Chapter 25. Chapter 25: Biofuels

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Guiding Question 25.1

What are biofuels, and what are potential biofuel sources?

Why You Should Care

Biofuels are "hot" these days because they are currently offering the most promise as a replacement for petroleum-based fuels. A biofuel is, not surprisingly, fuel produced from living organisms. Nearly all such fuel is either produced directly by autotrophs or by yeasts or bacteria fermenting the carbohydrates produced by autotrophs. These fuels can be hydrocarbons, oils, or alcohols, but all share the quality of being able to release a lot of energy when combusted. Many different sources of biofuels are being researched: Algae, grass, corn, and oil palms are just a few examples. One biofuel is already being used commercially: Biodiesel has been available for years as an alternative to petroleum-based diesel fuel. Biodiesel is produced by chemically altering vegetable oil (usually used frying oil reclaimed from restaurants and food manufacturing plants), and can be used interchangeably with diesel in vehicles, machinery, and household oil-furnaces. Although a renewable, carbon-neutral fuel source, biodiesel alone can’t meet the world’s fuel needs because there isn’t enough used vegetable oil. Since it is likely that other biofuels will soon join the market, it is important to be informed about their pros and cons.

Test Your Vocabulary

Choose the correct term for each of the following definitions:

Term Definition
Solids, liquids, or gases that produce energy from biological material.
Plants that live for more than a year, growing and producing seed year after year.
Biomass sources used to make biofuels.
An alcohol fuel made from crops like corn and sugarcane in a process of fermentation and distillation.
Crops specifically grown to be used to produce biofuels.
A liquid fuel made from vegetable oil, animal fats, or waste oil that can be used directly in diesel internal combustion machine.
Plants that live for a year, produce seed, and then die.
Material from living or recently living organisms or their by-products.
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1.

Most of the biofuel currently produced in the United States is derived from:

A.
B.
C.
D.
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6.

Thought Question: Are the composite briquettes above a direct biomass energy source or a biofuel? Why?
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Being pictured with the other direct biofuel sources is the first clue that these briquettes are also considered a direct source, but why? The briquettes are definitely manufactured, so they are different in form from the original biomass, which makes them seem to fit into the biofuel category. But, the waste biomass that makes up the briquettes hasn't actually been chemically changed into a different substance, and that makes them a direct source.

Match the descriptions below with all of the possible energy sources that fit them:

7.

Non-edible source that can be used for direct biomass energy and produced expressly for that purpose:

Wood

Corn stalks

Manure

Switchgrass

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Hint: Think about which source(s) is/are not waste products and used directly for biomass energy.

11.

Although a source of biofuel, ____ is NOT typically used to produce bioethanol.

A.
B.
C.
D.
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15.

Select the number in the figure that best corresponds with the items below:

Glycerin:

Lye and methanol:

Methanol:

Feedstock:

Water:

Pre-processing:

Step that includes filtering solids:

Washing to remove impurities from biodiesel:

Chemical reaction:

By-product that can be sold for other uses:

Can be reused for creating fuel:

Can be reused to remove impurities:

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18.

Algae are BEST described as:

A.
B.
C.
D.
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