A. A. Fomkin

Methane adsorption on a microporous carbon adsorbent in the precritical and hypercritical regions

Conclusions1.The use of a new method for the measurement of adsorption on entirely microporous adsorbents permits the study of the absolute adsorption of gases and vapors in a broad range of adsorption equilibrium parameters.2.The methane adsorption isosteres on PAU-10 microporous activated charcoal are satisfactorily approximated by straight lines in the entire temperature range (120–600‡K) and pressure range (0.1 Pa – 20 MPa). The adsorption isosteres interrupted on the saturated vapor pressure line then extend linearly in the hypercritical region.

ADSORPTION OF A LIQUID ON A MICROPOROUS ADSORBENT ALONG THE LIQUID--VAPOR EQUILIBRIUM LINE. COMMUNICATION 2. AVERAGE DENSITY OF ADSORBED SUBSTANCES IN A MICROPOROUS ADSORBENT

Conclusions1.The average densities of adsorbates at p=ps in the pores of zeolites and the temperature dependences of the adsorption values were determined for the previously studied argon, krypton, xenon-NaX zeolite, CO2-NaX, and trifluorochloromethane-NaX systems and for the newly studied H2O-NaA zeolite and ethanol-NaX zeolite systems.2.The values of the average densities and their temperature coefficients were compared with the values calculated with the Dubinin-Nikolaev and Basmadjian-Cook methods. It was shown that there are significant differences between the measured and calculated values.3.It was shown that the value of the average densities of the adsorbates and their thermal expansion coefficients differ significantly from the corresponding values for normal bulk liquid phases.4.It was found that for all nonpolar adsorbates, there is a temperature at which the densities of the ads.orbate and the corresponding liquid are equal. This point, expressed in a reduced temperature scale (τ=T/Tcr), is equal to 0.88 ± 0.04.5.The average density of water adsorbed by zeolite at all temperatures is greater than the density of liquid water.

Investigation of the adsoeption of xenon on NaX zeolite within a broad range of pressures and temperatures

1. The adsorption of xenon on NaX zeolite was measured in the range of pressures from ∼0.1 Pa to ∼1.4·104 kPa (eight orders of magnitude) and temperatures from 150 to 370‡K, i.e., from a temperature below the melting point of xenon to a temperature 80‡K above the critical point. The results of the measurements were tabulated. 2. In the initial portion of all the isotherms, a Henry region was detected, extending to the adsorption of ∼0.15 mmole/g. The values of the Henry constants for all the temperatures were tabulated. 3. The adsorption isosteres are linear within the entire range of pressures and temperature studied. Just as in the system CF3C1-NaX zeolite, the isosteres, terminating on the saturated vapor pressure curve of xenon, then continue in the region of temperatures above the critical point. 4. The linearity of the isosteres permits a calculation of the adsorption equilibria at high pressures on the basis of the data characterizing the region of comparatively low pressures and temperatures.

Heats of adsorption and heat capacity of the system Xenon-NaX zeolite

1. The thermodynamics of adsorption was considered for the case when the equilibrium gas phase is sharply nonideal, and it was shown, in particular, that in this region it is advisable to use not the values of the heats of adsorption, but the values of the partial molar enthalpies as the energy characteristic of the adsorbed substance. 2. The isosteric heats of adsorption were determined in the xenon-NaX zeolite system as a function of the value of the adsorption and temperature. The partial molar enthalpies and partial molar isosteric heat capacities of xenon in this system were calculated. 3. The partial molar isosteric heat capacity of the adsorbate increases with increasing temperature. The dependence of the differential molar heat of adsorption on the temperature is due to the difference between the isosteric heat capacities of the gas phase and the adsorbed substance.

Temperature dependence of helium adsorption on Nax and NaA zeolites

Conclusions1.The adsorption of helium on NaX and NaA zeolites has been studied experimentally in the region of high reduced temperatures where the adsorption isosteres (of the total content) deviate sharply from linearity in coordinates of ln p vs. T−1.2.It is proposed that the change in the behavior of the adsorption isosteres over a relatively narrow temperature interval may be associated with a change in the adsorption mechanism, namely the transition from localized to delocalized adsorption.3.Estimation of the temperature at which such a change in mechanism is possible is in qualitative agreement with the overall behavior of the adsorption isosteres.

Determination of the parameters of the microprobe structure of solid adsorbents. Communication 1. Method of determination of the specific volume of totally microporous adsorbents

Conclusions1.A method for determining the specific volume of microporous adsorbents with micropores based on high-temperature helium pycnometry of the adsorbent and measurement of the excess adsorption of vapor and liquid was proposed.2.High-temperature helium pycnometry makes it possible to experimentally establish the dividing surface and to specify the measured excess adsorption values.3.The proposed method permits making the measurement of the absolute adsorption in microporous adsorbents more precise.

Liquid adsorption on microporous adsorbents under liquid-vapor equilibrium Communication 1. Hydrocarbons-Nax zeolite

Conclusions1.The adsorption of various liquid hydrocarbons on NaX zeolite has been measured at saturated vapor pressure, working at temperatures in the interval from 260 to 480°K.2.Mean densities of the adsorbate in the zeolite cavities have been calculated, and it has been found that the adsorbate density is less than the liquid density at lower temperatures and greater than the liquid density at temperatures in the neighborhood of the critical point.3.The temperature at which the densities of adsorbate and liquid become equal is approximately 100°K above the boiling point, i.e., at a delta temperature of 0.88.

Adsorption of krypton and xenon on zeolite NaX

1. The adsorption of krypton on zeolite NaX was measured in the pressure range from ∿0.1 Pa to ∿14 MPa and the temperature range from 120 to 600°K. The adsorption isosteres are linear in the entire range of studied temperatures and pressures. 2. The adsorption of xenon on the same zeolite was measured in the pressure range from 0.1 to 6 MPa and the temperature range from 370 to 600°K.

Thermodynamic ratios in adsorption system: Krypton-zeolite NaX

1. The initial heat of krypton adsorption on zeolite NaX is 15.3 kJ/mole. 2. The partial molar enthalpy of the adsorbate under isosteric conditions increases with increase in the temperature. 3. The partial molar isosteric heat capacity of the adsorbate is independent of the temperature at small adsorption values, and increases with temperature at high adsorption values.

Application of the modified volumetric micropore occupancy theory equation for the description of methane adsorption on a microporous carbon adsorbent

Conclusions1.A thermal adsorption equation was proposed, which permits the calculation of adsorptional equilibria on microporous carbon adsorbents in the pre- and supercritical regions as well as in the region of the liquid state of the adsorbate using two adsorption isotherms, calculated on the basis of the VMOT, and the property of linearity of the adsorption isosteres.2.The adsorption of methane on the completely microporous carbon adsorbent PAU-10 at 120–600 K and 0.1 Pa-20 MPa is described satisfactorily by the adsorption equation obtained if n is a function of temperature.