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In this paper, we present an analysis of argon adsorption in cylindrical pores having amorphous silica structure by means of a nonlocal density functional theory (NLDFT). In the modeling, we account for the radial and longitudinal density... more
In this paper, we present an analysis of argon adsorption in cylindrical pores having amorphous silica structure by means of a nonlocal density functional theory (NLDFT). In the modeling, we account for the radial and longitudinal density distributions, which allow us to consider the interface between the liquidlike and vaporlike fluids separated by a hemispherical meniscus in the canonical ensemble. The Helmholtz free energy of the meniscus was determined as a function of pore diameter. The canonical NLDFT simulations show the details of density rearrangement at the vaporlike and liquidlike spinodal points. The limits of stability of the smallest bridge and the smallest bubble were also determined with the canonical NLDFT. The energy of nucleation as a function of the bulk pressure and the pore diameter was determined with the grand canonical NLDFT using an additional external potential field. It was shown that the experimentally observed reversibility of argon adsorption isotherms at its boiling point up to the pore diameter of 4 nm is possible if the potential barrier of 22kT is overcome due to density fluctuations.
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Research Interests: Chemical Engineering, High Pressure, Prediction, Density, DISTRIBUTION, and 16 morePhase Transitions, Adsorption, Activated Carbon, Fluid, Density Functional Theory, Free Energy, Waste minimisation, Solid, Interaction Design for Energy, Distribution, Activated carbons, Carbon Black, Monolayer, Potential Energy, Minimization, and Capillary Condensation
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A model for the dynamics of isothermal absorption of a binary mixture of an organic substance, soluble in water, and water vapor in a fixed bed of activated carbon was proposed. It includes the equations of material balance and the... more
A model for the dynamics of isothermal absorption of a binary mixture of an organic substance, soluble in water, and water vapor in a fixed bed of activated carbon was proposed. It includes the equations of material balance and the Myers—Prausnitz model for equilibrium adsorption. The possibility of formation of the condensed phase during the adsorption of an organic substance
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This paper presents a refined technique to describe two-dimensional phase transitions in dense fluids adsorbed on a crystalline surface. Prediction of parameters of 2D liquid-solid equilibrium is known to be an extremely challenging... more
This paper presents a refined technique to describe two-dimensional phase transitions in dense fluids adsorbed on a crystalline surface. Prediction of parameters of 2D liquid-solid equilibrium is known to be an extremely challenging problem, which is mainly due to a small difference in thermodynamic functions of coexisting phases and lack of accuracy of numerical experiments in case of their high density. This is a serious limitation of various attempts to circumvent this problem. To improve this situation, a new methodology based on the kinetic Monte Carlo method was applied. The methodology involves analysis of equilibrium gas-liquid and gas-solid systems undergoing an external potential, which allows gradual shifting parameters of the phase coexistence. The interrelation of the chemical potential and tangential pressure for each system is then treated with the Gibbs-Duhem equation to obtain the point of intersection corresponding to the liquid/solid-solid equilibrium coexistence....
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Commensurate-incommensurate (C-IC) transition of krypton molecular layer on graphite received much attention in recent decades in theoretical and experimental researches. However, there still exists a possibility of generalization of the... more
Commensurate-incommensurate (C-IC) transition of krypton molecular layer on graphite received much attention in recent decades in theoretical and experimental researches. However, there still exists a possibility of generalization of the phenomenon from thermodynamic viewpoint on the basis of accurate molecular simulation. Recently, a new technique was developed for analysis of two-dimensional (2D) phase transitions in systems involving a crystalline phase, which is based on accounting for the effect of temperature and the chemical potential on the lattice constant of the 2D layer using the Gibbs-Duhem equation [E. A. Ustinov, J. Chem. Phys. 140, 074706 (2014)]. The technique has allowed for determination of phase diagrams of 2D argon layers on the uniform surface and in slit pores. This paper extends the developed methodology on systems accounting for the periodic modulation of the substrate potential. The main advantage of the developed approach is that it provides highly accurate...
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We present for the first time in the literature a new scheme of kinetic Monte Carlo method applied on a grand canonical ensemble, which we call hereafter GC-kMC. It was shown recently that the kinetic Monte Carlo (kMC) scheme is a very... more
We present for the first time in the literature a new scheme of kinetic Monte Carlo method applied on a grand canonical ensemble, which we call hereafter GC-kMC. It was shown recently that the kinetic Monte Carlo (kMC) scheme is a very effective tool for the analysis of equilibrium systems. It had been applied in a canonical ensemble to describe vapor-liquid equilibrium of argon over a wide range of temperatures, gas adsorption on a graphite open surface and in graphitic slit pores. However, in spite of the conformity of canonical and grand canonical ensembles, the latter is more relevant in the correct description of open systems; for example, the hysteresis loop observed in adsorption of gases in pores under sub-critical conditions can only be described with a grand canonical ensemble. Therefore, the present paper is aimed at an extension of the kMC to open systems. The developed GC-kMC was proved to be consistent with the results obtained with the canonical kMC (C-kMC) for argon ...
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A new model for equilibrium adsorption of a binary mixture on zeolites that takes into account the energy nonuniformity of the adsorption field in the zeolite cavities was developed on the basis of statistical thermodynamics. The... more
A new model for equilibrium adsorption of a binary mixture on zeolites that takes into account the energy nonuniformity of the adsorption field in the zeolite cavities was developed on the basis of statistical thermodynamics. The nonuniformity of the adsorption field produces rearrangement of molecules in the cavity volume, decreasing the entropy, internal energy, and Helmholz free energy. A procedure for calculation of the thermodynamic functions from the data on the adsorption of pure components was proposed. The limiting cases of maximum ordering of the molecules in the cavity and their random distribution were considered. The approach proposed was exemplified by the substantially non-ideal system nitrogen--argon--zeolite NaX at 160 K. The proposed model describes the behavior of this mixture much better than that of the ideal adsorbed solution theory.
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In this paper, we present an analysis of argon adsorption in cylindrical pores having amorphous silica structure by means of a nonlocal density functional theory (NLDFT). In the modeling, we account for the radial and longitudinal density... more
In this paper, we present an analysis of argon adsorption in cylindrical pores having amorphous silica structure by means of a nonlocal density functional theory (NLDFT). In the modeling, we account for the radial and longitudinal density distributions, which allow us to consider the interface between the liquidlike and vaporlike fluids separated by a hemispherical meniscus in the canonical ensemble. The Helmholtz free energy of the meniscus was determined as a function of pore diameter. The canonical NLDFT simulations show the details of density rearrangement at the vaporlike and liquidlike spinodal points. The limits of stability of the smallest bridge and the smallest bubble were also determined with the canonical NLDFT. The energy of nucleation as a function of the bulk pressure and the pore diameter was determined with the grand canonical NLDFT using an additional external potential field. It was shown that the experimentally observed reversibility of argon adsorption isotherms at its boiling point up to the pore diameter of 4 nm is possible if the potential barrier of 22kT is overcome due to density fluctuations.
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This paper presents a thermodynamic analysis of capillary condensation phenomena in cylindrical pores. Here, we modified the Broekhoff and de Boer (BdB) model for cylindrical pores accounting for the effect of the pore radius on the... more
This paper presents a thermodynamic analysis of capillary condensation phenomena in cylindrical pores. Here, we modified the Broekhoff and de Boer (BdB) model for cylindrical pores accounting for the effect of the pore radius on the potential exerted by the pore walls. The new approach incorporates the recently published standard nitrogen and argon adsorption isotherm on nonporous silica LiChrospher Si-1000. The developed model is tested against the nonlocal density functional theory (NLDFT), and the criterion for this comparison is the condensation/evaporation pressure versus the pore diameter. The quantitative agreement between the NLDFT and the refined version of the BdB theory is ascertained for pores larger than 2 nm. The modified BdB theory was applied to the experimental adsorption branch of adsorption isotherms of a number of MCM-41 samples to determine their pore size distributions (PSDs). It was found that the PSDs determined with the new BdB approach coincide with those determined with the NLDFT (also using the experimental adsorption branch). As opposed to the NLDFT, the modified BdB theory is very simple in its utilization and therefore can be used as a convenient tool to obtain PSDs of all mesoporous solids from the analysis of the adsorption branch of adsorption isotherms of any subcritical fluids.
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ABSTRACT Comparative patterns of equilibrium adsorption of argon on the surface of graphitized thermal carbon black (GCB) and the inhomogeneous surfaces of nongraphitized carbon black and silica at 77 and 87.3 K were considered. It was... more
ABSTRACT Comparative patterns of equilibrium adsorption of argon on the surface of graphitized thermal carbon black (GCB) and the inhomogeneous surfaces of nongraphitized carbon black and silica at 77 and 87.3 K were considered. It was shown that argon acquires the properties of a special phase with a layered structure and exhibits two-dimensional phase transitions with the formation of crystal-like layers near the homogeneous surface of GCB even at a temperature exceeding the triple point. However, already at a distance of three-four molecular diameters from the surface, adsorbed argon behaves as a bulk phase in a weak external field. The defect surface of nongraphitized carbon black and the amorphous surface structure of silica destroy the longrange order of adsorbed argon and lower its solidification temperature. Therefore, argon adsorbed at a temperature of 77 K, i.e., below the triple point, exhibits the properties of a supercooled liquid. The applicability of density functional theory to describe argon isotherms and heat of adsorption on inhomogeneous surfaces was demonstrated.
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The equilibrium adsorption of oxygen, nitrogen, and their mixtures on zeolite NaX at temperatures of from −20 to +30C was analyzed by statistical thermodynamics methods on the basis of the data published by Gorbunov et al. [1]. The... more
The equilibrium adsorption of oxygen, nitrogen, and their mixtures on zeolite NaX at temperatures of from −20 to +30C was analyzed by statistical thermodynamics methods on the basis of the data published by Gorbunov et al. [1]. The regularization method was used to calculate the dependence of the internal energy and entropy of pure gases in zeolite cavities on the number of molecules per cavity. This substantially increased the reliability of the functions found. The heat of sorption as a function of the degree of filling and gas mixture composition was analyzed using the dependences obtained and a new algorithm developed for binary adsorption calculations. The trends revealed can be used to model air separation by pressure swing adsorption.
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Analysis of a binary equilibrium in a distinct micropore showed that the noouniformity of the adsorption field results in a negative deviation of the adsorption solution from ideal behavior. This deviation is due to a decrease in the... more
Analysis of a binary equilibrium in a distinct micropore showed that the noouniformity of the adsorption field results in a negative deviation of the adsorption solution from ideal behavior. This deviation is due to a decrease in the entropy and internal energy caused by rearrangement of adsorbed molecules. Different interactions between identical and different molecules in distinct micropores also result
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A statistical approach was applied to describe the model of a homogeneous microporous adsorbent and obtain the dependences of the thermodynamic functions on the number of molecules and the temperature for molecular aggregates in discrete... more
A statistical approach was applied to describe the model of a homogeneous microporous adsorbent and obtain the dependences of the thermodynamic functions on the number of molecules and the temperature for molecular aggregates in discrete micropores over a wide region of fillings that lead to the Dubinin—Radushkevich equation. The energy nonuniformity of the adsorption space is the fundamental property of
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Dependences of the Helmholtz energy, entropy, and internal energy in single micropores on the total number of guest molecules and the oxygen to nitrogen ratio were found by analysis of experimental data on adsorption of the binary... more
Dependences of the Helmholtz energy, entropy, and internal energy in single micropores on the total number of guest molecules and the oxygen to nitrogen ratio were found by analysis of experimental data on adsorption of the binary oxygen-nitrogen mixture on zeolite NaX using the statistical model. A substantially non-ideal character of the adsorption phase, which exhibits negative deviations from Raout's
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The data on adsorption of cyclopentane, benzene, and their mixture on active carbon were analyzed by the statistical thermodynamic model. A method to describe the state of a binary mixture in single micropores was offered. A substantial... more
The data on adsorption of cyclopentane, benzene, and their mixture on active carbon were analyzed by the statistical thermodynamic model. A method to describe the state of a binary mixture in single micropores was offered. A substantial negative deviation from Raoult's law predicted by the concept of an ideal adsorption solution is a consequence of a decrease in the excessive
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A simple method is proposed for carrying out analytical calculations on adsorption dynamics; by its use one can make allowance for longitudinal effects in determining coefficients of external mass transfer and internal diffusion, and... more
A simple method is proposed for carrying out analytical calculations on adsorption dynamics; by its use one can make allowance for longitudinal effects in determining coefficients of external mass transfer and internal diffusion, and dynamic bed activities.
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