Sorption of water vapor on cation-substituted vermiculite

Deformations of Na, Ca, and Ba vermiculites upon sorption of water vapor have been determined by a dilatometric method. Sequential stages in the hydration of interlayer exchange cations have been identified. The experimental results have been compared with data obtained in studies using adsorptive, calorimetric, and x-ray methods.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Colloid Chemistry and the Chemistry of Water, Academy of Sciences of the Ukraine, Kiev. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 34–39, January, 1992.     

Adsorption studies of organosubstituted laminated silicates

The hysteresis of sorptive deformation of sorbents has been studied for the first time. Based on the results obtained, it is assumed that the deformation of sorbents could be the universal reason for the sorptive hysteresis.For Part 1, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1477–1479, August, 1995.     

Adsorptive Deformation of Organo-Substituted Laminar Silicates

Deformations of organo-substituted laminar silicates (Pyzhevsk montmorillonite and synthetic fluorohectorite) upon water, hexane, and benzene vapor sorption have been studied. To solve this problem a dilatometer was used. Its main part was a line differential transformer, the core of which was connected to the sorbent by means of a rod. Any changes of the sorbent height caused a change in the core position in the transformer, which influenced the signal recorded from its secondary winding. The calibrated dilatometer was located in a liquid thermostat with a given temperature and was connected with the measurement unit (frequency meter, voltmeter, generator). Montmorillonite and synthetic fluorohectorite were modified by cetylpyridinium bromide and used in the form of tablets. As a result of the sample preparation conditions, the modified clay silicates swelled isotropically. These results were compared with the adsorption isotherms obtained gravimetrically. High sensitivity of the dilatometric method to the structural changes of the organo-substituted laminar silicates has been shown. The dilatometer used allowed the measurement of absolute deformations in the range 1 x 10(-4) to 3 mm. Copyright 1999 Academic Press.     

Supramolecular microporous structures based on carbon nanotubes and coordinating cumene (C<Subscript>9</Subscript>H<Subscript>12</Subscript>) molecules

A method has been proposed for the formation of self-organized ensembles of carbon nanotubes with the use of coordinating cumene molecules and the development of secondary porosity in the obtained structures. It has been shown that the fraction of nanotubes coordinated into an array grows with increasing molar ratio between cumene molecules and carbon nanotubes upon the synthesis of the supramolecular structures. The secondary porosity develops due to partial desorption of the coordinating molecules from the obtained structure. A supramolecular structure with a residual cumene content of 50 wt % possesses the best adsorption characteristics for the described system. Specific adsorption of nitrogen on the “carbon nanotubes–cumene (50 wt %)” supramolecular structure at 293 K is more than an order of magnitude higher than that on the initial nanotubes. The structure-related energy parameters of the experimentally obtained supramolecular systems have been determined by molecular dynamics methods. The calculation in terms of the theory of volume filling of micropores has shown that the secondary pores of the obtained structures can accumulate methane and hydrogen in amounts as large as 213 nm³/m³ and 4 wt %, respectively.     

Methane adsorption on microporous carbon adsorbent with wide pore size distribution

Methane adsorption on a microporous carbon adsorbent with a bimodal pore size distribution is studied at temperatures of 303–333 K at pressures up to 30 MPa. The total micropore volume of the adsorbent, as determined by the Dubinin method, is as large as 1.02 cm³/g. Maximum values of methane adsorption of ≈18 mmol/g are attained at a temperature of 303 K and a pressure of 30 MPa. Methane adsorption isosteres are plotted based on experimental data, and adsorption equilibria at low temperatures are calculated using the linearity of the plots. Experimental isotherms of methane adsorption are compared with the isotherms calculated by the Dubinin–Nikolaev equation with variations in parameters E and n. Temperature dependences of these parameters are determined. Specific characteristics of methane adsorption accumulation are calculated.