Heavy Liquid Phase Research Articles

Liquid-Liquid equilibrium measurements analysis of synthetic multicomponent solvent (n-Pentane, n-Hexane, n-Heptane, Cyclo-Hexane, Toluene)/Bitumen System: Implications for solvent-aided in-situ bitumen extraction

Understanding the Liquid-Liquid Equilibrium (LLE) of multicomponent solvent/bitumen systems is pivotal in optimizing in-situ bitumen extraction. While Vapor-Liquid Equilibria (VLE) of solvent-bitumen systems has been extensively studied, LLE data and predictive models for these mixtures, especially those involving synthetic multicomponent solvents, are scarce. This study provides comprehensive LLE measurements of bitumen and a multicomponent synthetic solvent (n-pentane + n-hexane + n-heptane + cyclo-hexane + toluene) conducted under controlled equilibrium conditions at temperatures of 295 to 352 K, solvent concentrations up to 70 wt% at 1.291 MPa. Application of common correlation used in the construction of solvent-aided process fluid models exhibited average absolute relative deviations (AARDs) of 0.37 % for density and 8.87 % for viscosity. We identified the boundaries marking the shift from homogenous single-phase liquid to two-phase (LLE) states, which occurs within the synthetic multicomponent solvent concentration range of 50 to 60 wt%. We also successfully constructed calibration curves to measure solvent concentrations in both phase regions. The molecular weight distribution and saturates, aromatics, resins, and asphaltene (SARA) fractionation of both liquid phases were determined, highlighting that the heavy liquid phase is primarily asphaltene (∼46 wt%). The insights gained from the measurements and analysis find applications in designing and optimizing solvent-assisted thermal recovery processes for bitumen extraction.

Liquid-liquid equilibrium of CO2/bitumen and CO2/bitumen/ethyl acetate systems with application to diluted bitumen transportation

Bitumen transportation by pipelines requires dilution with solvents. These diluents are often expensive. Therefore, the utilization of liquid CO2 as a diluent to reduce or eliminate diluent consumption is of interest. However, there is limited data in the literature on the liquid-liquid equilibrium (LLE) of CO2 and bitumen. In this work, we report a new set of LLE data for MacKay River bitumen and liquid CO2 at ambient temperature. First, the LLE of bitumen/CO2 at various CO2 feed concentrations was studied. The density of light and heavy liquid phases, the viscosity of the heavy phase, and the heavy phase volume fraction were measured. It was shown that a CO2 feed concentration of 30 wt% is optimum for achieving maximum dissolution of CO2 in bitumen. Then, the effect of pressure on the LLE of bitumen/CO2 at a 30 wt% CO2 concentration was studied. The results revealed a significant reduction in bitumen viscosity from 300,000–1250 cP could be achieved at 21 °C. The results suggest that liquid CO2 can be utilized to reduce diluent consumption in pipeline transportation. The role of ethyl acetate (EA) as a co-solvent with CO2 was also examined. It was shown that the addition of EA to a mixture of bitumen/CO2 could further reduce the bitumen viscosity to satisfy the pipeline transportation criterion. The results reveal that CO2-assisted bitumen transportation in Canada can lead to the utilization of 0.16 Mt of CO2 daily, which is equivalent to a utilization potential of about 80 kg CO2/bbl of raw bitumen. The results also suggest a 73% reduction in fossil-based diluent usage, equivalent to ∼0.5 million barrels of crude oil.

Cubic-plus-association equation of state parameterization of liquid-liquid equilibrium of propane + n-butane + bitumen and dimethyl ether + bitumen systems

Steam-based oil recovery processes are energy-intensive, leading to excessive greenhouse gas emissions. Solvent-assisted oil recovery methods have become of considerable significance as oil industry is moving toward developing new recovery processes with less environmental impact. As a result, thermodynamic modeling of the phase equilibria of oil/solvent systems is essential in designing and optimizing the new recovery processes. In this work, liquid-liquid equilibria (LLE) of bitumen/ liquefied petroleum gas (LPG, a mixture of propane and normal butane) and bitumen/dimethyl ether (DME) are studied. The cubic plus association equation of state (CPA EoS) is utilized to calculate the fugacity coefficient of each component in the two liquid phases. Finally, the experimental weight fractions of the two light and heavy liquid phases are used to tune the model parameters. The model parameters for bitumen/ LPG are considered a linear function of temperature. The tuning over all temperatures resulted in an absolute average relative deviation (AARD) of 8.6 % in predicting the experimental weight fractions. The model also provided acceptable predictions of density, heavy yield, and K-values. For the bitumen/DME system, the tuning was conducted separately for each temperature. The tuned parameters show a meaningful relationship with the test temperature, and the overall AARD in the prediction of the experimental weight fractions is 9.7 %. The tuned EoS model predicted the density and heavy yield reasonably but failed to predict K-values for the bitumen/DME system.

Competition of spinon Fermi surface and heavy Fermi liquid states from the periodic Anderson to the Hubbard model

We study a model of correlated electrons coupled by tunnelling to a layer of itinerant metallic electrons, which allows to interpolate from a frustrated limit favorable to spin liquid states to a Kondo-lattice limit favorable to interlayer coherent heavy metallic states. We study the competition of the spinon fermi surface state and the interlayer coherent heavy Kondo metal that appears with increasing tunnelling. Employing a slave rotor mean-field approach, we obtain a phase diagram and describe two regimes where the spin liquid state is destroyed by weak interlayer tunnelling, (i) the Kondo limit in which the correlated electrons can be viewed as localized spin moments and (ii) near the Mott metal-insulator-transition where the spinon Fermi surface transitions continuously into a Fermi liquid. We study the shape of LDOS spectra of the putative spin liquid layer in the heavy Fermi liquid phase and describe the temperature dependence of its width arising from quasiparticle interactions and disorder effects throughout this phase diagram, in an effort to understand recent STM experiments of the candidate spin liquid 1T-TaSe$_2$ residing on metallic 1H-TaSe$_2$. Comparison of the shape and temperature dependence of the theoretical and experimental LDOS suggest that this system is either close to the localized Kondo limit, or in an intermediate coupling regime where the Kondo coupling and the Heisenberg exchange interaction are comparable.

Phase behavior of bitumen and n-pentane

The phase boundaries for mixtures of n-pentane and bitumen were determined at temperatures from 21 to 280 °C and pressures up to 14 MPa. Both vapor-liquid equilibria and liquid-liquid (solvent-rich and asphaltene-rich phases) equilibria were observed for these mixtures. Saturation pressures (vapor-liquid boundary) were measured using both a PVT cell and a blind cell apparatus at temperatures ranging from 90 to 280 °C. The compositions at which a separate asphaltene-rich heavy phase is formed (asphaltene onset point or liquid-liquid boundary) were measured using a high pressure microscope apparatus for a temperature range of 20–180 °C and were extrapolated from asphaltene yield data at temperatures up to 250 °C.At low temperature, the asphaltene-rich heavy phase appears as dispersed glassy particles. However, at temperatures above approximately 140 °C, this heavy phase separates as a continuous liquid and; therefore, a sample of this phase can be isolated and collected. A PVT cell procedure was developed to collect and assay heavy liquid phases in order to determine the asphaltene yield and composition in terms of solvent, maltene, and C5-asphaltene (n-pentane insoluble asphaltenes) contents. A blind cell apparatus was also designed to measure C5-asphaltene yields for multiple samples simultaneously using a similar procedure.The asphaltene yield, (mass of C5-asphaltene partitioning to the heavy phase) was measured for a range of mixtures of bitumen and n-pentane with feed compositions from 50 to 90 mass % n-pentane at temperatures from 21 to 250 °C and pressures up to 13.8 MPa. Heavy phase compositions were measured for feed compositions of 59–72 mass % n-pentane at 180 °C and 4.8 MPa. The ability of a modified Peng-Robinson cubic equation-of-state model to predict the phase boundaries and the yield and phase composition data is assessed.

Properties of lithium under hydrothermal conditions revealed by in situ Raman spectroscopic characterization of Li2O-SO3-H2O (D2O) systems at temperatures up to 420 °C

Lithium (Li) is an important component of hydrothermal fluids, especially submarine hydrothermal fluids. Investigation of the species and ion complexation of Li+ at elevated temperature and pressure can improve our knowledge on the behavior of Li under hydrothermal conditions. In this study, in situ optical and Raman spectroscopic experiments were conducted on the Li2SO4-H2SO4-H2O system and its D2O analogue at temperatures≤420°C. An unexpected liquid-liquid phase separation (immiscibility) was observed at temperatures above 336.5°C; the aqueous phase was separated into a sulfate-rich heavy liquid phase and a sulfate-poor light liquid phase at vapor-saturation pressures. The liquid-liquid phase separation temperature decreased as the Li2SO4 concentration increased in dilute solutions (≤1.25 m), increased as the Li2SO4 concentration increased in concentrated solutions (>1.25 m), and exhibited a lower critical solution temperature (LCST) at ~336.5°C. The presence of excess H2SO4 (or D2SO4) increased the liquid-liquid phase separation temperature at a constant Li2SO4 concentration. Liquid-liquid phase separation is common in organic-bearing solutions, and LCST is considered to be a macro-scale property of polymer solutions, indicating complicated ion pairing between Li+ and SO42− at high temperature. In situ Raman spectra of the v1(SO42−) band indicated the presence of “free” SO42−, LiSO4−, possible Li2SO40 and other poly-ion associations. The Li+-SO42− association increased with increasing temperature at a constant Li2SO4 concentration. These results indicate that Li+ can form contact ion pairs with ligands despite its strong hydration tendency.In submarine hydrothermal systems, various contact ion pairs should be important Li species during the high-temperature leaching of Li from basalts (e.g., >200°C). The formation of strong and various Li+-SO42− pairs can enhance the leaching of Li because the mobility and diffusion of the Li+-SO42− complex has been reported to be stronger than that of “free” ions. During the low-temperature (e.g., <150°C) uptake of Li+ into secondary minerals (e.g., clays), free Li+ and outer-sphere ion pairs are the dominant Li+ species. Contact ion pairs are also important Li species during the hydrothermal alteration/precipitation of Li-rich minerals in pegmatite systems. Moreover, liquid-liquid phase separation was found to play important roles in the formation of low-temperature minerals (e.g., calcite). However, similar crystallization pathways have rarely been documented for inorganic systems under high temperatures. Anhydrous Li2SO4 was observed to precipitate within the dense liquid phase at ≥360°C in 1.5 m Li2SO4, confirming that the immiscible dense liquid phase can serve as a precursor for the crystallization of sulfates and other minerals under hydrothermal conditions. The possible processes for the dense-liquid-based crystallization by particle attachment can be summarized as (1) strong and reversible ion association induces liquid-liquid phase separation, (2) nucleation and crystallization within the dense liquid phase, and (3) continued growth on the surface of early formed solid phase. Submarine hydrothermal fluids often contain low-dielectric components such as methane and other organic components, which lower the dielectric constant of hydrothermal fluids and promote ion association. Therefore, liquid-liquid phase separation may occur in submarine hydrothermal fluids and can play important roles in the precipitation of sulfates and other minerals.

Catalytic aquathermolysis of Shengli heavy crude oil with an amphiphilic cobalt catalyst

An interfacially active cobalt complex, cobalt dodecylbenzenesulfonate, was synthesized. Elemental analysis, atomic absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis, and surface/interfacial tension determination were performed to investigate the properties of the catalyst. Results showed that the synthesized catalyst showed active interfacial behavior, decreasing the surface tension and interfacial tension between heavy oil and liquid phase to below 30 and 1.5 mN/m, respectively. The catalyst was not thermally degraded at a temperature of 400 °C, indicating its high thermal stability. Catalytic performance of the catalyst was evaluated by carrying out aquathermolysis. The viscosity determination showed that the viscosity of the heavy oil decreased by 38 %. The average molecular weight, group compositions, and average molecular structure of various samples were analyzed using elemental analysis, FT-IR, electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR MS), and 1H nuclear magnetic resonance. Results indicated that the catalyst could attack the sulfur- and O2-type heteroatomic compounds in asphaltene and resin, especially the compounds with aromatic structure, leading to a decrease in the molecular weight and then the reduction in the viscosity of heavy oil. Therefore, the synthesized catalyst might find an application in catalytic aquathermolysis of heavy oil, especially for the high-aromaticity heavy oil with high oxygen content.

Dimer-induced heavy-fermion superconductivity in the Shastry-Sutherland Kondo lattice model

We study the Kondo lattice model on the geometrically frustrated Shastry-Sutherland lattice focusing on the quantum phase transition between the valence bond solid and the heavy fermion liquid phase. By explicitly including spinon pairing of local moments at the mean-field level, we establish the emergence of a unique heavy fermion superconducting phase induced by dimer ordering of the local moments coexisting with Kondo hybridization. Furthermore, we demonstrate that for suitable choices of parameters, a partial Kondo-screening phase, where some of the valence bonds are broken, precedes the aforementioned dimer-induced superconducting phase. Our results have important implications in understanding the experimental observations in the heavy fermion Shasstry-Sutherland compounds.

Competition between Kondo screening and magnetism at theLaAlO3/SrTiO3interface

We present a theory of magnetic and magneto-transport phenomena at LaAlO$_3$/SrTiO$_3$ interfaces, which as a central ingredient includes coupling between the conduction bands and local magnetic moments originating from charge traps at the interface. Tuning the itinerant electron density in the model drives transitions between a heavy Fermi liquid phase with screened moments and various magnetic states. The dependence of the magnetic phenomena on the electron density or gate voltage stems from competing magnetic interactions between the local moments and the different conduction bands. At low densities only the lowest conduction band, composed of the $d_{xy}$ orbitals of Ti, is occupied. Its antiferromagnetic interaction with the local moments leads to screening of the moments at a Kondo scale that increases with density. However, above a critical density, measured in experiments to be $n_c\approx 1.7\times 10^{13} cm^{-2}$, the $d_{xz}$ and $d_{yz}$ bands begin to populate. Their ferromagnetic interaction with the local moments competes with the antiferromagnetic interaction of the $d_{xy}$ band leading to eventual reduction of the Kondo scale with density. We explain the distinct magneto transport regimes seen in experiments as manifestations of the magnetic phase diagram computed from the model. We present new data showing a relation between the anomalous Hall effect and the resistivity in the system. The data strongly suggests that the concentration of local magnetic moments affecting the transport in the system is much lower than the carrier density, in accord with the theoretical model.

Weak ferromagnetism with the Kondo screening effect in the Kondo lattice systems

We carefully consider the interplay between ferromagnetism and the Kondo screening effect in the conventional Kondo lattice systems at finite temperatures. Within an effective mean-field theory for small conduction electron densities, a complete phase diagram has been determined. In the ferromagnetic ordered phase, there is a characteristic temperature scale to indicate the presence of the Kondo screening effect. We further find two distinct ferromagnetic long-range ordered phases coexisting with the Kondo screening effect: spin fully polarized and partially polarized states. A continuous phase transition exists to separate the partially polarized ferromagnetic ordered phase from the paramagnetic heavy Fermi liquid phase. These results may be used to explain the weak ferromagnetism observed recently in the Kondo lattice materials.

Theory of charge order and heavy-electron formation in the mixed-valence compound KNi2Se2

The material KNi$_2$Se$_2$ has recently been shown to possess a number of striking physical properties, many of which are apparently related to the mixed valency of this system, in which there is on average one quasi-localized electron per every two Ni sites. Remarkably, the material exhibits a charge density wave (CDW) phase that disappears upon cooling, giving way to a low-temperature coherent phase characterized by an enhanced electron mass, reduced resistivity, and an enlarged unit cell free of structural distortion. Starting from an extended periodic Anderson model and using the slave-boson formulation, we develop a model for this system and study its properties within mean-field theory. We find a reentrant first-order transition from a CDW phase, in which the localized moments form singlet dimers, to a heavy Fermi liquid phase as temperature is lowered. The magnetic susceptibility is Pauli-like in both the high- and low-temperature regions, illustrating the lack of a single-ion Kondo regime such as that usually found in heavy-fermion materials.

Minimization of Coke in Thermal Cracking of Athabasca Vacuum Residue in a High-Temperature Short-Residence Time Continuous Flow Aerosol Reactor

Yield of coke in thermal cracking of Athabasca vacuum residue in a continuous flow aerosol reactor was minimized by atomization of the feed into submicrometer droplets, which enhanced the vaporization and conversion of the heavy liquid phase with boiling point above 524 °C. The reaction temperature ranged from 700 to 800 °C, and the pressure was atmospheric. The residence time varied from 100 to 115 ms. The yield of coke was found to be insensitive to conversion, with an average value of 6.3 wt %. The average size of the coke particles in the product was less than 190 nm. Alkenes were the dominant components among the gas products, with total yield of ethene and propene ranging from 5 to 18 wt % with conversion. The molar ratio of hydrogen to carbon decreased monotonically with conversion from 1.4 for unconverted feed to 0.98 at 78% conversion, consistent with high yields of hydrogen-rich gas products.

Thermodynamic and transport signatures of a fractionalized Fermi liquid

Several heavy-fermion metals display a quantum phase transition from an antiferromagnetic metal to a heavy Fermi liquid. In some materials, however, recent experiments seem to find that the heavy Fermi liquid phase can be directly tuned into a non-Fermi liquid phase without apparent magnetic order. We analyze a candidate state for this scenario where the local moment system forms a spin liquid with gapless fermionic excitations. We discuss the thermal conductivity and spin susceptibility of this fractionalized state both in two and, in particular, three spatial dimensions for different temperature regimes. We derive a variational functional for the thermal conductivity and solve it with a variational ansatz dictated by Keldysh formalism. In sufficiently clean samples and for an appropriate temperature window, we find that thermal transport is dominated by the spinon contribution which can be detected by a characteristic maximum in the Wiedemann-Franz ratio. For the spin susceptibility, the conduction electron Pauli paramagnetism is much smaller than the spinon contribution whose temperature dependence in three dimensions is logarithmically enhanced as compared to the Fermi liquid result.

Heavy fermions in an optical lattice

We employ a mean-field theory to study ground-state properties and transport of a two-dimensional gas of ultracold alklaline-earth metal atoms governed by the Kondo Lattice Hamiltonian plus a parabolic confining potential. In a homogenous system this mean-field theory is believed to give a qualitatively correct description of heavy fermion metals and Kondo insulators: it reproduces the Kondo-like scaling of the quasiparticle mass in the former, and the same scaling of the excitation gap in the latter. In order to understand ground-state properties in a trap we extend this mean-field theory via local-density approximation. We find that the Kondo insulator gap manifests as a shell structure in the trapped density profile. In addition, a strong signature of the large Fermi surface expected for heavy fermion systems survives the confinement, and could be probed in time-of-flight experiments. From a full self-consistent diagonalization of the mean-field theory we are able to study dynamics in the trap. We find that the mass enhancement of quasiparticle excitations in the heavy Fermi liquid phase manifests as slowing of the dipole oscillations that result from a sudden displacement of the trap center.

Higher angular momentum Kondo liquids

Conventional heavy Fermi liquid phases of Kondo lattices involve the formation of a "Kondo singlet" between the local moments and the conduction electrons. This Kondo singlet is usually taken to be in an internal s-wave angular momentum state. Here we explore the possibility of phases where the Kondo singlet has internal angular momentum that is d-wave. Such states are readily accessed in a slave boson mean field formulation, and are energetically favorable when the Kondo interaction is between a local moment and an electron at a nearest neighbor site. The properties of the d-wave Kondo liquid are studied. Effective mass and quasiparticle residue show large angle dependence on the Fermi surface. Remarkably in certain cases, the quasiparticle residue goes to zero at isolated points (in two dimensions) on the Fermi surface. The excitations at these points then include a free fractionalized spinon. We also point out the possibility of quantum Hall phenomena in two dimensional Kondo {\em insulators}, if the Kondo singlet has complex internal angular momentum. We suggest that such d-wave Kondo pairing may provide a useful route to thinking about correlated Fermi liquids with strong anisotropy along the Fermi surface.

Characterisation of phase segregation during back extrusion of ZA27 semisolid alloy

Effort was made to characterise segregation tendency of mechanically stirred ZA27 alloy with back extrusion as a thixoforming process. At sufficiently high ram speeds, at which liquid phase flows forcefully, pooling of the heavy liquid phase owing to gravitational segregation contributes to homogeneity of back extruded products in terms of solid phase distribution. The amount of this contribution depends on the contact time of this liquid with solid skeleton during liquid exertion to the clearance. Hence, at high ram speeds, small rams which demand taller initial slugs are more efficient in minimising the segregation. However, in the case of low speed back extrusion tests, liquid impotency gives rise to higher performance of the ram which sooner induces combined flow of both phases and thus, thick rams are advantageous over thin ones.

Fractionalization and Fermi-Surface Volume in Heavy-Fermion Compounds: The Case ofYbRh2Si2

We establish an effective theory for heavy-fermion compounds close to a zero temperature antiferromagnetic (AFM) transition. Coming from the heavy Fermi liquid phase across to the AFM phase, the heavy electron fractionalizes into a light electron, a bosonic spinon, and a new excitation: a spinless fermionic field. Assuming this field acquires dynamics and dispersion when one integrates out the high energy degrees of freedom, we give a scenario for the volume of its Fermi surface through the phase diagram. We apply our theory to the special case of YbRh2(Si1-xGex)2 where we recover, within experimental resolution, several low temperature exponents for transport and thermodynamics.

Acoustic and combined methods for measuring the levels of two-layer liquids

Methods for the simultaneous measurement of the levels of light and heavy liquid phases in a tank by using electroacoustic transducers, temperature sensors, and hydrostatic pressure gauges are considered. According to the calculations, the measurement of the levels of, e.g., oil, petroleum products, and underlying water is possible with relative standard errors of the order of 0.1–1%.

UNUSUAL RETROGRADE CONDENSATION AND ASPHALTENE PRECIPITATION IN A MODEL HEAVY OIL SYSTEM

ABSTRACT A partial phase diagram for the system athabasca bitumen vacuum bottoms (ABVB) (24.6 wt% / 2 mole % ) + dodecane (73.8 wt. % / 47 mole % ) + hydrogen (1.6 wt % / 51 mole % ) was constructed in the temperature range 425 K to 725 K and the pressure range 2 MPa to 7 MPa using an X-ray view cell apparatus. This fluid system is shown to exhibit two phase L1V and three phase L1 L2 V phase behaviour over parts of this P-T region. The shape of the low temperature boundary between the L1V and L1 L2 V zones is characteristic of dilute asymmetric mixtures where a heavy liquid phase, L2 appears then disappears within the light liquid phase L1 on isothermal compression. Such phase behaviour is referred to as unusual retrograde condensation and is of both practical and theoretical interest. Transitions between the multiphase regions were found to be reversible at temperatures less than 660 K., in all cases. At higher temperatures irreversible “ asphaltene precipitation” arose within the L2 phase “ Asphaltene precipitation” did not arise in the absence of the L2 phase, i.e.: within the L1 V region, even at temperatures in excess of 700 K. These data provide a strong link between “ asphaltene precipitation” and multiphase behaviour, and demonstrate a physical rather than kinetic basis for asphaltene precipitation at elevated temperatures

Liquid-liquid-vapour phase equilibria in the system methane + ethane + eicosane: retrograde behaviour of the heavy liquid phase

Gregorowicz, J., Smits, P.J., de Loos, Th.W. and de Swaan Arons, J., 1993. Liquid-liquid-vapour phase equilibria in the system methane + ethane + eicosane: retrograde behaviour of the heavy liquid phase. Fluid Phase Equilibria, 85: 225-238. The fluid phase behaviour of the ternary system methane + ethane + eicosane was studied experimentally with special emphasis on liquid-liquid-vapour equilibria and retrograde condensation of the second, heavier liquid phase in this region. P, T sections for mixtures of constant composition were determined according to the synthetic method for nine constant molar ratios of ethane and eicosane and different mole fractions of methane. The temperature range investigated was 290–307 K and the pressure range 5.0–6.4 MPa. Addition of methane to a binary ethane + eicosane mixture expands the three-phase curve to a region and shifts it to lower temperatures. The influence of the concentration of eicosane and of methane on the phase behaviour in the three-phase region and on retrograde phenomena is discussed.