is ethanol (ethyl alcohol) produced from cellulose
(the stringy fiber of a plant) rather than from the plant's seeds or
fruit. It is a biofuel produced from grasses, wood, algae, or other
plants. The fibrous parts of the plants are mostly inedible to
animals, including humans, except for ruminants (grazing, cud-chewing
animals such as cows or sheep).
Considerable interest in cellulosic ethanol exists because it has the
potential for strong economic importance. Growth of cellulose by
plants is a mechanism that captures and stores solar energy chemically
in nontoxic ways with resultant supplies that are easy to transport
and store. Additionally, transport may be unneeded anyway, because
grasses or trees can grow almost anywhere temperate. This is why
commercially practical cellulosic ethanol is widely viewed as a next
level of development for the biofuel industry that could reduce demand
for oil and gas drilling and even nuclear power in ways that
grain-based ethanol fuel alone cannot. Potential exists for the many
benefits of carbonaceous liquid fuels and petrochemicals (which
today's standard of living depends on) but in a carbon
cycle–balanced and renewable way (recycling surface and atmosphere
carbon instead of pumping underground carbon up into it and thus
adding to it). Commercially practical cellulosic alcohol could also
avoid one of the problems with today's conventional (grain-based)
biofuels, which is that they set up competition for grain with food
purposes, potentially driving up the price of food. To date, what
stands in the way of these goals is that production of cellulosic
alcohol is not yet sufficiently practical on a commercial scale.
3 Production methods
Cellulolysis (biological approach)
3.1.1 Cellulolytic processes
22.214.171.124 Chemical hydrolysis
126.96.36.199 Enzymatic hydrolysis
3.1.2 Microbial fermentation
3.1.3 Combined hydrolysis and fermentation
Gasification process (thermochemical approach)
Hemicellulose to ethanol
6 Enzyme-cost barrier
8 Environmental effects
10 Corn-based vs. grass-based
Cellulosic ethanol commercialization
12 See also
14 External links
Cellulosic ethanol is a type of biofuel produced from lignocellulose,
a structural material that comprises much of the mass of plants.
Lignocellulose is composed mainly of cellulose, hemicellulose and
lignin. Corn stover,
Panicum virgatum (switchgrass),
species, wood chips and the byproducts of lawn and tree maintenance
are some of the more popular cellulosic materials for ethanol
production. Production of ethanol from lignocellulose has the
advantage of abundant and diverse raw material compared to sources
such as corn and cane sugars, but requires a greater amount of
processing to make the sugar monomers available to the microorganisms
typically used to produce ethanol by fermentation.
Miscanthus are the major biomass materials being
studied today, due to their high productivity per acre. Cellulose,
however, is contained in nearly every natural, free-growing plant,
tree, and bush, in meadows, forests, and fields all over the world
without agricultural effort or cost needed to make it grow.
One of the benefits of cellulosic ethanol is it reduces greenhouse gas
emissions (GHG) by 85% over reformulated gasoline. By contrast,
starch ethanol (e.g., from corn), which most frequently uses natural
gas to provide energy for the process, may not reduce
GHG emissions at
all depending on how the starch-based feedstock is produced.
According to the
National Academy of Sciences
National Academy of Sciences in 2011, there is no
commercially viable bio-refinery in existence to convert
lignocellulosic biomass to fuel. Absence of production of
cellulosic ethanol in the quantities required by the regulation was
the basis of a United States Court of Appeals for the District of
Columbia decision announced January 25, 2013, voiding a requirement
imposed on car and truck fuel producers in the United States by the
Environmental Protection Agency requiring addition of cellulosic
biofuels to their products. These issues, along with many other
difficult production challenges, led George Washington University
policy researchers to state that "in the short term, [cellulosic]
ethanol cannot meet the energy security and environmental goals of a
The French chemist, Henri Braconnot, was the first to discover that
cellulose could be hydrolyzed into sugars by treatment with sulfuric
acid in 1819. The hydrolyzed sugar could then be processed to form
ethanol through fermentation. The first commercialized ethanol
production began in Germany in 1898, where acid was used to hydrolyze
cellulose. In the United States, the Standard
Alcohol Company opened
the first cellulosic ethanol production plant in South Carolina in
1910. Later, a second plant was opened in Louisiana. However, both
plants were closed after World War I due to economic reasons.
The first attempt at commercializing a process for ethanol from wood
was done in Germany in 1898. It involved the use of dilute acid to
hydrolyze the cellulose to glucose, and was able to produce 7.6 liters
of ethanol per 100 kg of wood waste (18 US gal
(68 L) per ton). The Germans soon developed an industrial process
optimized for yields of around 50 US gallons (190 L) per ton of
biomass. This process soon found its way to the US, culminating in two
commercial plants operating in the southeast during World War I. These
plants used what was called "the American Process" — a one-stage
dilute sulfuric acid hydrolysis. Though the yields were half that of
the original German process (25 US gallons (95 L) of ethanol per
ton versus 50), the throughput of the American process was much
higher. A drop in lumber production forced the plants to close shortly
after the end of World War I. In the meantime, a small but steady
amount of research on dilute acid hydrolysis continued at the USFS's
Forest Products Laboratory. During World War II, the US
again turned to cellulosic ethanol, this time for conversion to
butadiene to produce synthetic rubber. The Vulcan Copper and Supply
Company was contracted to construct and operate a plant to convert
sawdust into ethanol. The plant was based on modifications to the
original German Scholler process as developed by the Forest Products
Laboratory. This plant achieved an ethanol yield of
50 US gal (190 L) per dry ton, but was still not
profitable and was closed after the war.
With the rapid development of enzyme technologies in the last two
decades, the acid hydrolysis process has gradually been replaced by
enzymatic hydrolysis. Chemical pretreatment of the feedstock is
required to prehydrolyze (separate) hemicellulose, so it can be more
effectively converted into sugars. The dilute acid pretreatment is
developed based on the early work on acid hydrolysis of wood at the
USFS's Forest Products Laboratory. Recently, the Forest Products
Laboratory together with the University of Wisconsin–Madison
developed a sulfite pretreatment to overcome the recalcitrance of
lignocellulose for robust enzymatic hydrolysis of wood cellulose.
US President George W. Bush, in his
State of the Union
State of the Union address
delivered January 31, 2006, proposed to expand the use of cellulosic
ethanol. In his
State of the Union
State of the Union Address on January 23, 2007,
President Bush announced a proposed mandate for 35 billion US
gallons (130,000,000 m3) of ethanol by 2017. It is widely
recognized that the maximum production of ethanol from corn starch is
15 billion US gallons (57,000,000 m3) per year, implying a
proposed mandate for production of some 20 billion US gallons
(76,000,000 m3) more per year of cellulosic ethanol by 2017.
Bush's proposed plan includes $2 billion funding (from 2007 to 2017?)
for cellulosic ethanol plants, with an additional $1.6 billion (from
2007 to 2017?) announced by the USDA on January 27, 2007.
In March 2007, the US government awarded $385 million in grants aimed
at jump-starting ethanol production from nontraditional sources like
wood chips, switchgrass, and citrus peels. Half of the six projects
chosen will use thermochemical methods and half will use cellulosic
The American company
Range Fuels announced in July 2007 that it was
awarded a construction permit from the state of Georgia to build the
first commercial-scale 100-million-US-gallon
(380,000 m3)-per-year cellulosic ethanol plant in the US.
Construction began in November, 2007. The
Range Fuels plant was
built in Soperton, GA, but was shut down in January 2011, without ever
having produced any ethanol. It had received a $76 million grant from
the US Department of Energy, plus $6 million from the State of
Georgia, plus an $80 million loan guaranteed by the U.S. Biorefinery
Assistance Program. The United States (US) and Brazil have been
the two leading producers of fuel ethanol since the 1970s.
Bioreactor for cellulosic ethanol research.
The two ways of producing ethanol from cellulose are:
Cellulolysis processes which consist of hydrolysis on pretreated
lignocellulosic materials, using enzymes to break complex cellulose
into simple sugars such as glucose, followed by fermentation and
Gasification that transforms the lignocellulosic raw material into
gaseous carbon monoxide and hydrogen. These gases can be converted to
ethanol by fermentation or chemical catalysis.
As is normal for pure ethanol production, these methods include
Cellulolysis (biological approach)
The stages to produce ethanol using a biological approach are:
A "pretreatment" phase, to make the lignocellulosic material such as
wood or straw amenable to hydrolysis
Cellulose hydrolysis (that is, cellulolysis) with cellulases, to break
down the molecules into sugars
Separation of the sugar solution from the residual materials, notably
Microbial fermentation of the sugar solution
Distillation to produce roughly 95% pure alcohol
Dehydration by molecular sieves to bring the ethanol concentration to
In 2010, a genetically engineered yeast strain was developed to
produce its own cellulose-digesting enzymes. Assuming this
technology can be scaled to industrial levels, it would eliminate one
or more steps of cellulolysis, reducing both the time required and
costs of production.
Although lignocellulose is the most abundant plant material resource,
its usability is curtailed by its rigid structure. As a result, an
effective pretreatment is needed to liberate the cellulose from the
lignin seal and its crystalline structure so as to render it
accessible for a subsequent hydrolysis step. By far, most
pretreatments are done through physical or chemical means. To achieve
higher efficiency, both physical and chemical pretreatments are
required. Physical pretreatment is often called size reduction to
reduce biomass physical size. Chemical pretreatment is to remove
chemical barriers so the enzymes can have access to cellulose for
To date, the available pretreatment techniques include acid
hydrolysis, steam explosion, ammonia fiber expansion, organosolv,
sulfite pretreatment, AVAP® (SO2-ethanol-water)
fractionation, alkaline wet oxidation and ozone pretreatment.
Besides effective cellulose liberation, an ideal pretreatment has to
minimize the formation of degradation products because of their
inhibitory effects on subsequent hydrolysis and fermentation
processes. The presence of inhibitors will not only further
complicate the ethanol production but also increase the cost of
production due to entailed detoxification steps. Even though
pretreatment by acid hydrolysis is probably the oldest and most
studied pretreatment technique, it produces several potent inhibitors
including furfural and hydroxymethyl furfural (HMF) which are by far
regarded as the most toxic inhibitors present in lignocellulosic
hydrolysate. Ammonia Fiber Expansion (AFEX) is a promising
pretreatment with no inhibitory effect in resulting hydrolysate.
Most pretreatment processes are not effective when applied to
feedstocks with high lignin content, such as forest biomass.
Organosolv, SPORL ('sulfite pretreatment to overcome recalcitrance of
lignocellulose') and SO2-ethanol-water (AVAP®) processes are the
three processes that can achieve over 90% cellulose conversion for
forest biomass, especially those of softwood species. SPORL is the
most energy efficient (sugar production per unit energy consumption in
pretreatment) and robust process for pretreatment of forest biomass
with very low production of fermentation inhibitors. Organosolv
pulping is particularly effective for hardwoods and offers easy
recovery of a hydrophobic lignin product by dilution and
precipitation. AVAP® process effectively fractionates all types
of lignocellulosics into clean highly digestible cellulose, undegraded
hemicellulose sugars, reactive lignin and lignosulfonates, and is
characterized by efficient recovery of chemicals.
There are two major cellulose hydrolysis (cellulolysis) processes: a
chemical reaction using acids, or an enzymatic reaction use
The cellulose molecules are composed of long chains of sugar
molecules. In the hydrolysis of cellulose (that is, cellulolysis),
these chains are broken down to free the sugar before it is fermented
for alcohol production.
In the traditional methods developed in the 19th century and at the
beginning of the 20th century, hydrolysis is performed by attacking
the cellulose with an acid. Dilute acid may be used under high
heat and high pressure, or more concentrated acid can be used at lower
temperatures and atmospheric pressure. A decrystalized cellulosic
mixture of acid and sugars reacts in the presence of water to complete
individual sugar molecules (hydrolysis). The product from this
hydrolysis is then neutralized and yeast fermentation is used to
produce ethanol. As mentioned, a significant obstacle to the dilute
acid process is that the hydrolysis is so harsh that toxic degradation
products are produced that can interfere with fermentation. BlueFire
Renewables uses concentrated acid because it does not produce nearly
as many fermentation inhibitors, but must be separated from the sugar
stream for recycle [simulated moving bed (SMB) chromatographic
separation, for example] to be commercially attractive.
Agricultural Research Service
Agricultural Research Service scientists found they can access and
ferment almost all of the remaining sugars in wheat straw. The sugars
are located in the plant’s cell walls, which are notoriously
difficult to break down. To access these sugars, scientists pretreated
the wheat straw with alkaline peroxide, and then used specialized
enzymes to break down the cell walls. This method produced 93 US
gallons (350 L) of ethanol per ton of wheat straw.
Cellulose chains can be broken into glucose molecules by cellulase
This reaction occurs at body temperature in the stomachs of ruminants
such as cattle and sheep, where the enzymes are produced by microbes.
This process uses several enzymes at various stages of this
conversion. Using a similar enzymatic system, lignocellulosic
materials can be enzymatically hydrolyzed at a relatively mild
condition (50 °C and pH 5), thus enabling effective cellulose
breakdown without the formation of byproducts that would otherwise
inhibit enzyme activity. All major pretreatment methods, including
dilute acid, require an enzymatic hydrolysis step to achieve high
sugar yield for ethanol fermentation. Currently, most pretreatment
studies have been laboratory-based, but companies are exploring means
to transition from the laboratory to pilot, or production scale.
Various enzyme companies have also contributed significant
technological breakthroughs in cellulosic ethanol through the mass
production of enzymes for hydrolysis at competitive prices.
Trichoderma reesei is used by
Iogen Corporation to secrete
"specially engineered enzymes" for an enzymatic hydrolysis
process. Their raw material (wood or straw) has to be pre-treated
to make it amenable to hydrolysis.
Another Canadian company, SunOpta, uses steam explosion pretreatment,
providing its technology to Verenium (formerly Celunol Corporation)'s
facility in Jennings, Louisiana, Abengoa's facility in Salamanca,
Spain, and a
China Resources Alcohol Corporation in Zhaodong. The CRAC
production facility uses corn stover as raw material.
Novozymes have received United States Department of
Energy funding for research into reducing the cost of cellulases, key
enzymes in the production of cellulosic ethanol by enzymatic
hydrolysis. A recent breakthrough in this regard was the discovery and
inclusion of lytic polysaccharide monooxygenases. These enzymes are
capable of boosting significantly the action of other cellulases by
oxidatively attacking a polysaccharide substrate.
Other enzyme companies, such as Dyadic International, are
developing genetically engineered fungi which would produce large
volumes of cellulase, xylanase and hemicellulase enzymes, which can be
used to convert agricultural residues such as corn stover, distiller
grains, wheat straw and sugarcane bagasse and energy crops such as
switchgrass into fermentable sugars which may be used to produce
In 2010, BP Biofuels bought out the cellulosic ethanol venture share
of Verenium, which had itself been formed by the merger of
Celunol, and with which it jointly owned and operated a
1.4-million-US-gallon (5,300 m3) per year demonstration plant in
Jennings, LA, and the laboratory facilities and staff in San Diego,
CA. BP Biofuels continues to operate these facilities, and has begun
first phases to construct commercial facilities.
Ethanol produced in
the Jennings facility was shipped to London and blended with gasoline
to provide fuel for the Olympics.
KL Energy Corporation, formerly KL Process Design Group, began
commercial operation of a 1.5-million-US-gallon (5,700 m3) per
year cellulosic ethanol facility in Upton, WY in the last quarter of
2007. The Western
Biomass Energy facility is currently achieving
yields of 40–45 US gallons (150–170 L) per dry ton. It is the
first operating commercial cellulosic ethanol facility in the nation.
The KL Energy process uses a thermomechanical breakdown and enzymatic
conversion process. The primary feedstock is soft wood, but lab tests
have already proven the KL Energy process on wine pomace, sugarcane
bagasse, municipal solid waste, and switchgrass.
Traditionally, baker’s yeast (Saccharomyces cerevisiae), has long
been used in the brewery industry to produce ethanol from hexoses
(six-carbon sugars). Due to the complex nature of the carbohydrates
present in lignocellulosic biomass, a significant amount of xylose and
arabinose (five-carbon sugars derived from the hemicellulose portion
of the lignocellulose) is also present in the hydrolysate. For
example, in the hydrolysate of corn stover, approximately 30% of the
total fermentable sugars is xylose. As a result, the ability of the
fermenting microorganisms to use the whole range of sugars available
from the hydrolysate is vital to increase the economic competitiveness
of cellulosic ethanol and potentially biobased proteins.
In recent years, metabolic engineering for microorganisms used in fuel
ethanol production has shown significant progress. Besides
Saccharomyces cerevisiae, microorganisms such as Zymomonas mobilis and
Escherichia coli have been targeted through metabolic engineering for
cellulosic ethanol production.
Recently, engineered yeasts have been described efficiently fermenting
xylose, and arabinose, and even both together. Yeast
cells are especially attractive for cellulosic ethanol processes
because they have been used in biotechnology for hundreds of years,
are tolerant to high ethanol and inhibitor concentrations and can grow
at low pH values to reduce bacterial contamination.
Combined hydrolysis and fermentation
Some species of bacteria have been found capable of direct conversion
of a cellulose substrate into ethanol. One example is Clostridium
thermocellum, which uses a complex cellulosome to break down cellulose
and synthesize ethanol. However, C. thermocellum also produces
other products during cellulose metabolism, including acetate and
lactate, in addition to ethanol, lowering the efficiency of the
process. Some research efforts are directed to optimizing ethanol
production by genetically engineering bacteria that focus on the
Gasification process (thermochemical approach)
Fluidized Bed Gasifier in
The gasification process does not rely on chemical decomposition of
the cellulose chain (cellulolysis). Instead of breaking the cellulose
into sugar molecules, the carbon in the raw material is converted into
synthesis gas, using what amounts to partial combustion. The carbon
monoxide, carbon dioxide and hydrogen may then be fed into a special
kind of fermenter. Instead of sugar fermentation with yeast, this
Clostridium ljungdahlii bacteria. This microorganism
will ingest carbon monoxide, carbon dioxide and hydrogen and produce
ethanol and water. The process can thus be broken into three steps:
Gasification — Complex carbon-based molecules are broken apart to
access the carbon as carbon monoxide, carbon dioxide and hydrogen
Fermentation — Convert the carbon monoxide, carbon dioxide and
hydrogen into ethanol using the
Clostridium ljungdahlii organism
Ethanol is separated from water
A recent study has found another Clostridium bacterium that seems to
be twice as efficient in making ethanol from carbon monoxide as the
one mentioned above.
Alternatively, the synthesis gas from gasification may be fed to a
catalytic reactor where it is used to produce ethanol and other higher
alcohols through a thermochemical process. This process can also
generate other types of liquid fuels, an alternative concept
successfully demonstrated by the Montreal-based company
their facility in Westbury, Quebec.
Hemicellulose to ethanol
Studies are intensively conducted to develop economic methods to
convert both cellulose and hemicellulose to ethanol. Fermentation of
glucose, the main product of cellulose hydrolyzate, to ethanol is an
already established and efficient technique. However, conversion of
xylose, the pentose sugar of hemicellulose hydrolyzate, is a limiting
factor, especially in the presence of glucose. Moreover, it cannot be
disregarded as hemicellulose will increase the efficiency and
cost-effectiveness of cellulosic ethanol production.
Sakamoto (2012) et al. show the potential of genetic engineering
microbes to express hemicellulase enzymes. The researchers created a
Saccharomyces cerevisiae strain that was able to:
hydrolyze hemicellulase through codisplaying endoxylanase on its cell
assimilate xylose by expression of xylose reductase and xylitol
The strain was able to convert rice straw hydrolyzate to ethanol,
which contains hemicellulosic components. Moreover, it was able to
produce 2.5x more ethanol than the control strain, showing the highly
effective process of cell surface-engineering to produce ethanol.
The shift to a renewable fuel resource has been a target for many
years now. However, most of its production is with the use of corn
ethanol. In the year 2000, there was only 6.2 billion liters produced
in the United States and it has expanded over 800% to 50 billion
litres in just a decade (2010). Government pressures to shift to
renewable fuel resources has been apparent since the U.S.
Environmental Protection Agency has implemented the 2007 Renewable
Fuel Standard (RFS) to use a percentage of renewable fuel in products
or face penalties. The shift to cellulosic ethanol production instead
of corn has been strongly promoted by the US government. Even with
these policies in place and the government attempting to create a
market for cellulose ethanol, there was no commercial production of
this fuel in 2010 and 2011. The Energy Independence and Security
Act originally set goals of 100 million, 250 million and 500 million
gallons for the years 2010, 2011 and 2012 respectively. However, as of
2012 it was projected that the production of cellulosic ethanol would
be approximately 10.5 million far from its target. In 2007 alone,
the US government provided 1 billion US dollars for cellulosic ethanol
projects, while China invested 500 million US dollars into cellulosic
Due to the lack of existing commercialized plant data, it is difficult
to determine the exact method of production that will be most commonly
employed. Model systems try to compare different technologies costs,
however these models cannot be applied to commercial-plant costs.
Currently, there are many pilot and demonstration facilities open that
show cellulosic production on a smaller scale. These main facilities
are summarized in the table below.
Start-up costs for pilot scale lignocellulosic ethanol plants are
high. On 28 February 2007, the U.S. Department of Energy announced
$385 million in grant funding to six cellulosic ethanol plants.
This grant funding accounts for 40% of the investment costs. The
remaining 60% comes from the promoters of those facilities. Hence, a
total of $1 billion will be invested for approximately
140-million-US-gallon (530,000 m3) capacity. This translates into
$7/annual gallon production capacity in capital investment costs for
pilot plants; future capital costs are expected to be lower.
Corn-to-ethanol plants cost roughly $1–3/annual gallon capacity,
though the cost of the corn itself is considerably greater than for
switchgrass or waste biomass.
As of 2007, ethanol is produced mostly from sugars or starches,
obtained from fruits and grains. In contrast, cellulosic ethanol is
obtained from cellulose, the main component of wood, straw, and much
of the structure of plants. Since cellulose cannot be digested by
humans, the production of cellulose does not compete with the
production of food, other than conversion of land from food production
to cellulose production (which has recently started to become an
issue, due to rising wheat prices.) The price per ton of the raw
material is thus much cheaper than that of grains or fruits. Moreover,
since cellulose is the main component of plants, the whole plant can
be harvested. This results in much better yields—up to 10 short tons
per acre (22 t/ha), instead of 4-5 short tons/acre
(9–11 t/ha) for the best crops of grain.
The raw material is plentiful. An estimated 323 million tons of
cellulose-containing raw materials which could be used to create
ethanol are thrown away each year in US alone. This includes 36.8
million dry tons of urban wood wastes, 90.5 million dry tons of
primary mill residues, 45 million dry tons of forest residues, and
150.7 million dry tons of corn stover and wheat straw.
Transforming them into ethanol using efficient and cost-effective
hemi(cellulase) enzymes or other processes might provide as much as
30% of the current fuel consumption in the United States.[citation
needed] Moreover, even land marginal for agriculture could be planted
with cellulose-producing crops, such as switchgrass, resulting in
enough production to substitute for all the current oil imports into
the United States.
Paper, cardboard, and packaging comprise a substantial part of the
solid waste sent to landfills in the United States each day, 41.26% of
all organic municipal solid waste (MSW) according to California
Integrated Waste Management Board's city profiles.
These city profiles account for accumulation of 612.3 short tons
(555.5 t) daily per landfill where an average population density
of 2,413 per square mile persists. All these, except gypsum board,
contain cellulose, which is transformable into cellulosic ethanol.
This may have additional environmental benefits because decomposition
of these products produces methane, a potent greenhouse gas.
Reduction of the disposal of solid waste through cellulosic ethanol
conversion would reduce solid waste disposal costs by local and state
governments. It is estimated that each person in the US throws away
4.4 lb (2.0 kg) of trash each day, of which 37% contains
waste paper, which is largely cellulose. That computes to
244 thousand tons per day of discarded waste paper that contains
cellulose. The raw material to produce cellulosic ethanol is not
only free, it has a negative cost—i.e., ethanol producers can get
paid to take it away.
In June 2006, a U.S. Senate hearing was told the current cost of
producing cellulosic ethanol is US $2.25 per US gallon (US
$0.59/litre), primarily due to the current poor conversion
efficiency. At that price, it would cost about $120
to substitute a barrel of oil (42 US gallons (160 L)), taking
into account the lower energy content of ethanol. However, the
Department of Energy is optimistic and has requested a doubling of
research funding. The same Senate hearing was told the research target
was to reduce the cost of production to US $1.07 per US gallon (US
$0.28/litre) by 2012. "The production of cellulosic ethanol represents
not only a step toward true energy diversity for the country, but a
very cost-effective alternative to fossil fuels. It is advanced
weaponry in the war on oil," said Vinod Khosla, managing partner of
Khosla Ventures, who recently told a
Reuters Global Biofuels Summit
that he could see cellulosic fuel prices sinking to $1 per gallon
within ten years.
In September 2010, a report by Bloomberg analyzed the European biomass
infrastructure and future refinery development. Estimated prices for a
litre of ethanol in August 2010 are EUR 0.51 for 1g and 0.71 for
2g.[clarification needed] The report suggested
Europe should copy the
current US subsidies of up to $50 per dry tonne.
Recently on October 25, 2012, BP, one of the leaders in fuel products,
announced the cancellation of their proposed $350 million
commercial-scale plant. It was estimated that the plant would be
producing 36 million gallons a year at its location in Highlands
County of Florida. BP has still provided 500 million US dollars for
biofuel research at the Energy Biosciences Institute. General
Motors (GM) has also invested into cellulosic companies more
specifically Mascoma and Coskata. There are many other companies
in construction or heading towards it.
Abengoa  is building a 25
million-gallon per year plant in technology platform based on the
Myceliophthora thermophila to convert lignocellulose into
fermentable sugars. Poet is also in midst of producing a 200 million
dollar, 25-million-gallon per year in Emmetsburg, Iowa. Mascoma now
partnered with Valero has declared their intention to build a 20
million gallon per year in Kinross, Michigan. China Alcohol
Resource Corporation has developed a 6.4 million liter cellulosic
ethanol plant under continuous operation.
Also, since 2013, the Brazilian company GranBio is working to become a
producer of biofuels and biochemicals. The family-held company is
commissioning an 82 million liters per year (22 MMgy) cellulosic
ethanol plant (2G ethanol) in the state of Alagoas, Brazil, which will
be the first industrial facility of the group. GranBio's second
generation ethanol facility is integrated to a first generation
ethanol plant operated by Grupo Carlos Lyra, uses process technology
from Beta Renewables, enzymes from
Novozymes and yeast from DSM.
Breaking ground in January 2013, the plant is in final commissioning.
According to GranBio Annual Financial Records, the total investment
was 208 million US Dollars.
Cellulases and hemicellulases used in the production of cellulosic
ethanol are more expensive compared to their first generation
counterparts. Enzymes required for maize grain ethanol production cost
2.64-5.28 US dollars per cubic meter of ethanol produced. Enzymes for
cellulosic ethanol production are projected to cost 79.25 US dollars,
meaning they are 20-40 times more expensive. The cost differences
are attributed to quantity required. The cellulase family of enzymes
have a one to two order smaller magnitude of efficiency. Therefore, it
requires 40 to 100 times more of the enzyme to be present in its
production. For each ton of biomass it requires 15-25 kilograms of
enzyme. More recent estimates are lower, suggesting 1 kg
of enzyme per dry tonne of biomass feedstock. There is also relatively
high capital costs associated with the long incubation times for the
vessel that perform enzymatic hydrolysis. Altogether, enzymes comprise
a significant portion of 20-40% for cellulosic ethanol production. A
recent paper estimates the range at 13-36% of cash costs, with a
key factor being how the cellulase enzyme is produced. For cellulase
produced offsite, enzyme production amounts to 36% of cash cost. For
enzyme produced onsite in a separate plant, the fraction is 29%; for
integrated enzyme production, the faction is 13%. One of the key
benefits of integrated production is that biomass instead of glucose
is the enzyme growth medium.
Biomass costs less, and it makes the
resulting cellulosic ethanol a 100% second-generation biofuel, i.e.,
it uses no ‘food for fuel’.
In general there are two types of feedstocks: forest (woody) Biomass
and agricultural biomass. In the US, about 1.4 billion dry tons of
biomass can be sustainably produced annually. About 370 million tons
or 30% are forest biomass. Forest biomass has higher cellulose and
lignin content and lower hemicellulose and ash content than
agricultural biomass. Because of the difficulties and low ethanol
yield in fermenting pretreatment hydrolysate, especially those with
very high 5 carbon hemicellulose sugars such as xylose, forest biomass
has significant advantages over agricultural biomass. Forest biomass
also has high density which significantly reduces transportation cost.
It can be harvested year around which eliminates long term storage.
The close to zero ash content of forest biomass significantly reduces
dead load in transportation and processing. To meet the needs for
biodiversity, forest biomass will be an important biomass feedstock
supply mix in the future biobased economy. However, forest biomass is
much more recalcitrant than agricultural biomass. Recently, the USDA
Forest Products Laboratory
Forest Products Laboratory together with the University of
Wisconsin–Madison developed efficient technologies that can
overcome the strong recalcitrance of forest (woody) biomass including
those of softwood species that have low xylan content. Short-rotation
intensive culture or tree farming can offer an almost unlimited
opportunity for forest biomass production.
Woodchips from slashes and tree tops and saw dust from saw mills, and
waste paper pulp are common forest biomass feedstocks for cellulosic
The following are a few examples of agricultural biomass:
Switchgrass (Panicum virgatum) is a native tallgrass prairie grass.
Known for its hardiness and rapid growth, this perennial grows during
the warm months to heights of 2–6 feet.
Switchgrass can be
grown in most parts of the United States, including swamplands,
plains, streams, and along the shores & interstate highways. It is
self-seeding (no tractor for sowing, only for mowing), resistant to
many diseases and pests, & can produce high yields with low
applications of fertilizer and other chemicals. It is also tolerant to
poor soils, flooding, & drought; improves soil quality and
prevents erosion due its type of root system.
Switchgrass is an approved cover crop for land protected under the
Conservation Reserve Program
Conservation Reserve Program (CRP). CRP is a government
program that pays producers a fee for not growing crops on land on
which crops recently grew. This program reduces soil erosion, enhances
water quality, and increases wildlife habitat. CRP land serves as a
habitat for upland game, such as pheasants and ducks, and a number of
Switchgrass for biofuel production has been considered for
Conservation Reserve Program
Conservation Reserve Program (CRP) land, which could increase
ecological sustainability and lower the cost of the CRP program.
However, CRP rules would have to be modified to allow this economic
use of the CRP land.
Miscanthus × giganteus is another viable feedstock for cellulosic
ethanol production. This species of grass is native to Asia and is the
sterile triploid hybrid of
Miscanthus sinensis and Miscanthus
sacchariflorus. It can grow up to 12 feet (3.7 m) tall with
little water or fertilizer input.
Miscanthus is similar to switchgrass
with respect to cold and drought tolerance and water use efficiency.
Miscanthus is commercially grown in the European Union as a
combustible energy source.
Corn cobs and corn stover are the most popular agricultural biomass.
It has been suggested that
Kudzu may become a valuable source of
The environmental impact from the production of fuels is an important
factor in determining its feasibility as an alternative to fossil
fuels. Over the long run, small differences in production cost,
environmental ramifications, and energy output may have large effects.
It has been found that cellulosic ethanol can produce a positive net
energy output. The reduction in green house gas (GHG) emissions
from corn ethanol and cellulosic ethanol compared with fossil fuels is
Corn ethanol may reduce overall
GHG emissions by about 13%,
while that figure is around 88% or greater for cellulosic
ethanol. As well, cellulosic ethanol can reduce carbon dioxide
emissions to nearly zero.
A major concern for the viability of current alternative fuels is the
cropland needed to produce the required materials. For example, the
production of corn for corn ethanol fuel competes with cropland that
may be used for food growth and other feedstocks. The difference
between this and cellulosic ethanol production is that cellulosic
material is widely available and is derived from a large resource of
things. Some crops used for cellulosic ethanol production include
switchgrass, corn stover, and hybrid poplar. These crops are
fast-growing and can be grown on many types of land which makes them
Cellulosic ethanol can also be made from wood residues
(chips and sawdust), municipal solid waste such as trash or garbage,
paper and sewage sludge, cereal straws and grasses. It is
particularly the non-edible portions of plant material which are used
to make cellulosic ethanol, which also minimizes the potential cost of
using food products in production.
The effectiveness of growing crops for the purpose of biomass can vary
tremendously depending on the geographical location of the plot. For
example, factors such as precipitation and sunlight exposure may
greatly effect the energy input required to maintain the crops, and
therefore effect the overall energy output. A study done over five
years showed that growing and managing switchgrass exclusively as a
biomass energy crop can produce 500% or more renewable energy than is
consumed during production. The levels of
GHG emissions and carbon
dioxide were also drastically decreased from using cellulosic ethanol
compared with traditional gasoline.
Corn-based vs. grass-based
See also: Environmental and social impacts of ethanol fuel in the
U.S., Indirect land use change impacts of biofuels, and Low-carbon
Summary of Searchinger et al.
comparison of corn ethanol and gasoline GHG emissions
with and without land use change
(Grams of CO2released per megajoule of energy in fuel)
Notes: Calculated using default assumptions for 2015 scenario for
ethanol in E85.
Gasoline is a combination of conventional and reformulated
In 2008, there was only a small amount of switchgrass dedicated for
ethanol production. In order for it to be grown on a large-scale
production it must compete with existing uses of agricultural land,
mainly for the production of crop commodities. Of the United States'
2.26 billion acres (9.1 million km2) of unsubmerged
land, 33% are forestland, 26% pastureland and grassland, and 20%
crop land. A study done by the U.S. Departments of Energy and
Agriculture in 2005 determined whether there were enough available
land resources to sustain production of over 1 billion dry tons
of biomass annually to replace 30% or more of the nation’s current
use of liquid transportation fuels. The study found that there could
be 1.3 billion dry tons of biomass available for ethanol use, by
making little changes in agricultural and forestry practices and
meeting the demands for forestry products, food, and fiber. A
recent study done by the University of Tennessee reported that as many
as 100 million acres (400,000 km2, or
154,000 sq mi) of cropland and pasture will need to be
allocated to switchgrass production in order to offset petroleum use
by 25 percent.
The neutrality of this article is disputed. Relevant discussion may be
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Currently, corn is easier and less expensive to process into ethanol
in comparison to cellulosic ethanol. The Department of Energy
estimates that it costs about $2.20 per gallon to produce cellulosic
ethanol, which is twice as much as ethanol from corn. Enzymes that
destroy plant cell wall tissue cost 30 to 50 cents per gallon of
ethanol compared to 3 cents per gallon for corn.
The Department of Energy hopes to reduce production cost to $1.07 per
gallon by 2012 to be effective. However, cellulosic biomass is cheaper
to produce than corn, because it requires fewer inputs, such as
energy, fertilizer, herbicide, and is accompanied by less soil erosion
and improved soil fertility. Additionally, nonfermentable and
unconverted solids left after making ethanol can be burned to provide
the fuel needed to operate the conversion plant and produce
electricity. Energy used to run corn-based ethanol plants is derived
from coal and natural gas. The Institute for Local Self-Reliance
estimates the cost of cellulosic ethanol from the first generation of
commercial plants will be in the $1.90–$2.25 per gallon range,
excluding incentives. This compares to the current cost of
$1.20–$1.50 per gallon for ethanol from corn and the current retail
price of over $4.00 per gallon for regular gasoline (which is
subsidized and taxed).
One of the major reasons for increasing the use of biofuels is to
reduce greenhouse gas emissions. In comparison to gasoline,
ethanol burns cleaner, thus putting less carbon dioxide and overall
pollution in the air. Additionally, only low levels
of smog are produced from combustion. According to the U.S.
Department of Energy, ethanol from cellulose reduces greenhouse gas
emission by 86 percent when compared to gasoline and to
corn-based ethanol, which decreases emissions by 52 percent.
Carbon dioxide gas emissions are shown to be 85% lower than those
Cellulosic ethanol contributes little to the greenhouse
effect and has a five times better net energy balance than corn-based
ethanol. When used as a fuel, cellulosic ethanol releases less
sulfur, carbon monoxide, particulates, and greenhouse gases.
Cellulosic ethanol should earn producers carbon reduction credits,
higher than those given to producers who grow corn for ethanol, which
is about 3 to 20 cents per gallon.
It takes 0.76 J of energy from fossil fuels to produce 1 J worth of
ethanol from corn. This total includes the use of fossil fuels
used for fertilizer, tractor fuel, ethanol plant operation, etc.
Research has shown that fossil fuel can produce over five times the
volume of ethanol from prairie grasses, according to Terry Riley,
President of Policy at the Theodore Roosevelt Conservation
United States Department of Energy
United States Department of Energy concludes that
corn-based ethanol provides 26 percent more energy than it
requires for production, while cellulosic ethanol provides
80 percent more energy.
Cellulosic ethanol yields 80 percent
more energy than is required to grow and convert it. The process
of turning corn into ethanol requires about 1700 times (by volume) as
much water as ethanol produced.[dubious – discuss] Additionally, it
leaves 12 times its volume in waste.
Grain ethanol uses only the
edible portion of the plant.
U.S. Environmental Protection Agency
Draft life cycle
GHG emissions reduction results
for different time horizon and discount rate approaches
(includes indirect land use change effects)
100 years +
30 years +
Corn ethanol (natural gas dry mill)(1)
Corn ethanol (Best case NG DM)(2)
Corn ethanol (coal dry mill)
Corn ethanol (biomass dry mill)
Corn ethanol (biomass dry mill with
combined heat and power)
Brazilian sugarcane ethanol
Cellulosic ethanol from switchgrass
Cellulosic ethanol from corn stover
Notes: (1) Dry mill (DM) plants grind the entire kernel and generally
only one primary co-product: distillers grains with solubles (DGS).
(2) Best case plants produce wet distillers grains co-product.
Cellulose is not used for food and can be grown in all parts of the
world. The entire plant can be used when producing cellulosic ethanol.
Switchgrass yields twice as much ethanol per acre than corn.
Therefore, less land is needed for production and thus less habitat
Biomass materials require fewer inputs, such as
fertilizer, herbicides, and other chemicals that can pose risks to
wildlife. Their extensive roots improve soil quality, reduce erosion,
and increase nutrient capture. Herbaceous energy crops reduce soil
erosion by greater than 90%, when compared to conventional commodity
crop production. This can translate into improved water quality for
rural communities. Additionally, herbaceous energy crops add organic
material to depleted soils and can increase soil carbon, which can
have a direct effect on climate change, as soil carbon can absorb
carbon dioxide in the air. As compared to commodity crop
production, biomass reduces surface runoff and nitrogen transport.
Switchgrass provides an environment for diverse wildlife habitation,
mainly insects and ground birds.
Conservation Reserve Program
Conservation Reserve Program (CRP)
land is composed of perennial grasses, which are used for cellulosic
ethanol, and may be available for use.
For years American farmers have practiced row cropping, with crops
such as sorghum and corn. Because of this, much is known about the
effect of these practices on wildlife. The most significant effect of
increased corn ethanol would be the additional land that would have to
be converted to agricultural use and the increased erosion and
fertilizer use that goes along with agricultural production.
Increasing our ethanol production through the use of corn could
produce negative effects on wildlife, the magnitude of which will
depend on the scale of production and whether the land used for this
increased production was formerly idle, in a natural state, or planted
with other row crops. Another consideration is whether to plant a
switchgrass monoculture or use a variety of grasses and other
vegetation. While a mixture of vegetation types likely would provide
better wildlife habitat, the technology has not yet developed to allow
the processing of a mixture of different grass species or vegetation
types into bioethanol. Of course, cellulosic ethanol production is
still in its infancy, and the possibility of using diverse vegetation
stands instead of monocultures deserves further exploration as
A study by Nobel Prize winner
Paul Crutzen found ethanol produced from
corn had a "net climate warming" effect when compared to oil when the
full life cycle assessment properly considers the nitrous oxide (N20)
emissions that occur during corn ethanol production. Crutzen found
that crops with less nitrogen demand, such as grasses and woody
coppice species, have more favourable climate impacts.
Cellulosic ethanol commercialization
Cellulosic ethanol commercialization
This section needs to be updated. Please update this article to
reflect recent events or newly available information. (November 2017)
Cellulosic ethanol commercialization
Cellulosic ethanol commercialization is the process of building an
industry out of methods of turning cellulose-containing organic matter
into fuel. Companies such as Iogen, POET, and
Abengoa are building
refineries that can process biomass and turn it into ethanol, while
companies such as DuPont, Diversa, Novozymes, and Dyadic are producing
enzymes which could enable a cellulosic ethanol future. The shift from
food crop feedstocks to waste residues and native grasses offers
significant opportunities for a range of players, from farmers to
biotechnology firms, and from project developers to investors.
The cellulosic ethanol industry developed some new commercial-scale
plants in 2008. In the United States, plants totaling 12 million
liters (3.17 million gal) per year were operational, and an additional
80 million liters (21.1 million gal.) per year of capacity - in 26 new
plants - was under construction. In Canada, capacity of 6 million
liters per year was operational. In Europe, several plants were
operational in Germany, Spain, and Sweden, and capacity of 10 million
liters per year was under construction.
Italy-based Mossi & Ghisolfi Group broke ground for its 13 MMgy
cellulosic ethanol facility in northwestern Italy on April 12, 2011.
The project will be the largest cellulosic ethanol project in the
world, 10 times larger than any of the currently operating
Ethanol Plants in the U.S.
(Operational or under construction)
Biomass Energy Corporation
Waste rice straw
Biomass, Agricultural and Municipal wastes
Corn cobs, switchgrass
Municipal solid waste
Gulf Coast Energy
Mossy Head, FL
KL Energy Corp.
POET-DSM Advanced Biofuels
Corn cobs, husks, and stover
Treutlen County, GA
Little Falls, MN
Highlands County, FL
Renewable energy portal
Cellulosic ethanol commercialization
Clonostachys rosea f. rosea
Life cycle assessment
Non food crops
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Biomass heating systems
Cellulosic ethanol commercialization
Energy content of biofuel
Food vs. fuel
Glued laminated timber
Oriented strand board
Oriented structural straw board
Structural insulated panel
Ramial chipped wood
List of woods
Non-timber forest products