R1.3.4 Biofuels

Biofuels: A Renewable Energy Source

You’re at a fuel station, and alongside the regular gasoline pump, there’s one marked "Ethanol Blend – Renewable Fuel."
You pause for a moment and wonder, “What exactly makes this fuel renewable? How does it differ from traditional fossil fuels, and why is it gaining attention globally?”

What Are Biofuels?

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 ( $C O_{2}$ ) and water ( $H_{2} O$ ) to produce glucose ( $C_{6} H_{12} O_{6}$ ) and oxygen ( $O_{2}$ ): $6 C O_{2} (g) + 6 H_{2} O (l) \to C_{6} H_{12} O_{6} (a q) + 6 O_{2} (g)$
The glucose generated can then be converted into biofuels like ethanol through fermentation.

Analogy

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): $C_{6} H_{12} O_{6} (a q) \to 2 C_{2} H_{5} O H (a q) + 2 C O_{2} (g)$
While this process releases carbon dioxide, the $C O_{2}$ 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

If 180 g of glucose ( $C_{6} H_{12} O_{6}$ ) undergoes fermentation, how much ethanol is produced?

Molar mass of glucose = 180 g/mol, ethanol = 46 g/mol.
From the balanced equation, 1 mol of glucose produces 2 mol of ethanol.
Mass of ethanol produced = $2 \times 46 = 92 g$ .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 $C O_{2}$ when burned: $C_{2} H_{5} O H (l) + 3 O_{2} (g) \to 2 C O_{2} (g) + 3 H_{2} O (l)$
The key difference is that the $C O_{2}$ 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.

Note

While biofuels are often described as "carbon neutral," this assumes that all $C O_{2}$ 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:

1. Renewable and Sustainable

Biofuels are derived from resources that can be regrown or replenished, ensuring a sustainable energy supply.

2. Carbon Neutral Potential

The $C O_{2}$ released during combustion is offset by the $C O_{2}$ absorbed during photosynthesis, potentially reducing their net contribution to greenhouse gas emissions.

3. Biodegradability

Unlike fossil fuels, biofuels break down more easily in the environment, reducing the risk of long-term contamination from spills.

4. Economic Security

By producing biofuels domestically, countries can reduce their dependence on imported oil, enhancing energy security.

Tip

Ethanol is commonly blended with gasoline to improve fuel efficiency and lower greenhouse gas emissions. For example, E10 fuel contains 10% ethanol and 90% gasoline.

Disadvantages of Biofuels

Despite their benefits, biofuels come with challenges that must be addressed:

1. Land Use Concerns

Producing biofuels on a large scale requires significant agricultural land, which could otherwise be used for food production.

Note

This raises ethical concerns about food security, particularly in regions experiencing hunger.

2. Lower Energy Density

Biofuels like ethanol have a lower energy density than fossil fuels.

Example

Ethanol contains about 30% less energy per liter than gasoline, meaning vehicles require more fuel to travel the same distance.

3. Environmental Impact

The farming practices required for biofuel crops can lead to soil degradation, water pollution, and biodiversity loss.

Additionally, deforestation to create farmland for biofuel crops can release large amounts of $C O_{2}$ , counteracting their environmental benefits.

4. High Production Costs

Growing, harvesting, and processing biofuel crops can be expensive, making biofuels less economically competitive in some cases.

Common Mistake

It’s a common misconception that biofuels are entirely "green." Their environmental impact depends on factors like how crops are grown, land use changes, and the energy required for production.

Reflection Prompts

Self review

Write the balanced chemical equation for the fermentation of glucose to produce ethanol.
Explain why ethanol is considered a renewable fuel.
List two advantages and two disadvantages of biofuels.

Theory of Knowledge

How should societies balance the need for renewable energy with ethical concerns about land use and food security?
What policies could governments implement to ensure sustainable biofuel production?

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