I have written before that Butanol is a much more real, viable, and more serious contender as a gasoline replacement fuel than ethanol. There are many reasons for it, not least because it has high energy density, does not mix well and hence transports easily, and burns cleanly.
There are many reasons why I think biofuels still have a long way to go, esp those derived from bio-mass using enzymatic reactions. One key problem is the energy costs expended in the distillation process because the bacteria do not last in alcohol concentrations greater than 10%. hence the alcohol has to be distilled from a 90% water solution. That said, I think the scientific community (and entrepreneurial community) largely agrees that the real success of bio-enzymatic fuels will only happen when cellulosic alcohol problem is cracked. i.e. alcohol is derived by breaking down the complex lignocellulose that make up the bulk of the bio-mass available today for fermentation.
There many companies doing research on cellulosic ethanol: some with brighter futures and/or more influential backers than others. There are even more technologies still in academic labs waiting for the gestation period to be over so they cold be successfully commercialized. But here is some news on a laboratory success story on making butanol from wheat straw, a common and cheap bio feedstock available in many parts of the world. At least two problems remain: (a) reaction time in batch reactors, (b) distillation.
from Green Car Congress by Mike Millikin
Scientists at the USDA Agricultural Research Services (USDA ARS) are exploring the production of cellulosic biobutanol from wheat straw using Clostridium Beijerinckii.
The research is part of a larger, ongoing research project: Cost-Effective Bioprocess Technologies for Production of Biofuels from Lignocellulosic Biomass.
In work to be published in the Journal of Biotechnology, Nasib Qureshi, Badal Saha and Michael Cotta achieved a rate of production of wheat straw hydrolysate to butanol of 214% over that from glucose.
Wheat straw contains about 70% complex carbohydrate that can serve as a low cost feedstock for conversion to fuel ethanol.
Clostridium beijerinckii P260 can utilize five and six carbon sugars present in cellulosic biomass and convert them to butanol. The researchers pretreated wheat straw with dilute sulfuric acid and hydrolyzed it using commercial carbohydrases to lignocellulosic component sugars (glucose, xylose, arabinose, galactose, and mannose) prior to their conversion to butanol.
Hydrolysis, fermentation, and product recovery were combined in a single step using a 2.5-liter bioreactor. Fermentation performance was enhanced by simultaneously recovering products [Acetone-butanol (AB)] from the fermentation broth by gas stripping, thereby avoiding inhibition of the end product.
The reactor operated in a fed-batch mode, and fermentation lasted for more than 500 hours.
- Qureshi, N., Saha, B.C., Cotta, M.A. 2007. “Bioconversion of wheat straw to butanol (a superior liquid fuel): simultaneous saccharification, fermentation, and product recovery” [abstract]. Biotechnology for Fuels and Chemicals. Paper No. 4-16.