How To Turn Seawater Into Fuel

For the first time, Rochester chemical engineers have demonstrated a ‘potassium-promotedcatalyst’s potential for use on an industrial scale. Now, the Navy’s quest to power its ships by converting seawater into fuel is nearer fruition.

University of Rochester chemical engineers—in collaboration with researchers at the Naval Research Laboratory, the University of Pittsburgh, and OxEon Energy—have demonstrated that a potassium-promoted molybdenum carbide catalyst efficiently and reliably converts carbon dioxide to carbon monoxide, a critical step in turning seawater into fuel.

Gulf of Aden, April 27, 2011- The Military Sealift Command fleet replenishment oiler USNS Joshua Humphreys (T-AO 188), left, refuels the amphibious assault ship USS Boxer (LHD 4) during a replenishment at sea. Boxer is underway supporting maritime security operations and theater security cooperation efforts in the U.S. 5th Fleet area of responsibility.

This is the first demonstration that this type of molybdenum carbide catalyst can be used on an industrial scale,” says Marc Porosoff, assistant professor in the Department of Chemical Engineering at Rochester. In a paper in the journal Energy & Environmental Science, the researchers describe an exhaustive series of experiments they conducted at molecular, laboratory, and pilot scales to document the catalyst’s suitability for scale-up.

If navy ships could create their own fuel from the seawater they travel through, they could remain in continuous operation. Other than a few nuclear-powered aircraft carriers and submarines, most navy ships must periodically align themselves alongside tanker ships to replenish their fuel oil, which can be difficult in rough weather.

In 2014, a Naval Research Laboratory team led by Heather Willauer announced it had used a catalytic converter to extract carbon dioxide and hydrogen from seawater and then converted the gases into liquid hydrocarbons at a 92 percent efficiency rate.

Since then, the focus has been on increasing the efficiency of the process and scaling it up to produce fuel in sufficient quantities.
The carbon dioxide extracted from seawater is extremely difficult to convert directly into liquid hydrocarbons with existing methods. So, it is necessary to first convert carbon dioxide into carbon monoxide via the reverse water-gas shift (RWGS) reaction. The carbon monoxide can then be converted into liquid hydrocarbons via Fischer-Tropsch synthesis.
Typically, catalysts for RWGS contain expensive precious metals and deactivate rapidly under reaction conditions. However, the potassium-modified molybdenum carbide catalyst is synthesized from low-cost components and did not show any signs of deactivation during continuous operation of the 10-day pilot-scale study. That’s why this demonstration of the molybdenum carbide catalyst is important.