Natural gas sorption evaluation on microporous materials

Abstract

In this work, detailed comparisons of the natural gas (NG) mixture adsorption capacity, cycling stability and physical properties of ten microporous samples were conducted. The BET specific surface area and micropore volume of the adsorbents are shown to correlate to their maximum excess NG adsorption capacity at 298 K and up to 70 bar, irrespective of the chemistry and functionalities of the materials. The cycling stability highly depends on the material's pore size and pore size distribution. A narrow pore size distribution with an optimum pore width of 8–11 Å is known to improve the maximum excess methane adsorption. However, when considering NG blends containing components with higher binding energies and slower diffusion rates than methane, we show that large micropores and even mesopores are necessary to provide easy diffusion paths for the adsorbate molecules to be desorbed from and diffuse out of the pore network. Pores which are too small, e.g. < 5 Å, are not desired since it's highly possible that the large species can be trapped in, resulting in a decrease in storage capacity with cycling. Adsorbent tailoring and development for NG storage applications appears to be sensibly different than for pure methane.