9b. BIOFUELS - biogas, biodiesel, alternative fuels - hydrogen

See also 9a. Chemistry and uses of alcohols - ethanol

Doc Brown's GCSE/IGCSE/O Level KS4 science–CHEMISTRY Revision Notes

Oil, useful products, environmental problems, introduction to organic chemistry

9b.  Biofuels

Section 9b on biofuels and alternative fuels e.g. bioethanol, biogas, biodiesel, hydrogen. These revision notes on biofuels like biogas, biodiesel and other cleaner fuels like hydrogen should prove useful for the NEW AQA GCSE chemistry, Edexcel GCSE chemistry & OCR GCSE chemistry (Gateway & 21st Century) GCSE (9–1), (9-5) & (5-1) science courses.


GCSE/IGCSE/O Level Oil Products & Organic Chemistry INDEX PAGE

See also Alcohols, Ethanol, manufacture, physical properties and chemical reactions

ALL my Advanced Level Organic Chemistry revision notes

  for more advanced notes on alcohols

9b. Biofuels

  • A discussion on biofuels and using plant materials for fuels
    • What is a biofuel? What does 'carbon neutral mean'?
      • Biofuels are alternative fuels to fossil fuels produced from plant material.
      • 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.
          • Waste biomass is obtained from the parts of plants that have no particular use and would normally be thrown away or just burned.
          • Examples, which apply to any country, include wood pulp/dust/shavings/chippings, straw, rice husks, corn stalks etc.
          • What these examples of biomass have in common is they all contain a high percentage of cellulose, a much more stable molecule that carbohydrates which are easily broken down to sugars and fermented with yeast to produce ethanol.
          • So yeast fermentation cannot be used on this kind of biomass material. Instead, genetically modified E. coli bacteria are used to break down the cellulose and convert it into ethanol. A good example, I hope, of a non-controversial use of GM biochemistry.
          • The optimum conditions for this process are 35oC and pH 6, so near body temperature and very slightly acidic.
          • The optimum conditions for the E. coli induced reactions are illustrated by the graphs below, i.e. the graph peaks show where the fastest rate of reaction happens, therefore showing the most economic reaction conditions for the process.
          • (c) doc b and
          • There is no reason why making ethanol from waste biomass isn't a viable and sustainable route for making ethanol compared to the fermentation of sugar.
          • Both processes have similarities e.g. they both use renewable plant materials, both use a relatively simple reaction chamber system.
          • Some advantages for the biomass method include (i) you don't need to grow more crops, conserving land use, (ii) you are using material that might otherwise be thrown away, but, the amount of biomass waste material is small compared to the mass of the original crop material, so large scale production of ethanol by this method is limited.
    • 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.
        • Details of this process are on the 'Ethanol Chemistry' page.
      • Making renewable fuels like bioethanol from plant materials
        • Benefits of using plant 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.
          • Slow growth eg trees for wood fuels, fast to burn! could demand be matched?,
          • or slow industrial processes like fermentation.
    • 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.
    • '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.

 

Comparison of three alternatives to vehicle fossil fuels  – their 'pros' and 'cons'

FUEL (all renewable in theory) Advantages of the biofuel, the 'pros' Disadvantages of the biofuel, the 'cons'
ETHANOL

Note that ethanol made from ethene is NOT a renewable method because ethene is made from cracking hydrocarbons from crude oil.

Advantages

a) Can be cheaply produced from sugar cane/beet on an industrial scale by fermentation.

See also 9a. Chemistry of alcohols - ethanol

b) Ethanol is easily stored and distributed as a liquid fuel.

c) Bioethanol is theoretically carbon neutral. In other words the carbon dioxide produced on burning ethanol is taken in, and balanced, by plants via photosynthesis, so the overall level of carbon dioxide in the atmosphere is not increased, minimising global warming.

d) The only products on combustion are carbon dioxide and water with no pollutants like sulfur dioxide

Disadvantages

a) Slow rate of mass production

b) Requires large areas of agricultural land or cleared woodland AND farmers may switch from growing food crops – increasing food prices and possible causing food shortages in third world countries.

c) Does produce the greenhouse gas carbon dioxide (and water), theoretically reabsorbed by plants, but fast to burn and plants slow to grow.

d) Ethanol fuels are not widely available.

e) Car engines need modifying to work with ethanol fuels.

f) Ethanol costs five times more to produce than 'straight–run' gasoline (and hydrogen is even more expensive). Quite a lot of energy is needed to distil the fermented mixture to obtain the concentrated ethanol.

HYDROGEN Advantages

a) Endless supply of water

b) Water is the only product of burning hydrogen, so its very clean non–polluting combustion. Hydrogen is the most clean burning of any fuel.

See also use of hydrogen in fuels cells

Disadvantages

a) Efficient large scale technology not yet developed to produce hydrogen on a large scale eg from electrolysis using solar power electricity – photovoltaic power system, wind turbines or hydroelectric power.

b) Although water is cheap and plentiful, it requires expensive electrical energy to electrolyse water to split it into hydrogen and oxygen.

c) Hydrogen, as a gas it is more difficult to store, needs a larger storage space (volume) and distribute safely due to it being highly flammable, easily ignited, so risk of explosion if leaked.

d) You need a special expensive? hydrogen burning car engine that is not widely available.

e) As already mentioned, hydrogen is an explosive gas and difficult to store and transport safely from the point of view of distribution to consumers.

f) Most hydrogen used in industry is actually made from fossil fuel hydrocarbons!  (see making hydrogen for the Haber Synthesis of ammonia).

BIOGAS Microorganisms can be used to break down organic waste under anaerobic conditions to produce biogas, which is mainly the hydrocarbon methane gas, CH4. You can use a variety of materials to be broken down e.g. animal waste, dead plant material.

Advantages

a) The biogas can be burned like any other fuel to produce heat. The heat can be used to generate steam to drive a turbine and electrical generator. This is quite handy for small scale electricity production in remote areas far from a national grid supply. It could also power road vehicles to.

b) Theoretically it is a renewable resource and carbon neutral  The decomposed plants are replaced by new crops, and, with the animal waste from eating plant material, the carbon is recycled by carbon dioxide formation on burning. The growth of new crops removes and balances the same carbon dioxide by the process of photosynthesis in plant leaves.

c) The raw materials for biogas are relatively cheap and readily available, mainly from agricultural sources.

d) Burning biogas is relatively clean fuel, although it produces carbon dioxide and water on combustion it does not produce much sulfur dioxide, oxides of nitrogen or carbon/hydrocarbon particulates

Disadvantages

a) At the moment biogas cannot be produced on a huge scale.

A more advanced level fuel survey which overlaps with the discussion above

This is perhaps too advanced for GCSE & IGCSE chemistry students, but its a 'mine' of information!

Fuel

Consideration Factor

Hydrogen

H2

Methane

(Natural Gas)

CH4

LPG Liquefied Petroleum Gas, mostly

Propane C3H8

& Butane C4H10

Methanol

CH3OH

An oxygenate fuel

Ethanol

CH3CH2OH

An oxygenate fuel

Coal

Mainly Carbon but contains some Sulphur

 

Suitability for road transport

Large storage volume. Not as convenient as petrol

Large storage volume. Not as convenient as petrol

Not as convenient as petrol but more dense than hydrogen or methane gases

Hygroscopic, absorbs water, causes corrosion

Hygroscopic, absorbs water, causes corrosion

NO, too inconvenient, polluting and back to the steam engine!

Safety in use

No more flammable or explosive than other gas fuels but more dangerous than liquids

No more flammable or explosive than other gas fuels but more dangerous than liquids

No more flammable than other gas fuels but more dangerous than liquids

Volatile, very flammable, toxic liquid, not as dangerous as gaseous fuels

Volatile, very flammable, toxic liquid, not as dangerous as gaseous fuels

Very safe, not flammable but a bit ‘mucky’!

Availability and cost of supply

Not readily available,   made from  water by electrolysis  –  needs energy source - Sun! but is renewable

Large naturally occurring reserves at the moment, not renewable

Large naturally occurring reserves at the moment, not renewable

More costly, has to be synthesised from CO + H2

More costly, has to be synthesised from ethene + water, can be from fermentation of plant material, so can be renewable

Big reserves, easily transported

Energy Density

J/ kg

Very high

143000kJ/kg

High

55600 kJ/kg

High

50000 kJ/kg

Lower

22700 kJ/kg

Moderate-lower

29717 kJ/kg

Moderate

~32800 kJ/kg

Can existing car engines be adapted

Yes

Yes

Yes

Yes

Yes

Not applicable!

Ease of storage and distribution-can existing network be modified

As for natural gas, so OK

Piped delivery, OK

Stored under pressure, much more dense than natural gas

Readily stored and transported just like petrol or diesel

Readily stored and transported just like petrol or diesel

Readily stored and transported

Effect on Environment

CO toxic

SO2, NO2 irritant, toxic, acid rain

Unburned CxHy carcinogens, hydrocarbon/carbon particulates

Product on combustion water, cleanest possible fuel, no pollutants emitted

Produces carbon dioxide, less polluting (less CO, NO2) than petrol or diesel, but still a contributor to the ‘Greenhouse Effect’

Produces carbon dioxide, a contributor to the ‘Greenhouse Effect’, less polluting than petrol or diesel

Cleaner burning than alkane hydrocarbon fuels, produces less CO, unburned CxHy, NO2

Cleaner burning than alkane hydrocarbon fuels, produces less CO, unburned CxHy, NO2

Very polluting, lung irritant, SO2 causes acid rain, carcinogens, Greenhouse Effect gases etc. etc.

GCSE/IGCSE/O Level Oil Products & Organic Chemistry INDEX PAGE

See also Alcohols, Ethanol, manufacture, physical properties and chemical reactions

ALL my Advanced Level Organic Chemistry revision notes * for more advanced notes on alcohols

Multiple Choice Quizzes and Worksheets

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (easier–foundation–level)

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (harder–higher–level)

KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry

and (c) doc b 3 linked easy Oil Products gap–fill quiz worksheets

ALSO gap–fill ('word–fill') exercises originally written for ...

... AQA GCSE Science (c) doc b Useful products from crude oil AND (c) doc b Oil, Hydrocarbons & Cracking etc.

... OCR 21st C GCSE Science (c) doc b Worksheet gap–fill C1.1c Air pollutants etc ...

... Edexcel GCSE Science Crude Oil and its Fractional distillation etc ...

... each set are interlinked, so clicking on one of the above leads to a sequence of several quizzes

keywords equations: C6H12O6 ==> 2C2H5OH + 2CO2 * C2H5OH + 3O2 ==> 2CO2 + 3H2O * CH2=CH2 + H2O ==> CH3CH2OH (or C2H5OH) Revision notes on biofuels biogas biodiesel bioethanol alternative fuels hydrogen KS4 Science GCSE/IGCSE/O level Chemistry Information on biofuels biogas biodiesel bioethanol alternative fuels hydrogen for revising for AQA GCSE Science, Edexcel Science chemistry IGCSE Chemistry notes on biofuels biogas biodiesel bioethanol alternative fuels hydrogen OCR 21st Century Science, OCR Gateway Science notes on biofuels biogas biodiesel bioethanol alternative fuels hydrogen WJEC gcse science chemistry notes on biofuels biogas biodiesel bioethanol alternative fuels hydrogen CIE O Level chemistry CIE IGCSE chemistry notes on biofuels biogas biodiesel bioethanol alternative fuels hydrogen CCEA/CEA gcse science chemistry (help for courses equal to US grade 8, grade 9 grade 10) science chemistry courses revision guides explanation chemical equations for biofuels biogas biodiesel bioethanol alternative fuels hydrogen educational videos on biofuels biogas biodiesel bioethanol alternative fuels hydrogen guidebooks for revising biofuels biogas biodiesel bioethanol alternative fuels hydrogen textbooks on biofuels biogas biodiesel bioethanol alternative fuels hydrogen gcse chemistry revision free detailed notes on biofuels to help revise igcse chemistry igcse chemistry revision notes on biofuels O level chemistry revision free detailed notes on biofuels to help revise gcse chemistry free detailed notes on biofuels to help revise O level chemistry free online website to help revise biofuels for gcse chemistry  free online website to help revise biofuels for igcse chemistry free online website to help revise O level biofuels chemistry how to succeed in questions on biofuels for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on biofuels to help to pass gcse chemistry questions on biofuels a good website for free help to pass igcse chemistry with revision notes on biofuels a good website for free help to pass O level chemistry

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GCSE/IGCSE/O Level Oil Products & Organic Chemistry INDEX PAGE

See also Alcohols, Ethanol, manufacture, physical properties and chemical reactions

ALL my Advanced Level Organic Chemistry revision notes

for more advanced notes on alcohols

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