가스하이드레이트 냉동기 응용을 위한 하이드레이트 상평형 및 포집률 변이에 관한 연구

Abstract

“Gas hydrate” is formed by physical reaction between relatively small guest molecules such as methane, ethane and carbon dioxide and host water molecules under high pressure and low temperature conditions. Gas hydrates have been used in a variety of industrial fields not only as a large energy resource but also as a target medium for various technologies using its physicochemical characteristics. There are a lot of practical applications such as separation processes, natural gas storage and transportation, and carbon dioxide sequestration. In particular the refrigeration system using gas hydrate is expected to be an environment-friendly process that non-toxic and energy saving coolants can be used to replace CFCs which are well known as a main reason of destroying the ozone layer. In this study, the phase equilibrium and cage occupancy of the multi-guest hydrate systems including methane and carbon dioxide are observed to investigate the applicability of gas hydrate to the refrigeration system. In order to test and prove the validity and reproducibility of newly designed experimental apparatus, the dissociation pressures of pure methane hydrates are measured at the range of 268-285 K and 2.0-7.5 MPa and compared with the literature values. The three-phase equilibrium conditions of methane + acetone, carbon dioxide + acetone, methane + tert-butyl methyl ether, carbon dioxide + tert-butyl methyl ether, and carbon dioxide + tetrahydrofuran (THF) hydrates are measured at a wide range of temperatures and pressures. To calculate the heat of dissociation of gas hydrate, the cage occupancy of relatively small guests are estimated using the van der Waals-Platteeuw model.