Microscopic molecular and experimental insights into multi-stage inhibition mechanisms of alkylated hydrate inhibitor

A deep understanding of the mechanism of hydrate inhibitors on hydrate formation is crucial for the development of efficient natural gas hydrate inhibitors. However, the current understanding of the inhibitory mechanism of hydrate inhibitors in the nucleation and formation processes is still very limited, which greatly hinders the development of new types of hydrate inhibitors. In this study, the solution polymerization method was employed to prepare poly (N-vinyl pyrrolidone-co-N,N-dimethyl acrylamide), as a new kinetic hydrate inhibitor. The inhibition properties were investigated by the constant cooling test and the step cooling test. Meanwhile, the multi-stage inhibition mechanisms of alkylated hydrate inhibitor were also revealed based on molecular simulations. The results of experiments and molecular simulations illustrate that the mechanism of the inhibitors varies at different stages. The inhibitors retard hydrate formation by reducing the solubility of methane molecules in water during the nucleation phase. However, during the formation phase, the hydrate inhibition is achieved by adsorption. In particular, the absorption of poly (vinyl pyrrolidone) on the surface of hydrate can be effectively improved by alkylation, and the interaction energy of poly (N-vinyl pyrrolidone-co-N,N-dimethyl acrylamide) with the hydrate nucleus was increased by 3.22 times compared to poly (vinyl pyrrolidone). It resulted in an increase in subcooling of 8.2 °C. Also, the effective induction time of poly (N-vinyl pyrrolidone-co-N,N-dimethyl acrylamide) at 8 °C was extended to 987 min. A molecular model for evaluating the interaction of inhibitors with hydrates is also successfully developed, which corresponds well to the experimental results. These results contribute to a better understanding of hydrate formation in drilling fluids and implications for developing new materials for high-performance hydrate drilling fluids.