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 commercialisation. "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.
|Contact: Michelle Martella|