Phase Equilibria Research Articles

Crystallization behavior of BOF slag during the cooling process towards leaching for CO2 sequestration

This work addresses the crystallization behavior and microstructure feature of the molten basic oxygen furnace (BOF) slag during a slow cooling process. The aim is to provide a reference for the modification of BOF slag for subsequent leaching of Ca as part of CO2 sequestration. Integrated analysis of XRD, SEM-EDS, and thermodynamic calculations suggest a crystallization behavior of BOF slag during the cooling process. RO phases ((Mg, Fe, Mn) O) was the equilibrium phase at a high temperature of around 1600 °C, followed at lower temperatures by the formation of Ca3SiO5 (C3S) and α-Ca2SiO4 (α-C2S). The Ca2Fe2O5 (C2F) phase forms during the latter stages of melt solidification. On the basis of the combined analysis of the leaching test results and crystallographic analysis, a future direction of modification of BOF slag is suggested that enriches Ca into the C2S and hinders the formation of C2F. However, inhibiting the generation of C2F by adjusting the cooling process alone is difficult since its crystallization rate is fast. The phase of C2F was observed in XRD and SEM even if the BOF slag was quenched from 1600 °C. Furthermore, the chemical characterization and morphological evolution of the crystalline phase of molten BOF slag during the slow cooling process was observed.

Assessment of dissociation enthalpies of methane hydrates in the absence and presence of ionic liquids using the Clausius-Clapeyron approach

The Clausius-Clapeyron (CC) equation is generally preferred to obtain dissociation enthalpies (ΔH) of hydrate-forming systems due to its ease of use. The application of other direct and indirect methods becomes more problematic if complex additives such as ionic liquids (ILs) are also present in the system. In this work, around 400 equilibrium data points for methane hydrates in the presence of over 80 ILs were collected from the literature in the temperature and pressure ranges of (272.10 – 306.07) K and (2.48 – 100.34) MPa, respectively. The ΔH of methane hydrates in the absence and presence of ionic liquids (ILs) have been calculated using the CC equation. The compressibility factor (z), required to calculate ΔH at each phase equilibrium condition has been obtained from three different approaches viz., Peng-Robinson (PR) equation of state, Soave-Redlich-Kwong (SRK) equation of state and Pitzer (Pz) correlation. The results were compared to the experimentally reported dissociation enthalpy (54.5 ± 1.5 kJ.mol−1) of methane hydrates. The role of the compressibility factor along with the slope of the equilibrium data set and the temperature/pressure range in determining the outcome of the CC equation has been discussed. The effect of molar mass, molar volume, and hydrate suppression temperature of the ILs on the ΔH of methane hydrates has been explored. The tested ILs do not show a systematic and significant influence on enthalpies, rather they show a large scattering in the ΔH values, which might mask any existing subtle effect of the ILs on the dissociation enthalpies. Therefore, this approach should be dealt with care to obtain molecular-level insights.

Unveiling the high-pressure behavior of thymol+carvone NADES: A combined experimental-computational approach

this study considers the high-pressure behavior of thymol + carvone Natural Deep Eutectic Solvent using a combined experimental and computational approach. Experimentally, PVT (pressure – volume/density - temperature) measurements were conducted to characterize the fluid volumetric behavior as well as compressibility and internal pressure, which are directly related with hydrogen bonding and nanoscopic structuring. Likewise, these measurements provide crucial insights into the thermodynamic properties of the considered fluid under high pressure, which is pivotal for scaling up and process design for high pressure operations. Computationally, the PC-SAFT equation of state was employed to predict phase equilibria and PVT behavior, Machine Learning for density predictions, while Density Functional Theory and Classical Molecular Dynamics simulations were considered for the structural and dynamic characterization. These simulations provides insights into the electronic structure, intermolecular interactions (hydrogen bonding), liquid structuring and they unveil the pressure's impact on microscopic interactions, structural organization, and transport properties. This comprehensive investigation aims to shed light on the behavior under high pressure, facilitating their optimization for applications in chemical processing, energy storage, and materials science.

Integrated experimental and thermodynamic modelling study of phase equilibria in the “CuO0.5”-PbO-CaO system in equilibrium with Cu/Pb metal

Phase equilibria studies were undertaken on the “CuO0.5”-PbO-CaO system in equilibrium with Cu/Pb metal as part of the integrated experimental and thermodynamic modelling study of phase equilibria in the Cu-Pb-Zn-Fe-Ca-Si-Al-Mg-O-S-(As, Sn, Sb, Bi, Ag, Au, Ni, Cr, Co and Na) gas/oxide liquid/matte/speiss/metal/solids system in support of the development and optimisation of pyrometallurgical processes. The equilibration and quenching technique followed by the electron probe X-ray microanalysis (EPMA) was used in the present study. The primary phase fields of massicot (PbO), copper plumbite (Cu2PbO2), cuprite (Cu2O) and lime (CaO) were experimentally characterised. The experimental data obtained in the present study, as well as available literature data on the phase equilibria and thermodynamics of the “CuO0.5”-PbO-CaO system in equilibrium with Cu/Pb were used for the optimisation of the model parameters of the discussed system in agreement with the Cu-Pb-Zn-Fe-Ca-Si-Al-Mg-O-S-(As, Sn, Sb, Bi, Ag, Au, Ni, Cr, Co and Na) gas/oxide liquid/matte/speiss/metal/solids system to obtain a self-consistent set of parameters of the thermodynamic model for all phases. The predicted liquidus surface of the “CuO0.5”-PbO-CaO system was presented for the first time in the complete range of temperatures and compositions.

Phase Behavior of System Carbon Dioxide + Hydrogen Sulfide

The global phase equilibrium behavior of the CO2+H2S system is discussed in this work for temperatures ranging from 160 K up to the critical region. Solid phases of CO2 and H2S and corresponding equilibria have been modeled by considering either a 4th-order equation of state (also used for the fluid phases) or a solid fugacity model for the pure components combined with an activity coefficient model (both coupled with a reference equation of state for the fluid phases).Phase equilibrium calculations have been performed by the minimization of the Gibbs Free Energy of mixing and compared to existing literature data.The types of pressure-mole fraction phase diagrams that can be encountered in the low-temperature thermodynamic region have been described. The temperature and pressure ranges where the phase behavior of the system changes have been identified and a representative phase diagram is presented for each range.

Thermodynamic stability and component heterogeneity of CO2/N2 mixed hydrates: Implications for hydrate-based CO2 capture and sequestration

Injecting CO2/N2 into marine sediments to form gas hydrates for CO2 storage is an emerging Carbon Capture and Storage (CCS) technology, holding the potential to significantly reduce the costs of CCS while simultaneously enhancing environmental persistence. However, there is currently a lack of comprehensive investigation into the critical parameters and stability evaluations of CO2/N2 mixed hydrates (Mix-H) formation. This study delves into the impact of gas–liquid ratios, pressure–temperature gradients, and hydrate formation degree on the phase equilibrium, formation kinetics, and thermodynamic stability of Mix-H. Experimental findings elucidate the excess water significantly enhances CO2 dissolution, increasing the thermodynamic barrier for Mix-H formation. Consequently, this leads to weakened kinetics and reduced total CO2 composition within the Mix-H (54.2%–96.4%). Raman spectroscopy confirmed varying heterogeneous compositions and thermodynamic stability of hydrate crystals within the bulk Mix-H. The heterogeneity is quantitatively assessed using a novel test – stepwise depressurization, which revealed increased heterogeneity with decreasing initial pressure–temperature as well as increasing gas–liquid ratios and hydrate formation degree. The heterogeneity of Mix-H significantly impacts the CO2 capture efficiency and long–term stability of CO2 sequestration under environmental disturbances. The results also pave the way for evaluating the performance of mixed hydrate application in hydrate–based chemical engineering and CCS technology.

Phase equilibria and guest gas occupancy characteristics of H2-DIOX sII hydrates based on calorimetric and Raman analysis

Hydrogen (H2) as the most abundant element offers a clean energy solution for a sustainable future. Thermodynamic hydrate promoters can enhance hydrate-based H2 storage under mild pressure conditions. 1,3-dioxolane (DIOX) as a low-toxicity promoter has attracted attention for its potential to improve H2 hydrate kinetics. However, the phase equilibria of H2-DIOX in the presence of DIOX and its thermodynamic promotion mechanism are not fully elaborated and warrant thorough investigation. In this study, the phase equilibria of H2-DIOX hydrates were measured for DIOX concentrations (CDIOX) ranging from 2.0 mol% to 5.56 mol%. The equilibrium temperature of H2-DIOX hydrate shifted rightward by 2.3 K at 15.0 MPa for 5.56 mol% DIOX compared to 2.0 mol% DIOX. The measured thermodynamic data were validated by fitting the H2-DIOX hydrate phase equilibira using the Clausius-Clapeyron equation. The cage occupancy of H2 and DIOX in H2-DIOX sII hydrates was revealed through Raman spectroscopy and DSC thermal analysis. Two types of hydrates (DIOX and H2-DIOX) were observed for all CDIOX. Single H2 molecules were enclathrated in the 512 cages of H2-DIOX hydrates and increasing CDIOX effectively enhanced DIOX molecules enclathration in the 51264 cages but had limited effect on the H2 molecules in the 512 cages. The findings of this study provide fundametnal thermodynamic data and cage occupancy charateristics for H2-DIOX sII hydrates below 15.0 MPa. The results provide guidance on the optimal thermodynamic promoter concentrations for future large-scale hydrate-based H2 storage application.

Solid-liquid phase equilibria in the aqueous system containing the chlorides of potassium, ammonium, and calcium at 298.2, 323.2, and 348.2 K

In order to obtain the crystalline forms of the salts of the potassium, ammonium, calcium coexisting chloride system, the phase equilibria relationship of quaternary system K+, NH4+, Ca2+//Cl–-H2O at 298.2, 323.2, and 348.2 K was studied by isothermal dissolution equilibrium method. The solubility and density of equilibrium liquid phases of the system were experimentally determined; X-ray powder diffractometer was used to determine the compositions of the equilibrium solid phase at the quaternary invariant point. It is found that the quaternary system is a complex system at these three temperatures. The phase diagram at 298.2 K consists of three invariant points, seven univariate curves and five crystalline phase regions, forming the solid solutions (NH4Cl)x(KCl)1–x and (KCl)x(NH4Cl)1–x; while at 323.2 and 348.2 K the phase diagram consists of five invariant points, eleven univariate curves and seven crystalline phase regions, the double salts (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O), solid solutions (KCl)x(NH4Cl)1–x and (NH4Cl)x(KCl)1–x were formed. Among them, the crystalline phase region of solid solution (KCl)x(NH4Cl)1–x is the largest at three temperatures, indicating that it is the easiest to crystallize in this system. Comparing the phase diagrams of the quaternary system at 298.2, 323.2, and 348.2 K, it can be seen that the crystalline form of CaCl2 changes with the increase of temperature: CaCl2·6H2O at 298.2 K, CaCl2·2H2O at 323.2 and 348.2 K. From 323 to 348 K, the crystalline phase regions of (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O) increased gradually.

Phase equilibria and volumetric properties of mixtures of highly fluorinated alcohols and water

New thermodynamic data are reported for aqueous solutions of highly fluorinated alcohols of different chain lengths. The liquid-liquid equilibrium (LLE) T-x diagram of the binary mixture (1H,1H-perfluoropropanol + water) was determined, as well as the LLE phase diagram of the ternary mixture (1H,1H-perfluoropropanol + 1-propanol + water) at 298.15 K and atmospheric pressure. The mutual solubilities of water with several linear perfluorinated alcohols (CF3(CF2)nCH2OH, n = 1–5) and the tertiary alcohol perfluoro-t-butanol ((CF3)3COH) were also measured at 298.15 K. Finally, volumetric properties such as the excess molar volumes and partial molal volumes at infinite dilution of the different fluorinated alcohols in water were also determined and discussed comparing with equivalent data from the literature for the corresponding hydrogenated alcohols.

Prediction of Hydrate Formation in Supercritical CO2 Containing Impurities Long-Distance Transportation Pipelines with a Capacity of 0.36 Million t/a

Abstract Long-distance pipeline transportation is the most economical and feasible way to transport CO2. Hydrates can easily form during the transportation of supercritical CO2 containing impurities, leading to pipeline blockage. Therefore, accurate prediction of the deposition location and amount of hydrates in pipelines is crucial. This paper established a prediction model for hydrate growth in the long-distance CO2 transportation pipeline containing impurities. The phase equilibrium diagram and kinetic growth model were combined to simulate the formation behaviour of CO2 hydrate. The long-distance CO2 transportation pipeline of 0.36 million t/a in Yunlin was taken as an example. The results show that the volume of CO2 hydrate increased whereas the growth rate of CO2 hydrate gradually decreased with time. Hydrates begin to form in pipeline L11 at a distance of 35-44.3 km away from the inlet, whereas at a distance of 8.1 km away from the inlet for pipeline L12. The places with the highest amount of hydrate formation in both of the pipelines were at the end of pipelines. The area for hydrates formation in pipeline L12 was much longer than that in pipeline L11 due to the lower temperature. The cleaning cycle for pipeline L12 should be much shorter than that of pipeline L11. This paper will provide guidance for the operation of CO2 long distance pipelines.

A parallel compositional reservoir simulator for large-scale CO2 geological storage modeling and assessment

Storing CO2 in deep aquifers and depleted gas reservoirs is an effective way to achieve carbon neutrality. However, the numerical simulation of CO2 storage in these formations is challenging due to the complexity of gases-brine systems. The number of gas species included in the gases-brine fluid models of existing simulators cannot meet the rapidly evolving CO2 sequestration scenarios. To address this intricate issue, we developed a three-dimensional fully implicit parallel CO2 geological storage simulator (PRSI-CGCS) on distributed-memory computers based on our in-house parallel platform. This simulator uses a compositional fluid model with a diverse range of gas species, including CO2, C1 ~ C3, N2, H2S, as well as newly added gases H2 and O2, which may be encountered in geological CO2 storages. Besides, we provide more suitable scaling factors for different gases in the stability analysis bypassing (SAB) method to accelerate the gases-brine phase equilibrium calculations. PRSI-CGCS does not incorporate energy conservation equations, and salt precipitation or dissolution is also not considered. Numerical experiments show that our simulator is scalable, robust and validated to simulate large-scale CO2 storage problems with hundreds of millions of grid blocks on a parallel supercomputer cluster. Besides, after our modification on scaling factors, the SAB method can reduce the number of stability analyses by 61.39 % to 88.71 %, thereby reducing simulation time. Furthermore, case studies indicate that injecting O2 and H2 along with CO2 reduces the stability or capacity of CO2 storage and increases the pressure required for injection. However, this impact is not significant when the impurity content is less than 10 %.

Multi‐Stage Magmatism During Slab Exhumation Drives the Geochemical Evolution of Continental Crust: Insights From Paleozoic Granitoids in South Altyn, Western China

AbstractThe present continental crust is characterized by a felsic upper crust and a mafic lower crust, resulting from significant geochemical differentiation over geological time. While various processes have been proposed to explain this differentiation, subduction zones remain pivotal regions for understanding the compositional evolution of continental crust. This study focuses on the South Altyn (SA) continental subduction‐collision belt in western China, a unique setting that experienced ultra‐deep (>300 km) continental subduction followed by multi‐stage exhumation. We present a comprehensive study of four granitoid suites from Tatelekebulake (TTLK) area in SA: biotite granite (BG), monzogranite (MG), K‐feldspar granite (KG), and leucogranite (LG). Comprehensive studies on petrology, geochemistry and zircon U‐Pb dating show that these granitoids formed at 494, 451, 414, and 418 Ma, respectively, and originated from protoliths with affinity to the subducted continental crust in SA. Phase equilibrium modeling suggests that BG formed at ∼800°C and 0.6 GPa, while the MG, KG, and LG formed by differentiation crystallization of the BG magma under progressively decreasing temperature and pressure conditions (750°C, 0.5 GPa; 740–700°C, 0.2 GPa; and 700–640°C, 0.1 GPa, respectively). These results, combined with previous studies, allow us to reconstruct the tectonic processes of continental exhumation and subsequent orogenic collapse in SA during the Early Paleozoic. Importantly, our findings reveal that magmatism derived from partial melting of subducted continental crust can promote the geochemical evolution of continental crust toward more felsic compositions, even in the absence of significant crustal growth or mantle‐derived magmatism. This study provides a valuable case for understanding the compositional evolution of continental crust in deep subduction zones and challenges conventional models that rely heavily on arc magmatism for crustal differentiation. Moreover, our results contribute to a broader understanding of crustal evolution processes in collisional orogens worldwide and highlight the importance of recycling and differentiation of subducted continental material in shaping crustal compositions.

An experimental methodology to validate the use of hydroethanolic mixtures as suspending medium / modifier for the supercritical CO2 extraction of suspensions

We developed a methodology to study the extraction of high-value solutes directly from suspensions of finely disrupted substrates. For that, we modelled the high-pressure phase equilibrium for the ternary (CO2 + ethanol + water) system using experimental literature data. Different compositions of hydroethanolic mixture and CO2 were loaded into an extraction vessel set at 30–35MPa and 40–50 °C during static extraction, and a gaseous mixture with the composition of the CO2-rich gaseous phase in the extraction vessel was continuously fed during dynamic extraction. Losses of the fed hydroethanolic mixture occurred mainly during dynamic extraction (10-30wt%) and were properly distributed to account for actual flows and compositions of experimental streams. Mostly, equilibrium conditions were reached following about 1h of the 2-h dynamic extraction, and good reproducibility was achieved. In conclusion, equilibrium is reached in which two phases coexist in equilibrium within the extraction vessel: a water-rich liquid phase and a CO2-rich gaseous phase.

Phase equilibrium calculations at low and high pressures with a modified COSMO-SAC model

Phase equilibrium calculations at low and high pressures with a modified COSMO-SAC model

Calculation of critical endpoints and phase diagrams of highly asymmetric binary systems

The computation of Global Phase Equilibrium Diagrams (GPED) for binary systems, including critical and three-phase equilibrium curves, is crucial for analyzing process conditions and assessing thermodynamic models. In the past two decades, algorithmic strategies and GPEC software have become essential tools. However, numerical problems can arise with the original algorithm for highly asymmetric systems, such as gases or water with heavy compounds or polymers, hindering the completion of GPED and related diagrams.This study presents an innovative calculation methodology to address these challenges. Our approach extends existing algorithms to achieve automatic GPED generation without user intervention, focusing on nearly pure phases. We apply our methodology to systems such as methane or water with heavy alkanes, and CO2 + silicones. The proposed algorithmic strategies effectively handle asymmetric systems, different types of phase behavior, and the estimation of extremely low concentrations in nearly pure phases along the vapor-liquid-liquid equilibrium curve.

Selectivity and Phase Equilibrium Data for Extractive Distillation of Hexafluoropropylene from Its Oxide

Selectivity and Phase Equilibrium Data for Extractive Distillation of Hexafluoropropylene from Its Oxide

Hydrogen purification via hydrate-based methods: Insights into H2-CO2-CO hydrate structures, thermodynamics, and kinetics

Hydrate-based H2 purification is promising for removing impurities owing to the cage-like structures formed by water molecules. Understanding the competition mechanism of multicomponent gas molecule in hydrate is critical for improving gas purification efficiency. This study investigated the hydrate structure, thermodynamics, and kinetics of ternary gas mixture (H2–CO2–CO) from natural gas reforming products. The results identified H2–CO2–CO hydrate as type sI and determined the lattice parameters using X-ray diffraction. Raman spectroscopy results confirmed the presence of H2, CO2, and CO gas molecules in the hydrate phase. Increasing pressure, compared to cooling, enhanced CO2 content in hydrate phase. The phase equilibrium conditions and average hydrate dissociation enthalpy (53.47 J/g) were determined using a high-pressure microcalorimeter. Gas chromatography identified that the content of CO2 in the hydrate was the highest, followed by H2, and CO was the least abundant. The molecule dynamics simulation results show CO2 molecule numbers reflected trends in 51262 cages, H2 numbers correlated with changes in 512 cages, while CO numbers showed insignificant variation. Under the gas composition studied, the ability of gas molecules to be incorporated within hydrates decreases in the following order: CO2, H2, and CO.

Data-driven guided physics-informed segmented neural network for liquid–vapor flash calculation

Liquid–vapor phase equilibrium is ubiquitous in industrial and engineering field, which involves the flash calculation. The conventional flash calculation is solved with the numerical simulator, accompanying with large computational efforts. In this paper, we propose a data-driven guided physics-informed segmented neural network (DDG-PISNN) for the liquid–vapor pressure–temperature flash calculation. The training of DDG-PISNN is divided into two stages. First, a classifier for determining the stability of the system and a guiding network are built using data-driven methods. Subsequently, various control equations are employed to construct loss functions based on the results of classifier. In this way, DDG-PISNN fully leverages the advantages of data-driven approaches and physical equations. The accuracy and robustness of DDG-PISNN are calibrated by experiments under different conditions, and the performance is compared with that of DDG-PINN. In addition, a surrogate model for flash calculation is constructed based on DDG-PISNN. The accuracy of the surrogate model is also validated against a numerical case, and the computational efficiency is more than 800 times. Then, the surrogate model is embedded into the reservoir simulation technique to perform the flash calculation and form a surrogate-based compositional model. The surrogate-based model is employed to simulate the process of CO2 displacing crude oil. The results are in good agreement with the results of numerical solution.

A novel numerical simulation approach for cryogenic CO2 frosting in binary mixture gas by integrating desublimation and gas-solid phase equilibrium models

Cryogenic CO2 separation from natural gas is a promising technology due to its environmental benefits and smaller spatial requirement. Nonetheless, the dynamics of CO2 desublimation and subsequent frost layer formation under cryogenic conditions for natural gas pre-treatment remain largely unexplored. Addressing this gap, this paper presents a novel numerical simulation approach by integrating desublimation phase change model and vapor-solid phase equilibrium model to investigate CO2 frost layer formation on the cold wall, revealing that both the cold wall temperature and the initial CO2 concentration significantly influence the thickness of the CO2 frost layer. Moreover, the study finds that the density of frost layer intensifies over time, with the highest density observed near the cold surface. Furthermore, increasing the cold wall temperature and the flow rate not only increases the average density of the CO2 frost layer but also affects the outlet CO2 concentration. To adhere to specific outlet CO2 concentration targets and desublimation duration, it is critical to adjust the cold wall temperature and the inlet flow velocity dynamically. Therefore, cryogenic CO2 removal methods, by reducing the spatial requirements of CO2 pre-treatment units, offer a practical and efficient solution for small-scale natural gas liquefaction plants. This approach not only facilitates operational efficiency but also contributes to the broader effort of mitigating greenhouse gas emissions, aligning with environmental sustainability objectives.

Effect of alloying elements on coexisting phases and microstructure of M174 heat-resistant aluminum alloy

Abstract This article mainly focuses on high-power density diesel engine piston alloys, with the main component system being M174 heat-resistant aluminum alloy. On this basis, the main heat-resistant alloying elements Cu, Ni, and Fe were optimized and designed. This article is based on Thermo-Calc thermodynamic software, and comprehensively calculates and analyzes the multi-component alloy equilibrium phase diagram and Scheil non-equilibrium solidification of Al-(4-6)Cu-(1.5-3)Ni-(0.7-1.1Fe)-12.5Si-0.85Mg (mt.%) heat-resistant aluminum alloy system. Through the orthogonal experimental method of alloy composition, the phase distribution and microstructure composition of different alloy compositions are obtained. Research has found that Fe-rich phases such as Al5FeSi and Al9FeNi, as well as Ni-rich phases such as A13CuNi, A17Cu4Ni, and Al3Ni, are the main heat-resistant phases of the alloy in the temperature range of 350°C-420°C, providing important support for the high-temperature mechanical properties and creep damage resistance of piston aluminum alloy. At the same time, this article further studies the solidification history and microstructure precipitation of alloys. Fe-rich heat-resistant phases such as Al5FeSi and Al9FeNi have a higher solidification sequence. As primary and secondary phases, it is easy to generate coarse solidified structures. The organizational content is sensitive to the alloy composition. A13CuNi and A17Cu4Ni mainly precipitate in a multi-component eutectic structure, with layered and petal-shaped morphologies. The research results of this article have important theoretical significance and application value for the optimization design of high-power density piston aluminum alloy composition and the coordinated control of multi-phase structure.