d.schieder - bio-ethanol - existing pathways - paper

7/28/2019 D.schieder - Bio-Ethanol - Existing Pathways - Paper

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1st European Summer School on Renewable Motor Fuels

Birkenfeld, Germany, 29 31 August 2005

Bio-ethanol existing pathways

D. Schieder

Technical university of Munich

Monday, 29 August 2005, 14:40 15:20


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Bio-ethanol existing pathways

Dr. Doris Schieder

Institute of Technology of Biogenic Resources

Petersgasse 1894315 Straubing

Germany

Phone +49 9421 187 108 Fax +49 9421 187 111

Email [email protected]

1. Bio-ethanol in the transportation sector

Fuel ethanol for the transportation sector has been used as early as 1900. Famousforerunners in the automobile industry like Henry Ford strongly encouraged this option.

However, the expansion of the petroleum industry in the early 20th

century resulted in thepreference for the less cost-intensive mineral oil.

Today ethanol is a well-established transportation fuel. In 2004 around 32 billion litres of fuelethanol were produced worldwide. The production has been increasing continuously sincethe eighties especially in the US and Canada (Figure 1). Up to now the main producers andconsumers are Brazil and the US. This is the result of regulations in these countries whichhave been introduced to promote the home agricultural industry or the reduction of trafficemissions in conurbations (e. g. the proalcool-programme in Brazil in the early 1970s or theNorth-American clean-air-acts of the 1990s). It is because of the clean-air-act that as amatter of routine in many conurbations throughout the US up to 10% ethanol is added togasoline fuels.

0

5

10

15

20

25

30

35

1980 1985 1990 1995 2000 2001 2002 2003 2004

billionl

itres

peryear

World

Brazil

US/Canada

Europe

Figure 1: Production of fuel ethanol 1980-2004.

Today there is a foreseeable shortage of mineral oil and simultaneously an increasingdemand for energy in the industrial countries as well as in a growing number of fastdeveloping countries. Even in Europe the requirements of a sustainable protection of theclimate make bio-ethanol an important near-term option to gradually substitute renewableenergy sources for fossil ones. The EU bio-fuels directive 2003/30/EG therefore promotesbio-fuels including fuel ethanol, if it is produced from biogenic resources (bio-ethanol). Bio-ethanol (water free fuel ethanol produced from biogenic resources) can be a substitute of

prime importance in fuel blends with gasoline. To reach the EU-directives goal of arenewable bio-fuels share of 5.75%, around 12 billion litres of bio-ethanol will be needed in2010. As a consequence, the bio-ethanol production in European countries (figure 1, table 2)is expected to increase significantly during the next years.

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Positive effects of fuel blends of gasoline and ethanol are the substantial improvement in theantiknock resistance and the reduction of motor emissions mainly as far as particles, CO andNOx are concerned. In contrast to gasoline fuels, bio-ethanol contains neither sulfur noraromatic compounds. The research octane number (RON) of ethanol is around 108.Compared to gasoline fuels (RON around 92-96) it enables a higher engine power whereas

its energy content is around 30% lower (Table 1).

0-2181635Oxygen content [%]

0.760.740.740.79Density at 15C

[kg/l]

0.60.71.51.5Viscostiy at 20C

[mm2

/s]

1.00.800.830.66Fuel equivalent togasoline

92-96113-120115-118108Octane number (RON)

3225.926.921.3Heating value

[MJ/l]


[MJ/kg]

GasolineMTBEETBEBio-ethanol

0-2181635Oxygen content [%]

0.760.740.740.79Density at 15C

[kg/l]

0.60.71.51.5Viscostiy at 20C

[mm2

/s]

1.00.800.830.66Fuel equivalent togasoline

92-96113-120115-118108Octane number (RON)


[MJ/l]


[MJ/kg]

GasolineMTBEETBEBio-ethanol

Table 1: Selected fuel properties of bio-ethanol, gasoline and butyl-ethers.

There are long years of experience on the use of bio-ethanol in the transportation sector,esp. in Brazil and in the US. Without technical modifications, gasoline engines can beoperated up to blends of 10-20%v/v ethanol. The operation with higher blends or with pure,esp. with hydrous ethanol requires technically modified motors.

Throughout the EU, the addition of ethanol to gasoline is limited to 5%v/v by the fuelstandard DIN EN 228. Blends of 0 to 5%v/v ethanol, show a vapour pressure anomaly.Especially during the summer months the vapour pressure may exceed the limits of DIN EN228 (60 kPa).

The chemical reaction of ethanol with isobutene, a product of oil refineries, gives ETBE(ethyl-tertiary-butyl-ether). ETBE can be added to gasoline fuels up to 15%v/v according toDIN EN 228. It can be used to substitute MTBE (methyl-tertiary-butyl-ether) which iscommonly used to improve the antiknock resistance of unleaded gasoline fuels. As MTBE issupposed to cause serious health risks, ETBE is regarded to be a less harmful substitute.Blends of ETBE and gasoline show no excessive vapour pressure (Table 1). In France,blends of ETBE from bio-ethanol now have been used in the transportation sector for morethan 10 years.

Since the early nineties, different producers offer flexible-fuel vehicles which can be operatedwith blends from pure gasoline up to 85% ethanol (E85). The vehicles are equipped withsensors which identify the blending grade of the fuel in order to control and adjust the criticalmotor operation parameters, like fuel injection, air supply or ignition. Flexible-fuel vehiclesmeanwhile are very well established in the US. E85 blends are offered at separate gasolinepumps. In Europe, Sweden is performing projects to promote flexible-fuel vehicles since1995. Projects in other EU countries are on the launching pad, e.g. in Germany.

However, the EU member states currently seem to prefer the blending with ETBE. Table 2shows the typical use of bio-ethanol fuels in selected countries.

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Estimated fuel ethanolproduction in 2003

[million litres]Preferred feedstockTypical fuel use

startup of first plants in 2004

50

225

125

n.a.

10 600

around 14 000

wheatE10, E85, E95Sweden

wheat, ryeETBE ?Germany

wheat, barleyETBESpain

sugar beet, wheatETBEFrance

wheatE10Canada

cornE10 and E85US

sugar caneblends up to E26Brazil

Estimated fuel ethanolproduction in 2003

[million litres]Preferred feedstockTypical fuel use

startup of first plants in 2004

50

225

125

n.a.

10 600

around 14 000

wheatE10, E85, E95Sweden

wheat, ryeETBE ?Germany

wheat, barleyETBESpain

sugar beet, wheatETBEFrance

wheatE10Canada

cornE10 and E85US

sugar caneblends up to E26Brazil

Table 2: Use of ethanol based fuels and preferred feedstock crops in selected countries.

The blending of diesel fuels with bio-ethanol has not been commercially experienced inEurope. With an increasing number of diesel engines, this option is currently discussedagain, e.g. in Germany. Blending of diesel is supposed to be possible at levels up to 15%with suitable additives. There have been recent commercial experiments in the US, Brazil,Australia, and Sweden, which indicate a reduction of motor emissions, esp. of particles andCO. However, the flashpoint reduction (from >50C to


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about 92-96%v/v quality, which must be dehydrated by e.g. molecular sieves to giveanhydrous bio-ethanol (min. 99%v/v). The fermentation residue contains not fermentedfeedstock material as well as yeasts. Fermentation residues of corn and grains like wheat orrye are called stillage. Stillages are valuable fermentation co-products which can be usedas high protein animal feed. Industrial ethanol plants commonly evaporate and dry the

stillage. According to its composition it is preferably sold as distillers dried grain (DDG) ordistillers dried grain with solubles (DDGS). Alternatively, the stillage can be used to produceenergy by the biogas pathway or by combustion of the DDGS.

The production of ethanol from sugar and starch crops is technically proven and has beenperformed in an industrial scale for many years. The conversion of lignocellulosic feedstock,however, needs a distinct treatment in some aspects.

Lignocellulose mainly consists of about 40-50% cellulose, 15-35% hemicellulose and 10-30%lignin. These components form a close, partially crystalline compound which is hardlyaccessible to microbiological degradation. Prior to ethanol fermentation this compound has tobe disintegrated and the polysaccharides cellulose and hemicellulose have to be hydrolyzedto give fermentable sugars. Crucial steps are the technical performance of the disintegration

and saccharification as well as the fermentation.Former technologies using acid percolation, e.g. the Scholler-process, are considered to beeconomical not feasible. Advanced technologies propose two staged processes for thefeedstock disintegration and saccharification. At the first stage, the feedstock is crushed andthe lignocellulosic compound is disintegrated by a chemical or physico-chemical treatmentwith acids, alkali and/or steam at 100-220C. The subsequent saccharification is performedusing acids or enzymes which hydrolyse cellulose and/or hemicelluloses. The enzymaticsaccharification is much more selective and less destructive towards the saccharides thanthe acidic saccharification. However, the saccharification of cellulose requires distinctenzyme types and higher amounts of enzymes than the conversion of starch. This makes theenzymatic hydrolysis of lignocellulose much more expensive. To improve the situation and

reduce the costs, current research and development efforts are directed towards animprovement of the catalytic activity and towards less expensive enzyme productiontechnologies.

Classical fermentation yeasts are not very well suited for the conversion of lignocellulosicfeedstock. Yeasts ferment glucose derived of cellulose but are not able to ferment the mainsaccharide components of hemicellulose, like xylose or arabinose. However, thefermentation of hemicellulose is important to achieve sufficiently high ethanol yields andgood economical performances. During the past decades, biotechnological methods wereused to reach this target. Genetically modified bacteria, e.g. E. Coliand Zymomonas mobilis,were successfully engineered which are able to ferment almost all types of saccharides inlignocellulosic feedstock with high yields and high selectivity. However, for a commercial

application there are still some crucial hurdles left.The fermentation residues, which contain mainly lignin, can be used as burner fuels to coverthe energy demand of the ethanol plant and even produce surplus heat and electricity.

The production of bio-ethanol from lignocellulosic feedstock by the enzymatic pathway is nowwell developed but has not yet been commercially used. The Canadian enzyme producerIogen Inc. runs a first technical-scaled demonstration plant since 2004. Further industrialscale pilot-plant projects using chemical or enzymatic saccharification are in preparation allover the world.

As an alternative to the fermentation pathway, conversion technologies are developed whichuse thermo-chemical gasification. The product gas can be converted to e.g. methanol in the

first stage. In a second step, methanol and the product gas give ethanol via homologation.The main benefit of the thermo-chemical pathway is the conversion of the entire biomass.Even lignin which is not accessible to microbiological fermentation can be converted.

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However, the subsequent conversion steps require the purification of the raw gas and areaffected by side-reactions which lower the product yields. Despite of the high feedstockconversion rate in the gasification step this reduces the overall energy efficiency and theeconomy of the process.

Figure 2 reflects the most important bio-ethanol production pathways from different feedstock

crops.

Sugar crops

Sugar beetSweet sorghumSugar cane

Starch crops

CornWheatRyeBarley

Lignocellulosicfeedstock

HardwoodSoftwoodMiscanthusSwitchgrass

StrawCorn stoverWood residuesVerge grassCellulosicwastes

Crushing

Wet or dry milling

Mashing with hotwater/steam

Sugar extraction

with steam/hotwater

Enzymaticliquefaction andsaccharificationby amylases

Crushing

Pretreatment

- Steam explosion- Acid hydrolysis- Alcaline

hydrolysis- NH3 fiber

explosion

Enzymaticsaccharificationby cellulases

Feedstock Conversion Pathways and Ethanol Recovery Co-products

Acidicsaccharification

Crushing

Themochemicalgasification

Production ofMethanol

Homologationand ethanolrecovery

Fermentation

Rectification

Ethanolpurification

Heat

Electricity

VinasseAnimal feed

BagasseHeat, Electricity

Animal feed,e.g. DDGS

(HeatElectricity)

LigninHeat , Electricity

CaSO4

(Animal feed)

Sugar crops

Sugar beetSweet sorghumSugar cane

Starch crops

CornWheatRyeBarley

Lignocellulosicfeedstock

HardwoodSoftwoodMiscanthusSwitchgrass

StrawCorn stoverWood residuesVerge grassCellulosicwastes

Crushing

Wet or dry milling

Mashing with hotwater/steam

Sugar extraction

with steam/hotwater

Enzymaticliquefaction andsaccharificationby amylases

Crushing

Pretreatment

- Steam explosion- Acid hydrolysis- Alcaline

hydrolysis- NH3 fiber

explosion

Enzymaticsaccharificationby cellulases

Feedstock Conversion Pathways and Ethanol Recovery Co-products

Acidicsaccharification

Crushing

Themochemicalgasification

Production ofMethanol

Homologationand ethanolrecovery

Fermentation

Rectification

Ethanolpurification

Heat

Electricity

VinasseAnimal feed

BagasseHeat, Electricity

Animal feed,e.g. DDGS

(HeatElectricity)

LigninHeat , Electricity

CaSO4

(Animal feed)

Figure 2: Production pathways of bio-ethanol from various feedstock.

Compared to the fermentation of starch and sugar crops, the conversion of lignocellulosesoffers important benefits, esp. concerning the feedstock availability. On the other hand, theenzymatic as well as the thermo-chemical pathway require much more sophisticatedconversion technologies than traditional sugar or starch fermentation pathways.

4. Energetic, economical and ecological aspects

The fermentation pathways require thermal energy, esp. steam, for feedstock pre-treatment,

rectification and for evaporation and drying of the fermentation residues. Modern conversionprocesses are highly optimized and their energy consumptions are minimized. Multi-stagedevaporators and heat recovery systems serve to reduce the remaining need of energy.However, extensive heat recovery systems enhance the costs for investments andmaintaining of the ethanol plant. Therefore, an individual balance has to be found betweenthe costs of heat recovery and of energy consumption.

The overall production chain also requires energy for the supply of the feedstock and for thedistribution of the fuel ethanol. This means for cultivation, harvesting, transportation, andstorage. The ratio between energy output (fuel ethanol) and fossil energy input of the overallprocess is reported to be in the range of 0.95-3.2 for advanced corn, grain, and sugar beetprocessing. The efficiency preferably depends on the feedstock type and on the assumptionsof credits for co-products, e. g. stillage, of the conversion process. Without co-productcredits, the ratio is in the range of 0.95-1.8 while it is around 1.2-3.2 including co-productcredits. For gasoline it is around 0.79. For sugar cane processing in Brazil the input of fossilenergy is considerably low, as usually bagasse is used to produce process heat and

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electricity. Recent studies report energy efficiencies in the range of 8-10. The efficiency ofcorn or grain processing also could be improved significantly, if feedstock or fermentationresidues were used to provide process heat and electricity by combustion or by biogasproduction. However, currently the production of animal feed from stillage is still ofeconomical preference. The situation may change e.g. with raising costs for burner fuels and

enhanced benefits for biomass derived electricity. Lignocellulosic ethanol engineering studiescommonly assume the use of feedstock residues (lignin) and of biogas from internal wastewater treatment to cover the energy demand of the ethanol plant. Therefore, fossil energyefficiencies in the range of Brazilian cane processing or even higher may be reached.

The production costs of bio-ethanol mainly depend on the plant capacity, the type offeedstock used and on the location. As a consequence of the economy of scale, industrialfuel ethanol plants today are preferably designed for annual production capacities of morethan 100 million litres. Table 3 shows an estimation of the average production costs ofindustrial scaled plants for Europe and the US. Estimations for industrial fuel ethanol plantsin Europe given by different authors differ very much, as plant size, location properties, andfeedstock costs also differ considerably.

262198> 50> 5060-260> 50Ethanol capacity

[Million litres per year]

0.282 $0.36 $0.30 $0.40-0.62 0.49-0.55 0.41-0.60 Total production costs perlitre ethanol

start up 2010

Corn stover

(NREL 2002)

near-term

Poplar wood

(NREL 1999)

0.43 $0.55 $0.46 $0.64-0.94 0.74-0.83 0.62-0.91 Total production costs perlitre gasoline equivalent

0.025 $0.019 $0.09 $0.03-0.07 0.06 Co-product benefits per litreethanol

0.219 $0.282 $0.17 $0.20-0.24

0.25-0.31

0.19-0.27 Operating costs per litreethanol

0.088 $0.097 $0.22 $0.20-0.44 0.24-0.26 0.24-0.34 Feedstock costs per litreethanol

318283370-470100383345-385Ethanol yield

[litres per Mg feedstock]

residue(lignin)

residue (lignin)gas / coalgas / coalgas / coalgas / coalProcess energy supply

Lignocellulosic feedstock**

CornSugar beetRye *

(Germany)

WheatFeedstock

USEurope

262198> 50> 5060-260> 50Ethanol capacity

[Million litres per year]

0.282 $0.36 $0.30 $0.40-0.62 0.49-0.55 0.41-0.60 Total production costs perlitre ethanol

start up 2010

Corn stover

(NREL 2002)

near-term

Poplar wood

(NREL 1999)

0.43 $0.55 $0.46 $0.64-0.94 0.74-0.83 0.62-0.91 Total production costs perlitre gasoline equivalent

0.025 $0.019 $0.09 $0.03-0.07 0.06 Co-product benefits per litreethanol

0.219 $0.282 $0.17 $0.20-0.24

0.25-0.31

0.19-0.27 Operating costs per litreethanol

0.088 $0.097 $0.22 $0.20-0.44 0.24-0.26 0.24-0.34 Feedstock costs per litreethanol

318283370-470100383345-385Ethanol yield

[litres per Mg feedstock]

residue(lignin)

residue (lignin)gas / coalgas / coalgas / coalgas / coalProcess energy supply

Lignocellulosic feedstock**

CornSugar beetRye *

(Germany)

WheatFeedstock

USEurope

* Source: Schmitz, N., Bioethanol in Deutschland (2003)** Source: International Energy Agency IEA (2004), US-National Renewable Energy Laboratory NREL (2002)

Table 3: Average cost estimations for the production of fuel ethanol by the fermentationpathway in industrial scale plants (data of different studies).

The production from sugar or starch crops is strongly influenced by the feedstock costs,which make about 50-70% of the total costs at industrial scale plants. The operating costsare mainly dominated by capital and energy costs. Due to higher costs of feedstock, energy,and capital recovery, the production from grain in Europe is currently more expensive thanfrom corn in the US. Co-product credits can be achieved by selling DDGS or surpluselectricity generated by internal heat and power stations. The average conversion costs forsugar beet are somewhat lower than for grain, but the average feedstock costs are expectedto be higher. Some amounts of low price beet may be supplied from surplus production forthe sugar industries.

Compared to the Europe and the US, ethanol can be produced at much lower costs (around0.2 /l) from sugar cane in Brazil, due to extremely low feedstock and operation costs. The

process energy is covered using the co-product bagasse as burner fuel. As a consequence,without import taxes the production of fuel ethanol in Europe could hardly compete withBrazilian ethanol. Actually the price of Brazilian ethanol in Europe is a result of the marketprice in Brazil, the additional cost for over seas transportation (around 0.05 /l) and the

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import taxes (0.1 /l). In the recent years, the resulting price was fluctuating in the range of0.340.42 /l.

For the processing of lignocellulosic feedstock there are only estimations available derivedfrom theoretical calculations mainly based on small scale pilot plants. The data presented inTable 3 refer to the fermentation pathway. They are derived from studies of the International

Energy Agency and the US National Renewable Energy Laboratory NREL. The near termperspective of 1999 for the feedstock poplar wood estimates production costs in the US ofabout 0,36 $/l at plant capacities of about 200 million litres per year. The NREL study of 2002refers to corn stover and to a further optimized plant design with reduced operating costs.Compared to the production from corn in the US, the operating costs for lignocellulosicbiomass are supposed to be higher, due to the more complex conversion technology. Incontrast, the feedstock costs are supposed to be much lower. This may be feasible, usingresidual material from agriculture or forestry. Similar to the sugar cane processing in Brazil,the energy demand of the ethanol plant is expected to be covered by the combustion offermentation residues, and surplus electrical energy is supposed to be sold. The 2010scenario assumes further improvements in the conversion technology and in the enzymeproduction, which lead to higher ethanol yields, reduced operating costs, and enhanced co-product credits. It has to be pointed out, that these estimations still have not been proven ona technical scale. Cost assessments of NREL and IEA for the next decades even estimateproduction costs of less than 0,2 $/l, assuming cost reduction effects of commercialization(nth plant) and of further optimized conversion technologies. However, up to now it is stilluncertain if the assumed costs of the near term scenarios actually can be realised.

Per litre gasoline equivalent, the production costs of European grain or sugar beet ethanolare in the range of about 0.62-0.91 . Without taxation, bio-ethanol therefore can besupposed to be competitive to gasoline fuels.

Well-to-wheel studies estimate the effects of renewable fuels on greenhouse gas reductioncompared to fossil fuels. The studies reflect the net impact of greenhouse gases of the entirelife cycle including feedstock and fuel production as well as fuel distribution and consumptionper km of vehicle driven. Crucial points of bio-ethanol well-to-wheel studies are usually theconsumption of fossil energy and the assumption of co-product credits, i.e. the greenhousegas reduction potentials of co-products like animal feed. The greenhouse gases generallyconsidered for the estimation of the global warming potential (GWP) are CO2, N2O and CH4.

0% 20% 40% 60% 80% 100% 120%

Corn

Wheat

Rye

Sugar beet

Lignocellulosic

feedstock

Reduction of global warming potential (CO2 equivalent)

compared to gasoline

min

max

Figure 3: Well-to-wheel green house gas emissions of (fermentation) fuel ethanol from

various feedstock crops: estimated reduction of global warming potential

compared to gasoline fuels. The base line (0%) refers to gasoline.

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The net emission of CO2 mainly depends on the amounts of fossil energy consumed for thefeedstock and ethanol production as well as for the product distribution. Emissions of N2Oare preferably emitted from the agricultural crop production and therefore are usually higherfor fuels derived from agricultural feedstock than for fossil fuels. Other gases which areknown to affect the climate are NOx, CO or non methane organic compounds. They are

emitted from combustion processes, e.g. from the generation of process heat or from vehicleoperation.

Figure 3 shows the average net reduction potentials which are expected for fuel bio-ethanolfrom various feedstock crops. It indicates that fuel ethanol from biomass can provide asignificant reduction of the global warming potential compared to gasoline. Fuel ethanol fromsugar and starch crops, which is produced using fossil fuels (e.g. gas or coal) for thegeneration of process heat, is expected to provide a reduction of up to 65%. Thefermentation of lignocellulosic biomass is assumed to provide a reduction potential of 50% tomore than 100%, as the process heat and even surplus energy is supposed to be generatedfrom fermentation residues.

5. ConclusionThe use of bio-ethanol as a transportation fuel offers a significant reduction potential of greenhouse gas emissions from the transportation sector. Fuel ethanol therefore can be a powerfulnear-term option to hit GWP-reduction targets. However, current production costs of bio-ethanol in Europe and in the US are still much higher than of (tax free) gasoline and taxbreaks are required to make bio-ethanol able to compete on the fuel market. For theprocessing of corn, grain or sugar crops, no technical breakthroughs and therefore nosignificant cost reductions can be expected in the next couple of years. In addition, with anincreasing global population, excessive agricultural production of grain or sugar crops for fuelmay lead to future food or fuel conflicts. The processing of lignocellulose provides theoption to enlarge the feedstock array and to reduce feedstock costs by processing

agricultural and forestry wastes. Set aside land can also be used for dedicated cellulosic cropcultivation. First cellulosic ethanol pilot plants are now in operation and their actualperformances have to be studied. Further technical and biotechnical improvements are to beexpected or under development. On the long term, the success of bio-ethanol fortransportation will depend on the economical competition with other bio-fuels as well as onfuture vehicle concepts.

6. References

English

Aden, A., et. al., Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing

Co-Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover, NationalRenewable Energy Laboratory NREL, USA, Technical Report NREL/TP-510-32438(2002)

Badger, P. C., Ethanol from Cellulose: A General Review, in: Trends in New Crops and NewUses, Eds: J. Janick and A. Whipkey, ASHS Press, Alexandria, VA, (2002), 17

De Carvalho Macedo, I., et. al., Greenhouse Gas Emissions in the Production and Use ofEthanol in Brazil: Present Situation (2002), (2003)

International Energy Agency, Biofuels for Transport - An International Perspective,Publication of the International Energy Agency IEA, Paris, (2004), ISBN 92 64 01 51 24

F.O. Lichts, World Ethanol and Fuels Report, (2003 and 2004)

General Motors, et. al., GM Well-to-Wheel Analysis of Energy Use and Greenhouse GasEmissions of Advanced Fuel/Vehicle Systems A European Study, (2002)

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Kosaric, N., Duvnjak, Z., Ethanol; Ullmanns Encyclopedia of Industrial Chemistry, Vol. A9

McCormick, R., Parish, R., Milestone Report: Technical Barriers to the Use of Ethanol inDiesel Fuel, National Renewable Energy Laboratory NREL, USA, Milestone ReportNREL/MP-540-32674 (2001)

Roehr, M. (Ed.), The Biotechnology of Ethanol Classical and Future Applications, Wiley-VCH, Weinheim (2001), ISBN 3-527-30199-2

Shapouri, H., Duffield, J. A., Wang, M., The Energy Balance of Corn Ethanol: An Update, USDepartment of Agriculture, Agricultural Economic Report Number 813 (2002)

Sheehan, J., Himmel, M., Enzymes, Energy and the Environment: A Strategic Perspective onthe U.S. Department of Energys Research and Development Activities for Bioethanol,Biotechnol. Prog. 15 (1999), 817

Sheehan, J., et. al., Energy and Environmental Aspects of Using Corn Stover for FuelEthanol, Journal of Industrial Ecology, Vol. 7/3-4 (2004), 117

Ward, O. P., Singh, A., Bioethanol Technology: Developments and Perspectives, Advances

in Applied Microbiology 51 (2002), 53Wyman, C. E., Ethanol from Lignocellulosic Biomass: Technology, Economics, and

Opportunities, Bioresource Technology 50 (1994) 3

Wyman, C. E., Twenty Years of Trials, Tribulations and Research Progress in BioethanolTechnology, Applied Biochemistry and Biotechnology 91-93 (2001), 5

Zaldivar, J., et. al., Fuel ethanol production from lignocellulose: a challenge for metabolicengineering and process integration, Appl. Microbiol. Biotechnol. 56 (2001), 17

German

Hartmann, H., Kaltschmitt, M., Biomasse als erneuerbarer Energietrger, Schriftenreihen

Nachwachsende Rohstoffe Bd.3, Landwirtschaftsverlag, Mnster, (2002), ISBN 3-7843-3197-1

Schmitz, N., Bioethanol in Deutschland, Schriftenreihe Nachwachsende Rohstoffe, Band21, Landwirtschaftsverlag, Mnster, (2003)

Schmitz, N., Innovationen bei der Bioethanolerzeugung, Schriftenreihe NachwachsendeRohstoffe, Band 26, Landwirtschaftsverlag, Mnster, (2005)

Wagner, U., Igelspacher, R., Ganzheitliche Systemanalyse zur Erzeugung und Anwendungvon Bioethanol im Verkehrssektor, Landtechnische Berichte aus Forschung und Praxis Gelbes Heft 76, Bayerisches Staatsministerium fr Landwirtschaft und Forsten,Mnchen, (2003)

Internet

Alternative Fuels Data Center, website of the US-Department of Energy,www.eere.energy.gov/afdc/

Berg, C., World Fuel Ethanol Analysis and Outlook, (2004), www.distill.com/World-Fuel-Ethanol-A&O-2004.html

Website of the American Coalition for ethanol, (2005), www.ethanol.org

Website of the BioAlcohol Fuel Foundation, rnskldsvik, Sweden, (2005), www.baff.info

Website of the Iogen Corporation, Ottawa, Canada, (2005), www.iogen.ca

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http://www.eere.energy.gov/afdc/http://www.distill.com/World-Fuel-Ethanol-A&O-2004.htmlhttp://www.distill.com/World-Fuel-Ethanol-A&O-2004.htmlhttp://www.ethanol.org/http://www.baff.info/http://www.iogen.ca/http://www.iogen.ca/http://www.baff.info/http://www.ethanol.org/http://www.distill.com/World-Fuel-Ethanol-A&O-2004.htmlhttp://www.distill.com/World-Fuel-Ethanol-A&O-2004.htmlhttp://www.eere.energy.gov/afdc/

d.schieder - bio-ethanol - existing pathways - paper

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