New Catalysts Lead
to Near Total Conversion
(December 5, 2015) Ethanol,
which is produced from corn, is commonly-used as an additive in engine fuel as
a way to reduce harmful emissions and scale back U.S. reliance on foreign
oil. But since ethanol is an oxygenated
fuel, its use results in a lower energy output, as well as increased damage to
engines via corrosion.
But now a research team, led by William Jones at the
University of Rochester, has developed a series of reactions that results in
the selective conversion of ethanol to butanol, without producing unwanted
byproducts.
“Butanol is much better than ethanol as an alternative to
gasoline,” said Jones, the C.F. Houghton Professor of Chemistry. “It yields
more energy, is less volatile, and doesn’t cause damage to engines.”
In fact, Jones was able to increase the amount of ethanol
converted to butanol by almost 25 percent over currently used methods. Jones
describes his process in a paper just published in the Journal of the American
Chemical Society.
Converting ethanol to butanol involves creating a larger
chemical molecule with more carbon and hydrogen atoms. Although both molecules have a single oxygen
atom, the higher carbon-to-oxygen ratio in butanol gives it a higher energy
content, while the larger size make it less volatile.
One method of converting the ethanol to butanol is the three-step
Guerbet reaction, which involves temporarily giving up hydrogen atoms in an
intermediate step, then adding them back in to create the final product. One
problem with the Guerbet reaction is that an intermediate
product—acetaldehyde—can react with both itself and the butanol product to
create unwanted molecules.
Jones modified the Guerbet reaction by using iridium as the
initial catalyst and nickel or copper hydroxide, instead of potassium hydroxide
(KOH), in the second step. While the best current conditions for the Guerbet
reaction convert ethanol to butanol with about 80% selectivity, Jones’ reaction
produced butanol in more than 99 percent selectivity. No undesirable side products are produced.