|From Ohio to California and back on butanol.|
An Ohio inventor has taken to the road to promote butanol as an alternative fuel to ethanol as well as his process for producing it from the anaerobic fermentation of biomass waste. The two-stage, dual-path process, which relies on two different Clostridia strains (earlier post), also yields hydrogen as a product.
According to the inventor, David Ramey, his butanol process delivers about 42% more energy than ethanol for a given amount of feedstock, based on the higher energy content of butanol (some 25% greater than ethanol), plus the hydrogen.
|a David Ramey, Environmental Engineering, Inc. |
b EIA Annual Energy Review, Appendix A1
|BTU/gallon||105K a||84K b||123K b|
|Vapor Pressure @ 100 F||0.33 psi||2.0 psi||4.5 psi|
Butanol (C4H10O) is a four-carbon alcohol in widespread use as an industrial solvent, with a US market size of some 370 million gallons per year at a price of about $3.75 per gallon (approximately $1.4 billion).
Originally produced by fermentation starting nearly 90 years ago (using Clostridia acetobutylicum), butanol shifted to becoming a petrochemically-derived product in the 1950s as the price of petrochemicals dropped below that of starch and sugar substrates such as corn and molasses. Virtually all of the butanol is use today is produced petrochemically.
In conventional fermentations, the butanol yield from glucose is low—between 15%–25%—and the butanol concentration in the fermentation is usually lower than 1.3%. (Butanol at a concentration of 1% can significantly inhibit cell growth and the fermentation process.) There have been numerous efforts over the years to improve butanol yield by using a variety of techniques to minimize product inhibition.
|Environmental Energy Inc.’s Biomass-to-Butanol Process|
Ramey took the approach of using two types of microbes in two separate process steps. Other processes had tried multiple strains of bacteria, but in synergy within the same slurry.
The first, Clostridium tyrobutyricum, optimizes the production of hydrogen and butyric acid, while the other, Clostridium acetobutylicum, converts the butyric acid to butanol. (Diagram at right, Click to enlarge.)
Ramey claims his butanol yield from this process is 42% from glucose.
The conventional fermentation process produced a number of products as well as butanol: acetic, lactic and propionic acids, acetone, isopropanol and ethanol production. Ramey’s fermentation only produces hydrogen, butyric acid, butanol and carbon dioxide, and doubles the yield of butanol from a bushel of corn from 1.3 to 2.5 gallons per bushel—equivalent to corn ethanol’s fermentative yield, but with higher heat content and hydrogen as a co-product.
Butanol’s energy content is closer to gasoline than ethanol’s. It is non-corrosive, can be distributed through existing pipelines, and can be—but does not have to be—blended with fossil fuels. Butanol itself could be reformed for hydrogen for use in fuel cells, and the production process itself produces hydrogen.
As good as that might sound, however, there are a number of unknows.
Primarily, the economics of production using Ramey’s process are unproven. He is seeking some $3 million to build a 250-gallon/week prototype and then a 1,250-gallon/week pilot plant. (From 1991, his company, Environmental Energy, Inc., has operated on $1.5 million provided by 40 private investors and by several federal research grants.)
He has produced butanol from his process in small amounts here and there—but for the promotional drive, he and his team bought four barrels of conventional butanol from Ashland Chemical.
Assuming he finds his funding, and the process scales, his plans call initially to sell the butanol into the commercial solvents market to generate a sustainable revenue stream. (It’s a big, existing market, always on the lookout for a less expensive product.)
Ramey ultimately envisions small, turnkey biorefineries of 5 to 30 million gallons per year capacity for small municipalities and surrounding farming communities that would produce butanol as a gasoline substitute.
Penn State University: Genetic Engineering of Clostridium acetobutylicum for Enhanced Production of Hydrogen Gas
Continuous two-stage ABE-fermentation using Clostridium beijerinckii NRRL B592 operating with a growth rate in the first stage vessel close to its maximal value, J Mol Microbiol Biotechnol. 2000 Jan;2(1):101-5.
Acetone-butanol fermentation revisited, Microbiol Rev. 1986 December; 50(4): 484–524.
(A hat-tip to Robert Schwartz!)