ClayGashydrate Intercalates

1
ClayGas-hydrate Intercalates
Stephen Guggenheim, Department of Earth and
Environmental Sciences, University of Illinois at
Chicago

• Methane hydrate is abundant in continental shelf
  and ocean floor sediments, and is believed to
  form the major reservoir of methane on Earth.
  Like ice, methane hydrate is stable at
  temperatures near freezing and below, but require
  elevated pressures.
• New hydrates, claymethane-hydrate intercalates,
  were synthesized in a X-ray environmental chamber
  at temperatures near 0 oC and CH4 pressures of
  25-50 bars. Claymethane-hydrate complexes may
  be potentially important in planetary climate
  change, because methane is an efficient
  greenhouse gas. In addition, they may be
  important in energy resource development and in
  understanding ocean-floor hazards. The goal of
  the project is to determine and understand the
  fundamental properties of these new phases.
  Results and conclusions include.
• the intercalate phases are thermodynamically
  stable
• a general phase diagram (Figure 1)
• stability fields for different intercalates are
  defined (Figure 2)
• H2O activity determines the stability fields of
  the intercalates
• at reduced salinity, clay (smectite) may
  intercalate CH4 at conditions from
  intermediate to a deep ocean-floor environment
• these complexes may store substantial quantities
  of carbon

Fig. 1. NaN Na-rich nontronite clay. NaM
Na-rich montmorillonite clay, MH NH4 hydrate
In an allied project, clay-organic complexes were
used as nucleation sites to improve protein
crystallization. Protein crystals are required
for structure determinations, and knowledge about
protein structures play an important role in
molecular biology, but these materials are
difficult to crystallize. Parameters that
produced enhanced crystallization included the
type of complex and clay, particle size, and
chemical composition.
Figure 2. Stability fields for different
intercalate phases as defined by d values. The
field labeled lt 16 ? probably lacks NH4.
Fig. 3. Protein crystal formed from a
clay-organic complex nucleation site.