Mechanistic Study of Water Droplet Coalescence and Flocculation in

Subscriber access provided by - Access paid by the | UCSB Libraries

Article

Mechanistic Study of Water Droplet Coalescence and Flocculation in Diluted Bitumen Emulsions with Additives Using Microfluidics Arash Nowbahar, Kathryn Whitaker, Adam K. Schmitt, and Tzu-Chi Kuo Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01619 • Publication Date (Web): 05 Sep 2017 Downloaded from http://pubs.acs.org on September 7, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 38

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

Mechanistic Study of Water Droplet Coalescence and Flocculation in Diluted Bitumen Emulsions with Additives Using Microfluidics Arash Nowbahar1, Kathryn A. Whitaker, Adam K. Schmitt, Tzu-Chi Kuo Formulation Sciences, Core R&D, The Dow Chemical Company, Midland, MI, 48674

KEYWORDS: Bitumen, Emulsion, Additive, Microfluidics, Coalescence

1

Current Address: Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA, 93106

ACS Paragon Plus Environment

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

ABSTRACT Synthetic crude oils derived from mined oil sands processed via the Clark hot water extraction process do not meet current specifications for pipeline transport and are corrosive to upgrader equipment by virtue of the high residual water content (2-5%) and salts. Formulated chemical additives used in this process can improve the oil quality by accelerating and enhancing the separation of water from oil. The identification and selection of these formulated additives is typically based on performance data collected in field testing for each component or blend. Herein, two methods are reported to study the effect of chemical additives on the phase separation behavior of water in diluted bitumen emulsions prepared in microfluidic devices. First, water droplets in diluted bitumen were created in the presence of chemical additives and the kinetics of droplet coalescence were compared for various additives and concentrations. Second, using a custom made device geometry, water droplets in diluted bitumen were formed and aged prior to the addition of chemical additives. The treated droplets were observed to calculate the kinetics of droplet coalescence. The frequency of coalescence events was the same order of magnitude in both studies. The effectiveness of various additives can be determined by measuring the coalescence time, which is dominated by film drainage in the case of the best chemical additives.


Page 2 of 38

Page 3 of 38

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

INTRODUCTION As the world energy demand increases, oil sands have become an important source of petroleum fuels.1 However, the processing of this resource has remained a challenge.

One of the

commercial methods uses surface mining, where bitumen in the surface-mined ore is extracted via the Clark Hot Water Extraction process. In this process oil is separated from sands by mixing with hot water and is recovered by flotation. The recovered material is called bitumen froth, and it is further processed with organic solvent to remove most water and minerals. In the naphthenic froth treatment process, the bitumen froth is diluted with aromatic naphtha and is referred to as diluted bitumen (dilbit). Dilbit has entrained water droplets, which are difficult to separate due to indigenous surfactants, asphaltenes and particulates, which form a stabilizing elastic film at the water/oil interface.2–5 In addition, these water droplets can be corrosive because of their high salt content, and they pose a risk to downstream separation and transport processes. Chemical additives can be used at various stages of the extraction process as a costeffective means to separate water from dilbit. Effective additives are typically oil-soluble, amphiphilic polymers that disrupt the stabilizing film, which is composed of a complex mixture of asphaltenes, resins, and naphthenates.6,7 A variety of additives have previously been studied including ethylene oxide/propylene oxide (EO/PO) copolymers,8–12 alkylphenol poly-alkoxylated resins,7 polyurethanes,7 ethyl cellulose,13 and silicones.14 Additives are most often evaluated using a bottle test in which the additive is hand-shaken with the dilbit in a small jar or centrifuge vial and the amount of water that separates from the oil phase is recorded. For additives to effectively remove water from oil, it is believed that additives require greater interfacial activity than the asphaltenes and resins to penetrate the elastic film at the interface. Additives are expected to reduce the interfacial


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

viscosity (soften the film),15,16 and to minimize surface tension gradients in order to reduce the Marangoni-Gibbs effect and film drainage time of coalescing droplets.17,18 Many studies have looked at structure-property relationships between additives and water removal performance. Xu et al.9 have found that for the same class of additives (EO/PO copolymers), there is a correlation between high relative solubility number (RSN), which is associated with higher water solubility, and enhanced water removal performance. For EO/PO copolymers, the RSN has been shown to be correlated with hydrophilic-lipophilic balance (HLB) numbers.10,11 Molecular weight has also been linked to performance, but trends vary from study to study; a low molecular weight molecule allows for rapid adsorption to the interface,18,19 while a high molecular weight polymer may be more effective at disrupting the interfacial film.7,10,11,20 Additionally, there is typically a concentration range with which optimal performance is observed. Too low a concentration can be ineffective. At high concentrations, the performance may plateau, and the excess additive in the system does not provide any benefit.13,21 High concentrations may also saturate the interface with additive and stabilize it, a situation referred to as overdosing.1,7,15,22 Additive performance also varies depending on whether the additives have time to adsorb to the water/oil interface before being exposed to asphaltenes or if they need to interact with asphaltenes that are already present at an aged interface.15,23 While structure-property relationship studies have improved additive understanding, trends seem to apply only within specific additive chemistry classes. Few studies have looked at a wide range of additives simultaneously. Removing water from crude oil with an additive is a complex, dynamic process that involves droplet growth and sedimentation.24 As droplets get larger and accumulate more mass, the sedimentation rate increases.

It is hypothesized that droplet coalescence is the primary

mechanism for droplet growth, but flocculation of droplets would have the same effect on


Page 4 of 38

Page 5 of 38

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

sedimentation rates. Droplet coalescence is a multi-step process in which (1) the droplets approach and collide, (2) the interfacial film drains, and (3) the film ruptures after a critical film thickness is reached.7,24,25 After the film ruptures, the droplets combine to a single coalesced droplet. Droplet coalescence has been widely studied and continues to be an active area of research, since flow types, viscosity ratios, interfacial rheology, and interfacial instabilities complicate film drainage and rupture.25 However, simplistic models exist, such as one presented by Chesters26 for a partially mobile interface (moderate viscosity ratios), where the film drainage rate is given by:

− ~

/

/

,

{1}

where ℎ is the film thickness, is the drop radius, is time, is the interfacial tension, is the viscosity of the dispersed phase, and is the interaction force between the two droplets. Klaseboer et al. gave an expression for the film drainage of an immobile interface where the tangential velocity at the interface is zero:27

=

ℎ

!

,

{2}

where " is the viscosity of the continuous phase, is the radial distance from the center of the film, and # is the excess pressure in the film relative to the bulk: #=

$ %

$ &

− .

{3}

These expressions give estimates for drainage rates. Alternatively, droplet coalescence rates can be expressed using a probabilistic view, where droplets collide with a given frequency ' and probability of coalescence (, such that:25,26,28


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 6 of 38

〈 〉 * 1〈 -./0/ 〉

, {4}

where '" is the frequency of coalescence events, 〈" 〉 is the mean coalescence time (film drainage time + rupture time), and 〈"234" 〉 is the mean contact time during a collision. Experiments from Hu et al. have found that for droplet coalescence under flow, drops need to travel slowly enough such that there is enough time for film drainage (〈"234" 〉 > 〈463478 〉).29 The capillary number 9: =

; $

relates viscous forces to capillary forces, where 9:" , and the droplets did not coalesce. When the flow was reduced, 9: < 9:" and coalescence was observed. In the second part, we


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

formed droplets in dilbit without additive and allowed the droplet interfaces to age before introducing the additive and examining the resulting droplet coalescence. This resembles the actual bitumen separation process where an emulsion is created before additive is introduced. In addition, the separation process of bitumen occurs under flow conditions, thus studying performance in this fashion is relevant. Because the focus of the study is on the effects of the additives, shear rates were kept constant. The exact dynamics of film drainage depend on the specific flow conditions and geometry, thus the conclusions drawn are related to additive performance.

EXPERIMENTAL Materials. Norland Optical Adhesive (NOA) 81, SYLGARD™ 184 polydimethyl siloxane (PDMS) kit, and KMPR 1050 photoresist were obtained from Norland Products, Inc., Ellsworth Adhesives, and MicroChem Corp., respectively. Oil sands were obtained from Alberta Innovates Technology Futures (AITF, Alberta Canada). To extract the heavy oils, the sands were mixed with hot water and bubbled with air to create a froth. The froth was then collected and diluted with 40% aromatic naphtha. The diluted bitumen (dilbit) was then centrifuged at 22,465 g force (14,000 rpm in a SORVALL LEGEND X1R centrifuge, Thermo Fisher Scientific, with a FIBERLite F15-8x50c rotor) for 10 min and an aliquot of the top 50% was taken for experiments to remove any solids or water originally present in the dilbit. Potassium chloride (KCl) was obtained from Sigma Aldrich and prepared as 600 ppm solutions in deionized water for all experiments. Xylene and 2-propanol (IPA) were obtained from Sigma Aldrich and used as received. Table 1 shows the additives used in this study with their measured relative solubility numbers (RSN) and the kinematic viscosities reported in their technical data sheets. The RSN


Page 8 of 38

Page 9 of 38

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

was measured by preparing a solution containing 1 g additive in 30 mL of toluene (2.6 vol%) and ethylene glycol dimethyl ether (97.4 vol%). The reported RSN is the volume (mL) of water titrated into the solution that resulted in a persistently cloudy solution. Additive A is a proprietary blend developed in The Dow Chemical Company. The other additives are commercially available and were used as received. The choice of additives provides a range of additive classes, molecular weights, and solubility (RSN). Additives were prepared as 2 wt% solutions in 3:1 xylene:2-propanol (by mass). Dilbit samples and KCl solutions used were filtered through 5 µm PTFE syringe filters (ReZist Syringe Filters 09302186, Fisher Scientific) to ensure debris did not clog devices. Additive solutions were then added to dilbit samples to make 300 ppm, 1000 ppm, or 2000 ppm solutions by weight and mixed in a FlackTek dual-axis mixer (Model DAC 150 FLZ-K, FlackTek Inc., Landrum, SC) at 3500 rpm for 1.5 min.

Table 1: Physical properties of additives used in this study Additive A B C D E F

Additive Type Proprietary Cellulose ether (lower Mw) Cellulose ether (higher Mw) Nonionic polyether polyol Polyether-modified, hydroxyfunctional polydimethylsiloxane Polyether-modified siloxane

RSN 10-13 5.2 4.2 14.6

Kinematic Viscosity (cSt) ~1000 N/A N/A 231

9.3

1.1

17.2

62.5

Premixed Additive Experiments. Microfluidic experiments with additive premixed in the dilbit during drop creation were performed using the commercial hydrophobic droplet incubation chip from Dolomite Microfluidics (Figure 1a). In addition, inline valves from IDEX (Oak Harbor, WA) were placed at each inlet and outlet to turn on and off the flow. New Era NE-511 syringe


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 10 of 38

pumps with 1 mL syringes from B-D were used to drive fluid flow. Prior to every experiment, the device was first flushed with toluene and then dried by pushing air through the device. The dilbit with additive was flowed (from injection by hand) through three of the inlets and water with 600 ppm KCl was flowed through the fourth inlet. The valves on two of the dilbit inlets were then closed as they were not needed for these experiments (Figure 1b). Droplets were produced and flowed into the serpentine channel shown in the schematic of Figure 1a.

Figure 1. (a) Schematic of droplet incubation chip for experiments with additive premixed in the dilbit. The droplets were generated in the T-junction, as detailed in (b) where two valves were closed and water droplets were formed in the stream of additive/dilbit mixture. The constriction is 50 µm wide, while the width of serpentine channel is 1000 µm.

In order to prevent droplet coalescence while flowing droplets into the channel, i.e. before experimental observation, a flow rate of 2 µL/min of the oil phase and 1 µL/min of the aqueous phase was used. At this flow rate, 〈"234" 〉 from Equation 4 was small enough compared to 〈" 〉 that few coalescence events were observed. The chip was left flowing for 40 min to ensure pressure had equilibrated. Images were then acquired and the valves were closed to stop the


Page 11 of 38

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

flow. The flow did not completely stop due to a back pressure from the unused channels, but was reduced dramatically. When the flow was stopped, 〈"234" 〉 was increased and droplets coalesced. Initial droplet sizes were about 40 µm. Aged Droplets Experiments. A custom microfluidic device was made from NOA 81 using a soft lithography approach described by Bartolo et al.37 Briefly, a mold was made using conventional lithography and KMPR-1050, spin coated at 1000 rpm for a thickness of about 100 µm. A PDMS mold was then made by curing the PDMS on top of the patterned wafer. After removing the PDMS mold from the wafer, uncured NOA 81 was sandwiched between the PDMS mold and a glass slide. The NOA 81 was cured partially with a UV lamp. The PDMS mold was removed, leaving the imprinted NOA 81 on the glass slide. A PET sheet was laser-cut with inlet holes and sealed with tubing connectors. The PET sheet was pressed onto the NOA 81 and cured furtherly with a UV lamp to form the device. The device used for aged droplets experiments is shown in Figure 2a. Water droplets were made at a T-junction on the far left of the device and traveled along the serpentine channel. At the midpoint of the device, there was a second inlet to the main serpentine channel where a stream of additive/dilbit mixture was injected. With inlet flow rates of 3 µL/min dilbit in inlet 1 and 2 µL/min water in inlet 2, the droplets aged for about 1 min 10 sec before encountering the additive (~70 sec of aging). Micropipette experiments2 have shown that this was a sufficient amount of time for an asphaltene skin to form at an interface. At the point where the additive was introduced to the serpentine channel, the channel constricted to provide more efficient mixing of the additive, but the flow rates were maintained such that the capillary number 9: < 1 so this ensured minimal droplet deformation and disturbance to the interface.. The dilbit in inlet 3 had


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 12 of 38

an additive concentration of 2000 ppm or 1000 ppm, and it was diluted by the dilbit in inlet 4 (0 ppm additive), which crossed at a T-junction (Figure 2b). The flow rates were varied to adjust the concentration at the additive inlet, but the total flow rate of inlets 3 and 4 was constant at 3 µL/min. As opposed to the premixing additive experiments where the flow was stopped, here droplets were continuously flowing and coalescing. Images were acquired for 10 min at 9.69 frames per second of the row immediately before the additive was introduced and the 5 subsequent rows (the field of view is outlined in Figure 2b).

Figure 2. (a) Schematic of microfluidic device for aging droplets before introducing additive. The width of the serpentine channel was 1000 µm with a constriction to 100 µm at inlets 3 and 4. (b) Photograph of the device with water droplets being generated in dilbit. The droplets only coalesced after the additive was introduced. The dashed red box outlines the field of view that was imaged during the experiments.

Image Analysis. Droplet number and sizes were measured through image analysis in MATLAB (Mathworks, Natick, MA). Each image was converted to binary where droplets became white features on the black background. The size of the droplets was then calculated from the area of


Page 13 of 38

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

each feature, and the number of droplets per image was recorded. After the first coalescence event, droplets become pancake shaped where the height is approximately that of the channel. Given that the drops all have the same height, the relevant length scale for coalescence is the radius of the drop ~?@/A, where A is the area viewed from above. When two droplets coalesced, the total number of droplets in the image was reduced by one. Therefore, in any image, the number of coalescence events B" that have occurred is B" = CD − C,

{5}

where CD is the number of droplets in the image representing the initial reference point and C is the number of droplets in the image being analyzed. In addition to measuring size distribution and the number of droplets in an image, similar to Krebs et al.,34 the location of individual droplets was also tracked. If two droplets were identified in consecutive frames and their centers were within a designated cut-off distance, then the tracking algorithm identified them as the same droplet in the two frames. This tracking helped to identify pairs of droplets that underwent coalescence. The coalescing pairs can be analyzed according to their size and the coalescence time needed for the droplets to combine. Interfacial Tension. Interfacial tension (IFT) of dilbit drops in 600 ppm aqueous KCl solution was measured using the pendant drop technique in a Krüss DSA100 (Krüss USA, Matthews, NC). The density of dilbit (0.900 g/cm3) was less than that of water, therefore an inverted needle was used with large drops, ~35 µL in volume, to ensure appreciable deformations from the buoyant force, i.e. Bond number FG =

∆I7% $

> 1, where ∆J is the density difference between

the droplet and continuous phases and K is the acceleration due to gravity. Using the Krüss Drop


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 14 of 38

Shape Analysis (DSA4) software, the shape of the drop was fitted and the Young-Laplace equation solved to back out the interfacial tension.

RESULTS Premixed Additive. Figure 3 shows an example of an experiment where Additive B was premixed into the dilbit at 1000 ppm when the drops were created. Figure 3a shows the moment when the valves were closed and the flow was stopped (a small residual flow existed over a longer timescale that oscillated due to a back pressure). Notice that the drops had flowed into the channel and were fairly monodisperse, with some coalescence events that occurred while flowing. When the droplets flowed through the channel, 9: > 9:" and 〈"234" 〉 < 〈" 〉. Therefore, the probability of coalescence was small because the droplets were stripped away from each other before film drainage and rupture could be achieved. When the flow was stopped, the droplets were nearly in contact and 〈"234" 〉 > 〈" 〉, allowing coalescence to take place. Coalescence occurs when the film between two droplets drains and ruptures. The results of multiple coalescence events are shown in Figure 3b and Figure 3c at times t = 40 sec and t =1 68 sec, respectively. At t = 168 sec, some drops remained small and did not coalesce. These droplets were not in contact with any other droplet, and had no way of colliding with another droplet to coalesce. Coalesced drops seemed to be located near the walls, hence wall effects might alter coalescence dynamics, but it did not affect the conclusions regarding the additives.


Page 15 of 38

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. Brightfield stereoscopic images of a water in dilbit emulsion with 1000 ppm Additive B in the dilbit at (a) t = 0 sec (flow reduced), (b) t = 40 sec, and (c) t = 168 sec. Channel width is 1000 µm. A video of this experiment is available in the Supporting Information (S1).

Both the size distribution and number of droplets as a function of time can be quantified. Figure 4 shows the number of coalescence events B" normalized by the initial number of droplets CD at = 0; the results are averaged from all seven channels and are shown in Figure 3. The slopes of the curves are the frequency of coalescence events. There was no coalescence in the control experiment (dashed black line), with no additive present except 3:1 xylene:IPA (the same amount as added with other additive solutions). A video of a control experiment is available in the Supporting Information (S2). A stable emulsion was formed, which agrees with the literature2 in which a rigid elastic film prevents coalescence. Good reproducibility between experiments with Additive D was shown in Figure 4. Comparing the different additive types at 300 ppm, it can be seen that Additive A coalesces fastest because it has the highest slope in Figure 4, followed by Additive D. Additives B and E and coalesce at nearly the same frequency. The relative coalescence frequencies of the additives shown in Figure 4 correlates with the


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

dewatering performance seen in our bottle tests conducted at 60 °C (not reported here), such that additives with higher coalescence frequencies remove more water from dilbit in the bottle tests.


Page 16 of 38

Page 17 of 38

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 4. Number of coalescence events B" normalized by the initial number of drops CD as a function of time for various additives: 300 ppm Additive A (red), 1000 ppm Additive B (dark green), 300 ppm Additive B (light green), 75 ppm Additive B (lightest green, flat at zero), 300 ppm Additive C (purple), 300 ppm Additive D (orange), 300 ppm Additive E (blue), 300 ppm Additive F (light blue), control without additive (dashed black). Brown × is a repeat experiment of Additive D (orange), showing typical reproducibility.

Figure 4 shows that within an additive type, a change to the molecular structure of the additive can greatly influence the demulsification property. For example, the two siloxanes (Additives E and F) performed very differently. Additive F (light blue) showed no coalescence while the hydroxyl-functional Additive E (blue) broke the emulsion. The results from Additives B and C, shown in green and purple respectively in Figure 4, demonstrate how a difference in molecular


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 18 of 38

weight can significantly change the coalescence frequency. After 25 min, B" /CD for Additive C rises to about 0.05. This difference in time needed to disrupt, or prevent the interfacial layer from forming, agrees with what has been reported in the literature;18,19 lower molecular weight additives can diffuse faster to the interface and act more rapidly.

Figure 5. (a) Brightfield stereoscopic image of the channels with 300 ppm Additive B at t = 268 sec. Droplets have coalesced at different frequencies in the different channels. Channel width is 1000 µm. (b) Number of coalescence events for Additive B at 1000 ppm (dashed lines) and 300 ppm (solid lines) for channels 1 (blue), 3 (red), 5 (gold), and 7 (purple). (c) Number of coalescence events for Additive B at 300 ppm in channels 1 (blue), 3 (red), 5 (gold), and 7 (purple) shifted to correct for the time at which the droplets were created.

The concentration dependence of Additive B on the coalescence frequency can be seen in Figure 4 as the number of coalesced drops decreases with decreasing concentration. At the highest concentration of 1000 ppm, Additive B resulted in approximately the same number of coalescence events as Additive A at 300 ppm. However, the difference in the initial slope of the curves indicates that even at a lower concentration, Additive A caused the coalescence to occur


Page 19 of 38

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

at a higher frequency. At 75 ppm, Additive B showed no coalescence events. The concentrations used in this study were higher than those of other studies,13,20,21 due to the specific dilbit system and a much larger volume fraction of water used in this study. No overdosing effects were observed in this study for the range of additive concentrations used. Data from Figure 4 were computed by taking the average of all 7 channels. When the droplets rapidly coalesce, this average is a good representation of the coalescence. However, at lower concentrations, the droplets coalesce at different frequencies in different channels (Figure 5a). Figure 5b shows the number of coalescence events separated by individual channel for Additive B at 1000 ppm and at 300 ppm. At 1000 ppm (dashed lines), droplets in all of the channels coalesced at the same frequency. However at 300 ppm (solid lines), droplets in each channel coalesced at different frequencies, with the fastest coalescence being observed farthest from the droplet generation point. The distribution in droplet sizes between channels 1 and 7 during observation in Figure 5a is in contrast to the relatively monodisperse droplets across all channels shown in Figure 3b and c for Additive B at 1000 ppm. This result can be rationalized by realizing that the droplets in the seventh channel were created before the droplets in the first channel. The mean residence time for the droplets in a channel to have reached their position in the device at the time D that the flow is turned off is 〈M8N 〉. As such, 〈M8N 〉 is the age of the droplets at the beginning of the video recorded during the experiment. There is also a timescale M4 , over which the additive disrupts the elastic interfacial film or prevents it from forming (by lowering the elastic modulus or interfacial tension). If M4 < 〈M8N 〉, then when the flow is stopped, the droplets in all of the channels will coalesce at the same frequency, as is seen with Additive B at 1000 ppm in Figure 5a. If M4 > 〈M8N 〉 , there will be a lag time before the droplets begin to coalesce in a channel, but the frequency of


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 20 of 38

coalescence events in each channel will be the same (B" /CD curves will be staggered by differences in 〈M8N 〉). If M4 ~〈M8N 〉 then some channels will have the same coalescence frequencies, while some channels will be delayed. The 300 ppm data in Figure 5b were replotted as a function of + 〈M8N 〉 to account for the age of the droplets (Figure 5c). The B" /CD curves for all of the channels would be expected to collapse once corrected for 〈M8N 〉, but instead the coalescence is seen to occur at different frequencies, which suggests another mechanism for the variation in coalescence frequencies. In addition to the later channels having a longer residence time, they also have more opportunities to mix as they go around each bend. At low additive concentrations, the coalescence mechanism is diffusion-limited and M4 is a combination of diffusion of the additive to the interface and the time for the additive to adsorb and weaken the interface. Locally around the droplet, the additive adsorbs to the droplet interface and is depleted from the solution. The additive adsorption rate is decreased due to the lack of available additive at the droplet interface until more additive diffuses from the bulk solution. With the solution flowing, additive was replenished from the bulk. In addition, as the droplets and solution flow around the corners, the solution is re-mixed which locally increases the additive concentration at the interface. Each time the droplets turn a corner, this enhanced mixing enables more additive to adsorb on the droplet interface. At the start of the observation period for Additive B at 300 ppm, the droplets in channel 7 have had more time and mixing, thus the surface concentration of the additive is also higher. This change in surface concentration of the additive results in channel-dependent coalescence frequencies where the longer residence time and more mixed droplets have faster coalescence kinetics versus the newly formed droplets.


Page 21 of 38

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

In addition to counting the number of coalescence events, pairs of coalescing droplets can be tracked in order to measure the time it takes for them to coalesce. We define the coalescence time as the amount of time the droplets were in contact before coalescing. Droplets were considered to be in contact if their surface-to-surface separation was less than 27 µm apart (Figure 6a). The probability density function of the coalescence time is shown in Figure 6b for Additive A at 300 ppm and Additive B at 1000 ppm and 300 ppm. The inset to Figure 6b shows the mean of the distributions for the same conditions as well as 300 ppm Additive D and 300 ppm Additive E. The trends seen in Figure 4 for additive effectiveness at promoting coalescence events is also seen in 〈" 〉 of Figure 6b. The value of 〈" 〉 is the sum of the drainage time and the rupture time. Typically, for non-asphaltene laden systems, the time to rupture is instantaneous. Here, there was competitive adsorption of stabilizing components in the dilbit and the additive. If the additive was ineffective, or if the concentration was too low, a barrier to film rupture existed, and an elastic modulus slowed film drainage. On average, for Additive B at 300 ppm, droplets spent over 60 seconds next to each other before coalescing, whereas only ~10 seconds at 1000 ppm were necessary for coalescence. Such large differences in 〈" 〉 could be due to the effectiveness of the additive at preventing or disrupting the elastic film from forming rather than differences in interstitial fluid drainage for this specific flow.


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 22 of 38

Figure 6. (a) Distance between droplet surfaces as a function of time, and (b) probability density function of coalescence time for droplets in Additive A at 300 ppm (red), Additive B 1000 ppm (dark green), and Additive B 300 ppm (light green). The inset shows the mean of the distributions for various additives.

To explore this further, IFT measurements were performed using the pendant drop method to explore the competitive adsorption between asphaltenes, resins, and additives (Table 2). Since the additives were formulated in 3:1 xylene:IPA, the IFT of a control sample with an equivalent mass of xylene:IPA without any additives was measured to provide a benchmark. The solvent had no effect as dilbit itself showed the same interfacial tension (data not shown). In each experiment, the IFT was plotted as a function of time. The equilibrium IFT was taken as the average of ~30 sec of data after the IFT was observed to reach a plateau. To compare the dynamics of the different additives and how quickly they alter the interface, the initial slope of the IFT was calculated using the data collected between 10 and 30 sec after forming the droplet.


Page 23 of 38

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 7a shows examples of such IFT curves. All of the additives tested, even those that show no coalescence in the microfluidic experiments, reduced the equilibrium IFT with respect to the control. At 300 ppm, Additive C showed a higher equilibrium surface tension than Additive B, suggesting a molecular weight effect on the interfacial activity. Additive B equilibrated to a value of approximately 12 mN/m when dosed at 300 ppm and 1000 ppm. However, the higher concentration approached the equilibrium at a faster rate as shown by the higher magnitude of the initial IFT slope. To determine the impact of IFT on the coalescence dynamics, the coalescence frequencies calculated from the slopes of the curves in Figure 4 are plotted as a function of the equilibrium IFT (Figure 7b) and the magnitude of the initial IFT slope (Figure 7c). Figure 7b shows that the coalescence frequency correlates poorly with the equilibrium IFT. The equilibrium IFT of the ineffective Additive F was very similar to Additive E, which showed coalescence in the microfluidic experiments. Likewise, at 300 ppm, Additives B and D also showed similar interfacial activity to Additives E and F, but all of these materials had different coalescence frequencies.

The coalescence frequencies correlate more strongly with the

magnitude of the initial slope of the IFT (Figure 7c). This suggests that the rate at which the additive is able to alter the interface plays a significant role in the additive’s ability to promote coalescence. The rate at which the IFT reduction takes place is influenced by the additive diffusion to the interface and rate of adsorption. Therefore, additive concentration, molecular weight, and solubility can all affect the IFT and the coalescence frequency in a system.


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 24 of 38

Table 2. Interfacial tension for a dilbit-water interface Additive 3:1 Xylene:IPA Additive A Additive B Additive B Additive C Additive D Additive E Additive F

Concentration in Dilbit (ppm) N/A 300 300 1000 300 300 300 300

Equilibrium IFT† (mN/m) 25.4 12.9 12.3 12.1 22.5 19.0 17.5 18.5

†

IFT Slope‡ (mN/m/s) -0.030 -0.094 -0.040 -0.117 -0.037 -0.050 -0.028 -0.057

Average of ~30s of data after the IFT was observed to reach a plateau. Initial slope of IFT as a function of time calculated for the IFT data collected between 10-30s after the droplet forms. ‡


Page 25 of 38

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 7. (a) IFT of dilbit in water as a function of time for a control sample and for 300 ppm Additive D in the dilbit phase. A line is fit to the data between 10-30 sec (highlighted in red) to determine the initial slope of the IFT. Droplet coalescence frequency as a function of (b) the equilibrium IFT and (c) the magnitude of the initial slope of the IFT for all samples listed in Table 2.


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 26 of 38

Figure 8. Coalescence times as a function of drop radius for Additive A at 300 ppm (red) and Additive B at 1000 ppm (green). Drop radius is the geometric mean of the two coalescing droplets, assuming a 2D system. The data have been binned by droplet radii and the coalescence times for all droplets within a bin are averaged. Power-law fits with exponents of 0.67 for both data sets are shown in dashed black. Data from experiments with other additives are not used for this analysis because the size ranges of the coalesced droplets are not large enough to obtain a correlation.

In addition to correlating with the slope of the IFT, coalescence time also depends on droplet size. To correlate coalescence time and droplet size, droplet pairs were binned by the geometric mean of their radii. The coalescence times of all droplet pairs in a bin were averaged and plotted as a function of droplet size for Additive A at 300 ppm and Additive B at 1000 ppm (Figure 8). Power-law fits give exponents of 0.667 for Additive A at 300 ppm and 0.660 for Additive B at


Page 27 of 38

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

1000 ppm. The coalescence time measured is the sum of the film drainage time and the rupture time. The film drainage time is expected to be much longer than the rupture time and likely dominates the measured coalescence time. Typically, for axisymmetric droplets approaching each other, film drainage time scales with droplet radius such that 463478 ~ P , where Q varies depending on whether the interface is immobile, mobile, or partially mobile.27,38,39 The experimentally determined power-law fit for exponent α values agree well with the value

expected for coalescing droplets with mobile interfaces,27 which is calculated to be . Although there is good agreement with the film drainage time for mobile interfaces, droplets were confined by the top and bottom of the channel after one coalescence event in the microfluidic device used in this study. Such confinement has been seen to affect dynamics of droplet coalescence as it resembles a 2D cylindrical system as opposed to 2D axisymmetric condition.40–43 While the exact drainage dynamics are governed by the specific flow scenario, the effects observed from the additives are general: Additive A at 300 ppm and Additive B at 1000 ppm disrupt the interfacial film such that coalescence is limited by film drainage, while the other additives are ineffective at disrupting the interfacial film that prevents coalescence.

Flocculation of droplets. In premix systems, it was observed that if the flow rates were slow enough (< 0.5 µL/min) and droplet creation was infrequent (dilute conditions), floccules of droplets could form with some of the additives. Figure 9 displays an image of four channels of droplets with Additive B at 300 ppm in dilbit during drop creation. All four channels were at the same flow rate at less than 0.5 µL/min, yet only the three channels on the right showed flocculation. When the number density of the droplets is high, their motions are dominated by


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 38

collisions, while at a low number density they are dominated by fluid forces. An estimate for dilute conditions is when

I %RS

< 1, where J is the density of the dispersed phase, R is the

droplet radius, T is the relative velocity between droplets, and " is the viscosity of the continuous phase.44 Thus, in Figure 9, where the number density of droplets was varied from the first channel to the second, droplets went from dispersed to flocculated. In addition, a low shear rate was required so as not to overcome the force that held the droplets together. The critical shear rate at which droplets did not flocculate was not measured due to sensitivity limitations of the syringe pumps. This is the first in-situ observation to confirm the flocculation mechanism suggested by Xu and coworkers.13,20,21 In addition to Additive B, Additive E also exhibited flocculation at low number density and flow rate. This finding suggests that depending on flow conditions and concentrations of additives, different mechanisms for water separation exist. For droplets in dilbit with 1000 ppm Additive B, coalescence dominates, but at 300 ppm, flocculation may occur under certain flow conditions.


Page 29 of 38

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 9. Brightfield microscopy image of flowing droplets in four channels with 300 ppm Additive B in dilbit during droplet creation. The first channel shows no flocculation at high density of droplets. Channel width is 1000 µm.

Aged Droplet Experiments. Using the device shown in Figure 2a, water droplets with 600 ppm KCl were formed in dilbit that did not contain any additives. After the droplets had aged in the first half of the device, an additive was introduced.

This device design eliminated the

competition between the additive, asphaltenes, and resins that existed in the experiments where the additive was mixed with the dilbit during droplet generation. In these experiments, the additive must work to disrupt an established asphaltene and resin layer at the interface. The droplets were continuously flowing, and thus shear rates became important; however, all experiments were conducted at the same flow rates so that comparisons could be made between additives. Figure 10a shows a snapshot of an experiment using Additive B. After mixing with the aged droplets, the final concentration of additive in dilbit was 500 ppm. Aged droplets were brought into channel 1, after which the additive/dilbit mixture was introduced. The additive/dilbit stream diluted the concentration of droplets, as can be seen by comparing the first two columns.


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 30 of 38

As the droplets traveled down the serpentine channel they collided with a certain frequency and coalesced. Figure 10b shows the number of coalescence events normalized by the initial number of droplets B" /CD as a function of mean residence time M8N in the channels after introducing the additive. To account for the dilution of the droplets by the additive/dilbit mixture inlet stream, the initial number of droplets CD = C U, where C is the number of droplets in channel 1 and U is a dilution factor. The dilution factor was found experimentally by introducing dilbit without additive at the inlet between channels 1 and 2. Without the additive, coalescence did not occur, and the concentration of droplets per channel after dilution could be determined. Therefore, U = 〈C 〉/〈C 〉, where 〈C6 〉 is the mean number of droplets in channel V. The value of U is ~0.652, the ratio of the flow rates. The mean residence time 〈M8N 〉 indicates the mean time that it takes for a droplet to reach the midpoint of the channel under observation. The residence time in channel 2 was set to zero and the residence times for the subsequent channels are calculated relative to channel 2 by using the droplet flow rates and the distance between the channel midpoints.

Figure 10. (a) Brightfield microscopy image of aged droplets flowing through a microfluidic device. Additive B was introduced between channels 1 and 2 so that the additive concentration


Page 31 of 38

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

in the dilbit in channels 2 through 6 was 500 ppm. A video of this experiment is available in the Supporting Information (S3). (b) Number of coalescence events as a function of mean residence time in seconds in each channel for various concentrations of Additive B: 667 ppm (green), 500 ppm (purple), 333 ppm (yellow), 143 ppm (red), and no additive (blue). The error of the mean residence time is ±6sec. (c) Coalescence frequencies given by the slope of B" ⁄CD as a function of residence time for different additives: Additive A (red), Additive B (green), Additive D (orange), and Additive E (blue).

As the droplets traveled through the device there were more opportunities to coalesce. Each curve in Figure 10b shows coalescence events at various concentrations of Additive B. At a constant 〈M8N 〉, higher concentrations of Additive B resulted in a larger number of coalescence events B" ⁄CD . By maintaining a constant flow rate for all experiments, the frequency of collisions ' and the contact time during a collision "234" remained the same. The increase in coalescence events must therefore be the result of the increased probability of coalescence increasing with additive concentration (Equation 4). Also by Equation 4, the coalescence time decreases as the additive concentration increases.

The same relationship between additive

concentration and coalescence time was observed in the experiments with the additive mixed with the dilbit during droplet generation. The slope UXB" ⁄CD Y⁄U is the frequency of coalescence events. Figure 10c shows the frequency of coalescence events of four additives as a function of concentration. Additive A shows the highest frequency at all concentrations. At concentrations greater than 333 ppm, Additive D exhibits a decrease in coalescence frequency; this is indicative of overdosing. Additive E shows the lowest performance as compared to Additives A, B, and D. Also, at certain concentrations, Additive B seems to perform faster than


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 32 of 38

Additive D. The relative coalescence frequencies of the additives are different for the aged droplets than what was observed in the experiments with the additives mixed in the dilbit during droplet generation. For example, at 300 ppm additive in dilbit during droplet generation, the coalescence frequencies of Additives B and E were approximately equal (Figure 4). However, in the aged droplet experiments, the coalescence frequencies with Additive E are consistently lower than the coalescence frequencies with Additive B. This shows that the ability to disrupt a preexisting film is not equivalent to the competitive adsorption of additive, asphaltenes, and resins; two additives may be equally successful at reaching a newly formed interface before the asphaltenes and resins, but there is no guarantee that they are equally capable of changing a stable, aged interface.

CONCLUSIONS The kinetics of coalescence of water in diluted-bitumen emulsions were studied in a microfluidic platform for the first time by either mixing the additive in dilbit before creating water droplets or by letting the droplets age and then introducing an additive to the continuous phase. In the first case, the frequency of coalescence events is shown to vary by additive type and concentration. Of the additives tested, the frequency of coalescence events was highest with Additive A. The coalescence frequencies correlated with the mean coalescence time for individual droplet pairs. Experiments with Additive B at a lower concentration suggest the demulsifier is diffusionlimited to the interface, allowing drop-stabilizing film formation, which reduces performance. The equilibrium IFT of the dilbit-in-water interface does not correlate with coalescence frequency, but there may be a qualitative trend between coalescence frequency and the initial slope of the IFT. The connection of the frequency of coalescence events with the slope of the


Page 33 of 38

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

IFT indicates that the dynamics of the additive reaching the interface and altering the interfacial properties contributes significantly to coalescence. While the additives ability to rapidly adsorb to the interface correlates with performance, the properties which make one additive more effective over another at preventing elastic film formation remain unclear. Such inquiry is left for further studies. The aged droplet studies demonstrate that many of the additives tested are capable of disrupting an aged interface, but Additive A still acted the fastest, and the relative ranking of coalescence frequencies with the additives is not the same as it was when the additive was mixed in the dilbit at the start of the experiment. Therefore, some additives are less effective when they must disrupt an established interface. In addition, we have showed that under certain conditions, flocculation may play a role in removing water from a water-in-dilbit emulsion. However, the low shear condition used may not be applicable in the industrial processes for bitumen extraction.

ACKNOWLEDGMENTS The authors thank Tom Kalantar for insightful discussions and suggestions; Matt Reichert, Rohini Gupta, and Daniel Miller for early method development; Heather Wiles, Andrew Banks, Taylor Keysor, and Jeff Mitchell for lab support.

SUPPORTING INFORMATION S1. Video of microfluidic channels containing water droplets in dilbit with premixed 1000 ppm Additive B in the dilbit. Filename: S1.mpg. S2. Video of microfluidic channels containing water droplets in dilbit without additive. Filename: S2.mpg.


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 34 of 38

S3. Video of microfluidic channels with aged droplets. Additive B was introduced between channels 1 and 2 from the left side of the image. Filename: S3.mpg. ™ Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow

REFERENCES (1)

He, L.; Lin, F.; Li, X.; Sui, H.; Xu, Z. Interfacial Sciences in Unconventional Petroleum Production: From Fundamentals to Applications. Chem. Soc. Rev. 2015, 44 (15), 5446– 5494.

(2)

Gao, S.; Moran, K.; Xu, Z.; Masliyah, J. Role of Bitumen Components in Stabilizing Water-in-Diluted Oil Emulsions. Energy and Fuels 2009, 23 (5), 2606–2612.

(3)

Yeung, A.; Dabros, T.; Masliyah, J.; Czarnecki, J. Micropipette: A New Technique in Emulsion Research. Colloids Surfaces A Physicochem. Eng. Asp. 2000, 174 (1–2), 169– 181.

(4)

Tsamantakis, C.; Masliyah, J.; Yeung, A.; Gentzis, T. Investigation of the Interfacial Properties of Water-in-Diluted-Bitumen Emulsions Using Micropipette Techniques. J. Colloid Interface Sci. 2005, 284 (1), 176–183.

(5)

Tchoukov, P.; Yang, F.; Xu, Z.; Dabros, T.; Czarnecki, J.; Sjöblom, J. Role of Asphaltenes in Stabilizing Thin Liquid Emulsion Films. Langmuir 2014, 30 (11), 3024– 3033.

(6)

Wu, X. Investigating the Stability Mechanism of Water-in-Diluted Bitumen Emulsions through Isolation and Characterization of the Stabilizing Materials at the Interface. Energy and Fuels 2003, 17 (1), 179–190.

(7)

Peña, A. A.; Hirasaki, G. J.; Miller, C. A. Chemically Induced Destabilization of Waterin-Crude Oil Emulsions. Ind. {&} Eng. Chem. Res. 2005, 44 (5), 1139–1149.

(8)

Pensini, E.; Harbottle, D.; Yang, F.; Tchoukov, P.; Li, Z.; Kailey, I.; Behles, J.; Masliyah, J.; Xu, Z. Demulsification Mechanism of Asphaltene-Stabilized Water-in-Oil Emulsions by a Polymeric Ethylene Oxide–Propylene Oxide Demulsifier. Energy & Fuels 2014, 28 (11), 6760–6771.

(9)

Xu, Y.; Wu, J.; Dabros, T.; Hamza, H.; Venter, J. Optimizing the Polyethylene Oxide and Polypropylene Oxide Contents in Diethylenetriamine-Based Surfactants for Destabilization of a Water-in-Oil Emulsion. Energy and Fuels 2005, 19 (3), 916–921.

(10)

Wu, J.; Xu, Y.; Dabros, T.; Hamza, H. Effect of EO and PO Positions in Nonionic Surfactants on Surfactant Properties and Demulsification Performance. Colloids Surfaces A Physicochem. Eng. Asp. 2005, 252 (1), 79–85.

(11)

Kailey, I.; Feng, X. Influence of Structural Variations of Demulsifiers on Their Performance. Ind. Eng. Chem. Res. 2013, 52 (2), 785–793.


Page 35 of 38

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)

Kailey, I.; Blackwell, C.; Behles, J. Collaborative Interactions between EO-PO Copolymers upon Mixing. Ind. Eng. Chem. Res. 2013, 52 (50), 17913–17919.

(13)

Feng, X.; Xu, Z.; Masliyah, J. Biodegradable Polymer for Demulsification of Water-inBitumen Emulsions. Energy and Fuels 2009, 23 (1), 451–456.

(14)

Dalmazzone, C.; Noik, C.; Komunjer, L. Mechanism of Crude-Oil/Water Interface Destabilization by Silicone Demulsifiers. SPE J. 2005, 10 (1), 5–8.

(15)

Mohammed, R. A.; Bailey, A. I.; Luckham, P. F.; Taylor, S. E. The Effect of Demulsifiers on the Interfacial Rheology and Emulsion Stability of Water-in-Crude Oil Emulsions. Colloids Surfaces A Physicochem. Eng. Asp. 1994, 91 (C), 129–139.

(16)

Zhang, L. Y.; Xu, Z.; Masliyah, J. H. Langmuir and Langmuir-Blodgett Films of Mixed Asphaltene and a Demulsifier. Langmuir 2003, 19 (23), 9730–9741.

(17)

Krawczyk, M. a; Wasan, D. T.; Shetty, C. S. Chemical Demulsification of Petroleum Emulsions Using Oil-Soluble Demulsifiers. Ind. {&} Eng. Chem. Res. 1991, 30 (2), 367– 375.

(18)

Wasan, D. T. Destabilization of Water-in-Oil Emulsions. In Emulsions — A Fundamental and Practical Approach; Springer Netherlands: Dordrecht, 1992; pp 283–295.

(19)

Kim, Y. H.; Wasan, D. T.; Breen, P. J. A Study of Dynamic Interfacial Mechanisms for Demulsification of Water-in-Oil Emulsions. Colloids Surfaces A Physicochem. Eng. Asp. 1995, 95 (2–3), 235–247.

(20)

Feng, X.; Wang, S.; Hou, J.; Wang, L.; Cepuch, C.; Masliyah, J.; Xu, Z. Effect of Hydroxyl Content and Molecular Weight of Biodegradable Ethylcellulose on Demulsification of Water-in-Diluted Bitumen Emulsions. Ind. Eng. Chem. Res. 2011, 50 (10), 6347–6354.

(21)

Feng, X.; Mussone, P.; Gao, S.; Wang, S.; Wu, S. Y.; Masliyah, J. H.; Xu, Z. Mechanistic Study on Demulsification of Water-in-Diluted Bitumen Emulsions by Ethylcellulose. Langmuir 2010, 26 (5), 3050–3057.

(22)

Abdel-Azim, A.-A. A.; Zaki, N. N.; Maysour, N. E.-S. Polyoxyalkylenated Amines for Breaking Water-in-Oil Emulsions: Effect of Structural Variations on the Demulsification Efficiency. Polym. Adv. Technol. 1998, 9 (2), 159–166.

(23)

Zarkar, S.; Couzis, A.; Banerjee, S. Effect of Premixed Asphaltenes and Demulsifier on Oil-Water Interfacial Properties. J. Dispers. Sci. Technol. 2015, 36 (10), 1465–1472.

(24)

Frising, T.; Noïk, C.; Dalmazzone, C. The Liquid/Liquid Sedimentation Process: From Droplet Coalescence to Technologically Enhanced Water/Oil Emulsion Gravity Separators: A Review. J. Dispers. Sci. Technol. 2006, 27 (7), 1035–1057.

(25)

Janssen, P. J. A.; Anderson, P. D. Modeling Film Drainage and Coalescence of Drops in a Viscous Fluid. Macromol. Mater. Eng. 2011, 296 (3–4), 238–248.


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 36 of 38

(26)

Chesters, A. K. The Modelling of Coalescence Processes in Fluid-Liquid Dispersions : A Review of Current Understanding. Chem. Eng. Res. Des. 1991, 69 (A4), 259–270.

(27)

Klaseboer, E.; Chevaillier, J. P.; Gourdon, C.; Masbernat, O. Film Drainage between Colliding Drops at Constant Approach Velocity: Experiments and Modeling. J. Colloid Interface Sci. 2000, 229 (1), 274–285.

(28)

Krebs, T.; Schroën, C. G. P. H.; Boom, R. M. Coalescence Kinetics of Oil-in-Water Emulsions Studied with Microfluidics. Fuel 2013, 106, 327–334.

(29)

Hu, Y. T.; Pine, D. J.; Leal, L. G. Drop Deformation, Breakup, and Coalescence with Compatibilizer. Phys. Fluids 2000, 12 (3), 484–489.

(30)

Kupai, M. M.; Yang, F.; Harbottle, D.; Moran, K.; Masliyah, J.; Xu, Z. Characterising Rag-Forming Solids. Can. J. Chem. Eng. 2013, 91 (8), 1395–1401.

(31)

Harbottle, D.; Chen, Q.; Moorthy, K.; Wang, L.; Shengming, X.; Liu, Q.; Sjoblom, J.; Xu, Z. Problematic Stabilizing Films in Petroleum Emulsions: Shear Rheological Response of Viscoelastic Asphaltene Films and the E Ff Ect on Drop Coalescence. Langmuir 2014, 30, 6730–6738.

(32)

Teh, S.-Y.; Lin, R.; Hung, L.-H.; Lee, A. P. Droplet Microfluidics. Lab Chip 2008, 8 (2), 198–220.

(33)

Baret, J. C.; Kleinschmidt, F.; Harrak, A. E.; Griffiths, A. D. Kinetic Aspects of Emulsion Stabilization by Surfactants: A Microfluidic Analysis. Langmuir 2009, 25 (11), 6088– 6093.

(34)

Krebs, T.; Schroen, K.; Boom, R. A Microfluidic Method to Study Demulsification Kinetics. Lab Chip 2012, 12 (6), 1060.

(35)

Morin, B.; Liu, Y.; Alvarado, V.; Oakey, J. A Microfluidic Flow Focusing Platform to Screen the Evolution of Crude Oil-Brine Interfacial Elasticity. Lab Chip 2016, 16 (16), 3074–3081.

(36)

Sieben, V. J.; Tharanivasan, A. K.; Andersen, S. I.; Mostowfi, F. Microfluidic Approach for Evaluating the Solubility of Crude Oil Asphaltenes. Energy {&} Fuels 2016, 30 (3), 1933–1946.

(37)

Bartolo, D.; Degre, G.; Nghe, P.; Studer, V. Microfluidic Stickers. Lab Chip 2008, 8 (2), 274–279.

(38)

Yang, H.; Park, C. C.; Hu, Y. T.; Leal, L. G. The Coalescene of Two Equal-Sized Drops in a Two-Dimensional Linear Flow. Phys. Fluids 2001, 13 (5), 1087–1106.

(39)

Borrell, M.; Yoon, Y.; Leal, L. G.; Park, C. C. Viscosity Ratio Effects on the Coalescence of Two Equal-Sized Drops in a Two-Dimensional Linear Flow. J. Fluid Mech. 2005, 525 (2005), 355–379.

(40)

Yokota, M.; Okumura, K. Dimensional Crossover in the Coalescence Dynamics of


Page 37 of 38

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

Viscous Drops Confined in between Two Plates. Proc. Natl. Acad. Sci. 2011, 108 (16), 6395–6398. (41)

Christopher, G. F.; Bergstein, J.; End, N. B.; Poon, M.; Nguyen, C.; Anna, S. L. Coalescence and Splitting of Confined Droplets at Microfluidic Junctions. Lab Chip 2009, 9 (8), 1102–1109.

(42)

Baroud, C. N.; Gallaire, F.; Dangla, R. Dynamics of Microfluidic Droplets. Lab Chip 2010, 10 (16), 2032.

(43)

Okumura, K. Viscous Dynamics of Drops and Bubbles in Hele-Shaw Cells: Drainage, Drag Friction, Coalescence, and Bursting. Adv. Colloid Interface Sci. 2017, 1–12.

(44)

Crowe, C.; Schwarzkopf, J.; Sommerfeld, M.; Tsuji, Y. Multiphase Flows with Droplets and Particles, Second.; CRC Press, 2011.


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

TABLE OF CONTENTS/ABSTRACT GRAPHIC


Page 38 of 38

Mechanistic Study of Water Droplet Coalescence and Flocculation in

Recommend Documents