In-situ Raman spectroscopic observations of C3F8 enclathration in the presence of various help gases

Abstract

Octafluoropropane (C3F8, or R-218) can be sequestered into type-H (sH) clathrate hydrate using methane (CH4) as a help gas. In this study, we examine how well CH4 and other hydrate-forming gases might function as help gases for this hydrate. In our experiments, pure water and C3F8 mixed with known help gases for sH hydrate (CH4, xenon, and carbon dioxide) are pressurized in the vessel below their saturated pressure at about 274 K for micro-Raman spectroscopic measurements. Then we use the Raman peak shift of C3F8 to detect its enclathration. We also examine the possibility of C3F8 enclathration in the type-II structure (sII) hydrates with sII-hydrate formers, specifically propane and CH4-containing mixed gases. Under these conditions, only CH4 functions a help gas for enclathration of C3F8, and only in the sH hydrate structure.