添加環戊酮、環己酮及2-甲基-2-丙醇對於二氧化碳水合物分解狀態與動力學之實驗量測

Abstract

本研究使用一套高壓低溫的設備，以等容溫度循環法量測二氧化碳+純水+添加劑之熱力學相平衡數據，以及在等容之系統中以升壓方式進行動力學實驗。本研究選用之添加劑為環酮類之環戊酮與環己酮、環醚類之1,3,5-三氧六環、2,5-二氫呋喃和1,3-二氧五環及醇類之2-甲基-2-丙醇。 由本研究之實驗結果顯示當添加環戊酮、1,3,5-三氧六環、2,5-二氫呋喃和1,3-二氧五環，對於水合物的生成皆有促進效果，使二氧化碳水合物穩定生成之區域擴大，而其促進效果隨著添加之濃度增加而提升，15wt% 之環戊酮、1,3,5-三氧六環、2,5-二氫呋喃和1,3-二氧五環之平衡溫度分別可增加約6.9 K、6.4 K、8.1 K和5.6 K。此外，為了模擬海水的環境，本研究也進行二氧化碳＋鹽水＋環醚類之水合物系統相平衡條件的量測，由實驗結果發現當添加環醚類藥品至鹽水系統中亦有促進二氧化碳水合物生成之效果，但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。另外，添加環己酮和 2-甲基-2-丙醇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，其具有抑制二氧化碳水合物生成之效果，在給定的壓力下，平衡溫度最高可分別減少約0.5 K和2.2 K。 另外，在熱力學實驗中發現添加2-甲基-2-丙醇可能有動力學上之促進效果，故以2-甲基-2-丙醇作為添加劑進行動力學實驗。由實驗之結果證實，相較於純水系統而言，添加2-甲基-2-丙醇可縮短水合物生成之誘導時間並增加水合物生成之速率，水合物生成時間約可縮短26小時並且增加約一倍的生成速率。

In this study, an apparatus which can be operated at high pressure and low temperature conditions was built and operated to measure the thermodynamic properties of liquid water-hydrate-vapor (Lw-H-V) three-phase dissociation temperatures and pressures for cabon dioxide hydrate in the presence of additives by employing the isochoric method, and the kinetic formation rate of carbon dioxide hydrates was measured by the method of pressurization in isochoric system.

In thermodynamic work, two cyclic ketons(Cyclopentanone and Cyclohexanone), three cyclic ethers (1,3,5-Trioxane, 2,5-Dihydrofuran and 1,3-Dioxolane) and 2-Methyl-2-Propanol were chosen as additives. The experimental results showed that the addition of Cyclopentanone, 1,3,5-Trioxane, 2,5-Dihydrofuran and 1,3-Dioxolane 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 concentration of 15wt% Cyclopentanone, 1,3,5-Trioxane, 2,5-Dihydrofuran and 1,3-Dioxolane additives, the dissociation temperatures were increased about 6.9 K、6.4 K、8.1 K and 5.6 K respectively. 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 environments were also observed with cyclic ether additives. However, the promotion effects in the presence of cyclic ether 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 Cyclohexanone and 2-Methyl-2-Propanol in carbon dioxide system; the equilibrium conditions shifted to higher pressure and lower temperature in comparison with pure water system. The dissociation temperature for additions of Cyclohexanone and 2-Methyl-2-Propanol in carbon dioxide systems decreased respectively 0.5 K and 2.2 K at most at a given pressure in comparison with those in pure water system. It seemed that 2-Methyl-2-Propanol could increase the quantity and the formation rate of carbon dioxide hydrates in thermodynamic results so 2-Methyl-2-Propanol was chosen as additive in kinetic experiments. The kinetic results proved 2-Methyl-2-Propanol could reduce the induction time of forming carbon dioxide hydrates in comparison with pure water system, and hydrate formation rate and amount of hydrate forming in 2-Methyl-2-Propanol system increased about twofold than pure water system. In conclusion, 2-Methyl-2-Propanol was effective kinetic promoter to form carbon dioxide hydrates in this work.