6 Biofuels

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Objectives

• Students should learn:• that biofuels can be made from natural

products by anaerobic fermentation• that there are advantages and disadvantages

in using ethanol-based biofuels.

Outcomes

• Most students should be able to:• describe how yeast can produce ethanol for fuel• describe the advantages and disadvantages of using

ethanol-based fuels• describe how second-generation biofuels are being

developed.• Some students should also be able to:• interpret economic and environmental data relating

to the production of fuels by fermentation and their uses.

Specification

Biofuels can be made from natural products by anaerobic fermentation.

Deforestation has occurred so that: ■ crops can be grown from which biofuels,

based on ethanol, can be produced

Biology B3 4.6 Biofuels

Answers to in-text questions

a They are fast-growing and contain a lot of sugar that can be fermented. b There is no overall increase in the levels of carbon dioxide in the air as a result of the industry in question.

Summary answers

 1 2 a i 725 million gallons. ii 730 million gallons. iii 4850 million gallons.

b Use of ethanol as a fuel grew steadily through the 1980s and 1990s but has increased dramatically in the first 7 years of the 21st century. Any other points givingsuggested reasons can be credited.     

Compulsory slides you must complete and use;

biofuels can be made from natural products by anaerobic fermentation

• How• Is it increasing?• Give a word equation for fermentation in

microbes• Say what gasohol is• Could use http://www.treepower.org/

http://www.ecocentre.org.uk/

advantages and disadvantages in using ethanol-based biofuels.

• advantages • disadvantages

‘fun’ activity

• Show these 2 movies• http://www.youtube.com/watch?v=TY

HoeIvb8I4 texaco gasohol movie

• http://www.youtube.com/watch?v=GOFbsaNeZps top gear biodiesel

Slides you may wish to use;

What are biofuels?

Unlike fossil fuels, biofuels provide a renewable source of energy. Biofuels are also thought to have less of an impact on the environment than fossil fuels.

Biogas – produced from the breakdown of organic material.

Biofuels are fuels made using living organisms or the waste that they produce. These include:

Ethanol – produced by the fermentation of sugar from plant material.

What is ethanol-based fuel?Ethanol produced by the anaerobic fermentation of glucose by yeast is used to make fuels such as gasohol.

Gasohol normally contains 10% ethanol and 90% petrol. This allows gasohol to be used in unmodified petrol engines.

It is successfully used as a fuel for cars in Brazil and the USA. Brazil produces ethanol from sugar cane, whereas the USA uses maize.

How is ethanol produced?Ethanol is produced by carrying out the following steps.

3. Once fermentation is complete pure ethanol is obtained by distilling the mixture.

1. Glucose is obtained from either:

2. Yeast are added to the glucose, they respire anaerobically, producing ethanol and carbon dioxide.

maize starch broken down into glucose by the action of carbohydrase enzymes

sugar cane juices.

What are the advantage of biofuels?Biofuels are thought to produce lower greenhouse gas emissions and particulates than conventional transport fuels.

Biofuels can also be cheaper to use for drivers, as governments often introduce schemes to encourage people to reduce their emissions.

Biomass is a renewable source of energy, therefore biofuels are a more sustainable form of energy as it will not run out.

Using biofuels instead of fossil fuels can also help to conserve the world’s non-renewable fuel resources.

Carbon neutral?

What are the disadvantages of biofuels?Biofuels are not completely carbon neutral because energy is used in the production and transportation of the biofuel. This energy is often provided by fossil fuels.

There are also concerns that the production of biofuels could affect food production. As biofuel production increases, more land is being used for growing crops for fuels such as gasohol. This could mean that less land is being used for food production, causing a shortage of food.

Land previously unused is being harnessed for biofuel crops, this could contribute to a loss in biodiversity.

Which biofuel?

Using ethanol as biofuel for cars• Advantages• Co2 neutral• Little pollution• Efficient• Can mix with petrol so current cars can be converted to it

• Disadvantages• Expensive to produce/right conditions needed• Use lots of land/need large amount of plant material• Still pollution if mixed with petrol• Lots of cellulose waste – can we develop this in future?

Which biofuel would you use to:

Power a vehicle?

Generate electricity?

Cook your food?

Heat your home?

Yak faeces

Energy output: 2Ease of use: 3 OK, need to dry out before use

Ease of production: 4

Poor

Simple - if you keep yaks!

Uses: 1 Mainly for cooking in special stovesEquipment needed: 3 Modified stovesFumes produced: 1 Very smoky!FA

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Willow

Energy output: 3Ease of use: 3 Good

Ease of production: 3

Good

Two years to produce crop

Uses: 2 Mainly in modified power stations

Equipment needed: 3 Modified burners

Fumes produced: 3 Smoke can be produced if burning is not controlled carefully

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Gasohol

Energy output: 4Ease of use: 4 Same as ordinary petrol

Ease of production: 2

Excellent

Requires a fermentation plant to produce the alcohol which is then added to petrol.

Uses: 2 Mixed with petrol in standard cars

Equipment needed: 4 Some cars need to be modified (particularly if alcohol:petrol mix uses more than 10% alcohol)Fumes produced: 4 Cleaner than petrol alone

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Biodiesel

Energy output: 4Ease of use: 4 Same as standard diesel

Ease of production: 2

Excellent

Requires a chemical plant to extract the oil from crops and then modify it to make diesel.

Uses: 2 In diesel-engined road vehiclesEquipment needed: 5 Standard diesel engineFumes produced: 4 Cleaner than standard dieselFA

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Biogas

Energy output: 4Ease of use: 4 Same as standard gas

Ease of production: 2

Excellent

Requires a digester which can convert old organic wastes to methaneUses: 4 Heating, cooking and power stations

Equipment needed: 5 Standard gas applianceFumes produced: 4 Very cleanFA

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