Alexey Victorov

Thermodynamic properties of pure fluids and solutions from the hole group-contribution model

The hole lattice model for pure fluids and fluid mixtures of molecules differing in size and shape is presented. Orientational effects are taken into account with the aid of the quasichemical approximation. The equation of state and relations for the wide range of thermodynamic quantities are deduced. The calculations are made for pure n-alkanes, n-alkanols, acetic acid, H2S, H2O, for binary mixtures of these substances with n-alkanes and for ternary hexaneheptaneoctane and hexanepropanoldecanol solutions. Systems under elevated pressures (up to 100 atm) are taken into consideration. The homologue series are treated in the group-contribution approach.

Fluid phase equilibria in water : natural gas component mixtures and their description by the hole group-contribution equation of state

Abstract Victorov A.I., Fredenslund Aa. and Smirnova N.A., 1991. Fluid phase equilibria in water:natural gas component mixtures and their description by the hole group-contribution equation of state. Fluid Phase Equilibria, 66: 187-210. Experimental data on fluid phase equilibria in binary mixtures of water with typical natural gas and oil components (light and heavy alkanes, nitrogen, hydrogen sulfide, carbon dioxide) have been examined and the phase behavior of these mixtures over wide ranges of temperature and pressure is reviewed. A quasi-chemical group-contribution hole model is used for calculating the phase equilibria in these systems. With few exceptions the model predicts correctly the basic types of phase behavior and, except for gas-gas equilibria, the accuracy for all the binaries and two multicomponent aqueous mixtures tested is satisfactory.

Description of asphaltene polydispersity and precipitation by means of thermodynamic model of self-assembly

A thermodynamic approach describing the precipitation of asphaltene materials from petroleum fluids as a consequence of aggregate break-up is presented. The aggregation equilibrium for asphaltenes and resins is considered along with the bulk-phase equation of state (EOS) to account for the effects of pressure and solvents on the thermodynamic behavior of asphaltene dispersions. Polydispersity of asphaltene aggregates is taken into account. The effect of the resin molecular shape on the size distribution is considered. Relation between the shape factors and elastic constants of the resin shell of the aggregates is given. Precipitation curves for several real crude oil mixtures are calculated and structural characteristics of the aggregates are estimated. Comparison with the experimental data shows that the results are reasonable.

Application of the hole quasi-chemical group contribution equation of state for phase equilibrium calculation in systems with association

Abstract Victorov A.I. and Fredenslund Aa., 1991. Application of the hole quasi-chemical group contribution equation of state for phase equilibrium calculation in systems with association. Fluid Phase Equilibria, 66: 77-101. Hole group contribution quasi-chemical model parameters for mixtures containing methanol, water and acetone together with light and heavy alkanes, nitrogen, hydrogen sulfide and carbon dioxide are determined. A list of model parameters is given, encompassing about 30 different functional groups. The results of liquid-gas and liquid-liquid equilibrium calculations for many binary and several multicomponent mixtures at normal and elevated pressures (up to 40 MPa) are discussed.

Molecular thermodynamics for swelling of a mesoscopic ionomer gel in 1 : 1 salt solutions

For a microphase-separated diblock copolymer ionic gel swollen in salt solution, a molecular-thermodynamic model is based on the self-consistent field theory in the limit of strongly segregated copolymer subchains. The geometry of microdomains is described using the Milner generic wedge construction neglecting the packing frustration. A geometry-dependent generalized analytical solution for the linearized Poisson-Boltzmann equation is obtained. This generalized solution not only reduces to those known previously for planar, cylindrical and spherical geometries, but is also applicable to saddle-like structures. Thermodynamic functions are expressed analytically for gels of lamellar, bicontinuous, cylindrical and spherical morphologies. Molecules are characterized by chain composition, length, rigidity, degree of ionization, and by effective polymer-polymer and polymer-solvent interaction parameters. The model predicts equilibrium solvent uptakes and the equilibrium microdomain spacing for gels swollen in salt solutions. Results are given for details of the gel structure: distribution of mobile ions and polymer segments, and the electric potential across microdomains. Apart from effects obtained by coupling the classical Flory-Rehner theory with Donnan equilibria, viz. increased swelling with polyelectrolyte charge and shrinking of gel upon addition of salt, the model predicts the effects of microphase morphology on swelling.

Equilibrium of ion-exchange polymeric membrane with aqueous salt solution and its thermodynamic modeling

A thermodynamic model is proposed to describe distribution of the components between a liquid solution and a swollen membrane undergoing structural transformations. Free energy contributions related to formation of solution-filled micro-cavities in the membrane interior are estimated. Formation of the cavities of different shape is accounted for by using the Helfrich expressions for the bending energy of a curved interface. Three adjustable parameters of the model are related to the hydrophobic polymer matrix of the membrane, while the electrostatic contribution is estimated explicitly. Structural changes in the membrane are described as a transition from spherical to cylindrical cavities. Predominance of cavities having definite shape (spheres, cylinders) results in a specific shift of the Donnan equilibrium, which thus, becomes dependent on the structure of the membrane on the mesoscale. The results of model calculations are compared with the experimental data on the distribution of ions (H+, Li+, Cs+, K+, Na+, Ca2+, Mg2+) between the aqueous solution and the membrane. Different types of predicted thermodynamic behavior of the membrane in the liquid solution, including the hysteresis of ion-exchange equilibrium curves, are discussed. The model takes into account the effect of micro-inhomogeneties and helps to establish a link between molecular characteristics of the perfluoropolymer membrane and its macroscopic behavior in the liquid solution.

Equilibrium swelling and mesoscopic structure of a diblock copolymer gel in a selective solvent

Our previous analytic model [A.I. Victorov, C.J. Radke, J.M. Prausnitz. Molec. Phys., 100, 2277 (2002)] of a block-copolymer gel swollen in selective solvent was obtained from self–consistent field theory in the strong–segregation approximation; it takes into account the structure of the gel on the mesoscopic scale but is restricted to the case where the solvent–selective polymer subchains are located in the inner (minority) domains. In this work, the model is generalized to include swollen outer domains. The dependence of the equilibrium microdomain size on solvent uptake has been established. We calculate equilibrium swelling and determine relative stabilities for gels of different morphologies. Predicted equilibrium profiles of polymer segments are compared with computer simulation. Based on the average–solvent–fraction approximation, results obtained for an athermal solvent are very close to those from equilibrium profiles. Attention is given to the effect of partial restrictions in self–assembly of polymer chains on microdomain spacing and on equilibrium swelling.

A simple analytical approach to electrostatics for nanoparticles with torus-like elements in 1:1 electrolyte solution

For charged wormlike particles immersed in 1:1 electrolyte solution, a theory is based on approximate analytical solution of the linearized Poisson–Boltzmann (PB) equation. Analytical expressions have been obtained for the electrostatic free energy of a bent cylinder and for the electrostatic contribution to its persistence length. Different regimes of deformation of a wormlike particle lead to different expressions for the electrostatic persistence length. For different regimes, the dependence of the electrostatic persistence length on salinity has been established and compared with that from previously known theories. The theory is applied to solutions of polyelectrolyte chains and to solutions of wormlike micelles of ionic surfactants. Apart from systems considered in this work, the simple electrostatics may be useful in many other engineering applications.

Phase equilibria modeling by the quasilattice equation of state for binary and ternary systems composed of carbon dioxide, water and some organic components

Abstract The hole lattice quasichemical group-contribution model (HM) has been applied to described liquid-liquid, liquid-liquid-vapour and vapour-liquid equilibria at elevated and high pressures in binary and ternary mixtures containing CO 2 , water, alkanols, paraffinic and aromatic hydrocarbons. An estimation of the concentration of alkanol monomers in the binaries with CO 2 has been performed. The results of modeling by the HM EOS and the Associated Perturbed Anisotropic Chain Theory (APACT) are compared. In most cases both EOS give satisfactory agreement with experimental data.

Prediction of multiphase equilibria in associating fluids by a contact-site quasichemical equation of state

A contact-site quasichemical equation of state has been used Tor the modeling of different kinds of fluid phase equilibria (between a gas phase and one or more liquids) over a wide range of conditions. Among the systems of interest are the ternary mixtures water + alkanols + hydrocarbons (alkanes or alkynes), water + alkanols (or acetone)+ CO2, water + polyoxyethyleneglycol ethers + heavy alkanes. The model has been applied to describing the thermodynamic properties of the binary subsystems and to predict the phase behavior of the ternary systems. For longer-chain alkanols and hydrocarbons a group-contribution approach is implemented, which allows the modeling when no experimental data are available. The model gives reasonable predictions of phase behavior and the correct trends in the calculated phase diagrams in most cases. The concentrations of associates in liquid and gas phases are estimated by the model and compared with some experimental and computer simulation data. The predictive abilities of the model, its limitations, and possible ways of its improvement are discussed.