Liquid Biofuels for Transport Prospects, risks and opportunities
1. What are biofuels?
- 1.1 What is bioenergy?
- 1.2 What are the different types of liquid biofuels for transport?
- 1.3 What are second-generation biofuels?
- 1.4 How much liquid biofuel could be produced?
1.1 What is bioenergy?
Traditional biomass is largely used in developing countries
for cooking and heating
Credit: Roberto Faidutti
Bioenergy is energy derived from
biofuels. Biofuels are
fuels produced directly or indirectly from organic material –
biomass – including plant
materials and animal waste.
Overall, bioenergy covers approximately 10% of the total world
energy demand. Traditional unprocessed
biomass such as
fuelwood, charcoal and
animal dung accounts for most of this and represents the main
source of energy for a large number of people in developing
countries who use it mainly for cooking and heating.
More advanced and efficient conversion technologies now allow
the extraction of
from materials such as wood, crops and waste material. Biofuels
can be solid, gaseous or liquid, even though the term is often
used in the literature in a narrow sense to refer only to liquid
biofuels for transport.
Biofuels may be derived
from agricultural crops, including conventional food plants or
from special energy crops. Biofuels may also be derived from
forestry, agricultural or fishery products or municipal wastes,
as well as from agro-industry, food industry and food service
by-products and wastes.
A distinction is made between primary and secondary
biofuels. In the case of
primary biofuels, such as
fuelwood, wood chips and
pellets, organic materials are used in an unprocessed form,
primarily for heating, cooking or electricity production.
Secondary biofuels result from processing of
biomass and include liquid
biofuels such as ethanol
and biodiesel that can be
used in vehicles and industrial processes.
Bioenergy is mainly used in homes (80%), to a lesser extent in
industry (18%), while
liquid biofuels for transport
still play a limited role (2%).
Even though the production of liquid
biofuels for transport has
grown rapidly in recent years it currently represents only 1% of
total transport fuel consumption and only 0.2 to 0.3% of total
energy consumption worldwide.
1.2 What are the different types of liquid biofuels for transport?
The most widely used liquid
biofuels for transport are
is a type of alcohol that
can be produced using any
significant amounts of sugar, such as sugar cane or sugar beet,
or starch, such as maize
and wheat. Sugar can be directly fermented to alcohol, while
starch first needs to be converted to sugar. The
fermentation process is
similar to that used to make wine or beer, and pure ethanol is
obtained by distillation. The main producers are Brazil and the
Ethanol can be blended
with petrol or burned in nearly pure form in slightly modified
spark-ignition engines. A litre of ethanol contains
approximately two thirds of the energy provided by a litre of
petrol. However, when mixed with petrol, it improves the
combustion performance and lowers the emissions of carbon
monoxide and sulphur oxide.
is produced, mainly in the European Union, by combining
vegetable oil or animal fat with an
alcohol. Biodiesel can be
blended with traditional diesel fuel or burned in its pure form
in compression ignition engines. Its energy content is somewhat
less than that of diesel (88 to 95%). Biodiesel can be derived
from a wide range of oils, including rapeseed, soybean, palm,
coconut or jatropha oils and therefore the resulting fuels can
display a greater variety of physical properties than
Diesel engines can also run on vegetable oils
and animal fats, for instance used cooking oils
from restaurants and fat from meat processing industries.
The production processes for both bioethanol and
biodiesel yield additional
by-products such as animal feed.
1.3 What are second-generation biofuels?
Currently used liquid
biofuels, which include
ethanol produced from crops
containing sugar and starch
and biodiesel from
oilseeds, are referred to as
first-generation biofuels. These fuels only use
a portion of the energy potentially available in the
Most plant matter is composed of
and lignin, and
technologies refer to processes able to convert these components
to liquid fuels. Once commercially viable, these could
significantly expand the volume and variety of sources that
could be used for biofuel production.
sources include municipal waste and waste products from
agriculture, forestry, processing industry as well as new energy
crops such as fast growing trees and grasses. As a result second
production could present major advantages in terms of
sustainability and reduced
competition for land with food and feed production. It could
also offer advantages in terms of
greenhouse gas emissions.
Various techniques are currently being developed to produce
second generation biofuels.
However, it is uncertain when such technologies will enter
production on a significant commercial scale.
conversion of cellulose to ethanol
involves two steps. The
hemicellulosic components of the plant material are first broken
down into sugars, which are then fermented to obtain ethanol.
The first step is technically difficult, although research
continues on developing efficient and cost-effective ways of
carrying out the process. Lignin cannot be converted to ethanol,
but it can provide the necessary energy for the conversion
Gasification is a technique that converts
solid biomass such as wood
into a fuel gas. Gasifiers operate by heating biomass to high
temperatures in a low-oxygen environment releasing an
energy-rich gas. This gas can be burned in a boiler, used in a
gas turbine to generate electricity.
1.4 How much liquid biofuel could be produced?
Current world oil demand amounts to about 4000 Million tonnes
of oil equivalent (Mtoe) while the production of liquid
biofuels amounts to 36 Mtoe
representing less than 1% of this world demand.
Around 85% of the liquid
biofuels are currently
produced in the form of bioethanol with the main producers being
Brazil and the USA.
Biodiesel production is
essentially concentrated in the European Union.
Table 1: Biofuel production by country, 2007
Large-scale production of
biofuels from crops
requires large land areas to grow them, which generates
increasing competition for natural resources, notably land and
water.Crop yields per hectare vary widely depending on the type
of crop, the country and the production system. Currently,
ethanol production from
sugar cane and sugar beet produces the highest yields per
Table 2: Biofuel yields for different feedstocks and countries
In its World Energy Outlook 2006, the IEA projected an
increase in the share of the world’s fertile land used to grow
plants for liquid biofuel
production from 1% in 2004 to around 4% in 2030, assuming
favourable government policies and reasonable technical
biofuel technologies, this
land use would allow 5% of
transport fuel demand to be met. If second-generation biofuel
technologies were available, this could rise to 10%.
This illustrates that
biofuels can only be
expected to displace
fossil fuels for transport
to a very limited extent. Nevertheless, they have a significant
effect on global agriculture and agricultural markets because of
the large volumes of
feedstocks and land areas
needed for their production.