Preparation of bitumen from oil sand by ultracentrifugation

Preparation of bitumen ultracentrifugation Deborah

Henry

and Bryan

from

oil sand by

Fuhr

Oil Sands and Hydrocarbon Recovery Department, Alberta Research Council, PO Box 8330, Edmonton, Alberta, Canada T6H 5X2 (Received 23 December 1997; revised 6 July 7992)

Ultracentrifugation was investigated as a means to obtain solvent-free bitumen from oil sand. The bitumen from three oil sands of varying grades was separated by placing the sands in specially designed tubes and centrifuging for 2 h at 198 000 g at 20°C. For all grades of oil sand, approximately 70% of the bitumen was recovered. The recovered bitumen was compared to the residual remaining on the sand, and to that extracted by the conventional Soxhlet technique. The ultracentrifuged bitumen contained some emulsified water and a small amount of fine solids. The solvent-extracted material was water-free, but contained a small amount of residual solvent and fine solids. The ultracentrifuge caused some fractionation of the bitumen, resulting in a product slightly enriched in asphaltene components compared to the solvent-extracted material. The residual bitumen remaining on the sand was correspondingly slightly depleted in asphaltenes. However, as evidenced by gas chromatographic simulated distillation data, ultracentrifugation did retain the light (180-220°C) components of the bitumen which were lost during the solvent removal step following solvent extraction. Other analyses such as density, viscosity and elemental composition verified that ultracentrifugation resulted in some fractionation of bitumen components. (Keywords:

bitumen; oil sand; ultracentrifugation)

Bitumen removal from its sand matrix in oil sand is typically achieved on a laboratory scale by extraction with a solvent. If the purpose is to produce a bitumen for characterization, the extracting solvent must be

removed. The solvent removal process invariably changes the character of the bitumen by removing lower boiling components and also retaining some residual solvent. The ultracentrifuge, on the other hand, removes bitumen mechanically from the oil sand and should result in a bitumen unaltered by solvent handling techniques. Unfortunately, the ultracentrifuge removes only a portion of the total bitumen available, leaving a residual bitumen on the sand. Nagra and Armstrong’, and Wallace et ~1.~ attempted to isolate bitumen from oil sand using centrifugation at low speeds. Recoveries from the oil sand were inconclusive. Williams and Sennhaueserj reported good recoveries using an ultracentrifuge technique but did not characterize the produced bitumen. Gunter et ~1.~reported on the use of the ultracentrifuge to extract the connate water for subsequent analysis. The purpose of the current study is to compare the bitumen removed from oil sand using the ultracentrifuge with that obtained using solvent extraction techniques. Information on the properties of the different bitumens would indicate the usefulness of the ultracentrifuge as an analytical preparatory technique. For completeness, comparisons are also made with the bitumen remaining on the sand following ultracentrifugation.

Presented at ‘Eastern Oil Shale Symposium’, Lexington,

KY, USA

00162361/92/121515-04 i” 1992 ButterworthPHeinemann

Ltd

13-15

November

1991,

EXPERIMENTAL The three oil sands of varying grades used in these experiments were taken from the Suncor Inc. and Syncrude Canada Ltd mines in the Athabasca deposit of northern Alberta. Bitumen was removed from the oil sands using three techniques. Two of the techniques employed a Soxhlet extraction using a modified Dean Stark apparatus5, with toluene at 110°C and methylene chloride at 40°C as the solvents. Toluene was removed from the bitumen-solvent extract to below 1% by rotary evaporation at 60°C and 160 mmHg for 4 h and < 1 mmHg for an additional 8 h. Methylene chloride was removed at 40°C in the same manner. The third technique employed the ultracentrifuge where approximately 30 g of oil sand was spun in a specially constructed centrifuge tube which held the oil sand above a sample reservoir. The bitumen flowed into the reservoir through a 20 pm stainless steel porous disc. A diagram of the tube is shown in Figure 1. Balanced centrifuge tubes were placed in a Beckman model L8-M ultracentrifuge and spun at 198 000 g for 120 min at 20°C. The material collected in the reservoir contained bitumen, water and a cake of fine solids. The water normally formed one or two droplets which were easily removed with a pipette. The bitumen was then recovered from the reservoir taking care not to disturb the fines cake. The bitumen remaining on the sand in the upper portion of the tube was extracted from the sand using a modified Dean Stark apparatus and toluene as the solvent. The toluene was removed from this sample in the same manner as previously described. The bitumens prepared by the three techniques as well

FUEL,

1992,

Vol 71, December

1515

Preparation

of bitumen

by uitracentrifugation:

0. Henry and B. Fuhr

Axis of rotation

Oil sand chamber

Oil

Oil collection chamber

Figure

1

Design

of the ultracentrifuge

tube

as the residual bitumen recovered from the ultracentrifuged sand were analysed for water content by Karl Fisher titration, residual solvent by gas chromatography and ash content by heating to 540°C for 15 h. The bitumens were then characterized by simulated distillation analysis (ASTM P167), density using the Paar densimeter, carbon, hydrogen, nitrogen, oxygen and sulphur by pyrolysis, and viscosity using the Brookfield cone and plate viscometer.

RESULTS

AND DISCUSSION

A comparison of the bitumen, water and solids recovered by the ultracentrifuge and by solvent extraction techniques is given in Table I. Assuming that the solvent techniques remove 100% of the bitumen from the sand, the ultracentrifuge recovers 50-70% of the bitumen available to it. Connate water recovery was in some cases extremely difficult as the water formed a microemulsion in the bitumen. Sample 3 is the best example of this type of behaviour. The ash content of the bitumens was determined to provide an indication of their solids content. The data, shown in Table 2, indicate that fine solids migrated through the 20pm filter into the ultracentrifuged bitumen. The residual bitumen had very low ash contents as did the methylene chloride extracted bitumen. In the former, the fines are preferentially removed during the ultracentrifuging process. Overall, the ultracentrifuged bitumen is low in solids, and solid levels are not significantly higher than that of the toluene extracted bitumen. As also seen in Table 2, ultracentrifuged bitumens contain water which sometimes, as in sample 3, can be seen as several tiny droplets dispersed throughout the bitumen. The water is more typically in a single droplet which is removed, leaving a smaller amount of water in a microemulsion throughout the bitumen. Solvent extraction separates all the water from the bitumen and after rotary evaporation very little solvent remains. The amount of residual solvent remaining in the Soxhlet extracted bitumens is also shown in Table 2. The simulated distillation data, shown in Table 3,

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indicate that the solvent extracted bitumen had consistently higher initial boiling points (IBPs) than the ultracentrifuged bitumen. A set ofcomplete boiling curves for each bitumen recovery technique from sample 2 is shown in Figure 2. The lower boiling point components have been lost with the removal of toluene or methylene chloride. These light components contributed l-3% of the total sample for Athabasca bitumen. This percentage would likely increase with a lighter crude. Coupled with its retention of low boiling components, the ultracentrifuged bitumen had the least amount distilled off by 540°C indicating an enrichment in the higher boiling components. On the other hand, the bitumen extracted from the residual sand after ultracentrifuging contained the highest amount distilled off by 540°C which is consistent with the preceding observation. The low boiling point components, which are retained in the ultracentrifuged bitumen, are lost from the solvent extracted bitumen during the solvent removal step. In summary the simulated distillation data indicate that the ultracentrifuge process results in a fractionation of the heavy bitumen components. According to Stokes’ law, the heaviest molecules in the bitumen should move fastest under the g-forces applied

Table 1 Soxhlet sand samples Sample (no. of subsamples

extraction

and ultracentrifuge

Bitumen (wt%)

analysed)

Sample 1 Ultracentrifuge (19) Toluene extraction (2) Methylene chloride extraction

recoveries

from oil

Water (wt%)

Solids (wt%)

(2)

8.6 (8.4)” 14.7 14.6

0.6 3.0 2.6

nd. 82.3 82.4

(4)

6.8 (5.7)” 8.3 7.8

3.8 10.0 9.7

n.d. 81.6 81.5

(3)

5.6 (4.7)” 9.7 10.0

0.5 3.6 4.1

n.d. 85.9 85.9

Sample

Residual solvent (wt%)

Water (wt%)

Ash content (wt%)

Sample 1 Ultracentrifuge Ultracentrifuge residual Toluene extraction Methylene chloride extraction

n.d.
2.81 n.d. nd n.d.

0.72 0.16 0.45 0.17

Sample 2 Ultracentrifuge Ultracentrifuge residual Toluene extraction Methylene chloride extraction

n.d.
7.31 n.d. n.d. n.d.

0.44 0.14 0.33 0.40

Sample 3 Ultracentrifuge Ultracentrifuge residual Toluene extraction Methylene chloride extraction

n.d. 10.1 0.2
16.14 n.d. nd. n.d.

0.57 0.27 0.48 0.16

Sample 2 Ultracentrifuge (15) Toluene extraction (4) Methylene chloride extraction Sample 3 Ultracentrifuge (15) Toluene extraction (3) Methylene chloride extraction “Corrected for percentage n.d., not determined

Table 2

Impurities

n.d., not determined

water

in the recovered

bitumen

Preparation

of bitumen

by ultracentrifugation:

D. Henry and B. Fuhr

Ultracentrifuge Toluene Extraction Ethylene

Chloride Extraction

Ultracentrifuge

Residual

I

I

I

I

I

10

20

30

40

50

Cumulative % Figure

Table 3

Simulated

2

Results

distillation

of simulated

of the recovered

distillation

IBP (“C)

Ultracentrifuge

%Off at 540°C

of bitumens

recovered

from sample

2

bitumens

Ultracentrifuge Sample

analysis

residual

IBP (“C)

%Off at 540°C

Toluene IBP (“C)

extraction

Methylene

%Off at 540°C

IBP (“C)

chloride

%Off at 540°C

1

195

39

250

41

229

44

221

46

2

179

42

224

53

209

49

224

49

3

180

43

222

51

215

48

215

49

Table 4

Sample 1 2 3

Asphaltene

analysis

Ultracentrifuge 16.6 16.1 16.5

(wt%)

of recovered

Ultracentrifuge residual 15.6 13.0 14.8

Toluene extraction 16.4 14.9 15.1

bitumens Methylene chloride extraction 16.4 15.1 15.8

extraction

Table 5 Density of recovered bitumens at 15°C (g ml-’ ). Data in parentheses are densities for the sample with low boiling components removed mathematically

Sample

Ultracentrifuge

Ultracentrifuge residual

1 2 3

1.0141 (1.0238) 1.0059 ( 1.0090) 1.0085 (1.0148)

1.0180 1.0084 1.0125

Toluene extraction

Methylene chloride extraction

1.0153 1.0058 1.0109

1.0117 1.0093 1Xl096

to the

sample. This theory in fact has been applied to bitumen samples where molecular weight of asphaltenes is determined by ultracentrifuge techniques6-8. In all three samples the residual bitumen exhibited a consistently lower asphaltene level, as seen in Table 4, compared to that of the ultracentrifuged bitumen, providing further evidence for the fractionation between heavy and light components. Most of the solvent extracted bitumens are slightly lower in asphaltene content than are the ultracentrifuged bitumens, but slightly higher than those of the residual bitumens. Although these differences in asphaltene content are small, they are still outside the 3% relative confidence limits for the method5 The density data shown in Table 5 indicate a reasonable agreement between ultracentrifuged bitumen and solvent extracted bitumen. The water contained in

Table 6 Viscosity of recovered bitumens at 25°C (poise). Data corrected for percentage solvent using the Cragoe equation“‘; correction has been made for water or solid contents

Sample

Ultracentrifuge

Ultracentrifuge residual

1 2 3

1140 474 162

1740 551 638

are no

Toluene extraction

Methylene chloride extraction

2300 740 900

2230 1080 1090

the former should not have a significant effect since its density is unity. Apparently, the effects of low boiling components and slightly higher asphaltene contents in the ultracentrifuged bitumens almost cancel each other. A density correction for the low boiling material in the

FUEL, 1992, Vol 71, December

1517

Preparation Table 7

of bitumen

Elemental

by ultracentrifugation:

composition

Sample Sample

extraction

Methylene

chloride

Ultracentrifuge

bitumen

Carbon (wt%)

Hydrogen (wt%)

Nitrogen (wt%)

extraction

residual

extraction

Methylene

chloride

Ultracentrifuge

Sulphur (wt%)

83.50

10.40

0.50

1.09

4.91

83.46

10.46

0.46

0.92

4.63

82.73

9.96

0.29

1.36

4.40

extraction

residual

83.66

10.56

0.47

1.50

4.37

83.32

10.50

0.59

1.11

4.28

83.21

9.81

0.32

1.42

4.04

83.59

10.07

0.50

1.13

4.54

83.15

10.53

0.63

0.88

4.48

82.86

10.06

0.26

1.41

4.15

3

Toluene

extraction

Methylene

chloride

Ultracentrifuge

extraction

residual

ultracentrifuged bitumen is shown in parentheses in Table 5. Sample 1 had 3% of its low boiling components in range. Taking an average density of the C,,-C,, 0.700 g ml- ’ for the light components, the density of 1.0141 g ml-’ for sample 1 is corrected to a density of 1.0283 g ml- ’ without the 3% low boiling components. Similar calculations were done for sample 2 with 1% light components and sample 3 with 2% light components, giving densities of 1.0090 and 1.0148 g ml- I, respectively. The corrected densities are, in five of the six cases, higher than the solvent extracted bitumen densities, as would be expected from the slightly higher asphaltene content. A lower density for the ultracentrifuge residual would have been expected due to its slightly lower asphaltene content, but this was not observed. The dynamic viscosities, at 25°C of the bitumens were also determined and are shown in Table 6. The true ultracentrifuged values are probably less than measured, since emulsified water usually increases the viscosity. The effect of the low boiling components on viscosity must be greater than that of asphaltene content in order to explain the low ultracentrifuge data. Comparing the bitumen from residual and two solvent extractions (none of which contain light ends due to the solvent removal step), a lower viscosity is noted for the residual which is explained by its slightly lower asphaltene content. The water in the ultracentrifuged bitumen prevented accurate carbon, hydrogen, nitrogen, oxygen and sulphur analysis since the water is dispersed into small droplets throughout the bitumen and the sample size for analysis is of the order of milligrams. The water in the sample is not uniform enough at these small sample sizes to give a representative subsample. However, the solvent extracted bitumen and the residual bitumen are compared in Table 7 and are consistent with the fractionation of bitumen in the ultracentrifuge. The data show that the nitrogen and sulphur decrease in the residual sample. Sulphur and nitrogen are associated with the asphaltenes’ of bitumen and demonstrate once again that the asphaltenes have a greater tendency to flow out of the oil sand under ultracentrifuge conditions.

also contains a small amount of solids in proportion to the fines content but not significantly more than that obtained by solvent extraction. Bitumen recovery cannot be linked to oil sand grade. Bitumen recovered by ultracentrifugation contains its original light ends (l-3% in C,,-C1, range for Athabasca bitumen) but is enriched in asphaltenes, with correspondingly higher sulphur and nitrogen contents compared to the bitumen remaining on the sand and solvent extracted bitumen. Bitumen removed by solvent extraction, however, is depleted in light ends during the removal of solvent. The enrichment of light ends in the ultracentrifuged bitumen has a larger effect on viscosity than do the heavy components and asphaltenes. The ultracentrifuged bitumen has significantly lower viscosities than the residual or solvent extracted bitumens. On the other hand, densities of the ultracentrifuged bitumen are in reasonable agreement with those of the solvent extracted bitumens. ACKNOWLEDGEMENT The authors thank the Alberta Oil Sands Technology and Research Authority who funded this work through the Oil Sands Sample Bank project. REFERENCES 1

5

6 7 8

CONCLUSIONS Bitumen recovered from ultracentrifugation contains

1518

Oxygen (wt%)

2

Toluene

Sample

and residual

1

Toluene

Sample

of extracted

D. Henry and B. Fuhr

FUEL, 1992,

Athabasca oil some emulsified

Vol 71, December

sand by water. It

9 10

Nagra, S. S. and Armstrong, D. A. Alberta Oil Sands Technology and Research Authority, Agreement No. 14, University of Calgary, 1978 Wallace, D., Polikar, M. and Ferracuti, F. Fuel 1984, 63, 862 Williams, P. J. and Sennhaueser, G. Presented at ACOSA Workshop, Calgary, Alberta, 1986 Gunter, W. D., Fuhr, B., Bird, G. W. and Holloway, L. paper presented at American Association of Petroleum Geologists Research Conference on Prediction of Reservoir Quality Through Chemical Modelling, Park City, Utah, 21-26 June 1987 Bulmer, J. T. and Starr, J. (Eds) ‘Syncrude Analytical Methods for Oil Sand and Bitumen Processing’, The Alberta Oil Sands Technology and Research Authority, Edmonton, Alberta, 1979 Reerink, H. and Lijenzga, J. J. Inst. Petroleum 1973, 59, 211 Speight, J. G., Wernick, D. L., Gould, K. A., Rao, B. L. M. and Savage, D. W. Reu. Inst. Franc& Petrole 1985, 40, 51 Weeks, R. W. and McBride, W. L. Am. Gem. Sot. Div. Pet. Chem. Prepr. 1979, 24, 990 Vercier, P. Am. Chem. Sot. Mu. Chem. Ser. 1981, 195, 203 Cragoe, C. S. in Proceedings of the World Petroleum Congress, London, 1933, Vol. II, p. 529