properties correlations and characterization of athabasca oil … · 2017-08-27 · vol.4 no.3...

Petroleum Science 2007 Vol.4 No.3

Properties Correlations and Characterization of Athabasca Oil Sands-derived Synthetic Crude Oil

Wang Jun1, 2, Zhao Suoqi1*, Xu Chunming1 and Chung Keng H.1, 3

(1. State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China)

(2. Petrochemical Institute of PetroChina, Beijing 10083, China)

(3. EnergyINet, Calgary, Alberta, Canada)

Abstract: Narrow fractions of Athabasca oil sands-derived synthetic crude oil (SCO) from Canada were obtained by distillation at 20 ºC to 500 ºC and characterized. The yield and properties, such as density, refractive index, viscosity, freezing point, sulfur and nitrogen content and UOP K-index, were correlated as a function of boiling temperature (Tb). The properties of naphtha fractions, jet fuel and diesel fractions could be predicted accurately with the correlations, which are useful for process design considerations, such as optimizing operating conditions of refinery processing units. The other key properties and characteristics of naphtha fractions, jet fuel, diesel and vacuum gas oil were also determined.

Key words: SCO, properties, correlation, characterization

* Author to whom correspondence should be addressed ([email protected])

1. Introduction Oil sands are the largest heavy oil reserves. Since oil

sand bitumen is of high viscosity and contains high contents of contaminants, various upgrading processes are used to remove most of the contaminants and to produce synthetic crude oil (SCO) suitable for pipeline transport. With the high demand for transportation fuels, many countries, including China, are considering importing SCO as a refinery feedstock.

SCO exhibits many specific characteristics that are different from conventional crude oil, partly due to the use of various upgrading processes. Although there has been many reports of properties of SCO (Laureshen, 2005; Isaacs, 2005; Ancheyta-Jua´rez, et al., 2001; Sok Yu and Chung, 2001), further investigation is needed to obtain more SCO data that will be useful in optimizing utilization of SCO in Chinese refineries and have special significance to Chinese refineries.

In this paper, correlations of SCO properties were developed, which are useful for process design and optimization. Narrow fractions of SCO were obtained through distillation and characterized. Correlations derived from narrow-fractions characteristics were used to predict the properties of commercial products, such as naphtha fractions, jet fuel, diesel and vacuum gas oil.

2. Main properties of SCO Table 1 shows the main properties of SCO.

Compared with conventional light crude oil, SCO is almost free from vacuum residues with only 0.003 wt% of carbon residue. But it is comparatively heavy with 40

wt% of vacuum distillates. With a kinematic viscosity of 4.66 mm2/s at 40 ºC and a freezing point less than -60 ºC, SCO exhibits good fluidity. The sulfur and nitrogen contents of SCO are 0.136 wt% and 0.079 wt%, respectively. The contents of asphaltenes, resin and wax are 0.06 wt%, 0.96 wt% and 0.79 wt%, respectively. Nickel, vanadium, iron, aluminum and lead contents are all less than 0.1 ppm, and the amounts of other metals are all less than 1 ppm. These characteristics are likely related to the nature of SCO, which is obtained by various upgrading processes of bitumen extract from oil sands. The characterization index (UOP K-index) of SCO is 11.35, indicating that SCO is a sweet naphthenic crude oil.

Table 1 Properties of Athabasca SCO Density, g/cm3 Elemental, wt%

20 ºC 0.8732 Carbon 87.5370 ºC Hydrogen 12.32

API gravity, ºAPI 29.8 Sulfur 0.136Kinematic viscosity, mm2/s Nitrogen 0.079

40 ºC 4.66 Metals, ppm 80 ºC 2.11 Nickel <0.1100 ºC Vanadium <0.1

Freezing point, ºC <-60 Iron <0.1Open-cup flash point, ºC 19 Sodium 1 Salt, (NaCl) mg/L 8.1 Copper 0.1Water, wt% trace Calcium 0.1Carbon residue, wt% 0.0028 Magnesium 1 Acidity, (KOH)mg/g 0.05 Aluminium <0.1Asphaltenes, wt% 0.06 Lead <0.1Resins, wt% 0.96 UOPK 11.35Waxes, wt% 0.79 Classification Sweet naphthenic base crude oil

Properties Correlations and Characterization of Athabasca Oil Sands-derived Synthetic Crude Oil Vol.4 No.3 85

In general, the main properties of SCO suggest that it is a high quality refinery feedstock. However, it is important to know the distribution of properties to optimize the processing of SCO.

3. Properties of SCO narrow fractions and their correlations

Narrow fractions of SCO were obtained by distillation at 20 ºC to 500 ºC. The distillation curve of SCO is shown in Fig. 1. The yield of fractions at 200 ºC is 16.19 wt%, 55.42 wt% at 350 ºC and 94.62 wt% at 500 ºC, and only 5 wt% of residues above 500 ºC. Figs. 2-8 show the distribution of various properties as a function of boiling point temperature.

Fig. 1 SCO distillation curve

Fig. 2 Density and refractive index for SCO fractions

Fig. 3 Freezing point of SCO fractions

Fig. 4 Viscosity of SCO fractions at different temperatures

Fig. 5 Aniline point of SCO fractions

Figs. 1-3 show that the fraction yield, density and refractive index of SCO increase with increasing boiling point (Tb). The yield, density and refractive index of SCO narrow fractions could be correlated as functions of Tb as follows:

Yield 32bb 10930.7448.2222.283 −×−+= TT

94b

53b 10619.510132.1 −− ×−×+ TT (1)

Density= 3b 10697.31661.0 −×+− T

93b

62b 10640.110164.4 −− ×+×− TT (2)

Refractive Index 4b 10661.91304.1 −×+= T 72

b 10759.5 −×− T (3) The average absolute deviation (AAD) of predicted

yield, density and refractive index were 2.02%, 0.34% and 0.038%, respectively.

Fig. 3 shows the freezing point curve of SCO fractions. For SCO fractions with a boiling temperature lower than 250 ºC, freezing point was below -60 ºC, which is beyond the detection limit of the measuring device. For SCO fractions with a Tb between 250 ºC and 350 ºC, freezing point increases sharply with increasing boiling temperature. For SCO fractions of Tb>350 ºC, freezing point increases gently. The freezing point of SCO fractions could be correlated as a function of Tb as follows, with an AAD of 3.49%.

Petroleum Science 86 2007

Fig. 6 PONA composition in distillation cuts of SCO

Fig. 7 Acidity of SCO fractions

Freezing Point= 41.140 22.218

atan−−

137.57679.575bT (4)

Fig. 4 shows that the viscosities of SCO fractions increase greatly with increasing boiling temperature. The viscosity of SCO fractions at different temperatures, T, could be expressed as the following equation, with an AAD of 9%:

Fig. 8 Sulfur and nitrogen contents of SCO fractions

TTv

b log491.4))log(4179.0256.1exp())775.0log(log(

×−×+=+

(5)

Fig. 5 shows that the aniline point of SCO fractions decreases with increasing boiling temperature at first and reaches a minimum at 200 ºC and then increases with increasing Tb. The aniline point as a function of Tb could be expressed as follows, with an average absolute deviation of 2.03%:

bb /77.62077297.0946.225Point Aniline TT ++−= (6)

The trend of the aniline point from the initial boiling point (IBP) to 200 ºC was not consistent with that of the density or refractive index of SCO fractions. In most cases for straight-run distillation, the aniline point and aromatics content increase as the fractions becomes heavier. Fig. 6b shows that the aromatics content of SCO fractions of 200-500 ºC determined by GC-MS increases with increasing Tb. Fig. 6a shows that the aromatics content in SCO fractions from initial boiling point to 200 ºC increases with increasing carbon number till C9 fractions. However, the aromatics content in C10 to C12 fractions decreases with increasing carbon number, which is probably due to unclear cut of the distillation, in which C10 to C12 fractions are parts of light diesel. Also, it is known that the molecular structure of aromatics has a significant influence on aniline point and poly-aromatics have a lower aniline point.

Fig. 7 shows that the acidity of SCO fractions is low and relatively constant at Tb<250 ºC. It increases dramatically and reaches a maximum at a Tb between 340 ºC and 360 ºC, and levels off at Tb>450 ºC. The acidity of SCO fractions in (KOH)mg/100mL as a function of Tb could be expressed as Equation (7), with an AAD of 22.5% due to high measurement errors of acidity. Nevertheless, the acidity data of SCO fractions show the trend of change.

2b

411.36036.626

1

402.3386.0Acidity−

+

+=T

(7)


Fig. 8 shows the distribution of sulfur and nitrogen contents in SCO. The curves have an “S” shape and sulfur and nitrogen contents could be expressed as follows, with the ADD of 8.80% and 9.54%, respectively:

( )−+

+=

410.39205.549

-exp1

6.3171.650exp Sulfur bT

(8)

( )−+

+=

150.58183.567-exp1

6.3401.844expNitrogenbT

(9)

The average absolute deviation of sulfur and nitrogen were relatively higher due to the large range of variations in sulfur and nitrogen contents from below 10 ppm in light fractions to more than 2,000 ppm in heavy fractions.

Fig. 9 shows the characterization index (UOP K-index) of the SCO fractions. Fig. 9 shows that the K-index decreases with increasing Tb at first and reaches a minimum at 250 ºC and then increases thereafter. For SCO fractions with a Tb between 200 ºC and 420 ºC, the K-index values are less than 11.5, indicating that the fractions are naphthenics. For the other SCO fractions, the K-index values vary from 11.5 to 12.1, indicating that the fractions are of slightly paraffinic nature. In general, SCO is of naphthenic nature.

Fig. 9 UOP K-index of SCO fractions

4. Properties of SCO products 4.1 Naphtha fractions

In commercial gasoline products, the boiling temperature range of naphtha is commonly set from initial boiling point (IBP) to 130 ºC and from IBP to 220 ºC. The IBP-to-130 ºC naphtha from SCO could be used as feedstocks for pyrolysis and catalytic reforming. The properties of SCO IBP-to-130 ºC naphtha are

shown in Table 2. The yield of SCO IBP-to-130 ºC naphtha was 8.43 wt%. The content of sulfur or nitrogen was less than 10 ppm. Doctor test and copper strip corrosion test indicated that SCO IBP-to-130 ºC naphtha was sweet and non-corrosive and was a good reforming feedstock with a latent aromatics content of 32.63 wt%.

The predicted values of properties of SCO IBP-to-130 ºC naphtha using the following three calculation methods are also shown in Table 2:

(a) Mid boiling point average; (b) Five-point average of 10, 30, 50, 70 and 90 vol%

distillation; (c) Integration over the distillation range. The predicted values calculated with the above three

methods are in good agreement with the experimental values (Tables 2 and 3).

Table 2 Properties of SCO IBP-130 ºC naphtha Predicted values

Measured values Method

a Method

b Method

c Yields wt% 8.43 7.81 7.81 7.81 vol% 10.34 Density (20 ºC), g/cm3 0.7032 0.6965 0.6962 0.7030API gravity, ºAPI 68.3 Freezing point, ºC <-60 -70.1 -70.3 -70.09Refractivity (20 ºC) 1.4021 1.4030 1.4030 1.4060Sulfur, ppm <10 5.5 5.5 5.6 Nitrogen, ppm <10 7.5 7.6 7.8 Mercaptans, wt% 0.0001 Doctor test Sweet Acidity, (KOH)mg/100mL 0.22 0.45 0.45 0.45Copper strip test (50 ºC,

3 h), grade <1

Aniline point, ºC 58.6 53.61 53.87 53.27Group analysis, wt% Normal paraffins 32.9 Isoparaffins 28.66 Naphthenics 29.03 Olefins 0.07 Aromatics 9.34 Total 100 Latent content of aromatics,

wt% 32.63

Distillation, ºC IBP 51 10 vol% 65 30 vol% 76 50 vol% 86 70 vol% 98 90 vol% 106 FBP 133 Correlation index, BMCI 14.12 Characterization factor, K-index

12.17


Table 3 Properties of SCO IBP-to-200 C naphtha

Predicted values Measured

values Method a

Methodb

Methodc

Yields wt% 16.19 16.57 16.57 16.57

vol% 18.89

Density (20 ºC), g/cm3 0.7449 0.7478 0.7463 0.7466

API gravity, ºAPI 57.2

Refractivity (20 ºC) 1.429 1.4252 1.4251 1.4254

Freezing point, ºC <60 -69.02 -68.63 -68.53

Sulfur, ppm <10 6 6.7 6.8

Nitrogen, ppm <10 8.9 10 10.2

Mercaptans, wt% 0.0003

Doctor test Sweet

Acidity, (KOH)mg/100mL 0.26 0.47 0.48 0.49Copper strip test (50 ºC,

3 h), grade <1

Aniline point, ºC 46.8 47.97 49.23 49.49

Octane number 57.7

Group analysis, wt%

Normal paraffins 24.49

Isoparaffins 30.17

Naphthenics 25.58

Olefins 0

Aromatics 19.76

Total 100 Latent content of aromatics,

wt% 22.81

Distillation, ºC

IBP 57

10 vol% 79

30 vol% 100

50 vol% 128

70 vol% 154

90 vol% 187

FBP 204

Correlation index, BMCI 19.17 Characterization factor, K-index

11.98

The yield of SCO IBP-to-200 ºC naphtha was 16.19

wt%. The properties of SCO IBP-to-200 ºC naphtha are shown in Table 3. The content of sulfur or nitrogen was less than 10 ppm. Doctor test and copper strip corrosion test indicated that SCO IBP-to-130 ºC naphtha was sweet and non-corrosive. The octane number of SCO IBP-to-200 ºC naphtha was 57.7, much lower than the specification for gasoline (GB17930-99). Except for the octane number, the other properties of SCO IBP-to-200

ºC naphtha met or exceeded the specifications for gasoline. The boiling temperatures of 10 vol% and 50 vol% distillation cuts were all higher than the specifications for gasoline. The Bureau of Mines Correlation Index (BMCI index) of SCO IBP-to-200 ºC naphtha was 19.17 within the range of 18 to 23, indicating that the SCO IBP-to-200 ºC naphtha was a feedstock for intermediate pyrolysis.

4.2 Jet Fuel fraction In commercial product of jet fuel, the boiling

temperature range of kerosene fraction is set at 130 ºC to 230 ºC. The yield of SCO kerosene was 13.86 wt%. Table 4 shows the properties of SCO kerosene. The density,

Table 4 Properties of SCO kerosene


values Method a

Methodb

Methodc

Yields wt% 13.86 13.27 13.27 13.27 vol% 14.87 Density (20 ºC), g/cm3 0.8117 0.8067 0.8066 0.8046API gravity, ºAPI 41.9 Kinematic viscosity (20

ºC), mm2/s 1.4

1.76

1.86

1.86

Refractivity (20 ºC) 1.4537 1.4529 1.4530 1.4521Acidity, (KOH)mg/100mL 0.53 0.54 0.55 0.55 Aniline point, ºC 45.1 45.64 45.92 46.06Sulfur, ppm <10 9.4 10.7 10.9 Nitrogen, ppm 15 15 16.3 16.5 Mercaptans, ppm 3.9 Copper strip test (50 ºC,

3h), grade <1

Closed-cup flash point, ºC 15 Freezing point, ºC <-60 -65.85 -65.55 -65.57Smoke point, mm 15.6 Group analysis, wt% Saturates 72.6 Olefins 1.8 Aromatics 25.6 Distillation range, ºC IBP 142

10 vol% 161

30 vol% 171

50 vol% 187

70 vol% 202

90 vol% 218

95 vol% 225

Correlation index, BMCI 35.37 Characterization factor, K-index

11.51


kinematic viscosity, total sulfur and mercaptan contents, copper strip corrosion test, freezing point and acidity met the specifications for #1 jet fuel. The aromatics content of SCO kerosene was 25.6 wt% which exceeded the specifications of #1, #2 and #3 jet fuels (<20 wt% aromatics for each specification). The SCO kerosene had a lower smoke point of 15.6 mm (25 mm for each specification of #1, #2 and #3 jet fuels) and a lower flash point of 15 ºC (>28 ºC for each specification). So SCO kerosene could be used as blending stocks for jet fuels.

4.3 Diesel fraction The boiling temperature ranges for light and heavy

diesels are 200 ºC to 320 ºC and 250 ºC to 350 ºC, respectively. The yields of SCO light and heavy diesels were 32.8 and 33.13 wt%, respectively; much higher than those from Chinese crude oil. The properties of SCO light diesel are shown in Table 5. The sulfur content

Table 5 Properties of SCO light diesel


values Method a

Methodb

Methodc


ºC), mm2/s 4.28

5.05

5.49

5.61

Refractivity (20 ºC) 1.4802 1.4806 1.4786 1.481Acidity, (KOH)mg/100mL 0.92 0.81 0.87 1.01 Aniline point, ºC 50.4 48.61 48.56 49.34Sulfur, ppm 140 57.6 90.6 140.6Nitrogen, ppm 94 56.5 67.6 91.6 Mercaptans, ppm 2.2 Copper strip test (50 ºC,

3h), grade <1

Closed-cup flash point, ºC 65 Freezing point, ºC -54 -56.12 -55.85 -53.24Cold filter plugging point,

ºC -44

Cetane number 34.4 Distillation, ºC IBP 200 10 vol% 221 30 vol% 238 50 vol% 257 70 vol% 246 90 vol% 300 95 vol% 311 Correlation index, BMCI 45.6 Characterization factor, K-index

11.36

(140 ppm), acidity (0.92 (KOH)mg/100mL) and freezing point (-54 ºC) were much lower than those of the specifications for -50# diesel (500 ppm, 5 (KOH)mg/ 100mL and -35 ºC, respectively). However, SCO light diesel had a relatively lower cetane number (34.4) and higher density (0.8627 g/cm3) that did not meet the specifications for -50# diesel (45 CN and 0.800-0.840 g/cm3, respectively).

Table 6 Properties of SCO heavy diesel


values Method a

Methodb

Methodc


ºC), mm2/s 9.02

9.67

11.68

12.3

Refractivity (20 ºC) 1.4922 1.4921 1.4923 1.4944Acidity, (KOH)mg/100mL 1.56 1.44 1.51 1.67 Aniline point, ºC 52.8 52 52 52.87Sulfur, ppm 290 220.1 311.7 430.4Nitrogen, ppm 213 138 174.4 228.8Mercaptans, ppm 1.44 Copper strip test (50 ºC,

3h), grade <1

Closed-cup flash point, ºC 115 Freezing point, ºC -36 -45.62 -44.56 -42 Cold filter plugging point,

ºC -24

Cetane number 36.2 Distillation, ºC IBP 250 10 vol% 260 30 vol % 277 50 vol % 291 70 vol % 308 90 vol % 327 95 vol % 336 Correlation index, BMCI 49.62 Characterization factor, K-index

11.33

The properties of SCO heavy diesel are shown in

Table 6. The sulfur content (290 ppm), acidity (1.56 (KOH)mg/100mL) and freezing point (-36 ºC) were much lower than those of the specifications for -35# diesel (500 ppm, 7 (KOH)mg/100mL and -10 ºC, respectively). However, SCO heavy diesel had a relatively lower cetane number (36.2) and higher density (0.8835 g/cm3) that did not meet the specifications for -35# diesel (49 CN and 0.800-0.840 g/cm3, respectively). So SCO light and heavy diesels could be good blending stocks for blending with high cetane diesels from paraffinic Chinese crude.


4.4 Vacuum gas oil fraction (VGO) The boiling temperature range of VGO is 350-500 ºC.

VGO from SCO could be used as feedstocks for catalytic cracking. Table 7 shows the properties of SCO VGO. The sulfur (0.23 wt%) and nitrogen (0.19 wt%) contents were within the ranges for feedstock for catalytic cracking (0.18-0.26 wt% sulfur and 0.13-0.22 wt% nitrogen). However, SCO VGO had a relatively lower content of paraffinic carbons (47.31%) and a higher level of aromatic carbons (25.80%), indicating that the performance of SCO VGO for catalytic cracking was not good. It was expected that the products from catalytic cracking of SCO VGO would meet the environmental requirements, but the yield of its liquid products would be low.

Table 7 Properties of SCO VGO


values Method a

Methodb

Methodc

Yields wt% 39.2 38.08 38.08 38.08 vol% 36.86

20 ºC 0.9265 0.9167 0.9203 0.9275Density (20 ºC), g/cm3 70 ºC 0.8983

40 ºC 65.66 32.19 71.29 139.69Kinematic viscosity, mm2/s 100 ºC 6.69 4.13 5.59 8.55API gravity, ºAPI 20.6 Molecular weight 322 Freezing point, ºC -17 -20.24 -19.11 -16.94Carbon residue, wt% 0.009 Acid number, (KOH)mg/g 0.02 Refractivity (20 ºC) 1.5036 1.5159 1.5183 1.5231Structural group analysis* CP, % 47.31 CN, % 26.89 CA, % 25.8 RA 1.03 RN 1.55 RT 2.58 Elemental analysis, wt% Carbon 87.76 Hydrogen 11.74 Sulfur 0.23 0.19 0.21 0.23 Nitrogen 0.19 0.11 0.14 0.19Characterization factor,

K-index 11.31

Distillation, ºC IBP 282 5 vol % 368 10 vol % 369 30 vol % 379 50 vol % 381 70 vol % 402 90 vol % 442 95 vol % 460

Notes: * CP: paraffinic carbons; CN: naphthenic carbons; CA: aromatic carbons; RA: number of aromatic rings of molecule; RN: number of naphthenic rings of molecule; RT: total number of aromatic and naphthenic rings of molecule

5. Conclusions The Athabasca SCO is a sweet naphthenic feedstock

for refinery with good flow properties, such as lower viscosity and freezing point. It has good chemical properties, such as low contents of waxes and resins, and very low content of contaminants, such as sulfur, nitrogen and metals.

The properties correlations give good description of SCO narrow cuts and good prediction for wide fractions from naphtha to VGO.

The light naphtha fractions could be used as feedstock for catalytic reforming and pyrolysis.

Since Athabasca SCO has higher aromatics content, its heavy fractions are not good feedstock for jet fuel and diesel, but may be good blending stocks for the production of low freezing point jet fuel, diesel, and feedstock for FCC.

Acknowledgement China National Petroleum Corporation (CNPC)

provided research funding.

References

Laureshen C. (2005) Processing challenges for Alberta crude in Chinese refineries. China-Canada Heavy Oil Recovery, Processing and Utilization Workshop, September, Beijing

Isaacs E. (2005) Energy innovation to suit tomorrow’s market. China-Canada Heavy Oil Recovery, Processing and Utilization Workshop, September, Beijing

Ancheyta-Jua´rez J., Betancourt-Rivera G., Marroquýń-Sańchez G. M., Pe´rez-Arellano A., Maity, S. K. Cortez, † Ma. T. and R. del Rýó-Soto. (2001) An exploratory study for obtaining synthetic crudes from heavy crude oils via hydrotreating. Energy & Fuels, 15, 120-127

Sok Yu and Chung K. H. (2001) Processing oilsands bitumen. Oil & Gas Journal, 46-52

About the first author Wang Jun was born in 1971. He

received his Master degree from China University of Petroleum (East China) in 2004. Now as a PhD candidate, he is studying at the China University of Petroleum (Beijing) and works on technology management in the petrochemical institute of PetroChina Company Limited.

E-mail: [email protected]

(Received January 15, 2007)

(Edited by Zhu Xiuqin)

properties correlations and characterization of athabasca oil … · 2017-08-27 · vol.4 no.3...

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