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

• Molecular sieving effect of THF clathrate hydrate was experimentally investigated.
• Apparent diffusion coefficients of seven gases in THF hydrate were estimated.
• Separation of H2/N2 was achieved using the difference in gas uptake rates.
• Separation of H2/C2H6 was achieved using the difference in equilibrium states.

The molecular sieving effect of tetrahydrofuran (THF) clathrate hydrate was experimentally investigated. The capture and release of seven gases, i.e., helium (He), hydrogen (H2), neon (Ne), nitrogen (N2), xenon (Xe), methane (CH4), and ethane (C2H6), 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 CH4 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, H2/N2 and H2/C2H6 separation experiments were conducted. Gas separation of H2/N2 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 H2/C2H6 was also achieved utilizing the molecular sieving effect of THF clathrate hydrate.