Biofuels

Renewable resources will not run out in the foreseeable future because they can be replaced over a relatively short period of time
They can also be called infinite
They can be considered sustainable as they can be produced at the same rate, or faster, than they are being used
Biofuels are an example of a renewable resource

Non-renewable resources will run out in the foreseeable future as there are limited supplies
- They cannot be replaced within a short time period
They can also be called finite
They are not a sustainable resource
Fossil fuels are an example of a non-renewable resource

Reduce pollution from the combustion of fossil fuels
Have positive impacts on global warming and climate change
The finite supply / limited amount and depletion of fossil fuels, which are non-renewable resources

Green plants absorb atmospheric carbon dioxide and convert it into glucose via photosynthesis
- Word equation for photosynthesis:

carbon dioxide + water → glucose + oxygen

6CO₂ (g) + 6H₂O (l) → C₆H₁₂O₆ (aq) + 6O₂ (g)

The glucose is then further converted into ethanol by fermentation
- The name bioethanol is simply identifying how the ethanol has been produced
When biofuels are produced this way, they can be considered carbon neutral
- This is because the carbon dioxide absorbed during photosynthesis equals the carbon dioxide produced by the combustion of the biofuel

Biodiesel is made from renewable vegetable oils rather than non-sustainable petrochemicals
Natural triglyceride oils are converted to esters of methanol, which makes them less viscous
Biodiesel made from rapeseed oil, for example, is produced by transesterification
- The triglyceride is converted into the less viscous fatty acid methyl ester (FAME) using methanol
  - An acid works by protonating the carbonyl group
  - An alkali works by deprotonating the alcohol / methanol
  - However, it is more common to use an alkaline catalyst such as NaOH / KOHAcids and alkalis can both be used to catalyse the reaction
The transesterification is reversible, so an excess of methanol is used to drive the equilibrium to the right
Under optimum conditions, this process can produce a very successful yield of 98%

Transesterification forming methyl esters

Biogas is a renewable fuel that is released when organic matter, such as food or animal waste, is broken down by microorganisms in the absence of oxygen
It consists mainly of methane and carbon dioxide but can also include small amounts of hydrogen sulphide and other chemicals
The relative amounts of the components of biogas depend on the type of waste used
- The bacterial decomposition of carbohydrates such as produces biogas with 50.0% methane content

C₆H₁₂O₆ (s) → 3CO₂ (g) + 3CH₄ (g)

- Fatty acids such as heptadecanoic acid, commonly called oleic acid, can undergo bacterial decomposition in a more moisture-rich environment to produce biogas with a 69.4% methane content

4C₁₇H₃₃COOH (l) + 34H₂O (l) → 21CO₂ (g) + 51CH₄ (g)

Carbon neutral, renewable and sustainable if crops / trees are replanted
Reduce greenhouse emissions / pollution
Biodiesel and biogas can reduce the amount of waste going to landfill sites as the waste can be used to produce them
Biofuel production could provide money for less developed countries as they have the space to grow the crops required
Can provide jobs in the agriculture and energy sectors

High costs
- Conversion of engines and machinery to run on biofuels instead of petrol / diesel
- Harvesting and transportation
Many developed countries don't have the space to be able to produce enough plants to make biofuels because the land is needed for food production
- This can lead to deforestation in an effort to meet the demand
Removes nutrients from the ground / uses large amounts of fertilisers and pesticides
Biofuels typically have lower specific energy than fossil fuels

Biofuels (HL IB Chemistry)