Spectroscopic analysis of carbon dioxide and nitrogen mixed gas hydrates in silica gel for CO2 separation

Abstract

In this study solid-state NMR spectroscopy was used to identify structure and guest distribution of the mixed N-2 + CO2 hydrates. These results show that it is possible to recover CO, from flue gas by forming a mixed hydrate that removes CO2 preferentially from CO2/N-2 gas mixture. Hydrate phase equilibria for the ternary CO2-N-2-water system in silica gel pores were measured, which show that the three-phase H-L-w-V equilibrium curves were shifted to higher pressures at a specific temperature when the concentration of CO2 in the vapor phase decreased. C-13 cross-polarization (CP) NMR spectra of the mixed hydrates at gas compositions of more than 10 mol% CO, with the balance N-2 identified that the crystal structure of mixed hydrates as structure 1, and that the CO2 molecules occupy mainly the abundant 5 12 6 2 cages. This makes it possible to achieve concentrations of more than 96 mol% CO2 gas in the product after three cycles of hydrate formation and dissociation. (c) 2006 Elsevier B.V. All rights reserved.