Understanding the Demulsification of Water-in-Diluted Bitumen Froth

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Understanding the Demulsification of Water-in-Diluted Bitumen Froth Emulsions Xianhua Feng, and Jacqueline Ann Behles Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b00798 • Publication Date (Web): 15 Jun 2015 Downloaded from http://pubs.acs.org on June 16, 2015

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Understanding the Demulsification of Water-in-Diluted Bitumen Froth Emulsions† Xianhua Feng* and Jacqueline A. Behles Baker Hughes, 7020 45 Street, Leduc, Alberta, Canada T9E 7E7

ABSTRACT Demulsification of water-in-diluted bitumen froth emulsions is greatly affected by the presence of solids in the emulsions. In this paper, the wettability, composition, and particle size distribution of the solids extracted from bitumen froth emulsions and diluted bitumen after demulsification, in the absence and presence of demulsifier, were investigated using partitioning tests, X-ray diffraction, and scanning electron microscopy. It was found that the application of demulsifier assisted in the removal of water-wet solids, and the main components of the solids in the diluted bitumen – siderite and clays. The median particle size of the solids (D50) was reduced from 8 µm in the bitumen froth emulsions to less than 2 µm in the diluted bitumen phase after the use of a demulsifier in the diluted bitumen froth treatment. The presence of fine solids in the diluted bitumen froth increased the water/bitumen interfacial tension and increased the difficulty of demulsification as the fines are bi-wettable and adsorb strongly at the water/bitumen interface. The effect of solids on diluent loss to the settled water and solids phase after demulsification was also studied using model emulsions. The diluent loss was found to increase with the solids content of the emulsions. At the same solids content and composition, the diluent losses increased with the fine solids content of the solids. The application of demulsifier led to a greater diluent loss, and the loss increased with the demulsifier dosage. The results from the

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diluent loss studies revealed that diluent loss is caused by the adsorption of diluent on the solids. The target of demulsification of water-in-diluted bitumen froth emulsions is to achieve clean and dry diluted bitumen ( S2 > S1, as roughly estimated from their volume change. The swelling of


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solids in tailings has been noticed and was ascribed to the swelling of kaolinite and mica of nanometers in size.30 The swelling of solids in the naphtha/brine environment is perhaps due to their bi-wettable surface properties. After the partitioning tests, the solids in the naphtha, water, and at naphtha/water interface were collected. Table 1 shows the distribution of solids in the three phases. There were nearly no solids in the organic phase, based on the limitations of the method used. The mass ratios of solids at the interface to the solids in water are 1.0, 2.0, and 2.7 for S1, S2, and S3, respectively. The results in Table 1 indicate that in the bitumen froth solids (S1), half of the solids are bi-wettable and half are hydrophilic. After froth treatment without the application of a demulsifier, 2/3 of the solids in the diluted bitumen (S2) were bi-wettable and 1/3 were hydrophilic, suggesting settling helped remove the hydrophilic solids. The application of demulsifier in the froth treatment process helped further remove these particles from the diluted bitumen. Consequently, the S3 solids had less water-wet particles, which is consistent with a lower water content of the diluted bitumen (Figure 1). Of course, large particles may also settle to the water phase in the partitioning tests regardless of whether they are hydrophilic or hydrophobic in nature. Therefore, the solids in the water phase observed in the partitioning tests contained hydrophilic solids and large hydrophobic solids, if any. Chen et al.31 investigated the partitioning of fine particles (ca. 1 µm) extracted from bitumen froth in a water/heptane/toluene system. They found that 60% of the solids were in the organic phase, 30% at the interface, and 10% in the aqueous phase. Since their solids were washed by heptane, the surface of the solids was possibly coated with asphaltenes. In the present study, the surface of the solids was nearly bitumen free as the solids were repeatedly washed with toluene, which was confirmed by the


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FTIR spectra of the solids. As seen in Figure 4, the peak at 2900 cm-1, representing methyl and methylene groups, is negligible, which indicates little organic matter was detected on the surface of the solids. The complete removal of surface bitumen may be the reason why there were no particles remaining in the organic phase in the present partitioning studies. However, both partitioning studies clearly showed that a portion of particles in the froth solids (S1) are biwettable as they remain at the diluent/water interface. The effect of demulsification on the solids composition was examined using XRD analysis. The composition of the solids from XRD analyses is given in Table 2. Findings from Table 2 are summarized as follows: (a) there are 15 components common in all three types of solids. Demulsification caused the variation of the percentages of the components present in the solids, but none of components were completely removed from solids by demulsification; (b) the main components of the solids in the bitumen froth (S1) are quartz (55.8%), siderite (14.7%), and clays (12.9%, including kaolinite, illite, and clinochlore). These components constitute 83.4% of the total mass. After froth treatment, most of the quartz was removed; (c) in the solids from after froth treatment without the demulsifier application (S2), the main components are siderite (FeCO3, 36.0%), clays (16.6%, primarily kaolinite), and pyrite (FeS2, 9.9%) which together constitute 62.5% of the total; and (d) in the solids after froth treatment with 40 ppm of Demulsifier A (S3), the main components are the same as those in the S2 solids. However, the siderite and clays are 2.1% and 1.3% lower than those in the S2 solids, respectively. The comparison of the S1 and S2 solids indicates that in the S1 solids, siderite and clays were close to equal in quantity. After froth treatment, the percentage of siderite was twice that of the percentage of clays in the S2 solids. This finding indicates that siderite is harder to remove than clays in demulsification, although the demulsifier application assisted, to some extent, in the


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removal of siderite and clays from the diluted bitumen. It should be noted that the XRD data represents the percent composition of the solids only. It has nothing to do with the mass of the solids. For example, the S3 solids have 2.1% less siderite and 1.3% less clays compared to the S2 solids by composition, but the S3 solids have 43.5% less siderite and 44.3% less clays than the S2 solids by weight since the weight of S3 solids is only 40% of S2 solids. On the other hand, XRD data is only representative for the crystalline components in the sample. The amorphous components, if any, were not included in the XRD results. It has been found that the content of siderite and pyrite was high in the weathered and high fines oil sands ores, but negligible in the low fines ores.21 The present finding indicates that the bitumen froth used in this work was probably generated from an ore with a high fines content. The effect of demulsification on the particle size distribution of solids was studied for the S1, S2, and S3 solids. Figures 5 and 6 show the particle size distribution of the solids. As seen in Figure 5, compared to the S1 solids, the S2 solids contained much more small particles ( 8 µm) than the S3 solids. The values of the median particle size (D50), i.e., the size at 50% cumulative for S1, S2, and S3 solids are 8.6, 2.4, and 1.5 µm, respectively. These data indicate that after settling, large solids were removed from the diluted bitumen and the demulsifier application caused more of the larger particles to settle. As a result, the average particle size followed S3 < S2 < S1. As shown earlier in Figure 1, when 40 ppm of Demulsifier A was used, 40% more of the solids were removed as compared with no demulsifier application. The results of Figure 6 confirmed that most of the solids removed were the solids of large particle size, which are higher in density.


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As stated above, about half of the solids in the diluted bitumen after froth treatment are siderite and clays. In the solvent extraction of oil sands, Kotlyar et al.32 discovered that siderite was the major solids component in organic matter–mineral complexes in diluted bitumen, suggesting a strong association of siderite with bitumen. In geology, sedimentology and geoengineering, it is generally accepted that clay particles are identified as < 4 µm in size, whereas the value of < 1 µm is often accepted in colloid science.33 Owing to their small size and biwettability, as shown in the partitioning studies, clays are able to adsorb at the oil/water interface. After froth treatment, the unresolved water remains in the diluted bitumen in the form of water droplets. The clays reside on the surface of the water droplets by van der Waals, steric, and hydrogen bonding interactions between the asphaltenes and clays.34 To effectively remove siderite and clays from diluted bitumen, well-designed demulsifiers have to strongly interfere with or break these interactions. Diluent/Bitumen Losses in Demulsification. In the industrial naphtha-based bitumen froth treatment process, the loss of diluent and bitumen to the tailings is a concern. To understand how the losses happen, the bitumen and diluent contents in the underflow were measured after demulsification. Figure 7 shows the bitumen loss as a function of the demulsifier dosage. In the absence of demulsifier, 6.0% bitumen was lost to the underflow. The application of 30 – 50 ppm demulsifier led to 7.2 – 7.8% bitumen loss. The results indicate that the application of a demulsifier in demulsification caused more bitumen loss and the loss increased slightly with the demulsifier dosage. In the process of demulsification, water droplets coalesce to become larger water drops and settle, and it is thought that the bitumen on the water drop surface is brought to the underflow along with the water drop. The bitumen adsorbed on the solids is also brought to the underflow by the settled solids. The demulsifier application led to


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more water and solids settled to the underflow (Figure 1) and thus more bitumen loss to the underflow. Figure 8 shows diluent loss as a function of demulsifier dosage. Note that the diluent loss here is the total loss to the underflow, including the losses to the supernatant and to the water and solids phase after centrifugation. Without the demulsifier application, 6.2% diluent was lost to the underflow. The application of 30 – 50 ppm of demulsifier led to 9.0 – 9.7% diluent loss, and the loss increased slightly with increasing demulsifier dosage. The results indicate that application of demulsifier in demulsification caused more diluent loss than without demulsifier application. As stated above, bitumen may be lost to the underflow through adsorption to the settled water and solids. Since bitumen is soluble in diluent, bitumen loss would cause diluent loss as well. Diluent may also be emulsified by water and/or adsorb on solids, through which diluent is lost to the underflow. To determine whether the water in the underflow contains diluent, the underflow was centrifuged and the water was separated from the underflow and its diluent content was measured. A negligible amount of diluent was found in the water. Therefore, the diluent loss to the underflow is due to the loss to the solids. After centrifuging the underflow, the supernatant and the water and solids phase were collected separately and their diluent contents were measured. The supernatant is diluted bitumen which settled to the underflow in the demulsification and was unbound or weakly bound to the settled solids in the underflow. Upon centrifugation, this free bitumen was separated from the water and solids. Figure 9 shows diluent losses to the free bitumen and to the solids as a function of the demulsifier dosage. The results show that 86 – 91% of the diluent loss was due to the losses to the free bitumen. The diluent loss to the solids was 9 – 14% of the total losses. In industrial froth treatment, after


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settling of diluted froth, hydrocyclone or centrifugation operations follow. In these operations, free bitumen in the underflow is driven to the diluted bitumen phase and bitumen adsorbed on the solids remains in the underflow. Therefore, the bitumen and diluent losses to the underflow are through adsorption to the settled solids. Figure 9 shows that the demulsifier application caused a higher diluent loss to the solids than without the demulsifier application. The diluent loss to the solids increased with an increase in demulsifier dosage. This finding agrees with the fact that more solids were rejected to the underflow after the demulsifier application and the solids rejected to the underflow increased when the demulsifier dosage was increased (Figure 1). To understand the diluent loss in the demulsification, the effect of solids on diluent loss is further studied using model emulsions. Figure 10 shows the diluent loss as a function of the solids content in the model emulsions. The solids contained 50% fines and 50% coarse solids. No demulsifier was used in the demulsification. As indicated in Figure 10, diluent loss to the free bitumen increased from 2.1% to 5.7% and 6.5% when the emulsions had 2.7%, 5.3%, and 10% solids, respectively. The diluent loss to the solids was negligible when the emulsion contained 2.7% solids, but it increased to 0.7% and 1.8% when the emulsions contained 5.3% and 10% solids, respectively. The results indicate that emulsions with a higher solid content have more diluent loss as there would be more solids settled to the underflow in demulsification, and the diluent loss caused by adsorption on the solids is thus greater. It should be noted that the solids added in the emulsions had the same composition and the same particle size distribution, although the quantities of solids used were different. It has been reported that the emulsion stability increases with decreasing the size of solids in the emulsions.21 The presence of fine solids makes emulsions harder to resolve. However, once the emulsion is resolved, the solids would settle and fine solids would bring more diluent to


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the underflow as compared with an equal weight of coarse solids due to the larger surface area of fine solids. The effect of the fines content on the diluent loss is shown in Figure 11, where all emulsions contained 5.26% solids and the coarse solids or fines had the same composition and particle size distribution. As seen in Figure 11, whether in the absence or presence of demulsifier, the diluent loss to the free bitumen or to the solids greatly increased when the fines content in the emulsion increased from 50% to 100%. Again, the results in Figure 11 show that the demulsifier application increased the diluent loss, which agrees with the conclusion drawn from Figure 8. In the oil sands industry, diluent loss is defined as the barrels of diluent lost to the tailings pond per 1000 barrels of dry bitumen production. In this study, the diluent loss is calculated as the percent of diluent in the water/solids phase (tailings) to the diluent added into the diluted froth before demulsification. Although definitions are different, the mechanism of diluent loss in both methods remains the same. The diluent loss studies above revealed that the diluent lost to the underflow is dependent on the solids rejected from the diluted bitumen. An emulsion with a higher solid content or a higher fines content has a greater diluent loss. The demulsifier application increases the solids removal from the diluted bitumen, resulting in a greater diluent loss. To achieve a lower diluent loss to the underflow, the demulsifier must weaken the diluent– solids or bitumen–solids interactions. In the formulation of demulsifier products, one or more components can be targeted toward changing the wettability of the solids and/or dispersing the bitumen/solids aggregates in order to reach a lower diluent loss and keep a higher water and solids removal efficiency in the demulsification of water-in-diluted bitumen froth emulsions.


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CONCLUSIONS The demulsification of water-in-diluted bitumen froth emulsions depended on the characteristics of the solids in the emulsions. The presence of fine solids in the diluted bitumen froth enhanced the water/bitumen interfacial tension and the difficulty of demulsification as the fines are bi-wettable and adsorb at the water/bitumen interface. The demulsifier application assisted in the removal of siderite and clays, which have a strong association with bitumen. Using 40 ppm Demulsifier A, the median particle size of the solids (D50) was reduced from 8 µm in the bitumen froth emulsions to less than 2 µm in the diluted bitumen phase. The diluent loss to the water and solids phase after demulsification increased with increasing solids content in the emulsions. At the same solids content and composition, the diluent loss increased with the fine solids content. As compared to demulsification without a demulsifier application, the application of demulsifier led to more bitumen and diluent losses to the settled water and solids phase, and the losses increased with an increase in demulsifier dosage.

† A part of this work was presented at the World Heavy Oil Congress, New Orleans, Louisiana, 2014.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]


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ACKNOWLEDGMENT The authors would like to thank our colleagues in the Baker Hughes Evan Ginn Research & Development Center, Sugar Land, TX, and in the Baker Hughes Center, Fort McMurray, AB for their valuable support. Mark Williams, Dana Morrison, and Graham Smith at Baker Hughes are gratefully acknowledged for their internal review of this paper. The permission from Baker Hughes to publish this paper is greatly appreciated.

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Table 1. Percentage of solids in the different phases in partitioning tests.

Water

S1 49.7

S2 33.4

S3 27.3

Naphtha

0

0

0

Interface

50.3

66.6

72.7


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Table 2. Percent composition of solids. Name Quartz Kaolinite Illite Clinochlore Siderite Pyrite Microcline Albite Anatase Rutile Aragonite Zircon Tenorite Hausmannite Iron Phosphate

S1 55.8 8.6 3.3 1.0 14.7 3.2 2.7 0.8 2.0 1.3 1.5 1.2 1.2 1.1 1.6

S2 5.6 12.5 2.7 1.4 36.0 9.9 4.0 1.5 5.9 4.2 4.9 0.8 2.5 3.4 4.7

S3 6.0 11.4 2.5 1.4 33.9 11.0 4.1 1.5 4.4 3.5 4.1 1.4 3.4 3.6 7.8


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Figure 1. Water content of diluted bitumen after 10 and 30 min settling and solids content after 30 min settling at 80 °C as a function of Demulsifier A dosage.

1 Water, 10 min Water, 30 min Solids

3.5

0.8

3.0 0.6 2.5 0.4 2.0 0.2

1.5

Solids in diluted bitumen, %

4.0

Water in diluted bitumen, %

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0

1.0 0

20

40

60

80

Demulsifier Dosage, ppm


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Figure 2. Interfacial tension of the water/60% naphtha-diluted bitumen interface as a function of demulsifier dosage in the absence and presence of added fines.

30 28

IFT, mN/m

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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26 24 No fines

22

3% fines 20 0

20

40

60

80



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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 3. Partitioning tests for the solids from the froth before froth treatment (S1), from the diluted bitumen after froth treatment without the demulsifier application (S2), and from the diluted bitumen after froth treatment with the application of 40 ppm Demulsifier A (S3). The solids in tubes 1, 2, and 3 are S1, S2, and S3, respectively.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 35

Figure 4. FTIR spectra of the solids from the bitumen froth (S1) and diluted bitumen after froth treatment without (S2) and with (S3) demulsifier application.

−OH

−CH2 −CH3

S1 S2 S3

−CO3

−Si-O

4000

3500

3000

2500

2000

1500

1000

500

Wavenumber, cm-1


Page 29 of 35

Figure 5. Particle size distribution of S1 and S2 solids. A total of 500 particles from each set of solids were examined. The frequency indicates the number of particles and the cumulative% represents cumulative per cent of the particles.

100

100 S1, freq S2, freq

80

S1, cumu% S2, cumu%

60

60

256

128

64

32

16

8

4

0

2

0

1

20

0.5

20

0.25

40

0.13

40

Cumulative%

80

Frequency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Particle Size, µm


Energy & Fuels

Figure 6. Particle size distribution of S2 and S3 solids. A total of 500 particles from each set of solids were examined. The frequency indicates the number of particles and the cumulative% represents cumulative per cent of the particles.

100

120 100 80

S3, freq

60

S2, cumu%

60

S3, cumu%

40 40

256

128

64

32

16

8

4

2

1

0

0.5

0

0.25

20

0.13

20

Cumulative%

80

S2, freq

Frequency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 35

Particle Size, µm


Page 31 of 35

Figure 7. Bitumen loss as a function of demulsifier A dosage.

10

Bitumen Loss , %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

8 6 4 2 0 0

30

40

50



Energy & Fuels

Figure 8. Diluent loss as a function of demulsifier A dosage.

12 10

Diluent Loss, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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8 6 4 2 0 0

30

40

50



Page 33 of 35

Figure 9. Diluent losses to the free bitumen and to the solids in the underflow as a function of demulsifier A dosage.

10

Diluent Loss, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

8

In Free Bitumen On Solids

6 4 2 0 0

30

40

50



Energy & Fuels

Figure 10. Diluent losses to the free bitumen and to the solids in the underflow as a function of the solids content in the model emulsion. The solids contained 50% fines. No demulsifier was used in the demulsification.

8

Diluent Loss, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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In Free Bitumen On Solids 6 4 2 0 2.70

5.26

10.00

Solids in Model Emulsion, %


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Figure 11. Diluent losses to the free bitumen and to the solids in the underflow as a function of fines content in the model emulsion. The emulsions contained 5.26% solids.

15

In Free Bitumen On Solids

12

Diluent Loss, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

9

6

3

0 No demulsifier, 50% fines

No 100 ppm 100 ppm demulsifier, Demulsifier A, Demulsifier A, 100% fines 50% fines 100% fines


Understanding the Demulsification of Water-in-Diluted Bitumen Froth

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