添加二乙二醇二甲醚、四丁基氫氧化銨及1,1,3,3-四甲基胍對於二氧化碳水合物熱力學與動力學之實驗量測

Measurement of Thermodynamics and Kinetics of Carbon Dioxide Hydrate in the Presence of 2-Methoxyethyl ether, Tetrabutylammonium hydroxide and 1,1,3,3-Tetramethylguanidine

林玥妘(Yueh-Yun Lin)

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(2016年)

https://doi.org/10.6342/NTU201600520

摘要

本研究利用已建立之高壓相平衡設備，並採用等容溫度循環法，進行二氧化碳水合物之熱力學相平衡與動力學實驗量測。本研究目的為量測含有添加劑之二氧化碳水合物三相 (H-Lw-V) 相平衡曲線，及添加劑對於二氧化碳水合物生成動力學之影響，作為未來工程應用設計、水合物開採等的基礎物性資料。

熱力學相平衡方面，首先，進行純水系統的相平衡點量測，實驗結果顯示本研究所量測之相平衡點與文獻中數據相符，確認本研究之實驗設備與操作手法的可行性。接著進行含有添加劑之二氧化碳水合物相平衡點測量，本研究選用的添加劑為二乙二醇二甲醚 (2-Methoxyethyl ether)、四丁基氫氧化銨(Tetrabutylammonium hydroxide) 及1,1,3,3-四甲基胍(1,1,3,3-Tetramethylguanidine)，並將初始壓力設定在1.68 ~ 3.44 MPa之間。根據實驗量測結果，二乙二醇二甲醚及1,1,3,3-四甲基胍為熱力學抑制劑，使二氧化碳水合物之相平衡曲線往低溫高壓方向移動，縮小水合物的生成相區，且抑制效果隨著添加濃度提高而增加，添加30 wt% 二乙二醇二甲醚最大抑制溫度約5.7 K，而添加30 wt% 1,1,3,3-四甲基胍最大抑制溫度約11.1 K。另一方面，結果顯示四丁基氫氧化銨為一促進劑，使二氧化碳水合物之相平衡曲線往高溫低壓方向移動，擴大水合物的生成相區，且促進效果隨著添加濃度提高而增加，添加20 wt% 四丁基氫氧化銨最大促進溫度約11 K。為了接近未來工程應用，本研究亦模擬海水環境 (3.5 wt% NaCl)，挑選效果最明顯之添加劑濃度，進行二氧化碳水合物之相平衡點量測，結果顯示三支添加劑在鹽水環境中，不論是促進或抑制效果皆更加明顯，約提升1~3 K。本研究亦利用Clausius-Clapeyron equation判斷水合物的結構及分解熱。結果顯示添加二乙二醇二甲醚及1,1,3,3-四甲基胍之二氧化碳水合物屬於sI型結構；而添加四丁基氫氧化銨之二氧化碳水合物，根據文獻顯示，這類含有長碳鏈的大分子鹽類會形成半籠狀水合物，因此將其與相似結構之半籠狀水合物比較，發現其斜率與TS-I型結構之半籠狀水合物相近，故推測添加四丁基氫氧化銨所形成之水合物結構為TS-I型。

動力學方面，本研究以二乙二醇二甲醚為添加劑，進行添加濃度20及30 wt% 時之動力學實驗量測，以起始壓力為變因，固定系統之操作溫度，並以過飽和梯度 (S*=(Pin/Peq)-1) 為驅動力。實驗結果顯示，在系統添加30 wt% 二乙二醇二甲醚時，當驅動力越大，可縮短水合物生成之誘導時間，亦可增加二氧化碳之氣體總消耗量，然而，對於水合物初期生成速率則無明顯的影響；而在系統添加20 wt% 二乙二醇二甲醚時，當驅動力越大，可縮短水合物生成之誘導時間，亦能提升水合物初期生成速率及二氧化碳之氣體總消耗量。此外，將添加20及30 wt% 二乙二醇二甲醚進行比較，結果顯示添加濃度下降時，有縮短誘導時間的趨勢，表示能使水合物較快時間內生成，而對於二氧化碳之氣體總消耗量及水合物初期生成速率則無明顯的影響。

關鍵字

二氧化碳水合物 ； 相平衡 ； 等容溫度循環法 ； 促進劑 ； 抑制劑 ； 二乙二醇二甲醚 ； 四丁基氫氧化銨 ； 1,1,3,3-四甲基胍 ； 動力學

並列摘要

In this study, phase equilibrium conditions for carbon dioxide hydrates in the presence of 2-methoxyethyl ether, tetrabutylammonium hydroxide and 1,1,3,3-tetramethylguanidine were experimentally measured. The three-phase (H-Lw-V) equilibrium pressures and temperatures were determined by isochoric method in the pressure range from 1.68 to 3.44 MPa with various concentrations of the additives. Also, the kinetic behaviors were investigated in the presence of 2-methoxyethyl ether at 0.2 and 0.3 mass fraction.

Compared with pure water system, addition of 2-methoxyethyl ether and 1,1,3,3-tetramethylguanidine in the system cause inhibition effect on carbon dioxide hydrate formation and the maximum decrease of dissociation temperature is about 5.7 K and 11.1 K, respectively. On the other hand, addition of tetrabutylammonium hydroxide in the system gives rise to promotion effect on carbon dioxide hydrate formation and the maximum increase temperature is about 11 K, compared with pure water system. To simulate the seawater environment, this study also measured the additives in brine system with 0.035 mass fraction of NaCl. Moreover, the structure and dissociation enthalpy of hydrates are estimated by using Clausius-Clapeyron equation. The structures of carbon dioxide hydrates with addition of 2-methoxyethyl ether and 1,1,3,3-tetramethylguanidine are both classified as structure I, whereas those with addition of tetrabutylammonium hydroxide are classified as structure TS-I.

In this study, the kinetics of carbon dioxide hydrate with 2-methoxyethyl ether as the additive at 0.2 and 0.3 mass fraction were also investgated. With an increase in initial operating pressure, the driving force increased. That is due to the fact that higher initial pressure created higher supersaturation, which induced stronger driving force. At 0.3 mass fraction of 2-methoxyethyl ether in the system, the induction time was shortened as the driving force increased. In addition, the carbon dioxide consumption was increased almost linearly with increasing the driving force. However, the average hydrate formation rate stayed almost constant with the increased driving force. Also, addition of 2-methoxyethyl ether at 0.2 mass fraction in the system was studied. The results showed the induction time was shortened in comparison to that of 0.3 mass fraction. However, the average hydrate formation rate and carbon dioxide consumption were not effectively influenced.

並列關鍵字

carbon dioxide hydrates ； phase equilibrium ； isochoric method ； promoter ； inhibitor ； 2-methoxyethyl ether ； tetrabutylammonium hydroxide ； 1,1,3,3-tetramethylguanidine ； kinetics

參考文獻

吳翊萍. (2013). 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，國立臺灣大學化學工程學研究所碩士論文.

Ahn, Y. H., Kang, H., Koh, D. Y., Park, Y. and Lee, H. (2015). Gas hydrate inhibition by 3-hydroxytetrahydrofuran: Spectroscopic identifications and hydrate phase equilibria. Fluid Phase Equilib., 413, 65-70.

Anklam, M. R. and Firoozabadi, A. (2004). Driving force and composition for multicomponent gas hydrate nucleation from supersaturated aqueous solutions. J. Nat. Gas Chem., 121(23), 11867-11875.

Bishnoi, P. and Dholabhai, P. (1993). Experimental study on propane hydrate equilibrium conditions in aqueous electrolyte solutions. Fluid Phase Equilib., 83, 455-462.

Cha, J. H., Kang, S. P., Han, S., Kang, J. W. and Kim, K. S. (2016a). Phase equilibria of CH4 and CO2 hydrates formed from aqueous solutions of glutaric acid and malonic acid. Fluid Phase Equilib., 413, 71-74.