M. L. Gubkina

Measurement of Adsorption Isotherm of Methanol on a Humidified Active Carbon by the Dynamic Method

Elution dynamics of the adsorption of methanol vapors on humidified active carbon is studied. Elution curves are obtained for the various lengths of adsorbent layer. The isotherm of adsorption of methanol–water vapor mixtures on active carbon is calculated, using the model of the equilibrium adsorption layer.

Adsorption of vapor mixtures of water and organic substance on activated carbons

The isotherms of water adsorption in the presence of an organic substance vapor with a specified concentration are calculated from experimental data on the joint frontal dynamics of adsorption of water vapor and several organic substances (benzene, hexane, cyclohexane, tetrachloromethane, and perfluorotripropylamine) on two samples of activated carbons. The influence of the organic substances on the equilibrium water adsorption decreases with an increase in the molecule size.

Dynamics of the adsorption of freons

The elution adsorption dynamics of some adsorption systems (freon-active carbon) has been studied at two temperatures. The peculiarities of the adsorption dynamics, which are determined by the properties of the adsorption system, have been established. A possibility to calculating elution curves based on the equilibrium adsorption layer model is shown. Preliminary results of the influence of the parameters of the adsorption system on the coefficient of the effective kinetic model are obtained.

Elution and frontal dynamics of adsorption of organic substances on activated carbon

The elution dynamics of adsorption on activated carbon was studied at various carrier-gas flow rates for a series of organic substances. With the help of the model of the equilibrium adsorption layer that uses the adsorption isotherm described by the theory of volume filling of micropores the outlet curves for the elution and frontal dynamics of adsorption can be adequately predicted. The effective kinetic coefficient and the parameters of the adsorption isotherm were found to be constant for the elution curves calculated both in the elution and frontal regimes of the adsorption dynamics over the whole range of concentrations studied. The effective kinetic coefficient in the mathematical model employed for the systems with microporous adsorbents is independent in fact of the nature of an adsorptive and is mainly determined by the parameters of porous structure of activated carbon and the experimental conditions of a dynamic run.

ELUTION DYNAMICS OF ADSORPTION OF CHLADON 113 AND METHYL BROMIDE ON ACTIVE CARBONS

The elution dynamics of adsorption of Chladon 113 (at high contents of the adsorptive) and methyl bromide on active carbons with different lengths of the layer was studied. The adsorption isotherms were described by the equation of the theory of volume filling of micropores. The elution curves were calculated using the model of the equilibrium adsorption layer. The effective kinetic constant calculated in the framework of the model is 1.5 cm for Chladon 113 at a linear velocity of vapor-air flow of 1250 cm min−1 and 1.0 cm for methyl bromide at the velocity of 700 cm min−1.

Dynamics of joint adsorption of mutually soluble substances by activated carbons

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 on moist activated carbon was shown.

Thermodynamic investigation of the state of water adsorbed by carbonaceous adsorbents

The state of water adsorbed on active carbons and canal soot was studied using the “chemical potential—entropy—temperature” diagram. In the range of the relative pressures from 0.174 to 1, the state of adsorbed water is similar to the state of a stretched liquid. The molar volume, heat of evaporation, and surface tension of stretched water were calculated at different relative pressures. Near the spinodal, the molar volume of stretched water is 25% higher, and the surface tension is considerably lower compared to water.

The onset of formation of the water liquid phase in pores of carbon adsorbents

A two-stage mechanism of adsorption, including nucleation and condensation, was proposed to describe the formation of the water liquid phase in carbon adsorbents. Adsorption is assumed to occur in cylindrical pores. Nucleation is described by a modified BET model, and condensation is treated by the model of a stretched liquid film on a bent surface. The onset of formation of the liquid phase (OFLP) is determined from the intersection of the adsorption isotherms for these stages. The theoretical value of the relative pressure of OFLP varies over a wide range, decreasing with a decrease in the pore radius and reactiing the relative vapor pressure of 0.178 for the spinodal state of water. The comparison method using isotherms of graphitized carbon black as the reference isotherms was applied for the determination of OFLP of water in real active carbons. This resulted in good agreement between theory and experiment.

Adsorption of vapors and gases by carbon sorbents with homogeneous microporous structures in the initial region of the adsorption isotherm

Examination of the adsorption isotherm equation derived from the theory of volume filling of micropores (TVFM) showed that the region of low pressures of experimental isotherms is not always described by this equation. A method for describing the initial region of adsorption isotherms using the parameters of TVFM was proposed.

Adsorption of organic substances with different physicochemical properties 2. The heats of adsorption of freon 13B1 on active carbons

The linear regions of the adsorption isotherms of freon 13B1 (CF3Br) on active carbons with different porous structures were studied by gas chromatography at 343–573 K. The Henrys constants were determined, and the isosteric heats of adsorption (Q) were calculated in the region of zero filling. It was established that theQ values for active carbons with different pore size distributions are almost the same and vary within 38–41 kJ mol−1. This coincidence can be explained assuming that the interaction between the adsorbed molecules and the active carbons occurs in the pores whose sizes are comparable with those of the adsorbed molecules.