Thermodynamic and Raman spectroscopic studies on H2+tetrahydrofuran plus water and H2+tetra-n-butyl ammonium bromide plus water mixtures containing gas hydrates

Phase equilibrium curves of H-2+ tetrahydrofuran and H-2+ tetra-n-butyl ammonium bromide mixed gas hydrates were measured in a pressure range from 0.1 to 13.6 MPa. Each three-phase equilibrium curve converges at the maximum temperature point of pure tetrahydrofuran and tetra-n-butyl ammonium bromide hydrates, respectively. The difference of maximum temperatures is about 8 K, that is, the equilibrium curve of H-2+ tetra-n-butyl ammonium bromide mixed gas hydrate shifts to the high-temperature side from that of H-2+ tetrahydrofuran mixed gas hydrate. It is directly confirmed by use of Raman spectroscopy that H-2 is enclathrated in the hydrate cages by adding a small amount of tetrahydrofuran or tetra-n-butyl ammonium bromide. In both mixed hydrates, H-2 is enclathrated in only the small cage while tetrahydrofuran or tetra-n-butyl ammonium bromide occupies the large cages of each mixed hydrate. (c) 2006 Elsevier Ltd. All rights reserved.