Adsorption of Methane in Porous Materials as the Basis for the Storage of Natural Gas

Porous Metal-Organic Frameworks: Promising Materials for Methane Storage

Structure modeling of activated carbons used for simulating methane adsorption – A review

Adsorbed natural gas has various advantages and is relatively more economical than liquefaction and compression. Carbon nanotubes can be introduced as a new candidate for natural gas storage. In this study, adsorption of methane was firstly studied on the as-prepared multi-walled carbon nanotubes, and then chemical and physical treatment of MWCNTs was performed to enhance the methane adsorption. Treatment by acid washing and annealing with air improved purity, surface area and methane adsorption. The adsorption and equilibrium isotherm data of T-MWCNTSs, were measured by a static volumetric technique at different temperatures of 298, 291, 273 and 263 K and pressures up to 7 MPa. The maximum value of methane storage at normal temperature of 298 K was achieved to 2.81 mmole/g in our experiments. This amount of methane adsorption is equal to 108 v/v, meanwhile the target value of the adsorbed natural gas is 120 v/v to become as the accepted material for ANG process. The isosteric heat of adsorption of T-MWCTs was determined in the studied range of pressures and temperatures. The results revealed an energetically heterogeneous surface in methane adsorption. Furthermore, different isotherm models were fitted on the experimental adsorption data and the model parameters were correlated. Within the different studied isotherms, Sips equation provided best fitting to the experimental data.

Climate change, global warming, urban air pollution, energy supply uncertainty and depletion, and rising costs of conventional energy sources are, among others, potential socioeconomic threats that our community faces today. Transportation is one of the primary sectors contributing to oil consumption and global warming, and natural gas (NG) is considered to be a relatively clean transportation fuel that can significantly improve local air quality, reduce greenhouse-gas emissions, and decrease the energy dependency on oil sources. Internal combustion engines (ignited or compression) require only slight modifications for use with natural gas; rather, the main problem is the relatively short driving distance of natural-gas-powered vehicles due to the lack of an appropriate storage method for the gas, which has a low energy density. The U.S. Department of Energy (DOE) has set some targets for NG storage capacity to obtain a reasonable driving range in automotive applications, ruling out the option of storing methane at cryogenic temperatures. In recent years, both academia and industry have foreseen the storage of natural gas by adsorption (ANG) in porous materials, at relatively low pressures and ambient temperatures, as a solution to this difficult problem. This review presents recent developments in the search for novel porous materials with high methane storage capacities. Within this scenario, both carbon-based materials and metal-organic frameworks are considered to be the most promising materials for natural gas storage, as they exhibit properties such as large surface areas and micropore volumes, that favor a high adsorption capacity for natural gas. Recent advancements, technological issues, advantages, and drawbacks involved in natural gas storage in these two classes of materials are also summarized. Further, an overview of the recent developments and technical challenges in storing natural gas as hydrates in wetted porous carbon materials is also included. Finally, an analysis of design factors and technical issues that need to be considered before adapting vehicles to ANG technology is also presented.

Effect of lithofacies on gas storage capacity of marine and continental shales in the Sichuan Basin, China

Porous carbon-based material as a sustainable alternative for the storage of natural gas (methane) and biogas (biomethane): A review

With the increasing proportion of natural gas in energy supply, considering the changes in urban natural gas consumption time and peak pipeline pressure, how to balance gas supply and consumption will become the key to ensuring winter supply. This article aims to study and solve the problem of natural gas storage peak shaving, analyze the current situation and the advantages and disadvantages of different situations, and propose specific solutions. By studying underground gas storage facilities, liquefied natural gas (LNG) storage, compressed natural gas (CNG) storage, distributed gas storage systems, intelligent scheduling, and policy market mechanisms, new ideas are provided for building a low-carbon, efficient, and flexible gas storage peak shaving system.

Porous molecular solids are promising materials for gas storage and gas separation applications. However, given the relative dearth of structural information concerning these materials, additional studies are vital for further understanding their properties and developing design parameters for their optimization. Here, we examine a series of isostructural cuboctahedral, paddlewheel-based coordination cages, M24(tBu-bdc)24 (M = Cr, Mo, Ru; tBu-bdc2- = 5-tert-butylisophthalate), for high-pressure methane storage. As the decrease in crystallinity upon activation of these porous molecular materials precludes diffraction studies, we turn to a related class of pillared coordination cage-based metal-organic frameworks, M24(Me-bdc)24(dabco)6 (M = Fe, Co; Me-bdc2- = 5-methylisophthalate; dabco = 1,4-diazabicyclo[2.2.2]octane) for neutron diffraction studies. The five porous materials display BET surface areas from 1057-1937 m2/g and total methane uptake capacities of up to 143 cm3(STP)/cm3. Both the porous cages and cage-based frameworks display methane adsorption enthalpies of -15 to -22 kJ/mol. Also supported by molecular modeling, neutron diffraction studies indicate that the triangular windows of the cage are favorable methane adsorption sites with CD4-arene interactions between 3.7 and 4.1 Å. At both low and high loadings, two additional methane adsorption sites on the exterior surface of the cage are apparent for a total of 56 adsorption sites per cage. These results show that M24L24 cages are competent gas storage materials and further adsorption sites may be optimized by judicious ligand functionalization to control extracage pore space.

Theoretical and Experimental Study on the Adsorption and Desorption of Methane by Granular Activated Carbon at 25°C

The preparation of porous carbons by KOH activation from three different coal wastes in South Africa was modeled and optimized using an artificial neural network and whale optimization algorithm (ANN-WOA). The potential for methane adsorption of the optimized porous carbons was investigated. The optimal conditions for preparing the porous carbons, as determined by maximum surface area and micropore volume, according to ANN-WOA results, were as follows: Temperature of reaction: 800°C; activation time: 120 minutes; impregnation ratio: 1:4. SEM/EDS and BET methods were used to examine the surface properties and structural morphology of the optimized activated carbons. The methane adsorption isotherm on the three optimized porous carbons was fitted with the Toth isotherm model, which had an average R2 value of 0.9999. The maximum adsorption capacity of the three optimized porous carbons were 158.4, 147.6, and 123.1 cm3/g at 25°C and an average pressure of 37 bar. In addition, because of their high surface area and methane adsorption capacity, these materials have the potential to be used in natural gas storage, demonstrating that coal wastes in South Africa have the potential to be used as a sustainable starting material for the synthesis of porous carbons for gas storage.

A series of activated carbons (AC) were prepared from waste of the olive oil production in the Cuyo Region, Argentine by two standard methods: a) physical activation by steam and b) chemical activation with ZnCl2. The AC samples were characterized by nitrogen adsorption at 77 K and evaluated for natural gas storage purposes through the adsorption of methane at high pressures. The activated carbons showed micropore volumes up to 0.50 cm3.g-1 and total pore volumes as high as 0.9 cm3.g-1. The BET surface areas reached, in some cases, more than 1000 m2.g-1. The methane adsorption -measured in the range of 1-35 bar- attained values up to 59 VCH4/VAC and total uptakes of more than 120 cm3.g-1 (STP). These preliminary results suggest that Cuyo's olive oil waste is appropriate for obtaining activated carbons for the storage of natural gas.

Stable heterometallic metal-organic frameworks and pellet composites for low-temperature natural gas storage

Adsorption equilibrium of methane on activated carbon and typical metal organic frameworks

Success of adsorbed natural gas (ANG) storage process is mainly based on the characteristics of the adsorbent, so various synthesized adsorbents were analyzed for methane adsorption on a thermodynamic basis. Activated carbon from rice husk (AC-RH) was synthesized and its methane adsorption capacities were compared with phenol based activated carbons (AC-PH2O and AC-PKOH). The adsorption experiments were conducted by volumetric method under various constant temperatures (293.15, 303.15, 313.15 and 323.15 K) and pressure up to 3.5MPa. Maximum methane adsorption was observed in AC-RH as its surface area is higher than the other two adsorbents. The experimental data were correlated well with Langmuir-Fruendlich isotherms. In addition, isosteric heat of adsorption was calculated by using Clausius-Clapeyron equation.

Metal-organic frameworks (MOF), potentially porous coordination structures, are envisioned for adsorption-based natural gas (ANG) storage, including mobile applications. The factors affecting the performance of the ANG system with a zirconium-based MOF with benzene dicarboxylic acid as a linker (ZrBDC) as an adsorbent were considered: textural properties of the adsorbent and thermal effect arising upon adsorption. The high-density ZrBDC-based pellets were prepared by mechanical compaction of the as-synthesized MOF powder at different pressures from 30 to 240 MPa at 298 K without a binder and mixed with polymer binders: polyvinyl alcohol (PVA) and carboxyl methylcellulose (CMC). The structural investigations revealed that the compaction of ZrBDC with PVA under 30 MPa was optimal to produce the ZrBDC-PVA adsorbent with more than a twofold increase in the packing density and the lowest degradation of the porous structure. The specific total and deliverable volumetric methane storage capacities of the ZrBDC-based adsorbents were evaluated from the experimental data on methane adsorption measured up to 10 MPa and within a temperature range from 253 to 333 K. It was measured experimentally that at 253 K, an 100 mL adsorption tank loaded with the ZrBDC-PVA pellets exhibited the deliverable methane storage capacity of 172 m3(NTP)/m3 when the pressure dropped from 10 to 0.1 MPa. The methane adsorption data for the ZrBDC powder and ZrBDC-PVA pellets were used to calculate the important thermodynamic characteristic of the ZrBDC/CH4 adsorption system—the differential molar isosteric heat of adsorption, which was used to evaluate the state thermodynamic functions: entropy, enthalpy, and heat capacity. The initial heats of methane adsorption in powdered ZrBDC evaluated from the experimental adsorption isosteres were found to be ~19.3 kJ/mol, and then these values in the ZrBDC/CH4 system decreased at different rates during adsorption. In contrast, the heat of methane adsorption onto the ZrBDC-PVA pellets increased from 19.4 kJ/mol to a maximum with a magnitude, width, and position depended on temperature, and then it fell. The behaviors of the thermodynamic state functions of the ZrBDC/CH4 adsorption system were interpreted as a variation in the state of adsorbed molecules determined by a ratio of CH4-CH4 and CH4-ZrBDC interactions. The heat of adsorption was used to calculate the temperature changes of the ANG systems loaded with ZrBDC powder and ZrBDC pellets during methane adsorption under adiabatic conditions; the maximum integrated heat of adsorption was found at 273 K. The maximum temperature changes of the ANG system with the ZrBDC materials during the adsorption (charging) process did not exceed 14 K that are much lower than those reported for the systems loaded with activated carbons. The results obtained are of direct relevance for designing the adsorption-based methane storage systems for the automotive industry, developing new gas-power robotics systems and uncrewed aerial vehicles.