乙醇對於甲烷與二氧化碳水合物的生成、解離及置換動力學影響

Abstract

本研究利用冰晶法進行定壓下甲烷與二氧化碳氣體水合物的合成、解離以及置換的動力學行為研究，並探討添加乙醇造成的影響。本研究中的乙醇液體並無直接與冰晶樣品接觸，而是以揮發後蒸氣的形式吸附於冰晶樣品上。本研究探討的溫度範圍涵蓋−15至−1.0 °C，甲烷水合物生成於16.65 MPa，二氧化碳水合物生成及置換於2.10 MPa，解離實驗則操作於一大氣壓下。合成水合物用的冰晶則是使用直徑介於180到250 μm的冰晶顆粒。 研究結果顯示，乙醇蒸氣對於甲烷水合物的合成具有動力學上的促進效果。對於沒有添加乙醇的系統而言，甲烷水合物的轉化率在24小時約為0.26，而對於添加乙醇的系統則會在4小時內上升到0.80。由乙醇促進生成的甲烷水合物，經過拉曼光譜以及粉末X光繞射可以確定其結構與一般的甲烷水合物相同，為sI結構。而在解離方面，乙醇對於甲烷水合物的解離亦具有抑制自保效應的效果(即加速解離)。當甲烷水合物的轉化率大於0.3時，能觀察到水合物的自保效應，解離速度較慢。但是當乙醇添加於系統中時，在一小時內水合物可以幾乎完全解離。而乙醇對於二氧化碳的合成影響則會受到溫度影響。當溫度高於−9 °C時，乙醇扮演動力學抑制劑的角色，但當溫度低於−9 °C時，乙醇則是具有動力學促進劑的效果。乙醇在二氧化碳的解離的動力學上一樣具有抑制自保效應的效果。 在置換的研究中，當溫度約為−2 °C時，乙醇可以大幅提升甲烷釋放的速度。然而僅有部份釋放出的是被二氧化碳置換。當溫度約為−14 °C時，甲烷釋放的速度與二氧化碳置換為水合物的總量相較−2 °C時大幅提高。但添加乙醇則無明顯影響。

In this study, effect of adding ethanol on the kinetics of methane, carbon dioxide synthesis, dissociation, and replacement were explored at constant pressure using ice seed method. In this study, liquid ethanol did not direct contact with ice powder, but adsorbed on ice powder from vapor phase. The experimental temperature was ranging from −15 to −1.0 °C. The formation pressure of methane hydrate was 16.65 MPa and that of carbon dioxide hydrate was 2.10 MPa. For the dissociation experiments, the operating pressure was at atmospheric pressure. The ice powder with diameter ranging from 180 to 250 μm was used for hydrate synthesis. Our results indicated that the addition of ethanol could promote the kinetics of methane hydrate formation. For the system without ethanol additive, the conversion was about 0.26 in 24 hours, and for the ethanol added system, the conversion rose to 0.80 in 4 hours. The methane hydrate formation promoted by ethanol vapor was analyzed by Raman spectroscopy and powder X-ray diffraction and the structure was determined to be sI structure, which was same with simple methane hydrate. For hydrate dissociation, ethanol would suppress the self-preservation phenomena (which means enhancement of the dissociation rate). When the conversion of methane hydrate was higher than 0.3, the self-preservation could be observed and had a slow dissociation rate. However, when ethanol was added into the system, almost all the hydrate dissociated in the first hour of dissociation stage. The effect of ethanol on the formation of carbon dioxide would depend on the temperature. When the temperature was higher than −9 °C, ethanol acted as a kinetic inhibitor, but when the temperature was lower than −9 °C, ethanol acted as a kinetic promotor. For the dissociation of carbon dioxide, ethanol also suppressed the self-preservation phenomena. In the replacement research, when the temperature was about −2 °C, ethanol additive could enhance the methane releasing rate. However, only part of released methane was replaced by carbon dioxide. When the temperature was about −14 °C, the methane releasing rate and the amount of carbon dioxide that encaged in the hydrate were much higher than that at −2 °C. However, the effect of adding ethanol was no obvious.