 4 5 6 7 8 9 10 11

Ashtart Ostra Bijupira Castilla Escalante Fionaven Heidrun Oriente Patos Marinza Upper Zakum Vasconia

0.8730 0.9433 0.8744 0.9774 0.9043 0.8750 0.9036 0.9115 0.9902 0.8510 0.8968

1.12 0.38 0.43 2.36 0.19 0.29 0.52 1.52 5.27 1.84 0.89

15.12 2.98 6.16 29.81 7.65 0.26 1.24 28.07 30.03 7.02 28.81

VROyield = 131.735d420 + 3.863COS − 98.7 R2 = 0.8892

contents of the 11 crude oils along with their VRO asphaltene contents. Figure 4 shows the agreement between measured and estimated by eqs 9−11 sulfur contents in diesel, VGO, and VRO of the 11 crude oils. These data indicate a relatively good

(16)

Another crude oil property, the asphaltene content in the petroleum, was found to strongly correlate with the VRO 7844


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Figure 4. Agreement between measured and estimated from crude oil sulfur content by eqs 9−12 sulfur content in diesel (a), VGO (b), VRO (c), and VRO asphaltene content (d) of the additionally tested 11 crude oils.

prediction of sulfur content in the fractions from the crude oil sulfur content. From all tested equations, eq 10 best predicts the VGO sulfur content from crude oil sulfur (the squared correlation coefficient R2 = 0.959 is the highest) and then follows eq 9 with R2 = 0.902, and eq 11 predicts the VRO sulfur content from the crude oil sulfur with the least accuracy (R2 = 0.846). Figure 4 also indicates the agreement between measured and estimated by eq 12 VRO asphaltene content. It is evident from these data that eq 12 does not predict well the VRO asphaltene content from the sulfur content of the 11 tested crude oils (R2 = 0.027), which would mean that not for all crude oils their sulfur content is strongly related to the asphaltene content of their VRO fractions. While the sulfur content of diesel, VGO, and VRO were reasonably well predicted from eqs 10 and 11, the VRO asphaltene content was not satisfactorily predicted from eq 12. The examination of eqs 10−12 for their predictability suggests that the equations developed in this work are specific to the starting database of the 22 crude oils and not all of them could be considered predictive for other crude oils. Therefore, an additional verification is required before their application to other crude oils. From the data in Table 8 one can see that there is no strong relation between the hydrocarbon compositions of the different crude oil fractions. The common feature of all investigated crude oils is the increase of the aromatic content with the increase of the boiling point of the fractions. Statistically meaningful strong relations were found between the different properties of the vacuum residual fractions. They are summarized as follows:

VRONi + V = 4E − 05(νVRO)2 − 0.0618νVRO + 150.63 R2 = 0.9089

VROasphalt = 0.1045(VROCCR )2 − 2.5029VROCCR + 17.589

R2 = 0.9390

R2 = 0.9099

(20)

VROasphalt = 5.7E − 11(νVRO)3 − 1.3E − 06(νVRO)2 + 0.0117νVRO + 1.7652 VROCCR = 147.58d420 − 130.47

R2 = 0.9364

(21)

R2 = 0.8719 (22)

A weak statistically meaningful relation was found between VRO saturate content and VRO density (weak negative consonance, μ = 0.219). It is given as follows: VROsat = 266.61 − 232.61d420

R2 = 0.6272

(23)

It can be concluded from eqs 18−23 that the higher the VRO saturates content, the lower the density, the lower the Conradson carbon content, and the lower VRO viscosity. These equations also indicate that density, viscosity, and Conradson carbon content provide sufficient information to predict the VRO saturate and asphaltene content. As can be seen later in this work, this is related to the colloidal stability of the vacuum residual fraction and also to the crude oil colloidal stability. Another manuscript is in the process of preparation where the relations between properties of vacuum residual oils from primary and secondary origin are presented in more detail. The simulated distillation (ASTM D-2887) has been recently proven to be equivalent to the true boiling point (TBP) distillation of oil fractions boiling up to 360 °C at atmospheric

⎛ 1 ⎞2 1 νVRO = 4567970.79⎜ ⎟ − 233056.10 VROsat ⎝ VROsat ⎠ + 3082.84

(19)

(18) 7845


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Table 8. Statistically Meaningful Relations between Properties of the Wide Fractions from the Investigated Crude Oils Obtained by Application of Intercriteria Analysisa

a

P, paraffins; sat, saturates; ARO, aromatics; asphalt, asphaltenes; VIS, viscosity; V, vanadium; Ni, nickel.

pressure.40 The high temperature simulated distillation according to ASTM D-7169 has not proven yet its capability to simulate crude oil TBP. The relation between TBP and the high temperature simulated distillation of the wide oil fractions of the crude oils investigated in this work is summarized as follows:

The data generated in this work and the equations derived thereof suggest that density and sulfur content are fundamental properties of petroleum. The density is known to be related to the aromatic content of hydrocarbon mixtures as crude oil is. However, sulfur also appears to be related to the aromatic content of the crude oil because it is concentrated in the heavier high boiling fractions, which were shown to be more aromatic. The strong relation between the petroleum sulfur and the content of the most aromatic and polar compounds in the crude oilasphaltenes (eq 15)supports the idea of the relation between crude oil aromatics content and sulfur content. This can explain the statement made by Swafford and McCarthy that the petroleum properties gravity and sulfur content, and preferably the simulated distillation, are sufficient to predict most petroleum properties by the use of advanced nonlinear statistics.12 In this work, we also employed the intercriteria analysis to assess the degree of similarity between the studied crude oils on the basis of all analyzed petroleum properties and on the basis of the three fundamental petroleum properties: density, sulfur content, and simulated distillation. The data in Table 9 present an evaluation of the degree of similarity between the investigated crude oils based on the consonances obtained from 67 measured properties of each studied crude oil. These data indicate that, for example, the crude oil Basrah has a very high degree of similarity with Arabian medium (strong positive consonance, μ = 0.974) and with the crude oils El Bouri and Oryx (strong positive consonance, μ = 0.962). A very interesting observation was obtained when the intercriteria analysis was applied to the three crude oil bulk properties: density, sulfur content, and high temperature simulated distillation for assessment of the degree of similarity between the investigated crude oils. The results of application of the intercriteria analysis to the three crude oil bulk properties, density, sulfur content, and high temperature simulated distillation, are presented in Table 10. The data from Tables 9 and 10 are completely the same, which suggests that the information that is contained in the three crude oil bulk properties, density, sulfur content, and high temperature simulation, is equivalent to the information on the

R2 = 0.5488

LNTBP yield = 1.4228SDIBP − 240 + 1.38

(24)

R2 = 0.9054

HNTBP yield = 1.0672SD110 − 180 + 1.38

(25) 2

ker oTBP yield = 0.7797SD180 − 240 + 1.59

R = 0.8415 (27) 2

R = 0.8584

diesel TBP yield = 0.9728SD240 − 360 − 1.43

(28) 2

VGOTBP yield = 1.0629SD360 − 540 − 5.78

R = 0.7199

VROTBP yield = 1.0777SD540 + − 1.06

2

R = 0.9602

ARTBP yield = 1.1056SD360 + − 8.99

2

(29)

(30)

R = 0.9632 (31)

As can be seen from eqs 24−31, the accuracy of prediction of wide oil fractions TBP from data of the high temperature simulated distillation according to ASTM D-7169 (0.5488 < R2 < 0.9632) was not good for all fractions. The precision of prediction of TBP from high temperature simulated distillation was the best for the heavy oil fractionsAR and VRO (R2 > 0.96)and the worst for the lightest crude oil fractionthe light naphtha (R2 = 0.5488). This could be explained by the fact that the high temperature simulated distillation is a technique developed to characterize predominantly heavy oils, although it should characterize hydrocarbon mixtures containing hydrocarbons from C5 to C100. 7846


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Table 9. Degree of Similarity between the Investigated Crude Oils Determined Based on Application of Intercriteria Analysis and 67 Measured Petroleum Properties

Table 10. Degree of Similarity between the Investigated Crude Oils Determined Based on Application of the Intercriteria Analysis and the Bulk Petroleum Properties: Density, Sulfur, and High Temperature Simulated Distillation

molecular weight polynuclear aromatic fraction, insoluble in alkane solvents, which is typically called “asphaltenes”, in an oil fraction or in the petroleum itself, is the main reason for lack of compatibility. In this study, we employed Nalco residual stability analyzer (RSA), which is a rapid and accurate system, producing stability results equivalent to ASTM D-7157 within 15−20 min from receipt of a sample, for measurement of the vacuum residue

crude oil quality characterized by 67 measured parameters. This finding is in line with the statement of Swafford, and McCarthy that the petroleum properties gravity and sulfur content, and the simulated distillation, are sufficient to predict most petroleum properties by the use of advanced nonlinear statistics.12 3.2. Crude Oil Compatibility and Its Dependence on the Other Petroleum Properties. The presence of a high 7847


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Figure 5. Determination of the toluene equivalence test for Oryx crude oil.

Figure 6. Determination of the heptane dilution test for Oryx crude oil.

stability expressed by S-value, Sa, and So.41 It should be noted here that S-value is similar to the P-value (or P-test as described by Wiehe in1) and the meaning of the parameters S-value, Sa, and So from the point of view of Wiehe’s oil compatibility model is the following:

IN = 100(1 − Sa)

(32)

SBN = 100So

(33)

S ‐value =

So SBN = 1 − Sa IN

without precipitating asphaltenes, vH.43 The crude oil IN and the crude oils SBN were calculated by the use of43

IN =

TE 1−

vH 25d

⎡ vH ⎤ SBN = IN⎢1 + ⎥ ⎣ 5 ⎦ P ‐value =

(34)

SBN IN

(35)

(36)

(37)

Equation 37 is from ref 44. In our study, the crude oil insoluble asphaltenes were detected by spot technique. In the spot method, a drop of the blend of test liquid mixture and the crude oil is put on a piece of filter paper and allowed to dry. If the asphaltenes are insoluble, a dark ring or circle will be seen about the center of the yellow-brown spot made by the oil. If the asphaltenes are soluble, the color of the spot made by the crude oil will be relatively uniform.42 Figures 5 and 6 illustrate how the flocculation point in the toluene equivalence test and in the heptane dilution test was defined for Oryx crude oil. In that case, it can be seen that the toluene equivalence test is TE = 33 because the minimum percent of toluene in the toluene−heptane mixture, at which the asphaltenes in Oryx crude oil are soluble, is 33 vol %. The heptane dilution test is vH = 5 mL because this is the maximum volume of

The RSA turned out to be unsuitable for measurement of crude oil insolubility number (IN) and the crude oil solubility blending number (SBN), and for that reason we decided to apply the method described in refs 1 and 42. The crude oil insolubility number and the crude oil solubility blending number were determined by performing the toluene equivalence test and the heptane dilution test. In the toluene equivalence test, a series of vials are prepared containing 2 g of crude oil and 10 mL of toluene−heptane mixture. By varying the percent toluene in the toluene−heptane mixture, the minimum percent toluene required to keep asphaltenes in solution is determined, and this is the toluene equivalence, TE. In the heptane dilution test, 5 mL of crude oil is titrated with n-heptane to determine the maximum volume, in milliliters, of n-heptane that can be added 7848


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Energy & Fuels n-heptane added to the blend n-heptane−Oryx crude oil, which does not precipitate the Oryx crude oil asphaltenes. Both the RSA analyzer and the technique using the toluene equivalence test and the heptane dilution test were applied to commodity fuel oil produced in the LNB refinery. The data of both methods in terms of S-value, Sa, So, and IN, SBN, and P-value are presented in Table 1. It is evident from these data that the difference between P-value and the S-value is 0.113 and it is within reproducibility according to ASTM D-7157 for S-value, which is 0.27 for that case. Based on this comparison, one may conclude that both techniques used in this work provide comparable data regarding oil colloidal stability. The data in Tables 1 and 2 indicate that LNB refinery has processed six crude oils, which were self-incompatible. Crude oils-1, -2, -3, -6, -12, and -14 contained insoluble asphaltenes, which did not require addition of any quantity of normal heptane to these crude oils to reach the flocculation point. They had already achieved the flocculation point and even the addition of 10 mL of toluene to 2 g to these crude oils was insufficient to dissolve the insoluble asphaltenes. The data in Tables 1 and 2 also show that three of the crude oils processed in the LNB refinery did not contain insoluble asphaltenes. These were Okwuibome, Azeri light, and Bonga. Any addition of heptane (higher than 25 mL) to these crude oils was insufficient to flocculate the asphaltenes. Unlike the crude oils, all vacuum residual fractions obtained from all investigated crude oils, as evident from the data in Table 3b, were colloidally stable. Their S-values (the analogue of P-value) of the VROs were not lower than 2.2. Therefore, all investigated VROs were compatible in contrast to the crude oils. The region of near incompatibility is when the mixture of oils has a P-value less than 1.4 (especially less than 1.3).45 With a look at the data in Table 1, one can see that the P-value of the studied crude oils varies between 1.0 for the self-incompatible crude oils and infinity for the crude oils not containing insoluble asphaltenes. The data in Table 3b show that the VRO S-value varies between 2.2 and infinity. Five VROs did not contain insoluble asphaltenes, Okwuibome, Azeri light, Bonga, Aseng, and Vald’Agri, and their Sa was equal to 1. The crude oils Okwuibome, Azeri light, and Bonga did not contain insoluble asphaltenes either. However, the crude oils Aseng and Vald’Agri did contain insoluble asphaltenes. Therefore, the presence of the lighter than the VRO fractions in the crude oils Aseng and Vald’Agri made the asphaltenes in these crudes be converted from lack of insoluble in VRO asphaltenes into the presence of insoluble asphaltenes in the crude oils. In order to understand which is the factor that controls asphaltene solubility, we measured the element composition of 15 asphaltenes (carbon, hydrogen, sulfur, and nitrogen contents). Besides the straight run asphaltenes obtained from the investigated crude oils, secondary asphaltenes from visbreaker and from residue ebullated bed hydrocracking H-Oil, processing VROs obtained from the studied crude oils were also analyzed. The purpose of inclusion of the secondary asphaltenes was to extend the range of variation in the asphaltene solubility (Sa), because the secondary asphaltenes had lower solubility. The data in Figure 7 show that the asphaltene solubility correlates with the asphaltene hydrogen content. The lower the hydrogen content is, the lower the asphaltene solubility. Therefore, the higher the aromaticity of the asphaltenes is , the lower their solubility. The oil colloidal stability depends not only on the asphaltene solubility but also on the oil solubility power. That is why we

Figure 7. Relation between the asphaltene solubility (Sa) and the asphaltene hydrogen content.

investigated which VRO parameter had the greatest influence on the oil solubility power. It turned out that the VRO saturate content best correlated with the oil solubility power. The data in Figure 8 indicate that the higher the VRO saturate content

Figure 8. Relation between oil solubility power of the vacuum residual fractions and the content of saturate compounds.

(hydrogen content), the lower the oil solubility power. In other words, the rule “like dissolves like” controls the colloidal stability of the vacuum residual fractions. If the asphaltenes are very aromatic, they will require a very aromatic oil to keep them in a solvated form. Figure 9 presents data of the relation between the whole vacuum residue Conradson carbon (CCR) content and the asphaltene solubility (Sa). These data clearly indicate that the higher the VRO CCR content is (the lower the hydrogen, and saturate content), the lower the asphaltene solubility. The investigated straight run vacuum residual oils were colloidally stable because the asphaltene and the oil fractions had compatible aromatics content. The secondary visbroken vacuum residual oils had lower colloidal stability because their asphaltenes were less soluble and required higher aromaticity of the maltene fraction to keep them in solution. The secondary converted H-Oil (hydrocracked) vacuum residual fraction is characterized with the asphaltene fraction that has the lowest hydrogen content, and, therefore, the lowest solubility. However, the whole H-Oil vacuum residue does not have the highest 7849


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self-incompatible crude oils. Thus, each of the six selfincompatible crude oils was added to 5 mL of the Caspian heavy crude oil, and the maximum volume in milliliters of nonsolvent oil (in our case the six self-incompatible crude oils) that could be added without precipitating asphaltenes was determined. The mixture at the flocculation point must have the same solubility blending number as when heptane was added to the Caspian heavy crude oil. The solubility blending number of the six self-incompatible crude oils (nonsolvent oils) was calculated from the following expression:1 S NSO =

SCaspian heavy[VNSO − VH] V VNSO⎡⎣1 + 5H ⎤⎦

(38)

In this way, the solubility blending numbers of the six selfincompatible crude oils were found to be following:

Figure 9. Relation between the vacuum residual fraction Conradson carbon content and the asphaltene solubility.

SBNcrude oil‐1 = 15.3;

Conradson carbon content, which suggests that the oil fraction is not so aromatic to keep the converted H-Oil vacuum residual asphaltenes in a solvated form. That is why this vacuum residual oil has the lowest S-value = 1.1, which means that it is colloidally instable. Similar is the interaction between the aspaltenes and the oil fractions in the investigated crude oils. If the asphaltenes do not have compatible aromatic oil fractions, they may become prone to flocculation. In the previous section of this work, it was shown that there is no strong relation between the hydrocarbon compositions of the different crude oil fractions. This means that if the vacuum residual fraction of a crude oil is aromatic, it does not purport that in the same crude oil the naphtha and kerosene fractions are aromatic, too. Therefore, in the presence of a higher amount of naphtha and kerosene fractions, which are known to be poor solvents, if they are not aromatic, the highly aromatic asphaltene fraction could flocculate. This seems to be the case in our study, because the self-incompatible crude oils have the highest content of naphtha and kerosene fractions as evident from Table 2, and the naphtha and kerosene fractions from all studied crude oils as seen from Table 3 are low aromatic. Crude oil-1 has the highest content of naphtha and kerosene fractions = 46.4%, and the crude oil Vald’Agri is the second crude oil with the highest content of naphtha and kerosene fractions = 39.7%. Then follow crude oil-2 = 35.5%, crude oil-14 = 34.1%, crude oil-3 = 31.1%, and crude oil-6 = 30.7%. The higher content of naphtha and kerosene fractions in the crude oil Vald’Agri made the asphaltenes in this crude oil to be converted from lack of insoluble in VRO asphaltenes into the presence of insoluble asphaltenes in the crude oil. It was not possible to estimate the IN and the SBN (of the selfincompatible crude oils and of the crude oils, which did not contain insoluble asphaltenes) by the application of the procedure with measuring the toluene equivalence test and the heptane dilution test. For that reason, nonsolvent oil dilution test, as described by Wiehe,1 was applied to the self-incompatible crude oils, and solvent oil equivalence test was employed for the crude oils Okwibome, Azeri light, and Bonga. For the nonsolvent oil dilution test, the most stable crude oil in this studyCaspian heavy (P-value = 3.4)was used as the reference oil. Oryx crude oil was selected as a reference oil for performing the solvent oil equivalence test since its toluene equivalence test was higher than 20, as recommended by Wiehe.1 The heptane dilution test was rerun on the Caspian heavy crude oil, but the n-heptane was replaced with each of the six

SBNcrude oil‐2 = 15.7;

SBNcrude oil‐3 = − 73.4; SBNcrude oil‐12 = 26.4;

SBNcrude oil‐6 = − 25.7; SBNcrude oil‐14 = 20.7

It should be noted here that the self-incompatible crude oils-3 and -6 demonstrated poorer solubility than the n-heptane. Having in mind that the solubility blending number of n-heptane is equal to zero,1 oils that have a poorer than n-heptane solubility obtain a negative value for their solubility blending number according to eq 38. For the crude oils Okwibome, Azeri light, and Bonga not containing insoluble asphaltenes, the toluene equivalence test was rerun on the Oryx crude oil, but toluene was replaced by each of the crude oils Okwibome, Azeri light, and Bonga. Thus, the concentration of 2 g of Oryx crude oil per 10 mL of test liquid was maintained. The minimum volume percent solvent oil in the test liquid (rest is n-heptane) to keep asphaltene in solution was determined. The mixture at that flocculation point must have the same solubility blending number as the mixture of the toluene equivalence test on Oryx crude oil. SBN of the crude oils Okwuibome, Azeri light, and Bonga (SSO) was estimated by the following expression:1

SSO = 100

VT 10 VSO 10

(39)

In this way, the solubility blending number of the three crude oils, which do not contain insoluble asphaltenes, were found to be the following: SBNOkwuibome = 41.0;

SBNAzeri light = 36.6;

SBNBonga = 40.3

It should be noted here that the SBN of the self-incompatible crude oils depends on the reference oil used. For example, by the use of Caspian heavy as a reference oil, the SBN of crude oil-1 was 15.3, but when REBCO was used as a reference oil, then the SBN of crude oil-1 was found to be = −79.1. Crude oil-1 was a poorer solvent for REBCO than n-heptane. Considering the fact that the addition of 5% commodity fuel oil to REBCO did not allow separating water from the blend 95% REBCO/5% fuel oil (Figure 2) during the laboratory dewatering experiments, we decided to measure the compatibility of the blends of REBCO with fuel oil. The measurement indicated that even at 5% fuel oil in the blend 95% REBCO/5% fuel oil the 7850


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Figure 10. Throughput and fuel consumption in a LNB refinery crude distillation unit for the period when the desalter performance was poor.

mixture was colloidally instable. This can explain why water was not possible to separate from the mixture 95% REBCO/5% fuel oil. By performing a nonsolvent oil dilution test with REBCO as a reference oil and the fuel oil as the nonsolvent, the SBN of the fuel oil was estimated to be SBNfuel oil = −870. That was the lowest SBN determined in this study. One may conclude based on these results that the crude oils and, as a whole, oils with poorer SBN could create problems with the performance of dewatering and desalting in the refinery. The analysis of the fuel consumption in a crude distillation unit of the LNB refinery for the period when the desalting operation was unsatisfactory (as evident from Figure 1 this period was after the second half of 2013 onward) revealed that no increase of fuel consumption was registered (Figure 10). Therefore, no fouling in the heat exchange equipment had appeared. Otherwise, the consumption of fuel would have increased. Based on these findings, a conclusion could be made that processing of blends of oils, which are incompatible or nearly incompatible, may deteriorate the performance of the dewatering and desalting in the refinery, which consequently may damage the equipment due to accelerated corrosion, entailed by salt deposition. The results of this study have also shown, that the processing of blends of oils, which are incompatible, not always can be related to an increased fouling. The evaluation of the factors, which affect the colloidal stability of the investigated crude oils (their P-value), performed by the application of the intercriteria analysis (Table 11), indicate that the crude oil colloidal stability depends mainly on three crude oil properties: (1) the content of light naphtha, of heavy naphtha, and of kerosene; (2) the content of aromatic hydrocarbons in the diesel fraction; (3) the content of VGO boiling range polynuclear aromatics in the crude oil. These findings are in line with the observations reported in other works, which showed that the addition of the highly aromatic diesel boiling range fluid catalytic cracking (FCC) light cycle oil (LCO) and of the highly aromatic

VGO boiling range (FCC) heavy cycle oil (HCO, or slurry) to the vacuum residual feed for the processes thermal cracking and residue hydrocracking, and removal of the light hydrocarbons from the converted products, inhibits the process of asphaltene sedimentation.13,46−48 The data in Table 6 show that the crude oil sulfur content is negatively statistically meaningful as related to the asphaltene solubility, expressed by the parameter Sa (negative consonance, μ = 0.162). This suggests that the higher the crude oil sulfur content is, the lower the asphaltene solubility. This finding is in line with the observed negative effect of sulfur content in the visbreaker feedstock (vacuum residue) on the thermal conversion level at constant unconverted residue colloidal stability, as reported in our recent work.39 Sulfur content, as it was earlier discussed, seems to be related to the aromatics content and, as it was shown in previous text, the higher the asphaltene aromatic structure content is, the lower the asphaltene solubility. It is wellknown that the asphaltene solubility limits the conversion level that could be achieved during thermal conversion of vacuum residue. Wiehe and Jermansen49 have shown that besides the highly aromatic gas oils, the synthetic dispersants can also greatly increase the solubility of asphaltenes in crude oils at low concentrations. Considering the negative influence of the poor solubility of asphaltenes on the process of crude oil dewatering, we decided to perform dewatering experiments with REBCO crude oil and a blend of it with the commodity fuel oil that already proved to be the strongest nonsolvent with and without the presence of a synthetic demulsifier. The results of these experiments are presented in Figure 11. It is evident from these data that even the addition of 1% of the strongest nonsolvent the commodity fuel oil to the REBCO crude oilmade the process of water separation impossible to take place. The water cannot be segregated from the hydrocarbon mixture REBCO− fuel oil. The addition of 10 ppm synthetic demulsifier, however, 7851


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aromatics, resins, and asphaltenes (SARA) compositional analysis of crude oil blends to quantify the colloidal instability of oils:52

Table 11. Statistically Meaningful Relation between Properties Characterized Colloidal Stability of the Investigated 22 Crude Oils and the Other Petroleum Properties Obtained by Application of the Intercriteria Analysis (Consonance Values) toluene heptane equivalence dilution test test SBN light naphtha yield, wt % heavy naphtha yield, wt % kerosene, wt % AR yield, wt % light naphtha d20 4 diesel d20 4 kerosene saturates content, wt % diesel saturates content, wt % diesel aromatics content, wt % VRO resins content, wt % light naphtha paraffins, wt % of crude light naphtha saturates, wt % of crude heavy naphtha saturates, wt % of crude light naphtha + heavy naphtha saturates, wt % of crude PNA from VGO in crude, wt % of crude

IN

CII =

0.248 0.214 0.243 0.743

0.223 0.169 0.224 0.801

0.271 0.733 0.224 0.157 0.752 0.286 0.210

0.764 0.271 0.241

0.195

0.248 0.233

0.195

0.229 0.177

0.190

0.252 0.195

0.771

0.743 0.841

(40)

The CII was found by Hong and Watkinson to correlate with the suspended asphaltene concentration of blends of Cold Lake vacuum residue and Athabasca atmospheric tower bottoms with pure n-alkanes, a lube oil base stock, a heavy vacuum gas oil, and a resin-enriched fraction recovered from Cold Lake vacuum residue by supercritical fluid extraction and fractionation.53 Saleh et al. reported that the CII could be correlated with the concentration of insoluble solids when four crude oils used in Australia (Bach Ho, Gippsland, Cossack, and Kutubu) were blended.54 Hong and Watkinson established that CII was a useful empirical parameter for correlating fouling and precipitation results.55 Robert et al. reported that the unconverted ebullated bed residue hydrocracking H-Oil product CII correlated with the colloidal stability expressed by “spot test result”.56 Watkinson postulated that when CII < 1.0, the amount of resins plus aromatics is sufficient to maintain the asphaltenes in solution. The addition of saturates or removal of aromatics can shift the oil composition such that CII > 1.0, and asphaltenes will precipitate.57 There are also works which report that the CII does not correlate well with the crude oil and asphaltene stability.58−60 During investigation of 16 crude oils, Rogel et al. found that there was no clear relationship between CII and the stability of the studied crude oils.58 In fact, contrary to expectations, they suggested that CII and other composition related indices were not a key factor in determining the asphaltene stability for the studied 16 crude oils.58 Solaimany Nazar and Bayandory concluded that indexes such as the (aromatic + resins)/(asphaltene + saturates) ratio and (aromatics + resins)/ asphaltene ratio did not play a key role in the asphaltene stability for the three dead crude oils studied by them.59 Leon et al. established no relationship between the colloidal stability indexes: ratio of resins to asphaltenes and ratio of resins plus aromatics to saturates plus asphaltenes and flocculation onsets.60 They concluded that the composition of the dispersion medium does not seem to play a key role in the asphaltene stability for the studied crude oils.60 Our data showed a lack of correlation between those based on SARA data CII and the colloidal stability of the VROs measured by the ASTM D-7157 S-value (a correlation coefficient R = 0.034). All investigated VROs were colloidally stable according to S-values (the lowest S-value = 2.387),45 while according to the CII, five of the VROs (from crude oil-6, Boscan, Oryx, SLCO, and heavy Kazakh crude) should be unstable because their CII was lower than unity.56 Considering that the lower boiling fractions have their aromatics content lower than the VRO, their addition to the VRO would reduce the colloidal instability index due to reduction of the denominator in eq 40. The estimated CII of all crude oils except Boscan was found to be higher than unity, which would mean that all crude oils except Boscan should be colloidally unstable. The data in Table 2 show that only six out of 22 crude oils were colloidally unstable and do not support the proposition that CII correlates with oil colloidal stability. These findings are in line with the results reported by Rogel et al.,58 Solaimany Nazar and Bayandory,59 and Leon et al.60

SBN P-value

0.829 0.205 0.190 0.238

saturates + asphaltenes aromatics + resins

Figure 11. Dewatering efficiency with and without using synthetic demulsifier for pure REBCO crude oil and its blend with 1% commodity fuel oil.

made the process of water separation from the hydrocarbon mixture REBCO−fuel oil possible. The presence of the same concentration of 10 ppm demulsifier significantly improves the process of water separation of the REBCO crude oil itself. However, when the quantity of the insoluble asphaltenes becomes too high, as in the case with the blend 95% REBCO/5% commodity fuel oil, the synthetic demulsifier also becomes incapable of assisting the process of water separation from the hydrocarbon mixture. Therefore, more efficient synthetic demulsifiers are required to facilitate the process of water separation for incompatible crude oil blends. Some researchers applied colloidal stability indices based on the oil compositional analysis data to quantitatively describe the oil colloidal stability.50 Asomaning and Watkinson51 introduced a simple colloidal instability index, CII, based on saturates, 7852


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4. CONCLUSIONS By investigating 22 crude oils and their property relationships, which embraced all possible types of crude oils around the world, the following conclusions could be made: (1) The data generated in this work and the equations derived thereof suggest that density and sulfur content are fundamental properties of petroleum and both of them are related to the content of the aromatic species present in the investigated crude oils. The higher the petroleum fraction boiling point is, the higher its aromatic and sulfur content. (2) The petroleum properties density and sulfur content, along with the crude oil simulated distillation, seem to be capable of providing the same information as that from the full assay of a crude oil. (3) The equations derived in this work indicate that density, viscosity, and Conradson carbon content provide sufficient information to predict the VRO saturate and asphaltene content. (4) The high temperature simulated distillation according to ASTM D-7169 of a crude oil is not equivalent to the crude oil TBP analysis. It fits better the TBP of the higher boiling point fractions. Development of a procedure to convert the high temperature simulated distillation into TBP of crude oils is needed to accelerate the process of provision of the information that TBP gives. (5) Crude oils containing insoluble asphaltenes (selfincompatible oils) were found to have a high content of low aromaticity naphtha and kerosene. (6) The asphaltene solubility correlates with the asphaltene hydrogen content. The lower the asphaltene hydrogen content is, the higher their solubility. (7) The oil solubility power correlates with the oil saturate content. The higher the oil saturate content is, the lower the oil solubility power. (8) The oil colloidal stability seems to be controlled by the rule “like dissolves like”. The higher the aromaticity of the asphaltenes is, the higher the aromaticity of the oil is required to keep the asphaltenes in solution. (9) The processing of blends of oils, which are incompatible or nearly incompatible, may deteriorate the performance of the dewatering and desalting in the refinery, which consequently may damage the equipment due to accelerated corrosion, entailed by salt deposition. (10) The processing of blends of oils that are incompatible not always can be related to an increased fouling. (11) The application of synthetic dispersants might alleviate the negative consequences from processing of incompatible or nearly incompatible crude oil blends. (12) No correlation was found between colloidal instability index based on SARA data and the vacuum residual oils and crude oils investigated in this work.

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AUTHOR INFORMATION

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Corresponding Author

*E-mail: [email protected]. Notes

Article

LIST OF ABBREVIATIONS ARyield = yield of atmospheric residue AROTBP yield = TBP yield of atmospheric residual oil CII = colloidal instability index COA = crude oil asphaltenes COS = crude oil sulfur dieselsul = diesel sulfur dieselTBP yield = TBP yield of diesel E = Engler specific viscosity, °E FCC = fluid catalytic cracking HNTBP yield = TBP yield of heavy naphtha HNyield = yield of heavy naphtha IBP = initial boiling point ICrA = intercriteria analysis IN = insolubility number keroTBP yield = TBP yield of kerosene keroyield = Yield of kerosene LNTBP yield = TBP yield of light naphtha LNyield = yield of light naphtha metalsVRO = metal content in vacuum residual oil MNA = mononuclear aromatics content in the vacuum gas oil PV = P value PNA = polynuclear aromatic content in the vacuum gas oil S-value = intrinsic stability SCaspian heavy = solubility blending number of Caspian heavy crude oil SNSO = solubility blending number of the nonsolvent oil SSO = solubility blending number of the solvent oil Sa = peptisability or ability of the asphaltenes to remain in colloidal dispersion SARA = saturates, aromatics, resins, and asphaltenes SBN = solubility blending number SD = high temperature simulated distillation yield So = peptising power of oil, the “aromatic” equivalent of the oil TBP = true boiling point TE = toluene equivalence VH = volume of heptane VNSO = volume of nonsolvent oil VSO = volume of solvent oil VT = volume of toluene VGO = vacuum gas oil VGOsul = vacuum gas oil sulfur VGOTBP yield = TBP yield of vacuum gas oil VRO = vacuum residual oil VROasphalt = vacuum residual oil asphaltene content VROCCR = vacuum residual oil Conradson carbon content VRONi+V = Ni + V content in vacuum residual oil VROsat. = vacuum residual oil saturate content VROsul = vacuum residual oil sulfur VROTBP yield = TBP yield of vacuum residual oil VROyield = yield of vacuum residual oil ν = kinematic viscosity, mm2/s νVRO = vacuum residual oil kinematic viscosity, mm2/s

REFERENCES

(1) Wiehe, I. A. Process Chemistry of Petroleum Macromolecules; Taylor & Francis Group, CRC Press: Boca Raton, FL, USA, 2008. (2) Al-Rashidi, B. Reshaping of Refining Landscape in Europe, IRPC 2014, Verona, Italy, Jun. 24, 2014. (3) Goldhammer, B.; Weber, C.; Christensen, P.; Yeung, S.; Garrett, T.; Yeung, T. PTQ Mag. 2011, Q4, www.digitalrefining.com/article/ 1000384.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The present research has been partly supported by the National Science Fund of Bulgaria under Grant DFNI-I-02-5/2014 “InterCriteria AnalysisA New Approach to Decision Making”. 7853


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Energy & Fuels

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