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Carbon microporous adsorbents obtained on the basis of polymers are promising adsorbents for the tasks of adsorption storage of natural gas due to the possibility of creating a precise porous structure, as well as optimal mechanical characteristics. A study of the adsorption of methane in a carbon adsorbent based on a composite polymer of furfural and epoxy resin in the temperature range from 178 to 360 K and pressures up to 25 MPa has been carried out. The thermodynamic functions of the adsorption system—the differential molar isosteric and integral heats of adsorption, as well as the isosteric entropy, enthalpy, and heat capacity of the system are calculated. The obtained thermodynamic functions are of fundamental importance in the analysis of the properties of nanodispersed adsorbate in the micropores of the adsorbent, and can also be used as input data in modeling the thermodynamic states of experimental systems for methane storage and transportation.

Methane adsorption on a recuperated activated carbon, AR-V, was studied over the temperature range of 213–393 K and at pressures up to 10 MPa from the perspective of its potential application for adsorption-based storage and separation technologies. The porous structure, phase and chemical compositions of AR-V were examined by nitrogen adsorption at 77 K, x-ray diffraction, and scanning electron microscopy. The amount of adsorbed methane increased with pressure up to 6.3 mmol/g at 243 K and fell dramatically to ~ 1 mmol/g with a temperature rise to 393 K. The molar differential isosteric heat of methane adsorption on AR-V was evaluated from the linear isosteres within the studied P,T-range; the effects from the non-ideality of a gaseous phase and the AR-V non-inertness were considered. The maximal summarized contribution from the AR-V thermal expansion and directly measured adsorption-induced deformation to the molar differential isosteric heat of methane adsorption turned out to be less than that from the gas compressibility. The initial drastic changes in the thermodynamic state functions of the adsorption system were attributed to the binding methane molecules with non-uniformly distributed high-energy adsorption sites. When methane molecules occupied all high-energy adsorption sites, the subsequent variations in the thermodynamic functions were governed by the intensifying attractive forces between methane molecules upon methane adsorption resulting in the formation of adsorption clusters. The temperature dependence of the isosteric heat capacity of the methane/AR-V system varied during adsorption; its value exceeded 2–3 times the isochoric heat capacity of the equilibrium methane gaseous phase.

Adsorbed natural gas (ANG) storage systems are based on nanoporous adsorbents with a tailored porous structure. Activated carbons are among the most promising and widely used candidates for this application, which is explained by the availability and abundance of raw material resources. In the present work, several series of activated carbons prepared from various precursors (coconut shell, peat, polymers, silicon carbide, and mineral coal) by different routes of physical and thermochemical activation were considered in the context of the adsorbed natural gas storage applications. Based on the Dubinin theory of volume filling of micropores and BET method, the porous structure of these adsorbents was evaluated from standard adsorption isotherms. The XRD, SAXS, and SEM measurements revealed variations in the textural and morphological properties of the adsorbents and their dependence on the precursor and synthesis procedure. The pore sizes evaluated from the adsorption and SAXS data were compared. Experimental data on methane adsorption at the temperature of 303 K and pressures of 0.1, 3.5, and 10 MPa made it possible to identify the most effective adsorbents. It was shown that the adsorption properties of ACs prepared from peat and mineral coal are determined by surface chemistry inherited from the precursor and activating agent. In contrast, the adsorption performance of ACs from polymer and coconut shell depends solely on the pore volume and pore dimensions. The adsorption effectiveness of each AC varies with pressure as a function of textural properties. Thus, a selection of an optimal adsorbent should be adjusted for thermodynamical coditions of ANG system.

Abstract— An EC-103 microporous carbon adsorbent was synthesized from wood using thermochemically activation with Н3РО4 as an activating agent. Methane adsorption on the EC-103 adsorbent was studied within the temperature range from 303 to 333 K and at pressures up to 40 MPa. The total volume of sorbing pores was 1.71 cm3/g. The maximum values of methane adsorption were obtained at the temperature of 303 K and pressure of 40 MPa. The differential molar isosteric heat of methane adsorption 14.5 mmol/g (23.2 wt %) was on the average of 12−14 kJ/mol. Methane adsorption on the EC-103 adsorbent was calculated based on the Dubinin theory of volume filling of micropores (TVFM). It was shown that the Dubinin-Radushkevich equation and basic TVFM pattern provided the best description of experimental data on methane adsorption with the use of only the standard structural and energy characteristics of the adsorbent.

A Zr–BDC metal–organic framework was synthesized by the solvothermal method using N,N‑dimethylformamide as an organic solvent at the temperature 110°С. The adsorbent thus obtained is characterized by a developed porous structure with specific BET surface SBET = 1060 m2/g, micropore volume W0 = 0.44 cm3/g, and average micropore radius х0 = 0.54 nm, which is indicative of a potentially effective adsorbent for adsorbed natural gas storage systems. The shaping parameters were determined for the Zr–BDC-based composites with polyvinyl alcohol as a binder and without the use of any binder at various compacting pressures. The influence of the shaping pressure on the packing density and structural and energy characteristics of the obtained samples was investigated. Based on the Dubinin theory of volume filling of micropores, the pressure dependences of the methane deliverable capacity both in the initial powdered and shaped Zr–BDC adsorbents at the temperatures of 243, 273, and 303 K were calculated for the pressures up to 100 bar. The deliverable volumetric methane capacity of the adsorption system based on the shaped Zr–BDC samples was measured in the specified thermodynamic conditions.

A one-step notion of synthesis was developed to prepare microporous activated carbons from walnut shell by physical gas activation in a CO2 atmosphere for a low-temperature methane accumulation system operating at 120, 160, and 178 K. The raw material was carbonized within a temperature range from 240 to 950°C. Temperatures close to 900°С were found to be optimal for the development of microporosity in the adsorbent in a CO2 atmosphere. Activation under these conditions made it possible to achieve a burnoff degree up to 70% and form an optimal porous structure for adsorption accumulation of liquefied natural gas (LNG) vapors. The adsorbent thus obtained exhibits a high micropore volume W0 = 0.59 cm3/g, mesopore volume WМЕ = 0.33 cm3/g, specific surface SBET = 1490 m2/g, and half-width of micropores of 0.59 nm, which provided a high methane adsorption capacity. The presence of mesopores can make additional contribution to the adsorption process due to capillary condensation. The theoretical assessment of the methane adsorption capacity of the adsorbent showed that at temperatures of 120, 160, and 178 K and pressures up to 6 bars, the values of equilibrium adsorption were 15, 13.5, and 12 mmol/g, respectively.

Physicochemical regularities are studied for the synthesis of molded active carbons based on coconut shells and peat, with a latex emulsion and a carboxymethyl cellulose (CMC) sodium salt solution being used as binding agents. The materials are obtained at compacting pressures of 25, 50, and 100 MPa. The specific surface areas of the composite samples obtained from peat and coconut shells are SBET ≈ 1320 and ≈1290 m2/g, respectively. The specific micropore volumes of the composites based on peat and coconut shells are W0 = 0.50 and 0.45 cm3/g, respectively. Latex-modified carbon samples have a higher bulk density than those molded with CMC. The molding of the active carbons is accompanied by partial degradation of their porous structure. The Dubinin theory of volume filling of micropores (TVFM) has been employed to calculate the values of adsorption and active specific capacity of the molded adsorbents with respect to methane at a temperature of 273 K and a pressure of up to 100 bar. The experimental and calculated data have shown that the active capacity of the new microporous carbon composite materials may be as large as 180 m3 (NTP)/m3, when the pressure drops from 100 to 1 bar. It has been concluded that it is reasonable to employ the TVFM for preliminary calculations of the parameters of adsorption systems used for natural gas storage.

The isotherms of absolute methane adsorption in an Fe–BDC metal–organic porous structure after long-term storage were measured at a pressure as high as 40 MPa and the temperatures of 303, 313, 323, and 333 K. The dependences of differential molar isosteric heats of adsorption and entropies of adsorption on methane uptake were calculated. It was shown that taking into account the nonideality of a gaseous phase and steepness of the isotherm of adsorption leads to a temperature dependence of thermodynamic functions of adsorption. Both a sharp drop in the heat of adsorption and a local maximum of the entropy at the maximum values of methane uptake are indicative of rearranging the adsorbate structure and the probable formation of molecular methane associates in micropores.

Methane adsorption in MPU-007 microporous carbon adsorbent with a wide pore size distribution was studied at a pressure as high as 40 MPa and the temperatures of 303, 313, 323, and 333 K. The maximum value of methane adsorption of 43.36 wt % was achieved at 303 K and 40 MPa. The isosteres of adsorption derived from the obtained data were satisfactorily approximated by a linear function in coordinates ln P–1/Т at a constant value of adsorption. The dependences of differential molar isosteric heats of methane adsorption in MPU-007 microporous adsorbent on the value of methane adsorption were calculated at the temperatures of 303, 313, 323, and 333 K. The heat of methane adsorption of 14 kJ/mol was constant at a filling of micropores as low as ≈5 mmol/g. Then it declined evenly to 8 kJ/mol at 25 mmol/g and 303 K and to 2 kJ/mol at 24 mmol/g and 323 K. Such a run of the curves describing the heats of adsorption versus adsorption value might be caused by a wide pore size distribution and the association processes in the adsorbate.

Cu-BTC110 metal-organic framework has been synthesized by solvothermal method using N,N '‑dimethylformamide organic solvent at 110°C. Cu-BTC110 sample has the following adsorption characteristics: micropore volume W0 = 0.38 cm3/g, specific surface area SBET = 850 m2/g, micropore radius х0 = 0.36 nm, standard characteristic energy of benzene adsorption Е0 = 33.6 kJ/mol. Methane adsorption on a Cu-BTC110 sample at temperature from 210 to 293 K and pressure up to 140 kPa has been studied. Differential molar heat of methane adsorption has been calculated from adsorption isosteres.

In the present work, a method for producing new shaped composite materials by introducing a metal-organic framework structure Cu-BTC110 into a matrix of carbon material has been suggested. Powdered microporous activated carbons prepared from vegetable, polymer, and peat raw materials were used as carbon matrices. Physicochemical properties and structure-energy characteristics of the initial materials and shaped composites based on them were determined. It was demonstrated that the Cu-BTC110 composite with active carbon prepared from peat enabled one to achieve a balance between structure-energy characteristics, mechanical characteristics, and methane adsorption capacity. Depending on the temperature, the amount of accumulated methane can achieve 160–200 m3 (NTP)/m3 within a pressure range from 3.5 to 10.5 MPa.

The effects of different types of bindings, the pressure of shaping and carbon-containing additives on the structural and energy characteristics, density, and mechanical properties of the shaped composite adsorbents prepared based on metal-organic framework structures are studied. Their adsorption behaviors are also examined for application to methane accumulation systems.

A microporous carbon adsorbent labeled as LCN was prepared by thermochemical synthesis from lignocellulose, and methane adsorption on it was studied within the temperature range from 303 to 333 K and at pressures up to 40 MPa. The total pore volume was determined to be 0.68 cm3/g. The maximum values of methane adsorption of ~14.5 mmol/g (23.2 wt %) were obtained at the temperature of 303 K and the pressure of 40 MPa. The calculated differential molar isosteric heat of methane adsorption is, on average, ~12–13 kJ/mol. Methane adsorption on LCN was calculated with the use of the Dubinin–Radushkevich and Dubinin–Astakhov equations, as well as the linearity of adsorption isosteres. It was shown that the Dubinin–Radushkevich and fundamental regularities of the theory of volume filling of micropores provide the best description of experimental data using only the standard structural and energy characteristics of the adsorbent.

Adsorption of natural gas (methane) on the synthesized metal–organic framework (MOF) Al-BTC with specific surface area SBET = 1422 m2/g was studied at pressures up to 40 MPa and temperatures of 303, 313, 323, and 333 K. The maximum adsorption of methane on Al-BTC reaches 10.36 mmol/g at 303 K and 40 MPa, and the initial heat of adsorption is ~14 kJ/mol. The amount of methane accumulated in a system with Al-BTC attains a value of 120–130 m3(NTP)/m3 in a range of pressures from 3.5 to 10.0 MPa, which is the most relevant for methane accumulation. The volumes of methane stored in the systems with Al-BTC and without an adsorbent differ by a factor of about 2 at 3.5 MPa, there is almost no distinction between these options of methane storage at 7.0 and 20.0 MPa, and the amount of gas in the system without an adsorbent exceeds by 25% that in Al-BTC. The pressure range from 3.5 to 6.0 MPa is most efficient for the methane adsorption accumulation in the MOF structure Al-BTC. The absolute efficiency of methane adsorption accumulation increases with lowering of temperature.

The present work focused on the experimental study of the performance of a scaled system of adsorbed natural gas (ANG) storage and transportation based on carbon adsorbents. For this purpose, three different samples of activated carbons (AC) were prepared by varying the size of coconut shell char granules and steam activation conditions. The parameters of their porous structure, morphology, and chemical composition were determined from the nitrogen adsorption at 77 K, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and scanning electron microscopy (SEM) measurements. The methane adsorption data measured within the temperature range from 178 to 360 K and at pressures up to 25 MPa enabled us to identify the most efficient adsorbent among the studied materials: AC-90S. The differential heats of methane adsorption on AC-90S were determined in order to simulate the gas charge/discharge processes in the ANG system using a mathematical model with consideration for thermal effects. The results of simulating the charge/discharge processes under two different conditions of heat exchange are consistent with the experimentally determined temperature distribution over a scaled ANG storage tank filled with the compacted AC-90S adsorbent and equipped with temperature sensors and heat-exchanger devices. The amounts of methane delivered from the ANG storage system employing AC-90S as an adsorbent differ from the model predictions by 4&ndash, 6%. Both the experiments and mathematical modeling showed that the thermal regulation of the ANG storage tank ensured the higher rates of charge/discharge processes compared to the thermal insulation.

Two activated carbons (ACs) were prepared from peat using thermochemical K2SO4 activation at 1053&ndash, 1133 K for 1h, and steam activation at 1173K for 30 (AC-4) and 45 (AC-6) min. The steam activation duration affected the microporous structure and chemical composition of ACs, which are crucial for their adsorption performance in the methane storage technique. AC-6 displays a higher micropore volume (0.60 cm3/g), specific BET surface (1334 m2/g), and a lower fraction of mesopores calculated from the benzene vapor adsorption/desorption isotherms at 293K. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS) investigations of ACs revealed their heterogeneous morphology and chemical composition determined by the precursor and activation conditions. A thermodynamic analysis of methane adsorption at pressures up to 25 MPa and temperatures from 178 to 360K extended to impacts of the nonideality of a gaseous phase and non-inertness of an adsorbent made it possible to evaluate the heat effects and thermodynamic state functions in the methane-AC adsorption systems. At 270 K and methane adsorption value of ~8 mmol/g, the isosteric heat capacity of the methane-AC-4 system exceeded by ~45% that evaluated for the methane-AC-6 system. The higher micropore volume and structural heterogeneity of the more activated AC-6 compared to AC-4 determine its superior methane adsorption performance.

A procedure has been proposed for the self-assembly of carbon nanotubes into arrays with the use of coordinating molecules and the development of secondary porosity in the resulting supramolecular structures. Molecular dynamics has been employed to study the formation of such structures and determine the effective radius of pores formed in them. The average micropore sizes in the obtained supramolecular structures have been related to the sizes of coordinating molecules and their orientation with respect to nanotube surface. Adsorption of methane and hydrogen on such model systems has been calculated on the basis of the theory of volume filling of micropores. It has been shown that the porosity resulting from the organization of the nanotubes into arrays with the help of coordinating molecules makes it possible to accumulate methane and hydrogen at the level of the best model adsorbents.

Using numerical and analytical methods, a model for microporous carbon adsorbents with slit-shaped pores of different widths was developed. Such pores are formed during activation procedure by the removal of the hexagonal carbon layers burnt out in a graphite-like crystallites. Dubinin’s theory of volume filling of micropores was used to calculate methane adsorption equilibria on these model adsorbents. Isobaric dependences of methane adsorption on pore width, specific micropore volumes, and the specific surface were plotted in the range of pressures from 1 to 10 MPa. It was found that the isobaric adsorption curves had a maximum the position of which depends on both the structural-energy characteristics of the adsorbent and thermodynamic conditions chosen to operate the adsorption system. As pressure increased, the maximum of adsorption shifts to the porous systems with wider pores and larger micropore volume.

The use of gas fuel has considerable environmental advantages over traditional types of fuel based on petroleum products or fossil coal. The adsorption technology for methane (natural gas) uptake, storage and transportation can serve as a connecting link in gas supply to customers. The review considers characteristics of adsorption systems for methane storage. The key methods used for the synthesis of microporous carbon adsorbents based on various organic and inorganic carbon-containing compounds are described. Methods for increasing the efficiency of methane storage systems based on carbon adsorbents are analyzed. Theoretical approaches to optimization of the properties of methane – carbon adsorbent systems are discussed. The bibliography includes 174 references.

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 microporous carbon adsorbents AUK and AR-V with different genesis was measured in conditions of methane adsorption (temperature 273, 313, 353, 393 K; pressure 0–6 MPa). Thermal deformation of carbon adsorbents AUK and AR-V was measured in the temperature range of 273–573 K. Coefficients of linear thermal expansion (CTE) of carbon adsorbents were calculated in the temperature range of 273–573 K: for AUK, aT = (3 ± 0.15)·10–6 K–1; for AR-V, T = (8.4 ± 0.6)·10–5 K–1. A comparative analysis of the CTE of adsorbents and crystal graphite was implemented.

In this work a possibility of formation of supramolecular structures based on carbon nanotubes and coordinate molecules – cyclic hydrocarbons (including aromatic) was studied by means of molecular dynamics method. Model supramolecular structures were defined as arrays of nanotubes, coordinated by hydrocarbon molecules mainly in triangular package. A correlation between the sizes of coordinate molecules and average distances between nanotubes in the structures was defined as well as conditions of porosity development between the nanotubes while maintaining their ordered arrangement. Maximal adsorption of methane and hydrogen in model structures was estimated in space between the nanotubes as well as inside them

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 E 0 has been estimated. It has been shown that the value of density Ω increases as E 0 increases. The results of calculation of specific amount of accumulated methane V sp depending on energy and structural parameters of adsorbents have been presented.

Adsorption of methane on twelve microporous carbon adsorbents of different origin and structural and energy characteristics was studied at the pressures up to 20 MPa. Specific capacities have been calculated for methane adsorption storage systems. The effectiveness of adsorption accumulation was analyzed in terms of structural and energy characteristics, packing density and thermodynamic parameters of methane adsorption. Differential molar isosteric heats of adsorption and absolute efficiency of adsorption accumulation systems were evaluated. The effects of increased packing density and proper shape of adsorbent material on the adsorption accumulation efficiency were considered. It was shown that a selection of an adsorbent with the most optimal porous structure and density should be adjusted for thermodynamic parameters of accumulation system.

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 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.

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.

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 E 0. The average value of parameter for the studied adsorbents tends to grow at an increase in standard characteristic adsorption energy E 0.

A technique for the measurement of the equilibrium absolute adsorption of gases, in particular, of natural gas (methane), at pressures up to 10 MPa, is proposed. A plant for use in performing the measurements by means of a volumetric method is described. Estimators of the measurement errors are presented. Adsorption isotherms of methane by AU-1Sh miroporous carbon matter in the range of pressures 10–7–10 MPa and temperatures in the range 178–360 K are obtained by means of the proposed technique.