Raman spectroscopic study of H₂S hydrate online growth process

The gas mixture hydrates containing H₂S are easily formed while sour natural gas is transported in pipelines under low temperature and high pressure conditions. The formation of gas hydrates usually block pipelines and corrode equipment, thus affecting production of gas plants. Understanding the growth rate of H₂S hydrate has some significance for preventing natural gas pipelines from blocking. At the same time, gas hydrates can be considered as the storage media which can be used to store and transport and separate sour natural gas. It is conducive to evaluate the sorage capacity or H₂S hydrate by obtaining its fractional occupancy and hydration number. Based on the fused silica capillary tube and online observation system, combined with the in-situ Raman spectroscopy, a method of Raman spectroscopy analysis and online observation of H₂S hydrate was developed in this study. The growth process of H₂S hydrates were observed microscopically, and it was confirmed that hydrate growth was mainly controlled by mass transfer conditions, revealing that the growth rate of H₂S hydrate in solution. Characterizations of the Raman spectroscopy during the growth of H₂S hydrate were studied. With the decrease of temperature, the S-H stretching vibration band of H₂S dissolved in aqueous gradually turned into a double S-H stretching vibration bands of H₂S in hydrate phase, and liquid water O-H stretching vibration bands turned into structured water O-H stretching vibration bands. In addition, type Ⅰ of H₂S hydrate by Raman spectroscopy was identified. The fractional occupancy of big cage and small cage was 96.0% and 80.9% respectively, and hydration number was 6.23%. The high gas storage capacity and stability of H₂S hydrate provide a favorable support for hydrate desulfurization.