Effect of Kinetic Hydrate Inhibitor Polyvinylcaprolactam on Cyclopentane Hydrate Cohesion Forces and Growth

The effect of Polyvinylcaprolactam (PVCap), a commonly used kinetic hydrate inhibitor (KHI), on the cohesion force between cyclopentane hydrate particles was measured using a micromechanical force apparatus. The presence of PVCap in the aqueous bulk phase reduced the average hydrate cohesive force by 54% (from 1.49 to 0.69 mN/m). However, the cohesion forces did not vary significantly as a function of either the PVCap concentration (0.005-0.5 wt %) or the temperature (from 1.1 to 7.2 degrees C). When a layer of PVCap solution was applied to the surface of a pure cyclopentane hydrate particle in a bulk liquid cyclopentane phase, the interparticle cohesive force was reduced by 45% (from 4.3 to 2.4 mN/m). Hydrate growth on droplets of PVCap solutions was also studied by contacting a water droplet with a cyclopentane hydrate particle in a bulk cyclopentane phase. In cases where PVCap was absent, complete conversion of the water droplet to hydrate occurred within 30 s. However, when a water droplet of PVCap solution was brought into contact with a hydrate particle, hydrate film growth was significantly slowed, requiring over 2 h for complete conversion.