Hydrogen adsorption on model adsorbents in terms of volume filling of micropores: II. Hydrogen adsorption in the space between Single-Wall carbon nanotubes

Hydrogen adsorption in the space between Single-Wall carbon nanotubes arranged to form triangular packages is calculated at temperatures of 20–400 K in terms of the Dubinin theory of volume filling of micropores using the linearity of adsorption isosteres. Based on the data obtained, porous structure parameters are established that can be applied for hydrogen accumulation at pressures below 20 MPa and temperatures of 77–400 K.     

Relation between characteristic adsorption energy and internal pressure in the theory of volume filling of micropores

An equation for the internal pressure acting on an adsorbate in micropores was obtained on the basis of the assumption that the chemical potential of an adsorbate in micropores is equal to that in an equilibrium gas phase and using the Dubinin-Radushkevich equation. The empirical relation between the characteristic adsorption energy and the half width of pores was expressed in terms of internal pressure and diameter of adsorbate molecules. The two-dimensional pressure was calculated for micropores with plane-parallel walls, where the width of a micropore coincides with the diameter of an adsorbate molecule. The results obtained were compared with the two-dimensional pressure of a monolayer on a free planar surface for an adsorbate and adsorbent of the same nature.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1928–1930, October, 1995.     

Estimation of adsorption of ethane on the superactive microporous carbon adsorbent using the theory of volume filling of micropores

Russian Chemical Bulletin - Using the main statements of the Dubinin theory of volume filling of micropores (TVFM) the amount of adsorbed ethane was estimated at pressures up to 4 MPa in the...     

Modification of the theory of a three-dimensional filling of micropores

Compressibility of the adsorbate has been taken into account in calculating the maximum adsorption in micropores. On this basis, an equation has been derived for improvement of the theory of three-dimensional filling of micropores in application to the calculation of micropore volume by the Dubinin-Radushkevich equation. Evaluations for the case of benzene adsorption on activated carbons at 20°C have shown that the accounting for adsorbate compressibility leads to corrections of the Dubinin-Radushkevich theory amounting to approximately 10%.Institute of Physical Chemistry, Russian Academy of Sciences, Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 13–18, January, 1992.     

Hydrogen adsorption on nanoporous carbon adsorbents prepared from furaldehyde by thermochemical synthesis

Hydrogen adsorption on two samples of active carbon (FAS) produced from furaldehyde by the thermochemical synthesis method is investigated. Maximum hydrogen adsorption on these active carbons at hydrogen boiling temperature of 20.38 K and a pressure of 0.101 MPa is calculated in terms of the theory of the volume filling of micropores. Hydrogen adsorption on FAS-1-05 active carbon at temperatures of 77, 196, and 300 K and pressures of 7 and 20 MPa is calculated using the condition of linear isosteres. The calculated data are compared with the experimental results obtained for the same adsorbent at temperatures of 77 and 293 K and pressures below 5.1 and 16.1 MPa, respectively. The maximum adsorption value of hydrogen on FAS-1-05 amounts to 6.2 wt % at 5.1 MPa and 77 K.     

Hydrogen adsorption on a carbon adsorbent with slitlike micropores below and above the critical temperature

Hydrogen adsorption is calculated for model microporous adsorbents with slitlike micropore widths of 0.538, 0.878, and 1.218 nm obtained by the consecutive exclusion of one, two, and three layers of hexagonal carbon from graphite structure taken as a model cell. Calculations are performed using the basic concepts of the theory of volume filling of micropores, Dubinin-Radushkevich equation, and linear adsorption isosteres. For structures with one-and two-layer carbon walls, the calculation is carried out at temperatures of 20, 33, 77, 200, 300, and 400 K and pressures up to 20 MPa. For AC3:5 structure, the maximum hydrogen adsorption amounts to 7.9 wt % at 20 MPa and 300 K. The parameters of adsorbent porous structure are established. Hydrogen adsorption is shown to be governed by the capacity and the energy of adsorption.     

Discrete site model for methane adsorption on microporous adsorbents

A statistical thermodynamic treatment of adsorption on zeolites assuming quasiindependent sites has been applied to methane adsorption on the zeolite NaX and the carbon adsorbent PAU-10 from polyvinylidenechloride in the pressure range 0.1–10⁷ Pa and 120–410 K. The relation between the isosteric adsorption heats and the magnitude of adsorption at different temperatures was calculated for both adsorption systems. A sharp decrease in these heats was observed at high adsorption values up to and in the supercritical temperature range.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 974–978, May, 1990.The authors would like to thank V. A. Bakaev for discussions about this work.     

Theory of volume filling of micropores applied to the description of methane adsorption on the microporous carbon adsorbent AUK

Methane adsorption on the microporous carbon adsorbent AUK was calculated on the basis of Dubinin’s theory of volume filling of micropores in the temperature range 177.7—393 K and at pressures from 1 Pa to 6 MPa. The calculated isotherms of absolute adsorption were compared with the isotherms of methane obtained experimentally. Good agreement between the calculated and experimentally measured amounts adsorbed is observed in the area of applicability of the theory at micropore ranging in coverage θ from 0.25 to 0.95. The adsorption isosters were calculated for the same pressure and temperature ranges. The adsorption isosters satisfactorily represent the temperature dependence of the amount of methane adsorbed obtained experimentally. The calculations gave for the thermal coefficient of limiting adsorption a value of 6h_calc = 1.64• 10^-3 K^-1., which exceeds the experimental value by ∼15%.