The current energy quandary means a lot of basic research is being done in alternative energy solutions; that's good, it's what basic research is for. It also means political darlings of some politicians and environmentalists should be disqualified from future consideration if they are shown to be untenable.
The production of ethanol from lignocellulose-rich materials such as wood residues, waste paper, used cardboard and straw sounds like a great idea but that isn't a reason to start subsidizing it. A cost comparison in Biofuels, Bioproducts&Biorefining has concluded that using lignocellulose materials is unlikely to be competitive with starch any time soon.
Ethanol can be blended with gasoline to reduce our dependency on fossil fuels, though it does nothing for the prime reasons we want to reduce our dependency - cost and emissions. The last 15 years have seen a massive growth (due to subsidies and government mandates) of first-generation processes that use enzymes and bacteria to turn the starch and sugars in corn and sugarcane into ethanol, but as everyone but environmental advocates knew, corn and sugar cane are also important components of the human food web, so using them for ethanol production affects the price and availability of these basic commodities.
Lignocellulose materials are often hard to dispose of, but they are rich in sugars that can be fermented into ethanol following appropriate processing - so they would be much better suited for fuel.
"Not only is cellulose the most abundant polymer on Earth, it cannot be digested by humans, so using it for fuel production does not compete directly with food supplies," says the study's lead author Jamie Stephen, who works in the Department of Wood Science at the University of British Columbia in Vancouver, Canada.
The cost of building large scale ethanol-producing facilities will be even higher for second generation ethanol compared to first generation technologies, because sources of lignocellulose may require significant and costly pre-treatment. "Researchers and companies are going to have to concentrate on reducing the cost of pretreatment and increasing the output of the digester in order to reduce the costs of the lignocellulose-to-ethanol process," says Stephen.
Another reason costs are higher is that lignocellulose is made of multiple kinds of sugar, while corn starch consists of pure glucose. Corn starch can be reduced to glucose with low-cost amylase enzymes, while pre-treated lignocellulose requires a cocktail of cellulase enzymes. Providing these enzymes is one of the major costs of the whole process, but you currently need 12 times more cellulase than amylase protein to generate the same amount of ethanol from woody biomass.
"Despite much effort and progress over the last few years, the cost of using cellulase enzymes is still significantly higher than for amylase-based processes, and will need to be reduced substantially before lignocellulose starts to become competitive with corn and sugarcane as a feedstock," says Stephen.
Finally, while the input to sugarcane- and corn starch-based systems is fairly constant, the feedstocks that go into lignocellulose systems are much more variable. Different species of tree produce wood that has different properties, and waste paper and agricultural wastes will have many different types of material in them. To get maximum efficiency, each type of biomass needs to be processed under different conditions, which introduces another challenge for anyone wanting to make ethanol from these materials.
Overall Stephen believes we have a considerable way to go before second-generation ethanol production will be ready for commercialization. "Production requires significant cost reductions and at least the same level of financial support that was given to the first-generation systems if second-generation ethanol is going to be fully competitive by 2020," says Stephen.