Heterogeneous Catalysts for Biofuels

Tuesday, November 9, 2010
Hall 1 (Salt Palace Convention Center)
W. Curtis Conner, George W. Huber and Paul J. Dauenhauer, Chemical Engineering, University of Massachusetts-Amherst, Amherst, MA

We are challenged to develop new renewable sources of energy to meet societies needs to replace fossil fuels. While solar, wind and tides are being developed as green sources of electrical energy, fuels will be needed for transportation. Plants including algae are the only renewable potential sources for liquid fuels. While biological catalysts are employed for conversions of sugars to ethanol, heterogeneous catalysts will certainly play an ever increasing central role in the production of liquid fuels from biomass.

Considerable research and development effort is being marshaled to help develop routs to convert renewable resources to liquid fuels. The Department of Energy has funded several consortia of research laboratories to search for and to develop these new technologies. The majority of these are based on biological routes by which the components from plants can be converted to liquid fuels. The argument is apparently that since biochemistry produced the plants and their components, biochemistry is the logical pathway by which they can be transformed to useable fuels. The practical aspects of fuel processing are totally neglected in this approach. Recall that it takes plants months or years to convert the carbon dioxide into hydrocarbons as sugars, starches, oils, wood and/or algae. Nature produces these on large fractions of the earth by photosynthetic pathways and man does harvest a significant fraction for use as foods, wood and indirectly into other forms of life. However, these are not efficient processes either in their effective use of sunlight (A controversy also exists in the literature as to the green house gas, GHG, balance from the production of BioFuels with opponents arguing that the processes such as corn to ethanol produces more CO2 than it saves or that it reflects a net saving of GHG. We have discovered the primary causes for this polemic, differences in the system definitions and the initial assumptions, and these will be discussed.

The term efficiency has several possible applications in these processes. The first is the Production Efficiency that accounts for the energy that must be expended to produce the natural feedstocks. This would include planting, harvesting and fertilizing the plants. The second efficiency is the Process Efficiency that would include the energy required to turn the natural feedstock into a useable fuel. Process conditions such as high pressures (pumps) and temperatures as well the required separations steps would be included. The third is efficiency is thermodynamically “Calorimetric”. All of the natural feedstocks (sugars, starch, oils, lignocellulose or algae) could be burned and the heat of combustion released could be used. If these are turned into fuels (liquids or gases), what is the fraction of the energy that is present in the products, the Calorimetric Efficiency? This paper will discuss the last two of these, the Process and the Calorimetric efficiencies and how these will differ if heterogeneous catalysts are employed in contrast with enzymatic process alternatives. To do so we will evaluate the thermodynamics, kinetics, carbon dioxide balance and the required reactor engineering. We conclude that heterogeneous catalytic processes will be central and probably will dominate the production of BioFuels processing.

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See more of this Session: Poster Session: Sustainability and Sustainable Biorefineries
See more of this Group/Topical: Sustainable Engineering Forum