New process yields high-energy-density, plant-based transportation fuel

March 1, 2010

A team of University of Wisconsin-Madison engineers has developed a highly efficient, environmentally friendly process that selectively converts gamma-valerolactone, a biomass derivative, into the chemical equivalent of jet fuel. The simple process preserves about 95 percent of the energy from the original biomass, requires little hydrogen input, and captures carbon dioxide under high pressure for future beneficial use. The details of the advance are published in the Feb. 26 edition of the journal Science.

Much of the group's previous research of using cellulosic biomass for biofuels has focused on processes that convert abundant plant-based sugars into transportation fuels. However, in previously studied conversion methods, sugar molecules frequently degrade to form levulinic acid and formic acid -- two products the previous methods couldn't readily transform into high-energy liquid fuels.

The team's new method exploits sugar's tendency to degrade. In the presence of metal catalysts, the two acids react to form gamma-valerolactone, or GVL, which now is manufactured in small quantities as an herbal food and perfume additive. Using laboratory-scale equipment and stable, inexpensive catalysts, the group of engineers converts aqueous solutions of GVL into jet fuel. It is a two-step catalytic process with basic equipment to produce a pure stream of jet-fuel-range alkenes and a fairly pure stream of carbon dioxide.

While biofuels such as ethanol are becoming more popular as blending agents in automobile fuels, they have limitations for use in jet fuel because of their low energy density. And, given present internal combustion engine designs, conventional biofuels cannot fully replace petroleum-derived hydrocarbons. The biggest barrier to implementing the renewable fuel is the cost of GVL.

Now that they have demonstrated the process for converting GVL to transportation fuel, the group is developing more efficient methods for making GVL from biomass sources such as wood, corn stover, switchgrass and others.