| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 106 === In this study, phase equilibrium conditions for carbon dioxide hydrates in the presence of 1,3-Cyclohexanebis(methylamine)、urea and their mixture were experimentally measured. The three-phase (H-Lw-V) equilibrium pressures and temperatures were determined by isochoric method in the equilibrium pressure range from 1.52 to 3.29 MPa with various concentrations of the additives. Also, the kinetic behaviors were investigated in the presence of urea at 0.2 and 0.3 mass fraction.
Compared with pure water system, addition of 1,3-Cyclohexanebis(methylamine) and urea in the system causes inhibition effect on carbon dioxide hydrate formation and the maximum decrease of dissociation temperature is about 7.3 K and 10.2 K, respectively. Moreover, the mixture of those two additives was also tested to verify the synergistic effect. The result shows that the mixing of those two additive decreases the inhibit effect implying that there are no synergistic effect between them. Then, the structure and dissociation enthalpy of hydrates are estimated by using Clausius-Clapeyron equation. The structures of carbon dioxide hydrates with addition of 1,3-Cyclohexanebis(methylamine)、urea are classified as structure I, whereas those with addition of their mixture are classified as structure I. The only exception is when high concentration of 40 wt% of urea are added, the hydrates are classified as mixture of structure I & structure II.
In kinetic experiment part, the formation of carbon dioxide hydrates with urea as the additive at 0.2 mass fraction were investgated. With isobaric and isothermal condition, the driving force are defined as the difference between experimental temperature and operating temperature. The kinetic behaviors of systems with or without the addition of urea are experimented under the same driving force of 5.3K. Each system was testified for three times to ensure the reproducibility. The result shows that the addition of 20 wt% urea significantly decreases the induction time by 52%.
In literature, urea also plays as an inhibitor in methane hydrate system. By combining the results and the equilibria data obtained by this research, the addition of 20 wt% urea shows the ability to initiate the process of “Trapping CO2 as a hydrate phase during methane extraction.” In addition, accroding to our experimental data, urea is also a kinetic promoter in carbon dioxide hydrate system. As a result, the enhencement of trapping efficiency make urea one of the potential commercial additive for methane extraction process.
|
|---|
