Effect of Surfactant-coated Particles on Clathrate Hydrate Formation

Clathrate hydrates are crystalline compounds composed of hydrogen-bonded water molecules that form polyhedral cavities and trap small guest molecules such as methane, carbon dioxide, cyclopentane (CP), and tetrahydrofuran (THF). Understanding the formation and dissociation of clathrate hydrates is of significant importance to addressing some global challenges such as greenhouse gas mitigation and energy recovery. The fundamentals of the processes occurring in clathrate hydrate formation and dissociation remain unclear, which is largely due to lack of information on the nucleation process leading to the clustering that induces hydrate growth. In the present work, we investigated the effect of foreign particles of various degrees of hydrophobicity on the nucleation of CP and THF hydrates by measuring the induction time, lapse of time before the appearance of detectable volume of hydrate phase. The experiments were carried out at atmospheric pressure and 0.4 degree Celsius without agitation. If no foreign particles were added, no CP hydrate or THF hydrate could be observed over a sufficiently long testing period (48 hours). With the addition of clean silica (hydrophilic) glass beads, no CP hydrate formation was detected over 48 hours whereas the induction time of THF hydrate formation was reduced to 7.8 ± 4.2 hours. Adding octadecyltrichlorosilane (OTS)coated (hydrophobic) glass beads allowed the induction time of CP hydrate to be shortened to 5.3 ± 3.9 hours and that of THF hydrate to be further reduced to 1.6 ± 0.8 hours. Possible causes of the hydrate promotion by hydrophobic surfaces were discussed. Keywordsclathrate hydrate, surfactant coating, glass particles, induction time, hydrophobic surfaces, cyclopentane, tetrahydrofuran