The physisorption of methane in homogeneousarmchair open-ended SWCNT triangular arrays for the tubes of diameter of 10.85, 13.57, 16.28 and 19.00 A ° [(8,8), (10,10), (12,12) and (14,14), respectively] at temperature of 273, 298, 323 and 373 K and at fugacity of 0.5–9.0 Mpa is evaluated by means of Grand Canonical ensemble Monte Carlo simulation. The applied intermolecular forces are modeled using Lennard-Jones potential model. The absolute, excess and delivery adsorption isotherms of methane in various carbon nanotube arrays are calculated. Besides, specific surface areas and the isosteric heats of adsorption, Qst, are studied, also different isotherm models were fitted on the simulation adsorption data, and the model parameters are correlated. A novel geometrica relationship is introduced to calculate accessible interstitial and intratubular volumes. According to our simulation results, one can reaches to 96% of the US Department of Energy target for CH4 storage of 180 v/v at 298 K and 35 bar by using the SWCNT array with nanotube’s diameter of 19 A ° as adsorbent. For intertube distance equal 3.4 A ° , no gas adsorption is observed in interstitial channel except for the arrays bigger than 15.4 A ° in nanotube’s diameter, and multi-layer adsorption starts to form in notube’s diameter of 16.28 A ° at the pressure of 2.0 MPa.

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