The ionic clathrate hydrate of tetra-n-butylammonium bromide (TBAB) has a potential for gas separation technology. It forms from TBAB aqueous solutions, and the water molecules and TBAB form cage-like hydrogen bond network in the crystal structure. This structure has the common dodecahedral (D) water structure. The D cage can incorporate small gas molecules, such as CH4, CO2 and N2. [1, 2] Recently, the two types of D cages were found in the TBAB + CO2 hydrate structure, and the CO2 capacities significantly differ due to the distinct cage shapes. [1] This suggests a new separation mechanism for the gas molecules having a similar size but different shapes, e.g., CH4 and CO2. Here we report the characterization of the TBAB hydrate formed under CH4 + CO2 mixed gas pressure by the single X-ray diffraction measurement. The crystals were formed at 287.5 K and 3.1 MPa with 0.2 of TBAB mass fraction in the aqueous phase. (Figure 1) The preliminary results show that the dominant guest is CO2 in the both D cages, which suggests that the competitive guest incorporation occurred in the TBAB hydrate structure. [1] S. Muromachi, K. A. Udachin, K. Shin, S. Alavi, I. L. Moudrakovski, R. Ohmura, J. A. Ripmeester, Chemical Communications, 2014, 50, 11476–11479. [2] S. Muromachi, H. Hashimoto, T. Maekawa, S. Takeya, Y. Yamamoto, Fluid Phase Equilibria, in press.

Characterization of gas selectivity of the ionic clathrate hydrate formed with tetra-n-butylammonium bromide

251st National Meeting (2016)

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