For most of us, “liquid fuel” is the gasoline in our cars, and we tend to assume that a growing human population will require a growing supply of it.
But between the greater fuel efficiency of new cars and the increasing market share of hybrid and electric vehicles, the future demand for light-duty gasoline in the United States is actually projected to decrease slightly.
Two other high-energy liquids—diesel and jet fuel—will likely pick up the slack, with an estimated increase in demand of at least 30 percent by 2040. To meet this rising demand in a more sustainable fashion, energy companies are investing in research for technologies that produce diesel and jet fuel from biomass.
In September 2017, scientists at the University of Wisconsin-Madison and the energy company ExxonMobil published in the journal Joule their discovery of a new earth-abundant catalyst for one such technology that can be up to 1,000 times less expensive than previously used precious metal catalysts. A catalyst is a chemical that speeds up a reaction without being consumed.
“We were pleasantly surprised that our simple inexpensive catalyst, which consists of titanium dioxide and cobalt, was as selective as the rare, more expensive platinum catalysts previously used in the reaction of interest,” says George Huber, the Harvey D. Spangler Professor in chemical and biological engineering at UW-Madison. He notes that the fuel precursors this catalyst was able to generate had similar performance as those from platinum catalysts, although more work is needed to improve their yield.
Many conversion routes from biomass to transportation fuels exist, some of which involve very high temperature processing or relatively slow biological fermentation. Typically, biomass is first converted to sugars, which are then converted to fuels via biological or catalytic routes. The scientific strategy pursued in this study uses active catalysts to process cellulosic sugars at moderate temperatures in multiple steps.
“In the first step, which is easy to implement, we convert the biomass-derived sugars into sugar alcohols like sorbitol,” lead author Nathaniel Eagan explains. “Next, we pull off oxygen to create a class of molecules called monofunctionals, instead of making a single chemical.” Further reactions couple together these monofunctionals to obtain longer molecules for fuels.
“We now have a much better understanding of the new catalyst’s fundamental chemistry,” Huber says. “In our continuing partnership with ExxonMobil, we will build on this knowledge to design even better processes with a higher yield of desired products, and to explore other technologies for converting readily available biomass into heavy duty liquid fuels.”
The research team included graduate student Joseph Chada and James Dumesic, the Ernest Micek Distinguished Chair in chemical and biological engineering, and ExxonMobil scientists Scott Buchanan and Ashley Wittrig. The project was funded by ExxonMobil.