I. E. Men’shchikov

Methane adsorption on microporous carbon adsorbents in the region of supercritical temperatures

Methods for the description of adsorption equilibria for methane on microporous carbon adsorbents within the Dubinin theory of the volume filling of micropores are considered. Isotherms of methane adsorption on eight carbon adsorbents are calculated and compared with the experimental data in the temperature range of 170–350 K at pressures up to 20 MPa. An analysis of the errors of the description of experimental data by the methods used is performed. A method of description based on the use of two isotherms of methane adsorption (at the boiling point and critical temperature) calculated using the Dubinin-Radushkevich equation and the property of the linearity of adsorption isosteres is recommended.

A study of methane adsorption and accumulation on microporous carbon adsorbent in a wide temperature range

This work studies the adsorption properties of microporous activated carbon AU-2 to determine the efficiency of methane accumulation in a wide temperature range, particularly in the low temperature range. Absolute adsorption isotherms of methane are measured in the pressure range of 20 Pa to 25 MPa and temperature range of 178–260 K. It is shown that the adsorbent accumulates up to 130 m3(ntp, CH4)/m3 at 7 MPa and 298 K. A decrease in the temperature by 55° allows reaching the value of 180 m3(ntp, CH4)/m3. The experimental data are used to plot methane adsorption isosteres that are well approximated by straight lines in the coordinates of lnp = f(1/T)a. The values of differential and integral adsorption heats of methane on the adsorbents are calculated on the basis of the experimental isotherms and are used to calculate an increase in the adsorber temperature as a result of adsorption.

Adsorption of methane on an MOF-199 organometallic framework structure at high pressures in the range of supercritical temperatures

Synthesis of an adsorbent based on an organometallic framework of the MOF-199 type is performed. The Dubinin–Radushkevich equation is used to calculate the structure–energy characteristics of adsorbents on the basis of data on nitrogen adsorption at 77 K as per benzene. Methane adsorption is studied on the obtained MOF-199 adsorbent, and adsorption isosteres are plotted. The capacitive characteristics of the adsorption system for methane storage with the synthesized adsorbent are determined. Differential molar isosteric and integral adsorption heats are calculated.

Description of methane adsorption on microporous carbon adsorbents on the range of supercritical temperatures on the basis of the Dubinin–Astakhov equation

Temperature dependences of parameters n and E are calculated according to the adsorption equation of Dubinin–Astakhov for methane adsorption on eight active carbons in the range of supercritical temperatures of 170–340 K and pressures of 0–20 MPa. At temperatures above ~240 K, characteristic adsorption energy E of methane grows linearly at an increase in temperature. The temperature coefficients of characteristic energy of methane adsorption on active carbon tend to decrease at an increase in standard characteristic adsorption energy E0. The average value of parameter for the studied adsorbents tends to grow at an increase in standard characteristic adsorption energy E0.

Experimental study and numerical modeling: Methane adsorption in microporous carbon adsorbent over the subcritical and supercritical temperature regions

Adsorption properties of AU-4 microporous carbon adsorbent have been investigated for evaluating the effectiveness of methane accumulation over the temperature range from 178 to 360 K and at absolute pressures up to 25 MPa. It has been established that, within the pressure and temperature intervals under study, the maximum amount of methane achieved 160 nm3(СН4)/m3. Efficient accumulation of methane in the AC-4 adsorbent over the entire temperature range was possible only within the interval of pressures from 1 to 7 MPa. When the “methane−AU-4” accumulation system was used at room temperature, the highest effect of adsorption accumulation may be achieved at pressures of 3–7 MPa. The differential and integral adsorption heats have been calculated and the degrees of overheating have been evaluated for methane storage systems with adsorbent.

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.

Adsorption of Natural Gas Methane on Metal-Organic Framework Structures in the Range of Supercritical Temperatures

The Dubinin theory of volume filling of micropores (TVFM) was used to study the structure–energy characteristics of metal-organic frameworks based on salts of copper (C300), aluminum (A520), and zinc (Z205) produced by BASF. Isotherms of absolute adsorption of methane were measured on these adsorbents at the temperatures of 303, 313, 323, and 333 K and pressures up to 40 MPa. Dependences of differential molar isosteric heats of methane adsorption on the adsorption value and the dependence of the specific volume capacity of methane accumulation on pressure are calculated. In the technically significant range of pressures up to 10 MPa, adsorbents with high values of specific surface area cannot guarantee high specific capacities of methane accumulation. The thermodynamic Р,Т-parameters of adsorption systems of methane accumulation determine the optimum structural and energy characteristics of adsorbents suitable for high-performance methane accumulation.

Adsorption-Induced Deformation of Adsorbents

Adsorption-induced deformation of AR-V and AUK carbon adsorbents and NaX zeolite has been studied upon adsorption of n-С5Н12, n-С6Н18, n-С7Н16, and CO2 at temperatures of 193−423 K. It has been shown that adsorption-induced deformation is positive upon the physical adsorption of gases and vapors on the surface of a nonporous (macroporous) solid when the excess adsorption is positive. When calculating the adsorption-induced deformation in the region of the capillary-condensation filling of mesopores, the additional pressure in capillaries, which is negative (contraction of an adsorbent), must be taken into account in the case of wetting a solid surface with a liquid adsorbate. The compressibility of AUK microporous carbon adsorbent as a porous solid is almost independent of the temperature and the properties of an adsorbate, and, for adsorption of n-C5H10 and n-C7H16 hydrocarbons and CO2, it is γа = (5.6 ± 0.6) × 10−6 bar−1. The compressibility of AUK adsorbent appears to be 87% higher than that of nonporous graphite.

The energy of adsorption of methane on microporous carbon adsorbents

Differential molar isosteric and integral heats of methane adsorption on a range of microporous carbon adsorbents of different origin have been calculated. The values of densities of integral heats Ω of methane adsorption on the sorbents under study Ω have been determined as the ratio between integral heat of adsorption and micropore volume. The dependence of density of integral heat of adsorption on standard characteristic energy of adsorption E0 has been estimated. It has been shown that the value of density Ω increases as E0 increases. The results of calculation of specific amount of accumulated methane Vsp depending on energy and structural parameters of adsorbents have been presented.