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Creating Cellulosic Ethanol: Spinning Straw into Fuel
(Friday, May 20, 2005 -- CropChoice news) -- by Diane Greer In the Grimm Brother's fairy tale, Rumpelstiltskin spins straw into
gold. Thanks to advances in biotechnology, researchers can now transform
straw, and other plant wastes, into "green" gold - cellulosic ethanol.
While chemically identical to ethanol produced from corn or soybeans,
cellulose ethanol exhibits a net energy content three times higher than
corn ethanol and emits a low net level of greenhouse gases. Recent
technological developments are not only improving yields but also
driving down production cost, bringing us nearer to the day when
cellulosic ethanol could replace expensive, imported "black gold" with a
sustainable, domestically produced biofuel. Cellulosic ethanol has the potential to substantially reduce our
consumption of gasoline. "It is at least as likely as hydrogen to be an
energy carrier of choice for a sustainable transportation sector," say
the Natural Resources Defense Council (NRDC) and the Union of Concerned
Scientists in a joint statement. Major companies and research
organizations are also realizing the potential. Shell Oil has predicted
"the global market for biofuels such as cellulosic ethanol will grow to
exceed $10 billion by 2012." A recent study funded by the Energy
Foundation and the National Commission on Energy Policy, entitled
"Growing Energy: How Biofuels Can Help End America's Oil Dependence",
concluded "biofuels coupled with vehicle efficiency and smart growth
could reduce the oil dependency of our transportation sector by
two-thirds by 2050 in a sustainable way." ISN'T ALL ETHANOL THE SAME? Conventional ethanol and cellulosic ethanol are the same product, but
are produced utilizing different feedstocks and processes. Conventional
ethanol is derived from grains such as corn and wheat or soybeans. Corn,
the predominant feedstock, is converted to ethanol in either a dry or
wet milling process. In dry milling operations, liquefied corn starch is
produced by heating corn meal with water and enzymes. A second enzyme
converts the liquefied starch to sugars, which are fermented by yeast
into ethanol and carbon dioxide. Wet milling operations separate the
fiber, germ (oil), and protein from the starch before it is fermented
into ethanol. Cellulosic ethanol can be produced from a wide variety of cellulosic
biomass feedstocks including agricultural plant wastes (corn stover,
cereal straws, sugarcane bagasse), plant wastes from industrial
processes (sawdust, paper pulp) and energy crops grown specifically for
fuel production, such as switchgrass. Cellulosic biomass is composed of
cellulose, hemicellulose and lignin, with smaller amounts of proteins,
lipids (fats, waxes and oils) and ash. Roughly, two-thirds of the dry
mass of cellulosic materials are present as cellulose and hemicellulose.
Lignin makes up the bulk of the remaining dry mass. As with grains, processing cellulosic biomass aims to extract
fermentable sugars from the feedstock. But the sugars in cellulose and
hemicellulose are locked in complex carbohydrates called polysaccharides
(long chains of monosaccharides or simple sugars). Separating these
complex polymeric structures into fermentable sugars is essential to the
efficient and economic production of cellulosic ethanol. Two processing options are employed to produce fermentable sugars from cellulosic biomass. One approach utilizes acid hydrolysis to break down
the complex carbohydrates into simple sugars. An alternative method,
enzymatic hydrolysis, utilizes pretreatment processes to first reduce
the size of the material to make it more accessible to hydrolysis. Once
pretreated, enzymes are employed to convert the cellulosic biomass to
fermentable sugars. The final step involves microbial fermentation
yielding ethanol and carbon dioxide. Grain based ethanol utilizes fossil fuels to produce heat during the
conversion process, generating substantial greenhouse gas emissions.
Cellulosic ethanol production substitutes biomass for fossil fuels,
changing the emissions calculations, according to Michael Wang of
Argonne National Laboratories. Wang has created a "Well to Wheel" (WTW)
life cycle analysis model to calculate greenhouse gas emissions produced
by fuels in internal combustion engines. Life cycle analyses look at the
environmental impact of a product from its inception to the end of its
useful life. "The WTW model for cellulosic ethanol showed greenhouse gas emission
reductions of about 80% [over gasoline]," said Wang. "Corn ethanol
showed 20 to 30% reductions." Cellulosic ethanol's favorable profile
stems from using lignin, a biomass by-product of the conversion
operation, to fuel the process. "Lignin is a renewable fuel with no net
greenhouse gas emissions," explains Wang. "Greenhouse gases produced by
the combustion of biomass are offset by the CO2 absorbed by the biomass
as it grows." Feedstock sources and supplies are another important factor
differentiating the two types of ethanol. Agricultural wastes are a
largely untapped resource. This low cost feedstock is more abundant and
contains greater potential energy than simple starches and sugars.
Currently, agricultural residues are plowed back into the soil,
composted, burned or disposed in landfills. As an added benefit,
collection and sale of crop residues offer farmers a new source of
income from existing acreage. Industrial wastes and municipal solid waste (MSW) can also be used to
produce ethanol. Lee Lynd, an engineering professor at Dartmouth, has
been working with the Gorham Paper Mill to convert paper sludge to
ethanol. "Paper sludge is a waste material that goes into landfills at a
cost of $80/dry ton," says Lynd. "This is genuinely a negative cost
feedstock. And it is already pretreated, eliminating a step in the
conversion process." Masada Oxynol is planning a facility in Middletown, New York, to process
MSW into ethanol. After recovering recyclables, acid hydrolysis will be
employed to convert the cellulosic materials into sugars. "The facility
will provide both economic and environmental value," explains David
Webster, Executive Vice President of Masada. From an environmental
standpoint, the process reduces or eliminates the landfilling of wastes.
By-products of the process include gypsum, lignin and fly ash. "Under
normal operations, enough lignin will be recovered to make the plant
self-sufficient in energy," notes Webster. Perennial grasses, such as switchgrass, and other forage crops are
promising feedstocks for ethanol production. "Environmentally
switchgrass has some large benefits and the potential for productivity
increases," says John Sheehan of the National Renewable Energy
Laboratory (NREL). The perennial grass has a deep root system, anchoring
soils to prevent erosion and helping to build soil fertility. "As a
native species, switchgrass is better adapted to our climate and soils,"
adds Nathanael Criers, NRDC Senior Policy Analyst. "It uses water
efficiently, does not need a lot of fertilizers or pesticides and
absorbs both more efficiently." OVERCOMING THE RECALCITRANCE OF BIOMASS Reducing the cost and improving the efficiency of separating and
converting cellulosic materials into fermentable sugars is one of the
keys to a viable industry. "On the technology side, we need a major push
on overcoming the recalcitrance of biomass," continues Greene, referring
to the difficulty in breaking down complex cellulosic biomass
structures. "This is the greatest difficulty in converting biomass into
fuel." R&D efforts are focusing on the development of cost-effective
biochemical hydrolysis and pretreatment processes. Technological
advances promise substantially lower processing costs in these fields
compared to acid hydrolysis. "In the enzyme camp, we have only scratched
the surface of the potential of biotechnology to contribute to this
area," adds Reade Dechton of Energy Futures Coalition. "We are at the
very beginning of dramatic cost improvements." The Department of Energy (DOE) Biofuels program has identified the high
cost of cellulose enzymes as the key barrier to economic production of
cellulosic ethanol. Two enzyme producers, Genencor International and
Novozymes Biotech, have received research funding from DOE to engineer
significant cost reductions and efficiency improvements in cellulose
enzymes. In October of 2004, Genencor announced a 30-fold reduction in
the cost of enzymes to a range of $.10-$.20 per gallon of ethanol. To
achieve the savings, Genencor developed a mixture of genetically
modified enzymes that act synergistically to convert cellulose into
glucose. Novozymes Biotech has also progressed in reducing enzyme costs
from $5.00 to $.30 per gallon of ethanol. In April of 2004, Novozymes
was granted a one year extension and awarded an additional $2.3 million
to further reduce the cost of enzymes to $.10 per gallon. Another major thrust of R&D efforts is devoted to improving pretreatment
technologies. Pretreatment is required to break apart the structure of
biomass to allow for the efficient and effective hydrolysis of
cellulosic sugars. "Seventy percent of total mass is composed of
structural carbohydrates, either five or six carbon sugars," explains
Bruce Dale, a chemical engineering professor at Michigan State
University. "Getting higher yields of these sugars efficiently without
degrading the materials is the focus of pretreatment." Pretreatment technologies utilize dilute acid, steam explosion, ammonia
fiber explosion (AMFE), organic solvents or other processes to disrupt
the hemicellulose/lignin sheath that surrounds the cellulose in plant
material. Each technology has advantages and disadvantages in terms of
costs, yields, material degradation, downstream processing and
generation of process wastes. One of the most promising pretreatment technologies, Ammonia Fiber
Explosion (AMFE), employs liquid ammonia under moderate heat and
pressure to separate biomass components. "The goal is to get the plant
material to provide you with a lot of sugar without a lot of extra
cost," says Dale who is working on optimizing the process. CONSOLIDATED BIOPROCESSING Many experts believe consolidated bioprocessing (CBP) shows the greatest
potential for reducing conversion costs. CBP employs recombinant DNA
technology to alter the DNA of a microbe by joining it with genetic
material from one or more different organisms. In the case of cellulosic
ethanol production, the goal is to genetically engineer microbes with
the traits necessary for one-step processing of cellulosic biomass to
ethanol. Dartmouth engineering professor Lynd is utilizing CBP techniques to
produce microbial systems combining both enzymatic hydrolysis and
fermentation operations. Lynd's group is working to consolidate
cellulose production, cellulose hydrolysis, hexose fermentation and
process fermentation into one organism while maintaining sufficiently
high yields. FEEDSTOCK RESOURCES Can American agricultural systems support large-scale cellulosic ethanol
production? That is the big question. Do we have sufficient land? Can
biomass be supplied without impacting the cost of agricultural land,
competing with food production and harming the environment? The answer
to these questions ranges from no to a qualified yes, contingent upon
R&D efforts, technological innovation and government policy. Battelle's recent report entitled, "Near Term U.S. Biomass Potential",
looked at a scenario for producing 50 billion gallons of ethanol per
year from cellulosic biomass. "The primary biomass supply would consist
of waste biomass streams plus the production of energy crops." The waste
stream was estimated to contribute 40-50% of the supply. The report
concluded that the expansion of biomass supplies needed to achieve this
level of production "would not result in large impacts on the
agricultural system." Beyond this level of production, "dedicated energy
crops would be required with implications for the cost of cropland and
competition with food crops." The NRDC "Growing Energy" report approached the question from a
different angle. It asked if there were technological, process and
policy changes that would allow biofuels to fulfill a large proportion
of energy required by vehicles. The research constrained land
utilization to the amount already under cultivation while insuring
sufficient land for food and textile production in addition to employing
resources in a sustainable manner. "There is a lot that needs to happen if we are going to take advantage
of this technology," says Nathanael Greene, author of the "Growing
Energy" report. "If we are serious about ending our dependency on oil,
we need to innovate and change." Greene and his colleagues identified
several areas crucial to making biofuels work: increased vehicle
efficiency, smart growth policies, improvements in conversion
efficiencies, utilization of energy crops such as switchgrass,
co-production of animal protein and increased switchgrass yields. Assuming no increase in vehicle efficiency and a continued growth in
driving, the U.S. is on a path to consume 290 billion gallons of
gasoline in our cars and trucks by 2050. The report found increasing
vehicle efficiencies to 50 mpg or better and instituting smart growth
policies could reduce consumption to 108 billion gallons by 2050. "Our
goal is mobility, not energy consumption," says Lend. "For a given unit
of energy, two-thirds can be replaced by efficiency and one third by
supply. We are kidding ourselves if we think we can supply our way out
of this. We can make the biggest impacts fastest by impacting the
efficiency equation." The "Growing Energy" report projects conversion efficiencies, the number
of gallons of ethanol produced per dry ton of biomass, to improve from
50 gallons per dry ton to 117 gallons per dry ton. One hundred seventeen
gallons of ethanol per dry ton equates to 77 gallons of gas equivalent
per dry ton (one gallon of ethanol contains 66% of the energy content of
gasoline). The bulk of the increase is expected to come from R&D driven
advances in biological processing. "The key to producing enough ethanol is switchgrass," says Greene.
Switchgrass shows great potential for improving yields, offers
environmental benefits and can be grown in diverse areas across the
country. Current average yields are five dry tons per acre. Crop experts
have concluded standard breeding techniques, applied progressively and
consistently, could more than double the yield of switchgrass. Yield
improvements predicted by the report of 12.4 dry tons per acre are in
keeping with results from breeding programs with crops such as corn and
other grasses. The innovations discussed have a net effect of reducing
the total land required to grow switchgrass to an estimated 114 million
acres. Sufficient switchgrass could be grown on this acreage to produce
165 billion gallons of ethanol by 2050, which is equivalent to 108
billion gallons of gasoline. The next logical question is how do we
integrate switchgrass production into our agricultural systems. The
answer lies with the ability to produce animal protein from switchgrass.
"If we have cost-effective agricultural policy, farmers will rethink
what they plant," says Lynch "For example, we are using 70 million acres
to grow soybeans for animal feed. You can grow more animal feed protein
per acre with switchgrass. If there were a demand for biomass feedstocks
to produce ethanol and other biofuels, farmers would be able to increase
their profits by growing one crop producing two high value products."
While the promise of higher profits and more products is enticing,
planting new crops and introducing new methodologies will present risks
to farmers. Switchgrass is a perennial that takes several years to
mature. Farmers will not make such a commitment unless they feel
confident in the economics. TRANSITIONING TO CELLULOSIC ETHANOL One of the attractions of biofuels is they can be utilized in today's
internal combustion engines with little or no changes. "The only source
of liquid transportation fuels to replace oil is biomass," says Greene.
"Everyone is excited about hydrogen but there are some very serious
technical and infrastructure challenges. If you can stick with a liquid
fuel which is compatible with our infrastructure and the vehicles we
use, it is an easier transformation." Light duty cars and trucks can already run on gasoline containing 10%
ethanol. There are an estimated 1.2 million flex-fuel cars on the road
capable of running on a wide range of biofuels including E85, a mixture
of 85% ethanol and 15% gasoline. "Manufacturing flex-fuel vehicles is a
trivial change," said Dechton. "It costs less than $200 per vehicle.
They are selling them now and people do not know that they are buying
them." New vehicles with catalyst systems, certified for California Level II or
Federal Tier 2 standards, have very low CO, VOC and NOX emissions. Using
higher blends of ethanol in these vehicles should not pose any problem
in increased NOX emissions. Any increase in NOX emission due to ethanol
use will be short-term, dependent upon the rate at which old cars are
replaced with new, lower emission models. ECONOMICS, THE ENVIRONMENT AND ENERGY SECURITY The arguments in favor of cellulosic ethanol as a replacement for
gasoline in cars and trucks are compelling. Cellulosic ethanol will
reduce our dependence on imported oil, increase our energy security and
reduce our trade deficit. Rural economies will benefit in the form of
increased incomes and jobs. Growing energy crops and harvesting
agricultural residuals are projected to increase the value of farm
crops, potentially eliminating the need for some agricultural subsidies.
Finally, cellulosic ethanol provides positive environmental benefits in
the form of reductions in greenhouse gas emissions and air pollution. There is a growing consensus on the steps needed for biofuels to
succeed: increased spending on R&D in conversion and processing
technologies, funding for demonstration projects and joint investment or
other incentives to spur commercialization. "If you do not do all three
of these pieces, the effort is likely to stall," said Greene. "The
challenge is to be really focused and make the commitment to make
biofuels a part of our economy. We need to make these technologies
work." There is also agreement on one of the main factors impeding the
development of biofuels - inadequate government funding. "We are grossly
under investing in this area," says Dechton. "We are piddling along at
30 or 40 million dollars per year. This is a national security issue."
Sheehan agrees, adding "the other problem is over the last several years
Congressional earmarking has been horrendous. It is splintering critical
resources, as a result effectiveness is way down. We do not have well
aligned, consistently directed R&D effort." The "Growing Energy" report calls for $2 billion in funding for
cellulosic biofuels over the next ten years, with $1.1 billion directed
at research, development and demonstration projects and the remaining
$800 million slated for the deployment of biorefineries. Other advocated
subsidies and incentives for the industry include production tax
credits, bond insurance for feedstock sellers and biofuels purchasers
and efficacy insurance. "We would like to see private insurance but
lacking private sector involvement, government should offer the
insurance," said Greene. "The idea has two features, the amount of money
available goes down over time, so by 2015 the industry is ready to stand
on its own two feet and, second the dollars available to developers is
in a menu format. We will let them pick subsidies that work best for
their product." Given sufficient investment in research, development, demonstration and
deployment, the report projects biorefineries producing cellulosic
ethanol at a cost leaving the plant between $.59-$.91 per gallon by
2015. The price range is dependent upon plant scale and efficiency
factors. At these prices, biofuels would be competitive with the
wholesale price of gasoline. In the past, discussions regarding ethanol as a potential replacement
for gasoline have centered on the availability of suitable land in
addition to a feed versus fuel debate. Technological and process
advances coupled with the promise of biorefineries are allowing us to
refocus the debate. Scenarios exist where well directed public policies
emphasizing biofuels investment and incentives in addition to fuel
efficiency could promote a transition to cellulosic ethanol. Given the
right policy choices, America's farmers could one day be filling both
our refrigerators and our gas tanks. Development of Biorefineries One of the essential elements in the economical and efficient production
of cellulosic ethanol is the development of biorefineries. The concept
of a biorefinery is analogous to a petroleum refinery where a feedstock,
crude oil, is converted into fuels and co-products such as fertilizers
and plastics. In the case of a biorefinery, plant biomass is used as the
feedstock to produce a diverse set of products such as animal feed,
fuels, chemicals, polymers, lubricants, adhesives, fertilizers and
power. While similar to oil refineries, biorefineries exhibit some important
differences. First, biorefineries can utilize a variety of feedstocks.
Consequently, they require a larger range of processing technologies to
deal with the compositional differences in the feedstock. Second, the
biomass feedstock is bulkier (contains a lower energy density) relative
to fossil fuels. Therefore, economics dictate decentralized
biorefineries closer to feedstock sources. The economics of biorefineries are dependent upon the production of
co-products such as power, protein, chemicals and polymers to provide
revenue streams to offset processing costs, allowing cellulosic ethanol
to be sold at lower prices. Generation of co-products also results in
greater biomass and land use efficiencies along with a more effective
use of invested capital. Process and technological innovations are focusing on utilizing every
component of the biomass feedstock. Essentially, the waste or
by-products from one process become the raw materials for another
product. "The objective will be to utilize the entire barrel of
biomass," adds Bruce Dale, professor of chemical engineering at Michigan
State. Economics will drive biorefineries to undergo "continuous,
incremental process improvements" in a quest to improve yields, increase
the value of co-products and utilize "every fraction of the raw
materials." Lignin and protein, two important co-products, have the potential to
significantly improve the economics of biorefineries. Lignin is a
non-fermentable residue from the hydrolysis process. It has an energy
content similar to coal and is employed to power the operation, thereby
reducing production costs. "There is enough residue [lignin] left over
to meet the energy needs of the process plus make additional ethanol or
electricity," says Eric Larson, a research engineer at the Princeton
Environmental Institute. DEVELOPMENT OF BIOREFINERIES Power can be produced from lignin via direct combustion with steam power
generation or gasification. Gasification burns the lignin in a closed
process with elevated air pressure and small amounts of oxygen. The
result is a raw fuel gas and ash. Ash is a good material to put back on
the field, while waste heat is recovered from the process and reused. Production of protein will not only bolster process economics but also
increase land efficiencies by allowing the production of both fuel and
animal feed on the same acre. The NHOC "Growing Energy" report estimates
the co-production of animal protein could lower the cost of cellulosic
ethanol by $0.11-$0.13 per gallon, depending on the size of the
production facility. The leaves and stems of the plants are the source of protein found in
cellulosic biomass feedstocks. The protein, referred to as leaf protein,
is used in animal feed. Agricultural residues contain four to six%
protein while crops like switchgrass and alfalfa contain 10% and 15 to
20% respectively. Leaf protein is extracted from the feedstock utilizing
an alkaline water solution heated to 50 to 60 degrees centigrade.
Standard membrane filtration technology is employed to separate the
protein from the other feedstock components. "You get 60% of the
protein," says Dale. "Up to 80-90% of the protein can be extracted with
extensive washing." COMMERCIALIZING BIOREFINERIES To date, only a few small demonstration biorefineries are producing
ethanol from cellulosic feedstock. Iogen is operating a facility in
Ottawa, Canada, utilizing proprietary enzyme hydrolysis and fermentation
techniques to produce 260,000 gallons a year of ethanol from wheat
straw. The company has announced plans for a commercial-scale facility
in western Canada, the U.S or Germany. Iogen is seeking government
financial support and other incentives to help fund the $350 million
expected cost. "The technology is ready for commercial-scale demonstration," says Reade
Dechton, of the Energy Futures Coalition. "The industry is stuck on
first of a kind technology. There is a role and need for government
assistance. We think that the investment that would be required to get
these first plants built is very small compared to the benefits that
would result and the risks that we are facing." John Sheehan of National Renewable Energy Laboratory has been utilizing
process simulation software to look at biorefinery design. "Scale is a
huge issue," said Sheehan. "The cost of capital is extremely scale
specific." He has discovered that biorefineries need to be able to
process 5,000 to 10,000 tons of biomass per day to be economically
viable. "Below 2,000 tons per day, capital costs skyrocket." "Capital is a problem," says Brent Erikson, Vice President of the
Biotechnology Industry Organization (BIO). "Nobody has constructed a
commercial size biorefinery. They cost between $200 and $250 million to
build." Erickson's group is trying to facilitate funding of commercial
biorefineries. "We have a proposal sent to the White House for federal
loan guarantees to build these biorefineries," comments Erikson. The
proposal requests upwards of $750 million in loan guarantees for
full-scale commercial plants. Sheehan believes existing niche markets can play a vital role in the
development of cellulosic biorefinery technologies. "There is technology
now, under niche market circumstances, that is almost ready to go," says
Sheehan. "A good place to put investments is testing core pieces of the
technology in existing corn ethanol plants." Two companies are exploring new technologies and processes to integrate
cellulosic biomass in existing corn ethanol and wet grain milling
facilities. Broin has received a $5.4 million grant from DOE to
investigate employing fiber and corn stover in the production of
ethanol. A $17.7 million grant from DOE is funding Abengoa's research on
processes to pretreat a blend of distillers' grain and corn stover to
produce ethanol. The protect calls for the building of a pilot-scale
facility in York, Nebraska. Several biorefineries under development are focused on applying
innovations to existing acid hydrolysis processing techniques. BC
International is applying a proprietary acid hydrolysis technology to
agricultural residues and forest thinning feedstocks to produce ethanol.
The company is developing facilities in Louisiana, California and Asia
and claims their process produces ethanol at costs lower than
conventional ethanol plants. Arkenol and Masada Corporation (mentioned
earlier) are also developing biorefineries in the U.S. utilizing acid
hydrolysis process to convert cellulosic wastes into ethanol. A Japanese
company, licensing Arkenol's acid hydrolysis technology, is already
producing ethanol in a plant in Izumi, Japan from waste. | |
