Pira International Ltd - Advances in Bioethanol

8/19/2019 Pira International Ltd - Advances in Bioethanol

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Advances in BioethanolPratima Bajpai

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Pira International Ltd

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Pira International Ltd 2007

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Contents

List of tables vList of figures vi

Introduction 1

Background 1

Scope of the report 8

Methodology 9

Glossary 9

Ethanol: an overview 13

Key drivers 13

Trends 14

Chemistry 15

Types of ethanol 16

Sources 16

The energy balance of ethanol 19Future of bioethanol 21

Production of bioethanol 23

Production of alcohol from corn 24

Dry milling 27

Wet milling 28

New technologies 28

Co-products 28Production of ethanol from lignocellulosic

biomass 29

Pre-treatment 30

Hemicellulose hydrolysis 31

Cellulose hydrolysis 33

Fermentation 37

Product recovery 39

Recycling of process stream 40

Promising developments in the

production of ethanol from

cellulose 41

Estimates of production costs of bioethanol

from different raw materials 47

Markets for bioethanol 49

Oxygenated and reformulated fuels 50

E5 51

E10 (gasohol) 51

E15 52

E20 52

E85 52

E95 54

E100 54

Niche markets 55

Fuel cells 55

E diesel 55

Aviation 56

Snowmobiles 56

Boats/marine 56

Small-engine equipment 57

Characteristics of ethanol 59

Using ethanol in engines 62

Fuel economy 64

Benefits of bioethanol 65

Environmental benefits 67

Carbon dioxide 67

Carbon monoxide 68

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Page iv © Copyright Pira International Ltd 2007

Nitrous oxide 68Other octane additives 68

Ozone 68

Particulate matter 69

Lead 69

Environmental behaviour 69

Health effects 70

Summary 71

Problems with ethanol/ethanol

blends 73

Storage 73

Transportation 73

Corrosion 73

Solvent effect 73

Separation of layer 74

Combustion 74

Effect on other vehicle parts 74

Scale of operation 74Environment 75

Bioethanol worldwide 77

EU 77

France 80

Germany 80

Spain 80

Sweden 81

Poland 81

Austria 82

Italy 82

UK 82

Australia 83

China 83

US 84

Brazil 88

Canada 91

India 91

Thailand 92

Japan 92References 95

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Advances in BioethanolContents


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Page v © Copyright Pira International Ltd 2007

List of tables

1.1 Biofuels summary 11.2 Pros and cons of ethanol fuel 3

1.3 Reductions in per-mile GHG

emissions by ethanol blend to

displace an energy-equivalent

amount of gasoline 5

1.4 GHG emission reduction per

gallon of ethanol to displace an

energy-equivalent amount of

gasoline 5

1.5 World ethanol production in 2006 7

1.6 Ethanol production in the US,1980–2006 7

2.1 Properties of bioethanol 16

2.2 Feedstocks for bioethanol

production 17

2.3 Typical composition of lignocellulosic

biomass 18

2.4 Ethanol’s net energy value:

a summary of major studies,

1995–2005 20

3.1 First- and second-generation raw

materials for ethanol production 23

3.2 Composition of corn 27

3.3 Comparison of various pre-treatment

options 33

3.4 Comparison of the different cellulosehydrolysis processes 37

4.1 Companies developing biofuel

technologies 44

6.1 Properties of fuel ethanol 59

6.2 Ethanol emissions compared to

gasoline 60

6.3 Comparison of fuel properties 60

6.4 Volumetric energy density of ethanol

compared to gasoline and other

fuels 61

9.1 EU bioethanol fuel production,2004–06 78

9.2 EU: leading ethanol producers 79

9.3 Ethanol industry expansion in the

US, 2000–07 84

9.4 US ethanol statistics, 2005–06 85

9.5 Ethanol imports in the US, 2006 85

9.6 Top ten ethanol producers by

capacity in the US, 2006 85

9.7 Flexi-fuel cars sold in Brazil,

2003–06 89

9.8 Ethanol production costs in different

countries 89


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Page vi © Copyright Pira International Ltd 2007

List of figures

1.1 The carbon cycle 31.2 World ethanol production,

1980–2006 6

3.1 Ethanol production from corn by the

wet milling process 25

3.2 Ethanol production from corn by the

dry milling process 26

3.3 Distillers grains from US ethanol

refineries 29

3.4 Biomass to ethanol process 30

3.5 SHF with separate pentose andhexose sugars and combined sugar

fermentation 35

3.6 SSF with combined sugars (pentoses

and hexoses) 35

4.1 Iogen’s cellulose ethanol process 41

4.2 Celunol process for production of

ethanol from biomass 43

9.1 EU: bioethanol fuel production,

1993–2006 79

9.2 Ethanol production in Brazil,

1982–2006 88


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Page 1 © Copyright Pira International Ltd 2007

Background The 1970 energy crisis stimulated research into alternative fuels, with an objectiveto reduce the dependency on oil in the strategic sector of transport (Wyman and

Hinman, 1990; Lynd and Wang, 2004; Herrera, 2004; Tanaka, 2006; Dien et al., 2006; Sun

and Cheng, 2004; Yacobucci and Womach, 2003; Chandel et al., 2007; Gray et al., 2006;

Kheshgi et al., 2000). At present, one of the main reasons for the interest in renewable

biofuels is the possibility of obtaining a considerable reduction of noxious exhaust

emissions from combustion, particularly as statutory limits are becoming more stringent

and more exhaust components are regulated. Table 1.1 summarises the developments.

Wider use of a chemically simple fuel such as bioethanol will mean that there are less

harmful effects on life and ecosystems. In particular, people living in urban areas may

in future appreciate the use of improved low-emission vehicles that do not smell, aresmokeless and are propelled either by reformulated bioethanol, by bioethanol blended

with gasoline or by neat biofuels. How the air quality can be improved is something that

is increasingly worth investigating for the sake of people and the environment.

Large-scale, sustainable, worldwide production and use of bioethanol from biomass

resources will produce tangible significant benefits for our growing and fast-evolving

society and also for the earth’s climate. The following list summarises the factors

favouring bioethanol.

Bioethanol is a proven global transport fuel, presently supplying 1.2% of the world’s

petrol.

It can be produced from virtually any organic material which means that it is a secureform of energy and in the long run will be relatively cheap.

Introduction

TABLE 1.1 Biofuels summary

What are biofuels? Benefits of biofuelsGeneral definition: Biofuel is a generic term Reduced dependency on fossil fuel

for any liquid fuel produced from sources other

than mineral reserves such as oil, coal and

gas. In general, biofuels can be used as a

substitute for, or additive to, petrol and diesel

in most transport and non-transport

applications

Biomass means any plant-derived organic Reductions in GHG (greenhouse gas) emissions

matter available on a renewable basis (biofuels recycle carbon dioxide that is extracted

from the atmosphere in producing biomass).

Examples: ethanol, methanol, Fischer-Tropsch Ethanol produced from corn can achieve moderate

diesel, gaseous fuels such as hydrogen and reductions in GHG emissions whereas ethanolmethane produced from cellulosic plants can achieve much

greater energy and GHG benefits

The most popular biofuels are ethanol Reductions in air pollution

and biodiesel

No new logistics and infrastructure required

Supportive of local agriculture

Source: Pira International Ltd


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Advances in BioethanolIntroduction


Bioethanol contains more useful energy than is required to produce it. Bioethanol reduces emissions of greenhouse gases, of carcinogens such as benzene and

of other harmful emissions such as particulates. It is biodegradable in water and soil.

Biofuel industries provide economic development and employment in rural areas. The

World Bank reports that biofuel industries require about 100 times more workers per

unit of energy produced than the fossil fuel industry.

Bioethanol enhances competitiveness through the development of new and efficient

technologies. Above all, it offers the prospect of converting lignocellulose into

fuel. This will, at a stroke, further improve energy security, reduce greenhouse gas

emissions and broaden economic development and employment opportunities.

Even with subsidies, the economic savings with bioethanol from avoided oil imports

are considerable.

Bioethanol has the potential to be used in compression engines as well as spark

ignition engines.

Bioethanol is unique amongst today’s sustainable transport fuel options in that it

can be used in internal combustion engines but is also a perfect fuel source for the

hydrogen fuel cell. So its development now offers a seamless transition into the

hydrogen energy system of the future.

Important environmental benefits could be achieved in the socio-economic development

of large rural populations and the diversification of energy supply, in particular for the

strategically vital sector of transport (Turkenberg, 2000). A life-cycle analysis of ethanol

production – from field to the car – by the US Department of Agriculture found that

ethanol has a large and positive energy balance. Ethanol yields 134% of the energy used

to grow and harvest the corn and process it into ethanol. By comparison gasoline yields

only 80% of the energy used to produce it. Bioethanol does not add to global CO2 levels

because it only recycles CO2 already present in the atmosphere. See Figure 1.1.


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More specifically, CO2 is removed from the atmosphere through photosynthesis when

crops intended for conversion to bioethanol are grown. CO2 is then released into the

atmosphere during combustion. In contrast, burning a fossil fuel such as petrol adds

to global CO2 because it releases new amounts of CO2 that were previously trapped

underground for millions of years. Finally, unlike oil, bioethanol is a renewable fuel, which

inherently helps the environment by allowing us to conserve other energy resources. The

pros and cons of ethanol fuel are detailed in Table 1.2.

FIGURE 1.1 The carbon cycle


TABLE 1.2 Pros and cons of ethanol fuel

Pros Cons

Positive net energy balance Reduced fuel economy

Reduced air pollution Gas cost for consumer initially similar

Carbon cycle maintains a balance of carbon Many modern cars cannot run ethanol

dioxide in the atmosphere when ethanol is concentrations higher than E10 gasohol

used as a fuel source under warranty

Reduced dependence on foreign oil Ethanol-powered vehicles will have trouble

starting at low temperatures


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Ethanol is already commonly used in a 10% ethanol/90% gasoline blend. Adapted

internal combustion engine vehicles (ICEVs) can use a blend of 85% ethanol/15%

gasoline (E85) or even 95% ethanol (E95). Addition of ethanol increases octane and

reduces CO, volatile organic compounds (VOCs) and particulate emissions of gasoline.

And, via on-board reforming to hydrogen, ethanol is also suitable for use in future fuel

cell vehicles (FCVs). Those vehicles are supposed to have about double the current ICEV

fuel efficiency (Lynd, 1996). Beginning with the model year 1999, an increasing number of

vehicles in the world are manufactured with engines which can run on any gasoline from

0% ethanol up to 85% ethanol without modification. Many light trucks are designed to

be dual fuel or flexible fuel vehicles, since they can automatically detect the type of fuel

and change the engine’s behaviour, principally the air-to-fuel ratio and ignition timing, to

compensate for the different octane levels of the fuel in the engine cylinders.

Ethanol has three major uses: as a renewable fuel, as a beverage and for industrial

purposes. Of the three grades of ethanol, fuel grade ethanol is driving record ethanol

production in many countries. About 95% of all ethanol is derived from sugar or

starch crops by fermentation; the rest is produced synthetically. The synthesis route

involves dehydration of hydrocarbons (e.g. ethylene) or by reaction with sulphuric

acid, to produce ethyl sulphate, followed by hydrolysis. The production routes from

biomass are based on fermentation or hydrolysis. According to FO Licht (Berg 2004),

synthetic alcohol production is concentrated in the hands of a few, mostly multinational,

companies such as:

Sasol, with operations in South Africa and Germany

SADAF of Saudi Arabia A 50:50 joint venture between Shell of the UK and the Netherlands

The Saudi Arabian Basic Industries Corporation

BP of the UK

Equistar in the US.

Fermentation ethanol is mainly produced for fuel, though a small share is used by

the beverage industry and the industrial industry. The bulk of the production and

consumption is located in Brazil and the US. Fermentation technologies for sugar and

starch crops are very well developed but have certain limits – these crops have a high

value for food application, and their sugar yield per hectare is very low compared with the

TABLE 1.2 (Continued)Pros Cons

Smooth transition from gasoline through Vehicles need alteration to run on ethanol

alcohol mixtures

Will slow global warming It is harder to transport

Greater production at refineries



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most prevalent forms of sugar in nature (cellulose and hemicellulose). Suitable processesfor lignocellulosic biomass therefore have room for further development:

A bigger crop variety can be employed

A larger portion of these crops can be converted.

Hence larger scales and lower costs are possible. There is a copious amount of

lignocellulosic biomass worldwide that can be exploited for fuel ethanol production.

According to the US Department of Energy, cellulosic ethanol reduces greenhouse gas

emissions by 85% over reformulated gasoline.

TABLE 1.4 GHG emission reduction per gallon of ethanol to displace an

energy-equivalent amount of gasoline

Ethanol blends Reduction (%)

E10 GV: DM

Corn ethanol –26

E10 GV: WM

Corn ethanol –18

E10 GV:Cellulosic ethanol –85

E85 FFV: DM

Corn ethanol –29

E85 FFV: WM

Corn ethanol –21

E85 FFV:

Cellulosic ethanol –86

Note: GV = gasoline vehicle; FFV = exible fuel vehicle; DM = dry milling; WM = wet milling

Source: Based on data from Wang (2005)

TABLE 1.3 Reductions in per-mile GHG emissions by ethanol blend to displace an

energy-equivalent amount of gasolineEthanol blends Reduction (%)

E10 GV: DM

Corn ethanol –2

E10 GV: WM

Corn ethanol –2

E10 GV:

Cellulosic ethanol –6

E85 FFV: DM

Corn ethanol –23

E85 FFV: WM

Corn ethanol –17

E85 FFV:Cellulosic ethanol –64

Note: GV = gasoline vehicle; FFV = exible fuel vehicle; DM = dry milling; WM = wet milling

Source: Based on data from Wang (2005)


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By contrast, sugar-fermented ethanol reduces greenhouse gas emissions by 18–19%compared with gasoline. Dan Sperling, UCD professor and director of the Institute of

Transportation Studies has commented that ethanol from cellulose is a great energy

strategy because for every gallon of ethanol, a small amount of fossil material is used. It

is much better from an energy perspective as a dramatic reduction in greenhouse gases is

observed. Ethanol-blended fuels reduced CO2-equivalent GHG emissions by approximately

7.8 million tonnes in 2005 which is equivalent to removing the annual GHG emissions

of 1.18 million cars from the road (RFA, 2006a). Beyond added environmental benefits,

cellulose-based ethanol could offer additional revenue streams to farmers for the

collection and sale of currently unused corn stover (leaves, stalks and cobs) or straw, for

example.

Close analysis of the current production and future expansion of ethanol production

in the US, Brazil and worldwide reveals that the generation of ethanol can hardly be

identified as a trend anymore: it is a well-defined and planned expansion programme

(Berg, 2004; Paszner, 2006). Most major oil-consuming or agricultural exporting countries

either have or are considering public policies to introduce ethanol as a blend agent into

their gasoline supplies. Many are encouraging ethanol production (BP, 2006). Total world

ethanol production increased substantially in 2006 totalling 13.5 billion gallons, with 70%

of this total produced by the US and Brazil. Other significant producers are China, India

and the EU (RFA, 2007a).

FIGURE 1.2 World ethanol production, 1980–2006 (million gallons)

Source: Based on data from RFA (2006a, 2007a); www.earth-policy.org/Updates/2005/Update49_data.htm


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Fuel ethanol production has been on the rise in the US since 1980, though production has

increased dramatically since 2001. US ethanol production is expected to grow from 4.9

billion gallons/yr in 2006 to 7.5 billion gallons/yr by 2013 (Jessel, 2006). The production

and use of nearly 5 billion gallons of domestic ethanol in the US reduced CO2-equivalent

GHG emissions by approximately 8 million tonnes in 2006. That would be the equivalent

of removing 1.21 million cars from US roads.

In Europe and other parts of the world, high gasoline prices and an urgency to find

cleaner fuel additives has increased the interest in ethanol production as well. However,

TABLE 1.5 World ethanol production in 2006 (%)US 39.1

Brazil 33.3

China 7.5

India 3.7

Others 16.4

Source: Based on data from RFA, 2007a

TABLE 1.6 Ethanol production in the US, 1980–2006

Year Million gallons

1980 175

1981 215

1982 350

1983 375

1984 430

1985 610

1986 710

1987 830

1988 845

1989 870

1990 900

1991 950

1992 1,100

1993 1,200

1994 1,3501995 1,400

1996 1,100

1997 1,300

1998 1,400

1999 1,470

2000 1,630

2001 1,770

2002 2,130

2003 2,810

2004 3,410

2005 3,900

2006 4,900

Source: Based on data from RFA, 2006c, 2007a


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the quantity of production still lags far behind Brazil and the US. The primary reasonfor this is said to be a lack of a single biomass source that would help standardise the

industry, although other economic hurdles also still exist. Asia’s three main countries

involved in the development of ethanol production are China, Thailand and India. China

has built the world’s biggest ethanol plant and is planning another just as big.

The technology on the whole has risen ever since the modest inception of a sizeable

ethanol industry, thus developing lower-cost methods of producing greater quantities of

fuel ethanol which are simultaneously more efficient in their use of fossil fuel inputs. These

combined effects have helped the production of ethanol fuel to increase in the US by more

than 225% between 2001 and 2005 (RFA, 2006a). Ethanol has also been used outside the

US, most notably in Brazil which started a programme of government-mandated ethanol

production in 1975 and has since encouraged production of flex-fuel vehicles (FFVs)

and cars fuelled entirely by ethanol (Luhnow and Samor, 2006). Due to its geographic

advantage in growing sugar cane (an ideal ethanol feedstock), Brazil is one of the biggest

producers of ethanol. Brazil is so efficient that it can produce a gallon of ethanol for

about €0.73 (Luhnow and Samor, 2006). The Brazilian ethanol market, which was once

dependent on governmental regulation and subsidies, has blossomed into a system that

thrives even without regulation. Fuel ethanol production in the US caught up with that

in Brazil for the first time, growing by 15% in 2005, as both remained the dominant

producers (REN21, 2006). Although there are cultural and institutional differences between

the US and Brazil , the general pattern of ethanol production and consumption under a

regulatory environment in the US could closely mirror what has happened in Brazil. Their

policy effectiveness can be used as a benchmark for the US market.

Scope of the report This report covers bioethanol that is predominantly produced from biomass, including

living organisms or their metabolic by-products. Bioethanol produced from traditional

biomass, for example fuel wood and charcoal, etc. as used in developing countries, falls

outside the scope of this report. This report provides a general background and looks at

the key drivers and the recent trends, chemistry, types of ethanol, sources and production

of the first- and second-generation bioethanol. For first-generation bioethanol, theproduction technologies have already been developed and can be implemented directly.

For second-generation bioethanol, the production technologies need to be developed

further before their production is possible on a large scale.

This report also discusses the advantages, biotechnology breakthroughs and

promising developments in the production of cellulosic ethanol. Furthermore, it addresses

the end-use application of bioethanol as a transportation fuel and the smaller niche

markets such as fuel-cell applications, E diesel, aviation, etc. where ethanol can be

utilised. It also presents information about the benefits, problems, environmental effects

and characteristics of fuel ethanol. Finally, the report provides detailed information about

the use of ethanol in different parts of the world and also highlights the challenges andfuture of ethanol.


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Methodology Information has been collected from scientific literature, reports from internationaland national agencies, websites, conference presentations, patent literature, statistics

databases, small and medium-sized biotechnology companies and university research

groups.

Glossary Alcohol : The family name of a group of organic chemical compounds composed of carbon,

hydrogen and oxygen. The molecules in the series vary in chain length and are composed

of a hydrocarbon plus a hydroxyl group. Examples are methanol, ethanol, etc.

Anhydrous ethanol : This is water free or ‘absolute’. The 95% pure product is dehydrated

using a molecular sieve or azeotropic processes to remove the water, resulting in 99%

pure ethanol. Anhydrous ethanol is normally blended with 10–25% petrol for use in most

unmodified or slightly modified engines or as a 3% blend in diesel.

Bacteria: Single-celled micro-organisms which can exist either as independent organisms

or as parasites that break down the wastes and bodies of dead organisms, making their

components available for reuse by other organisms.

Bagasse: The fibrous material left after the extraction of juice from the sugar cane. It is

often burned by sugar mills as a source of energy.

Biodiesel : Biodiesel is a general name for methyl esters from organic feedstock. Biodiesel

can be made from a wide range of vegetable oils, including rapeseed, and competitor

oils such as sunflower, palm oil and soy. It can also be derived from animal fats, grease

and tallow. Rapeseed is one of the main oil-seed crops grown in Europe and is the most

common feedstock used for biodiesel production. The oil undergoes a chemical process

(esterification) to make a methyl ester which has similar fuel specifications to fossil diesel.

Bioenergy : Energy (fuel, electricity, heat) produced from biomass.

Bioethanol : Ethanol produced from biomass feedstocks. This includes ethanol produced

from the fermentation of crops such as corn, as well as cellulosic ethanol produced from

woody plants or grasses. E5 contains 5% ethanol and 95% gasoline; E10 contains 10%

ethanol and 90% gasoline; E15 contains 15% ethanol and 85% gasoline; E20 contains

20% ethanol and 80% gasoline; E25 contains 25% ethanol and 75% gasoline; E85

contains 85% ethanol and 15% gasoline; E95 contains only 5% gasoline and 95% ethanol

and E100 is straight ethanol, which is most widely used in Brazil and Argentina.

Biofuel : Liquid or gaseous fuel for transport, produced from biomass.


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Biomass: Organic matter available on a renewable basis. Biomass includes forest and millresidues, agricultural crops and waste, wood and wood waste, animal waste, livestock

operation residues, aquatic plants, fast-growing trees and plants, municipal and industrial

waste, etc.

Biorefinery : A facility that processes and converts biomass into value-added products.

These products can range from biomaterials to fuels such as ethanol or important

feedstocks for the production of chemicals and other materials. Biorefineries can be

based on a number of processing platforms using mechanical, thermal, chemical and

biochemical processes.

Cellulase: Cellulase is an enzyme that hydrolyses cellulose to its constituent

monosaccharide (glucose) and disaccharide (cellobiose) units.

Cellulosic biomass: Biomass composed primarily of inedible plant fibres having cellulose

as a prominent component. These fibres may be hydrolysed to yield a variety of sugars

that can subsequently be fermented by micro-organisms. Examples of cellulosic biomass

include grass, wood and cellulose-rich residues resulting from agriculture of forest

products.

E diesel : Blends containing up to 15% ethanol, blended with standard diesel and a

proprietary additive, are called E diesel.

Emissions: Waste substances released into the air or water.

Energy crops: Crops grown specifically for their fuel value. These include food crops

such as corn and sugar cane, and non-food crops such as poplar trees and switchgrass.

Currently, two energy crops are under development: short-rotation woody crops, which are

fast-growing hardwood trees harvested in 5–8 years, and herbaceous energy crops, such

as perennial grasses, which are harvested annually after taking 2– 3 years to reach fullproductivity.

Enzyme: Protein that acts as a catalyst, or biocatalyst, in living organisms.

Ethyl tertiary butyl ether (ETBE): This is produced from bioethanol. This is used as a fuel

additive to increase the octane rating and reduce knocking.

Ethanol : Also known as ethyl alcohol, alcohol or grain-spirit. This is a clear, colourless,

flammable oxygenated hydrocarbon with a boiling point of 78.5°C in the anhydrous state.

In transportation, ethanol is used as a vehicle fuel by itself (E 100 – 100% ethanol by


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volume), blended with gasoline (E85 – 85% ethanol by volume), or as a gasoline octaneenhancer and oxygenater (10% by volume). It is produced by fermenting biomass high

in carbohydrates. Most ethanol is made using sugars and starches, but researchers are

working to more efficiently make alcohol from cellulose and other polymers in plants.

Ethanol made from cellulosic biomass is called cellulosic ethanol.

Feedstock : The source of carbon for production of organic fuels and chemicals via

industrial processes.

Fermentation: Conversion of carbon-containing compounds by micro-organisms for

production of fuels and chemicals such as alcohols, acids or energy-rich gases.

Flexible fuel vehicle (FFV): Vehicles whose engines can be operated with petrol as well as

with E85 or any interim products.

Fossil fuel : Solid, liquid or gaseous fuels formed in the ground after millions of years by

chemical and physical changes in plant and animal residues under high temperature and

pressure. Oil, natural gas and coal are fossil fuels.

Fuel cell : A device that converts the energy of a fuel directly to electricity and heat

without combustion.

Fuel ethanol : A liquid transportation fuel, which accounts for roughly two-thirds of world

ethyl alcohol. Most fuel ethanol is made from sugar cane, corn and other starch crops.

Fungi : Superficially this resembles a plant, but it does not have leaves and roots, and it

lacks chlorophyll, so that it must obtain its nutrients from other organisms by living either

as a parasite on living organisms or as a saprophyte on dead organic matter.

Gasoline: A liquid fuel for use in internal combustion engines where the fuel–air mixtureis ignited by a spark. It consists of a mixture of volatile hydrocarbon derived from the

distillation and cracking of petroleum. It normally contains additives such as lead

compounds or benzene to improve performance (the prevention of premature ignition) or

rust inhibitors. It is also called gas (in the US) or petrol.

Greenhouse effect : The effect of certain gases in the Earth’s atmosphere that traps heat

from the sun.

Greenhouse gases: Gases that trap the heat of the sun in the Earth’s atmosphere,

producing the greenhouse effect. The two major greenhouse gases are water vapour and


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carbon dioxide. Other greenhouse gases include methane, ozone, chlorofluorocarbons andnitrous oxide.

Hemicellulase: An enzyme that breaks down hemicellulose, which is not as complex as

cellulose and is easier to break down.

Hemicellulose: A type of polysaccharide found in plant cell walls, which is broken down

more easily than cellulose, the main component of the cell walls.

Hydrous ethanol : This can be used as a pure form of fuel in specially modified vehicles. It

has a purity of about 95% plus 5% water. Brazil is the only country that produces vehicles

that run on this form of ethanol.

Lignin: The structural constituent of wood and (to a lesser extent) other plant tissues,

which encrusts the cell walls and cements the cells together. It is not fermentable.

Mannanase: This is an enzyme that breaks down mannans. Mannans are mannose-

containing polysaccharides found in plants as storage material, in association with

cellulose (as hemicellulose).

Methyl tertiary butyl ether (MTBE): This is methyl tertiary butyl ether produced from

methanol and it is used as a fuel additive to increase the octane rating and reduce

knocking. It does not biodegrade and can contaminate groundwater.

Starch: Starch is a polymer made from thousands of glucose units.

Sustainable: An ecosystem condition in which biodiversity, renewability and resource

productivity are maintained over time.

Synthetic ethanol : Ethanol produced from ethylene, a petroleum by-product.

Xylanase: An enzyme that digests xylans and xylose, components of the plant cell wall.

These are used in animal feed and added to cereal-based diets to aid the efficiency of

carbohydrate breakdown. It is also used in the pulp and paper industry to cut and remove

hemicelluloses from fibres.

Yeast : A general term including single-celled, usually rounded fungi that produce

by budding. Some yeasts transform to a mycelial stage under certain environmental

conditions, while others remain single celled. They ferment carbohydrates.


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This chapter considers the key drivers, trends, chemistry, types, sources, energy balanceand future of bioethanol.

Key drivers The forces pushing for ethanol fuel vary considerably, but there are some common

features (Rosillo-Calle and Walter, 2006; FAO, 2006; Hazell and Pachauri, 2006;

Bergstrom, 2007):

Environmental: around the world concern with clean air is a social and political

priority. For example, the necessity to reduce pollutant emissions and achieve targets

defined by the Kyoto Protocol.

Energy security: increasing dependency on imported energy supply, especially in a

context of rising oil prices, is also a general concern, particularly in the US and EU.

Social and economic pressures: for example, the desire to support rural development

and to generate jobs.

In recent years, there has been growing interest regarding the use of renewable biofuels

in the transport sector, ethanol and biodiesel being the best short-term alternatives. More

than 30 countries have introduced or are interested in introducing programmes for fuel

ethanol (Rosillo-Calle and Walter, 2006). Other countries have done the same regarding

biodiesel, but to a lesser extent. Thus, the ethanol experience is so far much more

important than with biodiesel, excluding Europe where the prospects for biodiesel use are

much better than fuel ethanol due to the availability of feedstock.

Developing countries have a reasonably good potential for biofuels production due to

the availability of land, better weather conditions and the availability of a cheaper labour

force. Another important issue to be taken into account is that it is imperative for these

countries to strengthen their rural economies. Obviously each country is different, and a

careful analysis is required to assess the pros and cons of large-scale biofuels production,

particularly with regard to competition for land and water for food production and

potential pressures on food prices (Hazell and von Braun, 2006).

Another important driving force for ethanol production is the generation of a huge

amount of new employment. The ethanol industry in Brazil is responsible for about one

million direct jobs, approximately 50% of them being in sugar cane production. Indirect jobs are estimated at 2.5– 3 million. However, it should be mentioned that this high

employment is partly due to the low level of mechanisation of agricultural activities, as

well as poor automation at the industrial site.

From an environmental perspective, first the benefits of phasing out lead from

gasoline should be highlighted, as lead has adverse neurological effects. Hydrated ethanol

has a higher level of octanes than regular gasoline (Joseph, 2005), and its use in blends

allows the phasing out of lead at a low cost. This would be a very important advantage of

ethanol use in countries where lead is still in use, as is the case of many African and some

Asian and Latin American countries.

In order to protect the environment, developing countries need to change over toclean and renewable fuel from crude oil-based fuels. Large-scale use of biofuels is one

Ethanol: an overview 2


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Advances in BioethanolEthanol: an overview


of the main strategies for the reduction of GHG emissions (IPCC, 2001). Despite the factthat developing countries currently do not have binding GHG reduction targets under the

Kyoto Protocol, two main aspects should be considered:

Under the clean development mechanism (CDM), developing countries can sell credits

to those with reduction commitments. Considering a typical Brazilian figure of 2.7kg

of CO2 equivalent avoided per litre of anhydrous ethanol, biofuels use could represent

additional income of $0.02–$0.05 (€0.0146–€0.0365) per litre (on credits in the

range $7–$20 per tonne of CO2 equivalent), value that should be compared with

production costs in the $0.23–$0.28 per litre range (Nastari; Nastari et al., 2005).

Climate change effects are supposed to be worst in developing countries so it is

important to take action.

Trends The international market in fuel ethanol is in its initial stage and its full development will

require:

The diversification of production in terms of both feedstocks and the number of

producing countries;

Technological development in the manufacturing field;

Favourable policies to induce market competitiveness;

Sustainable development.

(Rosillo-Calle F and Walter A, 2006).

Bioethanol production based on lignocellulosic biomass is the technology of the

future. Lignocellulosic ethanol is made from a wide variety of plant materials, including

wood wastes, crop residues and grasses, some of which can be grown on marginal lands

not suitable for food production (Ghosh and Ghose, 2003). Lignocellulosic raw materials

minimise the potential conflict between land use for food and feed production and energy

feedstock production. The raw material is less expensive than conventional agricultural

feedstock and can be produced with lower input of fertilisers, pesticides and energy.

Biofuels from lignocellulose generate low net GHG emissions, reducing environmental

impacts, particularly climate change (Hahn et. al, 2006).

Global ethanol production more than doubled between 2000 and 2005, whileproduction of biodiesel, starting from a much smaller base, expanded nearly fourfold. In

contrast, oil production increased by only 7% over this period. In 2005, ethanol comprised

about 1.2% of the world’s gasoline supply by volume and about 0.8% by transport distance

travelled (due to its lower energy content). From 2002 to 2004, world oil demand increased

by 5. 3%. China’s consumption alone increased by 26.4%, while consumption in the US

increased by 4.9%; Canada 10.2%; and the UK 6. 3%. Demand in Germany and Japan,

meanwhile, reduced by 1% and 2.6% respectively. The World Bank reports that biofuel

industries require about 100 times more workers per unit of energy produced than the fossil

fuel industry. The ethanol industry is credited with providing more than 200,000 jobs


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in the US and half a million direct jobs in Brazil. Transportation, including emissions fromthe production of transport fuels, is responsible for about one-quarter of energy-related

greenhouse gas (GHG) emissions, and that share is rising.

The GHG balance of biofuels varies dramatically depending on such factors as

feedstock choice, associated land use changes, feedstock production systems and the type

of processing energy used. In general, most currently produced biofuels have a solidly

positive GHG balance. The greatest GHG benefits will be achieved with cellulosic inputs as

mentioned above. Energy crops have the potential to reduce GHG emissions by more than

100% (relative to petroleum fuels) because such crops can also sequester carbon in the

soil as they grow. The estimated GHG reductions for different feedstock are:

Fibres (switchgrass, poplar): 70–110%

Wastes (waste oil, harvest residues, sewage): 65–100%

Sugars (sugar cane, sugar beet): 40–90%

Vegetable oils (rapeseed, sunflower seed, soya beans): 45–75%

Starches (corn, wheat): 15–40%.

Major research challenges in the field of bioethanol production based on lignocellulosic

biomass are:

Improving the enzymatic hydrolysis with efficient enzymes.

Reduced enzyme production cost and novel technology for high solids handling.

Developing robust fermenting organisms which are more tolerant of inhibitors

and ferment all sugars in the raw material in concentrated hydrolysates at high

productivity and with high concentration of ethanol.

Extending process integration to reduce the number of process steps and the energy

demand and to reuse process streams for eliminating the use of fresh water and to

reduce the amount of waste streams.

(Hahn et al., 2006).

Chemistry Ethanol is a clear, colourless, volatile, flammable liquid that is the intoxicating agent in

liquors and is also used as a fuel or solvent. Ethanol is also called ethyl alcohol or grain

alcohol. Ethanol is the most important member of a large group of organic compoundsthat are called alcohol. It may be shown as:

In its pure form, ethanol is a colourless clear liquid with a mild characteristic odour.

Ethanol melts at –114.1°C, boils at 78.5°C and has a density of 0.789g/ml at 20°C.

2

H H

H–|C|

–|C|

–O–H or CH3CH2OH

H H


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Ethanol’s low freezing point has made it useful as the fluid in thermometers for

temperatures below –40°C, the freezing point of mercury, and for other low-temperature

purposes, such as for antifreeze in automobile radiators. The molecular weight is 46.07.

One gallon of 190 proof ethanol weighs 6.8lb. Ethanol has no basic or acidic properties.

When burned, ethanol produces a pale blue flame with no residue and considerable

energy, making it an ideal fuel. Ethanol mixes readily with water and with most organic

solvents. It is also useful as a solvent and as an ingredient when making many other

substances including perfumes, paints, lacquer and explosives.

Types of ethanol Ethanol can be produced in two forms:

Hydrous ethanol: it can be used as a pure form of fuel in specially modified vehicles.

It has a purity of about 95% plus 5% water. Brazil is the only country that produces vehicles that run on this form of ethanol.

Anhydrous ethanol: it is water free or ‘absolute’. A second-stage process is required

to produce high purity ethanol for use in petrol blends. The 95% pure product is

dehydrated using a molecular sieve or azeotropic processes to remove the water,

resulting in 99% pure ethanol. Anhydrous ethanol is normally blended with 10–25%

volume in petrol for use in most unmodified or slightly modified engines or as a 3%

blend in diesel.

Sources Ethanol can be produced from a variety of organic materials. These can be classified in to

three groups (see Table 2.2).

TABLE 2.1 Properties of bioethanolPhysical properties

Specific gravity 0.79g/cm3

Vapour pressure (38°C) 50mmHg

Boiling temperature 78.5°C

Dielectric constant 24.3

Solubility in water ∞

Chemical properties

Formula C2H5OH

Molecular weight 46.1

Carbon (wt) 52.1%

Hydrogen (wt) 13.1%

Oxygen (wt) 34.7%

C/H ratio 4

Stechiometric ratio (AIR/ETOH) 9.0

Thermal properties

Lower heating value 6,400Kcal/kg

Ignition temperature 35°C

Specific heat (Kcal/Kg °C) 0.60

Melting point –115°C

Source: Based on data from EUBIA (2006)


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Agricultural waste available for ethanol conversion includes crop residues such as wheat

straw, corn stover (leaves, stalks and cobs), rice straw, and bagasse (sugar cane waste).

Forestry waste includes underutilised wood and logging residues; rough, rotten and

salvable dead wood; and excess saplings and small trees. Municiple solid waste contains

some cellulosic materials such as paper. Energy crops, developed and grown specifically

for fuel, include fast-growing trees, shrubs and grasses such as hybrid poplars, willows and

switchgrass (US DOE, 1996a). Switchgrass is one source likely to be tapped for ethanol

production because of its potential for high fuel yields, hardiness and the ability to be

grown in diverse areas. Trials show current average yields to be about five dry tonnes

per acre. However, crop experts say that progressively applied breeding techniques could

more than double that yield. Switchgrass’s long root system – actually a fifty-fifty split

above ground and below – helps to keep carbon in the ground, improving soil quality. It is

drought tolerant, grows well even on marginal land and does not require heavy fertilising.

Other varieties including big blue stem and Indian grass are also possible cellulose sources

for ethanol production. Researchers estimate that ethanol yield from switchgrass is in the

range of 60–140 gallons per tonne; some say 80–90 gallons per tonne is a typical figure.

It is estimated that the energy output/energy input ratio for fuel ethanol made from

switchgrass is about 4.4 (Iowa State University, 2006). The US Department of Agriculture

estimates that by 2030 approximately 129 million acres of excess cropland could be used

for energy crops. If 40 million of these acres were utilised for energy crops for biofuels

such as ethanol, it would provide a transportation fuel equivalent to 550 million barrels

of oil per year (US DOE, 1996b). Sugar cane bagasse, the residue generated during the

milling process, is another potential feedstock for cellulosic ethanol. Research shows that

one tonne of sugar cane bagasse can generate 112 gallons of ethanol.

Lignocellulosic feedstock is composed of cellulose, hemicellulose, lignin and extractivesand ash. The cellulose and hemicellulose, which typically comprise two-thirds of the dry

mass, are polysaccharides that can be hydrolysed to sugars and eventually fermented to

ethanol. The combination of hemicellulose and lignin provides a protective sheath around

the cellulose, which must be modified or removed before efficient hydrolysis of cellulose

can occur, and the crystalline structure of cellulose makes it highly insoluble and resistant

to attack. Therefore, to hydrolyse hemicellulose and cellulose economically, more advanced

pre-treatment technologies are required than those used in processing sugar or starch

crops (Eggeman and Elander, 2005). After the cellulose and hemicellulose have been

saccharified, the remainder of the ethanol production process is similar to grain ethanol.

However, the different sugars require different enzymes for fermentation.

TABLE 2.2 Feedstocks for bioethanol productionSugar-based: Sugar cane, molasses, sugar beet, sweet sorghum, fruits

Starch-based: Cereal grains, potato, sweet potato, corn, cassava

Cellulose-based: Agricultural plant waste, forest residue, municipal solid waste, energy crops

Source: Based on data from Kim and Dale, 2004b; US DOE (2006a)

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Lignocellulosic crops are promising feedstock for ethanol production because of highyields, low costs, good suitability for low-quality land and low environmental impact. Most

ethanol conversion systems that are written about are based on a single feedstock. But

considering the hydrolysis fermentation process, it is possible to use multiple feedstock types.

Table 2. 3 presents biochemical compositions for several suitable feedstock. Pine has the

highest combined sugar content, implying the highest potential ethanol production. The

lignin content for most feedstock is about 27%, but grasses contain significantly less and

will probably co-produce less electricity.

Cellulosic resources are in general very widespread and abundant. For example, forests

comprise about 80% of the world’s biomass. Being abundant and outside the human food

chain makes cellulosic materials relatively inexpensive feedstocks for ethanol production.

Brazil uses sugar cane as primary feedstock whereas in the US more than 90% of the

ethanol produced comes from corn. Other feedstocks such as beverage waste, brewerywaste and cheese whey are also being utilised. In the EU, most of the ethanol is produced

from sugar beet and wheat. Crops with higher yields of energy, such as switchgrass

and sugar cane, are more effective in producing ethanol than corn. Ethanol can also be

produced from sweet sorghum, a dry-land crop that uses much less water than sugar cane,

does not require a tropical climate and produces food and fodder in addition to fuel. In

terms of gallons of fuel per acre, the best farm crop for ethanol production is sugar beet,

with the lowest water requirements to grow the crop. The beet plant drives a central tap

root deep into the soil and the entire beet is underground, minimimising evaporation.

One result of increased use of ethanol is increased demand for the feedstocks.

Large-scale production of agricultural alcohol may require substantial amounts of

TABLE 2.3 Typical composition of lignocellulosic biomass (%, dry basis)

Feedstock Hardwood Softwood Grass

Black Hybrid Eucalyptus Pine Switchgrasslocust poplar

Cellulose 41.61 44.70 49.50 44.55 31.98

Glucan 6C 41.61 44.70 49.50 44.55 31.98

Hemicellulose 17.66 18.55 13.07 21.90 25.19 Xylan 5C 13.86 14.56 10.73 6.30 21.09

Arbinan 5C 0.94 0.82 0.31 1.60 2.84

Glactan 6C 0.93 0.97 0.76 2.56 0.95

Mannan 6C 1.92 2.20 1.27 11.43 0.30

Lignin 26.70 26.44 27.71 27.67 18.13

Ash 2.15 1.71 1.26 0.32 5.95

Acids 4.57 1.48 4.19 2.67 1.21

Extractives 7.31 7.12 4.27 2.88 17.54

Heating values 19.50 19.60 19.50 19.60 18.60

(GJHHV /tonnedry )

Note: totals may not add up due to rounding

Source: Based on data from Hamelinck (2003)


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cultivable land with fertile soils and water. This may lead to environmental damage suchas deforestation or decline of soil fertility due to reduction of organic matter.

In 2003, about 5% of the ethanol produced in the world was actually a petroleum

product. It is made by the catalytic hydration of ethylene with sulphuric acid as the

catalyst. It can also be obtained via ethylene or acetylene, from calcium carbide, coal,

oil, gas and other sources. Two million tonnes of petroleum-derived ethanol are produced

annually. The principal suppliers are plants in the US, Europe and South Africa. Petroleum-

derived ethanol (synthetic ethanol) is chemically identical to bioethanol and can be

differentiated only by radiocarbon dating.

The energy balance One of the most controversial issues relating to ethanol is the question of net energy of

of ethanol ethanol production. The definition of net energy value (NEV) is the difference between the

energy in the fuel product (output energy) and the energy needed to produce the product

(input energy). While the topic has been hotly debated for years, the current prevailing

opinion is that ethanol has a net positive energy balance. It takes less than 35,000BTU of

energy to turn corn into ethanol, while the ethanol offers at least 77,000BTU of energy,

which shows that ethanol’s energy balance is clearly positive (Shapouri et al., 1995, 2002,

2003; Lorenz and Morris, 1995; Wang et al., 1999; Kim and Dale, 2004a; Farrell et al.,

2006) and an extremely high petroleum/fossil energy displacement ratio.

Since 1979, David Pimentel, of Cornell University has consistently argued – in more

than 20 published articles – that the amount of fossil fuel energy needed to produce

ethanol is greater than the energy contained in the ethanol. According to Pimentel and

his colleague Tad Patzek of the University of California, Berkeley, there is just no energy

benefit in using plant biomass for liquid fuel (Pimentel, 2003; Patzek, 2003; Ferguson,

2003). Their research used fundamentally flawed, decades old data that is not valid

considering today’s efficiencies in agriculture and in ethanol production. Now the advances

in the farming community as well as technological advances in the production of ethanol

have led to positive returns in the energy balance of ethanol. Studies have shown that

the ethanol energy balance is improving by the year (Wang, 2005b; Shapouri et al., 1995,

2002, 2003; Lorenz and Morris, 1995; Wang et al., 1999; Morris, 1995). These studies showthat the energy output to energy input ratio for converting irrigated corn to ethanol is now

1.67:1. In a July 1995 US Department of Agriculture (USDA) Economic Research Service

report entitled ‘Estimating the Net Energy Balance of Corn Ethanol’, it was concluded that

the ethanol energy balance had a gain of 24%. That same report was revisited the next

year, in a presentation entitled ‘Energy Balance of Corn Ethanol Revisited’ – the authors

concluded that the ratio had risen to 34%. This number is reinforced by a 2002 report, ‘The

Energy Balance of Corn Ethanol: An Update’ published by the USDA’s Office of the Chief

Economist and Office of Energy Policy and New Uses. The report concluded that ethanol

production is energy efficient because it yields 34% more energy than is used. In June

2004, the USDA looked at this issue again and determined that ethanol continues to bemore efficient and now provides the aforementioned 1.67:1 gain in energy.

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Many advances have led to the surge in ethanol production efficiency. One key issueis the ability to produce more gallons of ethanol per bushel of corn. In the early 1990s,

plants were able to produce about 2.5 gallons of ethanol per bushel. That number has

since increased to between 2.7 and 2.8 gallons per bushel.

Crops with a higher sugar content than corn, such as sugar beet, would result in

production with a much higher positive net energy balance. If corn farmers use

state-of-the-art, energy-efficient farming techniques, and ethanol plants use state-of-the-art

production processes, then the amount of energy contained in a gallon of ethanol and the

other co-products is more than twice the energy used to grow the corn and convert it into

ethanol. Studies indicated an industry average net energy gain of 1. 38:1. The industry-best

existing production net energy ratio was 2.09:1. If farmers and industry were to use all of

the best technologies and practices, the net energy ratio would be 2.51:1. In other words,

the production of ethanol would result in more than two-and-a-half times the available

energy than it took to produce it.

A 1999 study by Argonne National Laboratory found the energy balance of cellulosic

ethanol to be in excess of 60,000BTU per gallon (Wang, 1999). Given that feedstocks

for cellulosic ethanol are essentially waste products like corn stover, rice bagasse, forest

thinnings or even municipal waste, there are relatively few chemical and energy inputs

that go into the farming of feedstocks for cellulosic ethanol. A secondary factor, although

to a much lesser extent, is the fact that cellulosic ethanol plants will presumably produce

extra energy that can be fed into the power grid. Doing so will effectively displace the use

of electricity produced in power plants, which for the most part rely upon fossil fuels.

Table 2.4 shows ethanol’s net energy value as published by different researchers.

TABLE 2.4 Ethanol’s net energy value: a summary of major studies, 1995–2005

Authors and date NEV (BTU)

Shapouri et al. (1995) – USDA +20,436 (HHV)

Lorenz and Morris (1995) – Institute for Local Self-Reliance +30,589 (HHV)

Agri. and Agri-Food, Canada (1999) +29,826 (LHV)

Wang et al. (1999) – Argonne National Laboratory +22,500 (LHV)

Pimentel (2002) – Cornell University –33,562 (LHV)

Shapouri et al., update (2002) – USDA +21,105 (HHV)

Kim and Dale (2002) – Michigan State University +23,866 to +35,463 (LHV)

Graboski (2002) – Colorado School of Mines +17,508

Pimentel (2003) – Cornell University –22,300

Shapouri et al. (2003) – Argonne National Laboratory/USDA +21,105

Shapouri et al., update (2004) – USDA +30,258 (LHV)

Pimentel and Patzek (2005) – Cornell/UC-Berkeley –22,300

Note: HHV = higher heating value; LHV = lower heating value

‘The energy balance of corn ethanol revisited’ (2003) by Shapouri et al. included a new energy credit for

the co-product distillers dried grains with solubles (DDGS)

‘The 2001 net energy balance of corn-ethanol’ (2004) by Shapouri et al. included a revised energy credit

for DDGS

Source: Based on data from White (2006)


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Future of bioethanol The future of bioethanol appears to be bright as the need for renewable energy sourcesto replace dependence on foreign oil is growing. With many nations seeking to reduce

petroleum imports, boost rural economies and improve air quality, world ethanol

production rose to 13.5 billion gallons in 2006. The success of domestic ethanol industries

in the US and Brazil has sparked tremendous interest in countries around the globe

where nations have created ethanol programmes seeking to reduce their dependence

on imported energy, provide economic boosts to their rural economies and improve the

environment. As concerns over greenhouse gas emissions grow and supplies of world oil

are depleted, Europe and countries like China, India, Australia and some south-east Asian

nations are rapidly expanding their production and use of biofuels.

A lot of research is being done including turning biomass (materials from plants) into

ethanol using special biotechnological methods. Biomass ethanol is the future of ethanol

production because biomass feedstocks, like wheat straw or switchgrass, require less fossil

fuels to grow, harvest and produce. It also allows more marginal land, such as grasslands,

to be utilised rather than precious acreage devoted to food crops like corn or soya beans.

In this way, ethanol production from biomass does not negatively affect the livestock

and food industry. The biorefinery, analogous to today’s oil refineries, could economically

convert lignocellulose to an array of fuels and chemicals – not just ethanol – by

integrating bio- and thermo-chemical conversion (Fernando, 2006). Fundamental research

and partnerships with the emerging bioenergy industry are critical for the success.

There has been continued research to improve the energy output of ethanol and

improvements should continue. Currently, E85 stations are popping up everywhere and

more products, from generators to power tools and lawnmowers, will all start to use

alternative fuels. There are already engines that can run on 100% pure ethanol, and

improvements will help migrate these engines to other areas. Big auto manufacturers like

Nissan, Ford and Honda have all invested money into E85 models. Portable generators,

stand-by and emergency generators should all start using ethanol as a fuel source.

The emergence of carbon trading programmes in response to many countries’

ratification of the Kyoto Protocol will also enhance the affordability of ethanol fuels in

comparison to gasoline and diesel. Because ethanol fuels offer a substantial reductionin carbon dioxide emissions, users can obtain carbon credits that can be sold to heavy

polluters, again reducing ethanol costs while increasing that of fossil fuels. The EU

recently developed a carbon trading programme. Japan has conducted several scenario

simulations and hopes to initiate its own nationwide trading system. As Russia considers

ratification of the Kyoto Protocol, which would bring the agreement into effect, it seems

likely that similar carbon trading schemes will continue to emerge around the world.

A combination of well-reasoned government policies and technological advancements

in ethanol fuels could guide a smooth transition away from fossil fuels in the

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transportation sector. As environmental factors continue to be incorporated into policyand the fledgling industry emerges, ethanol fuels are likely to become an increasingly

attractive fuel alternative in the foreseeable future. Looking into the future, the ethanol

industry envisions a time when ethanol may be used as a fuel to produce hydrogen for

fuel-cell vehicle applications.


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3


Production of bioethanol requires fermentation of the sugar (mono- and polysaccharides)in nearly all kinds of biomass (Olsson et al., 2005). Today there are primarily two types

of process technology called first- and second-generation technology. First generation

produces bioethanol from sugars (a dimer of the monosaccharides glucose and fructose)

and starch-rich (polysaccharides of glucose) crops such as grain and corn.

Sugars can be converted to ethanol directly, but starches must first be hydrolysed to

fermentable sugars by the action of enzymes from malt or moulds. The technology is well

known, but high prices of the raw material and the ethics about using food products for

fuel are two major problems. This is not an issue with the second-generation production of

bioethanol – instead a new technology is required. The raw material in second-generation

process technology is lignocellulosic material such as straw, wood and agricultural residue,

which is often available as waste.

These kinds of materials are cheap but the process technology is more advanced than

converting sugar and starch. The major cause is the lignin which binds together pectin,

protein and the two types of polysaccharides, cellulose and hemicellulose, in lignocellulosic

biomass. Lignin resists microbial attack and adds strength to the plant. Pre-treatment

is therefore used to open the biomass by degrading the lignocellulosic structure and

releasing the polysaccharides. Pre-treatment is followed by treatment with enzymes which

hydrolyse cellulose and hemicellulose respectively. The cellulose fraction releases glucose

(C6 monosaccharide – sugar with six carbon atoms) and the hemicellulose fraction

releases pentoses (C5 monosaccharide – sugar with five carbon atoms) such as xylose. Out

of carbohydrate monomers in lignocellulosic materials, xylose is the second most abundant

Production of bioethanol

TABLE 3.1 First- and second-generation raw materials for ethanol production

First generation

Sugar cane

Corn

Wheat

Rye

Sorghum

Cassava

Second generation Agricultural waste

Leftover crop material, such as stalks, leaves and husks of corn plants

Forestry waste

Wood chips and sawdust from lumber mills, dead trees and tree branches

Energy crops

Fast-growing trees and grasses such as switchgrass

Municipal solid waste

Household garbage and paper products

Food processing and other industrial waste

Black liquor, a paper manufacturing by-product

Source: Based on data from Hamelinck (2003); US DOE (2006a)


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Advances in BioethanolProduction of bioethanol


after glucose. Glucose is easily fermented into ethanol, but another fermentation process isrequired for xylose – for example using special micro-organisms.

The second-generation technology holds great advantages for the fermentation of

biomass in the form of agricultural waste materials. The first-generation technology is

based on much more costly raw material and there are some ethical questions. This is not

an issue with the second-generation technology – instead there are some challenges such

as efficient pre-treatment and fermentation technologies together with environmentally

friendly process technology (for example the reuse of the process water).

Production of Ethanol is produced from corn by using one of two standard processes: wet milling or dry

alcohol from corn milling (Yacobucci and Womach, 2003).


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3



FIGURE 3.1 Ethanol production from corn by the wet milling process

Source: Source: Based on RFA (2007d)


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The main difference between the two processes is in the initial treatment of the grain.

Dry milling plants cost less to build and produce higher yields of ethanol (2.7 gallons per

bushel of corn), but the value of the co-products is less. The value of corn as a feedstock

for ethanol production is due to the large amount of carbohydrates, specifically starch,

present in corn.

FIGURE 3.2 Ethanol production from corn by the dry milling process

Source: Based on RFA (2007d)


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3



Dry milling In the US, most of the ethanol plants utilise a dry milling process. The major steps of dry

milling are outlined below:

1 Milling: after the corn (or other grain or biomass) is cleaned, it passes first through

hammer mills which grind it into a fine powder.

2 Liquefaction: the meal is then mixed with water and an enzyme (alpha amylase), and

passes through cookers where the starch is liquefied. A pH of 7 is maintained by adding

sulphuric acid or sodium hydroxide. Heat is applied to enable liquefaction. Cookers with

a high temperature stage (120–150°C) and a lower temperature holding period (95°C)

are used. The high temperatures reduce bacteria levels in the mash.

3 Saccharification: the mash from the cookers is cooled and the enzyme glucoamylase is

added to convert starch molecules to fermentable sugars (dextrose).

4 Fermentation: yeast is added to the mash to ferment the sugars to ethanol and

carbon dioxide. Using a continuous process, the fermenting mash flows through

several fermenters until the mash is fully fermented and leaves the tank. In a batch

fermentation process, the mash stays in one fermenter for about 48 hours.

5 Distillation: the fermented mash, now called ‘beer,’ contains about 10% alcohol, as well

as all of the non-fermentable solids from the corn and the yeast cells. The mash is then

pumped to the continuous flow, multi-column distillation system where the alcohol

is removed from the solids and water. The alcohol leaves the top of the final column

at about 96% strength, and the residue mash, called stillage, is transferred from thebase of the column to the co-product processing area. The stillage is sent through a

centrifuge that separates the coarse grain from the solubles. The solubles are then

concentrated to about 30% solids by evaporation, resulting in Condensed Distillers

Solubles (CDS) or syrup. The coarse grain and the syrup are then dried together

to produce dried distillers grains with solubles (DDGS), a high-quality, nutritious

livestock feed. The CO2 released during fermentation is captured and sold for use in

carbonating soft drinks and beverages and the manufacture of dry ice. Drying the

distillers grain accounts for about one-third of the plant’s energy usage (Bryan and

Bryan Inc., 2001).

TABLE 3.2 Composition of cornComponent Dry matter (%)

Carbohydrates (total) 84.1

Starch 72.0

Fibre (NDF) 9.5

Simple sugars 2.6

Protein 9.5

Oil 4.3

Minerals 1.4

Other 0.7



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6 Dehydration: the alcohol then passes through a dehydration system where theremaining water is removed. Most plants use a molecular sieve to capture the last bit of

water in the ethanol. The alcohol at this stage is called anhydrous (pure, without water)

ethanol and is approximately 200 proof.

7 Denaturing: ethanol that is used for fuel is then denatured with a small amount (2–5%)

of some product, like gasoline, to make it unfit for human consumption.

Wet milling The wet milling operation is more elaborate because the grain must be separated into its

components. After milling, the corn is heated in a solution of water and sulphur dioxide

for 24–48 hours to loosen the germ and the hull fibre. The germ is then removed from the

kernel, and corn oil is extracted from the germ. The remaining germ meal is added to the

hulls and fibre to form corn gluten feed. A high-protein portion of the kernel called gluten

is separated and becomes corn gluten meal which is used for animal feed. In wet milling,

only the starch is fermented, unlike dry milling, when the entire mash is fermented.

New technologies The production of ethanol is an example of how science, technology, agriculture, and

allied industries must work in harmony to change a farm product into a fuel. Ethanol

plants receive the large quantities of corn that they need by lorry, rail or barge. The corn

is cleaned, ground and blown into large tanks where it is mixed into a slurry of corn meal

and water. Enzymes are added and exact acidity levels and temperatures are maintained,

causing the starch in the corn to break down – first into complex sugars and then into

simple sugars.

New technologies have changed the fermentation process. In the beginning it took

several days for the yeast to work in each batch. A new, faster and less costly method of

continuous fermentation has been developed. Plant scientists and geneticists are also

involved. They have been successful in developing strains of yeast that can convert greater

percentages of starch to ethanol. Scientists are also developing enzymes that will convert

the complex sugars in biomass materials to ethanol. Cornstalks, wheat and rice straw,

forestry wastes and switchgrass all show promise as future sources of ethanol.

Co-products Each bushel of corn can produce 2.5–2.7 gallons of ethanol, depending on which milling

process is used. Only the starch from the corn is used to make ethanol. Most of the

substance of the corn kernel remains, leaving the protein and valuable co-products to

be used in the production of food for people, livestock feed and various chemicals. The

volume of co-products has increased dramatically with the growth in ethanol production.

In the US in 2006, ethanol dry mills produced a record 12 million tonnes of distillers grains.


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Of this, approximately 75–80% is fed to ruminants (dairy and cattle), 18–20% to swine

and 3–5% to poultry. Some estimate that production of distillers grains will reach more

than 20 million metric tonnes by the time the renewable fuel standard (RFS) is fully

implemented in 2012. This level of output will make it necessary to find new markets and

uses for co-products. New uses being considered include food, fertiliser and cat litter.

While the majority of feed is dried and sold as distillers dried grains with solubles (DDGS),

approximately 20–25% is fed wet locally, reducing energy costs associated with drying as

well as transportation costs. Ethanol wet mills produced approximately 430,000 tonnes of

corn gluten meal, 2.4 million tonnes of corn gluten feed and germ meal, and 565 million

pounds of corn oil.

Production of Lignocellulosic biomass can be converted to ethanol by hydrolysis and subsequent

ethanol from fermentation (Fan et al. 1987; Badger, 2002). Also thermo-chemical processes can be used

lignocellulosic to produce ethanol: gasification followed either by fermentation or by a catalysed reaction.

biomass Hydrolysis fermentation of lignocellulose is much more complicated than just fermentation

of sugar. In hydrolysis, the cellulosic part of the biomass is converted to sugars, and

fermentation converts these sugars to ethanol. To increase the yield of hydrolysis, a

pre-treatment step is needed that softens the biomass and breaks down cell structures

to a large extent. The pre-treatment and hydrolysis sections allow for many process

configurations. Present pre-treatment processes are primarily chemically catalysed, but both

FIGURE 3.3 Distillers grains from US ethanol refineries, 1999–2006

Source: Based on data from RFA, 2007a


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economic and environmental arguments drive the development of physical pre-treatments. The pre-treatment technology chosen affects the yield of both pre-treatment and

subsequent process steps. Acid hydrolysis processes have been used for many decades, but

have environmental consequences. Enzymatic processes under development are supposed

to have roughly equal costs to conventional processes today, but are more environmentally

sound, and these costs can be reduced further. Therefore, most studies focus on enzymatic

hydrolysis (Lynd, 1996; Ogier et al., 1999; Yu and Zhang, 2004; Sheehan, 2001). The

fermentation step, on its turn, does not yet convert all sugars with equal success. Future

overall performance depends strongly on development of cheaper and more efficient

micro-organisms and enzymes for fermentation. Newer micro-organisms may also allow for

combining more process steps in one vessel, such as fermentation of different sugars and

enzyme production (Lynd, 1996). Lastly, the biomass composition in hemicellulose, cellulose

and sugar influences the ethanol yield.

A simplified generic configuration of the hydrolysis fermentation process is shown in

Figure 3.4.

Pre-treatment Pre-treatment is required to alter the biomass macroscopic and microscopic size and

structure as well as its submicroscopic chemical composition and structure so that

hydrolysis of carbohydrate fraction to monomeric sugars can be achieved more rapidly

and with greater yields (Sun and Cheng, 2004; Mosier et al., 2005; Wyman et al., 2005a).

FIGURE 3.4 Biomass to ethanol process

Source: Based on RFA (2007d); Ladisch (2003); Wyman et al. (2005)


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Pre-treatment affects the structure of biomass by solubilising hemicellulose, reducingcrystallinity and increasing the available surface area and pore volume of the substrate.

Pre-treatment has been considered as one of the most expensive processing steps in

biomass to fermentable sugar conversion (Mosier et al., 2005).

Each type of feedstock requires a particular pre-treatment method to minimise the

degradation of the substrate and to maximise the sugar yield. There is huge scope in

lowering the cost of pre-treatment processes through extensive R&D approaches.

Pre-treatment of cellulosic biomass in a cost-effective manner is a major challenge of

cellulose to ethanol technology research and development.

Native lignocellulosic biomass is extremely recalcitrant to enzymatic digestion.

Therefore, a number of thermochemical pre-treatment methods have been developed

to improve digestibility (Wyman et al., 2005a). Recent studies have clearly proved that

there is a direct correlation between the removal of lignin and hemicellulose on cellulose

digestibility (Kim and Holtzapple, 2006). Thermochemical processing options appear

more promising than biological options for the conversion of lignin fraction of cellulosic

biomass, which can have a detrimental effect on enzyme hydrolysis. It can also serve as

a source of process energy and potential co-products that have important benefits in a

life-cycle context (Sheehan et al., 2003). Pre-treatment can be carried out in different ways

such as mechanical combination (Cadoche and Lopez, 1989), steam explosion (Gregg and

Saddler, 1996), ammonia fibre explosion (Kim et al., 2003), acid or alkaline pre-treatment

(Damaso et al., 2004; Kuhad et al., 1997) and biological treatment (Keller et al., 2003).

Each technology has advantages and disadvantages in terms of costs, yields, material

degradation, downstream processing and generation of process wastes.

Hemicellulose In order to make the cellulose feedstock more digestible by enzymes, the surrounding

hydrolysis hemicellulose and/or lignin is removed, and the cellulose microfibre structure is modified.

Chemical, physical or biological treatment are employed to solubilise the lignin and

hemicellulose. Subsequently, when water or steam is added, the free hemicellulose polymer

is hydrolysed to monomeric and oligomeric sugars. During hydrolysis, hemicellulose

sugars may be degraded to weak acids, furan derivates and phenolics. These compoundsinhibit the later fermentation, leading to reduced ethanol yields. The production of these

inhibitors increases when hydrolysis takes place at higher temperatures and higher acid

concentrations. In order to remove the inhibitors and increase the hydrolysate fermentability,

several chemicals and biological methods have been used (Martinez et al., 2000; Nilvebrant,

2001; Martin et al., 2002; Lopez et al., 2004). The detoxification of acid hydrolysates has

been shown to improve their fermentability. However, the cost is often greater than the

benefits achieved (Palmqvist and Hahn-Hagerdal, 2000; von Sivers et al., 1994).

Common chemical pre-treatment methods use dilute acid, alkaline, ammonia, organic

solvent, sulphur dioxide, carbon dioxide or other chemicals. The most important methods

are the use of acid and alkali. Acid catalysed hydrolysis uses dilute sulphuric, hydrochloric


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or nitric acids. Of all chemical pre-treatments, dilute sulphuric acid (0.5–1.5%, temperatureabove 160°C) has been most favoured for industrial application because it achieves

reasonably high sugar yields from hemicellulose: xylose yields of at least 75–90% (Sun

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