Role of Ethyl Cellulose in Bitumen Extraction from Oil Sands Ores

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Role of Ethyl Cellulose in Bitumen Extraction from Oil Sands Ores using Aqueous-Nonaqueous Hybrid Process Feng Lin, Lin He, Jun Hou, Jacob H Masliyah, and Zhenghe Xu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b01960 • Publication Date (Web): 22 Oct 2015 Downloaded from http://pubs.acs.org on October 24, 2015

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Role of Ethyl Cellulose in Bitumen Extraction from Oil Sands Ores Using Aqueous-Nonaqueous Hybrid Process *, Feng Lin,†,§ Lin He,†,‡ Jun Hou,†,‡Jacob Masliyah,‡ and Zhenghe Xu ‡

‡

Department of Chemical and Materials Engineering, University of Alberta, Edmonton,

Alberta T6G 2G6, Canada §

CANMET Energy Technology Centre-Devon, Natural Resources Canada, One Oil Patch

Drive, Devon, Alberta T9G 1A8, Canada ABSTRACT: A major drawback associated with current hot or warm water-based bitumen extraction process is the high consumption of energy. To address this issue, an aqueousnonaqueous hybrid bitumen extraction process (HBEP) — in which a portion of the diluents (solvent) were added upfront to soak mined oil sands prior to its water-based extraction, was proposed and demonstrated to be feasible to process mineable oil sands at ambient temperatures. This study investigates the effect of adding ethyl cellulose (EC) as a promising demulsifier to the solvent on bitumen recovery and froth quality in the ambient HBEP. The laboratory flotation results clearly showed a significant improvement in froth quality with a negligible setback on bitumen recovery by 100 to 200 ppm EC addition to the HBEP. Determined by an on-line visualization method, the addition of EC in solvent to the HBEP further enhanced separation kinetics of bitumen from sand grains of real oil sands ores. The addition of EC in solvent also increased the probability of bitumen droplet coalescence determined with micropipette technique, but hindered the attachment of air bubbles to solvent-soaked bitumen in particular at high EC dosages as evaluated by increased induction time of air bubble-bitumen attachment. Keywords: oil sands, hybrid bitumen extraction, ethyl cellulose, solvent

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1. INTRODUCTION Canadian oil sands in northern Alberta, with a proven reserve (i.e., crude oil that is recoverable using current technologies) of about 170 billion barrels,[1] represent one of the largest oil deposits in the world. Typically, oil sands contain bitumen (i.e., extra heavy oil), water, coarse silica sands, and fine clay minerals (< 44 µm particles). Depending on the bitumen and/or fines content in oil sands matrix, oil sands ores are classified as high-, medium- or low-grade ores. Bitumen in deposits of shallow overburdens is commercially recovered by mining-hot water bitumen extraction (HWBE) process where mined oil sand ores are first slurried with hot water (typically at 85 to 95oC) and chemical additive (mainly caustic).[2,3] Under the favourable physicochemical conditions, bitumen is receded and then detached from the sand particles, forming individual bitumen droplets. With proper hydrodynamic shear to promote collision, the liberated bitumen droplets are able to coalesce readily with one another. At the same time, bitumen droplets collide with the dispersed air bubbles present in the slurry, forming air-bitumen aggregates which are much less dense than the processing medium (water) and readily float to the top of separation vessel as bitumen froth. Using innovative hydro-transport slurry pipeline, the operating temperature of oil sands processing has been reduced to the practical limit of 45oC, below which the bitumen recovery and froth quality deteriorate severely. Despite its current success, many challenges in the current water-based technology, such as extensive consumption of energy and fresh water, rapid expansion of tailing ponds, and high intensity of greenhouse gas (GHG) emissions are putting the future of oil sands industry in potential jeopardy. There is therefore a clear need to develop more advanced extraction technologies that can reduce the energy intensity and lower carbon footprint without sacrificing the productivity and robustness of the process.


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Over the past few decades, solvent-based (or nonaqueous) extraction schemes have been studied at laboratory scale, as alternatives to aqueous processes. Cormack et al. investigated the relative importance of system parameters, e.g., solvent type, agitation rate, contact time, and oil sand to solvent ratio, on the efficiency of bitumen extraction from mined ores by solvents and the overall mass transfer coefficients.[4] Hooshiar et al. treated the oil sands with organic solvents of different aromaticity (i.e. the mixtures of toluene and heptane at different ratios) to achieve desired high bitumen recovery.[5] The bitumen extraction process by solvent was found to be insensitive to the bitumen content or fines content of the ores. One of major challenges in solvent-based bitumen extraction process is the solvent recovery and loss that was not addressed in these two studies. Wu and Dabros[6] studied digestion of oil sands ores using low-boiling-point solvents. In their study, the digested oil sands-solvent mixture was filtered at ambient pressure using a centrifuge to separate the solids from the diluted bitumen. The diluted bitumen/solvent remaining in the filtration cake was recovered by evaporation under vacuum at room temperature. For the high- and low- grade ores, their study showed a comparable bitumen recovery rate and product quality to those achievable by the HWBE process. The solvent loss was limited to less than 0.4 wt % of the extracted bitumen.[6] Although promising, the economic and technical challenges, particularly the requirement of large amounts of solvent and excessive capital investment, set the main obstacle to any large-scale piloting and commercialization of these solvent-based processes. Recently, the concept of aqueous-nonaqueous hybrid bitumen extraction process (HBEP) by distributing a portion of the solvent (which is used in the post-extraction bitumen froth treatment in the current commercial HWBE operations) up front to mined oil sands, was developed in our related study.[7] It was reported that the HBEP was a robust process that the


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addition of solvent (e.g. kerosene) to oil sands made the extraction not only feasible at ambient operating temperature but also less sensitive to ore grades. The kerosene addition at 10% of the bitumen content was sufficient to significantly enhance the flotation recovery of bitumen without need for caustic addition.[7] Further solvent addition resulted in a further increase in bitumen recovery, but to a much less extent. The solvent loss to the tailings water at about 0.1% based on the initial solvent amount was thought manageable, particularly if taking the recycle of the process-affected water into account.[7] Other solvent-and-water combined processes were also reported. In terms of process procedures of adding solvent and water, the amount of solvent, operating temperature, and the addition of a caustic, however, these processes are significantly different from the HBEP described in our-related paper. Schramm et al. reported a process in which kerosene and methylisobutyl carbinol (MIBC) were applied to slurry, supplementing 0.06 wt% (oil sand basis) of NaOH addition.[8] Adding 20 mg/g of kerosene (mg/g on the mass basis of oil sands) alone was able to bring bitumen recovery at 25 °C up almost to the recovery level achieved at 50 and 80 °C process temperatures. The co-addition of 1 mg/g MIBC with 20 mg/g of kerosene further boosted primary bitumen recovery to a level even higher than the level achieved using NaOH alone at the higher temperatures.[8] U.S. patent 4,424,112 reported the use of hot (70oC or above) water with addition of solvent into an oil sands ore, followed by jet mixing.[9] In a separate U.S. patent 4,875,998, ore was first slurried with hot water at about 70oC followed by counter-current contact with a solvent in a log washer for mechanical agitation.[10]

In the current HWBE operations, oil-soluble demulsifier was used to demulsify water-indiluted bitumen emulsions encountered in the post extraction bitumen froth treatment required to further reduce the amount of solid and water in the bitumen product to less than 0.5 wt% and 0.2


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wt%, respectively.[11,12] In this study, we focus on maximizing the value of chemical demulsifiers in oil sands processing by exploiting the idea of distributing both demulsifier and solvent upfront to the bitumen extraction process, i.e., incorporating the addition of a demusifier into the HBEP. The cost-effective and biodegradable polymer, ethyl cellulose (EC) is taken as an example of these demulsifiers. We will first design the flotation test protocols and study the effect of EC on the processability of high fines oil sands ores in terms of bitumen recovery and froth quality using low-temperature HBEP. To gain fundamental understanding of the role of EC in the HBEP, the impact of EC on the liberation of bitumen from sand grains, the coalescence of emulsified bitumen drops in water and the attachment of bitumen to air bubbles are studied.

2. EXPERIMENTAL SECTION 2.1. Materials. Ethyl cellulose (EC), purchased from Sigma-Aldrich, was used as received. The molecular weight of EC was determined using intrinsic viscosity measurement to be 46 kDa.[12] The ethoxyl content of EC was 48% and the degree of substitution (DS), i.e., ethoxylation per glucose residue was about 2.5. The viscosity of 5 wt% EC in 80:20 toluene/ethanol solution at 25oC was 4 mPa·s. ACS-grade toluene, purchased from Fisher Scientific, was used as solvent. Toluene was chosen as it is compatible with or soluble in bitumen that does not induce asphaltene precipitation and interfere with Dean-Stark analysis of bitumen froth. Furthermore, EC is soluble in toluene for the dose into the bitumen with minimum loss to the aqueous phase as emulsions. Three oil sands ores (marked as OS1, OS2 and OS3) from the Athabasca oil sands deposit were used. These three ores contained very high percentage of fines (more than 30 wt% of solids). The composition of these three ores is given in Table 1. To avoid any possible weathering effect, the ore samples packed in plastic bags were kept in a freezer. Prior to each test,


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the ore samples were defrozen naturally at room temperature for 3 to 4 h.[7] Process water supplied from Syncrude Canada was used in this study unless otherwise stated. The process water contained about 24 ppm K+, 656 ppm Na+, 16 ppm Mg2+, 26 ppm Ca2+, 663 ppm Cl−, 128 ppm SO42−, 607 ppm HCO3−, and 60 ppm carboxylic surfactants. The pH of process water was adjusted to 8.2±0.2 by NaOH or HCl solution (both from Fisher Scientific). Table 1. Composition (wt %) of the oil sands ores used in this study Oil sands

Bitumen

Water

Solids

Fines*

OS1

10.1

6.9

83.0

31.5

OS2

9.8

2.9

87.3

39.0

OS3

8.3

7.4

84.3

38.2

*

Fines are mineral solids with less than 44 µm and expressed as percent of total solids.

2.2. Flotation Procedure. Bench-scale bitumen extraction tests were conducted using 1-L Denver flotation cell. The cell was equipped with a water jacket connected to a temperaturecontrolled water bath to maintain a constant flotation temperature. 900 g process water with desired temperature was added to the defrozen oil sands ore (typically 300 g or 500 g) in the Denver cell to make the slurry at the desired flotation temperature (either 33±2oC or ambient temperature 23±1oC). After the slurry had been conditioned at 1500 rpm for 5 min, air was introduced at 150 ml/min and the froth was collected sequentially into four thimbles at different time intervals. The overall froth collection lasted for either 10 min or 20 min. The froth was then analyzed for bitumen, solids and water content using the Dean Stark apparatus. The mass ratio of bitumen in the froth to bitumen in the oil sands ore was used to represent bitumen recovery in percentage. The mass ratio of bitumen to solids (B/S) and bitumen to water (B/W) in froth was


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used as a measure of froth quality. Higher B/S and B/W values indicate a better froth quality. The details on bitumen extraction tests and froth analysis can be found elsewhere.[7] The test procedures, involving two experimental protocols, of applying EC to the flotation system are schematically illustrated in Figure 2. In protocol I, EC-in-toluene solution was added into the slurry (i.e. water and ore) at the beginning of the slurry conditioning. In protocol II, ECin-toluene solution was spread evenly over the oil sands ore and soaked for 10 min prior to making slurry with process water. A soaking time of 10 min was found to be sufficient for solvent to uniformly penetrate into to soften the bitumen in an oil sand ore. Bitumen recovery for an ore soaked for 10 min was found to be the same as that soaked for more than one hour. The quantity of toluene added was 4 or 3 wt% based on the weight of ore sample, corresponding to about 40 or 30 wt% of bitumen in the ore. The amount of EC applied was 1 to 3 wt% of the mass of toluene, equivalent to 100 to 300 ppm based on the total mass of slurry. EC is insoluble in aqueous phase and highly soluble in toluene. Early studies showed effective demulsification of water-in-diluted bitumen emulsions by 130 ppm EC addition.[11,12] From this knowledge, the dosage of EC tested in this study varied from 100 to 300 ppm, in an attempt to maximize the value of EC addition in both bitumen extraction and froth treatment, as the EC in the bitumen froth would be carried to the froth treatment process. 2.3. Determination of Bitumen Liberation. Bitumen liberation process from oil sand ores under the influence of EC addition was monitored in-situ in a flow-through visualization cell.[13] Approximately 1 g of the ore sample with or without the soaking of EC-in-toluene solution was placed on a sample holder (i.e. circle hole of 14 mm diameter and 10 mm depth) and pressed to obtain a flat surface of oil sands. About 2 mL process water at ambient temperature was added to the cell. Upon the contact with the added water bitumen films was noted to recede immediately 7 ACS Paragon Plus Environment

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and form bitumen droplets on the sand grains, a process known as bitumen liberation. For each run, bitumen liberation process was recorded in real time using a stereo-optical microscope equipped with a high-resolution camera (Olympus, SZX10). In this study, the overall dosage of EC-in-toluene solution containing 1 to 3 wt% of EC for soaking the ore was the same as used in bitumen flotation tests, i.e., 3 wt% of the ore or equivalent to 30 wt% of bitumen, as shown in Table 2. For all the experiments, the exposure time and magnification of camera were set at 57.93 ms and 0.64 µm/pixel, respectively, with a sensitivity of ISO 800 at the resolution of 1360 ×1240 pixels. Liberation test at each condition was repeated at least three times to obtain an average and credible result. The sequential snapshot liberation images were quantified by image analysis to determine the degree of bitumen liberation (DBL) dynamics. For the details of image analysis readers are referred to our previous publication.[14] The DBL curve was constructed by determining the percentage of clear sand grains out of the total sand grains visible on each frame as a function of testing time.

2.4. Quantification of Bitumen Coalescence. Effect of demulsifier addition in solvent on coalescence of solvent-diluted bitumen droplets was investigated using a micropipette technique. The details on the preparation of micropipette and the droplet-droplet contact experiment were given elsewhere.[15] Briefly, two individual emulsion oil droplets were captured at the tips of open-ended micropipettes. The inner diameter of the micropipette tips ranged from 7-10 µm. Through the use of manipulators that control the motion of two micropipettes at the µm-scale, direct “head-on” contact of two droplets was enabled. These contact experiments were visually monitored from an inverted optical microscope (Zeiss, Axiovert 200) and recorded with a digital 8 ACS Paragon Plus Environment

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camera. In this study, droplet pairs of roughly equal size around 20 µm in diameter with less than 5% variation were chosen. As a standard procedure, every droplet pair was held in contact for 1 min to ensure sufficient time for the aqueous film to drain between the two droplets.[16] To obtain consistent results, the deformation ratio (DR) defined as the ratio of the major to minor axes of a deformed drop was maintained at 1.1 for all the contacts. To avoid possible aging effect, all the experiments were carried out on freshly prepared oil-in-water emulsions that were used within 2 h of preparation. These emulsions were prepared by agitating approximately 0.5 g of EC/toluene/bitumen mixture (their mass ratio was 0.3 to 0.9 EC: 30 toluene: 100 bitumen) in 10 mL of process water in a sonication bath, resulting in emulsified droplets of 5-50 µm in diameter. The concentration of EC in this set of tests was the same as used in the bitumen extraction tests, i.e., approximately 100 to 300 ppm of EC in emulsion (see Table 2 for the estimation). Here, the bitumen was extracted directly from the relevant ore using centrifugation method.[17] All the droplet-droplet contact experiments were conducted at ambient temperature.

Figure 1. Schematics of two protocols of applying EC-in-toluene solution to bitumen flotation: I) EC prepared in toluene was introduced into the process water at the beginning of 5 min


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conditioning; and II) EC prepared in toluene was added directly to the oil sands ore prior to making the slurry and slurry conditioning.

2.5. Induction Time Measurement. To investigate the effect of EC on bitumen aeration, an inhouse built induction time device was used to measure the minimum contact time required for the attachment of an air bubble to a bitumen surface in testing liquid, which is known as induction time.[18] Bitumen extracted directly from the oil sands ore was used directly or for preparing samples of 0.3 to 0.9 EC: 30 toluene: 100 bitumen mass ratio. About 0.4 g of the bitumen, with or without EC-in-toluene solution addition, was placed equally in four halfspherical bowls each made on a circular Teflon disc. The bitumen relaxed at room temperature to obtain a mirror-like flat surface. The discs were then placed in a rectangular glass cell filled with 8 mL of process water. The addition of EC was equivalent to approximately 100 to 300 ppm of the total mass of bitumen/diluted bitumen and water (also refer to Table 2). After 30-min equilibrium, a fresh air bubble of 1.5 mm in diameter was brought in contact with the bitumen surface in the process water for a specific contact time and then retracted away from the surface at a contact speed of 8 mm/s. With the aid of a digital camera, one can distinguish whether the bubble attached to the bitumen surface or not. After repeating these events 20 times for a given contact time, the probability of attachment was obtained as the fraction of the contacts which resulted in the attachment. The probability of attachment was then plotted as function of contact time, from which the induction time was obtained as the contact time with 50% attachment. All the induction time measurements were conducted at ambient temperature, with the initial distance between the bubble and bitumen surface and the bubble displacement being set at 0.25 and 0.4 mm, respectively.


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It should be noted that for better comparison between bitumen droplet coalescence time and induction time of bitumen-bubble attachment, it would be highly desirable to conduct such measurements using bitumen droplets and bubbles of similar sizes in these two sets of measurements using either micropipette technique or induction timer. However, the technical difficulties in creating such similar geometries while conducting the measurement prevented us to do so. For example, it is almost impossible to create micron size bubbles using micropipette to perform induction time measurement of bitumen-bubble attachment. Similarly it is very difficulties to hold a large bitumen droplet in the glass capillary tube for coalescence time measurement of bitumen droplet-flat bitumen surface. As a result, we used micropipette technique to measure coalescence time measurement between two micron size bitumen droplets, and induction time instrument to measure the induction time of bubble-bitumen attachment, which are more suitable for each type of systems and more relevant to the environments encountered in bitumen extraction practices.

Table 2. Ratios (w/w) of different materials for the tests of three sub-processes which minimized the relevant ratio for the Denver-cell flotation test. (Bitumen mixture includes bitumen and toluene or ethyl cellulose-in-toluene.)

ethyl cellulose water toluene ethyl cellulose water slurry/suspension bitumen or bitumen mixture or bitumen bitumen toluene 20.0

0, 0.3

0, 0.01 to 0.03

0, 100 to 300 ppm

3. RESULTS AND DISCUSSION


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3.1. Effect of EC on Bitumen Flotation. Flotation experiments were first carried out using two different protocols (I and II) to select a proper method for evaluating the performance of chemicals (EC in particular) on bitumen flotation. The tests were conducted using OS3 ore at 33oC. The results in Figure 2 show that without chemical addition, the quality of bitumen product (froth) as indicated by B/S and B/W ratios was relatively low. With Protocol I, the addition of 12 g of toluene (equivalent to 4 wt% of the mass of the ore) to the slurry showed a negligible effect on the forth quality. However, the addition of the same 12 g of toluene directly to the ore (i.e., Protocol II) significantly increased both the B/S and B/W ratios, indicating a better bitumen froth quality with solvent soaking of ores. The results in Figure 2 show a further improvement in froth quality with EC addition to the solvent in either Protocol I or Protocol II, as compared to the case with toluene addition only to the ore, more so at higher EC dosages of 300 ppm in toluene. Furthermore, both B/S and B/W ratios of bitumen froth obtained using Protocol II remain higher than that obtained using Protocol I, indicating a cleaner and “drier” bitumen froth obtained using Protocol II. Figure 3 shows the effect of EC and toluene addition on bitumen recovery from OS3 ore using the two protocols. In protocol I, bitumen recovery with toluene addition to the slurry was similar to the case without chemical addition. However when using protocol II of adding toluene to the ore, bitumen recovery was increased significantly as compared to the case without toluene addition. The improved bitumen froth quality and bitumen recovery by toluene addition into the ore (i.e., using protocol II) were mostly a result of reducing bitumen viscosity by toluene penetration into the bitumen in the ore and hence liberation of bitumen from the sand grains.[7] In protocol II, directly spraying toluene on oil sands and soaking would make the added toluene 100% contact with bitumen. In contrast, adding toluene to the slurry in Protocol I appeared to be


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inefficient in delivering the toluene through water phase into bitumen of the oil sands ore. The added toluene into slurry is sheared to form droplets. The contact of the toluene droplets to bitumen in the slurry is highly dependent on hydrodynamics of mixing. As a result, the addition of toluene at the current level of practical acceptance to the slurry had a negligible effect on bitumen extraction.

Figure 2. (a) Bitumen to solids (B/S) and (b) bitumen to water (B/W) ratio of the froth collected over 20 min flotation for ore OS3 extracted at 33oC with the addition of toluene and EC-intoluene solutions at difficult dosage using Protocol I of adding the EC in toluene solution to the slurry and Protocol II of adding EC in toluene solution directly to the oil sands ore prior to extraction tests. The froth quality of bitumen froth obtained at 33oC in the absence of toluene and EC addition was used as a reference.

The results in Figure 3 further show that adding 100 or 200 ppm EC in toluene (scaled by the mass of slurry) improved bitumen recovery to the similar extent as in the case without EC addition for both protocols. Interestingly, a further increase in EC dosage to 300 ppm made the bitumen recovery to drop back to the level of without toluene addition for both protocols.


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In view of the effect of toluene and EC addition on overall bitumen recovery and froth quality, the above findings suggest the protocol of chemical addition is critical. In the current case, Protocol II of adding EC-in toluene solution directly to soak the ore is a much better option than Protocol I. It should be noted that our primary objective of adding EC in the hybrid bitumen extraction process (HBEP) was to further improve bitumen extraction performance by increasing bitumen froth quality and hopefully also bitumen recovery. Although the original objective of using hybrid bitumen extraction process by adding the solvent to the ore is to reduce the consumption of thermal energy, fresh water and the emissions of green-house gases, improving froth quality without sacrificing bitumen recovery would facilitate froth treatment to gain additional advantage over the current how/warm water bitumen extraction process and aqueousnonaqueous hybrid extraction process. To prove the robustness of our concept that EC addition further improves froth quality, Protocol II was applied to other two ores (OS1 and OS2) and results are shown in Figure 4. It should be noted that in processing of ores OS1 and OS2, the ratios (w/w) of water to ore and toluene to ore were reduced from the initial 3.0 and 0.04 to 1.8 and 0.03, respectively, in order to minimize the consumption of water and solvent while not sacrificing bitumen recovery. The soaking of ore by solvent toluene was aimed to decrease the viscosity of bitumen.[19] The amount of toluene addition at ambient temperature was determined by bitumen chemistry and hence bitumen viscosity in the ore.[7,17] The bitumen viscosity from these two (OS1 and OS2) ores was reported elsewhere.[17] Early studies established a threshold value of bitumen viscosity about 1 Pa·s to obtain a satisfactory bitumen recovery rate from Athabasca oil sands.[7,8] In our study, we found that the addition of toluene to a toluene to bitumen mass ratio of 0.3 (equivalent to 3 wt% of oil sands) is sufficient to achieve this target. Interestingly, the solvent to bitumen ratio at 0.3 is much smaller than solvent used in either


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naphthenic froth treatment (NFT) with a naphtha to bitumen mass ratio of 0.7 or paraffinic froth treatment (PFT) with a hexane to bitumen mass ratio of 2.0.

Figure 3. Effect of toluene and EC-in-toluene solution addition using two protocols on bitumen recovery from ore OS3 at 33oC: Protocol I of adding the EC in toluene solution to the slurry and Protocol II of adding EC in toluene solution directly to the oil sands ore prior to extraction tests. The bitumen recovery obtained at 33oC in the absence of toluene and EC addition was used as a reference.

The results in Figure 4 (a) show a noticeable increase in B/S ratio for both ores OS1 and OS2 when they were soaked with 3 wt% toluene of the ore while conducting bitumen extraction tests at ambient temperature. The addition of 100 to 200 ppm EC in toluene prior to soaking the ore further increased the B/S and B/W ratios, while a further increase in EC addition to 300 ppm showed no further gain in the froth quality. For ore OS2, the B/S ratio increased from 0.3 to 0.44


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with the addition of toluene, and then to 0.51 and 0.61 with the addition respectively of 100 to 200 ppm EC to toluene (also scaled by the mass of slurry) prior to soaking the ore. A further increase in EC dosage to 300 ppm decreased B/S ratio, if any, slightly to 0.59. As illustrated in Figure 4 (a), similar trend but with even more profound improvement in the B/S ratio by toluene and EC addition was observed for ore OS1. The addition of EC resulted in an increase in the B/W ratio for the two ores as well. As shown in Figure 4 (b), the addition of 200 ppm EC increased B/W ratio from about 0.11 to 0.27 and 0.31 for ores OS2 and OS1, respectively. Similar to those in Figure 3, the results in Figure 5 show an apparent effect of toluene soaking on increasing bitumen recovery rate for both ores, in particular for ore OS2 which showed very low bitumen recovery at ambient temperature without chemical addition. It is confirmed with our previous study [7] that this aqueous-nonaqueous hybrid extraction process (HBEP) was effective at lower temperature and less susceptible to ore characteristics, as reflected by the results in Figures 3 and 5. The three processing ores here could achieve almost similar bitumen recovery at an identical toluene dosage. Importantly, the results in Figure 5 reveal that the application of EC up to 200 ppm showed a negligible effect on bitumen recovery from the ores at ambient temperature. A further increase in EC addition to 300 ppm caused bitumen recovery to fall back slightly from optimal values. The results confirm our hypothesis that EC addition to the solvent in the HBEP operated at ambient temperature is beneficial for further enhancing the bitumen froth quality without sacrificing bitumen recovery, regardless of the ore characteristics. An EC dosage of 100 to 200 ppm of the slurry appeared to be optimal. Extra EC addition led to less gain in froth quality, while could cause the risk of reducing bitumen recovery and increasing operating cost.


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Figure 4. (a) Bitumen to solids (B/S) ratio, (b) bitumen to water (B/W) ratio, of the froth collected over 10 min flotation for the ores OS1 and OS2 at 23oC by the addition of toluene and EC-in-toluene solutions at difficult dosage using protocol II. The froth quality in the absence of toluene and EC addition was used as a reference.

Figure 5. Effect of toluene and EC-in-toluene solution on bitumen recovery from the ores OS1 and OS2 at 23oC using protocols II. Bitumen recovery in the absence of toluene and EC addition was used as a reference.


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In order to comprehend the observed effect of toluene or EC-in-toluene solution soaking of oil sands ores on bitumen froth quality and bitumen recovery, it is instructive to investigate its effect on three essential sub-processes of bitumen recovery: bitumen liberation, coalescence and aeration.[2] It is the purpose of the following sections to investigate the role of EC addition in those three key sub-processes using two ores (OS1 and OS2) investigated at ambient temperature (23°C).

3.2. Effect of EC on Bitumen Liberation from Real Ore. Two sets of photographs in Figure 6 compare bitumen liberation process from the same ore without and with the soaking of the ore with a controlled amount of EC-in-toluene solution. In this figure, the top two images in two columns show the initial stage of bitumen liberation upon contact of the (soaked) ore with the process water; while the middle images are taken after 15 s contact of the ores with the water; and the bottom images are the snapshots of bitumen liberation reaching an ultimate state. In contrast to the column (a) where no chemicals were added, much cleaner sand grains in column (b) were clearly seen for the ore soaked with the EC-in-toluene solution and visualized at the same liberation time. Quantitative degree of bitumen liberation (DBL) from EC-soaked OS1 and OS2 ores as a function of liberating time is shown in Figure 7 (a) and (b), respectively. For comparison, the results of bitumen liberation dynamics from the original ores without and with toluene-soaking are also included in Figure 7. It is interesting to note that at a given condition, bitumen liberation process followed the first-order process kinetics for both ores: DBL increased quickly at the beginning, then relaxed and plateaued to an ultimate value. Toluene-soaking of the ore was found to significantly increase both the ultimate DBL (expressed in the ultimate plateau of the


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plot) and the rate of bitumen liberation (as reflected in the initial slope of the plot) for both ores. Such much faster increase and higher ultimate DBL were also achieved by adding other solvents such as kerosene and fatty acid methyl ester in previous reports.[7,20]

They are attributed to

significant reduction in bitumen viscosity and therein the increased accumulation of natural surfactants at bitumen-water interface.

Figure 6. Sequential series of images depicting bitumen liberation process from the real ore in process water at different time (0, 15 and 350 s from the top to the bottom). The ore in series (a) is the original ore of OS1, while the ore in series (b) is the same ore but soaked with 3wt% of EC-in-toluene solution containing 1 wt% of EC.


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Figure 7. Effect of soaking oil sands ores with toluene or EC-in-toluene solution on degree of bitumen liberation (DBL) from OS1 (a) and OS2 (b) ores as a function of time at ambient condition. Bitumen liberation dynamics without toluene or EC addition are shown as a reference. Interestingly, as shown in Figure 7, the addition of EC at a proper dosage led to an additional improvement in not only the ultimate DBL but also rate of increasing DBL for both ores, translating to an extra cleaner sand grains and the reduced time required to reach the ultimate state. Overall, 100 ppm EC scaled by the total amount of ore and water (equivalent to 1 wt% in toluene) seemed to be the optimum dosage. Although the ultimate DBL for OS2, for instance, increased from 74% with only toluene addition to 81% and 85% when 100 to 300 ppm EC was added to toluene, the change in bitumen liberation dynamics reached the maximum at 100 ppm EC addition. One hypothesis on the additional improvement by EC addition is further reduction in bitumen-water interfacial tension and increase in solids wettability by displacing the bitumen components from sand grains.[21-23] It should be noted that at the same level of toluene and EC addition, OS2 ore showed a lower ultimate DBL and slower bitumen liberation dynamics than OS1 ore. Such differences in responding to toluene and EC addition reflects the level of chemical addition on modify bitumen-water and solid-water interfacial properties due to mostly the differences in bitumen chemistry, mineralogy of solids and water chemistry. 20 ACS Paragon Plus Environment

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3.3. Effect of EC on Coalescence of Bitumen Droplets. Under a given condition, the coalescence of two bitumen droplets suspended in the process water remains a probability. In general, if droplet pairs coalesce, it happens right after their contact, as shown by the sequential micrographs in column (a) of Figure 8. Given sufficient time, the coalescing drops merge and relax to a spherical geometry.

Figure 8. Sequential series of photographs, from top to bottom, illustrating non-deterministic nature of bitumen droplet coalescence in process water at 23oC. The droplet pairs were pressed together for 1 min before retraction. At identical experimental condition, two bitumen droplets may coalesce (column (a)) or remain stable (column (b)). In the events where coalescence did not occur even after an extended period of contact, the droplets are readily separated during the retraction of the micropipette(s) without sign of droplet cohesion between droplets, as depicted in the sequential micrographs in column (b) of Figure 8. 21 ACS Paragon Plus Environment

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Such non-deterministic characteristics of bitumen droplet coalescence in (process) water were also reported elsewhere.[15-16] The stochastic nature of bitumen droplet coalescence was attributed to the existence of heterogeneous charge distribution at the bitumen-water interface.[15,24,25] The proposed model of surface charge heterogeneity (SCH) was found to predict well both qualitatively and quantitatively the stability of bitumen emulsions.[15] To quantify bitumen droplet coalescence of stochastic nature, a probability defined as the percentage of bitumen droplet contacts that lead to successful coalescences (typically two sets of 50 trials) at each condition is used in this study. Figure 9 summarizes the probability of bitumen emulsion droplet coalescence with and without the addition of toluene or EC-in-toluene solution to bitumen. To mimic the condition closer to the flotation practice, virgin bitumen that derived directly from ores OS1 and OS2 (denoted as OS1 bitumen and OS2 bitumen hereafter) was used. The viscosities of these isolated OS1 and OS2 bitumen without diluent addition were determined at ambient temperature to be 127 Pa•s and 800 Pa•s, respectively. The asphaltene contents of OS1 and OS2 bitumen were determined to be 17.7% and 23.7%, respectively. The only experimental variable in the coalescence experiments was the bitumen characteristic, i.e., with or without the addition of toluene or EC in toluene solutions to bitumen prior to the experiments. The other experimental parameters including water chemistry (process water), temperature (ambient condition 23oC), bitumen drop size (10-µm in radius), and the extent of bitumen droplet deformation ratio DR (1.1) remained the same in all the cases. The first clear feature in Figure 9 is a significant increase in the probability of bitumen droplet coalescence with the addition of 30 wt% toluene (scaled by the mass of bitumen), regardless the source of bitumen. Addition of EC to toluene further improved the coalescence of bitumen droplets. An EC addition of 1 to 2 wt% in toluene


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(equivalent to 100 to 200 ppm of aqueous suspensions) appeared to be optimal. Further increase in EC addition appeared to diminish the return in improving the probability of bitumen droplet coalescence. For example, for OS2 bitumen, the results in Figure 9 indicate a substantial increase in the probability bitumen droplet coalescence from 38% to 66% when diluted with toluene. With 1 wt%, 2 wt% and 3 wt% of EC addition in toluene, the probability further increased to 75%, 81% and 82%, respectively. Also evident in Figure 9 is the higher probability of bitumen droplet coalescence for bitumen from OS1 ore than from OS2 ore, which appears to be related to higher asphaltene content and viscosity of bitumen from OS2 ores than from OS1 ore.

Figure 9. Effect of EC-in-toluene solution addition to bitumen on droplet coalescence of bitumen from OS1 and OS2 ores at 23oC. The probability of bitumen droplet coalescence in the absence of toluene and EC addition was used as a reference. 23 ACS Paragon Plus Environment

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The improvement in the probability of coalescence with toluene addition to the bitumen could be accounted for by viscosity reduction. A decrease in the viscosity of bitumen phase by toluene addition could increase the mobility of surface active chemical species at oil-water interface that stabilize bitumen droplets.[26-28] Since EC was shown to destroy the interfacial films that stabilize bitumen-water interfaces and water-in-diluted bitumen emulsions,[12,22,23] the observed increase in the probability of bitumen droplet coalescence is not unexpected. 3.4. Effect of EC on Bitumen Aeration. Induction time was used as a measure on the effectiveness of bitumen aeration (i.e., bitumen-air bubble attachment). It is well established that the shorter the induction time, the easier the bitumen aeration. Figure 10 shows the effect of EC addition in toluene on the induction time of toluene-diluted bitumen-air bubble attachment in process water under ambient condition. As a baseline, induction time of air bubble-bitumen attachment without toluene addition to bitumen was also measured. In this set of measurement, the virgin bitumen isolated from OS1 and OS2 ores was used. It is revealed in Figure 10 that induction time was highly sensitive to the source of bitumen. Induction time of 4 s measured using the bitumen of higher viscosity and asphaltene content from OS2 ore was higher than that (2.5 s) from OS1 ore. However, the impact of toluene addition with and without EC was observed to be insensitive to the source of bitumen. Compared with the baseline, a noticeable reduction in induction time from 4 s and 2.5 s to 2.4 s and 2.0 s was achieved when adding 30 wt% toluene to the bitumen from both OS2 and OS1 ores, respectively. Increasing the addition of EC in toluene added to bitumen increased progressively the induction time of toluene-diluted bitumen-air bubble attachment. At 300 ppm EC in toluene, for example, the induction time increased from 2.4 s and 2.0 s to 3.2 s and 2.5 s for the bitumen from OS2 and OS1 ores, respectively.


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Figure 10. Effect of toluene and EC-in-toluene solution addition to bitumen on the induction time of diluted bitumen-air bubble attachment at ambient condition. The virgin bitumen from OS1 and OS2 ores was used, and the measurement using bitumen without toluene and EC addition serves as reference.

The thinning and rupture of the intervening liquid film, and expansion of three-phase contact (TPC) line are considered as three essential steps of the bubble-particle (bitumen droplet) attachment.[29] It is believed that any factors that impact any of these three steps would change the measured induction time. The decrease in induction time with toluene addition could be largely ascribed to the increase in mobility of bitumen-water interface, resulting from the reduction of bitumen viscosity by the solvent addition.[7] The decrease in bitumen viscosity would translate to an increased interfacial mobility of natural surfactant adsorbed at bitumenwater interface. When pressed against the approaching air bubble, the migration of these mobile


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surfactant would expose more hydrophobic bitumen surfaces by pushing away the surfactant to allow the contact of air bubbles with these more hydrophobic regions of bitumen surfaces, facilitating the thinning of intervening water film and the spreading of the TPC line.[30] As a result, a reduction in the induction time of diluted bitumen-air bubble attachment would be expected as observed. Similar logics apply to the observed larger induction time for more viscous bitumen from OS2 ore than from OS1 ore. Ethyl cellulose is known to be a linear polymer with a backbone of cellulose structure. The side hydroxyl groups on the backbone are partly substituted by ethoxyl groups, making EC oilsoluble while maintaining its amphiphilic nature.[22] In the other word, EC is an interfacially active polymeric surfactant containing hydrocarbon chains (rings) and hydroxyl groups, which is effective in reducing the diluted bitumen-water interfacial tension[31] but could not alter the viscosity of the system at the current dosage (a few of 100 ppm). When EC absorbed at oil-water interface, its hydrocarbon chains (i.e. hydrophobic segments) would be embedded in the oil phase and hydroxyl groups oriented toward aqueous phase as schematically shown in Figure 11 (i), leading to the possible formation of an outer-hydrophilic-layer exposed to the water phase and therefore making the bitumen surface less hydrophobic. The adsorption of interfacially active EC molecules at diluted bitumen-water interface could therefore reduce the mobility of natural surfactant and EC molecules adsorbed at diluted bitumen-water interface, hindering the thinning of the intervening liquid films as a result of more hydrophilic nature of the interface. As a result, adding EC in toluene for dilution of bitumen would retard the thinning of intervening liquid films and hence increase the induction time of diluted bitumen-air bubble attachment as observed (i.e., the depression of floatability of bitumen droplets).


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Figure 11. (i) Schematic of a possible EC orientation at the diluted bitumen-water interface (red circles and black lines represent polar hydrophilic groups and hydrocarbon chains of EC, respectively). (ii) Effect of EC on organic-contaminant solid surface by adsorption or displacement (blue solid squares are polar groups of solid surface).[22] (iii) Representation of a possible demulsification process for water-in-diluted bitumen emulsion by EC.[12] It is interesting to correlate the observed bitumen flotation performance with the effect of EC on these three sub-processes. The significant improvement in bitumen froth quality (higher B/S and B/W ratios) with EC addition to the current aqueous-nonaqueous hybrid bitumen extraction process (HBEP) appears to correspond well with the increase in bitumen liberation kinetics and probability of bitumen droplet coalescence in process water. In the previous studies,[21, 22] ethyl cellulose (EC) was shown to be an effective solid surface modifier to increase the wettability (i.e., hydrophilicity) of organic-rich or oil-wet solids (e.g., contaminated clays). EC is able to increase the hydrophilicity of organic-contaminated solids either by binding with 27 ACS Paragon Plus Environment

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organic materials on the solid surface or by squeezing them away from the solid surface, as illustrated in Figures 11 (ii) and (iii).[22] Due to its amphiphilic nature and relatively high molecular weight, the hydrocarbon chains of EC might adsorb on organic species of solid surface while exposing its hydrophilic segments to the aqueous phase. In addition, a large number of hydroxyl groups of each EC molecules allows its competitive binding with oxygen atoms on the solid surface to displace the organic compounds from solid surface, leading to the possible hydrophilic polar groups exposed to the aqueous phase.[22] The increased wettability of organiccontaminated solids would lower their potential to enter the bitumen froth by unwanted attachment with bitumen droplets and/or air bubbles, leading to reduced amount of solids in the bitumen froth by EC addition. Similarly, EC is well-recognized to be an efficient demulifier for breaking water-in-diluted bitumen emulsions by either penetrating into the protective steric interfacial film or displacing the interfacial species in the film at the bitumen-water.[12,23,31] The hydrocarbon chains of EC could act as a bridge to flocculate water droplets, enhancing the coalescence of emulsified water droplets as schematically shown in Figure 11 (iii)[12] and leading to a reduced amount of water in bitumen froth with EC addition. The results of induction time measurement clearly show a decrease in bitumen-air bubble attachment with the addition of EC in toluene, although it is beneficial to bitumen liberation and bitumen coalescence. Since bitumen liberation and aeration collectively determine the performance of bitumen recovery, the improvement by EC addition on bitumen liberation and coalescence is offset by the reduction in bitumen aeration, showing no significant setback on bitumen recovery at 100 to 200 ppm EC addition, although high addition rate at 300 ppm reduced bitumen recovery. A compromise of EC addition at 200 pm is clearly needed to maximize the benefit of EC in bitumen recovery and bitumen froth quality.


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4. CONCLUSION The flotation protocols of demulsifier-assisted aqueous-nonaqueous hybrid bitumen extraction process (HBEP) at ambient temperatures were used to study the potential of ethyl cellulose (EC) as a process aid in HBEP for processing high-fine oil sands ores. The addition of 100 to 200 ppm EC was found to dramatically reduce solids and water content in the extracted bitumen froth, with no negative effect on bitumen recovery which was boosted greatly by solvent (known as diluent) soaking of oil sands ores prior to ambient temperature slurry conditioning. The improvement in bitumen froth quality was attributed to the increase in the rate and ultimate degree of bitumen liberation by EC addition, compounded by improvement in bitumen coalescence that reduced mechanical entrainment of fine solids to bitumen froth. However EC addition reduced bitumen aeration efficiency shown by an increase in induction time of bitumenair bubble attachment, which offset the benefit of improving bitumen liberation and coalescence to enhance bitumen recovery. As a result, bitumen recovery remained high with up to 200 ppm EC addition but reduced with further increasing EC addition. The findings from this study further reinforce the robustness of the HBEP process at ambient temperature, as one of advanced extraction alternatives in term of reducing the energy consumption and the GHG emissions, while illustrating the importance of chemical additives to HBEP for further improved performance.

■ AUTHOR INFORMATION Corresponding Author *

Tel.: +1-780-492-7667; fax: +1-780-492-2881; email: [email protected].


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Author Contributions †

Feng Lin, Lin He and Jun Hou contributed equally to this work. Notes The authors declare no competing financial interest.

■ ACKNOWLEDGEMENTS The authors thank financial support from NSERC Industrial Research Chair Program in Oil Sands Engineering. Partial support from Alberta Innovates - Energy and Environmental Solutions is also greatly appreciated.

■ REFERENCES (1)

Radler, M. Oil Gas J. 2002, 100, 113-145.

(2)

Masliyah, J.; Zhou, Z.; Xu, Z.; Czarnecki, J.; Hamza, H. Can. J. Chem. Eng. 2004, 82, 628-654.

(3)

Czarnecki, J.; Radoev B.; Schramm L. L.; Slavchev, R. Adv. Colloid Interface Sci. 2005, 114-115, 53-60.

(4)

Cormack, D. E.; Kenchington, J. M.; Phillips, C. R.; Leblanc, P. J. Can. J. Chem. Eng. 1977, 55, 572-580.

(5)

Hooshiar, A.; Uhlik, P.; Liu, Q.; Etsell, T. H.; Ivey, D. G. Fuel Process. Technol. 2012, 94, 80-85.

(6)

Wu, J.; Dabros, T. Energy Fuels 2012, 26, 1002-1008.

(7)

Harjai, S. K.; Flury, C.; Masliyah, J.; Drelich, J.; Xu, Z. Energy Fuels 2012, 26, 29202927.

(8)

Schramm, L. L.; Stasiuk, E. N.; Yarranton, H.; Maini, B. B.; Shelfantook, B. J. Can. Pet. Technol. 2003, 42, 55-61.

(9)

Rendall, J. S. U.S. patent 4,424,112, 1984.

(10)

Rendall, J. S. U.S. patent 4,875,998, 1989.

(11)

Hou, J.; Feng, X.; Masliyah, J.; Xu, Z. Energy Fuels 2012, 26, 1740-1745. 30 ACS Paragon Plus Environment

Page 31 of 31

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

(12)

Feng, X.; Xu, Z.; Masliyah, J. Energy Fuels 2009, 23, 451-456.

(13)

Srinivasa, S.; Flury, C.; Afacan, A.; Masliyah, J.; Xu, Z. Energy Fuels 2012, 26, 28832890.

(14)

He, L.; Zhang, Y.; Lin, F.; Xu, Z.; Li, X.; Sui, H. Can. J. Chem. Eng. 2015, 93, 11261137.

(15)

Esmaeili, P.; Lin, F.; Yeung, A. Langmuir 2012, 28, 4948-4954.

(16)

Moran, K. Langmuir 2007, 23, 4167-4177.

(17)

He, L.; Lin, F.; Li, X; Xu, Z.; Sui, H. Energy Fuels 2014, 28, 7403-7410.

(18)

Gu, G.; Xu, Z.; Nandakumar, K.; Masliyah, J. Int. J. Miner. Process. 2003, 69, 235-250.

(19)

Quraishi, S.; Bussmann, M.; Acosta, E. J. Surfact. Deterg. 2015, 18, 811-823.

(20)

Wang, Y.; Jia, W.; Ding, M.; Yang, H.; Hu, B.; Ren, S. Energy Fuels 2011, 26, 10191027.

(21)

Lin, F.; He, L.; Primkulov, B.; Xu, Z. J. Phys. Chem. C 2014, 118, 13552-13562.

(22)

Wang, S.; Segin, N.; Wang, K.; Masliyah, J.; Xu, Z. J. Phys. Chem. C 2011, 115, 1057610587.

(23)

Feng, X.; Mussone, P.; Gao, S.; Wang, S.; Wu, S.; Masliyah, J.; Xu, Z. Langmuir 2010, 26, 3050-3057.

(24)

Lin, F.; Esmaeli, P.; Long, J.; Bara, B.; Yeung, A. Colloids Surf. A 2014, 451, 144-150.

(25)

Lin, F.; Suda, J.; Yeung, A. J. Colloid Interface Sci. 2014, 430, 113-115.

(26)

Tarimala, S.; Ranabothu, S. R.; Vernetti, J. P.; Dai, L. L. Langmuir 2004, 20, 5171-5173.

(27)

Wu, C.; Tarimala, S.; Dai, L. L. Langmuir 2006, 22, 2112-2116.

(28)

Walz, J. Y. Adv. Colloid Interface Sci.1998, 74, 119-168.

(29)

Nguyen, A. V.; Schulze, H. J.; Ralston, J. Int. J. Miner. Process. 1997, 51, 183-195.

(30)

Pugh, R.; Yoon, R. J. Colloid Interface Sci. 1994, 163, 169-176.

(31)

Feng, X.; Wang, S.; Hou, J. Wang, L; Cepuch, C.; Masliyah, J.; Xu, Z. Ind. Eng. Chem. Res. 2011, 50, 6347-6354.


Role of Ethyl Cellulose in Bitumen Extraction from Oil Sands Ores

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