Excess Oil Phase Research Articles

Review on Some Confusion Produced by the Bicontinuous Microemulsion Terminology and Its Domains Microcurvature: A Simple Spatiotemporal Model at Optimum Formulation of Surfactant-Oil-Water Systems.

Fundamental studies have improved understanding of molecular-level properties and behavior in surfactant-oil-water (SOW) systems at equilibrium and under nonequilibrium conditions. However, confusion persists regarding the terms "microemulsion" and "curvature" in these systems. Microemulsion refers to a single-phase system that does not contain distinct oil or water droplets but at least four different structures with globular domains of nanometer size and sometimes arbitrary shape. The significance of "curvature" in such systems is unclear. At high surfactant concentrations (typically 30 wt % or more), a single phase zone has been identified in which complex molecular arrangements may result in light scattering. As surfactant concentration decreases, the single phase is referred to as a bicontinuous microemulsion, known as the middle phase in a Winsor III triphasic system. Its structure has been described as involving simple or multiple surfactant films surrounding more or less elongated excess oil and water phase globules. In cases where the system separates into two or three phases, known as Winsor I or II systems, one of the phases, containing most of the surfactant, is also confusedly referred to as the microemulsion. In this surfactant-rich phase, the only curved objects are micellar size structures that are soluble in the system and have no real interface but rather exchange surfactant molecules with the external liquid phase at an ultrafast pace. The use of the term "curvature" in the context of these complex microemulsion systems is confusing, particularly when applied to merged nanometer-size globular or percolating domains. In this work, we discuss the terms "microemulsion" and "curvature", and the most simple four-dimensional spatiotemporal model is proposed concerning SOW equilibrated systems near the optimum formulation. This model explains the motion of surfactant molecules due to Brownian movement, which is a quick and arbitrary thermal fluctuation, and limited to a short distance. The resulting observation and behavior will be an average in time and in space, leading to a permanent change in the local microcurvature of the aggregate, thus changing the average from micelle-like to inverse micelle-like order over an extremely short time. The term "microcurvature" is used to explain the small variations of globule size and indicates a close-to-zero mean curvature of the surfactant-containing film surface shape.

Late-stage coarsening of oil droplets of excess oil in microemulsions following a temperature quench

Abstract An oil-in-water microemulsion of the system C12E5/water/ n-decane with a fixed surfactant-to-oil volume fraction ratio φs/φo of 0.85 is studied. This clear microemulsion is temperature-quenched from a clear one-phase region (26 °C) with spherical microemulsion droplets to an unstable region (13 °C) where the excess oil phase is in equilibrium with the microemulsion droplets. Using a high-resolution version of a laboratory small-angle X-ray scattering (SAXS) instrument, the evolution of the excess oil and its growth as a function of time is studied. Unlike coarsening in alloys and polymer blends, a maximum in the intensity at a finite scattering vector is not observed. This clearly indicates that the droplet of the excess oil is formed homogeneously and that there is no depletion zone around the formed droplets. The scattering curves are quantitatively analysed as a function of time. The microemulsion droplets are modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints and the oil droplets are modeled as polydisperse spheres. The average radius of the oil droplets increases with a scaling exponent in agreement with that of coarsening of precipitates in alloys and phase separations in polymer blends, suggesting some degree of universality of coarsening processes.

An Experimental Study of Emulsion Flow in Alkaline/Solvent Coinjection with Steam for Heavy-Oil/Bitumen Recovery

SummaryWater is the dominant component in steam-injection processes, such as steam-assisted gravity drainage (SAGD). The central hypothesis in this research is that in-situ oil transport can be enhanced by generating oil-in-water emulsion, where the water-continuous phase acts as an effective oil carrier. As part of the research project, this paper presents an experimental study of how oil-in-water emulsion can improve oil transport in porous media at elevated temperatures.Diethylamine (DEA) was selected as the organic alkali that generates oil-in-water emulsions with Athabasca bitumen at a 1,000-ppm NaCl brine and a 0.5-wt% alkali concentration. This aqueous composition had been confirmed to be an optimum in terms of oil content in the water-external emulsion phase at a wide range of temperatures. Then, flow experiments with a glass-bead pack were conducted to measure the effective viscosities of emulsion samples at shear rates from 5 to 29 seconds−1 at 35 bar and temperatures from 373 to 443 K.Results show that the oil-in-water emulsions were more than 15 times less viscous than the original bitumen at temperatures from 373 to 443 K. At the shear rate of 5 seconds−1, for example, the emulsion viscosity was 12 cp at 373 K, at which the bitumen viscosity was 206 cp. The efficiency of in-situ bitumen transport was evaluated by calculating the bitumen molar flow rate under gravity drainage with the new experimental data. Results show that oil-in-water emulsion can enhance the in-situ molar flow of bitumen by a factor of 273 at 403 K and 345 at 373 K, in comparison with the two-phase flow of oil and water in conventional SAGD. At 443 K, only a fraction of bitumen is emulsified in water, but the bitumen transport by both oil-in-water emulsion and an excess oil phase in DEA-SAGD can enhance the molar flow of bitumen by a factor of 19 in comparison to SAGD. This is mainly because the mobility of the bitumen-containing phase is enhanced by the reduced viscosity and increased effective permeability. A marked difference between alkaline solvents and conventional hydrocarbon solvents is that only a small amount of an alkaline solvent enables enhancing the in-situ transport of bitumen.

A multidisciplinary approach for chemical EOR screening: Understanding alkali-oil interaction by the use of petroleum geochemistry

Alkali-based chemical enhanced oil recovery is used to increase the incremental oil production and relies on the interaction of alkali lye with crude oil. Optimizing the chemical formulation depends on screening multiple alkali concentration ranges to maximize the generated emulsion volume. However, the strong chemical variation of the crude oil, caused by biodegradation within the reservoirs, and its influence on generating in-situ soaps has never been studied in detail. In this paper, organic geochemical oil characterization was combined with phase screening data. Thereby, differences in terms of initial crude oil composition (slightly degraded, moderate degraded, and heavy degraded oils), but also regarding the excess alkali-equilibrated oil phase, and the hydrocarbons which are included in the in-situ soap (emulsion phase) were worked out.Different alkalis, concentration ranges, and water-oil-ratios were studied, to understand the control mechanism for the in-situ soap generation. The formed emulsions were observed over time (emulsion stability) and classified into possible emulsion types. Alterations caused by the alkali-oil interaction were quantified by the use of organic geochemistry.The degree of biodegradation seems to be an important control mechanism. Slightly degraded oils do not interact with the alkali lye due to a high content of non-polar compounds such as alkanes and isoprenoids. Moderately and heavily degraded oils show varying interactions with the alkali solution. The degree of interaction depends on the used degradation type, the alkali type as well as on the used concentration. Moderately degraded oils interact in a lower concentration range compared to heavily degraded oils, which show an increased non-soap forming acid content. Phase experiments conducted over a long period of time (100 days) were used to determine which emulsion types (micro or macro) were formed. Stable micro emulsions were preferably generated over time in formulations prepared with potassium carbonate (K2CO3). In contrast, formulations containing sodium carbonate (Na2CO3) hardly did not generate stable micro emulsions.The composition of alkali-equilibrated oil differs from the initial oil composition and shows a strong dependency of the used alkali type. Potassium carbonate caused mild alterations of the moderately and heavily degraded oils, whereas the impact of sodium carbonate was more severe. In addition, dissolution of naphthalenes, steranes, hopanes, and parts of the generated in-situ soap into the aqueous phase, was observed during the performed phase experiments of the moderately degraded oils (at the elevated pH values).

Reverse Hexosome Dispersions in Alkanes-The Challenge of Inverting Structures.

Monoglycerides form lipophilic liquid-crystalline (LC) phases when mixed with water. The corresponding LC nanostructures coexist with excess water, which is a necessary condition for the formation of internally nanostructured dispersed particles. These nanostructures comprise bicontinuous cubic phases, inverted hexagonal phases, and inverted micellar cubic phases. The dispersed particles are therefore named cubosomes, hexosomes, or micellar cubosomes. Such dispersions are usually stabilized by hydrophilic high-molecular-weight triblock (TB) copolymers. Another way to stabilize such dispersions is by forming the so-called Pickering or Ramsden emulsions using nanoparticles as stabilizers. In this contribution, we explore the possibility of forming and stabilizing inverted or reverse systems, that is, dispersions of hydrophilic LC phases in an excess oil phase like tetradecane. Our aim was to change from oil-in-water emulsions to water-in-oil emulsions, where the water phase is a LC phase in equilibrium with excess oil and where the oil is nonpolar, for example, an alkane. This work consists of three parts: (1) to find a hexagonal hydrophilic LC phase that can not only incorporate a certain amount of tetradecane but can also coexist with excess tetradecane in the case of higher oil concentration, (2) to find a suitable stabilizer-either polymeric or nanoparticle type-that can stabilize the emulsion without destroying the hexagonal LC phase, and finally (3) to check the stability of this reverse hexosome emulsion. We discovered that it is possible to create a hexagonal hydrophilic LC phase with short-chain nonionic surfactants such as polyethylene glycol alkyl ethers or with high-molecular-weight TB copolymers of type A-B-A. Furthermore, it is possible to successfully stabilize the reverse hexosomes with low hydrophilic-lipophilic balance TB copolymers-either synthesized in our laboratory or commercially available ones-as well as with hydrophobized, commercially available silica nanoparticles.

Using carbonaceous nanoparticles as surfactant carrier in enhanced oil recovery: A laboratory study

Carbonaceous nanoparticles multi-walled carbon nanotubes (MWNTs) and carbon blacks (CBs) exhibit promising properties for potential applications in crude oil production. The combination of large specific surface area and the strong affinity toward surfactants of nanoparticles mark their candidacy for delivering surfactant deep inside the reservoir. This study is aimed to assess the feasibility of surfactant carriers in tertiary oil recovery. Stable dispersions of aqueous-phase MWNTs or CBs that are formulated and able to propagate through the reservoir medium (3 wt% brine and 60 °C) were first examined as a prerequisite for reservoir application. Competitive adsorption of surfactant on nanoparticles was beneficial to decrease adsorptive loss on Ottawa sand at equilibrium concentration below critical micelle concentration (CMC). As a proof of concept, phase behavior of a ternary surfactant microemulsion system confirmed that the chosen nanoparticles (100 mg/L) successfully delivered surfactants and spontaneously released them to the O/W interface. The observed phenomenon is in accordance with calculation of the Gibbs free energy associated with oil/water/surfactant system. Besides, surfactants carried by nanoparticles achieved equilibrium ultralow interfacial tension between excess oil and aqueous phase similar to the value of surfactant-only formulation (0.007–0.009 mN/m). In one-dimensional sand pack tests, injection of MWNT-surfactant blend achieved faster and higher tertiary recovery than surfactant-only formulation, with cumulative tertiary oil recovery of 42.7% versus 38.1%. It has been noticed that once surfactant been released, destabilization of nanoparticle dispersion occurred and thus increased their retention in porous medium. In case of tight formations, further improvements may be addressed by applying functionalized carbonaceous nanoparticles to assure their transport in porous media after release of surfactant.

Partition of n‐Butanol Among Phases and Solubilization Ability of Winsor type III Microemulsions

AbstractThe partition of n‐butanol in Winsor type III (W‐III) microemulsions was investigated in this work. Three kinds of anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (DSS), and sodium dodecyl benzene sulfonate (SDBS)) and two kinds of anionic/cationic surfactant mixtures (SDS/octadecyl trimethyl ammonium chloride (OTAC) mixtures and DSS/OTAC mixtures) were studied. Internal standard gas chromatography was employed in n‐butanol content analysis. The results showed that no water exists in the excess oil (EO) phase and no oil exists in the excess water (EW) phase. For the W‐III microemulsions obtained by salinity scanning, relatively constant n‐butanol content in the EO (11–12 v%) and EW (1–4 v%) was found under different salinities. Accurate measurement of n‐butanol content in each phase is important for those systems having low solubilization ability. For the W‐III microemulsions prepared using SDS/OTAC surfactant mixture, the percentage of n‐butanol distributed into the interfacial layer decreased while the fraction of n‐butanol in the interfacial layer first increased sharply and then tended to be stable with the addition of n‐butanol. For the different optimum W‐III microemulsion systems tested, most of the surfactant‐to‐alcohol molar ratio data are near 1:3, but obvious deviation could be observed for some data. On the basis of the accurate measurement of n‐butanol content in the EO and EW phases, the standard free energy, ΔGo→in* (T = 298.15 K) of n‐butanol transferring from the EO phase to the interfacial region was calculated. The results show negative ΔGo→in* values. For microemulsions with the same components, n‐butanol content is an important factor influencing the ΔGo→in* value, and a high absolute value of ΔGo→in* leads to high solubilization ability.

Microemulsion Extraction of Monascus Pigments from Nonionic Surfactant using High Polarity of Diethyl Ether as Excess Oil Phase

Stripping of organic compound from nonionic surfactant micelle aqueous solution is indispensable for many industrial processes. In this paper, a relatively high polarity diethyl ether was screened for forming Winsor I microemulsion, which was used for stripping of organic compound from nonionic surfactant. Setting up extractive fermentation of Monascus pigments in Triton X-100 aqueous solution as a model, cloud point extraction of Monascus pigments from fermentation broth, and back-extraction of Monascus pigments from the coacervate phase of cloud point system by Winsor I microemulsion were conducted. Monascus pigments were successfully separated from nonionic surfactant into the excess diethyl ether phase.

글리시돌을 원료로 한 비이온 계면활성제 합성에 관한 연구

글리시돌과 라우릭산으로부터 PGLE와 PGLE3 비이온 계면활성제를 합성하였으며, 합성한 계면활성제들의 구조를 <TEX>$^1H$</TEX> 및 <TEX>$^{13}C$</TEX> NMR 분석을 통하여 확인하였다. PGLE와 PGLE3 비이온 계면활성제의 CMC는 각각 <TEX>$3.59{\times}10^{-2}$</TEX> mol/L, <TEX>$8.80{\times}10^{-1}$</TEX> mol/L이며, CMC에서의 표면장력 값은 각각 26.09 mN/m과 28.68 mN/m이었다. 동적 표면장력 측정 결과에 의하면 PGLE와 PGLE3 비이온 계면활성제 모두, 공기와 수용액의 계면이 계면활성제 단분자에 의하여 비교적 짧은 시간 내에 포화되었으며, 1 wt% PGLE와 PGLE3 계면활성제 시스템들의 접촉각은 각각 <TEX>$25.5^{\circ}$</TEX>와 <TEX>$9.5^{\circ}$</TEX> 나타내었다. 비극성 오일 n-decane과 1 wt% 계면활성제 수용액 사이의 계면장력은 시간에 따라 감소하며, PGLE와 PGLE3 시스템 모두 20분 이내에 평형에 도달하였고, 평형에서의 계면장력 값은 각각 0.42 mN/m와 0.53 mN/m를 나타내었다. PGLE 비이온 계면활성제가 PGLE3 비이온 계면활성제에 비하여 거품 안정성이 큼을 확인하였으며, 이러한 거품 안정성 측정 결과는 표면장력 측정 결과와도 일치하였다. 계면활성제, 물, 비극성 탄화수소 오일로 이루어진 3성분 시스템에 보조계면활성제를 첨가하여 <TEX>$25{\sim}60^{\circ}C$</TEX>의 온도에서 상평형 실험을 수행한 결과, lower phase 마이크로에멀젼 혹은 oil in water 마이크로에멀젼이 excess oil 상과 평형을 이루는 2상 영역만이 관찰되었다. The PGLE and PGLE3 nonionic surfactants were synthesized from the reaction between glycidol and lauryl acid and their structures were confirmed by <TEX>$^1H$</TEX> and <TEX>$^{13}C$</TEX> NMR analysis. The CMCs of PGLE and PGLE3 surfactants were found to be <TEX>$3.59{\times}10^{-2}$</TEX> mol/L and <TEX>$8.80{\times}10^{-2}$</TEX> mol/L respectively and the surface tensions at their CMC conditions were 26.09 mN/m and 28.68 mN/m respectively. Dynamic surface tension measurement has shown that the adsorption rate of surfactant molecules at the interface between air and surfactant solution was found to be relatively fast in both surfactant systems, presumably due to high mobility of surfactant molecules. The contact angles of PGLE and PGLE3 nonionic surfactants were <TEX>$25.5^{\circ}$</TEX> and <TEX>$9.5^{\circ}$</TEX> respectively. Dynamic interfacial tension measurement showed that both surfactant systems reached equilibrium in 20 minutes and the interfacial tensions at equilibrium condition in both systems were 0.42 mN/m and 0.53 mN/m respectively. The PGLE surfactant system has indicated higher foam stability than the PGLE3 surfactant system, which is consistent with surface tension measurement. The phase behavior experiments performed at <TEX>$25{\sim}60^{\circ}C$</TEX> in systems containing nonionic surfactant, water, n-hydrocarbon oil and cosurfactant showed a lower phase or oil in water microemulsion in equilibrium with excess oil phase at all conditions investigated during this study.

Emulsions Stabilized by Microfibrillated Cellulose: The Effect of Hydrophobization, Concentration and O/W Ratio

The properties of emulsions stabilized by nanosized cellulose particles (denominated also microfibrillated cellulose; MFC) were investigated. The wettability (hydrophobicity) of the MFC was changed through surface modification with chlorodimethyl isopropylsilane. The modified MFC was characterized with Fourier transform infrared spectroscopy (FTIR), and x-ray photoelectron spectroscopy (XPS). Using MFC of intermediate hydrophobicity resulted in water-in-oil emulsions within a range of oil/water ratios. The emulsifying capacity of the MFC was found to be proportional to both the relative amount of MFC used and its wettability (degree of surface substitution; DSS). The emulsions separated rapidly from the excess oil phase; the separated emulsion layers were highly stable towards gravity-induced sedimentation and, once a stable MFC network was formed, were also stable towards coalescence. The influence of the oil/water ratio, the concentration and DSS of the MFC on the stability of the emulsions toward coalescence, and the inversion to oil-in-water emulsions was also investigated. The results verify that MFC can be efficiently used as a stabilizer of oil/water emulsions within a range of oil/water ratios and particle concentrations.

Non-iterative phase behavior model with application to surfactant flooding and limited compositional simulation

Hand's method is typically used to empirically calculate the equilibrium compositions for ternary systems between two liquid phases. Oil field application of Hand's method is generally limited to surfactant phase behavior with oil and brine, primarily because the excess oil and brine phases are nearly immiscible. Hand's method is not accurate to represent liquid–vapor equilibrium, especially as oil and gas become miscible. It also requires iterations, which means there is no guarantee of convergence. In this paper, we present a new empirical phase behavior model to replace Hand's method. The new method is faster and more accurate, and applicable for both surfactant phase behavior and liquid–vapor equilibrium. The new approach is non-iterative and always finds a tie line or its extension even for the limiting tie line at the critical point. Our approach transforms tie lines to a new compositional space, where all tie lines become parallel. Equilibrium compositions are then easily determined in the transformed space. Besides improved accuracy and robustness, the flash calculations for ternary systems show that the new method is up to 100 times faster than conventional calculations using a cubic equations-of-state (EOS), and up to seven times faster than Hand's method. When incorporated in a compositional simulator, the new method reduces flash calculation time to nearly zero compared to the solution of the pressure/compositional equations. Thus, speedup is proportional to the fraction of time occupied by flash calculations within the simulator. For example, if flash calculations are 50% of total simulation time, speedup is nearly a factor of two using the new approach. This approach is ideally suited for fast recovery estimations for miscible gas floods, and fills the gap between standard or modified black-oil models and fully compositional simulations.

Morphological transition and emulsification failure in globular microemulsions

We consider the condensation transition of microemulsion droplets of oil which are dispersed in water in the presence of surfactant. Since a macroscopic oil phase is formed due to this transition, it is called "emulsification failure." Based on the free energy approach, we determine the transition lines between the spherical and the cylindrical droplet phases as well as the phase boundary lines of the emulsification failure. The phase diagrams are calculated by changing the physical properties of the surfactant monolayer such as the saddle-splay modulus and the spontaneous curvature. For a negative saddle-splay modulus, the spherical droplet phase coexists with the excess oil phase. In some cases, a re-entrant transition (sphere-->cylinder-->sphere) is expected to take place. For a positive saddle-splay modulus, the system undergoes a direct transition from the cylindrical droplet phase to the macroscopically phase separated state. The sphere-to-cylinder transition line approaches the emulsification failure boundary as the saddle-splay modulus becomes larger.

Phase Behavior and Kinetics of Phase Separation of a Nonionic Microemulsion of C12E5/Water/1-Chlorotetradecane upon a Temperature Quench

The phase behavior and phase separation kinetics of a model ternary nonionic microemulsion system composed of pentaethylene glycol dodecyl ether (C12E5), water, and 1-chlorotetradecane were studied. With increasing temperature, the microemulsion exhibits the following rich phase behavior: oil-in-water phase (L1+O), droplet microemulsion phase (L1), lamellar liquid crystalline phase (Lproportional), and sponge-like (liquid) phase (L3). The microemulsion with a fixed surfactant-to-oil volume fraction ratio (Phis/Phio) of 0.81 and droplet volume fraction of 0.087 was perturbed from equilibrium by a temperature quench from the L1 region (24 degrees C) to an unstable region L1+O (13 degrees C), where the excess oil phase is in equilibrium with the microemulsion droplets. The process of phase separation in the unstable region was followed by time-resolved small-angle X-ray scattering (TR-SAXS) and time-resolved turbidity methods. Due to the large range of scattering vector (q=0.004-0.22 A(-1)) that is possible to access with the TR-SAXS method, the growth of the oil droplets and shrinking of the microemulsion droplets as a result of phase separation could be studied simultaneously. By using an advanced polydisperse ellipsoidal hard-sphere model, the experimental curves have been quantitatively analyzed. The microemulsion droplets were modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints, and the oil droplets are modeled as polydisperse spheres. The radius of gyration (Rg) of the growing oil droplets, volume fraction of oil in the microemulsion droplets, and polydispersity were obtained from the fit parameters. The volume equivalent radius at the neutral plane between the surfactant head and tail of the microemulsion droplet decreased from 76 to 51 A, while the radius of oil drop increased to 217 A within the 160 min of the experiment. After about 48 min from the temperature quench, the system reaches a steady state and continues to coarsen at a constant fraction of the oil of 0.51 in the oil phase by Ostwald ripening with the power law dependence of Roil proportional, variant t1/3. The size of the oil droplets determined by the time-resolved turbidity method is in good agreement with that of the TR-SAXS, highlighting the usefulness of the method in the size determination of oil-in-water microemulsions on an absolute scale.

Viscoelastic Wormlike Micelles in Mixed Nonionic Fluorocarbon Surfactants and Structural Transition Induced by Oils

Formation and rheological behavior of viscoelastic wormlike micelles in an aqueous solution of a mixed system of nonionic fluorocarbon surfactants, perfluoroalkyl sulfonamide ethoxylate, C8F17SO2N(C3H7)(CH2CH2O)nH (abbreviated as C8F17EOn, n=20 and 3), was studied. A partial ternary phase diagram of water/C8F17EO20/C8F17EO3 was constructed at 25 degrees C by visual inspection through crossed polarizers. In the water/surfactant binary system, C8F17EO20 forms an isotropic micellar solution over a wide concentration range (approximately 80 wt %). The micellar solution of the C8F17EO20 can solubilize a significant amount of C8F17EO3, and the solubility increases with increasing C8F17EO20 concentration. With successive addition of C8F17EO3 to the aqueous C8F17EO20 solution, viscosity increases rapidly, and a viscoelastic solution is formed. The viscosity of the viscous sample was approximately 5th order of magnitude of pure water. The viscoelastic solution follows the Maxwell model typical of wormlike micelles at low-frequency region. With further addition of C8F17EO3 the viscosity decreases, and phase separation occurs. Addition of perfluoropolyether oil, (C3F6O)nCOOH, to the viscoelastic solution decreases the viscosity monotonically until phase separation. On the other hand, when perfluorodecalin oil, C10F18, is added, viscosity first decreases and attains a limiting value before excess oil phase separates out. The viscosity decrease in water/surfactant/oil systems is possibly caused by the microstructural transition in the network structure. Small-angle X-ray scattering (SAXS) measurements were performed to complement the rheological data. It has been found that the C8F17EO3 induces one-dimensional growth to the C8F17EO20 micelles. On the other hand, when (C3F6O)nCOOH is added, wormlike-sphere type transition is more likely to occur.

Diesel Oil Removal by Froth Flotation Under Low Interfacial Tension Conditions I: Foam Characteristics, and Equilibration Time

Froth flotation is a surfactant‐based separation process which is suitable for treating dilute wastewaters. To achieve high performance for the froth flotation operation, the combination of an ultra‐low interfacial tension (IFT) between excess oil and excess water phases, high foam production rates, and high stability of the foam produced, must be attained. To obtain the ultra‐low interfacial tensions, a Winsor Type III or middle phase microemulsion has to be formed. In this study, branched alcohol propoxylate sulfate sodium salt with 14–15 carbon number and 4 PO groups (Alfoterra 145–4PO) was used to form microemulsions with diesel oil. From the results of this work, an increase in surfactant concentration decreased the IFT, and increased foam stability. To obtain the minimum IFT in the region of a Winsor Type III microemulsion, the addition of 5 wt.% NaCl was needed. However, this optimum salinity does not result in effective froth flotation due to poor foam characteristics. The results indicate that both the IFT and the foam characteristics should be optimized to achieve high efficiency of oil removal in a froth flotation operation. Unlike the previously‐studied ethylbenzene system, agitation of the solution before introduction into the flotation column yielded the lowest diesel oil removal efficiency because of the poor foam characteristics compared to either unagitated systems or systems allowed to equilibrate for one month.

Favorable Attributes of Alkaline-Surfactant-Polymer Flooding

Summary A laboratory study of the alkaline-surfactant-polymer (ASP) process was conducted. It was found from phase-behavior studies that for a given synthetic surfactant and crude oil containing naph-thenic acids, optimal salinity depends only on the ratio of the moles of soap formed from the acids to the moles of synthetic surfactant present. Adsorption of anionic surfactants on carbonate surfaces is reduced substantially by sodium carbonate, but not by sodium hydroxide. The magnitude of the reduction with sodium carbonate decreases with increasing salinity. Particular attention was given to a surfactant blend of a pro-poxylated sulfate having a slightly branched C16–17 hydrocarbon chain and an internal olefin sulfonate. In contrast to alkyl/aryl sulfonates previously considered for EOR, alkaline solutions of this blend containing neither alcohol nor oil were single-phase micellar solutions at all salinities up to approximately optimal salinity with representative oils. Phase behavior with a west Texas crude oil at ambient temperature in the absence of alcohol was unusual in that colloidal material, perhaps another microemulsion having a higher soap content, was dispersed in the lower-phase microemulsion. Low interfacial tensions existed with the excess oil phase only when this material was present in sufficient amount in the spinning-drop device. Some birefringence was observed near and above optimal conditions. While this phase behavior is somewhat different from the conventional Winsor phase sequence, overall solubilization of oil and brine for this system was high, leading to low interfacial tensions over a wide salinity range and to excellent oil recovery in both dolomite and silica sandpacks. The sandpack experiments were performed with surfactant concentrations as low as 0.2 wt% and at a salinity well below optimal for the injected surfactant. It was necessary that sufficient polymer be present to provide adequate mobility control, and that salinity be below the value at which phase separation occurred in the polymer/surfactant solution. A 1D simulator was developed to model the process. By calculating transport of soap formed from the crude oil and injected surfactant separately, it showed that injection below optimal salinity was successful because a gradient in local soap-to-surfactant ratio developed during the process. This gradient increases robustness of the process in a manner similar to that of a salinity gradient in a conventional surfactant process. Predictions of the simulator were in excellent agreement with the sandpack results.

The HLD–NAC equation of state for microemulsions formulated with nonionic alcohol ethoxylate and alkylphenol ethoxylate surfactants

The net–average curvature (NAC) model ( Langmuir, 19, 186, 2003) is a simple, yet powerful, equation of state to fit and predict the phase behavior of microemulsions (μEs) formulated with ionic surfactants. However, its use for nonionic surfactants systems has not been evaluated until now. The objective of this work is to use the NAC equation of state to model the phase behavior of μEs formulated with pure alcohol ethoxylate (CiEj) and commercial nonylphenol ethoxylate (NPEj) surfactants with a range of alkanes (Cn). The NAC model requires three basic parameters: the characteristic curvature of the nonionic surfactant (Ccn), the characteristic length ( ξ), and the scaling length parameter ( L). The first part of this contribution presents a brief review of the NAC model and other thermodynamic models of μEs. Later, five example applications of the NAC model are presented and discussed: (I) fit/prediction of phase inversion temperature (PIT) values, (II) prediction of phase transition temperatures and characteristic lengths, (III) fit/prediction of interfacial tensions, (IV) prediction of “fish” phase diagrams, and (V) prediction of the composition of bicontinuous systems. The NAC model was able to fit the phase behavior observed in all the experimental scenarios, and predict within 30% the value of phase volumes and transition temperatures for CiEj systems. The largest deviations can be attributed to a poor estimation of ξ obtained through empirical correlations. It was also noted that for commercial NPEj surfactants, the NAC model can also fit and predict the phase behavior of these systems, only that more complex empirical correlations are needed for ξ and Ccn due to the partition of different surfactant n-mers into the excess oil and aqueous phases. In all cases, a good agreement was found when the length parameter ( L) was estimated as 1.4 times the extended length of the surfactant tail.

Partitioning of Fatty Acids in Oil/Water Systems Analyzed by HPLC

AbstractSurfactant/oil/water systems in which the surface‐active substance is a mixture of an undissociated fatty acid (FA) and its sodium salt soap, exhibit the typical phase behavior and the general emulsion phenomenology produced by a formulation scan. The phase behavior transition is induced by changing the FA concentration in the system at a fixed alkaline (NaOH) content in water, which results in a variable lipophilic acid/hydrophilic salt ratio. The partitioning is reported for different FA types (octanoic to myristic) and alcohol co‐surfactants between excess oil and water phases of Winsor three‐phase optimum formulation system. The concentrations are determined by using a method reported in a previous work to quantify the total acid fraction in each phase.

Late-stage coarsening of oil droplets of excess oil in microemulsions following a temperature quench

An oil-in-water microemulsion of the system C 12 E 5 /water/ n-decane with a fixed surfactant-to-oil volume fraction ratio φ s /φ o of 0.85 is studied. This clear microemulsion is temperature-quenched from a clear one-phase region (26 °C) with spherical microemulsion droplets to an unstable region (13 °C) where the excess oil phase is in equilibrium with the microemulsion droplets. Using a high-resolution version of a laboratory small-angle X-ray scattering (SAXS) instrument, the evolution of the excess oil and its growth as a function of time is studied. Unlike coarsening in alloys and polymer blends, a maximum in the intensity at a finite scattering vector is not observed. This clearly indicates that the droplet of the excess oil is formed homogeneously and that there is no depletion zone around the formed droplets. The scattering curves are quantitatively analysed as a function of time. The microemulsion droplets are modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints and the oil droplets are modeled as polydisperse spheres. The average radius of the oil droplets increases with a scaling exponent in agreement with that of coarsening of precipitates in alloys and phase separations in polymer blends, suggesting some degree of universality of coarsening processes.

Three-phase behavior and the roles of C 4E 1 in the water/C 12E 5/C 4E 1/decane system

The three-phase behavior and the roles of 2-butoxyethanol (C 4E 1) in the water/pentaethyleneglycol dodecyl ether (C 12E 5)/C 4E 1/decane system were studied with variation of temperature ( T). The fish-shaped three-phase region consisting of microemulsion, excess aqueous, and excess oil phases contacted the single microemulsion region at an optimum temperature ( T opt) at each weight fraction ( W 1) of C 4E 1/(C 4E 1 + C 12E 5) (water/oil = 1/1 (w/w)). When W 1 was varied, T opt and the highest T( T H) for the three-phase region went through a relative minimum and a relative maximum, respectively. In the quaternary composition tetrahedron, a three-phase region appeared in the water–C 4E 1–decane face at 24.5 °C, expanded with increasing T, and reached the water–C 12E 5–decane face at 36.8 °C. This region separated into two at 39.2 °C. One section took on a cone-like shape above 41 °C, and disappeared into a critical double tie line at 42.5 °C (the relative maximum of T H). The other section shrank with increasing T, and disappeared into the critical tie line in the water–C 4E 1–decane face at 46.5 °C. C 4E 1 plays dual roles, as a surfactant and as a cosolvent. C 4E 1 became more monomerically oil-soluble with increasing T.