Biofuels: A Renewable Energy Source
Definition
Biofuels
Biofuels are energy sources derived from biological materials such as plants, algae, or organic waste.
- Unlike fossil fuels, which take millions of years to form, biofuels are produced relatively quickly through processes like photosynthesis and fermentation.
- This rapid production cycle makes biofuels a renewable energy source.
Biological Carbon Fixation and Photosynthesis
- Plants are at the heart of biofuel production.
- Through photosynthesis, they absorb carbon dioxide ($CO_2$) and water ($H_2O$) to produce glucose ($C_6H_{12}O_6$) and oxygen ($O_2$): $$6CO_2(g) + 6H_2O(l) \rightarrow C_6H_{12}O_6(aq) + 6O_2(g)$$
- The glucose generated can then be converted into biofuels like ethanol through fermentation.
- Think of plants as nature’s solar panels.
- They capture sunlight and store its energy in the form of glucose, which can later be transformed into biofuels for human use.
Ethanol as a Biofuel
- Ethanol, a type of alcohol, is one of the most widely used biofuels.
- It can be blended with gasoline or used on its own as a renewable fuel.
- Ethanol is typically produced through the fermentation of glucose by yeast under anaerobic conditions (no oxygen present): $$C_6H_{12}O_6(aq) \rightarrow 2C_2H_5OH(aq) + 2CO_2(g)$$
- While this process releases carbon dioxide, the $CO_2$ emitted is part of a short-term cycle, as it was recently absorbed by plants during photosynthesis.
This is why ethanol is often considered "carbon neutral" (though this term has its complexities, as discussed later).
Example question
If 180 g of glucose ($C_6H_{12}O_6$) undergoes fermentation, how much ethanol is produced?
Solution
- Molar mass of glucose $= 180 \text{ g mol}^{-1}$, ethanol $= 46 \text{ g mol}^{-1}$.
- From the balanced equation, 1 mol of glucose produces 2 mol of ethanol.
- Mass of ethanol produced = $2 \times 46 = 92 \, \text{g}$.
- Thus, 180 g of glucose produces 92 g of ethanol.
Why Are Biofuels Considered Renewable?
- Biofuels are renewable because they are derived from resources like crops, algae, and organic waste, which can be replenished annually.
- This contrasts with fossil fuels, which require millions of years to form.
- However, biofuels still release $CO_2$ when burned: $$C_2H_5OH(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l)$$
- The key difference is that the $CO_2$ emitted during combustion is part of a short-term carbon cycle.
- It was absorbed from the atmosphere by plants during photosynthesis, making biofuels potentially more sustainable than fossil fuels, which release ancient, stored carbon into the atmosphere.
- While biofuels are often described as "carbon neutral," this assumes that all $CO_2$ emissions are offset by plant absorption.
- In reality, factors like land use changes and production processes can influence their overall carbon footprint.
Advantages of Biofuels
Biofuels offer several benefits that make them an attractive alternative to fossil fuels:
