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Advances in BioethanolPratima Bajpai
Published by
Pira International Ltd
Cleeve Road, Leatherhead
Surrey kt22 7ru
UK
T +44 (0) 1372 802080
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The facts set out in this publication
are obtained from sources which we
believe to be reliable. However, we
accept no legal liability of any kind
for the publication contents, nor any
information contained therein nor
conclusions drawn by any party from it.
No part of this publication may be
reproduced, stored in a retrieval
system, or transmitted, in any form or
by any means, electronic, mechanical,
photocopying, recording or otherwise
without the prior permission of theCopyright owner.
ISBN 1 85802 518 4
© Copyright
Pira International Ltd 2007
Head of publications and events
Philip Swinden
Publisher
Rav Lally
Head of editorial
Adam Page
Global editor
Nick Waite
Head of US publishing
Charles E. Spear, [email protected]
Assistant editor
Claire Jones
Customer services manager
Denise Davidson
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Typeset in the UK by
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Pira International Ltd acknowledges product, service and company names referred to
in this report, many of which are trade names, service marks, trademarks or registered
trademarks.
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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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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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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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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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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
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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
Source: Pira International Ltd
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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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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Advances in BioethanolEthanol: an overview
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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Advances in BioethanolEthanol: an overview
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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Advances in BioethanolEthanol: an overview
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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Advances in BioethanolEthanol: an overview
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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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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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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Advances in BioethanolProduction of bioethanol
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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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
Source: Pira International Ltd
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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