Catalytic routes to transportation fuels utilizing natural gas hydrates

Gas hydrates hold >50% of earth's total combustible carbon. To make this vast but dilute (CH₄∼3.9 wt%) energy source available, an economical three-step route is outlined. A major technological challenge is environmentally-benign mining of gas hydrates that releases "Aqueous CH₄" and makes it available at the surface (Step 1). Step 2 involves a cost-effective partial oxidation (POX) with air route that eliminates the O₂-separation plant (conventional POX with O₂) to produce synthesis gas. In Step 3, technologies that affect catalytic conversion of synthesis gas to Fischer-Tropsch (F-T) diesel, MeOH, and dimethylether (DME) transportation fuels are considered. The selection of MeOH and DME energy liquids is justified based on seven criteria: (1) low temperature; (2) low pressure; (3) high gas conversion per pass to eliminate recycle; (4) high space-time-yield; (5) high product selectivity; (6) robust catalyst; (7) overall high process efficiency. A Ni/Base catalyst system, presently undergoing pilot testing at Brookhaven National Laboratory (BNL), is described that by virtue of its homogeneous liquid phase operation selectively (>95%) produces methanol with unprecedented single pass conversion (>95%) at T<150°C and P=2-5 MPa essentially satisfies these set-forth process requirements. A preliminary kinetic study on the original BNL catalyst system is presented and a limited kinetic rate expression is deduced. Several areas for further research are identified that will allow economical production of MeOH or DME in the skid-mounted unit/flexible product option concept applicable to both on-land and off-shore gas hydrates.