添加1-乙基-3-甲基氯化咪唑、N-甲基甲醯胺及碳酸乙烯酯對於二氧化碳水合物熱力學與動力學之實驗量測

Measurement of Thermodynamic and Kinetic Data of Carbon Dioxide Hydrate in the Presence of 1-Ethyl-3-methylimidazolium Chloride, N-methylformamide and Ethylene Carbonate.

賴泱蓉(Yang-Jung Lai)

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(2018年)

https://doi.org/10.6342/NTU201801417

摘要

本實驗採用等容溫度搜尋法，利用已建立的高壓相平衡設備進行二氧化碳水合物的熱力學平衡以及動力學實驗量測。研究目的為獲得含有添加劑、二氧化碳及水合物三相之 (H-Lw-V) 相平衡曲線，及添加劑對於二氧化碳水合物生成之影響，將來可作為工程應用設計上的參考數據，亦可與文獻資料結合作為水合物開採或置換反應的基礎物性資料。

首先，熱力學部份先進行純水系統相平點量測以確保實驗設備的精準性與操作手法的可行性，結果顯示與文獻中的數據相符。接著進行含有添加劑的二氧化碳水合物系統相平衡點量測，本研究選用1-乙基-3-甲基氯化咪唑 (1-Ethyl-3-methylimidazolium chloride)、N-甲基甲醯胺 (N-Methylformamide) 以及碳酸乙烯酯 (Ethylene Carbonate) 作為添加劑進行熱力學實驗，並將平衡壓力控制在1.52 ~ 3.67 MPa之間。實驗結果顯示上述添加劑皆為熱力學抑制劑，會使二氧化碳水合物相平衡曲線往低溫及高壓的方向移動，縮小水合物生成的相區，且前二者抑制效果皆隨著添加濃度提升而增加。以30 wt%1-乙基-3-甲基氯化咪唑作為添加劑時，最大抑制溫度為7.9 K；而添加30 wt% N-甲基甲醯胺 + 500 ppm SDS 最大抑制效果約為9.6 K；添加20 wt%的碳酸乙烯酯，其最大抑制溫度則為2.3 K。本實驗亦量測了 N-甲基甲醯胺系統在20 wt%添加濃度下，未添加 SDS 的相平衡數據，經比較後得知其相平衡曲線幾乎不受 SDS 的添加所影響。本研究利用 Clausius-Clapeyron equation 判斷水合物的結構及分解熱，研究結果顯示個別含有1-乙基-3-甲基氯化咪唑、N-甲基甲醯胺、碳酸乙烯酯的系統之中，水合物皆維持 sI 型結構。

動力學部分，研究添加500 ppm SDS 於20 及30 wt% N-甲基甲醯胺之二氧化碳水合物系統的生成動力學行為，並以過冷溫度 (Teq-Texp) 做為二氧化碳水合物的生成驅動力。實驗結果顯示，在30 wt% N-甲基甲醯胺系統中添加500 ppm SDS可以大幅縮短水合物生成之誘導時間，減少幅度至少63%；而20 wt% N-甲基甲醯胺系統中添加500 ppm SDS，以相同驅動力條件並重複實驗二次，得知500 ppm SDS的添加亦會使20 wt% N-甲基甲醯胺的二氧化碳水合物系統水合物誘導時間減少，減少幅度約21%。由實驗結果顯示，添加500 ppm SDS 於 N-甲基甲醯胺可加速二氧化碳水合物的生成。

分別添加1-乙基-3-甲基氯化咪唑、N-甲基甲醯胺於甲烷水合物系統中，同樣是抑制效果 (Richard & Adidharma, 2013; Long et al., 2017; 邵琬淳, 2015)，將此結果與本研究之熱力學實驗結果結合之後，發現添加20 wt%的添加濃度時，相平衡曲線的移動洽會使特定極區中的甲烷水合物進入分解區，然而二氧化碳水合物卻仍在穩定生成區，因此推論添加1-乙基-3-甲基氯化咪唑以及 N-甲基甲醯胺有助於以二氧化碳置換甲烷水合物的工程。

關鍵字

二氧化碳水合物 ； 相平衡 ； 等容溫度循環法 ； 抑制劑 ； 1-乙基-3-甲基氯化咪唑 ； N-甲基甲醯胺 ； 碳酸乙烯酯 ； 動力學

並列摘要

In this study, phase equilibrium conditions for carbon dioxide hydrates in the presence of 1-ethyl-3-methylimidazolium chloride, N-methylformamide and ethylene carbonate 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 3.67 MPa with various concentrations of the additives. Also, the kinetic behaviors were investigated in the presence of N-methylformamide at 0.2 and 0.3 mass fraction with or without 500 ppm SDS.

In the thermodynamic experiments, the separate additions of 1-ethyl-3-methylimidazolium chloride, N-methylformamide with 500 ppm SDS and ethylene carbonate in the system were found able to cause inhibition effect on carbon dioxide hydrate formation, and the maximum decrease of dissociation temperatures compared with pure water system are about 7.9 K, 9.6 K and 2.3 K, respectively. Besides, this study also measured the three-phase equilibrium pressures and temperatures of 0.2 mass fraction of N-methylformamide without the addition of SDS. The result shows that the presence of SDS in the system has little effect on the three-phase equilibrium line. Furthermore, the structure and dissociation enthalpy of hydrates are estimated by using Clausius-Clapeyron equation. With the equation, the structures of carbon dioxide hydrates with addition of 1-ethyl-3-methylimidazolium chloride, N-methylformamide with 500 ppm SDS and ethylene carbonate are classified as structure I.

In kinetic experiment part, the formation behaviors of carbon dioxide hydrate with N-methylformamide as the additive at 0.2 and 0.3 mass fraction were investigated. The aim of this part is to find out whether the presence of SDS in the system accelerates the formation of carbon dioxide. The experiments were operated on isochoric condition, and the driving force is defined as the difference between experimental temperature and operating temperature. At 0.3 mass fraction of N-methylformamide in the system, the induction time was shortened by 63% with the addition of 500 ppm SDS. Also, in the system with 0.2 mass fraction of N-methylformamide which under the same driving force, the presence of 500 ppm SDS promotes the formation of hydrate, and it decreases the induction time by 21%. That is, the result obviously shows that the addition of 500 ppm SDS in the N-methylformamide carbon dioxide hydrate system accelerates the formation of carbon dioxide.

Additionally, all the additives above play as inhibitors in methane hydrate system. By combining the results and the equilibrium data obtained by this research and literatures, both the addition of 20 wt%1-ethyl-3-methylimidazolium chloride and the addition of 20 wt% N-methylformamide show the ability to initiate the process of “Trapping CO2 as a hydrate phase during methane extraction.” That is to say, they are potential additives for methane extraction process.

並列關鍵字

Carbon dioxide hydrates ； phase equilibrium ； isochoric method ； inhibitor ； 1-Ethyl-3-methylimidazolium chloride ； N-methylformamide ； Ethylene carbonate ； kinetics

參考文獻

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