Influence on Hydrate Dissociation for Methane Hydrates Formed in the Presence of PolyVinylCaprolactam versus PolyVinylCaprolactam plus Butyl Glycol Ether

It has previously been shown that hydrates formed in the presence of efficient kinetic hydrate inhibitors (KHI) such as PolyVinylCaprolactam (PVCap) dissociate at temperatures above the equilibrium dissociation temperature of the uninhibited hydrates. The question regarding how hydrates form and dissociate as a function of time is an important: issue for the industry. As KHI, commercial PVCap is commonly supplied in a solvent, e.g., butyl glycol ether (BGE), and the solvent acts as a synergist and improves the KHI performance of PVCap. In the present paper, the effect of BGE on dissociation of methane hydrates formed in the presence of PVCap has been examined. The pure BGE solvent showed no effect on the dissociation temperature at the applied concentrations. Two different molecular weight fractions of PVCap (M-w = 2k and 6k) have been tested either as pure substance or in mixture with BGE. The PVCap polymers have been synthesized in different solvents and stored for different periods of time prior to testing. The results show that both the production method and the time of storage influence their effect on the hydrate dissociation temperature. Hydrates formed in the presence of a fresh 1:1 solution of PVCap-2k and BGE (Inhibex 101) showed a reduction in dissociation temperature compared to hydrates formed in the presence of PVCap alone. On the other hand, hydrates formed in the presence of PVCap-6k + BGE showed a slightly increased dissociation temperature as compared to hydrates formed with PVCap alone. It appears that both production method and aging of PVCap and BGE can affect the influence on the hydrate dissociation temperature.