Measurement of Thermosynamics and Kinetics of Carbon Dioxide Hydrate in the Presence of Acetamide, Cyclopentanol and 1,3-Dioxane
由本研究之實驗結果顯示當添加1,3-二氧六環，對水合物的生成有促進之效果，使二氧化碳水合物穩定存在區域擴大。而其促進效果隨著添加之濃度增加而提升，20 wt% 之1,3-二氧六環平衡溫度最多可增加約7.8 K。另外，添加乙醯胺對二氧化碳水合物有抑制效果，抑制效果隨濃度增加而變大，在20 wt% 時最大，抑制溫度約5 K。此外，為了模擬海洋環境，本研究亦進行二氧化碳＋鹽水＋添加劑之水合物系統相平衡條件的量測，由實驗結果發現當添加1,3-二氧六環至鹽水系統中亦有促進二氧化碳水合物生成之效果；而添加抑制劑乙醯胺則是使二氧化碳水合物相平衡曲線往溫度更低和壓力更高的方向移動。由於受到鹽分的影響，其促進效果較添加至純水系統時為低；抑制效果較純水系統時為高。
In this study, an apparatus which can be operated at high pressure and low temperature conditions was built and operated to measure the carbon dioxide hydrate of thermodynamics phase equilibrium and kinetics formation rate. In the thermodynamic part, this study used isochoric method to measure the carbon dioxide-hydrate-liquid water phase equilibrium boundary curve. In kinetics parts, using the pressurization in isochoric system to measure the formation rate and the amount of carbon dioxide hydrate. In this research, 1,3-Dioxane, Acetamide, and Cyclopentanol were chosen as additives. In thermodynamic experimental results showed that the addition of 1,3-Dioxane in carbon dioxide system had effective promotion effects on formation of carbon dioxide in comparison with pure water system at a given pressure, and they could broaden the hydrates stability region. Furthermore, the promotion effect could increase as the concentration of additives increased. With the concentration of 20 wt% 1,3-Dioxane additives, the dissociation temperatures were increased about 7.8 K. With 20 wt% Acetamide, the equilibrium temperature decreased about 5 K at given pressure in comparisoon to that of pure water system. In addition, the hydrate dissociation conditions for brine systems with 3.5 wt% NaCl were also measured in this study. The promotion effect for carbon dioxide hydrate formation in brine environment was also observed with 1,3-Dioxane. However, the promotion effects in the presence of 1,3-Dioxane additives in the salt system was less than those in the pure water system. On the other hand, the inhibition effects were observed when adding Acetmaide in brine system, the equilibrium conditions shifted to higher pressure and lower temperature in comparison with pure water system. Although the promotion effect of adding Cyclopentanol in carbon dioxide hydrate system was not good. It seemed that Cyclopentanol could increase the formation rate and decrease the induction time of carbon dioxide hydrates in thermodynamic experiments, so Cyclopentaonl was chosen as additive in kinetic experiments. The kinetic results proved Cyclopentaonl could reduce the induction time of forming carbon dioxide hydrates in comparison with pure water system, and the initial rate of hydrate formation was effectively increased by adding Cyclopentanol. In conclusion, Cyclopentaonl was effective kinetic promoter to form carbon dioxide hydrates in this work.
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