The Adsorption Properties of Amorphous, Metal-Decorated Microporous Silsesquioxanes for Mixtures of Carbon Dioxide, Methane and Hydrogen

A set of adsorbents belonging to a class of amorphous, nanoporous materials composed of spherosilicate building blocks, containing isolated titanium metal sites, was investigated for their ability to separate equimolar binary gas mixtures of CH4/H-2, CO2/H-2, and CO2/CH4. The cubic silicate building blocks (spherosilicate units: Si8O20) in these adsorbents are cross-linked by SiCl2O2 bridges and decorated with -OTiCl3 and -OSiMe3 groups. Adsorption isotherms, selectivity and energies at 300 K for pressures up to 100 bar for CH4/H-2 and pressures up to SO bar for CO2/H-2 and CO2/CH4 were generated via molecular simulation describing physisorption using the Grand Canonical Monte Carlo method. Selectivity was also predicted using ideal adsorbed solution theory. Among the materials studied in this work, high-density material with no -OTiCl3 groups proved to be the best performing separator for the gas mixtures, with selectivities between 10 and 35 from high to low pressures for CH4/H-2 mixtures, 45 and 65 for CO2/H-2 mixtures, and 2 to 4 for CO2/CH4 mixtures.