Biofuels: Chemistry of Alcohols - Ethanol

Biofuels
 A discussion on biofuels and using plant materials for fuels

 As well as specific crops like sugar cane or vegetable oils, all sorts of other organic materials
can be used to make biofuels e.g. animal droppings, farm waste, landfill rubbish
o What is a biofuel? What does 'carbon neutral mean'?
 Biofuels are alternative fuels to fossil fuels produced from plant material.
 They are referred to as renewable because more can be grown, recycling the carbon absorbed
in photosynthesis.
 They can be burnt to power electricity generation or used as fuel in road vehicles.
 Ideally they are 'carbon neutral', that is the carbon dioxide the they give off on combustion is
matched by the plant absorbing the same amount of carbon dioxide.
 The absorbed carbon dioxide is then utilised in photosynthesis to regenerate the plant material
ie remaking the same amount of biofuel again. So, its a sort of mini–carbon cycle.
 Renewable Biofuels that can be burned to heat water to make steam to drive a turbine and
generator.
 Biofuels are renewable energy sources and come in a variety of forms eg woodchips (trees
or waste from timber products), alcohol (ethanol from fermenting sugar cane), biodiesel (from
vegetable oil) and biogas (methane from anaerobic digestion of sewage waste) and are all
derived from plant materials eg crops or bacterial digestion/decay of waste organic material.
 The theoretical 'carbon neutral' idea behind using biofuels is that the carbon dioxide released
on burning is re–absorbed by plants and utilised in photosynthesis to create the next fuel crop.
But, even though this sounds fine in principle, there are still environmental issues eg in Brazil
and other countries, huge areas of ecological valuable natural rain forest (habitats, species rich)
are being cut down to grow crops for biofuels.
 More on making ethanol from biomass.
 .
o Ethanol is an example of a renewable biofuel from plant material.
 See also 9a. Chemistry of alcohols - ethanol
 What is 'gasohol'? Ethanol and petrol can be mixed to make a motor vehicle fuel
 Countries like Brazil, that have no oil reserves of their own, and importing oil is costly, so they
are very interested in the manufacture of biofuels, i.e. fuels that can be derived from plant crop
materials.
 Some ethanol is used in blends of petrol ( a 'gasohol') eg in Brazil (called 'alcool') with a cheap
labour force (local population or migrant labour) and large land areas growing sugar cane.
 A typical composition of 'gasohol' might be 10% ethanol (ethyl alcohol) and 90% unleaded petrol
(gasoline).
 It is less polluting than ordinary petrol, it burns more cleanly-efficiently.
 It also makes the imported oil go a bit further!
 The renewable sugar cane crop is crushed and the sugar extracted with hot water and the
solution fermented with yeast.
 The alcohol is fractionally distilled from the filtered fermented solution and can then be used as
a biofuel.
 Making renewable fuels like bioethanol from plant materials
 Benefits of using plant or animal materials to produce fuels
 Naturally, they are all renewable.
 Drawbacks and risks to using plant materials to produce fuels
 Large areas of agricultural land or woodland required - the land is often prepared for crop
growing by clearing large areas of forest by burning - polluting smoke, removal of wildlife habitat,
reducing biodiversity.
 Slow growth eg trees for wood fuels, fast to burn! could demand be matched?,
 or slow industrial processes like fermentation.
o Biodiesel is another biofuel derived from plant material.
 Biodiesel can be made from vegetable oils (and animal fat or waste cooking oil) which contain
glycerol esters of long–chain fatty acids.
 These vegetable oils/fats like rapeseed oil and soybean oil can re–esterified (transesterification)
into methyl esters to make a fuel that can be used directly as diesel fuel or mixed with regular
diesel fuel.
 Vegetable oils are suitable for diesel fuel and release lots of energy on combustion just like
petrol or conventional diesel.
 Biodiesel has similar physical and chemical properties to ordinary diesel from crude oil and
burns in conventional diesel engines.
 The simple word equation for processing vegetable oil into biodiesel fuel is ...
 oil/fat + methanol ==> biodiesel + glycerol
 glycerol ester + methanol (an alcohol) ==> methyl ester + glycerol (another sort of alcohol)
 Pros – advantages of using biodiesel
 Biodiesel, is in theory, another 'carbon neutral' renewable fuel.
 Biodiesel is readily biodegradable, so less harmful to the environment if spilled compared to
hydrocarbon oils which take much longer to break down.
 Existing diesel engines don't need converting.
 Cons – disadvantages of using biodiesel
 Its relatively expensive to make (small scale production compared to the petrochemical industry
based on crude oil).
 There won't be enough to replace diesel from crude oil.
 Farmers (especially in third world countries) may switch from essential food production to
producing plant oils to make biodiesel, thereby increasing food prices and maybe creating food
shortages.
o 'Alternative fuels'
 Think in terms of use of renewable resources, storage and use of the fuels, their products of
combustion.
 Ethanol is one of the more recent 'alternative fuels' to traditional fossil fuels like coal, gas and
oil.
 If an efficient source of hydrogen production could be found, this could be another fuel.

Biofuels: Chemistry of Alcohols - Ethanol

Uploaded by

Copyright:

Available Formats

Biofuels: Chemistry of Alcohols - Ethanol

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Biofuels: Chemistry of Alcohols - Ethanol

Uploaded by

Copyright:

Available Formats

Biofuels

 A discussion on biofuels and using plant materials for fuels

You might also like