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Partial atomic charge, which determines the magnitude of the Coulombic non-bonding interaction, represents a critical parameter in molecular mechanics simulations. Partial charges may also be used as a measure of physical properties of the system, ie. covalency, acidic/catalytic sites, etc. A range of methods, both empirical and ab initio, exist for calculating partial charges in a given solid, and several of them are compared here for siliceous (pure silica) zeolites. The relationships between structure and the predicted partial charge are examined. The predicted partial charges from different methods are also compared with related experimental observations, showing that a few of the methods offer some guidance towards identifying the T-sites most likely to undergo substitution or for proton localization in acidic framework forms. Finally, we show that assigning unique calculated charges to crystallographically unique framework atoms makes an appreciable difference in simulating predicting N2 and O2 adsorption with common dispersion-repulsion parameterizations.

Ionic liquids have the potential to be used for extracting valuable chemicals from raw materials. These processes often involve water, and after extraction, the water or other chemicals must be removed from the ionic liquid, so it can be reused. To help in designing such processes, we present data on the vapor-liquid equilibrium of the system containing protic ionic liquid 7-methyl-1,5,7-triazabicyclo [ 4.4.0 ] dec-5-enium acetate, water, acetic acid, and 7-methyl-1,5,7-triazabicyclo [4.4.0] dec-5-ene. Earlier studies have only focused on mixtures of water and an ionic liquid with a stoichiometric ratio of the ions. Here, we also investigated mixtures containing an excess of the acid or base component because in real systems with protic ionic liquids, the amount of acid and base in the mixture can vary. We modeled the data using both the ePC-SAFT and NRTL models, and we compared the performance of different modeling strategies. We also experimentally determined the vapor composition for a few of the samples, but none of the modeling strategies tested could accurately predict the concentration of the acid and base components in the vapor phase.

We report new interfacial tension (IFT) measurements of the (H2O + CO2 + H2) and (H2O + H2) systems at pressures of (0.5 to 45) MPa, and temperatures of (298.15 to 448.15) K, measured by the pendant-drop method. The expanded uncertainties at 95% confidence are 0.05 K for temperature, 70 kPa for pressure, 0.017·γ for IFT in the both the binary (H2O + H2) system and the ternary (CO2 + H2 + H2O) system. Generally, the IFT was found to decrease with both increasing pressure and increasing temperature. However, for (H2O + H2) at the lowest two temperatures investigated, the isothermal IFT data were found to exhibit a maximum as a function of pressure at low pressures before declining with increasing pressure. An empirical correlation has been developed for the IFT of the (H2O + H2) system in the full range of conditions investigated, with an average absolute deviation of 0.16 mN m−1, and this is used to facilitate a comparison with literature values. Estimates of the IFT of the (H2O + CO2 + H2) ternary system, by an empirical combining rule based on the coexisting phase compositions and the interfacial tensions of the binary systems, were found to be unsuitable at low temperatures, with an average absolute deviation of 3.6 mN m−1 over all the conditions investigated.

In this paper, we present density and speed-of-sound experimental measurements for n-nonane at temperatures between (283.15 and 473.15) K and pressures up to 68 MPa and 390 MPa respectively. The density measurements were performed with a vibrating-tube densimeter and the speed-of-sound measurements were carried out in a dual-path pulse-echo apparatus. The vibrating-tube densimeter was calibrated using pure helium and water over the full range of temperature and pressure investigated, while the speed-of-sound apparatus was calibrated using pure water at low pressure over the full range of temperature. The expanded relative uncertainties of the measurements were 0.08% for density and between (0.1 and 0.3)% for sound speed at 95% confidence. The density data were correlated with the modified Tait equation over the entire temperature and pressure range, with an absolute average relative deviation of 0.006%. An empirical equation was developed to represent the sound speed data with an absolute average relative deviation of 0.03%. Both sets of data were compared with the predictions from the equation of state developed by Lemmon and Span. Comparisons have also been made with the available literature and satisfactory agreement was found. Correlations were developed for the density and isobaric heat capacity of the liquid as functions of temperature at a reference pressure of 0.1 MPa, the latter based on literature data. Combining these correlations with the sound-speed surface, properties of the liquid were computed by thermodynamic integration up to a pressure of 390 MPa. Density, isobaric heat capacity, isothermal compressibility and isobaric expansivity values are reported, and their uncertainties were carefully investigated.

Over the past 60 years, the diamond anvil cell (DAC) has been developed into a widespread high static pressure device. The adaptation of laboratory and synchrotron analytical techniques to DAC enables a detailed exploration in the 100 GPa range. The strain of the anvils under high load explains the 400 GPa limit of the conventional DAC. Here we show a toroidal shape for a diamond anvil tip that enables to extend the DAC use toward the terapascal pressure range. The toroidal-DAC keeps the assets for a complete, reproducible, and accurate characterization of materials, from solids to gases. Raman signal from the diamond anvil or X-ray signal from the rhenium gasket allow measurement of pressure. Here, the equations of state of gold, aluminum, and argon are measured with X-ray diffraction. The data are compared with recent measurements under similar conditions by two other approaches, the double-stage DAC and the dynamic ramp compression., Extreme static pressures exceeding a million atmospheres exist in a variety of natural environments, but obtaining such pressures in a laboratory is still a challenge. Here, the authors develop a toroidal diamond anvil design that allows for the generation of 600 GPa (6 million atmospheres) in routinely used diamond anvil cells.

In recent years, computational fluid dynamics (CFD) has been applied for the design and analysis of positive displacement machines (both compressors and expanders) with numerous challenges due to the dynamics of the compression (or expansion) process and deforming working chambers. The relative motion and in turn, the variation of the gaps during machine operation implies several obstacles for the implementation of reliable CFD models. The majority of the studies reported in literature focused on scroll, twin screw and reciprocating machines. The limitation of the developed methodologies to be applied directly to positive displacement machines with more complex meshing such as that of single-screw has been highlighted in literature. In this paper, a single screw expander is studied by means of (i) a moving mesh technique (dynamic mesh in the Key Frame Remeshing approach) and (ii) a real gas model of a R134a (Peng-Robinson model) implemented in OpenFOAM. On the top of that, all the possible techniques that come with the software are investigated in their application to single screw. An useful review of the state of the art CFD with open-source software (OpenFOAM-v1606+ and foam-extend4.0) is therefore carried out. The reliability of CFD model represents indeed the first step on which the design process and further optimization will be based. (C) 2017 The Authors. Published by Elsevier Ltd.

The methodologies generally adopted for synthesis of methane hydrates (e.g., the dissolved gas method, excess gas method and the ice seeding method) signifies the importance of appropriate thermodynamic conditions for the dissolution characteristics of methane in water and its subsequent crystallization to form hydrates. The 'dissolved gas method' and 'excess gas method', which mimics the natural formation and existence of methane hydrates beneath ocean bed, can be employed for controlled synthesis of hydrates by regulating the pressure and temperature. However, explicit research has not yet been conducted to understand the rate of temperature decrease in methane dissolution characteristics, prior to gas hydrate formation. At a definite pressure-temperature condition, the dissolution characteristics are largely dependent on the 'interaction time', or 'contact time', available for methane gas to dissolute in water. Therefore, an investigation was conducted to (i) ascertain the rate of hydrate formation, (ii) quantify the volume of gas hydrates formed, corresponding to different combinations of pressure and temperature, and (iii) to understand the impact of memory effect, in a closed cell. This study demonstrates that though the stability of gas hydrates is principally dependent on the pressure and temperature combinations, sufficient interaction time should be provided for their stable occurrence. Moreover, it was also proven that the relevance of memory effect was predominant after the fifth run of hydrate formation-dissociation cycle. (C) 2017 Elsevier B.V. All rights reserved.

Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions We report a combined experimental and theoretical study of the melting curve and the structural behavior of vanadium under extreme pressure and temperature. We performed powder x-ray-diffraction experiments up to 120 GPa and 4000 K, determining the phase boundary of the body-centered cubic-to-rhombohedral transition and melting temperatures at different pressures. Melting temperatures have also been established from the observation of temperature plateaus during laser heating, and the results from the density-functional theory calculations. Results obtained from our experiments and calculations are fully consistent and lead to an accurate determination of the melting curve of vanadium. These results are discussed in comparison with previous studies. The melting temperatures determined in this study are higher than those previously obtained using the speckle method, but also considerably lower than those obtained from shockwave experiments and linear muffin-tin orbital calculations. Finally, a high-pressure, high-temperature equation of state up to 120 GPa and 2800 K has also been determined.

7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (mTBD) has useful catalytic properties and can form an ionic liquid when mixed with an acid. Despite its potential usefulness, no data on its thermodynamic and transport properties are currently available in the literature. Here we present the first reliable public data on the liquid vapor pressure (temperature from 318.23 K to 451.2 K and pressure from 11.1 Pa to 10 000 Pa), liquid compressed density (293.15 K to 473.15 K and 0.092 MPa to 15.788 MPa), liquid isobaric heat capacity (312.48 K to 391.50 K), melting properties, liquid thermal conductivity (299.0 K to 372.9 K), liquid refractive index (293.15 K to 343.15 K), liquid viscosity (290.79 K to 363.00 K), liquid–vapor enthalpy of vaporization (318.23 K to 451.2 K), liquid thermal expansion coefficient (293.15 K to 473.15 K), and liquid isothermal compressibility of mTBD (293.15 K to 473.15). The properties of mTBD were compared with those of other relevant compounds, including 1,5-diazabicyclo(4.3.0)non-5-ene(DBN), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,1,3,3-tetramethylguanidine (TMG). We used the PC-SAFT equation of state to model the thermodynamic properties of mTBD, DBN, DBU, and TMG. The PC-SAFT parameters were optimized using experimental data.

For both ethical and practical reasons accurate tissue simulant materials are essential for ballistic testing applications. A wide variety of different materials have been previously adopted for such roles, ranging from gelatin to ballistics soap. However, while often well characterised quasi-statically, there is typically a paucity of information on the high strain-rate response of such materials in the literature. Here, building on previous studies by the authors on other tissue analogues, equation-of-state data for the elastomeric epithelial/muscular simulant material Perma-Gel ® is presented, along with results from a series of ballistic tests designed to illustrate its impact-related behaviour. Comparison of both hydrodynamic and ballistic behaviour to that of comparable epithelial tissues/analogues (Sylgard ® and porcine muscle tissue) has provided an insight into the applicability of both Perma-Gel ® and, more generally, monolithic simulants for ballistic testing purposes. Of particular note was an apparent link between the high strain-rate compressibility (evidenced in the Hugoniot relationship in the U s -u p plane) and subsequent ballistic response of these materials. Overall, work conducted in this study highlighted the importance of fully characterising tissue analogues – with particular emphasis on the requirement to understand the behaviour of such analogues under impact as part of a system as well as individually.

The phase diagram of zinc (Zn) has been explored up to 140 GPa and 6000K, by combining optical observations, x-ray diffraction, and ab initio calculations. In the pressure range covered by this study, Zn is found to retain a hexagonal close-packed (hcp) crystal symmetry up to the melting temperature. The known decrease of the axial ratio (c/a) of the hcp phase of Zn under compression is observed in x-ray diffraction experiments from 300K up to the melting temperature. The pressure at which c/a reaches root 3 (approximate to 10GPa) is slightly affected by temperature. When this axial ratio is reached, we observed that single crystals of Zn, formed at high temperature, break into multiple poly-crystals. In addition, a noticeable change in the pressure dependence of c/a takes place at the same pressure. Both phenomena could be caused by an isomorphic second-order phase transition induced by pressure in Zn. The reported melt curve extends previous results from 24 to 135 GPa. The pressure dependence obtained for the melting temperature is accurately described up to 135 GPa by using a Simon-Glatzel equation: T-m = 690 K(1 + P/10.5 GPa)(0.76), where P is the pressure in GPa. The determined melt curve agrees with previous low-pressure studies and with shock-wave experiments, with a melting temperature of 5060(30) K at 135 GPa. Finally, a thermal equation of state is reported, which at room-temperature agrees with the literature., The authors are thankful for the financial support to this research from the Spanish Ministerio de Economía y Competitividad, the Spanish Research Agency, and the European Fund for Regional Development under Grant Nos. MAT2016- 75586-C4-1-P, and MAT2015-71070-REDC (MALTA Consolider). British Crown Owned Copyright 2018/AWE.

Precise knowledge of vapor–liquid equilibrium (VLE) data of (CO2 + diluent) mixtures is crucial in the design and operation of carbon capture, transportation and storage processes. VLE measurements of the (CO2 + CO) system are reported along seven isotherms at temperatures ranging from just above the triple-point temperature of CO2 to 302.93 K and at pressures from the vapor pressure of pure CO2 to approximately 15 MPa, including near-critical mixture states for all isotherms. The measurements are associated with estimated standard uncertainties of 0.006 K for temperature, 0.009 MPa for pressure and 0.011x(1 − x) for mole fraction x. The new VLE data have been compared with two thermodynamic models: the Peng-Robinson equation of state (PR-EOS) and a multi-fluid Helmholtz-energy equation of state known as EOS-CG. The PR-EOS was used with a single temperature-dependent binary interaction parameter, which was fitted to the experimental data. In contrast, EOS-CG was used in a purely-predictive mode with no parameters fitted to the present results. While PR-EOS generally agrees fairly well with the experimental data, EOS-CG showed significantly better agreement, especially close to the critical point.

This contribution is based on our talk at the BIRS Workshop on “Coupled Mathematical Models for Physical and Biological Nanoscale Systems and Their Applications”. Our aim here is to summarize and bring together recent advances in wetting of nanostructured surfaces, using classical density-functional theory (DFT). Classical DFT is an ab initio theoretical-computational framework with a firm foundation in statistical physics allowing us to systematically account for the fluid spatial inhomogeneity, as well as for the non-localities of intermolecular fluid-fluid and fluid-substrate interactions. The cornerstone of classical DFT, is to express the grand free energy of the system as a functional of its one-body density, thus generating a hierarchy of N-body correlation functions. Unconstrained minimization of a properly approximated free-energy functional with respect to the one-body density then yields the basic DFT equation. And since most macroscopic quantities of interest can often be cast as averages over a one-body distribution, this equation provides a very useful and accessible computational tool. Indeed, there has been a rapid growth of classical DFT applications across a broad variety of fields, including phase transitions in solutions of macromolecules, interfacial phenomena, and even nucleation. Here we attempt to give a taste of what simple equilibrium DFT models look like, and what they can and cannot capture, as far as wetting on chemically heterogeneous substrates is concerned. We review recent progress in the understanding of planar prewetting and interface unbending on such substrates and compute substrate-fluid interfaces and wetting isotherms.

Experimental determination and theoretical predictions of the isothermal (344.15 K) mass densities and interfacial tensions for the sys tem carbon dioxide (CO2) with heptol (n - heptane + toluene) mixtures varying liquid volume fraction compositions of toluene (0, 25, 50, 75, 100 % v/v) and over the pressure range 0.1 to 8 MPa are reported. Measurements are carried out on a high - pressure dev ice that includes a vibrating tube densimeter and a pendant drop tensiometer. Theoretical modeling of mass densities phase equilibria and interfacial properties (i.e., interfacial tension and interfacial concentration profiles) are performed by employing t he Square Gradient Theory using an extension of the Statistical Associating Fluid Theory equation of state that accounts for ring fluids. The experimental bulk phase equilibrium densities and interfacial tensions obtained are in very good agreement with th e theoretical predictions. Although there are no previous experimental data of these mixtures at the conditions explored herein, the results follow the same trends observed from experimental data at other conditions. The combination of experimental and mod eling approaches provides a route to simultaneously predict phase equilibrium and interfacial properties within acceptable statistical deviations. For the systems and conditions studied here, we observe that the phase equilibrium of the mixtures display z eotropic vapor - liquid equilibria with positive deviations from ideal behavior. The mass bulk densities behave ordinarily whereas the interfacial tensions decrease as the pressure or liquid mole fraction of CO2 increases and/or the ratio toluene/heptane dec reases. The interfacial concentration along the interfacial region exhibits a remarkable high excess adsorption of CO2, which increases with pressure and it is larger in n - heptane than in toluene. Toluene does not exhibit any special adsorption activity wh ereas n - heptane displays surface activity only at low pressure in a very narrow range for the case of CO2 + (25% n - heptane + 75% toluene) mixture.

An experimental, theoretical, and molecular simulation consolidated framework for the efficient characterization of the adsorption and fluid-phase behavior of multi-component hydrocarbon mixtures within tight shale rocks is presented. Fluid molecules are described by means of a top-down coarse-grained model where simple Mie intermolecular potentials are parametrized by means of the statistical associating fluid theory. A four-component (methane, pentane, decane, naphthalene) mixture is used as a surrogate model with a composition representative of commonly encountered shale oils. Shales are modeled as a hierarchical network of nanoporous slits in contact with a mesoporous region. The rock model is informed by the characterization of four distinct and representative shale core samples through nitrogen adsorption, thermogravimetric analysis, and contact angle measurements. Experimental results suggest the consideration of two types of pore surfaces: a carbonaceous wall representing the kerogen regions of a shale rock, and an oxygenated wall representing the clay-based porosity. Molecular dynamics simulations are performed at constant overall compositions at a temperature of 398.15 K (257 °F) and explore pressures from 6.9 MPa up to 69 MPa (1000–10000 psi). Simulations reveal that it is the organic nanopores of 1 and 2 nm that preferentially adsorb the heavier components, while the oxygenated counterparts show little selectivity between the adsorbed and free fluid. Upon desorption, this trend is intensified, as the fluid phase in equilibrium with a carbon nanopore becomes increasing leaner (richer in light components) and almost completely depleted of the heavy components which remain trapped in the nanopores and surfaces of the mesopores. Oxygenated pores do not contribute to this unusual behavior, even for the very tight pores considered. The results presented elucidate the relative importance of considering both the pore size distribution and the heterogeneous nature of the confining surfaces when theoretically describing adsorption and transport of oil through shale rocks, and they provide a plausible explanation for the abnormal continuous leaning of shale gases seen during field production.

Ionic liquids (ILs) are an exciting class of compounds of high interest from a technological point of view. One of the applications that is raising more interest is their possible use as solvents to carry out the conversion of CO2 into more valuable compounds. Theoretical approaches provide an attractive option to screen ILs properties and give quick answers to guide the experiments, becoming a crucial tool for process design. This work illustrates a practical example based on the solubility of greenhouse and acid gases on the butylmethylimidazolium methylsulfate [C(4)mim][MeSO4] IL, in order to study its feasibility for gas separation and conversion. A simple but reliable molecular model is presented for the ionic liquid based on structural information and molecular simulations, and coarse-grained models are used to model the different gases. The absorption of relevant gases for the separation/conversion process (CO2, CH4, CO, H-2, SO2, H2S) in [C(4)mim][MeSO4] is modeled and compared with experimental data using a minimum amount of binary data. From this information, the ternary diagrams of [C(4)mim][MeSO4] with CO2 and the acid gases SO2 and H2S are predicted, and the selectivity of CO2 by respect all the gases is evaluated, with particular attention to the contaminants above mentioned. (C) 2015 Elsevier B.V. All rights reserved.

International audience; The E-PPR78 model is a predictive version of the widely used Peng-Robinson equation of state in which the binary interaction parameters are estimated by a group-contribution method. With the 24 groups available before the writing of this paper, such a model could be used to predict fluid phase equilibrium of systems containing hydrocarbons, permanent gases (CO2, N-2, H2S, H-2, CO, He, and Ar), mercaptans, alkenes, and water. During the process of the Carbon dioxide Capture and Storage (CCS), it is often necessary to know thermodynamic properties of mixtures containing carbon dioxide, water, hydrocarbons, and trace gases, such as nitrogen, argon, hydrogen, carbon monoxide, sulfur dioxide, oxygen, or nitric oxide. Basically, except sulfur dioxide, oxygen, and nitric oxide, most components encountered in systems regarding CCS processes could be modeled with the E-PPR78 model. So in order to predict the phase behavior and estimate energetic properties (e.g., enthalpy or heat capacity changes on mixing) of such systems, the applicability range of the E-PPR78 model is extended through the addition of three new groups: "SO2," "O-2," and "NO."

Despite decades of research, the modeling of moving contact lines has remained a formidable challenge in fluid dynamics whose resolution will impact numerous industrial, biological, and daily life applications. On the one hand, molecular dynamics (MD) simulation has the ability to provide unique insight into the microscopic details that determine the dynamic behavior of the contact line, which is not possible with either continuum-scale simulations or experiments. On the other hand, continuum-based models provide a link to the macroscopic description of the system. In this Feature Article, we explore the complex range of physical factors, including the presence of surfactants, which governs the contact line motion through MD simulations. We also discuss links between continuum- and molecular-scale modeling and highlight the opportunities for future developments in this area., Comment: 54 pages, 11 figures

Resistively heated diamond-anvil cells have been used together with synchrotron x-ray diffraction to investigate the phase diagram of calcium up to 50 GPa and 800 K. The phase boundaries between the Ca-I (fcc), Ca-II (bcc), and Ca-III (simple cubic, sc) phases have been determined at these pressure-temperature conditions, and the ambient temperature equation of state has been generated. The equation of state parameters at ambient temperature have been determined from the experimental compression curve of the observed phases by using third-order Birch-Murnaghan and Vinet equations. A thermal equation of state was also determined for Ca-I and Ca-II by combining the room-temperature Birch-Murnaghan equation of state with a Berman-type thermal expansion model., Part of the research was supported by the Spanish Government MINECO under Grants No. MAT2016-75586-C4-1/4P and No. MAT2015-71070-REDC.

International audience; We study the structure and liquid-crystalline phase behaviour of a model of confined non-convex circular soft-repulsive nanorings in a planar slit geometry using molecular-dynamics simulation. The separation distance between the structureless parallel soft-repulsive walls is made large enough to allow for the formation of a distinct bulk phase in the central region of the box which is in coexistence with the adsorbed fluid thus allowing the analysis of single-wall effects. As the density of the particles is increased, the fluid adsorbs (wets) onto the planar surfaces leading to the formation of well-defined smectic-A layers with a spacing proportional to the diameter of the rings. An analysis of the nematic order parameter at distances perpendicular to the surface reveals that the particles in each layer exhibit anti-nematic behaviour and planar (edge-on) anchoring relative to the short symmetry axis of the rings. This behaviour is in stark contrast to the behaviour observed in convex disc-like particles that have the tendency to form nematic (discotic) structures with homeotropic (face-on) anchoring. The smectic phases formed by nanorings in the bulk and under confinement are characterised by the formation of low-density layered liquid-crystalline states with large voids, referred to here as lacuna smectic phases. In contrast to what is typically found for confined liquid-crystalline systems involving convex particles, no apparent biaxiality is found for nanorings in planar confinement. We argue that formation of the low-density lacuna smectic layers with planar anchoring is a consequence of the non-convex shape of the circular rings that allow for interpenetration between the particles as observed for nanorings under bulk conditions [C. Avendaño, G. Jackson, E.A. Müller and F.A. Escobedo, Proc. Natl. Acad. Sci. U.S.A. 113, 9699 (2016); H.H. Wensink and C. Avendaño, Phys. Rev. E 94, 062704 (2016)]. ARTICLE HISTORY

Physical review / B 96(14), 144105 (2017). doi:10.1103/PhysRevB.96.144105, Through high-pressure Raman spectroscopy and x-ray diffraction experiments, we have investigated the formation, stability field, and structure of hydrogen iodide (HI). Hydrogen iodide is synthesized by the reaction of molecular hydrogen and iodine at room temperature and at a pressure of 0.2 GPa. Upon compression, HI solidifies into cubic phase I, and we present evidence for the emergence of a phase I′ above 3.8 GPa. Across the wide temperature regime presented here, HI is unstable under compression (11 GPa at 300 K, 18 GPa at 77 K), decomposing into its constituent elements, after which no further reaction between hydrogen and iodine was observed up to pressures of 60 GPa. This study provides both the constraints on the phase diagram of HI and its kinetic stability, Published by APS, Woodbury, NY

We present a theoretical analysis of the equation of state (EOS) of metals using a quasi-harmonic Einstein model with a dimensionless cohesive energy versus distance function (F(z)) involving the Wigner-Seitz radius and a material-dependent scaling length, as suggested in classical works by Rose, Ferrante, Smith and collaborators. Using this model, and “universal” values for the function and its first and second derivatives at the equilibrium distance (z=0), three general interrelations between EOS parameters and the cohesive energy are obtained. The first correlation involves the bulk modulus, and the second, the thermal expansion coefficient. In order to test these results an extensive database is developed, which involves available experimental data, and results of current ab initio density-functional-theory calculations using the VASP code. In particular, the 0 K values for volume, bulk modulus, its pressure derivative, and the cohesive energy of 27 elements belonging to the first (Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn), second (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd) and third (Hf, Ta, W, Re, Os, Ir, Pt, Au) transition row of the Periodic Table are calculated ab initio and used to test the present results. The third correlation obtained, allows an evaluation of the third derivative of F(z) at z=0 for the current elements. With this new information, a discussion is presented of the possibility of finding a “universal” F(z) versus z function able to account accurately for the pressure derivative of the bulk modulus of the transition elements. Fil: Bertoldi, Dalía Surena. Universidad Nacional de Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada; Argentina Fil: Ramos, Susana Beatriz. Universidad Nacional de Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería. Departamento de Física; Argentina Fil: Fernandez Guillermet, Armando Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina

Embedded Atom Method (EAM) potentials have been fitted for the atomistic simulation of small, ∼2–5 nm, binary, Pt Ni, nanoparticles completely from Density Functional Theory (DFT) total energy calculations. The overall quality of the DFT calculations and the final potential is obtained through the independent calculation of an array of properties of the pure metals and the stable alloys, which are normally used for the fitting of interatomic potentials. The ability of the fitted potentials to simulate nanostructures is evaluated by the reproduction of binary nanoslabs with thickness ∼1 nm, and nanoparticles in the extreme case of the smallest icosahedrons possible, with diameter ∼0.6 nm. The used approach requires high quality of convergence but otherwise low cost DFT as it is based on static total energy calculations. It also provides objective criteria for the evaluation of the fitted potentials during fitting and has been implemented with the open source code GULP.

Isobaric vapor-liquid equilibrium (VLE) data have been measured for the binary system 2,2'-oxybis[propane] + 2,5-Dimethylfuran at 50, 75, and 94 kPa and over the temperature range 321-364 K using a vapor-liquid equilibrium still with circulation of both phases. Atmospheric surface tension (ST) data have been also determined at 283.15 and 330.15 K using a maximum bubble pressure tensiometer. Experimental results show that the mixture is zeotropic and exhibits slight positive deviation from ideal behavior over the experimental range. Surface tensions, in turn, exhibit negative deviation from the linear behavior. For each isothermal condition, it is observed that the surface tension decreases as the mole fraction of 2,2'-oxybis[propane] increases, whereas at a fixed mole fraction, the surface tension decreases as the temperature increases. The VLE data of the binary mixture satisfy the Fredenlund's consistency test, and the dependence of ST on mole fraction was satisfactorily smoothed using the Redlich-Kister equation. The experimental VLE and ST data were accurately described by applying the square gradient theory to the Cubic-Plus-Association equation of state. This theoretical model was also applied to describe the surface activity of species along the interfacial region, from which it is possible to conclude that only the 2,2'-oxybis[propane] presents an interfacial accumulation which decreases as the concentration of DIPE or temperature increases. (C) 2013 Elsevier B.V. All rights reserved.

X-ray method to test the material properties and to obtain elastic constants is commonly based on the Reuss model and Kroner model. Y parameter has been turned out to be an effective method to estimate elastic properties of polycrystalline material. Since Y-parameters of cubic polycrystalline material based on the certain uniform stress (Reuss model) has not been given, our work aims to complete this part of the theoretical analysis, which can effectively compare elastic constants measured by the X-ray diffraction method. The structural and the elastic properties of cubic structures (CaO and MgO) and hexagonal structures (CH and Calcite CaCO3) are investigated by the density functional theory method. And then the credibility of Y parameters for determing elastic moduli of cubic structures is proved and elastic properties in typical crystallographic planes of [100], [110] and [111] are also calculated. Meanwhile, Young’s moduli of CH and Calcite structure are 58.08 GPa and 84.549 GPa, which are all close to references. Elastic properties of cubic and hexagonal structures under various pressures are calculated and the surface constructions of elastic moduli are drawn, showing the anisotropy at various directions. The crystal structure investigated in this work are typical of some primary or secondary components of Hardened Cements Pastes and their homogenized elastic properties are needed in a hierarchical multi-scale modeling, such as the one developed by some of the authors of this paper.

Capturing segregation behavior in metal alloy nanoparticles accurately using computer simulations is contingent upon the availability of high-fidelity interatomic potentials. The embedded atom method (EAM) potential is a widely trusted interatomic potential form used with pure metals and their alloys. When limited experimental data is available, the A-B EAM cross-interaction potential for metal alloys AxB1-x are often constructed from pure metal A and B potentials by employing a pre-defined 'mixing rule' without any adjustable parameters. While this approach is convenient, we show that for AuPt, NiPt, AgAu, AgPd, AuNi, NiPd, PtPd and AuPd such mixing rules may not even yield the correct alloy properties, e.g., heats of mixing, that are closely related to the segregation behavior. A general theoretical formulation based on scaling invariance arguments is introduced that addresses this issue by tuning the mixing rule to better describe alloy properties. Starting with an existing pure metal EAM potential that is used extensively in literature, we find that the mixing rule fitted to heats of mixing for metal solutions usually provides good estimates of segregation energies, lattice parameters and cohesive energy, as well as equilibrium distribution of metals within a nanoparticle using Monte Carlo simulations. While the tunable mixing rule generally performs better than non-adjustable mixing rules, the use of the tunable mixing rule may still require some caution. For e.g., in Pt-Ni system we find that the segregation behavior can deviate from the experimentally observed one at Ni-rich compositions. Despite this the overall results suggest that the same approach may be useful for developing improved cross-potentials with other existing pure metal EAM potentials as well. As a further test of our approach, mixing rule estimated from binary data is used to calculate heat of mixing in AuPdPt, AuNiPd, AuPtNi, AgAuPd and NiPtPd. Excellent agreement with experiments is observed for AuPdPt.

With increasing penetration of intermittent renewable energy into the electricity grid, one can expect thermal power plants to be required to operate in a more dynamic fashion, with more frequent departures from design point operation. However, the application of optimal control strategies can offer solutions to these operational challenges, associated with the integration of the power plant with the capture plant. In this paper a process control strategy is developed in order to select the optimal control variables for a PCC process. In addition, economically efficient control structures for operation of a post-combustion capture process with minimum energy requirements for coal and natural gas power plant are designed. The results have shown that with an appropriate and well-tuned control strategy, it is possible to maintain critical parameters, such as the degree of CO 2 capture, at the desired set-point, even during periods of significant fluctuation in the power plant load and even if based on simple and well established control technologies, such as PID, avoids the need for more risky solutions such as adding solvent storage tanks to the process.

This work is framed within the Eighth Industrial Fluid Properties Simulation Challenge, with the aim of assessing the capability of molecular simulation methods and force fields to accurately predict adsorption in porous media for systems of relevant practical interest. The current challenge focuses on predicting adsorption isotherms of n -perfluorohexane in the certified reference material BAM-P109 standard activated carbon. A temperature of T = 273 K and pressures of p / p 0 = 0 . 1 , 0.3, and 0.6 relative to the bulk saturation pressure p 0 (as predicted by the model) are the conditions selected in this challenge. In our methodology we use coarse-grained intermolecular models and a top-down technique where an accurate equation of state is used to link the experimental macroscopic properties of a fluid to the force-field parameters. The state-of-the-art version of the statistical associating fluid theory (SAFT) for potentials of variable range as reformulated in the Mie group contribution incarnation (SAFT- γ Mie) is employed here. The parameters of the SAFT- γ Mie force field are estimated directly from the vapour pressure and saturated liquid density data of the pure fluids using the equation of state, and further validated by molecular dynamic simulations. The coarse-grained intermolecular potential models are then used to obtain the adsorption isotherm kernels for argon, carbon dioxide, and n -perfluorohexane in graphite slit pores of various widths using Grand Canonical Monte Carlo simulations. A unique and fluid-independent pore size distribution curve with total micropore volume of 0.5802 cm 3 /g is proposed for the BAM-P109. The pore size distribution is obtained by applying a non-linear regression procedure over the adsorption integral equation to minimise the quadratic error between the available experimental adsorption isotherms for argon and carbon dioxide and purpose-built Grand Canonical Monte Carlo kernels. The predicted adsorption levels of n -perfluorohexane at 273 K in BAM-P109 are 72.75 ± 0.01, 73.82 ± 0.01, and 75.44 ± 0.05 cm 3 /g at Standard Temperature and Pressure (STP) conditions for p / p 0 = 0 . 1 , 0.3, and 0.6, respectively.

International audience; In 2008, the PPR78 model (Predictive Peng-Robinson 1978) was extended to mercaptan-containing systems by adding the sulfhydryl group (-SH). that is, by determining the values of the group-interaction parameters between the group -SH and the fourteen other groups already present in the PPR78 model. Unfortunately, due to a lack of experimental data reported in the open literature, it was not possible to characterize interactions between the group -SH and the three groups: ethane, CO2 and N-2. Very recently, vapor-liquid equilibrium data for three binary systems containing methanethiol and respectively methane, nitrogen and carbon dioxide were however measured. It was thus decided to use these data to estimate two of the missing group-interaction parameters (-SH/CO2 and -SH/N-2). For such systems, deviations observed with the PPR78 model are compared to those obtained with the CPA equation of state.

International audience; In this paper, the various concepts of idealmixtures found in the open literature are analyzed and compared. It is in particular shown that expressions conventionally admitted for the ideal-mixture propertychanges on mixing are incorrect when the idealmixture is obtained from pure components which are not in the same aggregation state as the mixture. Among these properties, a special attention is devoted to the ideal-mixture Gibbs energy change on mixing since it is used to determine the equilibrium conditions. After explaining how to properly estimate this quantity, it is shown how to correctly perform the double-tangent construction of coexisting phases for binary systems modeled with the gamma-phi approach.

International audience; The determination of the physical properties of pure water, especially the vapor-pressure curve of water, is one of the major issues identified by the Consultative Committee for Thermometry of the International Committee for Weights and Measures (CIPM) to improve the accuracy of the national references in humidity. At the present time the saturation-pressure data, corresponding to ice or liquid-vapor equilibrium, at low temperature are scarce and unreliable. This study presents new measurements of vapor and sublimation pressures of, respectively, water and ice, using a static apparatus. Prior to saturation-pressure measurements, the temperature and pressure sensors of the static apparatus were calibrated against reference gauges in use at the LNE-CETIAT laboratories. The effect of thermal transpiration has been studied. The explored temperature range lies between 250 K and 374 K, and the pressure range between 70 Pa and 10(5) Pa. An automatic data acquisition program was developed to monitor the pressure and temperature. The obtained results have been compared with available literature data. The preliminary uncertainty budget took into account several components: pressure measurements, temperature measurements, and environmental error sources such as thermal transpiration and hydrostatic correction.

In this paper the experimental setup of a new apparatus able to provide the critical properties of pure components and mixtures using either a dynamic or a static method is described. Critical temperatures ( T c ) and critical pressures ( P c ) of pure components ( n -pentane, n -heptane and n -decane) and critical loci of three binary mixtures ( n -pentane + n -heptane, n -pentane + n -decane and n -heptane + n -decane) are investigated using the dynamic method. For the system n -pentane + n -heptane, the results obtained with the dynamic method are compared with those obtained with the static method. The critical points are visually determined by observing the critical opalescence and the simultaneous disappearance and reappearance of the meniscus in the middle of the view cell which withstands operations up to 673 K and 20 MPa. The experimental critical data are compared with success to literature database and with their prediction from the PPR78 thermodynamic model.

Concentrated solutions of short blunt-ended DNA duplexes, as short as 6 base pairs, are known to order into the nematic liquid crystal phases. This self-assembly is due to the stacking interactions between duplex terminals that promotes their aggregation into polydisperse chains with a significant persistence length. Experiments show that liquid crystal phases form above a critical volume fraction depending on the duplex length. We introduce and investigate via numerical simulations, a coarse-grained model of DNA double-helical duplexes. Each duplex is represented as an hard quasi-cylinder whose bases are decorated with two identical reactive sites. The stacking interaction between terminal sites is modeled short-range square-well potential. We compare the numerical results with predictions based on a free energy functional and find satisfactory quantitative matching of the isotropic nematic phase boundary and of the system structure. Comparison of numerical and theoretical results with experimental findings confirm that the DNA duplex self-assembly can be properly modeled via equilibrium polymerization of cylindrical particles. This insight enables us to estimate the stacking energy.

An apparatus consisting of an equilibrium cell connected to two vibrating tube densimeters and two syringe pumps was used to measure the saturated phase densities of (CO2 + H2O) at temperatures from (293 to 450) K and pressures up to 64 MPa, with estimated average standard uncertainties of 1.5 kg · m−3 for the CO2-rich phase and 1.0 kg · m−3 for the aqueous phase. The densimeters were housed in the same thermostat as the equilibrium cell and were calibrated in situ using pure water, CO2 and helium. Following mixing, samples of each saturated phase were displaced sequentially at constant pressure from the equilibrium cell into the vibrating tube densimeters connected to the top (CO2-rich phase) and bottom (aqueous phase) of the cell. The aqueous phase densities are predicted to within 3 kg · m−3 using empirical models for the phase compositions and partial molar volumes of each component. However, a recently developed multi-parameter equation of state (EOS) for this binary mixture, Gernert and Span [32] , was found to under predict the measured aqueous phase density by up to 13 kg · m−3. The density of the CO2-rich phase was always within about 8 kg · m−3 of the density for pure CO2 at the same pressure and temperature; the differences were most positive near the critical density, and became negative at temperatures above about 373 K and pressures below about 10 MPa. For this phase, the multi-parameter EOS of Gernert and Span describes the measured densities to within 5 kg · m−3, whereas the computationally-efficient cubic EOS model of Spycher and Pruess (2010), commonly used in simulations of subsurface CO2 sequestration, deviates from the experimental data by a maximum of about 8 kg · m−3.

The aim of this study is to describe the phase equilibrium behavior of aqueous solutions of selected ionic liquids (ILs) as new potential pairs of absorption cooling systems. The ILs under study have a shared cation, 1-butyl-3-methylimidiazolium, [C(4)mim](+), and the following anions: methanesulfonate, [CH3SO3](-), trifluoromethanesulfonate, [CF3SO3](-), acetate, [CH3CO2](-), trifluoroacetate, [CF3CO2](-), tosylate, [TOS](-), bromide, [Br](-), and thiocyanate, [SCN](-). Each binary system was individually studied within the soft-SAFT framework. A mesoscopic simple molecular model was proposed for each IL, being characterized by a specific set of molecular parameters. In combination with one or, in some cases, two additional binary parameters, it was possible to simultaneously describe the vapor-liquid equilibrium (VLE) of the aqueous binary systems at three different pressures (0.10 MPa, 0.07 MPa and 0.05 MPa) and the correspondent isothermal water activity coefficients at 298.15 K, correctly incorporating the different deviations from ideality and water interactions characteristics for each IL. Infinite dilution coefficients were also predicted in reasonable agreement with the experimental data. The simple model used with soft-SAFT to represent ILs provides an overall good description of most of the systems. Results for particular systems showed some space for improvement, nevertheless at expense of increasing the model complexity by changing the originally proposed molecular model. (C) 2016 Elsevier B.V. All rights reserved.

The development of successful and economical CO2 geological storage projects requires a precise estimation of the saturated phase densities and interfacial tension of the CO2/H2O system. The axisymmetric drop shape analysis (ADSA) method was used for measuring the interfacial tension of this system at temperatures over the range (298 to 469) K and pressures up to 69 MPa. The phase densities, required to determine accurate IFT values, were determined by measuring the oscillation period of the equilibrated phases with an Anton Paar densitometer. A correlation to readily determine the density of the CO2-saturated water phase in the range of interest is proposed and the use of pure compound densities for the calculation of the interfacial tension values discussed. The Cubic-Plus-Association equation of state (CPA EoS) was used to estimate the phase behaviour pressure and temperature dependence of the system studied with very good results. Bulk phase properties and influence parameters adjusted to pure compounds surface tensions within the density gradient theory (DGT) were used to predict the CO2/H2O interfacial tensions with remarkably low deviations from the measured values. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.

Here, we present a simple method for optimizing the fitting of molecular parameters involving vapor-liquid equilibria (VLE) and selected second-order thermodynamic properties and experimental data. The procedure is applied, as an example to the soft Statistical Associating Fluid Theory (soft-SAFT) equation of state. The method involves the introduction and testing of coupling factors ranging from 0 (only one selected derivative property) to 1 (only VLE), to change the weight of one set of properties over the other in the fitting procedure; this allows one to assess the role of derivative properties in the robustness of the parameters and molecular model. The technique is illustrated by calculating a large number of thermodynamic properties of different compounds: the n-alkanes, n-perfluoroalkanes, and 1-alkanols families, and water, as representative of different types of molecular interactions, and in a wide range of thermodynamic conditions. The most relevant thermodynamic properties to be included in the parameters fitting, the weight they should have in the regression procedure, and the influence of association are discussed in detail. It has been found that the use of just VLE data in the fitting procedure for regular nonassociating compounds, such as n-alkanes or perfluoroalkanes, is enough to provide good predictions of derivative properties. The use of derivative properties helped in identifying the best fitting strategy for the perfluoroalkanes family, as some limitations of the original parameters showed up when used for estimating the derivative properties. In contrast, association plays a major role in derivative properties of associating compounds such as alkanols and water. A coupling factor of 0.5 (equal weight of derivative property coupled with VLE data to fit the molecular parameters) is required to regress robust pure compound parameters that are able to simultaneously describe vapor pressures, phase densities, and derivative properties for 1-alkanols and water. The method presented here is robust, simple, and straightforward to implement; since it is not equation-dependent, it can be transferred to any other equation, providing robust molecular parameters for global equations.

Binary fluid mixtures display a wide array of fluid phase behavior ranging from simple vapor-liquid equilibrium diagrams to more complicated topology like azeotropy and heteroazeotropy. As a first step towards understanding the phenomena of equilibrium of binary molecular systems, the properties of binary monoatomic fluids have been studied in this work. An additional simplification made in this work is that of a symmetrical binary system where all similar molecules interact via the hard-core Yukawa (HCY) potential, u(r), while the dissimilar molecules interact via a potential, delta u(r) where delta is a scalar parameter. The value of delta here is 0.75, which leads to the dissimilar molecules showing a tendency to dislike one another and the resulting phase diagram is such that the mixing-demixing line intersects the vapor-liquid equilibrium curve away from the vapor-liquid critical point. The effect of the variable potential range parameter of the HCY potential on the topology of the phase diagrams is investigated using grand canonical transition matrix Monte Carlo simulations and the conditions of temperature and pressure at which the system exhibits azeotropy and heteroazeotropy are ascertained. We find that the densities of the mixtures, as predicted by our simulation at equimolar concentrations, are in close agreement with the self-consistent Ornstein-Zernike approximation results of Scholl-Paschinger and co-workers. (C) 2016 Elsevier B.V. All rights reserved.

We calculated the pressure-area isotherm of a dipalmitoyl-phosphatidylcholine (DPPC) lipid monolayer from molecular dynamics simulations using a coarse-grained molecular model. We characterized the monolayer structure, geometry, and phases directly from the simulations and compared the calculated isotherm to experiments. The calculated isotherm shows liquid-expanded and liquid-condensed phases and their coexistence plateau. At high pressure, the monolayer surface is rippled; upon further compression, the monolayer undergoes a collapse. We studied the effect of temperature and system size on the isotherm slope and phase coexistence region. Thermodynamic and dynamic properties of the monolayer phases were also investigated.

Interfacial tension measurements of the (CO2 + N2 + H2O) and (N2 + H2O) systems are reported at pressures of (2 to 40) MPa, and temperatures of (298.15 to 448.15) K. The pendant drop method was used in which it is necessary to know the density difference between the two phases. To permit calculation of this difference, the compositions of the coexisting phases were first computed from a combination of the Peng–Robinson equation of state (applied to the non-aqueous phase) and the NRTL model (applied to the aqueous phase). Densities of the non-aqueous phase were computed from the GERG-2008 equation of state, while those of the aqueous phase were calculated knowing the partial molar volumes of the solutes. The expanded uncertainties at 95% confidence are 0.05 K for temperature, 0.07 MPa for pressure, 0.019γ for interfacial tension in the binary (N2 + H2O) system; and 0.032γ for interfacial tension in the ternary (CO2 + N2 + H2O) system. The interfacial tensions in both systems were found to decrease with both increasing pressure and increasing temperature. An empirical correlation has been developed for the interfacial tension of the (N2 + H2O) system in the full range of conditions investigated, with an average absolute deviation of 0.20 mN · m−1, and this is used to facilitate a comparison with literature values. Estimates of the interfacial tension for the (CO2 + N2 + H2O) ternary system, by means of empirical combining rules based on the coexisting phase compositions and the interfacial tensions of the binary sub-systems, (N2 + H2O) and (CO2 + H2O), were found to be somewhat inadequate at low temperatures, with an average absolute deviation of 1.9 mN · m−1 for all the conditions investigated. To enable this analysis, selected literature data for the interfacial tensions of the (CO2 + H2O) binary system have been re-analysed, allowing for improved estimates of the density difference between the two phases. The revised result on eleven isotherms were fitted with empirical models that generally represent the data to within 1 mN · m−1.

The last decade has seen a continued development of better experimental techniques to measure equation-of-state (EOS) for various materials. These improvements of both static and shock-compression approaches have increased the accuracy of the EOS and challenged the complimentary theoretical modeling. The conventional modeling of EOS, at least at pressure and temperature conditions that are not too extreme, is founded on density-functional theory (DFT). Naturally, there is an increased interest in the accuracy of DFT as the measurements are becoming more refined and there is a particular interest in the robustness and validity of DFT at conditions where experimental data are not available. Here, we consider a broad and large set of 64 elemental solids from low atomic number Z up to the very high Z actinide metals. The intent is to compare DFT with experimental zero-temperature isotherms up to 1 Mbar (100 GPa) and draw conclusions regarding the theoretical (DFT) error and quantify a reasonable and defensible approach to define the theoretical uncertainty. We find that in all 64 cases the DFT error at high pressure is smaller than or equal to the DFT error at lower pressures which thus provides an upper bound to the error at high compression.

As experimental measurements of thermodynamic properties have improved in accuracy, to five or six figures, over the decades, cubic equations that are widely used for modern thermodynamic fluid property data banks require ever-increasing numbers of terms with more fitted parameters. Functional forms with continuity for Gibbs density surface (p,T) which accommodate a critical-point singularity are fundamentally inappropriate in the vicinity of the critical temperature (T-c) and pressure (p(c)) and in the supercritical density mid-range between gas- and liquid-like states. A mesophase, confined within percolation transition loci that bound the gas- and liquid-state by third-order discontinuities in derivatives of the Gibbs energy, has been identified. There is no critical-point singularity at T-c on Gibbs density surface and no continuity of gas and liquid. When appropriate functional forms are used for each state separately, we find that the mesophase pressure functions are linear. The negative and positive deviations, for both gas and liquid states, on either side of the mesophase, are accurately represented by three or four-term virial expansions. All gaseous states require only known virial coefficients, and physical constants belonging to the fluid, i.e., Boyle temperature (T-B), critical temperature (T-c), critical pressure (p(c)) and coexisting densities of gas ((cG)) and liquid ((cL)) along the critical isotherm. A notable finding for simple fluids is that for all gaseous states below T-B, the contribution of the fourth virial term is negligible within experimental uncertainty. Use may be made of a symmetry between gas and liquid states in the state function rigidity (dp/d)(T) to specify lower-order liquid-state coefficients. Preliminary results for selected isotherms and isochores are presented for the exemplary fluids, CO2, argon, water and SF6, with focus on the supercritical mesophase and critical region. info:eu-repo/semantics/publishedVersion

A detailed study on the ternary Zr-based intermetallic compound Zr2TiAl has been carried out using first-principles electronic structure calculations. From the total energy calculations, we find an antiferromagnetic L11-like (AFM) phase with alternating (1 1 1) spin-up and spin-down layers to be a stable phase among some others with magnetic moment on Ti being 1.22 ${{\mu}_{\text{B}}}$ . The calculated magnetic exchange interaction parameters of the Heisenberg Hamiltonian and subsequent Heisenberg Monte Carlo simulations confirm that this phase is the magnetic ground structure with Neel temperature between 30 and 100 K. The phonon dispersion relations further confirm the stability of the magnetic phase while the non-magnetic phase is found to have imaginary phonon modes and the same is also found from the calculated elastic constants. The magnetic moment of Ti is found to decrease under pressure eventually driving the system to the non-magnetic phase at around 46 GPa, where the phonon modes are found to be positive indicating stability of the non-magnetic phase. A continuous change in the band structure under compression leads to the corresponding change of the Fermi surface topology and electronic topological transitions (ETT) in both majority and minority spin cases, which are also evident from the calculated elastic constants and density of state calculations for the material under compression.

International audience; The challenges in reducing the world's dependence on crude oil and the greenhouse gas accumulation in the atmosphere, while simultaneously improving engine performance through better fuel efficiency and reduced exhaust emissions, have led to the emergence of new fuels, with formulations blending petrodiesel, biodiesel, bioethanol and water in various proportions. In parallel, the sustainability of the new biofuel industries also requires to maintain a high level of biodiversity while playing on techno-diversity, using a variety of resources that do not compete with edible crops (nor by using arable land for energy crops or food crops for energy production) and flexible conversion technologies satisfying the eco-design, eco-energy and eco-materials criteria. In addition, it would be relevant to consider blending ethyl biodiesel, instead of methyl biodiesel, with petrodiesel, particularly if the fuel formulation is completed with bioethanol (or even water). The supercritical ethanolysis of lipid resources to produce ethyl biodiesel is a simple but efficient route that should have the potential to satisfy the sustainability criteria if analyzed holistically. Therefore, this review focuses specifically on the production of ethyl biodiesel via triglyceride supercritical ethanolysis within a global analysis "feedstocks-conversion-engine". The scientific and technical bottlenecks requiring further development are highlighted by emphasizing (i) the kinetic and thermodynamic aspects (experiments and modeling) required for the process simulation, the results of which aim at securing the life cycle assessment, first at the process level and then at the fuel level; (ii) the proposals to improve the supercritical process performance in terms of eco-material and eco-energy; (iii) the impacts of ethyl vs. methyl biodiesel fuels and of biodiesel ethanol petrodiesel blends (with or without water) on the diesel engine emissions and performance; (iv) the technological flexibility of the supercritical process allowing its conversion toward production of other key products. Finally, built on the state-of-the art review, a new R&D direction combining supercritical ethanolysis of lipids with the addition of CO2, glycerol recovery, and cogeneration, according to the biorefinery concept, is proposed and discussed.

In this work, a predictive model for binary diffusivities at infinite dilution (D-12) in SC-CO2 is proposed. It combines two terms - background and singular - with the objective to represent D-12 accurately not only far but also near the critical point, where critical enhancement is always observed. The model provides an average error of 6.20% for a large database including 149 systems and 4469 data points over wide ranges of temperature and pressure. The models selected for comparison (Wilke-Chang, Scheibel, Lusis-Ratcliff, Lai-Tan, Tyn-Calus and Reddy-Doraiswamy) achieve scattered and biased results, with average errors from 11.62% to 75.17%. In the whole, the new model exhibits an excellent performance for any kind of molecules in terms of size, molecular weight, polarity and sphericity, in all critical region. In order to help interested readers, a spreadsheet for the calculation of D-12 is given in Supplementary data. The input data is: temperature, pressure, CO2 viscosity, and solute properties (acentric factor, critical constants, molar volume at normal boiling point, and molecular weight - given in this paper for the systems studied). (C) 2014 Elsevier B.V. All rights reserved.

The water solubility in fatty acid esters and biodiesels and the vapor-liquid equilibria (VLE) of fatty acid ester + methanol/ethanol systems, formed at biodiesel production and purification industrial units, were modeled in this work to complete the development and application of the soft-SAFT equation of state (EoS) to the design and optimization of biodiesel production plants. The soft-SAFT EoS is able to accurately describe the water solubility and the VLE of methanol and ethanol with a large number of binary systems, composed of a variety of esters, in wide ranges of temperature, including near/supercritical conditions, with the use of just one binary interaction parameter. This parameter is chain length dependent for the water systems, while it is constant for the methanol and the ethanol binary mixtures. An entirely predictive scheme is proposed for the soft-SAFT EoS water solubility in biodiesels description, being only necessary to know the biodiesel fatty acid esters composition to determine the required molecular and binary interaction parameters. A new association scheme to explicitly consider the solvation phenomenon between esters and water/alcohols is also proposed. The results obtained in this work with soft-SAFT are clearly superior, regarding qualitative and quantitative agreement with the experimental data and predictive ability of the model, to those obtained with other similar modeling approaches, namely with the Cubic-plus-Association equation of state (CPA EoS) and other SAFT-type EoSs, as discussed throughout the work. The soft-SAFT EoS is shown here as a valuable tool to assist the design of biodiesel purification units, specifically for applications in the biodiesel washing, drying and alcohol removal, in order to obtain the biodiesel with the quality specifications required by the international standards. (C) 2014 Elsevier Ltd. All rights reserved.

International audience; The doubly bonded dimer association scheme (DBD) proposed by Sear and Jackson is extended to mixtures exhibiting both self- and cross-associations. The PC-SAFT equation of state is combined with the new DBD association contribution to describe the vapor-liquid equilibria of binary mixtures of carboxylic acids + associating compounds (water, alcohols, and carboxylic acids). The effect of doubly bonded dimers on the phase behavior in such systems is less important than in mixtures of carboxylic acids with nonassociating compounds, due to the cross-associations that compete with the formation of DBDs. Nevertheless, a clear improvement in the description of vapor-liquid coexistence curves is achieved over the classical 2B association model, particularly for the dew point curves.

International audience; Speeds of sound have been measured in ethyl myristate (C16H 32O2), methyl myristate (C15H 30O2), and methyl palmitate (C17H 34O2) at pressures up to 100 MPa along isotherms ranging from (293.15 to 403.15) K. The measurements were carried out using a pulse echo technique operating at 3 MHz. Additional compressed liquid density measurements were performed from (293.15 to 393.15) K with pressures from (0.1 to 100) MPa in order to evaluate isentropic compressibility using speed of sound measurements. An equation of state that represents both the density and the speed of sound temperature reported experimental data within their estimated uncertainties is given to evaluate the volume as well as its derivatives of these components.

A new free-volume model for tracer diffusion coefficients in supercritical CO2 and liquid water is proposed in this work. It embodies the concepts of free volume and activation energy. The free volume is calculated by the Carnahan-Starling expression, and the necessary effective hard sphere diameter was taken from a previous publication. The model is explicit, straightforward, contains one parameter per system (activation energy), and only requires temperature, solvent density, solute molecular weight, and the solvent LJ constants. The validation of the model was accomplished with a large database, comprehending 289 systems with 5485 data points, and achieved only 3.56% of error. The fine predictive capability of the new expression was also demonstrated. The correlations of Wilke-Chang, Tyn-Calus, He-Yu-Su, Zhu et al., and Dymond were adopted for comparison, but provided much poorer results and/or prediction values. A spreadsheet for the calculation of D-12 is given in Supplementary data. (C) 2012 Elsevier B.V. All rights reserved.

The use of monomolecular Langmuir films and multilamellar systems as models of biological membranes is widespread in the literature. However, several examples highlighted some different properties of monolayer and multilayer systems like miscibility, phase equilibrium, hydration or dynamics. Our work contributes to this question by comparing the lipid ordering in monolayers and stacks of flat bilayers. We have considered the monolayer spread at the air-water interface and the liquid-crystalline gel phase formed by 1,2-distearoylphosphatidylcholine (DSPC) at 20 degrees C. Grazing Incidence X-ray Diffraction (GIXD) and Small-Angle X-ray Scattering (SAXS) coupled with Wide-Angle X-ray Scattering (WAXS) were employed to analyse the ordering of DSPC chains in these model systems. Results show that the ordering of DSPC in monolayers and stacked bilayers is indeed different. The lattices in monolayers and stacked bilayers are distorted in different directions and at different rates. Additionally, we incorporated an unsaturated neutral lipid (1-stearoyl-2-arachidonoyl-glycerol, SAG) in DSPC monolayers and multilayers. Despite the same miscibility range, we found the same difference between monolayers and stacked bilayers in the mixed system DSPC-SAG as for pure DSPC. The in-plane structure of self-assembled lipids must be then considered with care when comparing monolayers and stacks of bilayers.