Phase behavior in binary and ternary water-salt systems at high temperatures and pressures

DISQUAC predictions on thermodynamic properties of ternary and higher multicomponent mixtures: I. Results for total pressure measurements at isothermal conditions of ternary systems

Ionic liquids (ILs) are important new solvents proposed for applications in different separation processes. Herein, an idea of possible use of high pressure in a general strategy of production of 2-phenylethanol (PEA) is discussed. In this work, we present the influence of pressure on the density in binary systems of {1-hexyl-1-methylpyrrolidynium bis{(trifluoromethyl)sulfonyl}imide, [HMPYR][NTf2], or 1-dodecyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [DoMIM][NTf2] + PEA} in a wide range of temperatures (298.15-348.15 K) and pressures (0.1-40 MPa). The densities at ambient and high pressures are measured to present the physicochemical properties of the ILs used in the process of separation of PEA from aqueous phase. The Tait equation was used for the correlation of density of one-component and two-component systems as a function of mole fraction, temperature, and pressure. The influence of pressure is not significant. These systems exhibit mainly negative molar excess volumes, VE. The solid-liquid phase equilibrium (SLE) of [DoMIM][NTf2] in PEA at atmospheric pressure was measured and compared to the SLE high-pressure results. Additionally, the ternary liquid-liquid phase equilibrium (LLE) at ambient pressure in the {[DoMIM][NTf2] (1) + PEA (2) + water (3)} at temperature T = 308.15 K was investigated. The solubility of water in the [DoMIM][NTf2] is quite high in comparison with that measured by us earlier for ILs ( x3 = 0.403) at T = 308.15 K, which results in not very successful average selectivity of extraction of PEA from the aqueous phase. The [DoMIM][NTf2] has shown strong interaction with PEA without the immiscibility region. The ternary system revealed Treybal's type phase equilibrium in which two partially miscible binaries ([DoMIM][NTf2] + water) and (PEA + water) exist. From the results of LLE in the ternary system, the selectivity and the solute distribution ratio of separation of water/PEA were calculated and compared to the results obtained for the ILs measured earlier by us. The popular NRTL model was used to correlate the experimental tie-lines in ternary LLE. These results may help in a new technological project of "in situ" extraction of PEA from aqueous phase during the biosynthesis.

A new method is developed to represent the phase behavior of multicomponent systems. This method uses fewer pseudocomponents than true components, but unlike conventional methods in which pseudocomponents are often chosen arbitrarily, the pseudocomponents are often chosen arbitrarily, the method uses regression analysis to find a "best" set of pseudocomponents.The method is applied to two surfactant systems of the type used for tertiary oil recovery. One system contains a crude oil (from the North Burbank Unit, Osage County, OK) and the other contains a pure hydrocarbon, 1-phenyltetradecane. For both systems the representation in terms of the pseudocomponents chosen by the regression analysis is significantly more faithful than that obtained by conventional methods.Since the considerations discussed here are general, they should be applicable to a wide range of phase studies in multicomponent systems. For example, they should be illuminating when applied to oil recovery by gas injection (carbon dioxide, natural gas, etc.), and to extraction processes, as well as to surfactant systems. Introduction Systems containing surface active agents have attracted a great deal of attention in connection with tertiary oil recovery. In many of these systems optimum oil recovery has been found to be strongly correlated with the phase behavior of these systems. To understand completely the basis for these correlations, one must be able to represent the phase behavior of systems containing surfactants adequately.Surfactant systems for tertiary oil recovery usually contain at least five components: oil, water, surfactant. cosurfactant, and electrolyte. The isothermal, isobaric phase diagram of these systems can be represented in a phase diagram of these systems can be represented in a four-dimensional space. Because physical representation (in three dimensions) of such a diagram is impossible. various techniques have been developed to attempt to represent the phase behavior in lower dimensional spaces. All these techniques correspond to projections of the original diagram onto lower dimensional spaces. Although almost unlimited methods of projection exist, only a small fraction convey useful information.Two projection schemes having some similarities but different intents and consequences are straight mathematical projection and "pseudocomponent" projection. Straight mathematical projection refers to the process of directly projecting the four-dimensional data for the entire phase diagram along some specified direction onto a three-dimensional space. All information parallel to the direction of the projection is lost. For example, if the rays of projections are parallel to the oil/water edge of the phase diagram, the resulting representation contains no information about the relative amounts of oil and water in the phases. In principle, this problem can be circumvented by generating two representations corresponding to projections of the same data along two different directions. For example. a second representation could be produced corresponding to a projection parallel to the water/alcohol edge of the phase diagram. parallel to the water/alcohol edge of the phase diagram. Although neither representation contains complete information, the pair of representations does contain all information about the system. The problem with this method is that the information is not perceived easily and, since the intent of using phase diagrams is usually to make visible a summary of the phase trends, such mathematical representations are not very useful.The second and generally more useful projection scheme uses pseudocomponents. A pseudocomponent is some mixture of pure components treated as a single component. SPEJ P. 289

A binary ionic liquid (IL) system based on a common cation, N-methyl-N-propylpyrrolidinium (C(3) mpyr(+)), and either bis(trifluoromethanesulfonyl)imide (NTf(2) (-)) or bis(fluorosulfonyl) imide (FSI(-) as the anion is explored over its entire composition range. Phase behavior, determined by DSC, shows the presence of a eutectic temperature at 247 K and composition around an anion ratio of 2:1 (FSI(-) :NTf(2)(-)) with the phase diagram for this system proposed (under the thermal conditions used). Importantly for electrochemical devices, the single phase melting transition at the eutectic is well below ambient temperatures (247 K). To investigate the effect of such anion mixing on the lithium ion speciation, conductivity and PFG-NMR diffusion measurements were performed in both the binary IL system as well as the Li-NTf(2) -containing ternary system. The addition of the lithium salt to the mixed IL system resulted in a decrease in conductivity, as is commonly observed in the single-component IL systems. For a fixed lithium salt composition, both conductivity and ion diffusion have linear behaviour as a function of the anion ratio, however, the rate of change of the diffusion coefficient seems greater in the presence of lithium. From the application point of view, the addition of the FSI(-) to the NTf(2)(-) IL results in a considerable increase in lithium ion diffusivity at room temperature and no evidence of additional complex ion behaviour.

We employ the PBC-GEBF-AL workflow, integrating active learning (AL), the linear-scaling generalized energy-based fragmentation approach under periodic boundary conditions (PBC-GEBF), and multiTPU-OPES enhanced sampling, to create a PBE0-D3(BJ)/aug-cc-pVDZ-accuracy machine learning potential for studying the carbon dioxide (CO2) molecular crystal phase diagram. Based on up to 170ns MLP-based multiTPU-OPES simulations, we obtain the phase diagram across a wide temperature range (250-700K) and pressure range (10.5-14.0GPa). It suggests a CO2-I/III coexistence line peaks at ∼12.3GPa, 525K, with a negative slope at higher temperatures, closely matching experimental I/III and I/VII transition pressures. Trajectory analysis revealed a concerted CO2-I/III transition mechanism driven by molecular rotation, lattice deformation, and non-monotonic volume changes (expansion followed by contraction). We propose a new Cmca space group structure for the true CO2-III phase, characterized by molecules tilted relative to the ac plane and lattice parameters a > b. It differs from the reported CO2-III structure determined by powder x-ray diffraction but closely resembles the CO2-VII crystal, where CO2 molecules are aligned parallel to the ac plane. This proposed tilted Cmca structure coexists with CO2-VII at high temperatures. We conject that CO2-III and CO2-VII belong to the same phase, with the discrepancies in their experimental Raman spectra primarily caused by slight structural changes due to the thermal effect. This work provides deeper insights into CO2 phase transitions and establishes a generalizable strategy for high-precision MLPs in complex rare event systems.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation E. B. Dolgusheva, V. Yu. Trubitsin; Vibrational spectra and anharmonic effects in crystals studied by molecular dynamics simulation. AIP Conf. Proc. 10 December 2012; 1504 (1): 1150–1153. https://doi.org/10.1063/1.4772130 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

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