Inhibition effect of novel amphiphilic poly(amino acid)s on methane hydrate

A series of novel amphiphilic poly(amino acid)s (PAAs) have been synthesized via the ring-opening polymerization of amino acid N-carboxyanhydrides, and their performance as kinetic hydrate inhibitors has been evaluated in high-pressure autoclaves by using methane gas. In the slow constant cooling tests, the PAAs with more hydrophobic groups lead to lower hydrate onset temperatures, and the best ones, such as 72% oxidized polymethionine, are with an inhibition effect about the same as the commercialized poly(N-vinyl pyrrolidone) (PVP) but worse than the powerful poly(N-vinyl caprolactam) (PVCap) at the concentration of 0.15 wt%. However, oxidized polymethionines are excellent hydrate crystal growth inhibitors since they have superior performance on retarding methane hydrate growth than both PVP and PVCap. In addition, molecular dynamics simulations have been used to insight into the inhibition mechanism of PAAs. It is found that the more hydrophobic PAAs are more efficient in preventing methane dissolution and water diffusion, consequently leading to the better hydrate inhibition performance.