Adsorption of kinetic inhibitors on clathrate hydrates

Adsorption studies of kinetic inhibitors on clathrate hydrates are essential for understanding the inhibition mechanism at the hydrate-water interface. This work presents the adsorption behaviors of two kinetic inhibitors, polyvinyl pyrrolidone (PVP) and polyvinylcaprolactam (PVCap), on cyclopentane (CP) hydrates. The particle charge of CP hydrates is negative in the absence of any inhibitors, and it becomes neutral as the inhibitor concentration increases. The isotherm of PVP is well fitted to the Langmuir-type whereas the adsorption isotherm of PVCap is of the BET-type. Although PVCap monomers preferably adsorb on hydrates compared with PVP monomers, the isotherms of PVP and PVCap overlap with each other at concentrations up to 50 μM that corresponds to a water-based weight fraction of 0.6% for PVP or 0.5% for PVCap. Above this concentration, a multilayer adsorption occurs for PVCap. This multilayer adsorption gives rise to a thicker adsorption layer than that for the PVP case, which makes PVCap more effective in reducing the diffusion of hydrate formers from the bulk phase to the hydrate surface where the hydrate growth prefers to proceed. The determination of polymer inhibitor adsorption isotherms can provide the implication of adsorption behaviors and can be utilized to screen a new effective kinetic hydrate inhibitor.