Surface Behaviour of Gas Hydrate Kinetic Inhibitors at the Air-Liquid Interface
Natural gas hydrates are ice-like molecular inclusion compounds forming commonly at high pressures and low temperatures. They are responsible for pipeline blockage during the oil and gas production and transportation. Addition of surface active chemicals, including antiagglomerants (AAs) and kinetic inhibitors (KIs) can maintain hydrate slurry flow by preventing small hydrated particles from agglomerating. According to a proposed mechanism, KIs adsorbed on hydrate surfaces delay the nucleation and the growth of gas hydrate crystals for periods of time dependent upon the subcooling in the system. In this study, the adsorption of polyvinylcaprolactam, one of the most well known KIs of natural gas hydrates has been evaluated at the air-liquid interface by dynamic and equilibrium surface tension measurements. The influence of polymer concentrations and the temperature on the adsorption of the polymer was determined. The effect of the hydrate liquid promoter tetrahydrofuran (THF) on the adsorption of the inhibitor was also studied at 5°C and the atmospheric pressure. The inhibitor was apparently active at the air-liquid interface. A weak temperature effect on the adsorption of the polymers was observed. A slow adsorption kinetics of the polymer molecules and the concentration dependence were demonstrated. A comparison with another gas hydrate kinetic inhibitor, the poly(N-vinyl caprolactam/N-vinylpyrrolidone/N,N-dimethylaminoethyl methacrylate) was also presented.