An Apple a Day Keeps the Gas Pump Away
by Jeremy Elton Jacquot, Los Angeles on 06.21.07
A team of scientists led by James Dumesic at the University of Wisconsin-Madison has discovered a way (subscription needed) to turn the sugar commonly found in fruits like apples and oranges into a biofuel with 40% greater energy density than ethanol. This two-stage process, which essentially converts the sugars (fructose and sucrose) into 2,5-dimethylfuran (DMF), consists of a series of steps involving acid and copper catalysts, salt and butanol as a solvent.
We have already discussed the merits and downsides to using ethanol, particularly corn-based ethanol, as a viable source of renewable energy at length several times in the past (most recently here). The low cost efficiency and very real possibility of precipitating unwanted secondary effects make the reliable, long-term use of ethanol more suspect at this point. But can using biomass-derived sugars solve our current and future energy needs more effectively?
Dumesic seems to think so. In addition to having a higher energy content, DMF circumvents several of ethanol's most glaring shortcomings, including its solubility in water (which makes ethanol more likely to become contaminated) and instability in storage. As Dumesic describes it: "But ethanol suffers from several limitations. It has relatively low energy density, evaporates readily, and can become contaminated by absorption of water from the atmosphere. It also requires an energy-intensive distillation process to separate the fuel from water."
Expanding upon their previous work in which they had shown how to make hydroxymethylfurfural (HMF), an important intermediate, from sugar, they found a way to convert this chemical into DMF over a copper-based catalyst. By removing two oxygen atoms from the molecule, the conversion process lowers its boiling point and makes it a stable, effective alternative to petrol and other transportation fuels.
As with other crop- and feedstock-based biofuels, however, the long-term use of DMF as an alternative to fossil fuels is not yet assured. Although its environmental health impact hasn't been thoroughly examined yet, early results seem to suggest its properties are similar to those of other current fuel components. Also, because its production is wholly dependent on the extraction of sugars like fructose and sucrose from fruits and plants, it remains to be seen what pressures its extended use will exert on the environment and agriculture.
"There are some challenges that we need to address," said Dumesic, "but this work shows that we can produce a liquid transportation fuel from biomass that has energy density comparable to petrol."
Via ::Fruit could make 'powerful fuel', ::Engineers Develop Higher-energy Liquid Transportation Fuel From Sugar
See also: ::Prospecting for Biofuels, ::A Sweet Deal: Kicking the Oil Habit with Sugar, ::TreeHugger Picks: Sugar - Not Just For Eating Any More, ::Ancient Plant May Become New Source of Biofuel, ::Biofuel That Grows Like A Magic Mushroom, ::Which BioFuel Produces the Least NOx?
What is energy efficiency in making DMF or ethanol in relation to the enzymes concoctions (or bacteria soups) that make hydrogen from sugar? (See other post on TH on enzymes and hydrogen.)
Ethanol is already oxidised, ie has lower available energy than sugar. Could one use enzymes to make carbon chains, like the hydrophobic tail of lipids? With only 4-10 carbons they probably still would be liquid at RT (I dunno about -20C). Can one "just" break up one sugar (C6 in any hexose like glucose) and reduce the 5 OH-groups and the 1 keto-group? Of course extra energy needs to be put into the system but is now in the fuel so not gone wasted.