A sweet new biofuel
Simple sugars aren’t just for fueling the kid generation; they may help fuel the next generation of vehicles. Researchers report in the June 21 issue of Nature (2007, 447, 982–985) on an improved way to harness the energy wallop in sweet fructose and glucose to make liquid fuel. James Dumesic and colleagues at the University of Wisconsin Madison developed a catalytic process to convert fructose into 2,5-dimethylfuran (DMF). The biofuel’s energy content is 40% higher than that of ethanol, and DMF avoids ethanol’s problem of absorbing water from the atmosphere.
Fruits are one obvious source of fructose, but Dumesic says that food crops such as apples and oranges would likely provide only a small part of the fructose supply on an industrial scale. Glucose, which is more widely available from biomass, can be converted efficiently to fructose for the process, the authors add, and the sugars and starches in nonfood biomass, such as paper-mill waste, could also be converted to DMF.
The new process is a hybrid of traditional thermochemical and biological approaches to biofuel production. Starches are first broken down by biological enzymes to produce fructose, which is then converted in an acid-catalyzed reaction to an intermediate compound, 5-hydroxymethylfurfural (HMF). The team developed a carbon-supported copper–ruthenium catalyst to convert the HMF into DMF as a final product. The process is much faster than ethanol fermentation and avoids the energy-intensive steps in biodiesel production that break biomass down into carbon monoxide and hydrogen (together called syngas) and then recombine these components into larger fuel molecules.
Before DMF can be seriously considered as a transportation fuel, however, its toxicology and environmental effects, such as emissions, need to be explored, the authors point out. In addition, cost-effective means to produce sugars from the complex structural materials in plant biomass remain a challenge for the biofuel industry.
Also, another group has recently developed a different catalytic method to convert sugars to HMF as a feedstock for plastics.
