Experimental Phase Behavior Research Articles

Anionic surfactant remediation of soil columns contaminated by nonaqueous phase liquids

A variety of column experiments have been completed for the purpose of selecting and evaluating suitable surfactants for remediation of nonaqueous phase liquids (NAPLs). The various NAPLs tested in the laboratory experiments were tetrachloroethylene (PCE), trichloroethylene (TCE), jet fuel (JP4) and a dense nonaqueous phase liquid from a site at Hill Air Force Base, UT. Both Ottawa sand and Hill field soil were used in these experiments. Surfactant candidates were first screened using phase behavior experiments and only the best ones were selected for the subsequent column experiments. Surfactants which showed high contaminant solubilization, fast coalescence times, and the absence of liquid crystal phases and gels during the phase behavior experiments were tested in soil column experiments. The primary objective of the soil column experiments was to identify surfactants that recovered at least 99% of the contaminant. The secondary objective was to identify surfactants that show low adsorption and little or no loss of hydraulic conductivity during the column experiments. Results demonstrated that up to 99.9% of the contaminants were removed as a result of surfactant flooding of the soil columns. The addition of xanthan gum polymer to the surfactant solution was shown to increase remediation efficiency as a lower volume of surfactant was required for recovering a given volume of NAPL. Based on these experimental results, guidelines for designing highly efficient and robust surfactant floods have been developed and applied to a field demonstration.

Spontaneous Emulsification of Oils Containing Hydrocarbon, Nonionic Surfactant, and Oleyl Alcohol

Phase behavior and videomicroscopy experiments were used to investigate spontaneous emulsification ofn-hexadecane/oleyl alcohol/C12E6mixtures in water at 30°C. It was found that complete emulsification of a drop of the oil phase to form small oil droplets having diameters of about 1 μm occurred only when diffusion of water into the initial oil drop first converted it completely into the lamellar liquid crystalline phase and/or a microemulsion and then caused this phase (or these phases) to become supersaturated in oil so that many oil droplets nucleated. This behavior occurred when the hydrocarbon/alcohol ratio of the initial oil drop was near that of the excess oil phase for a balanced system at this temperature, i.e., at the phase inversion temperature (PIT), and when surfactant content was sufficiently high. The stability of these emulsions was investigated by means of turbidity measurements. The most stable emulsion appeared to occur under conditions where the drops were coated by a layer of the lamellar phase.

Phase behaviour of rod with flexible side chains/coil/solvent systems: poly(α,l-glutamate) with tri(ethylene glycol) side chains, poly(ethylene glycol), and dimethylformamide

Phase behaviour is investigated for ternary solutions composed of rodlike α-helical poly(α,l-glutamate) having triethylene glycol monomethyl ether at the end of the side chains (P3EGLG), randomly-coiled poly(ethylene glycol), and N,N-dimethylformamide (DMF) as solvent. The solution containing lower molecular weight poly(ethylene glycol) (PEG10) separates into an isotropic phase, which is rich in PEG10, and an anisotropic (cholesteric) phase, which is rich in P3EGLG, when the total polymer volume fraction is higher than ca 0.13. The homogeneous anisotropic region, in which a detectable amount of PEG10 exists, is recognized along the P3EGLG-DMF axis in the triangle phase diagram. When the molecular weight of poly(ethylene glycol) is larger, additional phase-separation regions are observed: That is, isotropic-isotropic biphasic region and anisotropic-isotropic-isotropic triphasic region. Theoretical treatments based on the lattice model for nematic solutions are conducted for these rod/coil/solvent ternary systems. Calculated phase diagrams with considering flexible side chains of rodlike solute and isotropic interaction parameters are found to qualitatively reproduce the variation of the experimental phase behaviour with the change of the molecular weight of the coiled component.

A local composition model for paraffinic solid solutions

The description of the solid-phase non-ideality remains the main obstacle in modelling the solid-liquid equilibrium of hydrocarbons. A theoretical model, based on the local composition concept, is developed for the orthorhombic phase of n-alkanes and tested against experimental data for binary systems. It is shown that it can adequately predict the experimental phase behaviour of paraffinic mixtures. This work extends the applicability of local composition models to the solid phase.

Preliminary phase diagrams for ABVB + n-dodecane + hydrogen

The phase behaviour of athabasca bitumen vacuum bottoms (ABVB) + n-dodecane + hydrogen mixtures was investigated at temperatures and pressures ranging up to 725 K and 7 MPa using an X-ray view cell. Preliminary phase diagrams are presented. The most complex phase behaviour observed is tentatively identified as “S”LLV, although the nature of the “solid” is unclear. From the slope of the “S”LV to LV phase boundary, ΔH fusion is less than 7 kJ/kg. Thus it may be an amorphous solid, a viscous liquid, or micellular in nature. Observed multiphase behaviour is also compared with operating conditions for well known heavy oil upgrading processes. Most processes appear to skirt multiphase zones. A preliminary four component model for the phase behaviour of the ABVB + hydrogen system has been devised using CMG-PROP and HYSIM. An example calculation comparing modelled and experimental phase behaviour is also presented.

Phase Behavior and Scattering Experiments of an Oligo(ethylene oxide)−n-Perfluorooctyl Ether/Water System

Aqueous solutions of an oligo(ethylene oxide)−n-perfluorooctyl ether with an average number of 16 ethylene oxide groups (abbreviated CFEO16) were investigated. The phase diagram in the temperature composition plane qualitatively corresponds to the general behavior observed for oligo(ethylene oxide)−n-alkyl ether/water mixtures. A series of light-scattering studies on isotropic solutions reveals enhanced scattered intensity with increasing temperature. Small angle neutron-scattering (SANS) experiments show this to be due to anisotropic micellar growth.

Molecular Dynamics Simulation of Benzene on Graphite. 2. Phase Behavior of Adsorbed Multilayers

In a previous paper, we investigated the melting transition of benzene on the basal plane of graphite at monolayer coverage using molecular dynamics simulations. Here, we extend this study to include the effects of increasing the coverage to multiple layers. We consider the temperature dependence of certain static and dynamic quantities across a wide temperature range in terms of the published experimental phase behavior and also compare these results to those of the adsorbed monolayer.

Miscibility of poly(ε‐caprolactone), a semicrystalline polymer, with amorphous poly(styrene‐4‐hydroxystyrene) copolymers

AbstractThe miscibility of poly(ε caprolactone) (PCL) with poly(styrene‐co‐4‐hydroxystyrene) (PHS) copolymers was investigated as a function of comonomer composition experimentally and with calculations by two models; the binary interaction model and the association model. PCL was found to be completely miscible with PHS copolymers containing 5 or more mole percent of 4‐hydroxystyrene (HS) comonomer units for the entire range of blend compositions. Segmental interaction densities, Bijs, were determined by the analysis of the equilibrium melting point depression and by the application of the binary interaction model. By correlating the segmental interaction energy densities with the binary interaction model, thermodynamic miscibility is for comonomer composition over five mole percent of 4‐hydroxystyrene, which is in agreement with the experimental phase behavior. Application of the association model for specific interactions to blends also predicts the experimental miscibility boundary and phase behavior for all the PHS copolymers/PCL blends. © 1995 John Wiley & Sons, Inc.

On the nature of the intramicellar and intermicellar forces governing the liquid crystalline phase behavior of aqueous solutions of disklike micelles

The liquid crystalline phase diagrams for aqueous solutions of the homologous series of surfactants CF3(CF2)nCO−2Cs+ (n=5–8) have been determined. They all exhibit the classical isotropic (I)-to-discotic nematic (ND) and ND-to-smectic lamellar (L) sequences of transitions with increasing concentration, as previously established for the n=6 system [N. Boden, S. A. Corne, and K. W. Jolley, J. Phys. Chem. 91, 4092 (1987)]. The effect of increasing n is to displace the transitions to higher temperatures. The behavior of all of the surfactant systems can be represented on a universal phase diagram. Both the I-to-ND and the ND-to-L transitions at corresponding concentrations are found to occur when the axial ratio of the disklike micelles attains a singular value in each case, irrespective of the value of n. The form of the experimental phase diagrams can be qualitatively understood in terms of a simple ‘‘zeroth’’ order theory which uses the results of Onsager’s theory [L. Onsager, Ann. NY Acad. Sci. 51, 627 (1949)] applied to disks to find the critical axial ratios in the coexisting isotropic and nematic phases and, separately, a dilute solution, self-assembly theory of disklike micelles [W. E. McMullen, A. Ben-Shaul, and W. M. Gelbart, J. Colloid Interface Sci. 98, 523 (1984)] to determine the temperatures at which these axial ratios are achieved at each concentration. The same treatment is also shown to account for the experimental phase behavior of mixed-chain-length systems.

Equilibrium and dynamic behavior for systems containing nonionic surfactants, n-hexadecane, triolein and oleyl alcohol

Phase behavior and electrical conductivity experiments were carried out for systems containing water, nonionic surfactants, triolein, n-hexadecane and oleyl alcohol. In systems where the amount of triolein was equal to or greater than the amount of n-hexadecane, the surfactant appeared successively in the lamellar liquid crystalline phase L α, the sponge phase D′, a bicontinuous microemulsion D and an oil-rich microemulsion O m as the system was made more lipophilic. The temperatures of the various phase transitions decreased with increasing hydrocarbon content. In one system five phases were found to coexist simultaneously: L α, D′, D, and excess water and oil. Conductivity measurements indicated no major change in microstructure of either D′ or D phases when the n-hexadecane-to-triolein ratio was changed from zero to one. In systems where the amount of hydrocarbon was much greater than the amount of triolein, the usual microemulsion phase behavior was seen with continuous variation of oil and water solubilization over a wide range. Videomicroscopy contacting experiments were consistent with the phase behavior results in that the D′ phase was observed as one intermediate phase when drops rich in triolein were injected into aqueous surfactant solutions but not when the drops were mainly hydrocarbon. In the latter case, microemulsions were seen which inverted continuously until the surfactant concentration in the drops became high enough that the lamellar phase formed.

Phase stability of ternary blends

AbstractThe phase behavior of ternary blends of tetramethyl polycarbonate (TMPC), polycarbonate (PC), and styrenic polymers has been examined by experiment and analyzed in terms of thermodynamic theories. The phase boundaries were predicted using both the modified Flory‐Huggins theory and the lattice fluid theory. The boundaries predicted using the lattice fluid theory agree best with the experimental results. The experimental phase behavior of ternary blends was compared with binary blends having exactly the same chemical components and compositions except that the TMPC and PC units were present in the form of a copolycarbonate in the binary. The miscible region of these ternary blends is much narrower than that of the corresponding binary blends, even though the entropic and energetic terms of such ternary blends are more favorable than those of the binary blends. It is shown that a negative value of noncombinatorial free energy in multicomponent systems is not a sufficient condition for miscibility, because of asymmetries of mer‐mer interactions. A comparison of the stability conditions for these binary and ternary blends shows that increasing the degrees of freedom tends to destabilize the mixture.

Peculiarities in the high-pressure phase behaviour of binary mixtures of nitrogen with methane, helium and water

The experimental phase behaviour of binary mixtures of nitrogen with three very different components is discussed. The phase diagrams have also been determined theoretically but with modest success. It will be shown that our knowledge of the unlike potential parameters is insufficient.

Effect of structure on the cloud-point curves of silicone-based amphiphiles in supercritical carbon dioxide

The use of surfactants in nonpolar supercritical fluid (SCF) systems helps to increase solvating power of the SCF. Although C02 is the most widely used SCF, many commercially available surfactants generally exhibit poor solubility in this fluid. Our goal is to design and synthesize amphiphiles that are both functional and highly CO 2-soluble, and evaluate the relationship between structure and solubility. The basis of the design involves the synthesis of molecules whose hydrophobic groups interact favorably, in a thermodynamic sense, with CO 2 while the hydrophilic group(s) interacts with the chosen solute (water, polar molecules, metals). In this work, we will explore the relationship between structure and solubility of silicone-based amphiphiles in CO 2 via high-pressure phase-behavior experiments. The phase-behavior results clearly indicate that the silicone-based amphiphiles exhibit high CO 2 solubility at temperatures of 313 K and pressures below 40 MPa.

SURFACTANT-OIL-WATER SYSTEMS NEAR THE AFFINITY INVERSION PART VIII : OPTIMUM FORMULATION AND PHASE BEHAVIOR OF MIXED ANIONIC-NONIONIC SYSTEMS VERSUS TEMPERATURE.

ABSTRACT Surfactant-oil-water systems with a phase behavior insensitive to temperature and composition can be achieved by anionic-nonionic mixing. By using of a linear mixing rule and a linear temperature dependency, it is possible to interpret most of the features exhibited by the experimental phase behavior data obtained with sulfonate and ethoxylated alkylphenol mixtures. Deviation from the theoretical model are probably due to anionic and nonionic groups association which reduces the overall hydrophilic character.

Predictions of the miscibility behaviour of copolymer blends involving the monomers N-phenylitaconimide, methyl methacrylate, styrene and acrylonitrile

Using the six segmental interaction parameters that characterize the pair interactions between the monomer units N-phenylitaconimide, methyl methacrylate, styrene and acrylonitrile, the theoretical miscibility ranges of several copolymer-copolymer combinations have been calculated. Comparison with the experimental phase behaviour has shown that acceptable predictions can be obtained, but also suggests that the adoption of uniquely valued interaction parameters may be inadequate to describe all situations, and the effects of polymer chain environment may have to be considered.

LIQUID PARTITIONING OF AMPHIPHILIC SOLUTIONS RELATED TO THE SOLVENT EXTRACTION OF BITUMEN FROM TAR SANDS

Abstract The Wood-Beaver process is a solvent extraction process which uses a fatty acid blend (light hydrocarbons, aromatics, and fatty acids) as the solvent and utilizes amphiphilic phase behavior and phase shift to recover the fatty acids from the solvated bitumen. The process consists of mixing the solvated bitumen with an alcohol-water wash which precipitates the bitumen as the bottom phase of the primary settler. The top phase of the settler contains the fatty acid/alcohol/water/light hydrocarbons components. The fatty acid and light hydrocarbons are then recovered in a secondary settler by shifting the phase equilibrium by either over-dosing with water or by driving off alcohol by the application of heat. This paper presents experimental equilibrium phase behavior data and the correlations resulting from an analysis for the quaternary system of oleic acid, bitumen, isopropyl alcohol, and water. The data are presented in the form of psuedo ternary diagrams. The NRTL modelling equation was applied to the oleic acid/brine/isopropyl alcohol system in order to determine a set of interactive and non-randomness parameters that adequately describe the liquid-liquid phase behavior of this ternary system. The phase envelope and accompanying tie lines reproduced from the model showed acceptable agreement with the experimental data.

Developments in the thermodynamics of polymer systems

In the integration of polymer production, processing and material development the thermodynamics of polymer systems plays a key role. The more advanced the performance of the final polymer material is, the more complex its phase behaviour turns out to be. In this review we give some insight into the thermodynamic phenomena that occur in the production of these High-TECH materials. The high viscosity of polymer solutions and blends hampers the experimental study of these systems. Yet, recently a small-scale mixer became available that allows us to extrude small homogeneous samples that can be used for equilibrium studies with the Pulse Induced Critical Scattering Technique (PICS) or with indirect methods like DSC, T g-measurements and microscopic evaluation (TEM, SEM). In polymeric systems containing many constituents, like those used in the paint industry, solubility parameter approaches permit a best guess of the phase behaviour. For binary or ternary polymer systems, improved Flory-Huggins-Staverman theories proved to be able to quantitatively describe the experimental phase behaviour, at the cost of a small number of adjustable parameters. Important factors that should be included in the improvement are: the disparity of size and shape between the repeat units of the constituents, changes in polymer chain flexibility and dilute solution effects. The interaction function for statistical copolymers is more involved, but first attempts lead to satisfying descriptions of experimental phase behaviour. For block copolymer systems the thermodynamic modelling is still in a premature state. The influence of pressure can be incorporated in lattice models and reasonable descriptions of the P-T-x space of polymer systems can be achieved.

Carbon Dioxide Flooding Evaluation of High-Pour-Point, Paraffinic Red Wash Reservoir Oil

Abstract Engineering methods are being developed to evaluate reservoir fluid systems for suitability to CO2 flooding. This paper presents our evaluation procedure as applied to laboratory data for a high-pour-point [95°F (35°C)] oil from the Red Wash field in Utah. The data were obtained from phase behavior and slim tube experiments. The results of this work indicate that high pressures are required for a miscible displacement of the highly paraf-finic, high-pour-point Red Wash oil. The minimum miscibility pressure (MMP) was found to be 4,650 psia (32 060 kPa), increasing only 5% to 4,900 psia (33 784 kPa) when the injected CO2 contains a 10 mol% nitrogen contaminant. These pressures are not currently economically obtainable in the Red Wash field.

Development of Experimental Phase Equilibria For Miscible Hydrocarbon Enhanced Oil Recovery

Abstract A major factor in the success of a miscible hydrocarbon enhanced oil recovery process is the phase behaviour relationship between the injection and reservoir fluids. This paper describes the experimental procedures developed at Gulf Canada R&D to generate phase equilibrium data for specific reservoirs. The data have been applied in evaluating the potential for enhanced recovery in a number of Western Canadian carbonate reservoirs. The over-all procedure for a complete phase equilibrium study is described. This comprises field sampling, reservoir fluid characterization, injection fluid preparation, development of phase envelopes and correlation of phase behaviour. An integral part of the program involved the development Of a combination of analytical and high-pressure techniques to facilitate the rapid accumulation of vapour-liquid equilibrium data for reservoir-injection fluid systems. The Peng-Robinson equation of state and a new K value correlation were used successfully to rationalize the measured data. Experimental phase behaviour measurements in conjunction with appropriate correlation methods have proved valuable in tailoring the design of injection fluids to meet both miscibility requirements and economic constraints. Introduction Recent reports(1,2) have indicated that the use of enhanced recovery methods can increase Canada's available conventional oil reserves by approximately 2 to 3 billion barrels. Up to 95% of the additional oil with an API gravity greater than 25º could feasibly, and economically, be recovered using currently available miscible displacement techniques involving injection into the reservoir of either CO2 or hydrocarbon fluids. Realizing this potential, Gulf Canada Resources Inc. have been actively pursuing a program of initiating limited full-scale enhanced recovery projects and implementing pilot-scale floods(3) at various locations in Western Canada. To date, because of the types of reservoirs considered primarily carbonate and the local availability of suitable injection fluid components, attention has centred on the process of hydrocarbon miscible displacement. In support of these projects, the Gulf Canada R&D Department has developed an extensive experimental program to provide data both for preliminary screening of candidate reservoir and injection fluids and for detailed design of optimum injection fluids in specific reservoirs. This paper describes the experimental program that has evolved during application to such projects over the past five years. Miscible Displacement The residual oil saturation, after primary and secondary production of a reservoir, is a function of the formation geometry and the interfacial tensions of the fluids occupying the formation. The purpose of the injection fluid in enhanced recovery is to access the residual oil, and, by modifying the balance of interfacial tensions, to mobilize the residual oil to production. In miscible displacement processes, as the name implies, this purpose is achieved when miscibility is attained between the displacing fluid (injection fluid) and the residual oil, thereby eliminating the interfacial tension between the two. The miscibility of an injection fluid and reservoir oil is governed by the phase behaviour which is unique to each specific combination. The relationship between phase behaviour, miscibility and composition at reservoir temperature and pressure is illustrated on the pseudo-ternary Point R is the reservoir fluid composition and X represents the critical composition or plait point.

Phase Boundaries of Microemulsion Systems as a Way of Characterizing Hydrocarbon Mixtures

Abstract Phase behavior of microemulsions composed of TRS 10-80, brine (10.6 mg/g NaCl), isopropyl alcohol, and mixtures of pure hydrocarbons was studied to determine the location of phase boundaries of the single-phase microemulsion region. Studies were conducted on pseudoternary phase diagrams where the pseudocomponents were isopropanol, brine, and a constant ratio of surfactant to hydrocarbon (S/H). Phase boundaries were determined by the titration method developed by Bowcott and Schulman,1 which was extended to systems of interest for oil recovery by Dominguez et al.2,3 The titration method involves the addition of brine to a single-phase microemulsion until phase separation occurs. Then the system is titrated to transparency by addition of isopropanol. Dominguez et al.2,3 demonstrated the applicability of the titration method for systems containing pure alkanes. They found upper and lower phase boundaries (high and low alcohol concentrations) for the microemulsion regions on S/H pseudoternary diagrams that were represented by linear relationships between the volume of alcohol and the volume of brine required to attain a single-phase microemulsion. This region, termed Region 4, bounded by linear phase boundaries, extends over a wide range of brine concentrations including regions of interest to enhanced oil-recovery processes. The research reported in this paper extends the work of Dominguez et al.2,3 to mixtures of pure hydrocarbons. The locations of the lower phase boundaries for Region 4 were determined for four types of mixtures prepared with pure hydrocarbons ranging from C6 to C18. In all phase behavior experiments, the lower phase boundary of Region 4 was a straight line when volume of alcohol was plotted against volume of brine. Furthermore, the slope of this phase boundary was found to be a linear function of alkane carbon number (ACN) for pure hydrocarbons and equivalent alkane carbon number (EACN) for mixtures of pure hydrocarbons. The correlation of a property of the phase diagram (the slope of the lower phase boundary) with EACN suggests a new approach to characterization of hydrocarbon/surfactant systems. In our experience, the EACN determined from phase behavior studies is more reproducible than the EACN determined from methods involving measurements of interfacial tensions. This method has potential for characterization of surfactant/hydrocarbon systems for complex mixtures of hydrocarbons, including crude oils.