In-situ Raman Research On Transfer Characteristics Of Gas Molecule In Hydrates

In-situ microscopic Raman spectroscopy can provide information about hydrate structure type,composition and cage occupancy rate,hydrate formation and decomposition mechanism can also be studied through continuous measurement.In this paper,a sapphire high pressure optical reactor is improved and a set of apparatus for In-situ Raman measurement of hydrate is designed.The main research contents are divided into two parts:（1）About 5 mm thick THF hydrate layer is generated in the chamber,then injected into H₂,CH₄,（H₂ 77 mol%+CH₄ 23 mol%）and（H₂ 77 mol%+CO₂ 23 mol%）gas,the transfer regularity of gas molecules in the cage of THF the hydrates are researched by In-situ Raman spectroscopy.Results showed that only H₂ molecules can transmit in the small cage of THF hydrate and finally penetrate the hydrate layer.The structure of hydrates is not affected by the transfer of H₂ molecules.The diffusion process of H₂ molecules can be divided into fast stage,slow stage and saturated stage.The CH₄ and CO₂ molecules exist only within 0.30 mm of the hydrate interface.THF hydrate layer has a selection effects of gas molecules and can be used to separate hydrogen containing mixed gases.It is determined that the minimum pressure or partial pressure of H₂ molecule to transport and penetrate THF hydrate layer is about 2.9 MPa.（2）The decomposition regularities of C₂H₆ and CO₂ hydrates at atmospheric pressure and under ice point（272.15 K,271.15 K,270.15 K and 269.15 K）are studied by In-situ Raman spectroscopy.Results showed the decomposition degree of C₂H₆ and CO₂ hydrate varies monotonously with the temperature,the lower temperature,the lower degree of hydrate decomposition.Compared with CO₂ hydrate,C₂H₆ hydrate has stronger self-protection ability.The decomposition process of C₂H₆ hydrate at 271.15 K,270.15K and 269.15 K is divided into rapid decomposition stage,fluctuation stage and decomposition equilibrium stage.However,CO₂ hydrate directly reach decomposition equilibrium stage after rapid decomposition.