Gas separation using tetrahydrofuran clathrate hydrate crystals based on the molecular sieving effect

Abstract The molecular sieving effect of tetrahydrofuran (THF) clathrate hydrate was experimentally investigated. The capture and release of seven gases, i.e., helium (He), hydrogen (H 2 ), neon (Ne), nitrogen (N 2 ), xenon (Xe), methane (CH 4 ), and ethane (C 2 H 6 ), in THF clathrate hydrate were investigated. For gases with a diameter smaller than the window diameter, the order of the gas uptake rates in the THF clathrate hydrate was in accordance with the order of their van der Waals diameters, except for He. This result indicates that the gas uptake rate is generally controlled by the size of the gas molecules. The apparent diffusion coefficients for these gases in the THF clathrate hydrate were estimated. The van der Waals diameters of CH 4 and Xe are larger than the window diameter. However, gas uptake by THF clathrate hydrate was observed for both gases. This can be attributed to the formation of the type I clathrate hydrate of these gases. No significant gas uptake of ethane was observed. Based on the results, H 2 /N 2 and H 2 /C 2 H 6 separation experiments were conducted. Gas separation of H 2 /N 2 by THF clathrate hydrate was successfully achieved using the difference in their gas uptake rates of the gases, and the separation ratios were in the range 4–16 mol/mol. Gas separation of H 2 /C 2 H 6 was also achieved utilizing the molecular sieving effect of THF clathrate hydrate.