Simulation Of Phase Equilibria Research Articles

Crustal remelting origin of highly silicic magmatism on the Moon

Orbital observations of non-mare, highly silicic volcanic constructs on the Moon challenge the conventional view of the formation of silicic crusts in the presence of water and plate tectonics—the former the Moon has in very short supply and the latter it likely never ever had. Revealing the silica-rich magma origin may reshape our understanding of early planetary crust formation. However, the cause of lunar silicic magmatism remains enigmatic. Here we conduct phase equilibrium simulations for potential lunar igneous lithologies that demonstrate that the compositions of silicic volcanic constructs can be produced by partial melting of KREEP (potassium, rare earth elements, and phosphorus) basalts. Either internal radiogenic heating or external impact bombardment can provide the heat needed for KREEP basalt melting. Combined with silica-rich materials identified on other rocky planets, we suggest that highly evolved crusts might be more prevalent in the early solar system than anticipated as they can originate from crustal remelting in the absence of water and plate tectonics.

Lattice Boltzmann simulation of phase equilibrium of methane in nanopores under effects of adsorption

Owing to the strong interaction between fluid molecules and solid surface, thermodynamic phase behavior of fluids in nanopores deviates from that at bulk condition. In this work, a pseudopotential lattice Boltzmann method is employed to directly model phase equilibrium of methane in nanopores. The effects of adsorption and fluid–solid force on confined phase behavior are studied. In the absence of solid walls, our simulation of nanoscale droplets is consistent with prediction from thermodynamic model coupling Peng-Robinson equation of state and capillary pressure. The shifted phase equilibrium is compared with Kelvin equation. When the pore space is confined by solid walls, heterogeneous density distributions in nanopores are developed by adsorption. It is observed that the apparent critical temperature and critical pressure decrease whereas critical density increases in nanopores from the simulated co-existence curves. In addition, it is found that a larger fluid–solid force leads to a more heterogeneous density distribution in nanopores. However, the average liquid/vapor density and apparent critical temperature in confined space are not significantly affected by the strength of fluid–solid force. Density of gas in equilibrium with condensed liquid, on the other hand, is significantly decreased with increasing fluid–solid force. We propose that the phase equilibrium in nanopores under different fluid–solid forces can be characterized by using contact angle. In the end, we extend this method to model the phase equilibrium in a nanoporous medium with chemical heterogeneity.

Thermodynamic analysis and molecular dynamic simulation of solid-liquid phase equilibrium of imazapyr in twelve pure organic solvents

In this work, we determined the solubility of imazapyr in twelve mono organic solvents by gravimetric method over the temperature ranging from 283.15 K to 323.15 K at atmospheric pressure, and the results show that the equilibrium solubility is positively correlated with temperature in all solvents. Meanwhile, Hirshfeld surface analysis and molecular electrostatic potential surface were severally employed to probe into the intermolecular interactions and the overall charge distribution of imazapyr, the estimated results indicate that H···H and O···H contacts obviously predominate among all contact interactions and imazapyr has great hydrogen bonding donor and acceptor capacities. Besides, we investigated the effects of physicochemical properties of solvents on dissolution behaviors and found that solvent polarity plays a decisive role in the solubility of imazapyr in most cases. Molecular dynamic (MD) simulations were further applied to interpret the solute-solvent interactions behind different solubility behaviors of imazapyr. Additionally, the experimental solubility values were well correlated by the modified Apelblat equation, λh equation as well as NRTL model, respectively. And all of the ARD% values are less than 3%, indicating that the three thermodynamic models all achieve the perfect fitting performance. Finally, the mixing thermodynamic properties including ∆mixG0, ∆mixH0, and ∆mixS0 were calculated based on the NRTL model. The results suggest that the mixing process is spontaneous, exothermic and entropy driven as well.

Experimental study and theoretical simulation of fluid phase equilibrium in the subsystems of quinary system NaBr–KBr–MgBr2–SrBr2–H2O at 298 K

Abstract Underground brine known as one of special fluids existing in nature has been regarded as a kind of comprehensive mineral resource. After multi-step separation mining, it can realize the effective extraction and recovery of various mineral resources. Conducting a series of further studies on this kind of natural fluid, especially on the study of fluid phase equilibrium, will be of great significance to explore the rules of its geochemical evolution and formation, and to guide the follow-up fluid mineralization simulation. Based on the above considerations, stable phase equilibria and solubility data of unreported subsystems for quinary system NaBr–KBr–MgBr2–SrBr2–H2O at 298 K were determined by the method of isothermal dissolution equilibrium aiming at the compositions of the underground brine in western Sichuan Basin. The research contents in this work include two ternary systems (NaBr–SrBr2–H2O, KBr–SrBr2–H2O) and three quaternary systems (NaBr–KBr–SrBr2–H2O, NaBr–MgBr2–SrBr2–H2O, and KBr–MgBr2–SrBr2–H2O). The phase diagrams of listed above systems were all drawn by experimental data. The experimental results show that there are no solid solutions as well as any complex salts in the three ternary systems. These phase diagrams all contain two solid phase regions of crystallization, two isothermal dissolution curves and only one isothermal-isobaric invariant point. At 298 K, quaternary systems NaBr–KBr–SrBr2–H2O belongs to a simple type, and the phase diagram consists of only one isothermal-isobaric invariant point, three isothermal dissolution curves and three crystallization regions. In the phase diagram of quaternary system NaBr–MgBr2–SrBr2–H2O at 298 K, there are two isothermal-isobaric invariant points, five isothermal dissolution curves, and four crystallization regions. In the quaternary systems KBr–MgBr2–SrBr2–H2O at 298 K, it was found that one complex salt (KBr·MgBr2·6H2O) formed and the phase diagram has two isothermal-isobaric invariant points, five isothermal dissolution curves, and four crystallization regions. The solubilities of the above subsystems at 298 K were predicted accurately by referring to Pitzer's electrolyte solution theory. It was found that the predicted results were coincided basically with the experimental data.

Thermodynamic modeling of composition and propereties of self-fluxing materials based on the nickel

Self-fluxing nickel or cobalt-based alloys that use boron, phosphorus or silicon, as melting point depressants and fluxing agents are thermodynamic simulation of self-fluxing materials Ni-0.5C-15Cr-3.2Si-2B (PGSR-2) and Ni-1C-17Cr-4.1Si-3.6B (PGSR-4) was performed. As the software for simulation of phase and chemical equilibrium the TERRA software package was used. The simulation was carried out in the temperature range 300–3000 K at a total pressure P = 105 Pa in an argon atmosphere. The temperature dependences of the equilibrium composition and thermodynamic characteristics (enthalpy, entropy, and Gibbs energy) of the alloys of the investigated systems were calculated. It is shown that Ni, Cr, C, Ni3B, Ni2B, NiB, Ni2Si, NiSi, CrB, CrSi can be formed in the condensed phase under equilibrium heating of PGSR-2. When PGSR-4 is heated in the condensed phase, along with the above components, Cr5B3, CrB2 and Cr3C2 compounds can be formed. The temperature dependences of the thermodynamic characteristics of the systems studied have kinks that can be explained by phase transformations.

Thermodynamic analysis and molecular dynamic simulation of solid-liquid phase equilibrium of griseofulvin in three binary solvent systems

In this work, the solid-liquid phase equilibria of griseofulvin (GSF) in three binary solvent systems were investigated by both experimental and molecular dynamic simulation approaches. The equilibrium solubility of griseofulvin (GSF) in three binary solvent mixtures of isopropanol + acetone, isopropanol + 2-butanone, and isopropanol + 4-methyl-2-pentanone was determined by the gravimetric method at temperatures ranging from 283.15 K to 323.15 K under atmospheric pressure. The equilibrium solubility increases monotonously as the temperature increases at a given solvent composition or increases with increasing the solvent composition of good solvent acetone (2-butanone) in binary solvent mixtures, whereas there exists a maximum solubility value in isopropanol + 4-methyl-2-pentanone system. These solubility behaviors were found complying well with the empirical rule “like dissolves likes”. The experimental data were then correlated by the modified Apelblat equation, λh equation, modified Jouyban-Acree equation, and NRTL model, and the modified Apelblat equation receives the best fitting performance. Moreover, the thermodynamic functions including enthalpy, entropy, and Gibb free energy of mixing were derived and expectedly suggested an exothermic and spontaneous process of mixing. Molecular dynamic (MD) simulation was further employed to investigate the solute-solvent interactions behind the dissolution behaviors of griseofulvin. Radial distribution function (RDF) analysis reveals that the rank of solute-solvent interactions can be well correlated with solubility order in binary solvent mixtures and the intermolecular interactions between solute molecules and good solvent molecules are dominant. All the thermodynamic data and models presented here will certainly provide fundamental basis for designing and optimizing the crystallization of griseofulvin, a classic antifungal drug. Our MD simulation results are also helpful to understand the solid-liquid phase equilibrium behaviors in binary solvent systems.

Implementing Cyclopentane Hydrates Phase Equilibrium Data and Simulations in Brine Solutions

Cyclopentane hydrate-based salt removal is considered to be a possible promising technology for desalination. In order to optimize such processes, phase equilibrium data of cyclopentane hydrates (C...

Thermodynamic Simulation of the Phase Diagram of the Cu2O–Na2O–K2O System

Thermodynamic simulation of phase equilibria is carried out, allowing us to calculate the liquidus lines for the phase diagrams of the Cu2O–Na2O, Cu2O–K2O, and K2O–Na2O oxide binary systems, and also the liquidus surface of the Cu2O–Na2O–K2O ternary system. In the course of the work, the values of the model parameters used to calculate the activity of the oxide melts of the investigated systems are determined. The values of the activity of copper oxide and sodium oxide in the Cu2O–Na2O system for a temperature of 1250°C are calculated. The activity data are characterized by negative deviations from Raoult’s law. During the simulation, the enthalpy and entropy of the formation of a KNaO compound from the liquid components are estimated. According to the calculations, the liquidus surface of the phase diagram of the Cu2O–Na2O–K2O ternary system has two points of invariant equilibria.

Design and results of a first generation pilot plant for supercritical water desalination (SCWD)

A pilot plant of 5 kg/h based on the principle of supercritical water desalination (SCWD) has been designed, built and operated. The detailed design, operating procedures and performance of the plant is presented in this paper, along with the first results. Firstly, the plant has been tested for feed streams of 3.5 wt% NaCl to evaluate the stability and repeatability of the system, with the results indicating that mass balance closure is good and that reproducible results can be obtained. Furthermore, the results showed that 93% of the feed is recovered as fresh drinking water, which corresponds with expected results from phase equilibria simulations. The plant was further tested for higher feed concentrations of up to 16 wt% NaCl. For all feed concentrations, the NaCl concentration of the SCW was that of drinking water quality (<600 ppm). Experimentally, using a single stage separator, a concentrated brine (38 wt% NaCl) was obtained and calculations showed that with a two-stage flash-evaporation scheme, zero liquid discharge (ZLD) can be obtained. Further modifications to the plant and tests with other salt mixtures are recommended in order to advance to industrial application.

Process design and techno-economical analysis of hydrogen production by aqueous phase reforming of sorbitol

The present study was focused on detailed sorbitol aqueous phase reforming (APR) process design. Aspen HYSYS software was used to design a 500kg/h hydrogen production plant operation with sorbitol syrup as a feedstock. For reactor modelling a complex reaction network was taken into account along with phase equilibrium simulations which determined to have a significant impact on the total process heat due to possibility of water evaporation. The model was adjusted and verified using the experimental data with 1%Pt/Al2O3. The process optimization has included several conceptual improvements such as middle pressure steam co-generation and hot water recycle which can significantly decrease the operation costs. The total costs of hydrogen were estimated as 12.97$/kg, where feedstock costs take the major contribution of 91.8%. The most feasible way of making APR economical attractive is production of polyols from the lignocellulosic biomass.

Separation of a reaction mixture of ethyl acetate production via ethanol dehydrogenation

The simulation of phase equilibrium in a multicomponent reaction system of ethanol dehydrogenation process has been performed. The structure of the distillation diagram of this system has been found and its evolution during changes in pressure has been studied. An analysis of the diagram properties has made it possible to define the range of values of the operating parameters that allow for the separation of the reaction mixture in order to propose a structure of technological separation system and to carry out its parametric optimization.

Formation of Titanium Carbide Particles from Cu–Ti–C Metal MELT

Background: The relevance of this research is determined by the necessity of developing new hardened and high-conductivity alloys. Therefore, it aims at studying the possibility of producing disperse hardening carbide particles in a metal copper melt directly. Method: Fact Sage v.7.0 SW package (SGTE database) was used for the thermodynamic simulation of phase equilibria. Experimental work to review the results of interactions processes of a copper-titanium alloy and graphite was also conducted. Metal specimens of the Cu-Ti-C system were obtained during the experimental research. The shape and composition of produced non-metal inclusions were determined, while studying the experimental specimens using a scanning-electron microscope and electron microprobe analysis. Findings: A thermodynamic simulation of phase equilibria in the copper corner of the equilibrium diagram of a Cu-Ti-C system under the conditions of a copper-based liquid-alloy available in a temperature range of 1100 to 1500°С was done within the framework of this research. Simulation results are presented as a liquidus surface, specifying areas of existence of phases that are conjugated with the metal melt. According to our simulation, non-stoichiometric titanium carbide of variable composition will be a phase that is in equilibrium with the metal melt against significant titanium concentration in the copper liquid-alloy. It is found that non-metal inclusions in the experimental samples that were obtained under exposure of the metal melt in contact with graphite are represented by titanium carbide particles of the size 5 μm at most. Carbon to titanium ratio in the particles is C/Ti=0.76. No titanium carbides are produced, if the copper-titanium metal melt is poured into a graphite casting form. Improvements: Outputs may be used to analyze technological processes in copper and copper-based alloy production and to develop compositions of alloying compositions for metal matrix composite production.

Verification of ab-initio mixing enthalpy using thermodynamic simulation of phase equilibrium and the temperature dependences of the heat capacity of the bcc Fe- Cr alloys

The paper deals with application of physical-empirical models for the thermodynamic description of the bcc Fe-Cr alloys and phase equilibrium, as well as prediction of behavior of the temperature dependences of the specific heat of alloys. This approach allowed performing verification of ab-initio calculations results obtained by different authors for the mixing enthalpy at 0K which were used to assess the chemical part of the mixing enthalpy. Analysis of calculated phase diagram fragments and the temperature dependences of heat capacities for two alloy compositions and their comparison with experimental data, has allowed us to estimate the degree of reliability of various approximations used in ab-initio calculations, and thereby realize their verification for further practical use.

Direct Phase Equilibrium Simulations of NIPAM Oligomers in Water.

NIPAM (N-isopropylacrylamide)-based polymers in water show many interesting properties in experiments, including a lower critical solution temperature (LCST) at 305 K and a conformational transition of single chains at the same temperature. The results of many simulation studies suggest that standard force fields are able to describe the conformational transition and the phase equilibrium well. We show by performing long molecular dynamics simulations of the direct liquid-liquid phase equilibrium of NIPAM trimers in water that there is no LCST in the expected temperature range for any of the force fields under study. The results show further that the relaxation times of single-chain simulations are considerably longer than anticipated. Conformational transitions of single polymers can therefore not necessarily be used as surrogates for a real phase transition.

New petrological constraints on the last eruptive phase of the Sabatini Volcanic District (central Italy): Clues from mineralogy, geochemistry, and Sr–Nd isotopes

We report results from mineralogical, geochemical and isotopic analyses of the three youngest pyroclastic products (ca. 86 ky) belonging to the Sabatini Volcanic District (Roman Province, central Italy). By means of thermometers, hygrometers and oxygen barometers, we have estimated that the crystallization temperature of magma progressively decreases over time (910–740 °C), whereas the amount of water dissolved in the melt and f O 2 progressively increases as compositions of magmas become more differentiated (4.5–6.4 wt.% H 2 O and 0.4–2.6 ΔQFM buffer, respectively). Thermodynamic simulations of phase equilibria indicate that geochemical trends in mafic magmas (MgO > 4 wt.%) can be reproduced by abundant fractionation of olivine and clinopyroxene (~ 50 wt.% crystallization), while the trends of more evolved magmas (MgO ≤ 4 wt.%) originated by fractional crystallization of plagioclase and sanidine (~ 45 wt.% crystallization). The behavior of trace elements highlights that magmatic differentiation is controlled by polybaric differentiation that includes: (1) prolonged fractionation of mafic, anhydrous minerals from a primitive, H 2 O-poor magma at depth and (2) extraction of a more evolved, H 2 O-rich magma that crystallizes abundant felsic and subordinated hydrous minerals at shallow crustal levels. Assimilation and fractional crystallization modeling also reveal that magmas interacted with the carbonate rocks of the subvolcanic basement. The effect of carbonate assimilation accounts for both trace element and Sr–Nd isotopic variations in magmas, suggesting a maximum degree of carbonate assimilation of less than 5 wt.%. • We studied the youngest pyroclastic products of the Sabatini Volcanic District. • The crystallization temperature of magma progressively decreased over time, whereas the melt–water-content increased. • Trace element and isotope data indicate a multi-stage process controlled by assimilation and fractional crystallization.

Thermodynamic Characterization of Heavy Petroleum Fluids Using Group Contribution Methods

Application of an approach recently published [Carreon-Calderon et al. Ind. Eng. Chem. Res. 2012, 51, 14188–14198] to heavy petroleum fluids allows calculation of critical properties and molecular pseudostructures of their undefined fractions. This approach is based on group contribution methods, where classical thermodynamics is used as framework to assign functional groups to each undefined fraction by minimizing its free energy. The calculated properties are employed to determine parameters entering into cubic equations of state and their respective mixing rules requiring molecular structures. Thus, phase equilibrium simulations of heavy petroleum fluids were performed employing neither specific correlations nor parameters, reducing the impact of fluid models over the thermodynamic characterization. The results are in agreement with experimental results of petroleum fluids heavier than 14°API.

Phase Composition of a CrMo0.5NbTa0.5TiZr High Entropy Alloy: Comparison of Experimental and Simulated Data

Microstructure and phase composition of a CrMo0.5NbTa0.5TiZr high entropy alloy were studied in the as-solidified and heat treated conditions. In the as-solidified condition, the alloy consisted of two disordered BCC phases and an ordered cubic Laves phase. The BCC1 phase solidified in the form of dendrites enriched with Mo, Ta and Nb, and its volume fraction was 42%. The BCC2 and Laves phases solidified by the eutectic-type reaction, and their volume fractions were 27% and 31%, respectively. The BCC2 phase was enriched with Ti and Zr and the Laves phase was heavily enriched with Cr. After hot isostatic pressing at 1450 °C for 3 h, the BCC1 dendrites coagulated into round-shaped particles and their volume fraction increased to 67%. The volume fractions of the BCC2 and Laves phases decreased to 16% and 17%, respectively. After subsequent annealing at 1000 °C for 100 h, submicron-sized Laves particles precipitated inside the BCC1 phase, and the alloy consisted of 52% BCC1, 16% BCC2 and 32% Laves phases. Solidification and phase equilibrium simulations were conducted for the CrMo0.5NbTa0.5TiZr alloy using a thermodynamic database developed by CompuTherm LLC. Some discrepancies were found between the calculated and experimental results and the reasons for these discrepancies were discussed.

Prediction of perfluorohexane adsorption in BCR-704 zeolite via molecular simulation

The 7th Industrial Fluid Properties Simulation Challenge required prediction of the adsorption isotherm of perfluorohexane (PFH) in BCR-704 type faujasite at 293K over a relative pressure range from 0.01 to 0.8. For this purpose, the zeolite framework was reconstructed first by locating the extraframework Ca2+ ions. Next, the saturation pressure of PFH at 293K was estimated through a series of vapor–liquid phase equilibrium simulations in Gibbs and NPT ensembles. The resulting saturation pressure of 21.4kPa is in a very good agreement with the experimental value of 24kPa. The PFH adsorption isotherm was calculated via Monte Carlo simulations in fixed-pressure Gibbs ensemble. The calculated isotherm reproduced the experimental data satisfactorily, especially at lower relative pressures. Consequently, this work was awarded 1st runner-up for the challenge.

Phenomenological theory of phase diagrams with multicritical points

The breakup of multicritical points is studied in detail within the phenomenological theory of second-order phase transitions for a thermodynamic potential invariant with respect to the C3v (3m) group of transformations. The general conditions of this breakup are obtained and possible types of derived diagrams are plotted from a parent phase diagram containing a multicritical point. Examples of experimental phase diagrams are given that qualitatively confirm the results from theoretical and computer simulations of phase equilibria.

Thermodynamic Characterization of Undefined Petroleum Fractions using Group Contribution Methods

Properties of petroleum fractions of unknown composition, the so-called undefined petroleum fractions, are estimated using an approach based on group contribution methods. Using liquid density and molecular weight as experimental data and classical thermodynamics as framework, functional groups were assigned to each undefined fraction by minimizing its free energy. Thus, methods requiring molecular structures were used directly in phase equilibrium simulations of petroleum fluids. The proposed procedure also allows the critical properties of such undefined fractions to be calculated employing no specific correlations. The obtained results show reasonable accuracy concerning phase equilibrium experiments.