Biodiesel could be made from any biomass. That is what Green Car Congress reported on (6/3/05). Researchers at the University of Wisconsin (my alma mater) are working on a process to produce diesel fuel directly from the cellulose and hemicellulose (carbohydrates) that make up 70-75% of a plants dry weight, rather than from just the seeds. They have developed a reforming process, Aqueous Phase Dehydratiocn/Hydrogenation (APD/H), to convert the cellulosic materials to the long-chain hydrocarbons that constitute diesel fuel. So far the researchers have been able to produce hexane (C6H14) and now need to develop methods to produce the heavier C8-C15 alkanes that constitute diesel fuel.
The University site further explains the process, shown at left, claiming that the net energy value (NEV) is 2.2, compared with a NEV of 1.1 for ethanol. A large part of the energy savings results from the spontaneous separation of the Alkane's from the water compared to the requirement to distill the ethanol from water.
The MIT Technical Review further describes the process as follows: "The new method is divided into four parts. First, a stream of processed biomass consisting of water and sugars is fed over a nickel-tin catalyst to strip off some of its hydrogen atoms. Then the stream is treated with acids that take out most of the water. The resulting "goo" is then transported over a solid base catalyst, which forms it into long carbon chains, called alkanes. Finally, those alkanes are run through a platinum-silica-alumina catalyst at high temperatures, while the hydrogen from the first step is fed into the reactor. The resulting liquid has almost the exact same chemical structure as traditionally refined biodiesel and burns the same way in diesel engines. And the only byproducts are water and heat."
Further details of the process are available from a paid subscription to the journal Science. A presentation: Catalysis in Biomass Conversion: Hydrogen and Alkane's from Biomass-derived Molecules is available for those who can decipher it.
The UW process, if research proceeds as planned, would be of as much or more significance than the recently developed enzymes that can convert the cellulosic materials in biomass to sugars, allowing production of ethanol from virtually any plant material. The ability to use of any biomass to produce either biodiesel or ethanol greatly expands the potential for biofuels by appreciably reducing the land required to produce the biomass. The proposed process is much less complicated than the gasification/Fischer-Tropsch route, which is the other way of making diesel from any biomass. I disagree with the UW in the amount of energy created in the ethanol process, the NEV is more like 1.3 to 1.4 in a modern ethanol plant, with even higher values expected using enzymes. NEV includes all the life cycle energy inputs, including the energy used to produce the crop, I suspect that the UW number does not include that energy. This discrepency does not reduce the significance of this development.
Originally posted 6/3/05, additional material added 6/7/05