BUTANOL
Advances in Biofuels
Processing corn byproducts to create hydrogen and butanol fuels
benefits the environment, reduces petrochemical dependence, and
provides a potential new market for farmers.
What Is Butanol?
Butanol is a four carbon alcohol. It has double the amount
of carbon of ethanol, which equates to a 25 percent increase
in harvestable energy (Btu's).
Butanol is produced by fermentation, from corn, grass, leaves,
agricultural waste and other biomass.
Butanol is safer to handle with a Reid Value of 0.33 psi, which
is a measure of a fluid's rate of evaporation when compared to
gasoline at 4.5 and ethanol at 2.0 psi.
Butanol is an alcohol that can be but does not have to be blended
with fossil fuels.
Butanol when consumed in an internal combustion engine yields
no SOX, NOX or carbon monoxide all environmentally harmful byproducts
of combustion. CO2 is the combustion byproduct of butanol, and
is considered environmentally 'green'.
Butanol is far less corrosive than ethanol and can be shipped
and distributed through existing pipelines and filling stations.
Butanol solves the safety problems associated with the infrastructure
of the hydrogen supply. Reformed butanol has four more hydrogen
atoms than ethanol, resulting in a higher energy output and is
used as a fuel cell fuel.
Butanol is an industrial commodity, with a 370 million gallons
per year market with a selling price of $3.75 per gallon.
Hydrogen generated during the butanol fermentation process
is easily recovered, increasing the energy yield of a bushel
of corn by an additional 18 percent over the energy yield of
ethanol produced from the same quantity of corn.
Advances in Biofuels
Alternative Energy & New Markets for Farmers
David Ramey
There is abundant biomass present in low value agricultural
commodities or processing wastes requiring proper disposal to
avoid our pollution problem, for example, the corn refinery industry
generates more than 10 million metric tones of corn byproducts
that are currently of limited use and pose significant environmental
problems. Similarly, there are 60 billion pounds of cheese whey
generated annually in the dairy industry much of this byproduct
has no economical use at the present time and requires costly
disposal because of its high biological oxygen demand. These
various forms of biomass are inexpensive feedstocks for hydrogen,
chemicals and power grade alcohol fuel (butanol) production.
Production of industrial butanol and acetone via fermentation,
using Clostridia acetobutylicum, started in 1916, during World
War I. Chime Wizemann, a student of Louis Pasture, isolated the
microbe that made acetone. England approached the young microbiologist
and asked for the rights to make acetone for cordite. Up until
the 1920s acetone was the product sought, but for every pound
of acetone fermented, two pounds of butanol were formed. A growing
automotive paint industry turned the market around, and by 1927
butanol was primary and acetone became the byproduct.
The production of butanol by fermentation declined from the
1940s through the 1950s, mainly because the price of petrochemicals
dropped below that of starch and sugar substrates such as corn
and molasses. The labor intensive batch fermentation system's
overhead combined with the low yields contributed to the situation.
Fermentation-derived acetone and butanol production ceased in
the late 1950s.
In the 1970s the primary focus for alternative fuels was on
ethanol -- people were familiar with its production and did not
realize that dehydration (a very energy-consuming step) was necessary
in order to blend it with fossil fuels. Nor did we realize the
difficulty of distribution, since ethanol cannot be transferred
through the existing pipeline infrastructure. The selection of
ethanol, a lower-grade, corrosive, hard-to-purify, dangerously
explosive, and very evaporative alcohol is the result. Ethanol
is still subsidized by the government, since it is not profitable
enough to compete with gasoline. Over the past 30 years, however,
the very energy-intensive ethanol process has not solved our
fuel, power or clean-air requirements.
ABE FERMENTATION
Acetone butanol ethanol (ABE) fermentation by Clostridium acetobutylicum
is one of the oldest known industrial fermentations. It was
ranked second only to ethanol fermentation by yeast in its
scale of production, and is one of the largest biotechnological
processes ever known. The actual fermentation, however, has
been quite complicated and difficult to control. ABE fermentation
has declined continuously since the 1950s, and almost all butanol
is now produced via petrochemical routes . Butanol is an important
industrial solvent and potentially a better fuel extender than
ethanol. Current butanol prices as a chemical are at $3.75
per gallon, with a worldwide market of 370 million gallons
per year. The market demand is expected to increase dramatically
if green butanol can be produced economically from low cost
biomass.
In
a typical ABE fermentation, butyric, propionic, lactic and
acetic acids are first produced by C. acetobutylicum, the culture
pH drops and undergoes a metabolic “butterfly” shift,
and butanol, acetone, isopropanol and ethanol are formed.
In conventional ABE fermentations, the butanol yield from glucose
is low, typically around 15 percent and rarely exceeding 25 percent.
The production of butanol was limited by severe product inhibition.
Butanol at a concentration of 1 percent can significantly inhibit
cell growth and the fermentation process. Consequently, butanol
concentration in conventional ABE fermentations is usually lower
than 1.3 percent.
In the past 20+ years, there have been numerous engineering
attempts to improve butanol production in ABE fermentation, including
cell recycling and cell immobilization to increase cell density
and reactor productivity and using extractive fermentation to
minimize product inhibition. Despite many efforts, the best results
ever obtained for ABE fermentations to date are still less than
2 percent in butanol concentration, 4.46 g/L/h productivity,
and a yield of less than 25 percent from glucose. Optimizing
the ABE fermentation process has long been a goal of the industry.
With that in mind, a new process has been developed using continuous
immobilized cultures of Clostridium tyrobutyricum and Clostridium
acetobutylicum to produce an optimal butanol productivity of
4.64 g/L/h and yield of 42 percent. In simple terms, one microbe
maximizes the production of hydrogen and butyric acid, while
the other converts butyric acid to butanol.
Compared to conventional ABE fermentation, this new process
eliminates acetic, lactic and propionic acids, acetone, isopropanol
and ethanol production. The 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. That matches ethanol's track record -- and ethanol fermentations
do not yield hydrogen. Commercialization of this new technology
has the potential to reduce our nation's dependence on foreign
oil, protect our fuel generation grid from sudden disruption
while developing our agricultural base and reduce global warming.
FUTURE
Butanol is a pure alcohol with an energy content similar to that
of gasoline. It does not have to be stored in high pressure
vessels like natural gas, and can be but does not have to be
blended (10 to 100 percent) with any fossil fuel. Butanol can
also be transported through existing pipelines for distribution.
Butanol can help solve the hydrogen distribution infrastructure
problems faced with fuel cell development. The employment of
fuel-cell technology is held up by the safety issues associated
with hydrogen distribution, but butanol can be very easily
reformed for its hydrogen content and can be distributed through
existing gas stations in the purity required for either fuel
cells or vehicles.
Growing consumer acceptance and name recognition for butanol,
incentives to agriculture and industry, falling production costs,
increasing prices and taxes for fossil fuels, and the desire
for cleaner-burning sources of energy should drive an increase
in butanol production.
Building
new, smaller, turnkey biorefineries of 5 to 30 million gallons
per year for small municipalities and surrounding farming
communities could introduce state of the art technologies at
a faster rate than has been adopted in the past. These local
biorefineries would address many overwhelming problems associated
with the environment, such as regional landfill burdens, and
by disseminating fuel generation throughout the Corn and Bio-Belt,
any prospective disruption by terrorism is made more difficult,
thus improving “Homeland Security.” Cooperatively
owned facilities would allow the agricultural sector to employ
more people and retain profits within the local economy, bringing
the resulting sevenfold multiplication.
The production of butanol (15,500 BTU/lb. or 104,800 BTU/gallon)
and hydrogen (61,000 BTU/lb.) from biomass is not constrained
by technological difficulties as is the manufacturing of ethanol
(12,800 BTU/lb or 84,250 BTU/gal). New higher-value uses for
co products of fermentation are an even more likely source of
new revenues and could reduce the cost of butanol and hydrogen.
Recent advances in the fields of biotechnology and bioprocessing
have resulted in a renewed interest in the fermentation production
of chemicals and fuels, including n butanol. With continuous
fermentation technology, butanol can be produced at higher yields,
concentrations and production rates.
David Ramey can be contacted at
P.O. Box 15, Blacklick, Ohio 43004,
phone (614) 864 5650, fax (614) 864 0120,
e-mail dramey@butanol.com
Thanks to Acres USA November 2004
