Hydrogen infusion could boost synthetic biofuel yields

Seeking ways to improve biofuel production, researchers at the University of Purdue predict that an infusion of hydrogen during the gasification of biomass may increase final fuel yields by up to 30%.

Gasification involves the partial combustion of the biomass material, converting it into biofuel, as well as the byproducts of hydrogen, carbon monoxide and carbon dioxide. The synthetic gas can then be liquefied via a Fischer-Tropsch process to yield 'synthetic' biofuels (this production path is often described as 'biomass-to-liquids'). In current gasification processes (diagram, click to enlarge), approximately two thirds of the carbon energy in the biomass is lost in the form of CO2 and CO (earlier post).

Professor of Chemical Engineering Rakesh Agrawal and his team now postulate that additional hydrogen introduced in the gasification process would combine with the carbon dioxide to produce more carbon monoxide. That CO would then react with extra hydrogen, creating more biofuel and water.

The ability to make three liters of fuel from the same amount of biomass that currently produces only two liters would be an impressive feat. It would considerably reduce the amount of biomass feedstocks needed and the land required to grow them. However, the Purdue team's plan is only feasible if a plentiful source of relatively inexpensive hydrogen can be secured:
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To solve that problem, Agrawal is working with fellow Purdue Professor Hugh Hillhouse, an expert in developing nanomaterials for photovoltaics and thermoelectric energy production. in a recent interview with New Scientist Magazine, Agrawal said that he and Hillhouse are developing low-cost "spray-on" solar cells that could provide a cheap source of energy for making hydrogen.

Last month, the team successfully tested the spray-on nanomaterial, which produced an electric charge when exposed to light. Details of the Purdue team's findings are due to be published in the Proceedings of the National Academy of Sciences.

An apparent contradiction then opens up: if the energy carrier known as hydrogen can be produced efficiently using clean energy sources, then why would biofuels be needed at all? The contradiction is solved by the fact that liquid biofuels have the advantage that they can be used directly in existing fuel distribution infrastructures and automotive technologies, whereas hydrogen needs trillions worth of investment in this regard.

Likewise, using the hydrogen generated by the efficient solar cells, to produce electricity that would then be distributed over the grid to power battery driven cars, is a detour that makes little sense. It would obviously be easier to use the electricity generated from such solars cells directly.

But instead of representing the two different fuel paradigms - liquid biofuels and hydrogen - as opposites or rivals, it is more interesting to look for synergies between them. The researchers at Purdue are doing exactly that.