Phase coexistance in polydisperse mixture of hard-sphere colloidal and flexible chain particles

A theoretical scheme for the calculation of the full phase diagram (including cloud and shadow curves, binodals and distribution functions of the coexisting phases) for colloid-polymer mixtures with polymer chain length polydispersity and hard-sphere colloidal and polymeric monomer sizes polydispersity is proposed. The scheme combines thermodynamic perturbation theory for associating fluids and recently developed method used to determine the phase diagram of polydisperse spherical shape colloidal fluids (L.Bellier-Castella {\it et al.}, {\it J.Chem.Phys.} {\bf 113}, 8337(2000)). By way of illustration we present and discuss the full phase diagram for the mixture with polydispersity in the size of the hard-sphere colloidal particles.Comment: 6 pages, 4 figure

A generalized Kiselev crossover approach applied to Soave–Redlich–Kwong equation of state

International audienceThree different variants of the crossover Soave–Redlich–Kwong equation of state are applied to describe the equilibrium behaviour of 72 common non-associating fluids – 27 hydrocarbons (including the first 10 n-alkanes), 36 halogenated refrigerants, 5 cryogenics (fluorine, oxygen, nitrogen, argon and carbon monoxide) and 4 other industrially important inorganic fluids (carbon dioxide, sulfur dioxide, nitrous oxide and sulfur hexafluoride). The model contains six compound dependent parameters.Two of them (a0 and b of the classical part) are adjusted on the critical experimental temperature and the critical pressure. In a first model denoted as model A, the four remaining parameters are fitted to describe the saturated liquid and vapour densities and vapor pressures as well as PVT data at pressures up to P = 3 × Pc. In the second model (model B), the dispersion softness m is expressed as a function of the acentric factor ω and a relation between two of the crossover parameters is employed; the number of fitted parameters is thus reduced to two. Based on model B, we suggested our final Model C, in which all the parameters can be determined from the critical point, acentric factor or rectlinear diameter. This model is superior to the classical Soave–Redlich–Kwong equation of state because it improves considerably the description of the liquid densities over the whole coexistence region. Contrary to equations of state optimized to reproduce the liquid densities at low temperatures, the crossover equation does not overpredict the critical temperature and pressure. Model C is applied to describe the equilibrium behaviour of two compounds not included in the parameterization, hexafluoropropene (HFO1216) and hexafluoropropene oxide (HFPO)

Modeling of Transport Properties Using the SAFT-VR Mie Equation of State

International audienceCarbon capture and storage (CCS) has been presented as one of the most promising methods to counterbalance the CO 2 emissions from the combustion of fossil fuels. Density, viscosity and interfacial tension (IFT) are, among others properties, crucial for the safe and optimum transport and storage of CO 2-rich steams and they play a key role in enhanced oil recovery (EOR) operations. Therefore, in the present work the capability of a new molecular based equation of state (EoS) to describe these properties was evaluated by comparing the model predictions against literature experimental data. The EoS considered herein is based on an accurate statistical associating fluid theory with variable range interaction through Mie potentials (SAFT-VR Mie EoS). The EoS was used to describe the vapor-liquid equilibria (VLE) and the densities of selected mixtures. Phase equilibrium calculations are then used to estimate viscosity and interfacial tension values. The viscosity model considered is the TRAPP method using the single phase densities, calculated from the EoS. The IFT was evaluated by coupling this EoS with the density gradient theory of fluids interfaces (DGT). The DGT uses bulk phase properties from the mixture to readily estimate the density distribution of each component across the interface and predict interfacial tension values. To assess the adequacy of the selected models, the modeling results were compared against experimental data of several CO 2-rich systems in a wide range of conditions from the literature. The evaluated systems include five binaries (CO 2 /O 2 , CO 2 /N 2 , CO 2 /Ar, CO 2 /n-C 4 and CO 2 /n-C 10) and two multicomponent mixtures (90%CO 2 / 5%O 2 / 2%Ar / 3%N 2 and 90%CO 2 / 6%n-C 4 / 4%n-C 10). The modeling results showed low percentage absolute average deviations to the experimental viscosity and IFT data from the literature, endorsing the capabilities of the adopted models for describing thermophysical properties of CO 2-rich systems

Density functional theory and demixing of binary hard rod-polymer mixtures

A density functional theory for a mixture of hard rods and polymers modeled as chains built of hard tangent spheres is proposed by combining the functional due to Yu and Wu for the polymer mixtures [J. Chem. Phys. {\bf 117}, 2368 (2002)] with the Schmidt's functional [Phys. Rev. E {\bf 63}, 50201 (2001)] for rod-sphere mixtures. As a simple application of the functional, the demixing transition into polymer-rich and rod-rich phases is examined. When the chain length increases, the phase boundary broadens and the critical packing fraction decreases. The shift of the critical point of a demixing transition is most noticeable for short chains.Comment: 4 pages,2 figures, in press, PR

Predicting enhanced absorption of light gases in polyethylene using simplified PC-SAFT and SAFT-VR

International audienceAbsorption of light gases in polyethylene (PE) is studied using two versions of the Statistical Associating Fluid Theory (SAFT): SAFT for chain molecules with attractive potentials of variable range (VR) and simplified perturbed-chain (PC) SAFT. Emphasis is placed on the light gases typically present during ethylene polymerisation in the gas-phase reactor (GPR) process. The two approaches are validated using experimental binary-mixture data for gas absorbed in PE, and predictions are made for mixtures of more components. For most cases studied both SAFT versions perform equally well. For the case of ternary mixtures of two gases with PE, it is predicted that the less-volatile of the two gases acts to enhance the absorption of the more-volatile gas, while the more-volatile gas inhibits the absorption of the less-volatile gas. This general behaviour is also predicted in mixtures containing more gases, such as typical reactor mixtures. The magnitude of the effect may vary considerably, depending on the relative proximity of the gas-mixture saturation pressure to the reactor pressure; for example it is predicted that the absorption of ethylene may be approximately doubled if diluent gases, propane or nitrogen, are partially or completely replaced by less-volatile butane or pentane for a reactor pressure similar to 2 MPa. In the case of a co-polymerisation reaction, it is predicted that increases in absorption of both co-monomers may be obtained in roughly equal proportion. Our findings cast light on the so-called co-monomer effect, in which substantial increases in the rate of ethylene polymerisation are observed in the presence of hexene co-monomer, while suggesting that the effect is more general and not restricted to co-monomer. For example, similar rate increases may be expected in the presence of, e.g., pentane instead of hexene, but without the change in the branch structure of the produced polymer that is inevitable when the amount of co-monomer is increased

Modeling the phase equilibria of refrigerant fluids with the COSMO-SAC and COSMO-RS approaches. Application to process simulation

International audienceOn account of the constraints imposed by the European and International legislations, the refrigerant industry must constantly find alternative refrigerant fluids that have lower impacts on the global warming of Earth and Ozone layer. Working with refrigerant blends is often preferable to pure component fluids for energy saving and flexibility of operation. In order to select the optimal mixture composition for the design and operation of a refrigeration process, it is necessary to know the phase diagram and thermodynamic properties of mixtures. Vapor-liquid equilibria (VLE) and the location of azeotropes must be accurately known. In this work three different thermodynamic models based on the COSMO approach have been used to predict the phase equilibria of mixtures of refrigerant molecules: the COSMO-RS model developed by Klamt and co workers [1, 2], the 2002 version of COSMO-SAC model [3], and the COSMO-SAC-dsp model [4] that includes a dispersion term. The vapor-liquid equilibria can be reasonably well predicted by the COSMO-RS model, however bad predictions are obtained with COSMO-SAC 2002. In particular, the COSMO-SAC model is unable to predict the azeotropic behavior observed in mixtures of alkanes and fluorinated molecules. By adjusting some universal parameters, it is possible to obtain reasonable predictions with the COSMO-SAC dsp model

Experimental and modelling study of the densities of the hydrogen sulphide + methane mixtures at 253, 273 and 293 K and pressures up to 30 MPa

International audienceDensities of three binary mixtures of hydrogen sulphide and methane (xH 2 S + (1-x) CH 4), with mole fractions of 0.1315, 0.1803 and 0.2860 of acid gas, were determined experimentally at three temperatures (253, 273 and 293) K and at pressures up to 30 MPa. Densities were measured continuously using a high temperature and high pressure Vibrating Tube densitometer (VTD), Anton Paar DMA 512. The SAFT-VR Mie, PR and GERG2008 equations of state (EoS) are used to describe the experimental data with different levels of success

A comprehensive approach to incorporating intermolecular dispersion into the openCOSMO-RS model. Part 1: Halocarbons

The COSMO-RS (Conductor-like Screening Model for Real Solvents) is a predictive thermodynamic model that has found diverse applications in various domains like chemical engineering, environmental chemistry, nanotechnology, material science, and biotechnology. Its core concept involves calculating the screening charge density on the surface of each molecule and letting these surface patches interact with each other to calculate thermodynamic properties. In this study, we aim to enhance the performance of the open-source implementation openCOSMO-RS by incorporating dispersive interactions between the paired segments. Several parametrizations were systematically evaluated through the extensive regression analysis using a comprehensive database of Vapor-Liquid Equilibrium (VLE), Liquid-Liquid Equilibrium (LLE) and Infinite Dilution Activity Coefficients (IDACs). Furthermore, the influence of different combinatorial terms on the model performance was investigated. Our findings indicate that incorporating dispersive interactions significantly improves the accuracy of phase equilibrium predictions for halocarbons and refrigerant mixtures

Some universal trends of the Mie(n,m) fluid thermodynamics

By using canonical Monte Carlo simulation, the liquid-vapor phase diagram, surface tension, interface width, and pressure for the Mie(n,m) model fluids are calculated for six pairs of parameters $m$ and $n$. It is shown that after certain re-scaling of fluid density the corresponding states rule can be applied for the calculations of the thermodynamic properties of the Mie model fluids, and for some real substancesComment: 4 figure

New criteria for the equation of state development: Simple model fluids

Recently we have proposed (J. Chem. Phys. 128 (2008) 134508) a new rescaling of fluid density $\rho$ by its critical value $\rho_c^{2/3}$ to apply the corresponding states law for the attractive Yukawa fluids study. Analysis of precise simulation results allows us to generalize this concept to the case of simple fluids with different interparticle interactions, like Mie (n,m) and Sutherland pair potentials. It is shown, that there is a linear relationship between the critical pressure and critical temperature, as well as the critical density and inverse critical temperature for these frequently used pair potentials. As a consequence, the critical compressibility factor of these model fluids is close to its universal value measured experimentally for different real substances.Comment: 5 pages, 3 figure