2-Propanol As a Co-Guest of Structure II Hydrates in the Presence of Help Gases

Abstract

The enclathration of 2-propanol (2-PrOH) as a co-guest of structure II (sII) hydrates in the presence of CH4 and CO2 was experimentally verified with a focus on macroscopic phase behaviors and microscopic analytical methods such as powder X-ray diffraction (PXRD) and NMR spectroscopy. 2-PrOH functioned as a hydrate promoter in the CH4 + 2-PrOH systems, whereas it functioned as an apparent hydrate inhibitor in the CO2 + 2-PrOH systems despite the inclusion of 2-PrOH in the hydrate lattices. From the PXRD patterns, both double CH4 + 2-PrOH and double CO2 + 2-PrOH hydrates were identified to be cubic (Fd3m) sII hydrates. From the (13)C NMR spectra, it was found that, at a lower 2-PrOH concentration, the small 5(12) cages of the sII hydrate were occupied by CH4 molecules only, whereas the large 5(12)6(4) cages were shared by CH4 and 2-PrOH molecules. However, at a stoichiometric concentration, the large cages were occupied by 2-PrOH molecules only, and the corresponding chemical formula for this concentration is 1.50CH4·0.98 2-PrOH·17H2O.