Thermodynamic Phase Equilibria Research Articles

Significance of wettability of porous media and its implication for hydrate-based pre-combustion CO2 capture

Gas hydrate-based pre-combustion CO2 capture is considered a promising technology for CO2 separation. To further improve hydrate-based CO2 capture from gaseous mixtures (i.e., CO2 + H2) generated from pre-combustion processes, it is necessary to enhance the hydrate thermodynamic stability and formation kinetics. Surfactants and interstitial pore materials have been suggested to enhance formation kinetics, but the optimum confined space and wettability of the porous media, which are the key factors affecting kinetic performance, have not been fully determined when using thermodynamic promoters. In this study, the thermodynamic stability and formation kinetics (e.g., induction time, formation rate, gas composition, and gas uptake) of THF (5.56 mol%) hydrates of CO2 (40%) + H2 (60%) mixtures in the presence of SDS (0, 100, or 500 ppm) were evaluated in silica gels of various hydrophobicities. The results revealed that the hydrophobicity of the porous media significantly affects both the thermodynamic phase equilibria and kinetic properties. Interestingly, the weak hydrophobic silica gel enhanced the thermodynamic stability, induction time, formation rate, and gas uptake with 96% CO2 composition. The SDS (particularly 500 ppm) also improved the kinetic properties of the hydrate. The present findings provide a new guideline for designing the optimum hydrophobicity of porous media to enhance the thermodynamic stability and formation kinetics for hydrate-based pre-combustion CO2 capture.

A volume-of-fluid method for variable-density, two-phase flows at supercritical pressure

A two-phase, low-Mach-number flow solver is created and verified for variable-density liquid and gas with phase change. The interface is sharply captured using a split volume-of-fluid method generalized for a non-divergence-free liquid velocity and with mass exchange across the interface. Mass conservation to machine-error precision is achieved in the limit of incompressible liquid. This model is implemented for two-phase mixtures at supercritical pressure but subcritical temperature conditions for the liquid, as it is common in the early times of liquid hydrocarbon injection under real-engine conditions. The dissolution of the gas species into the liquid phase is enhanced, and vaporization or condensation can occur simultaneously at different interface locations. Greater numerical challenges appear compared to incompressible two-phase solvers that are successfully addressed for the first time: (a) local thermodynamic phase equilibrium and jump conditions determine the interface solution (e.g., temperature, composition, surface-tension coefficient); (b) a real-fluid thermodynamic model is considered; and (c) phase-wise values for certain variables (e.g., velocity) are obtained via extrapolation techniques. The increased numerical cost is alleviated with a split pressure-gradient technique to solve the pressure Poisson equation for the low-Mach-number flow. Thus, a fast Fourier transform method is implemented, directly solving the continuity constraint without an iterative process. Various verification tests show the accuracy and viability of the current approach. Then, the growth of surface instabilities in a binary system composed of liquid n-decane and gaseous oxygen at supercritical pressures for n-decane is analyzed. Other features of supercritical liquid injection are also shown.

Application of in-situ heat generation plugging removal agents in removing gas hydrate: A numerical study

Under the condition of low temperature and high pressure, natural gas will form solid gas hydrates in oil and gas wellbore and pipeline, resulting in blockage, pressure increase, production reduction, and even shutdown. Methods such as heat preservation, heating, and injection of inhibitors are often used in engineering to avoid the formation of hydrates. The latter, injection of inhibitors, is the most widely used means of hydrate prevention and control at present. A special inhibitor, namely an in-situ heat generation plugging removal agent, has the advantages of both heating and chemical plugging removal and is a kind of hydrate inhibitor with great potential. In this study, a new mathematical model is developed based on hydrate phase equilibrium thermodynamics and decomposition kinetics, which is used to solve the heat and mass transfer problems in the plugging removal process of the gas hydrate by using in-situ heat generation plugging removal agents. Numerical simulation is used to solve the mathematical model, and the plugging removal process and parameter variation of pure in-situ heat generation system (high/medium/low temperature), electrolyte in-situ heat generation system (containing Na+/Mg2+), and alcohol in-situ heat generation system (containing MeOH/DEG) are studied respectively. Based on the experimental results, the quantitative relationship between the plugging removal time, the dosage, and the concentration of the plugging removal agent is calculated and analyzed. Our proposed model is verified through experimental study and the calculated values of the mathematical model are in good agreement with the experimental values under different working conditions. It is concluded that the rapid removal of hydrates and the prevention of secondary formation of hydrates can be achieved by configuring the high-temperature in-situ heat generation plugging removal agents, and the efficiency of plugging removal can be enhanced by adding appropriate concentration of electrolyte and alcohol without changing the heating property of the original plugging removal agent. This study can provide theoretical guidance for the safety of oil and gas flow and the efficient development of hydrate.

Complex Effects of Assimilation on Sulfide Saturation Revealed by Modeling with the Magma Chamber Simulator: A Case Study on the Duluth Complex, Minnesota, USA

Abstract Wall-rock assimilation can cause effective sulfide saturation in magmas and lead to the formation of base and precious metal sulfide deposits. Detailed assessments of how assimilation affects the sulfur content at sulfide saturation (SCSS) in magmas have been scarce because of the lack of suitable thermodynamic modeling tools. The Magma Chamber Simulator (MCS) is the first geochemical modeling software that accounts for thermodynamic wall-rock phase equilibrium in open magmatic systems experiencing recharge-assimilation-fractional crystallization. We used the MCS to model SCSS in a magmatic system corresponding to the parental melt of the Partridge River intrusion of the Duluth Complex, Minnesota. This intrusion hosts several Cu-Ni deposits in troctolitic and noritic rocks, which both show evidence of assimilation of the adjacent Virginia Formation black shale. Our simulations show that the dominantly troctolitic rocks can form via fractional crystallization if the parental melt is hydrous (≥ 1 wt % H2O), while gabbroic rocks dominate when the parental melt is H2O poor (≤ 0.14 wt % H2O). Formation of norite from the hydrous parental melt requires ~20–30% of selective assimilation of black shale partial melts or bulk assimilation of stoped blocks. In the fractional crystallization simulations, increasing the H2O content of the parental melt lowers SCSS. In the hydrous fractional crystallization scenarios, SCSS is lowered further by the depletion of FeO from the residual melt, owing to enhanced olivine stability. In the assimilation simulations, the residual melt in the magma subsystem becomes enriched in SiO2, Al2O3, K2O, and H2O with simultaneous depletion in FeO, MgO, CaO, and Na2O. These compositional changes promote sulfide saturation—an effect that is more pronounced in selective rather than in bulk assimilation scenarios. Trace element models, used as a proxy for the efficiency of sulfur assimilation, show that sulfur should behave as an incompatible element (DWR (S) ≤ 1) to wall rock in the selective assimilation simulations, i.e., enriched in early-assimilated wall-rock fluids and/or partial melts, in order to fulfill the natural sulfur isotope criteria of the Duluth Complex. Bulk assimilation may also be efficient enough to modify the sulfur isotope composition, but it requires a large amount of crystallization in the magma and is, hence, considered less likely to be the main process for sulfur assimilation. If wall-rock sulfur is effectively transported to the magma, in situ precipitation of sulfides without notable subsequent upgrading by dynamic processes could produce the sulfide grade of an average Cu-Ni deposit in the Partridge River intrusion.

Data‐driven approximation of thermodynamic phase equilibria

AbstractWe present a new data‐driven approach for both accurate and computationally efficient approximation of vapor liquid equilibria (VLE) models. Our method is able to provide guaranteed enclosure to limit the approximation errors over the entire domain of interest, all just by sampling only at select points. The approximation relies on a mixed‐integer linear programming (MILP) formulation that exploits vertex polyhedral properties of theoretically guaranteed lower and upper bounds to enclose nonlinear and nonconvex equations of state (EOS) and empirical models. Another advantage is that, unlike traditional full simulation‐based data‐driven approaches, we do not solve nonlinear system of equations (f(x) = 0) for sampling. Instead of looking for only feasible samples, we evaluate f(x) over x‐domain. This functional evaluation eliminates the need for computationally‐demanding full‐scale simulations and the associated convergence issues. We demonstrate excellent performance of the proposed MILP formulation in predicting the solubility of hydrofluorocarbon (HFC) refrigerants in ionic liquids (IL).

Thermodynamic reassessment of Au–Pt–Sn system

Au–Pt–Sn alloys are a novel class of materials with promising catalytic properties. This study provides updated information on phase equilibrium structures and thermodynamics of the Au–Pt–Sn ternary system. The formation enthalpies of Au–Sn and Pt–Sn binary subsystems were predicted by first principles calculations and these values were further refined by CALPHAD method. The results obtained accurately reproduced the experimental data. The reassessed phase diagram of the Au–Pt–Sn ternary system accurately described the phase composition of several Au–Pt–Sn alloys, which is essential for further modifications of these materials.

Novel class of precursor-derived Zr–La–B–C(O) based ceramics containing nano-crystalline ultra-high temperature phases stable beyond 1600 °C

In this work, a novel ultra-high temperature resistant precursor-derived ceramic containing Zr, La, B, and C was synthesized through precursor modification of phenol formaldehyde resin. The thermal stability and resistance to crystallization of the ceramic at a temperature of 1600 °C was investigated and was found to be profoundly influenced by the boron content in the starting precursors. The ceramics remained amorphous at 1600 °C for 2 h in argon and upon sustained heat-treatment for up to 16 h resulted in nano-crystalline ultra-high temperature phases such as ZrB 2 , ZrC, LaB 6 and La 2 Zr 2 O 7 . Thermodynamic equilibrium phase calculations show that even longer durations of heat treatment may be required to achieve thermodynamic equilibrium. High-resolution transmission electron microscopy revealed encapsulation of nanocrystals (<5 nm) in an amorphous matrix surrounded by turbostratic layers of carbon inhibiting its growth. Spectrochemical techniques confirmed the presence of boron substituted carbon in the amorphous matrix of the ceramic. The unique nature of the amorphous matrix lends the ceramic resistance to crystallization and chemical degradation that can surpass the likes of classical silicon-based precursor-derived ceramics.

Incorporating phase behavior constraints in the multi-objective optimization of a warm vaporized solvent injection process

The warm vaporized solvent injection process has been proposed as a more environmentally friendly alternative to steam-based technologies for bitumen recovery. The process typically involves injecting heated solvent vapor into a horizontal injector; the solvent condenses and dissolves into bitumen, while the diluted oleic phase would flow towards a horizontal producer. Despite the promising results reported from several pilot projects near Fort McKay, Alberta, successful commercial-scale extraction is costly and would require a detailed optimization of the pertinent design variables. The main challenge is that this is a multi-objective optimization (MOO) problem, which aims to balance the trade-offs between conflicting performance objectives while honoring the various operational constraints. In this study, a systematic workflow is formulated to optimize these multiple conflicting performance objectives considering phase behavior constraints. A 2D synthetic model based on typical Athabasca oil sands properties is constructed to simulate the warm vaporized solvent process. The addition of non-condensable gas (methane) into the solvent (propane) is examined. The resultant changes in thermodynamic properties and equilibrium phase behavior are considered in determining the practical limits of the decision variables (e.g., bottom-hole injection pressure and temperature). The objective functions, including oil recovery factor, solvent retained-to-oil ratio, and energy consumption, are defined, and a factorial experimental design is employed to identify a subset of decision variables that exhibit minimal redundancy internally and create the dataset for proxy model development. To reduce the computational costs associated with reservoir simulations, proxy models, e.g., the artificial neural network (ANN), is developed and applied. Finally, a Pareto-based MOO scheme is implemented to estimate the optimal decision variables. Despite the higher front-end loading requirement of the ANN proxy modeling, the MOO with proxy modeling still requires significantly less execution/running time as compared to a MOO with traditional flow simulation (e.g., a 97% reduction in CPU time). This reduced running time is important for alleviating the computational load when evaluating the objective functions during the optimization process. More importantly, this optimization scheme is capable of identifying a set of optimal decision variables. This work presents a practical workflow for optimizing various design variables associated with many solvent-based bitumen recovery processes. Specific considerations including the practical limits for operating constraints and computational efficiency are examined and incorporated. It is anticipated that this workflow can be readily integrated into the design and decision-making processes in reservoir management.

Crystallization of hydrogenated biodiesel–ethanol–diesel blend based on the solid–liquid equilibrium theory

AbstractHydrogenated biodiesel–ethanol–diesel is a novel ternary fuel blend containing easily volatile, moderately volatile, and hardly volatile components. In this study, based on the thermodynamic phase equilibrium, a model was established to depict the phase transition under changeable pressure and temperature conditions. The crystallization behavior of hydrogenated biodiesel–ethanol–diesel ternary blends was estimated, and the influence of ethanol on the low temperature performance of ternary blends was interpreted in contrast to that of hydrogenated biodiesel–diesel binary blends. It was revealed that the crystallization points of ternary blends such as PHC5E5 (5% partially hydrogenated cottonseed biodiesel + 5% ethanol + 90% diesel), PHC10E10 (10% partially hydrogenated cottonseed biodiesel + 10% ethanol + 80% diesel), and PHC15E15 (15% partially hydrogenated cottonseed biodiesel + 15% ethanol + 70% diesel) were reduced by 4.5 K, 5.7 K and 6.1 K respectively as compared with their countering binary blends. Declines of 4.3 K, 5.3 K and 6.1 K in crystallization points were also demonstrated between partially hydrogenated soybean biodiesel ternary blends and binary blends. Meanwhile, apparent drops in crystallization quantities were perceived between ternary blends and binary blends under different temperatures. The role of ethanol affecting the crystallization of ternary blends was then comprehensively analyzed. At the onset of crystallization, ethanol was simultaneously precipitated in a eutectic manner with compositions of high melting point, impeding the tendency of nucleation and lagging the growth of solid crystals. In addition, most of non‐crystallized ethanol distributed in liquid fuel as well as the interstices of the network and the plate crystal. It beneficially increased the solubility of the crystalline composition in the base liquid to some extent. That is to say, the crystallization points and crystallization quantities were evaluated based on the solid–liquid equilibrium theory, which can provide an effective and reliable method for optimizing the low temperature performance of hydrogenated biodiesel.

Liquid-jet instability at high pressures with real-fluid interface thermodynamics

The injection of liquid fuel at supercritical pressures is a relevant topic in combustion but is usually overlooked. In the past, the wrong assumption whereby the liquid phase undergoes a fast transition to a supercritical state was made, thus neglecting any role of two-phase interface dynamics in the early stages of the atomization process. However, recent studies have shown that local thermodynamic phase equilibrium and mixing between the involved species allow the coexistence of both phases in this pressure range. In this work, a volume-of-fluid method adapted to variable-density real fluids is used to solve the low-Mach-number governing equations coupled with a thermodynamic model based on the Soave–Redlich–Kwong equation of state. The mixing process, interface thermodynamics, and early deformation of a cool liquid jet composed of n-decane surrounded by a hotter gas composed of oxygen at 150 bar are analyzed. Although heat conducts from the hotter gas into the liquid, net condensation can provide the proper local energy balance at high pressures. Then, vaporization and condensation may happen simultaneously at different interface locations. As pressure increases, liquid and gas mixtures become more alike in the vicinity of the interface. Thus, a combination of low surface tension force and gas-like liquid viscosities causes an early growth of surface instabilities. Early results indicate some similarity with high-Weber-number incompressible flows. The role of vortex dynamics on the interface deformation is analyzed by using the λρ dynamical vortex identification method.

Superancillary Equations for Cubic Equations of State

Calculation of thermodynamic phase equilibrium is error-prone and can fail both near the critical point and at very low temperatures because of the limited precision available in double precision arithmetic. Most importantly, these calculations frequently represent a computational bottleneck. In this work, we extend the “superancillary” equation approach developed for reference multiparameter equations of state to classical cubic equations of state (van der Waals, Redlich–Kwong–Soave, Peng–Robinson). Iterative calculations in double precision are replaced by noniterative evaluation of prebuilt Chebyshev expansions constructed with extended precision arithmetic. Exact solutions for the equation of state constants are given. The Chebyshev expansions are shown to reproduce the equation of state values to within nearly double precision (aside from in the very near vicinity of the critical point) and are more than 40 times faster to evaluate than the VLE calculations from the fastest computational library. In this way we further expand the domains in which iterative calculations for pure fluid phase equilibria may be rendered obsolete. A C++ header implementing these expansions (and with no external dependencies) is provided as deposited data.

Fly Ash–Ca(OH)2 Reactivity in Hypersaline NaCl and CaCl2 Brines

The disposal of highly concentrated brines from coal power generation can be effectively accomplished by physical solidification and chemical stabilization (S&S) processes that utilize fly ashes as a reactant. Herein, pozzolanic fly ashes are typically combined with calcium-based additives to achieve S&S. While the reactions of fly ash–(cement)–water systems have been extensively studied, the reactivity of fly ashes in hypersaline brines (ionic strength, Im > 1 mol/L) is comparatively less understood. Therefore, the interactions of a Class C (Ca-rich) fly ash and a Class F (Ca-poor) fly ash were examined in the presence of Ca(OH)2, and their thermodynamic phase equilibria were modeled on contact with NaCl or CaCl2 brines for 0 ≤ Im ≤ 7.5 mol/L. At low ionic strengths (<0.3 mol/L), reactivity and stable phase assemblages remain effectively unaltered. However, at high(er) ionic strengths (>0.5 mol/L), the phase assemblage shows a particular abundance of Cl-AFm compounds (i.e., Kuzel’s and Friedel’s salts). Although formation of Kuzel’s and Friedel’s salts enhances the Class F fly ash reactions in both NaCl and CaCl2 brines, NaCl brines compromise Class C fly ash reactivity substantially, while CaCl2 results in the reactivity remaining essentially unchanged. Thermodynamic modeling that accounts for the fractional and noncongruent dissolution of the fly ashes indicates that their differences in reaction behavior are provoked by differences in the prevalent pore solution pH, which affects phase stability. The outcomes offer new insights for matching fly ashes, Ca additives, and brines, and accounting for and controlling fly ash–brine interactions as relevant to optimizing physical solidification and chemical stabilization applications.

Thermodynamics of phase equilibrium in solid-liquid and solid-gas systems

The thermodynamic equilibrium of a two-phase system is described by the Gibbs equation, which includes state parameters. On the basis of the Gibbs equation and the combined equation of the first and second laws of thermodynamics, thermodynamic potentials are written: internal energy, enthalpy and Gibbs free energy. If the two phases are in equilibrium, then the temperatures, pressures and chemical potentials of these phases are equal to each other. Equalities express the conditions of thermal and mechanical equilibrium, as well as the condition for the absence of a driving force for the transfer of a component across the interface. For a two-phase system, the Gibbs-Duhem equation connects the volume and entropy of 1 mole of the mixture, the content of any component, expressed in mole fractions. Extraction from lupine particles with cheese whey (solid-liquid system) is considered. The driving force of the extraction process in the solid-liquid system is the difference between the concentration of the solvent at the surface of the solid C and its average concentration C0 in the bulk of the solution. The concentration at the interface is usually taken to be equal to the concentration of a saturated solution of Cn, since equilibrium is established rather quickly near the surface of a solid. Then the driving force of the process is expressed as Cn – C0. A curve for the extraction of extractives from lupine with cheese whey was plotted by superimposing low-frequency mechanical vibrations.

Solubility determination and thermodynamic modeling of bis-2-hydroxyethyl terephthalate (BHET) in different solvents

Studies on the degradation process of waste polyethylene terephthalate (PET) have become increasingly mature, but there are relatively few studies on the separation of degradation products. The products contain many components and the separation of which is difficult. Therefore, the study on phase equilibrium thermodynamics of bis-2-hydroxyethyl terephthalate (BHET) is of great theoretical significance and practical value to provide basic data for the BHET crystallization separation. In this work, the degraded products were purified and characterized. The solubility of BHET in methanol, ethanol, ethylene glycol, water and the mixture of ethylene glycol + water were determined by static method. The experimental results were correlated with different models, such as ideal solution (IS) model, λh equation, Apelblat equation and NRTL model. Based on the van't Hoff equation, the mixing Gibbs energy, enthalpy and entropy were calculated. From this work, the basic data which can be used to guide the crystallization process of BHET were obtained, including solubility data, correlation model and thermodynamic properties.

Recovering P–T–t paths from ultra-high temperature (UHT) felsic orthogneiss: An example from the Southern Brasília Orogen, Brazil

Mineral assemblages that are diagnostic of ultrahigh-temperature (>900 °C) metamorphism are generally restricted to Mg- and Al-rich rocks. However, in many metamorphic terrains such compositions do not occur, and the rocks are dominated by orthogneisses that typically contain high-variance mineral assemblages that are not diagnostic of particular pressure–temperature (P–T) conditions. Here we use whole-rock and mineral chemistry, thermodynamic phase equilibrium modelling, and zircon U–Pb–Hf isotopic data to constrain the P–T–time history of granulites from the Socorro-Guaxupé Nappe of the Southern Brasília Orogen. These rocks occur as part of a stack of Neoproterozoic nappes that were assembled during the formation of West Gondwana. Based on phase equilibrium modelling, the peak assemblage in a garnet-bearing felsic granulite (ortho- and clinopyroxene, garnet, K-feldspar, plagioclase, quartz, ilmenite, and silicate melt) records pressures of around 11.5 kbar and temperatures of ~1000 °C, consistent with the high-Al content of orthopyroxene. The retrograde path records a small decrease in pressure to 9 kbar marked by orthopyroxene replacing garnet and the exsolution of magnetite from ilmenite followed by near-isobaric cooling that led to the development of coronas of hornblende around pyroxene due to crystallization of the last vestiges of melt. Zircon cores yielding U–Pb ages of ca. 625 Ma are interpreted as dating close-to-peak conditions during high-temperature metamorphism. In one sample, zircon rims and ‘soccer ball’ zircon neoblasts both have high U contents and yield ages of ca. 615 Ma, interpreted to mark the onset of melt crystallization. In two other samples, low-U rims and ‘soccer ball’ zircons grains yield ages of ca. 600–595 Ma, interpreted to date the end of melt crystallization. These data reveal a protracted regional metamorphic event in which the lower crust remained at granulite-facies conditions for at least 30 Myr during collision and assembly of West Gondwana.

Thermodynamic modeling and phase diagram prediction of salt lake brine systems II. Aqueous Li+-Na+-K+-SO42− and its subsystems

Predicted result of complete structure phase diagram of Li 2 SO 4 -Na 2 SO 4 -H 2 O system at temperature ranging from eutectic point 251.19–373.15 K: P1, P2, P3, P4, P5 are Transition points of three solid co-saturated in the ternary system. • Thermodynamic model of aqueous Li+-Na+-K+-SO 4 2− systems across entire temperature range. • Predicting the polythermal full structure phase diagram of ternary and quaternary aqueous system.. • The multi-objective optimization method to obtain solid constants and liquid parameters. It is still a challenging task to accurately and temperature-continuously express the thermodynamic properties and phase equilibrium behaviors of the salt-lake brine with multi-component, multi-temperature and high concentration. The essential subsystem of sulfate type brine, aqueous Li + -Na + -K + -SO 4 2− and its subsystems across a temperature range from 250 K to 643 K are investigated with the improved comprehensive thermodynamic model. Liquid parameters ( Δ g IJ , Δ h IJ , and Δ C p , I J ) associated with the contributions of Gibbs energy, enthalpy, and heat capacity to the binary interaction parameters, i . e . the temperature coefficients of eNRTL parameters formulated with a Gibbs Helmholtz expression, are determined via multi-objective optimization method. The solid constants Δ f G k ° ( 298.15 ) and Δ f H k ° ( 298.15 ) of 11 solid species occurred in the quaternary system are rebuilt from multi-temperature solubilities. The modeling results show the accurate representation of (1) solution properties and binary phase diagram at temperature ranges from eutectic points to 643 K; (2) isothermal phase diagrams for Li 2 SO 4 -Na 2 SO 4 -H 2 O, Li 2 SO 4 -K 2 SO 4 -H 2 O and Na 2 SO 4 -K 2 SO 4 -H 2 O ternary systems. The predicted results of complete structure and polythermal phase diagram of ternary systems and the isothermal phase diagrams of quaternary system excellently match with the experimental data.

Thermodynamic phase equilibrium of single-guest hydrate and formation data of hydrate in presence of chemical additives: a review

The present work deals with a review of single-guest hydrate phase equilibrium data and also hydrate equilibrium in presence of chemical additives, which operate as inhibitors, promoters, or both together. In the recent years, a very limited number of data collections on hydrate equilibrium has been produced; moreover, these data have not been fully reported in these works, making further research necessary to obtain complete information. We provide a detailed collection of the equilibrium data of hydrate containing single guest as CH4, C2H6, C3H8, C4H10, CO2, N2, Xe, Ar and Kr and a brief review of las-scale reactors nowadays used for making research on gas hydrate. These two kinds of information, will be extremely helpful for researchers which are planning to realize a new experimental apparatus for studying gas hydrate. It is well known how, rather than process parameters (i.e. pressure, temperature, presence of a porous medium and its permeability and porosity, presence of impurities, and so on), also specifics of each reactor may strongly intervene on formation results. The second part of this work consists in a collection of the thermodynamic equilibrium data of hydrate in the presence of additives. Some substances are known to be selective inhibitors (promoters); other compounds have greater efficiency when coupled to further chemicals while, in some cases, such coupling can cancel the inhibitory (or promoter) effect. Finally, a state of the art of hydrate equilibrium experiments carried out with methane and carbon dioxide, with a simultaneous presence of inhibitors and promoters, was provided.

Phase equilibria thermodynamics and solidified microstructure in the Ag-Cr-Zr system

Ag-Cr-Zr alloy is a promising Zr-based alloy with excellent strength and hardness. Lack of investigations on phase equilibria and solidified microstructure of the Ag-Cr-Zr system limits the design of high-performance Zr-based alloys. Solidified microstructure and phase transition temperature in the Ag-Cr-Zr system are experimentally investigated using scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry. The microstructure of the ca-cast Ag-Cr-Zr is investigated in detail, and a liquid miscibility gap extending from Ag-Cr binary system is measured. The phase transition temperatures along three vertical sections are determined. Based on these experimental results and critical literature review, a thermodynamic modeling of the Ag-Cr and Ag-Cr-Zr systems was constructed by CALPHAD method, and the calculated phase diagram is in accordance with the experimental data. Besides, the Scheil solidification is simulated and the simulated results agree with the observed solidified microstructure. The reaction scheme for the whole Ag-Cr-Zr ternary system is calculated for the first time. This work not only fills in the gap in the thermodynamic description of the Ag-Cr-Zr system, but also provides a hybrid approach of thermodynamic calculations and key experiments for the sake of obtaining the desired solidified microstructure.

EOCENE MAGMA PLUMBING SYSTEM BENEATH CORTEZ HILLS CARLIN-TYPE GOLD DEPOSIT, NEVADA: IS THERE A DEEP-SEATED PLUTON?

Abstract The magmatic-hydrothermal conceptual model for Carlin-type gold deposit genesis calls upon deep-seated Eocene plutons as the primary source of gold-bearing fluids. However, geophysical surveys, geologic mapping, drilling, geochronology, isotopic tracers, and fluid inclusion chemistry have returned ambiguous evidence for the existence of such plutons. The high-grade Cortez Hills gold deposit in northern Nevada hosts shallow, Eocene syn- and postmineralization intrusions, offering an ideal site to investigate the existence of a deep-seated pluton beneath the district. Here, major and trace element analyses of quartz-hosted melt inclusions from four Eocene rhyolite dikes cropping out within the Cortez Hills pit and results from independent thermobarometers provide a window into the subsurface Eocene magmatic plumbing system to test the existence of a deep-seated source pluton. Dissolved volatile contents, melt inclusion entrapment pressures, and thermodynamic phase equilibria indicate that dike magmas were sourced from ~4- to ≥9-km depth from a polybaric magma reservoir residing as a physically and geochemically interconnected crystal mush with extractable or eruptible magma pockets. Magmas ascended adiabatically (nearly isothermally), exsolving fluids, evolving modestly by fractional crystallization, while trapping quartz-hosted melt inclusions steadily from depth to subvolcanic levels where they were emplaced. These data represent the first unequivocal evidence for a deep-seated magma reservoir from which fluid-saturated magma emanated and released magmatic fluids beneath the Cortez district during gold mineralization. However, further investigation into the specific metallogenic potential and metal budget of parental magmas and the partitioning of gold between silicate melt and aqueous fluids will be necessary to provide evidence that exsolved magmatic fluids may have been gold bearing.

Study of the Comprehensive Kinetic Model of Natural Gas Hydrate Formation in a Water-in-Oil Emulsion Flow System.

Hydrate growth is influenced by many factors, including thermodynamics, kinetics, mass and heat transfer, and so on. There is thus a practical significance in establishing a model that comprehensively considers these influencing factors for hydrate crystal growth in multiphase transportation pipelines. On this basis, this paper presents a more practical and comprehensive bidirectional growth model of hydrate shells for an actual pipeline system. Thermodynamic phase equilibrium theory and water molecule penetration theory are applied in this model to develop a method for calculating the concentration change of hydrate-forming guest molecules and the permeation rate of water molecules. The temperatures on both sides of the hydrate shell are predicted by the heat transfer model. Simultaneously, decreasing the mass transfer coefficient with continuous hydrate growth is used to describe the problem in which the mass transfer efficiency decreases with a thickened hydrate shell. Then, the hydrate growth kinetic parameters of the pipeline system are optimized according to hydrate growth experiments conducted in a high-pressure flow loop and the microscopic characteristics of the particles were provided using the PVM and FBRM probes. The improved hydrate growth model can improve the prediction accuracy of hydrate formation in slurry systems.