Engineered Porous Carbon for High Volumetric Methane Storage

Abstract

This paper covers the optimization of methane volumetric storage capacity by controlling the sub-nanometre (<1 nm) and supra-nanometre (1-5 nm) pore volumes. Nanospace engineering of KOH activated carbon generates an ideal structure for methane storage in which gas molecules are adsorbed as a high-density fluid by strong van der Waals forces into pores that are a few molecules in diameter. High specific surface areas, porosities, subnanometre (<1 nm) and supra-nanometre (1-5 nm) pore volumes are quantitatively selected by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. The formation of tuneable sub-nanometre and supra-nanometre pores is validated by sub-critical nitrogen adsorption. Aberration-corrected scanning transmission electron microscopy data show the atomic structure of highsurface-area activated carbon (2600 m 2 /g). While high surface area and high porosity are optimal for gravimetric methane storage, the results indicate that an exclusive sub-nanometre region, a low porosity and an acceptable surface area (approximately 2000 m 2 /g) are ideal for methane volumetric storage, storing 120 g CH 4 /l (184 vol/vol) at 35 bar and room temperature (22 ˚C). High-pressure methane isotherms up to 150 bar at 30, -25 and -50 °C on optimal activated carbons are presented. Methane volumetric storage capacity at 35 bar reaches 176 g/l (269 vol/vol) and 202 g/l (309 vol/vol) at -25 and -50 °C, respectively.

Predictable and targeted activation of biomass to carbons with high surface area density and enhanced methane storage capacity

“…This yield is much higher than the yields (i.e., 4 to 20%) obtained when carbonaceous matter that is generated via conventional pyrolysis and hydrothermal carbonisation (HTC) routes is used as the starting material. [6][7][8][9][10][11][12][13][14][15][16][17] We ascribe the higher yield to the fact that flash carbonisation, such as demonstrated here for date seeds and ACDS carbon, generates carbonaceous matter that is relatively resistant to activation with KOH due to having a low O/C ratio. [41][42][43][44] However, the critical mass balance parameter is the overall biomass (date seeds) to activated carbon yield, which is between 25 and 40%.…”

“…Furthermore, pore channels of size 0.8 to 1.5 nm are best suited for the most favourable adsorption of 2 or 3 methane molecules in a manner that optimises the packing of the adsorbed phase within the pores. [6][7][8][9][10][11][12][13][14] It has also been previously suggested that pore channels of size 1.1 nm are the most suited for methane storage. 13 The present carbons, with their mix of microporosity/mesoporosity (Table 2), are therefore expected to be excellent candidates to achieve a high methane storage capacity at moderate pressures.…”

“…For efficient methane storage at moderate to high pressure (35-100 bar), a porous material should be predominantly microporous with high surface area along with low mesoporosity. [6][7][8][9][10][11][12][13][14] A high microporous volume is essential to ensure strong adsorption of methane molecules, while some mesoporosity is required for efficient sorption kinetics. Furthermore, pore channels of size 0.8 to 1.5 nm are best suited for the most favourable adsorption of 2 or 3 methane molecules in a manner that optimises the packing of the adsorbed phase within the pores.…”

“…To circumvent the challenges of CNG and LNG, methane may be stored as adsorbed natural gas (ANG) via adsorption, at relatively low pressure, onto a suitable adsorbent material such as porous carbon. [6][7][8][9][10][11][12][13][14][15][16][17] Recent research has developed new ways of preparing porous carbons with properties that are useful for good performance in energy-related applications but much of the work still relies on trial and error approaches. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Careful activation of carbonaceous matter can dramatically improve properties for specific applications but there is need for a more predictable synthesis approach.…”

Activated Nanoporous Carbon from walnut shell as a Promising Adsorbent for Methane Storage in ANG Technology

“…The performance of the adsorbents is related to their pores that can be measured by the adsorbent-adsorbate interaction energy. Due to its textural properties such as high micropore volume and large surface area, Activated Carbon (AC) has attracted much attention as one of the most important materials for adsorbing a wide range of gasses from methane to CO 2 and H 2 [7][8][9][10][11][12]. The analysis of the adsorption of natural gas on suitable adsorbents can be carried out through statistical mechanics, adsorption models, and classic theoretical models [13,14].…”