Two-Step Formation of Methane-Propane Mixed Gas Hydrates in A Batch-Type Reactor

Vapor compositions of methane and propane mixed gas in a batch-type reactor were measured by gas chromatography during hydrate crystallization at 274 K with molar ratios of propane below 10 vol %. The volume ratio of propane in the vapor decreased as the hydrate crystallization progressed. When the initial propane concentration was between 4 and 8 vol %, rapid gas consumption occurred for about 1 h, causing an initial pressure drop, and after a temporary stabilization of the pressure, a second pressure drop occurred; that is, hydrate crystallization occurred in two steps. X-Ray diffraction and Raman spectroscopic analyses on samples taken from the reactor during each step revealed that the structure II methane–propane mixed gas hydrates crystallized in the first step, and structure I methane hydrates in the second step. This process was observed only when the partial pressure of methane was above the equilibrium pressure of methane hydrate at the end of the first step. © 2004 American Institute of Chemical Engineers AIChE J, 50: 518–523, 2004

[1]  W. F. Claussen,et al.  Suggested Structures of Water in Inert Gas Hydrates , 1951 .

[2]  C. Ratcliffe,et al.  Low-temperature cross-polarization/magic angle spinning carbon-13 NMR of solid methane hydrates: structure, cage occupancy, and hydration number , 1988 .

[3]  R. Szczepanski,et al.  Hydrate structure stability in simple and mixed hydrates , 1996 .

[4]  E. D. Sloan,et al.  Measurement of Clathrate Hydrates via Raman Spectroscopy , 1997 .

[5]  T. Ebinuma,et al.  Raman spectroscopic determination of hydration number of methane hydrates , 1999 .

[6]  C. Gutt,et al.  The structure of deuterated methane–hydrate , 2000 .

[7]  E. D. Sloan,et al.  Structural transitions in methane+ethane gas hydrates — Part I: upper transition point and applications , 2000 .

[8]  Steven F. Dec,et al.  Evidence of structure II hydrate formation from methane+ethane mixtures , 2000 .

[9]  E. D. Sloan,et al.  Structural transitions in methane + ethane gas hydrates. Part II : modeling beyond incipient conditions , 2000 .

[10]  C. Ratcliffe,et al.  Probing Transient Hydrate Structures with Hyperpolarized (129)Xe NMR Spectroscopy: A Metastable Structure II Hydrate of Xe. , 2001, Angewandte Chemie.

[11]  Tsutomu Uchida,et al.  Spectroscopic Observations and Thermodynamic Calculations on Clathrate Hydrates of Mixed Gas Containing Methane and Ethane: Determination of Structure, Composition and Cage Occupancy , 2002 .

[12]  E. Dendy Sloan,et al.  Trends in Vibrational Frequencies of Guests Trapped in Clathrate Hydrate Cages , 2002 .

[13]  J. Ripmeester,et al.  Phase behavior and structural characterization of coexisting pure and mixed clathrate hydrates. , 2003, Chemphyschem : a European journal of chemical physics and physical chemistry.

[14]  T. Ebinuma,et al.  Coexistence of structure I and II hydrates formed from a mixture of methane and ethane gases , 2003 .