Polymer-Coated Nanoparticles for Reversible Emulsification and

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Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers

Polymer-Coated Nanoparticles for Reversible Emulsification and Recovery of Heavy Oil Luqing Qi, Chen Song, Tianxiao Wang, Qilin Li, George J Hirasaki, and Rafael Verduzco Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b00655 • Publication Date (Web): 11 May 2018 Downloaded from http://pubs.acs.org on May 12, 2018

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Polymer-Coated Nanoparticles for Reversible Emulsification and Recovery of Heavy Oil Luqing Qi a, Chen Songa, Tianxiao Wangb, Qilin Lib,c, George J. Hirasakia *, Rafael Verduzcoa,c,d * a

Rice University, Department of Chemical and Biomolecular Engineering, 6100 Main Street, MS362, Houston TX, USA, 77005;

b

Rice University, Department of Civil and Environmental Engineering, 6100 Main Street, MS-519, Houston TX, USA, 77005; c

Rice University, Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment

d

Rice University, Department of Materials Science and NanoEngineering, 6100 Main Street MS325, Houston TX, USA, 77005

Keywords: nanoparticle; polymer; pH-responsive; emulsification; oil sand

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ABSTRACT

Heavy crude oil has poor solubility and a high density, making recovery and transport much more difficult and expensive than for light crude oil. Emulsifiers can be used to produce low viscosity oil-in-water emulsions for recovery and transport, but subsequent de-emulsification can be challenging. Here, we develop and implement interfacially-active, pH-responsive polymer-coated nanoparticles to reversibly stabilize, recover, and break oil/water emulsions through variation of solution pH. Silica particles with poly(2-(dimethylamino)ethyl methacrylate) (DMAEMA) chains covalently grafted to the surface are prepared though a reversible addition fragmentation chain transfer

(RAFT)

grafting-through

technique.

The

resulting

DMAEMA

polymer-coated

nanoparticles (PNPs) can stabilize emulsions of high viscosity Canadian heavy oil at polymercoated nanoparticle concentrations as low as 0.1 wt % and at neutral pH. The performance of the DMAEMA PNPs exceeds that of DMAEMA homopolymer additives, which we attribute to the larger size and irreversible adsorption of DMAEMA PNPs to the oil-water interface. After recovery, the emulsion can be destabilized by addition of acid to reduce pH, resulting in separation and settling of the heavy oil from the aqueous phase. Recovery of more than 10 wt % of the crude heavy oil-in-place is achieved by flooding with aqueous solution of 0.1 wt % DMAEMA PNPs without any additional surfactant or chemical. This work demonstrates the applicability of PNPs as surface active materials for enhanced oil recovery processes and for heavy oil transport.

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INTRODUCTION Large reserves of oil sands are found in various locations across the globe including Venezuela, Canada and Russia.1–3 Oil sand usually comes in the form of a mixture of sand, water, clay, and bitumen. Bitumen is a thick, heavy oil higher in viscosity and density and with lower solubility compared with other oils.4,5 These properties present challenges to the cost-effective recovery and transportation of heavy oils. Current methods of heavy oil recovery include surface mining, chemical flooding, steam assisted gravity drainage (SAGD), and Cyclic Steam Stimulation (CSS).6– 9

Chemical flooding is an attractive approach for oil recovery and has broad applicability for both

light oil and heavy oil recovery10–13 and lower capital expenditures relative to SAGD and CSS. However, additives that can effectively emulsify and de-emulsify heavy oil are needed. Nanoparticles are attractive as potential additives for heavy oil recovery.14 A number of studies have focused on micron- and nano-sized surface active nanoparticle additives for stabilizing oilwater emulsions, mobility control of the injected flood, and wettability alteration of the surface to increase the efficiency of EOR processes. Johnston and coworkers studied a series of iron-oxide nanoparticles coated with amphiphilic15 or charged polymers16,17 and found these nanoparticles decreased the oil-water interfacial tension and, in the case of charged polymer coatings, exhibited both good stability in high-salinity environments and low adsorption onto silica surfaces. The group also demonstrated that amphiphilic silica nanoparticle acted synergistically with zwitterionic surfactant to produce finer emulsions to with a greater stability to coalescence relative to the behavior with either nanoparticles or surfactant alone.18 Cui et al. found that nanoparticle/surfactant mixtures could be used to deform emulsion droplets into non-spherical shapes due to jamming of the nanoparticles at the oil-water interface.19 Tilton et al. reported that poly(2-(dimethylamino)ethyl methacrylate) grafted silica nanoparticles are extremely efficient emulsifiers. This group also

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demonstrated the ability to break emulsions created with this nanoparticle via elevated temperature.20 We developed a series of polymer-coated nanoparticles with charged polymers that could segregate to bicontinuous oil-water microemulsion phases and were stable at high salinities, as high at 14 wt %.21 Other studies with polymer-coated nanoparticles at the oil-water interface are discussed in recent review articles.22–24 These studies demonstrate that very stable oil-water Pickering emulsions can be produced through nanoparticle additives. Due to their large size compared with surfactants, nanoparticle additives occupy a much larger interfacial area at the oil-water interface and can strongly and irreversibly adsorb to the interface.25–28 Attaching surface-active polymers to the nanoparticle surface increases the stability of the emulsion, even at very low nanoparticle concentrations. Furthermore, pH responsive polymers grafted to the surface can enable reversible emulsification and de-emulsification with changes in pH.29–32 However, polymer-coated nanoparticles (PNPs) have not been developed or tested for the recovery of heavy oil, where stimuli-responsive nanoparticles capable of emulsifying and demulsifying heavy oil could provide a cost-effective approach to recovery, transport, and de-emulsification. Here, we develop and demonstrate stimuli-responsive polymer-coated nanoparticles that can be used to stabilize and break oil/water emulsions by the variation of pH, enabling both recovery of heavy oil and subsequent de-emulsificaiton as shown schematically in Figure 1. We show that silica particles with poly(2-(dimethylamino)ethyl methacrylate) (DMAEMA) chains covalently grafted to the surface can be used to stabilize Pickering emulsions of high viscosity Canadian bitumen at concentrations as low as 0.1 wt % in water and at neutral pH. Furthermore, on reducing the pH of the aqueous solution through addition of acid, the PNPs are charged and the emulsion is destabilized, allowing the heavy oil to coagulate and settle. We analyze the interfacial properties of

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the DMAEMA PNPs and compare their properties and performance to DMAEMA homopolymer additives. We further demonstrate sandpack flooding experiments using 0.1 wt % aqueous solution of DMAEMA PNPs to recover 10 wt % of the heavy crude oil in place. This work demonstrates the applicability of PNPs as additives for in chemical flooding processes heavy oil recovery. Nanoparticle Polymer Polymer-coated Nanoparticle (PNP)

Decrease pH

Figure 1. Schematic for the use of polymer-coated nanoparticles additives to recover heavy oil trapped in porous media (top) and the demulsification of oil-in-water emulsions with changes in solution pH (bottom).

EXPERIMENTAL Materials. Bitumen oil was obtained from Athabasca in Alberta, Canada. Silica nanoparticles were purchased from Nissan Chemical (MEK-ST, 30 wt % in MEK), with a diameter of 10 – 15 nm. 3aminopropyl

(dimethyl)ethoxysilane

(APDMES),

2-(dodecylthiocarbonothioylthio)-2-

methylpropionic acid (chain transfer agent, CTA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), N,N’-dicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyridine (DMAP) and

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2,2’-azobis(2-methylpropionitrile) (AIBN) were purchased from commercial suppliers and used as received. APDMES-CTA. The coupling of APDMES and CTA was performed as follows: CTA (0.1 g, 0.27 mmol), DCC (0.1 g, 0.48 mmol), DMAP (10 mg, 0.08 mmol) and oleic acid (0.6 g, 2.12 mmol) were added to a 50 mL round bottom flask. Next, 20 mL DCM (anhydrous) was added, and the flask was purged with nitrogen for 20 minutes. APDMES was added to the mixture under the protection of nitrogen. The solution was stirred on ice bath for 1 hour, and the reaction was conducted under room temperature for overnight with rigorous stirring. The solution was filtered prior to use in the next step. SiO2-CTA. 3 mL silica nanoparticle solution (30 wt %) and 20 mL THF were added into a 100 mL round bottom flask. The APDMES-CTA solution was added drop by drop to the flask while stirring. The mixture was purged with nitrogen for 20 minutes and the reaction was conducted under room temperature for 72 hours with rigorous stirring. SiO2-CTA was precipitated in methanol and was centrifuged at 3000 rpm for 15 min. Residual solvent was removed, and SiO2-CTA was redissolved in THF. The precipitation and centrifugation were repeated for 3 times, and SiO2-CTA was dried under vacuum. DMAEMA polymer-coated nanoparticles. 2-(dimethylamino)ethyl methacrylate was passed through a basic alumina column to remove inhibitor before polymerization. For the preparation of DMAEMA PNPs, SiO2-CTA (70 mg) was sonicated in 1,4-dioxane (4 mL) to produce a homogeneous solution prior to adding AIBN (0.63 mg, 0.004 mmol) and 2-(dimethylamino)ethyl methacrylate (150 mg, 0.95 mmol). The mixture was purged with nitrogen for 15 minutes and reacted at 70 ℃ overnight. The resulting product was purified by dialysis in water for 1 week using dialysis membrane (MWCO of 3000 Da) to produce a 5 wt % stock solution of DMAEMA PNPs in 6


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water. DMAEMA homopolymer. For the preparation of linear DMAEMA, 2-(dimethylamino)ethyl methacrylate (2.98 g, 18.95 mmol), AIBN (12.4 mg, 0.075 mmol) and CTA (137.7 mg, 0.38 mmol) were dissolved together in 20 mL 1,4-dioxane. The mixture was purged with nitrogen for 15 minutes and reacted at 70 ℃ for 5 hours. The resulting linear DMAEMA was precipitated in cold hexane 3 times and dried under vacuum.

Dynamic Light Scattering (DLS) Measurement. Dynamic light scattering was carried out using a Malvern Instruments Zen 3600 Zetasizer. Polymer-coated nanoparticles were dissolved in water at a concentration of 0.1 wt % for analysis. Phase Behavior Studies. Phase behavior studies of oil, water, surfactant, and Polymer-coated nanoparticles were carried out in 30 mL vials. A desired amount of crude oil, polymer-coated nanoparticle stock solution, and DI water was added to each vial sequentially. Except where noted, the amount of crude oil in each vial was 15 mg and a 15 mL solution of 0.1 wt % polymer-coated nanoparticle. To homogenize the mixture, the mixture was placed in an ice bath and sonicated for 5 minutes using a Q500 probe sonicator (power level 3). Samples were capped and sealed immediately after sonication to prevent evaporation and for long-term analysis. Thermo-Gravimetric Analysis (TGA). TGA measurements were carried out on a Q-600 TGA from TA instruments. The samples were heated from 25 °C to 900 °C at a rate of 10 °C/min under nitrogen atmosphere. Contact Angle and Interfacial Tension (IFT) Measurement. Contact angle and interfacial tension (IFT) measurement were performed with a tensiometer (Krüss DSA100). The sessile drop method was used to calculate the oil-water interfacial tension (IFT), as described by Coucoulas et al.33 7


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Nuclear Magnetic Resonance Spectroscopy (NMR). Proton NMR (1H NMR) spectra were recorded using tetramethylsilane as an internal standard in CDCl3 on a 400 MHz Bruker multinuclear spectrometer. Samples were placed in 5 mm O.D. tubes with a concentration of 10 mg/mL. Microscopy. Dispersion of oil drops in Pickering emulsion was observed under a polarizing optical microscope (Zeiss Axioplan 2). 40 μL of phase behavior solution was drop cast on a glass slide and covered carefully by glass coverslip. Total Carbon Analysis. Emulsion carbon concentration analysis was performed with SHIMADZU TOC-V analyzer. UV-absorption. UV absorption measurement was performed with a UV-Vis Spectrophotometer (Shimadzu UV-2550). Sandpack flooding. Sandpack flooding was performed through a glass column (1.5 cm in D and 17 cm in L) loaded with oil sand (30 wt % oil and 70 wt % sand). The porosity φ of the sandpack was 37.5 %. A wire heater was wrapped around the column to maintain a temperature of 80 °C. A syringe pump was used to inject the mobile phase (water or water with 0.1 wt % DMAEMA PNPs) at a flow rate of 1 mL/min, corresponding to an average flow velocity u of 0.57 cm/min and a Darcy velocity µw = u φ of 0.21 cm/min or 16.5 ft/day. This corresponds to an effective shear rate of approximately 17.5 s-1

34

The oil viscosity at 80°C is approximately 1000 cP, in the range of

other bitumen and heavy oil samples.35

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RESULTS AND DISCUSSION

Figure 2. Schematic for the synthesis of DMAEMA PNPs (top), thermogravimetric analysis of DMAEMA PNPs showing greater than 50 wt % DMAEMA polymer content, and transmission electron microscopy analysis of dry DMAEMA PNPs. Both DMAEMA PNPs and linear DMAEMA polymer were prepared by reversible additionfragmentation chain-transfer (RAFT) polymerization,36 as shown in Figure 2. For the DMAEMA PNPs, CTA was first attached onto the surface of nanoparticle through 3-aminopropyl (dimethyl)ethoxysilane linker. The polymer-coated nanoparticle was then prepared via a “graftfrom” RAFT polymerization of 2-(dimethylamino)ethyl methacrylate in 1,4-dioxane at 70 °C. The polymer content and size of the nanoparticles was measured through thermo-gravimetric analysis (TGA) transmission electron microscopy (TEM), UV-absorption, and dynamic light scattering

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(DLS), and the results are shown in Table 1 and Figure 2. TGA analysis (Figure 2) shows that the polymer content of the DMAEMA polymer-coated nanoparticles is greater than 50 wt %. The polymer chain density was measured using UV/VIS absorption to quantify the number of CTA functional groups attached to the nanoparticles (Figure S1), and the coating density was determined to be 1.8 chains/nm2, consistent with previously reported polymer-coated nanoparticles synthesized by RAFT.37,38 The Mn of linear DMAEMA was determined by 1H NMR (Figure S2) to be 7600 g/mol. Table 1. Analysis of DMAEMA PNPs

a

Polymer fractiona Number Avg. Diameterb Coating densityc Avg. DP of each chaind Avg. Mn of each chaine

57 wt % 110.3 nm 1.8 chains/nm2 14 2600 g/mol

measured by thermogravimetric analysis (TGA). measured by dynamic light scattering (DLS) in DI water. c,d,e calculated by the combination of DLS, TGA and UVabsorption. b

Interfacial Properties of DMAEMA polymer-coated nanoparticles A schematic illustration of the proposed oil recovery process using DMAEMA PNPs as additives is shown in Figure 1. An aqueous solution of DMAEMA polymer-coated nanoparticles is injected into the reservoir, and the polymer-coated nanoparticles migrate to the oil-water interface. Oil adsorbed to surfaces and trapped in pores is emulsified and mobilized as an oil-in-wateremulsion, which has a lower viscosity than the crude heavy oil. After collecting the emulsion, the heavy oil is recovered through de-emulsification. In order for this approach to be successful, the DMAEMA PNPs should be interfacially active at neutral pH and adsorb to the oil-water interface to produce a stable oil-in-water emulsion. The

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nanoparticles should also respond to a decrease in pH to destabilize the emulsion. As an initial test of the interfacial activity and pH-responsiveness of the nanoparticles, contact angle measurements of water and a solution of nanoparticles in water on heavy oil were performed. A layer of heavy oil was deposited on a flat silicon substrate by spin casting, and the contact angle of pure water and aqueous solutions of 0.1 wt % DMAEMA polymer-coated nanoparticles were measured at neutral (pH=7) and acidic (pH=2) solution conditions. These measurements do not provide the contact angle for the nanoparticles at the oil-water interface, rather they reflect interfacial tension and the effect the nanoparticles have on the interfacial tension at the oil-water interface. Aqueous Phase

Contact Angle

Figure 3. Contact angle measurements of water and DMAEMA polymer-coated nanoparticles (PNPs) in water at neutral and acidic solution conditions.

As shown in Figure 3, just 0.1 wt % DMAEMA nanoparticle additive results in a significant reduction in the water contact angle, from 76° to 62°. This indicates that the DMAEMA PNPs are interfacially active at neutral pH and reduce the oil-water interfacial tension. On reduction of pH, DMAEMA chains are protonated and become positively charged, and the contact angle increases from 62° to 81°, corresponding to an increase in the interfacial tension. This experiment demonstrates the pH responsiveness of DMAEMA PNPs and the impact on the interfacial tension. Small amounts of DMAEMA PNPs can produce significant changes to the oil-water interfacial tension and, as shown below, emulsion stability. 11


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To confirm that the DMAEMA PNPs were interfacially active at the oil-water interface, we measured the interfacial tension of heavy oil and water both with and without DMAEMA nanoparticle additives. A modified sessile drop method developed by Coucoulas et al.33 was used to analyze the curvature of the heavy oil drop in water. The interfacial tension was determined through analysis of the drop height, maximum radius, and surface contact angle of the oil drop (Figure S3). About 15 mg of bitumen oil was deposited onto the glass cell followed by a filling the container with DI water or 0.1 wt % DMAEMA polymer-coated nanoparticle solution. The entire sample was held at 80 °C to enable the heavy oil drop to deform and equilibrate. Size and angle parameters from the image were fitted into the nonlinear functions described by Coucoulas et al.33 Comparison of the heavy oil in pure water and in the presence of 0.1 wt % polymer-coated nanoparticle reveals a clear change in the oil-water interfacial tension, as shown in the Supporting Information Figure S4. The oil-water interfacial tension decreases from 27 mN/m to approximately 14 mN/m. While this is not a very large change in the interfacial tension, it does demonstrate that the DMAEMA PNPs are interfacially active and can lower the oil-water interfacial tension. To evaluate the potential for DMAEMA PNPs to stabilize oil-in-water emulsions, phase behavior studies were carried out with blends of oil, water, and DMAEMA nanoparticles. The phase behavior was analyzed by probe-sonication of oil-water-additive mixtures and evaluating the resulting formation and stability of emulsion. In all cases, 15 mg oil and 15 mL aqueous solution were used for analysis. As shown in Figure 4a, without any additives, the heavy oil aggregated to form a phase-separated drop at the bottom of the vial, even after probe sonication. In the case of 0.1 wt % DMAEMA linear polymer additives, some oil is emulsified after probe sonication as evidenced from the photograph of the mixture and the optical micrograph shown Figure 4b. However, much of the oil remains aggregated at the bottom of the vial. Finally, a solution of 0.1

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wt % DMAEMA polymer-coated nanoparticles significantly enhanced the emulsification of oil as shown in Figure 4c. The optical micrograph shows a relatively uniform distribution of micronsized oil drops in water, and the emulsion formed is stable for more than one month. The polymercoated nanoparticles are superior at emulsifying the heavy oil compared with the linear DMAEMA polymer additives. Finally, on reduction of pH, the emulsion is de-stabilized and the oil phase aggregates and sinks to the bottom of the vial, as shown in Figure 4d.

Figure 4. Analysis of emulsification of heavy oil (15 mg) in water (15 mL) along with different additives and after probe sonication: (a) crude oil in pure DI water (b) crude oil in DI water with 0.1 wt % DMAEMA linear polymer at pH=7. (c) crude oil in DI water with 0.1 wt % DMAEMA polymer-coated nanoparticle at pH=7. (d) crude oil in DI water with 0.1 wt % DMAEMA polymer-coated nanoparticle at pH=2.

Combustion analysis was used to quantify the total organic carbon (TOC) contained in the emulsion. The total amount of heavy oil present was calculated using the molecular formula CnH2n for bitumen. Prior to analyzing the TOC of emulsions in the presence if DMAEMA additives, a background reading was performed with no oil present to quantify the carbon signal from the DMAEMA PNPs or homopolymer and other impurities that may be present in the aqueous phase. This enabled measurement of the amount of oil emulsified in each case. In the presence of 0.1 wt %

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DMAEMA PNPs, 11.7 mg crude oil was emulsified after probe sonication. This represents more than 75 wt % of the 15 mg crude oil present in the vial. After addition of acid, the amount of crude oil emulsified dropped significantly, leaving only 1.1 mg heavy oil emulsified. In the case of 0.1 wt % DMAEMA polymer, about 1.2 mg heavy oil was emulsified, which is less than 10 wt % of the total oil in the vial. The DMAEMA PNPs are thus much more effective at emulsifying heavy oil. Table 2. Total organic carbon (TOC) analysis for oil-water emulsions. Emulsions were formed through probe sonication of 15 mg oil in 15 mL aqueous solution. All samples were tested after probe sonication. Total carbon Solubilized Solubilized Sample concentration crude oil crude oil (mg/L) (mg) (% of total) 0.1 wt % DMAEMA PNP no oil, pH=7 355 0.0 0.0 with oil, pH=7 1136 11.7 78 with oil, pH=2 425 1.1 7.3 0.1 wt % DMAEMA polymer no oil, pH=7 665 0.0 0.0 with oil, pH=7 743 1.2 8.0 with oil, pH=2 686 0.3 2.0

Sandpack chemical flooding studies were performed to test the efficacy of DMAEMA PNPs for recovering heavy oil. A schematic of the experimental configuration is shown in Figure 5. Dry sand with particle size of 106 – 250 μm was packed into a glass column (porosity φ = 37.5%), and a syringe pump was used to fill the column with water and then bitumen oil. The column was kept at a temperature of 80 °C to enable viscous flow of heavy oil and to simulate typical reservoir conditions. An approximate composition of 30 wt % crude oil and 70 wt % sand was used to mimic the actual sands present in in Alberta, Canada.39 Oil recovery experiments were performed by flushing the column either with pure water or with 0.1 wt % DMAEMA polymer-coated nanoparticle solution. The effluent was collected in 1.5 mL aliquots and analyzed for TOC by combustion analysis to quantify the amount of oil present. 14


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Figure 5. Schematic for sandpack flooding analysis (top), photograph of effluent during sandpack flooding with 40 pore volumes of pure water (middle) and with 20 pore volumes of a solution of 0.1 wt % DMAEMA PNPs. Both experiments were conducted at 80 °C. As can be seen in Figure 5, neglecting the heavy oil that flowed out of the column over the first three pore volumes which we attribute to heavy oil in or near the outlet column tubing, very little oil was recovered during water flooding, while an oil-in-water emulsion was recovered while flooding with 0.1 wt % DMAEMA PNPs. The DMAEMA PNPs produced an oil-in-water emulsion from 3 – 11 pore volumes, and subsequently no oil or emulsion was recovered with flooding up to 20 pore volumes. In the case of pure water, no emulsion was produced with flooding with 40 pore

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volumes of water. The total organic carbon analysis for the case of pure water (no additive) and 0.1 wt % DMAEMA PNP solution are shown in Table 3. While very little heavy oil is recovered with water flooding, approximately 10 wt % of the oil-in-place is recovered with 0.1 wt % DMAEMA nanoparticle solution flooding. The experiments were conducted at a Darcy velocity of 0.21 cm/s (16.5 ft/day) and an approximate shear rate of 17.5 s-1. We do expect that the shear rate will have an effect on oil recovery since shear can help mix and mobilize the oil-in-water emulsion phase. Temperature may also play a role in recovery due to flocculation of DMAEMA nanoparticles20 at elevated temperatures. Future studies will seek to quantify the roles of temperature, shear rate, porosity, and nanoparticle concentration on oil recovery. Table 3. Determination of oil recovered during sandpack flooding experiments through TOC combustion analysis.

Additive

Total oil in column (mg)

Oil recovery after 20 pore volumes (mg)

Fraction of oil recovered (wt %)

None

806

2

< 0.1

DMAEMA nanoparticle

822

81

9.9

Our results show that DMAEMA PNPs are superior emulsion staibilizers compared with linear DMAEMA homopolymer. We attribute this to the much larger size of the DMAEMA PNPs, which result

in

a

stronger,

irreversible

adsorption

to

the

oil-water

interface.40

As shown schematically in Figure 6, this irreversible adsorption will result in all or most DMAEMA PNPs associated to the oil-water interface due to a larger energy barrier for desorption, while in the case of the DMAEMA linear polymer a significant fraction is likely dissolved in the 16


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aqueous phase. This, along with the dense coverage of DMAEMA polymers of the nanoparticle surface prevents droplet coalescence.25 This is a general characteristic of PNPs and therefore demonstrates that PNPs are excellent candidates for the development of interfacially-active and stimuli-responsive additives.

Figure 6. Comparison between the emulsion stabilization of linear DMAEMA (top) and DMAMEA PNPs (bottom). The larger size of DMAEMA PNPs results in stronger, irreversible adsorption to the oil-water interface.

CONCLUSIONS In this work, we designed, synthesized, and evaluated DMAEMA PNPs for the stabilization of heavy oil-in-water emulsion. The additives were shown to be interfacially active and lower the interfacial tension between high viscosity crude oil and water at a concentration of just 0.1 wt %.

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The DMAEMA PNPs were shown to assist in the production and stabilization of a heavy-oil-inwater emulsion, and the emulsion could be broken by lowering of the solution pH due to the pH responsiveness of the DMAEMA polymer coating. Sandpack oil recovery studies were performed under the actual reservoir temperature condition and actual oil/sand composition of Canada oil sand. We found that flooding with 0.1 wt % DMAEMA PNPs resulted in recovery of approximately 10 wt % of crude oil-in-place compared with less than 1 wt % when flooding with linear DMAEMA polymer. The DMAEMA PNPs were found to be superior to linear polymer for emulsion stabilization, oil recovery, and transport, which we attribute to their larger size and stronger adsorption to the oil-water interface. These results indicate that DMAEMA PNPs are viable additives for the recovery and transport of heavy oil, and PNPs in general are excellent candidates for the development of interfacially-active and stimuli-responsive additives.

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AUTHOR INFORMATION Corresponding Authors George J. Hirasaki, 6100 Main Street, MS-362, Houston, TX 77005, [email protected] Rafael Verduzco, 6100 Main Street, MS-362, Houston, TX 77005, [email protected]

ACKNOWLEDGEMENTS The authors of this work acknowledge the financial support under the Rice University Consortium for Processes in Porous Media and the Welch Foundation for Chemical Research (C-1888). This work was supported by the NSF Nanosystems Engineering Research Center for NanotechnologyEnabled Water Treatment (EEC-1449500). We acknowledge Dr. Maura Puerto for helpful discussions regarding characterization of heavy oil samples.

SUPPORTING INFORMATION Supporting Information is attached with four (4) figures.

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For Table of Contents Only Heavy Oil Recovery and Transport

Reversible, pH controlled Emulsification Low pH Neutral pH

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Polymer-Coated Nanoparticles for Reversible Emulsification and

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