Bulk Oil Phase Research Articles

Aggregation in Deep Eutectic Solvents (DESs): Formation of Polar DES-in-Nonpolar DES Microemulsions.

The versatility of environmentally benign and inexpensive deep eutectic solvents (DESs) lies in their widely varying physicochemical properties. Depending on its constituents, a DES may be highly polar or nonpolar in nature. This offers an enticing possibility of formation of novel nonaqueous microemulsions (MEs). Evidence of the presence of polar DES-in-nonpolar DES MEs is presented with reline (formed by mixing choline chloride and urea in 1 : 2 mol ratio) as the polar DES forming the ME pools, Thy : DA [formed by mixing thymol (Thy) and n-decanoic acid (DA) in 1 : 1 mol ratio] nonpolar DES as the bulk oil phase and nonionic surfactant Brij-35 as the emulsifying agent. While only sparingly miscible in Thy : DA, as high as 2.5 M reline can be solubilized in this DES in the presence of 100 mM Brij-35; reline loading (w Rel = [reline]/[Brij-35]) as high as 25 can be achieved. The ternary phase diagram of the Thy : DA/Brij-35/reline system reveals a clear and transparent single-phase region where MEs may be forming. Dynamic light scattering confirms the presence of MEs of 2-10 nm size. Even as up to 2.5 M (ca. 0.35 mole fraction) reline, whose dynamic viscosity (η) and electrical conductivity (κ) are very high, is added to 100 mM Brij-35 solution of Thy : DA, the η and κ values of the solution increase insignificantly, thus conforming to the formation of MEs in the solution. Fourier transform infrared (FTIR) absorbance spectra and fluorescence probe responses further indicate that reline is not dispersed in the medium but rather forms polar pools of the MEs. These novel nonaqueous polar DES-in-nonpolar DES MEs will not only expand the application potential of DESs but also offer a new class of organized media with widespread potential.

Molecular dynamics simulation of wax micro-structure characteristics in the oil-water emulsion

As a key issue in the flow assurance of wax-containing crude oils, the microscopic mechanism of wax deposition in multiphase pipelines is still unclear. Based on macroscopic experimental data, two forms of crystallized wax have been found under an oil-water emulsion, including adsorbed wax on the interface of water droplets and suspended wax in the bulk oil phase, which are the important factors influencing wax deposition. However, the micro-formation mechanism of the adsorbed & suspended wax is not elucidated. In this work, molecular dynamics simulations are used to investigate the micro-structure characteristics of the adsorbed & suspended wax in the oil-water emulsion containing surfactant Span60. A method is proposed to quantitatively calculate the distributions of the adsorbed & suspended wax and the percentage of wax adsorption area at the oil-water interface. The results indicate that surfactant with the hydrophilic end will insert into the water phase and the trailing hydrophobic end stretching will point to the oil phase during co-crystallizing with wax molecules. Meanwhile, the interface tension is further reduced by tilting the adsorbed wax tail chain to enhance the adsorption stability. Based on the complicated influence of surfactants on wax adsorption, the quantitative distribution characteristics of the adsorbed & suspended wax in the oil-water emulsion are complex under different wax carbon numbers and surfactant/wax contents. This microscopic investigation of wax distribution in oil-water emulsion can support the establishment of better strategies for solving the wax deposition problem in multiphase flow.

Effects of polar fractions on interfacial and bulk properties at the oil/carbonated aqueous solution interface: Insight from molecular dynamics simulation

This study utilized molecular dynamics simulations to understand the liquid/liquid interfaces in a natural environment involving carbon dioxide and various acidic components. The aim is to unravel the impact of polar fractions with various chemical structures and functional groups, namely benzoic acid, decanoic acid, phenol, and decanol, on the interfacial phenomena of the oleic phase (decane) in contact with water or CO2-rich water at the molecular resolution. The findings indicate that carbon dioxide molecules enrich at the decane/water interface before dissolving into the oleic phase. When polar molecules are introduced to the oleic phase, there is a competition between carbon dioxide and acidic components to accumulate at the interface. The functional hydrocarbon fractions displace carbon dioxide at the interface and bridge the oleic and aqueous phases, reducing interfacial tension. Polar components change the charge distribution of water molecules in the biphasic system, signifying that the organized water layer at the interface with the non-aqueous phase has been disrupted. In contrast to the polar molecules, the carbon dioxide tends to diffuse into the oleic phase and changes the bulk properties like oil fluidity. Accordingly, the fluidity of the decane exhibited significant enhancement by CO2 diffusion throughout the bulk oil phase, which might lead to substantial viscosity reduction.

Experimental investigation of hydrocarbon-ion interaction in water-oil emulsions: A new insight into asphaltene structure and chemistry

Emulsification has been proved as one of the mechanisms contributing to improving oil recovery. Regarding the amphiphilic nature of the asphaltene and other polar hydrocarbons, their role should be understood. This research aims to investigate the chemistry and structure of the asphaltene molecules in the emulsions generated by the oil and ion-tuned water. The static bottle tests, containing the aqueous, emulsion, and bulk oil phases, were generated to study the emulsification. To have a mechanistic insight into the participation of asphaltene molecules in the emulsion phase, two oil samples of crude oil and asphaltene-rich toluene were used to generate the emulsions. After extracting the asphaltene from the bulk phases, the analytical techniques of Nuclear Magnetic Resonance (NMR), Fourier transform infrared (FTIR), and Energy-dispersive X-ray (EDX) were employed to study the asphaltene structural parameters, functional groups, and elemental content, respectively. Based on the NMR technique, the asphaltenes with smaller aromatic cores and shorter aliphatic chains, which contain polar functional groups have more tendency to adsorb onto the emulsion phase. It was shown that the magnesium and calcium ions have stronger electrostatic interactions with the asphaltene, leading to more attraction of the asphaltenes in the emulsion phase. In contrast, the sulfate ions showed a weaker attraction force to adsorb the asphaltenes in the emulsion phase. Based on the EDX spectroscopy, the heteroatom (oxygen, nitrogen, and sulfur) contents of the crude asphaltene is more than the bulk one, representing more affinity of the polar asphaltenes toward the emulsion phase. According to the FTIR spectroscopy of the bulk oil, while the aromatic hydrocarbons have a lower affinity toward the emulsion phase, the longer alkanes have more affinity to adsorb onto the emulsion phase. It should be mentioned that the chemistry and structural parameters of the bulk asphaltenes in the emulsions, which were generated by crude oil and asphaltene-rich toluene, were different. This observation indicated that the chemistry of the asphaltenes participating in the emulsion phase is influenced by the presence of other amphiphilic hydrocarbons. In this study, it was shown that chemical functional groups and structural parameters of asphaltene affect the emulsification process. Hence, studying the chemistry of asphaltene and other polar hydrocarbons is a vital step for the formulation of optimum ion-tuned water.

Molecular Dynamics Simulation of a Brine Droplet under an Electric Field: Distinct Behavior Shown by NaCl and CaCl2.

Electrostatic demulsification is a promising technique to disrupt petroleum emulsions. However, the presence of salts in the emulsion can influence the effectiveness of the electric field. In this work, we target an understudied area, namely, the effect of salt ion type and concentration on the stability of brine droplets when exposed to an electric field. Molecular dynamics (MD) simulations are performed on a series of water-in-oil emulsion systems consisting of a water or brine droplet surrounded by an oil phase containing toluene and model asphaltene molecules (N-(1-hexylheptyl)-N'-(5-carboxylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (C5Pe)). The brine droplet contains either NaCl or CaCl2, with concentrations varying from 0 to ∼11 wt %. An external electric field is applied, which has a strength ranging from 0 to 1 V/nm. Our results show that as the electric field increases, the bare water droplet exhibits progressive deformation from the original spherical shape to an ellipsoid, a spindle, and finally a cylinder. When the brine droplets are exposed to a low electric field (≤0.5 V/nm), they behave similar to the bare water droplet. However, at a high electric field (≥0.75 V/nm), both NaCl and CaCl2 brine droplets are stabilized in the bulk oil and maintain the spherical or ellipsoidal shape by ejecting salt ions toward the electrodes at high salt concentrations (≥7.8 wt %), which induces a counter electric field that weakens the destabilization of the droplet by the applied field. At low salt concentrations (≤4.5 wt %), brine droplets containing NaCl or CaCl2 display different behaviors: the former tends to shift toward an electrode, whereas the latter stays in the bulk oil phase. The contrasting phenomena are the result of combined effects of brine droplet net charge and C5Pe adsorption on the droplet surface: a large net charge and low C5Pe adsorption tend to drive the droplet toward an electrode. This study provides useful insights into the important role of salt ions in electrostatic demulsification of petroleum emulsions.

Effects of crystalline/non-crystalline emulsifiers on foamed emulsion: Microstructure, rheological properties, and 3D printing

In this paper, glycerol monostearate and fumed silica were used as the crystalline and non-crystalline emulsifier, respectively, to stabilize the oil-water interface together with polyglycerol polyricinoleate. Lacquer wax structured the oil phase as a gelling agent. Then, foamed emulsions were prepared by whipping. For crystalline emulsifier, a mass of wax crystallized on the oil-water interface due to the templating effect that promoted the heterogeneous nucleation. Droplets wrapped with “crystalline shell” could connect to matrix and contribute to system strength as active fillers. Therefore, the modulus of foamed emulsions increased with the water content correspondingly. Similarly, droplets with “crystalline shell” could connect to the wax that absorbed at the oil-air interface and aggregate around the bubble, which could be observed with microscopy. Whereas, the crystal was hardly observed at the oil-water interface stabilized by non-crystalline emulsifiers. The droplets simply filled in the bulk oil phase, and foamed emulsions with different water content had approximate modulus. To further convince the conclusion above, overrun and 3D printing were conducted. The overrun rates of crystalline emulsifier-based foamed emulsion were lower than that of non-crystalline emulsifier at higher water content (W:O=30:70, 50:50 w/w). It might due to the templating effect, which reduced the mass of crystal in bulk phase that could stabilize bubbles during whipping as the Pickering particle. In case of crystalline emulsifiers-based foamed emulsions, the modulus and height of the printed sample increased with the increasing water content, while there was no significant tendency for non-crystalline emulsifiers-based foamed emulsions.

Acidic Conditions Impact Hydrophobe Transfer across the Oil-Water Interface in Unusual Ways.

Molecular dynamics simulation and enhanced free energy sampling are used to study hydrophobic solute transfer across the water-oil interface with explicit consideration of the effect of different electrolytes: hydronium cation (hydrated excess proton) and sodium cation, both with chloride counterions (i.e., dissociated acid and salt, HCl and NaCl). With the Multistate Empirical Valence Bond (MS-EVB) methodology, we find that, surprisingly, hydronium can to a certain degree stabilize the hydrophobic solute, neopentane, in the aqueous phase and including at the oil-water interface. At the same time, the sodium cation tends to "salt out" the hydrophobic solute in the expected fashion. When it comes to the solvation structure of the hydrophobic solute in the acidic conditions, hydronium shows an affinity to the hydrophobic solute, as suggested by the radial distribution functions (RDFs). Upon consideration of this interfacial effect, we find that the solvation structure of the hydrophobic solute varies at different distances from the oil-liquid interface due to a competition between the bulk oil phase and the hydrophobic solute phase. Together with an observed orientational preference of the hydroniums and the lifetime of water molecules in the first solvation shell of neopentane, we conclude that hydronium stabilizes to a certain degree the dispersal of neopentane in the aqueous phase and eliminates any salting out effect in the acid solution; i.e., the hydronium acts like a surfactant. The present molecular dynamics study provides new insight into the hydrophobic solute transfer across the water-oil interface process, including for acid and salt solutions.

Demulsification of water-in-heavy oil emulsions by oxygen-enriched non-ionic demulsifier: Synthesis, characterization and mechanisms

Separation of water-in-heavy oil (W/HO) emulsions is a critical issue in petroleum industry (especially for the thickened oils and natural bitumen) due to its high viscosity and rigid interfacial film formed by natural stabilizers (e.g., asphaltenes). Herein, two different strategies have been proposed to enhance the demulsification of the W/HO emulsions from the aspects of interfacial reconstruction and bulk oil phase property regulation. Firstly, to break the rigid interfacial film at the oil–water interface, a novel demulsifier (TJU-3, Mn: 6131 g/mol) has been successfully designed, introducing high content of carboxyl groups and ester groups to the molecules. The chemical groups, molecular structure, content of oxygen-containing groups, solubility, turbidity and phase distribution rules of TJU-3 have been instrumentally determined. It was observed that TJU-3 performed well in breaking the W/HO emulsions with faster rate (reaching 100% dehydration in less 25 min) and no “tailing phenomenon” compared with other commercial demulsifiers. Secondly, to facilitate the diffusion of demulsifer molecules from bulk oil phase to oil–water interface which promote the demulsification rate, the effect of oil viscosity on the demulsification efficiency has been investigated. Results showed that, after working with demulsifiers, when only one single method (heating or dilution at ambient conditions) was used, the dehydration rate of W/HO emulsions is limited (no more than 50%). When combining demulsifiers with diluents at slight heating conditions, a complete dehydration (∼100%) of W/HO emulsions was obtained, which was optimized at 60 ℃, 400 ppm. This synergistic effect was mainly contributed to the fact that viscosity reduction weakens the obstruction of the demulsifier diffusion and increases the average kinetic energy of the thermal movement of demulsifiers. This work would provide insights for developing new low-carbon demulsification separation method for petroleum production.

The effect of CO2-philic thickeners on gravity drainage mechanism in gas invaded zone

The rate of mass transfer between the fractures and matrix in gas invaded zone can significantly influence on the oil recovery during the forcedgravitydrainageprocess.However, in this study, a new approach was suggested to improve the gravity drainage process in gas invaded zone. Poly(fluoroacrylate) (PFA), as a CO2-philic thickener, was injected into the gas invaded zone to illustrate the impact of interfacial mechanisms such as gas diffusion coefficient and interfacial tension (IFT) on oil recovery. Also, the cloud point pressures were measured to ensure that the PFA did not come out of the solution due to a phase change during IFT, gas diffusion coefficient, and gravity drainage experiments.Results showed that the CO2-PFA thickener (20000 ppm) could decrease the IFT from 56 to 24 dyne/cm compared to the pure CO2 scenario, improving the gravity drainage mechanism in the gas invaded zone. In addition, the CO2 diffusion coefficients were increased approximately more than two times during CO2-PFA injection in comparison with pure CO2 injection in both porous media and bulk oil phase scenarios at reservoir conditions. Also, an incremental oil recovery of 16 percent was achieved during PFA/CO2 compared to pure CO2 injection in the gas invaded zone. Therefore, gas gravity drainage is the most important mechanism once gas thickener or CO2 enters the fractures in the gas invaded zone.

Enhanced solubility and improved stability of curcumin in novel water-in-deep eutectic solvent microemulsions

Clinical application of curcumin, a phytochemical with diverse biological activities, are restricted by its low solubility and poor stability. Herein, we report exceptionally high solubility (up to 51 mg/mL under ambient conditions) and significantly improved stability (against sunlight and long-term storage) of curcumin in novel water-in-oil microemulsions formed using a non-ionic surfactant Triton X-100 and a hydrophobic deep eutectic solvent constituted of tetra-n-butylammonium chloride and n-decanoic acid in 1 : 2 mol ratio as the bulk oil phase.

Surfactant-Enhanced Spontaneous Emulsification Near the Crude Oil-Water Interface.

Spontaneous emulsification near the oil-water interface and destabilization of water-in-oil emulsions in the bulk oil phase may affect the efficiency of improved oil recovery. In this study, we investigate the effect of a demulsifier surfactant on spontaneous emulsification near the oil-aqueous phase interface and in the bulk oil phase through imaging. The results show that pronounced spontaneous emulsions may form near the oil-aqueous phase interfaces. The mechanism of diffusion and stranding is believed to dominate spontaneous emulsification. A demulsifier surfactant, which has been used for demulsification of water-in-oil emulsions in the bulk oil phase, is found to enhance spontaneous emulsification near the oil-water interface. The diffusive flux of water through the interface can be enhanced if the demulsifier is added into the aqueous phase, in which the demulsifier may act as a carrier. It can generate a region of local supersaturation combined with hydrated asphaltenes and result in faster and stronger spontaneous emulsification. We also investigate the effect of a viscosifier polymer on emulsion formation. The polymer is used to improve sweep efficiency in oil displacement. In this work, we show that it can inhibit emulsification in the bulk oil phase, but its effect on spontaneous emulsification near the interface is not pronounced.

Measurement of CO2 diffusion coefficients in both bulk liquids and carven filling porous media of fractured-vuggy carbonate reservoirs at 50 MPa and 393 K.

Diffusion coefficients are necessary to describe the mass transfer and adsorption rate of CO2 in formation fluids. However, data is scarcely reported for actual reservoir conditions of high pressure and temperature, which are normal in most scenarios of the CO2-enhanced oil recovery process in China's fractured-vuggy reservoirs and carbon storage process. Accordingly, this work employed the pressure decay method (PD) and relevant mathematical models to determine the CO2 diffusion coefficient in both liquids and cavern filling porous media at 50 MPa and 393 K. The effects of the type of reservoir fluids, the properties of carven filling porous media, and water saturation on CO2 diffusion coefficients were investigated. Results in bulk reservoir liquids showed that the CO2 diffusion coefficient in the oil sample was 4.1243 × 10−8 m2 s−1, much higher than those in the pure alkane phase, pure water and brine sample from reservoirs. Results of CO2 diffusion in carven filling porous media saturated with oil demonstrated a significant dependence on properties such as porosity and permeability, and a correlation in the CO2 diffusion coefficients between the bulk oil phase and cavern filling porous media in the form of touristy was documented. CO2 diffusion in the fractured cavern porous media was much higher than that without fracture. An increase in water saturation reduced CO2 diffusion coefficients in the carven filling porous medium studied, herein. Thus, the CO2 diffusion coefficient is essentially related to the type of liquid and properties of the filling media.

Hydrate Agglomeration in Crude Oil Systems in Which the Asphaltene Aggregation State Is Artificially Modified

Summary Some crude oils contain naturally occurring surfactants that avoid hydrate agglomeration. Natural hydrate antiagglomeration has been linked to different crude oil fractions, including asphaltenes. Asphaltenes can promote the formation of stable water-in-oil (W/O) emulsions due to their amphiphilic properties. The surfactant-like behavior of asphaltenes is related to their aggregation state. Asphaltenes are strong emulsifying agents when in an aggregated state but weak emulsifying agents when either precipitated or well solubilized in the bulk oil phase. The asphaltene aggregation state may be artificially modified, changing its interfacial activity, by mixing crude oil with heptane–toluene mixtures. This work investigated the influence of the asphaltene aggregation state on gas hydrate agglomeration. Results show that the natural hydrate antiagglomerant properties of crude oils can be highly dependent on the artificially induced asphaltene aggregation state. For instance, if asphaltenes were induced to be solubilized into the bulk oil phase, the natural hydrate antiagglomerant behavior was diminished. However, when asphaltene aggregation was induced, gas hydrate agglomeration was avoided. These new findings could have significant implications for the implementation of novel hydrate management strategies that can reduce or eliminate the need for external interventions and hence minimize capital and operational expenditures by taking advantage of the intrinsic natural antiagglomerant properties of some crude oils.

The Effect of the HLB Value of Sucrose Ester on Physiochemical Properties of Bigel Systems

The current research explored the effect of different sucrose esters (SEs), with different hydrophilic–lipophilic balance (HLB) values, on bigel structure and properties. Bigels consisting of a water phase with glycerol and gelatin and an oil phase with glycerol mono-stearate, lecithin, and SEs with different HLB values were prepared. Rheological and thermal analyses revealed similar gelation-melting transitions governed by glycerol-monostearate crystallization (at ≈55 °C) for all bigel samples. The bigel matrix of the H1 and H2 samples (bigels consisting of SEs with HLBs of 1 and 2, respectively) demonstrated physical gel rheological characteristics of higher elastic and solid-like behavior compared with the H6 sample (bigel consisting SE with HLB 6). A similar trend was observed in the mechanical analysis with respect to hardness, firmness, and spreadability values, which were in the order of H1 > H2 > H6. This behavior was attributed to droplet size observed in the microscopy analysis, revealing significantly smaller droplets in the H1 and H2 samples compared with the H6 sample. These differences in droplet size were attributed to the diffusion kinetics of the low-molecular-weight surfactants. More specifically, the ability of mono-esterified SEs to diffuse faster than fully esterified SEs due to lower molar mass leads to a higher SE content at the oil-in-water (O/W) interface as opposed to the bulk oil phase. The results demonstrate the importance of the interface content in O/W bigel systems, providing an effective way to alter and control the bigel bulk properties.

Effect of solvent type on emulsion formation in steam and solvent-steam flooding processes for heavy oil recovery

In this study, a series of steam and solvent-steam flooding experiments are conducted to study the produced oil quality in terms of water-oil emulsions. A set of seven experiments are performed, beginning with steam flooding, and solvent-steam flooding using propane, n-butane, n-pentane, n-hexane, and n-heptane as paraffinic solvents that are insoluble in asphaltenes, and toluene, which is a polar solvent soluble in asphaltenes. Co-injection of solvents along with steam improves the cumulative oil recovery and produced oil quality by promoting less water migration into the bulk oil phase, hence reducing water-asphaltenes polar interactions. Asphaltene content in the produced oil and the displaced residual oil is found to generally increase with increasing carbon number of paraffinic solvent. Hexane is found to be the most effective hydrocarbon solvent in solvent-steam flooding for bitumen recovery, with optimum amount of asphaltene content and dispersion in produced oil, and minimum amount of water trapped in the oil phase, hence alleviating emulsion complexity. This is a first attempt to assess the efficiency of a wide range of solvent-steam flooding performances in terms of obtained oil emulsion quality, which will be very influential for field applications in selecting a solvent for a particular reservoir.

Characterizing the Oil-like and Surfactant-like Behavior of Polar Oils

In this work, a bifunctional model was developed to fit and predict the phase inversion point (PIP) of microemulsions containing polar oils. This model incorporated the hydrophilic-lipophilic difference (HLD) equations, where HLD = 0 at the PIP. The model uses a Langmuir isotherm to account for the interfacial segregation of polar oils as a function of their concentration in the bulk oil phase. The segregated polar oil was treated as being surfactant-like, having a characteristic curvature (Cc). The polar oil in the bulk oil phase was characterized via an equivalent alkane carbon number (EACN). The Cc value was obtained considering deviations in the PIP at low polar oil concentrations. The EACN was determined considering PIP deviations at high polar oil concentrations. Naphthenic acid and dodecanol were used as model polar oils mixed with ionic and nonionic surfactants and nonpolar oils. The EACN of the polar oil was shown to be independent of the EACN of the nonpolar oil and likely independent of the surfactant. The Cc for dodecanol was likely independent of the surfactant used. For naphthenic acid, the Cc was independent of the nonpolar oil, and within a certain surfactant type (ionic, nonionic, or extended ionic), it was likely independent of the surfactant. For the naphthenic acid systems, the segregation predicted via the bifunctional model was consistent with experimental measurements of this segregation. Given that the bifunctional model only involves phase inversion experiments, it is a convenient method to determine the oil-like and surfactant-like nature of polar oils.

Combining in vitro digestion model with cell culture model: Assessment of encapsulation and delivery of curcumin in milled starch particle stabilized Pickering emulsions

To investigate the encapsulation and oral delivery efficiency of milled starch particles stabilized Pickering emulsions for lipophilic bioactive compounds, in vitro digestion model coupled with Caco-2 cells models were used. Physicochemical and biological properties of curcumin encapsulated Pickering emulsions were analyzed regarding to emulsion structure, curcumin retention, in vitro digestion, in vitro anti-proliferate ability and cellular uptake. Milled starch particles stabilized Pickering emulsion system was able to protect curcumin against harsh gastric conditions. Around 80% of the encapsulated curcumin was retained after 2 h of simulated gastric digestion. By being encapsulated in Pickering emulsion, the bioaccessibility of curcumin was increased from 11% for curcumin in bulk oil phase to 28% under simulated intestinal digestion process. The resulting curcumin-loaded micelle phase from digested emulsion exhibited significant anti-cancer ability and enhanced cellular uptake. This research provides an exploratory study on the possible future application of milled starch particles stabilized Pickering emulsions as nutraceutical delivery vehicles in the creation of novel functional foods.

Synthesis of silica-alginate nanoparticles and their potential application as pH-responsive drug carriers.

Composite silica-alginate nanoparticles were prepared via silica sol-gel technique using a water-in-oil microemulsion system. In our system, cyclohexane served as the bulk oil phase into which aqueous solutions of sodium alginate were dispersed as droplets that confined nanoparticle formation after addition of tetraethylorthosilicate (TEOS). Our studies showed that much of the particle growth is completed within the first 24 hours and reaction times up to 120 hours only resulted in an additional 5% increase in particle diameter. Average particle size was found to decrease with increasing water-to-surfactant molar ratio (R) and with increasing cocentration of alginate in the aqueous phase. The potential for drug loading during particle formation was demonstrated using rhodamine B as a model drug. In vitro release studies showed that particles incubated in pH 2.5 phosphate buffer released only about 7% of the drug load in 27 days, while 42% was released in pH 7.5 phosphate buffer over the same period. Analysis of the release profile suggested that rhodamine B was homogeneously distributed throughout the particle and that the drug diffusivity was 40-fold greater in pH 7.5 buffer compared to that at pH 2.5. These results suggest that silica-alginate nanoparticles could be used as a pH-responsive drug carrier for controlled drug release.

Interactions of Asphaltene Subfractions in Organic Media of Varying Aromaticity

Whole asphaltenes were fractionated by extended-saturates, aromatics, resins, and asphaltenes (E-SARA) analysis into four asphaltene subfractions: toluene-extracted interfacially active asphaltenes (T-IAA), toluene-extracted remaining asphaltenes (T-RA), Heptol 50/50-extracted interfacially active asphaltenes (HT-IAA), and Heptol 50/50-extracted remaining asphaltenes (HT-RA). The aggregation kinetics of fractionated asphaltenes measured by dynamic light scattering (DLS) showed that decreasing solvent aromaticity promoted asphaltene aggregation for all subfractions. In a given solvent, T-IAA exhibited the strongest aggregation tendency, followed by HT-IAA, then T-RA, and HT-RA. Such differences were attributed to the higher oxygen and sulfur contents (highlighted in sulfoxide content) in IAA subfractions than RA subfractions, as confirmed by elemental analysis and X-ray photoelectron spectroscopy (XPS). The interaction forces between immobilized fractionated asphaltenes were measured using an atomic force microscope (AFM) to obtain a fundamental understanding of asphaltene interactions in organic media of varying aromaticity. The results showed that decreasing solvent aromaticity reduced steric repulsion and increased adhesion between asphaltenes with asphaltenes adopting a more compressed conformation. IAA subfractions, in particular T-IAA, exhibited higher adhesion forces than RA subfractions during separation of two asphaltene films in contact. The results of AFM colloidal force measurements were in good agreement with the DLS data. In spite of the small sulfoxide content in asphaltenes, the sulfoxide groups are believed to play a critical role in enhancing asphaltene aggregation in the bulk oil phase.

An Experimental Study of Nonequilibrium Carbon Dioxide/Oil Interactions

SummaryIn this study, we use a custom-designed visual cell to investigate nonequilibrium carbon dioxide (CO2)/oil interactions under high-pressure/high-temperature conditions. We visualize the CO2/oil interface and measure the visual-cell pressure over time. We perform five sets of visualization tests. The first three tests aim at investigating interactions of gaseous (g), liquid (l), and supercritical (sc) CO2 with a Montney (MTN) oil sample. In the fourth test, to visualize the interactions in the bulk oil phase, we replace the opaque MTN oil with a translucent Duvernay (DUV) light oil (LO). Finally, we conduct an N2(sc)/oil test to compare the results with those of CO2(sc)/oil test. We also compare the results of nonequilibrium CO2/oil interactions with those obtained from conventional pressure/volume/temperature (PVT) tests.Results of the first three tests show that oil immediately expands upon injection of CO2 into the visual cell. CO2(sc) leads to the maximum oil expansion followed by CO2(l) and CO2(g). Furthermore, the rate of oil expansion in the CO2(sc)/oil test is higher than that in CO2(l)/oil and CO2(g)/oil tests. We also observe extracting and condensing flows at the CO2(l)/oil and CO2(sc)/oil interfaces. Moreover, we observe density-driven fingers inside the LO phase because of the local increase in the density of LO. The results of PVT tests show that the density of the CO2/oil mixture is higher than that of the CO2-free oil, explaining the density-driven natural convection during CO2(sc) injection into the visual cell. We do not observe either extracting/condensing flows or density-driven mixing for the N2(sc)/oil test, explaining the low expansion of oil in this test. The results suggest that the combination of density-driven natural convection and extracting/condensing flows enhances CO2(sc) dissolution into the oil phase, leading to fast oil expansion after CO2(sc) injection into the visual cell.