Synergistic kinetic inhibition of amino acids and ionic liquids on CH4 hydrate for flow assurance

Abstract

In this study, the kinetic inhibition effects of amino acids and ionic liquids and the potential synergism of their mixtures on CH4 hydrates were investigated by adopting three different approaches. The sigma (σ) profiles of inhibitor molecules obtained from the Conductor-Like Screening Model for Real Solvents (COSMO-RS) software were used to estimate inhibitor–water interactions for the pre-screening of potential inhibitors, and thus glycine (an amino acid) and [BMIM][BF4] (an ionic liquid) were selected as candidates for kinetic hydrate inhibitors (KHIs). A non-stirred high-pressure micro-differential scanning calorimeter (HP μ-DSC) revealed that the glycine (0.5 wt%) and [BMIM][BF4] (0.5 wt%) mixture showed a synergism for CH4 hydrate as a KHI. The kinetic inhibition synergism of the glycine (0.5 wt%) and [BMIM][BF4] (0.5 wt%) mixture on CH4 hydrate was double-checked using a stirred high-pressure autoclave. The onset temperature of the glycine (0.5 wt%) and [BMIM][BF4] (0.5 wt%) mixture was found to be lower than that of poly(N-vinylcaprolactam) (PVCap; 1.0 wt%). Time-dependent Raman spectra demonstrated that the cage-specific inhibition of glycine and [BMIM][BF4] caused kinetic inhibition synergism and the consequent slow growth rate of CH4 hydrate. The synergistic kinetic inhibition of amino acids and ionic liquids will be helpful in understanding the accurate roles of inhibitors in inhibitor–water interactions and will contribute to opening up a new field related to the synergism of eco-friendly inhibitors for flow assurance in oil and gas pipelines.