Kinetic and memory effects of methane hydrate by chemical inhibitors

Kinetic and memory effects of methane hydrate were investigated using chemical inhibitors. A stirring reactor was operated at constant temperature (273.65 K) and pressure (5.0 MPa) to form methane (CH₄, 99.99%) hydrate under the presence of kinetic inhibitors, poly vinyl carprolactam (PVCap) and poly ethylene oxide (PEO). The effects of the mixed solutions on the hydrate formation at 0.1 - 1wt% of the PVCap and 0.0025 - 0.005wt% of the PEO were evaluated. Hydrate formation kinetics was comprised of two steps: Nucleation and growth. The final gas consumption in the solution containing chemical inhibitors was lower than that in the pure water, depending on their dose. In addition, the consisted amount of the methane gas used to form methane hydrate at the different inhibitor doses were almost similar. However, the presence of the chemical inhibitors in the solution resulted in the delay of hydrate induction time (∼ 5 min at 2nd step for pure water vs. ∼ 420 min at 2nd step for 1wt% PVCap). The chemical inhibitors such as PVCap and PEO interfered with the hydrate formation. Generally memory effect of the hydrate formation is known to shorten the hydrate induction time. In this study, the induction times of hydrate formation in pure water with and without memory effect were similar (5.2 and 5.5 minutes, respectively). However, in the presence of chemical inhibitors such as PVCap and PEO the induction times with and without memory effect were changed to about 420 and 470 minutes, respectively. The comparison of induction time indicated that 50 minutes was delayed in the presence of inhibitors.