以掃描式熱卡計量測客體分子對氣體水合物融解熱之影響

Abstract

本研究利用高壓差示掃描熱卡計探討在壓力範圍內 5.0~30.0 MPa時，環醚類促進劑（四氫呋喃、1,3-二噁烷、1,3-二氧戊環、2,5-二氫呋喃、環氧丙烷）形成結構II型甲烷水合物之促進效果。其表現強弱為：四氫呋喃 > 2,5-二氫呋喃 ≒ 1,3-二噁烷 ≒ 1,3-二氧戊環 > 環氧丙烷。且對於同一構型之甲烷水合物來說融解熱與相邊界高低有一定相關性。此外也檢視1-甲基哌啶形成結構H之甲烷水合物之促進效果；其表現不如上述任一結構II型促進劑，但在每莫爾水的融解熱的量值要大過1,3-二氧戊環、環氧丙烷之甲烷氣體水合物。 更進一步，此研究探討不同氣體作為客體分子（甲烷、二氧化碳、氮氣、氬氣、氪氣）對於純氣體水合物以及四氫呋喃-氣體水合物時相邊界及融解熱的差異。其相邊界高低為：氪氣水合物 ≒ 二氧化碳水合物 > 甲烷水合物 > 氬氣水合物 > 氮氣水合物。對於四氫呋喃氣體水合物則是：氪氣水合物 > 甲烷水合物 > 氬氣水合物 ≒ 二氧化碳水合物 > 氮氣水合物 > 氦氣水合物。除了二氧化碳水合物之外，對於純氣體水合物及四氫呋喃氣體水合物，融解熱大致上和相邊界高低呈正相關。值得注意的是在相對低壓的區間 < 10.0 MPa，四氫呋喃-氣體水合物之融解熱明顯地隨壓力下降而降低；而對於純氣體水合物在壓力操作區間 > 10.0 MPa，則沒有明顯的變化趨勢。

Promotion effects of cyclic ethers, including tetrahydrofuran, 1,3-dioxane, 1,3-dioxolane, 2,5-dihydrofuran, and propylene oxide, were explored by a high pressure micro differential scanning calorimeter (μDSC) with the pressure range from 5.0 MPa to 30.0 MPa. The promotion abilities of these structure II promoters are in the order: tetrahydrofuran > 2,5-dihydrofuran ≒ 1,3-dioxane ≒ 1,3-dioxolane > propylene oxide. Furthermore, the magnitude of dissociation heats are relevant to the highness of dissociation temperatures when it comes to the same structure of methane hydrate. Besides, structure H methane hydrate with 1-methylpiperidine was also examined. The promotion effect is weaken than any sII promoter mentioned above while the dissociation heat based on one mole water is larger than that of 1,3-dioxolane hydrate and that of propylene oxide hydrate. Moreover, the influences of gases, (methane, carbon dioxide, nitrogen, argon, and krypton) on dissociation temperature and on dissociation heat were studied for pure gas hydrates and for THF mixed hydrates. The dissociation temperature are in the order: krypton hydrate ≒ carbon dioxide hydrate > methane hydrate > argon hydrate > nitrogen hydrate. And for THF mixed hydrates, the dissociation temperatures are in the order: krypton-THF hydrate > methane-THF hydrates > argon-THF hydrate ≒ carbon dioxide-THF hydrate > nitrogen-THF hydrate > helium-THF hydrate. Except for carbon dioxide hydrate, the dissociation heats are related to the highness of dissociation temperatures. It is noted that within 10.0 MPa, the dissociation heats of THF mixed hydrates decreased along with the pressure change obviously; however for pressure over 10.0 MPa, the dissociation heats of pure gas hydrates seemed independent from operation pressure.