Abstract
Adsorbed natural gas technology is an efficient technology for storing natural gas at low pressure and room temperature. This work investigates the properties of the adsorbed methane film in nanopores where methane is adsorbed by strong van der Waals forces in pores of few molecular diameter as a high-density fluid. BET surface area, porosity, and pore size distribution were measured using sub-critical nitrogen adsorption. The adsorbed film thickness, the film density, specific surface area, and methane average binding energy were extracted from a single supercritical methane adsorption isotherm using Langmuir and Ono-Kondo models. In addition, this method does not require a conversion between gravimetric excess adsorption and absolute adsorption. The adsorbed film thickness is between 4.2 and 4.4 Å and the density of the adsorbed film at maximum capacity is between 302 and 340 g/L. Specific surface areas obtained from supercritical isotherms are consistent with BET surface areas from subcritical nitrogen adsorption. The binding energies obtained from the two models are compared to the ones obtained from Clausius-Clapeyron method.
Highlights
Storing natural gas (NG) by adsorption offers several advantages over exiting technologies
Liquefied natural gas (LNG) and compressed natural gas (CNG) have drawbacks when applied in the automotive industry and the petroleum industry
The Langmuir fit provides the specific surface areas from supercritical methane isotherm, which are comparable to the BET surface area obtained from subcritical nitrogen isotherm
Summary
Storing natural gas (NG) by adsorption offers several advantages over exiting technologies. The program aims to develop adsorbents for natural gas storage at low pressure and room temperature. The binding energy of methane on adsorbent is usually determined using two isotherms at nearby temperatures using Clausius-Clapeyron equation. This method requires a conversion from excess to absolute adsorption by assuming or computing the volume of the adsorbed film.[14] Firlej et al proposed a method to determine the high-coverage binding energy using a single isotherm and the pore-size distribution.[15] In this work, the average binding energy at low coverage and the overall average binding energy are extracted from supercritical methane adsorption isotherms. The specific surface area, the adsorbed film thickness, and the film density at maximum capacity are determined using the Ono-Kondo and Langmuir models
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