Experimental and Density Functional Theory Computational Evaluation of Poly(N-vinyl caprolactam-co-butyl methacrylate) Kinetic Hydrate Inhibitors

Abstract Natural gas hydrate inhibitor has been serving the oil and gas industry for many years. The development and search for new inhibitors remain the focus of research. In this study, the solution polymerization method was employed to prepare poly(N-vinyl caprolactam-co-butyl methacrylate) (P(VCap-BMA)), as a new kinetic hydrate inhibitor (KHI). The inhibition properties of P(VCap-BMA) were investigated by tetrahydrofuran (THF) hydrate testing and natural gas hydrate forming and compared with the commercial KHIs. The experiment showed that PVCap performed better than copolymer P(VCap-BMA). However, low doses of methanol or ethylene glycol are compounded with KHIs. The compounding inhibitors show a synergistic inhibitory effect. More interesting is the P(VCap-BMA)-methanol system has a better inhibitory effect than the PVCap-methanol system. 1% P(VCap-BMA) + 5% methanol presented the best inhibiting performance at subcooling 10.3 ℃, the induction time of natural gas hydrate was 445min. Finally, the interaction between water and several dimeric inhibitors compared by natural bond orbital (NBO) analyses and density functional theory (DFT) indicated that inhibitor molecules were able to form the hydrogen bond with the water molecules, which result in gas hydrate inhibition. These exciting properties make the P(VCap-BMA) compound hydrate inhibitor promising candidates for numerous applications in the petrochemical industry.