Fundamental Researches On Concentrating Organic Water Solution Via Gas Hydrate Formation

The concentration technology for organic water solution via hydrate formation is an important branch of the hydrate separation technology. The process of concentration via hydrate formation is similar to freezing crystallization, but more economical, because hydrate could be formed beyond the freezing point of water leading to the less energy consumption.Nowadays, some researches on fruit juice concentration via hydrate formation have been carried out, but little for the concentration of organic water solution. On the basis of prophase researches in our laboratory, we researched the concentration of organic water solution via hydrate formation. The theoretical foundation of organic water solution concentration via gas hydrate formation is the kinetics of hydrate formation in organic water solution.Under the near-critical conditions of ethylene, the ethylene hydrate formation kinetic data that was in different initial pressure, temperatures and various concentrations of glycol conditions was measured. The experiments also measured the concentrations of glycol at 400 minutes. The ethylene hydrate formation kinetic behaviors in glycol aqueous solution were discussed. We discovered that the behavior curves in glycol aqueous solution were similar to that in pure water. But there were more frequent phenomenon of hydrate secondary nucleation in glycol aqueous solution. The influences of initial pressure, temperature and concentration on hydrate formation behavior were analyzed. Higher initial pressure and lower temperature accelerated hydrate formation. When the initial pressure is higher than 4.0MPa, the probability of ethylene hydrate secondary nucleation increased greatly. The higher glycol concentration was in aqueous solution, the deeper inhibition was displayed on hydrate formation. But the inhibition didn't depend on the concentration between the low concentrations (lower than 5.0wt%), sometimes low concentrations even pushed ahead hydrates formation.With the rise of initial glycol concentration, the result of concentration became worse, but this law disappeared between low initial concentrations.When the initial glycol concentrations were high, the result of concentrating the solution via ethylene hydrate formation was not much satisfactory. The rise of concentration was only about 10% in the solution whose initial concentrations were 10.0wt%. Higher initial pressure favored the rise of concentration. But the rise of concentration had no steady relation with initial pressure. The rise of concentration was relative insensitivity to the variation of temperature. The suitability of ethylene hydrate formation kinetic model was explored in glycol aqueous solution. The inaccuracy between theoretical value and experimental value was big, especially in hydrate growth stage. The model was needed to modify the choice of the parameters, such as Henry constant.