Leonid K. Filippov

Coherent and incoherent frontal patterns for multicomponent dynamics of adsorption—I. Analysis of frontal-pattern isothermal adsorption dynamics for convex mixture isotherms of adsorption

Abstract Theoretical models have been analysed taking into account all major distinctive features of the interphase mass exchange within the porous grains and their surfaces, and the conditions entailing the type of frontal patterns for various isotherms of adsorption (including Langmuirs isotherms). The essential influence of mass exchange kinetics is shown.

MULTICOMPONENT NON-ISOTHERMAL ADSORPTION DYNAMICS

The present state of the theoretical basis of adsorption dynamics of multicomponent mixture with account for thermal effects accompanying adsorption is presented. Theoretical models for the non-isothermal kinetics and dynamics of adsorption in multicomponent mixtures are analyzed. A classification of these models is given, and model equations accounting for all major qualitative physicochemical features of heat and mass transfer through interfaces and in the intergranular space of porous media are presented. The following topics are considered: (1) Considerable role of thermal effects in the adsorption and desorption processes; (2) Considerable interaction of mixture components due to the non-linear nature of the adsorption isotherms of the mixture; (3) Considerable dependence of heat and mass transfer coefficients on concentration of mixture component and temperature; (4) Considerable effect of the mutual diffusion of the mixture component; (5) The role of the thermal diffusion effect (the Soret effect) and the diffusion-thermal effect (the Dufour effect) on heat and mass transfer when local concentration and temperature gradient inside the porous grains of the adsorbents are significant. The effect of slow heat and mass kinetics on the nature of distribution of concentration and temperature in the adsorber is considered. The qualitative differences between the equilibrium theory and non-equilibrium theory of multicomponent non-isothermal adsorption dynamics are shown. The coherent (steady) and incoherent (transient) patterns of concentration and thermal waves in the adsorber are analysed. The conditions of existence of the frontal patterns of mixture separation are found, and simple formulae estimating major parameters of frontal behavior in adsorption separation of mixture, which take into account of all basic qualitative features of interphase heat and mass transfer outlined in items (1) trough (5) above, are given

Coherent and incoherent frontal patterns for multicomponent adsorption dynamics. II: Non-uniqueness of frontal patterns in the isothermal case for convex isotherms of two-component mixtures

Abstract It has been shown that of frontal patterns can be non-unique in the isothermal case for convex adsorption isotherms of two-component mixtures with variable coefficients of separation. The uniqueness of frontal patterns have been analysed by using extreme conditions. The influence of the dispersive factors on the nature of the concentration distribution is considered. It has shown that the dispersive factors can qualitatively change the nature of concentration distribution in the adsorber too: (a) convert coherent patterns into incoherent ones; (b) transform some coherent patterns into other coherent ones.

A combined method for measurement of isotherms of adsorption of vapors and gases

Abstract This paper reports a combined method for measuring isotherms of adsorption of vapors and gases of individual and multicomponent mixtures over a wide range of pressure and temperatures. The principal advantage is the use of a chromatographic column and a piezodetector at the outlet of the column, which makes it possible to avoid the preparation of numerous gas mixtures with various concentrations of components at fixed pressures.

Study of adsorption on polymer by ellipsometry

Abstract The theory of diffusion-controlled adsorption on planar surfaces is developed. The adsorption and heats of adsorption on polymers on planar surfaces were studied by ellipsometric (equilibrium and kinetic) methods and contact angle techniques. The method of planar surfaces analysis for polymer films based on an analysis of adsorption kinetics is introduced. This method offers advantages over the methods based on the analysis of adsorption equilibrium and on the contact angle technique, since it lends itself to direct study of the non-equilibrium processes on planar polymer surfaces.

Multicomponent adsorption dynamics of polymers in a fixed bed

Abstract The theoretical analysis of concentration-patterns of frontal adsorption and desorption dynamics of mixtures in a fixed bed for the Langmuir adsorption isotherms is considered for the equilibrium and non-equilibrium models. For the equilibrium model, the concentration-constant-patterns and concentration-proportional-patterns may be described by using the Riemann invariants R k and H i invariant analytical expressions which are found. The methods of calculation of adsorption and desorption isotherms based on the use of outlet-concentration-distributions are developed. Adsorption and desorption isotherms of mixtures of the water soluble associative polymer for two end-groups (R ≔ C 16 H 33 and R ≔ H) onto particulate surfaces of titanium dioxide are obtained. It is shown that the method developed can be used to measure the adsorption and desorption isotherms over a wide range of associative polymer concentrations.

Coherent and incoherent frontal patterns of multicomponent adsorption dynamics for variable linear fluid velocity in the fixed bed—I. Frontal patterns for linear adsorption isotherms☆

The coherent constant and proportional patterns for the equilibrium and nonequilibrium models of adsorption dynamics have been analyzed for linear adsorption isotherms at variable linear fluid velocity in the fixed bed. The Riemann, Rk, and Li invariants are found in the simple analytical form. The conditions of existence of the coherent patterns are obtained for the equilibrium and nonequilibrium models. The influence of the dispersive factors (kinetics and longitudinal dispersion) on the nature of the concentrations distributions is considered. For different nonequilibrium theoretical models, the simple formula is derived to calculate the mass transfer zone for the coherent constant patterns. It is shown that the dispersive factors can convert coherent patterns into incoherent ones.

ADIABATIC ADSORPTION IN FIXED BEDS FOR QUASI-LINEAR ISOTHERMS

Abstract An analysis of patterns of adiabatic adsorption in fixed beds for quasi-linear isotherms is based on the simultaneous use of the classical conditions L, conditions F and integral curves, corresponding to the simple concentration and thermal waves These patterns, allowing to increase the efficiency of adsorption separation, are considered. The simple formulae to calculate the heat-mass transfer zone are obtained.

THEORETICAL MODELS FOR ADSORPTION SEPARATION PROCESSES IN NON-ISOTHERMAL CASES

ABSTRACT The correctness conditions using the simplest equilibrium theoretical model of the ideal displacement for the description of frontal adsorption separation processes of multicomponent mixtures in non-isothermal cases have been obtained. The procedure of “rejection” of the terms of model equations of non-isothermal adsorption dynamics of multicomponent mixtures that took into account the dispersive factors (both kinetics of mass and heat transfer, also longitudinal mixing and longitudinal hear conductance) has been analyzed. It is emphasized that the procedure of “rejection” of the terms, which some investigators performed groundlessy, is not always correct, but takes place only when certain conditions are satisfied.