Tetrahydrofuran (THF) hydrate microscopic occurrence in glass beads

Hydrate distribution concentration and occurrence modes in porous media have been investigated widely and concerned constantly by hydrate academic community. It was acknowledged that there was not a consistent argument about these topics notwithstanding heaps of scholars had conducted numerous works using diverse precise favorably instruments and respective methods. Unlike visual tools like X-CT (X-ray computed tomography), MRI (magnetic resonance imaging), SEM (scanning electron microscopy) is a splendid way to characterize directly surface morphology information of samples due to high resolution and depth of field, etc., which caters completely to hydrate crystalline and porous media size limitation. In this article, we use cryo-cold field SEM (cryo-CFESEM) to capture the texture of ice and tetrahydrofuran (THF) hydrate, glass beads, and observe the distribution modes of ice and hydrate in porous media. Ice shows mainly hexagonal and spherical shape, which the latter is more than the former in quantity. Moreover, there are a small number of atypical polycrystalline attributed to sintering and/or Ostwald ripening. THF hydrates are block-like, irregular crystals adhering to a few ice crystals on their surface and differ notably in size of the two. This is because THF hydrates forestall the mass transfer of ice-water-vapor system so that it is difficult to form polycrystalline structure of ice without reaching the condition for sintering and/or Ostwald ripening. Additionally, both of them have different growth habitsice obeys the“pore-filling”and“coating”pattern but packs together tightly and disseminates discretely while THF hydrate size is larger than ice, sprawling densely as well as exhibiting“patchy”mode through secondary electron imaging and energy disperse spectroscopy (EDS) qualitative analysis. Moreover, the operation condition of EDS characterizing hydrate samples is determined, which provides a powerful guide for the application of EDS. © 2020, Chemical Industry Press Co., Ltd.. All rights reserved.