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Hydrogen Clusters in Clathrate Hydrate

VIEWS: 13 PAGES: 25

									  Energy Storage in Clathrates
and Related Molecular Compounds




                     Wendy L. Mao
  Geological and Environmental Sciences & Photon Science, SLAC
                        Stanford University
    Molecular Compounds

   Clathrates
   Filled Ices
   van der Waals Compounds
    Molecular Compounds

   Clathrates
       Crystalline structures based on a
        hydrogen-bonded water framework
        (‘host’ lattice) with cavities which
        contain ‘guest’ molecules
   Filled Ices
   van der Waals Compounds
      Clathrate structures

sI                                                cubic




                                                  cubic
sII




sH                                             hexagonal


                             W. Mao et al, Physics Today 2007
    Clathrates – an old science

   In 1778, Joseph Priestley may have been the first to
    discover clathrates taking advantage of the cold winters in
    Birmingham to refrigerate his samples of sulfur dioxide +
    water
   Credit for the discovery is usually given to Michael
    Faraday’s boss, Sir Humphry Davy who reported a
    clathrate in the chlorine + water system in 1811
       Clathrates on Earth

   Clathrates represent major flow
    assurance problem in natural gas
    and oil pipelines
   Methane clathrate in sI structure is
    the most abundant form of
    hydrocarbon on Earth (> 60%)
   Found in terrestrial marine
    sediments and permafrost
   Source of global climate change?
   Potential energy resource?
       Clathrates on Earth

   Clathrates represent major flow
    assurance problem in natural gas
    and oil pipelines
   Methane clathrate in sI structure is
    the most abundant form of
    hydrocarbon on Earth (> 60%)
   Found in terrestrial marine
    sediments and permafrost
   Source of global climate change?
   Potential energy resource?
                                           Image courtesy of Petrobas
       Clathrates on Earth

   Clathrates represent major flow
    assurance problem in natural gas
    and oil pipelines
   Methane clathrate in sI structure is
    the most abundant form of
    hydrocarbon on Earth (> 60%)
   Found in terrestrial marine
    sediments and permafrost
   Source of global climate change?       Methane ice worm
   Potential energy resource?
       Clathrates on Earth

   Clathrates represent major flow
    assurance problem in natural gas
    and oil pipelines
   Methane clathrate in sI structure is
    the most abundant form of
    hydrocarbon on Earth (> 60%)
   Found in terrestrial marine            Figure courtesy of G. Dickens
    sediments and permafrost
   Source of global climate change?
   Potential energy resource?
       Clathrates on Earth

   Clathrates represent major flow
    assurance problem in natural gas
    and oil pipelines
   Methane clathrate in sI structure is
    the most abundant form of
                                           Image courtesy of G. Klinkhammer
    hydrocarbon on Earth (> 60%)
   Found in terrestrial marine
    sediments and permafrost
   Source of global climate change?
   Potential energy resource?




                                                Flare from the Mallik
                                              2002 production test well
        Clathrates in the Solar system

   Ubiquitous presence in the Universe?
       CO2 and CH4 clathrates on Mars
       CH4 clathrates on Titan
       Source of plumes on Saturn’s moon
        Enceladus
       Clathrates in Halley’s comet


                                            Porco et al, Science 2006
                                            Kieffer et al, Science 2006
    Molecular Compounds

   Clathrates
   Filled Ices
       Hydrates with structures related to
        known ice phase
       Guest molecules occupy channels
        within ice structure rather than
        cages
   van der Waals Compounds
     Filled Ices
   Formed at higher pressures
        He hydrate (ice II), Londono et al JCP, 1992
        Hydrogen hydrates (ice II and ice Ic), Vos et al, PRL 1993
        Methane hydrate III (ice Ih), Loveday et al, PRL 2001




                                                        Filled ice Ih
                             Filled ice Ic
    Filled ice II
    Molecular Compounds

   Clathrates
   Filled Ices
   van der Waals Compounds
       Stoichiometric crystals of mixtures
        of atoms and molecules held
        together by weak van der Waals
        forces
     van der Waals compounds

   He(N2)11, Vos et al, Nature 1992
   Ne(He)2, Loubeyre et al, PRL 1993        He(N2)11

   Ar(H2)2, Loubeyre et al, PRL 1994
   CH4-H2, Somayazulu et al, Science 1996




                                             9 GPa
Hydrogen Storage

Requirements:
1.   High hydrogen content (by mass and volume)
2.   Moderate P-T synthesis
3.   Moderate P-T storage
4.   Easy hydrogen release
5.   Environmentally friendly by-products
6.   Cost and availability
7.   Safety
 H2 + H2O system




                                                       C2




                         C2 (filled Ice Ic) H2-H2O
                         C1 (filled Ice II) H2-6H2O



Vos et al, PRL 1993
    H2 + H2O system
                                     H2O                 300 MPa
                                               H2
                                                         250 K


                                                          249 K
                                                          t=0




   HHsII (Hydrogen hydrate in sII                       t = 30 min
    clathrate structure) H2-2H2O
                                           W. Mao et al, Science 2002
       H2 + H2O system

   Two filled ices and sII H2 clathrate found at
     high P
   Can be quenched to much lower P with low T
Studied using XRD, Neutron diffraction,
Raman and IR spectroscopy
   Chemical stabilization of clathrate phase
 Not enough hydrogen storage, kinetic
limitations
   Different P-T range (e.g. C2 filled Ice Ic)


                                                  Lokshin et al, PRL 2004
      Chemical stabilization


   Use THF as a promoter
    molecule to fill large cage
   Forms sII clathrate at
    277.3 K at ambient P




                                  Florusse et al, Science 2004
       H2 + H2O system

   Two filled ices and sII H2 clathrate found at
     high P
   Can be quenched to much lower P with low T
Studied using XRD, Neutron diffraction,
Raman and IR spectroscopy
   Chemical stabilization of clathrate phase
 Not enough hydrogen storage, kinetic
limitations
   Different P-T range (e.g. C2 filled Ice Ic)


                                                  W. Mao et al, Science 2002
                                                  Lokshin et al, PRL 2004
H2 + CH4 system




                                  CH4(H2)2


                  Somayazulu et al, Science 1996
      H2 + CH4 system
                        liquid


                                                          CH4(H2)4 has 33.4 wt% H2
                                                          (not including H in CH4)
                        H4M
                       crystals

       0.4 GPa, 86 K                 1.0 GPa, 120 K

                                 W. Mao et al, CPL 2005

   Needs more characterization
      Structure

      Hydrogen occupancy

      Phase diagram

      Metastable synthesis paths
Hydrogen storage capacity
                                  0.35
                                             density: 5 g/cm3                                               CH4(H2)4
                                                                         2 g/cm3
                                  0.30
                                                                                                  1 g/cm3
Volumetric H2 density (kg H2/L)




                                  0.25                                                                       0.7
                                                                                                             g/cm3

                                  0.20

                                  0.15                          Light element
                                              Transition           hydrides
                                             metal hydrides
                                                                    C2             Hydrocarbons
                                  0.10
                                                                2015

                                  0.05        HHsII     2010                                                               Liquid
                                                      2007                                                                hydrogen

                                  0.00
                                         0         5            10    15      20     25      30                      35     100
                                                                                                                             40
                                                                 Gravimetric H2 density (wt %)
                                                                                                   W. Mao et al, Physics Today 2007
             Astrophysics



                            Trifid Nebula


               0.05
                                           100 kPa, 140 K
Absorbance




                                           100 kPa, 126 K

                                           100 kPa, 107 K


                                           100 kPa, 80 K


                                           500 MPa, 80 K


        4100      4120      4140    4160       4180         4200
                                                                   Spectra from WL5, protostar in the
                         Wavenumber (cm -1)                           r Ophiuchus cloud complex
                      Experimental Results                           Sandford et al, Science 1993

             •HH-sII in small, icy bodies?                          Telescope Observations

								
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