添加乙醯胺、環戊醇及1,3-二氧六環對甲烷水合物熱力學與動力學影響之實驗量測

Measurements for Thermodynamics and Kinetics of Methane Hydrate in the Presence of Acetamide, Cyclopentanol and 1,3-Dioxane

李立婷(Li-Ting Li)

指導教授 ： 陳延平

國立臺灣大學/工學院/化學工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.11258

摘要

本研究延續採用先前已建立之高壓設備裝置，並利用等容溫度循環法量測甲烷水合物分解之熱力學三相相平衡曲線 (H-Lw-V)，以及等容先降溫後升壓之方法量測甲烷水合物生成之動力學實驗數據。本研究主要目的為探討不同添加劑對於甲烷水合物系統是否於熱力學與動力學上具有之促進或抑制效果。以增加未來天然氣水合物開發應用之經濟效益。

本研究選用添加劑為乙醯胺 (Acetamide)、環戊醇 (Cyclopentanol) 以及1,3-二氧六環 (1,3-Dioxane)。結果顯示當乙醯胺存在時，則使甲烷水合物相平衡曲線往低溫高壓移動，因此縮小水合物穩定形成的溫壓區域，表示乙醯胺為熱力學抑制劑，且此抑制效果亦隨著添加劑濃度增加而提升。添加30 wt% 乙醯胺，約可抑制8.7 K；當環戊醇或1,3-二氧六環存在時，使甲烷水合物相平衡曲線往高溫低壓移動，因此擴大水合物穩定形成的溫壓區域，表示環戊醇以及1,3-二氧六環為熱力學促進劑，且此促進效果隨著添加劑濃度增加而提升。當添加8 wt% 環戊醇，約可促進6.8 K。而添加20 wt% 1,3-二氧六環，約可促進13.7 K。將本研究所使用添加劑與其他文獻添加劑比較歸納，發現添加劑的幾何形狀與官能基會影響水合物穩定的溫壓區域。另外，以3.5 wt% 氯化鈉模擬海洋環境，進行添加劑鹽水系統的熱力學相平衡量測，鹽類存在具有熱力學相對抑制的效果。在水合物生成動力學部分，則針對二丙酮醇 (Diacetone Alcohol) 來進行實驗。實驗結果顯示，與純水系統相比，二丙酮醇的存在的確可縮短水合物生成所需的誘導時間，並加速水合物生成的初始速率，此外，亦由實驗結果發現，添加二丙酮醇會大幅提升水合物的生成量，達到動力學上促進的效果。另外，針對具有加速水合物生成效果的環戊醇以壓力為變因，固定溫度的方式進行動力學實驗，並以過飽和梯度視為實驗趨動力。

關鍵字

甲烷水合物 ； 熱力學相平衡 ； 等容溫度循環法 ； 水合物生成動力學 ； 乙醯胺 ； 環戊醇 ； 1,3-二氧六環 ； 二丙酮醇

並列摘要

In this study, an apparatus which can be operated at low temperature and high pressure conditions was set up to measure the hydrate-liquid water-vapor (H-Lw-V) three-phase dissociation conditions of methane hydrate in the presence of additives by employing the isochoric method. The certain additives to system of methane + water were investigated for their effects on the phase boundary of methane hydrate. Also, the kinetic behavior of methane hydrate was investigated in an isochoric system to see how factors (e.g. sub-cooling temperature, experimental pressure) would affect the formation kinetics of methane hydrate.

In this work, acetamide, cyclopentanol and 1,3-dioxane were chosen as additives. The addition of acetamide in methane hydrate system shifted hydrate phase boundaries to higher pressure and lower temperatureand thus the hydrate stability region was broadened, therefore it had a inhibition effect on the formation of methane hydrate. Furthermore, the inhibition effect increased when the concentration of Acetamide in hydrate system increased. With 30 wt% acetamide the equilibrium temperature decreases about 8.7 K at given pressure in comparison to that of pure water system. On the other hand, the results of adding cyclopentanol or 1,3-dioxane showed the promotion effect on the formation of methane hydrate. Similarly, the promotion effect increased when the concentration of cyclopentanol or 1,3-dioxane in hydrate system increased. With 8 wt% cyclopentanol, the equilibrium temperature increases about 6.8 K at given pressure in comparison to that of pure water system. With 20 wt% 1,3-dioxane, the equilibrium temperature increases about 13.7 K at given pressure in comparison to that of pure water system. In addition, 3.5 wt% NaCl(aq) was usedas brine solution to simulate the salinity of the seawater environment. The dissociation conditions of methane hydrate in brine were also measured in this study with the addition of acetamide, cyclopentanol and 1,3-doxane.

In the formation kinetics of methane hydrate, 4-Hydroxy-4-methyl-2-pentanone (Diacetone Alcohol) was chosen as additive. The results showed that diacetone alcohol could reduce the induction time in comparison to that of pure water system and the initial rate of hydrate formation was effectively increased by adding diacetone alcohol. In conclusion, diacetone alcohol was an effective kinetic promoter to form methane hydrate in this work. In addition, cyclopentanol seems that it could shorten the induction time needed for hydrate formation so cyclopentanol was chosen as additive to test new formation kinetics experiments.

並列關鍵字

Methane hydrate ； Isochoric method ； Dissociation condition ； Formation kinetics ； Cyclopentanol ； 4-Hydroxy-4-methyl-2-pentanone (Diacetone Alcohol) ； Brine

參考文獻

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