Energy & Fuels, Vol.32, No.6, 6619-6626, 2018
Direct Measurements of Contact Angles on Cyclopentane Hydrates
When clathrate hydrate particles come into contact, they tend to agglomerate together, resulting from capillary liquid bridges that form between the particles. The strength of these capillary bridges is a function of several physical variables, many of which have been directly obtained for clathrate hydrate systems. A less thoroughly explored variable is the contact angle of water on the clathrate hydrate surface. Analyses have shown that the contact angle of a surface can have a strong effect on the cohesion behavior of clathrate hydrates; however, direct measurements of water on a hydrate surface are not prevalent. To better understand this important parameter, a method was developed to directly measure the contact angle of a water droplet deposited onto the surface of a cyclopentane hydrate particle. Using a novel method, the contact angles of water droplets on cyclopentane hydrate surfaces were directly measured. In combination of these new measurements with an updated interfacial tension value for a cyclopentane and water system, the immersion depth of the capillary bridge on a clathrate hydrate particle was estimated. Different anti-agglomerants (AAs) were tested for both contact angle and cohesion force, which showed that the micromechanical force measurement apparatus was capable of ranking the anti-agglomeration tendency of clathrate hydrate particles in the presence of AAs. These tests revealed a correlation between low cohesion force and higher contact angle, corresponding to a hydrophobic surface. Morphological changes were also observed in the hydrate particles upon the addition of AAs, and two main types of morphological changes, water extrusion and hydrate sloughing, were identified.