Chapter 29. Chapter 29: Biofuels

What are biofuels and what are potential biofuel sources?

Interactive Study Guide

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Guiding Question 29.4

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.

Question Test Your Vocabulary

Choose the correct term to match each of the following definitions.

Term	Definition
LWQ5qsGZH2P1f49TDYxGdYvifubmuSEqMM14vLBkIUzPeFHJFSbKxNLUAECK6itDRLR/mTSpBiKiMLLQWOWKTL9cNHIekX4b	Farming method in which one variety of one crop is planted, typically in rows over large areas with large inputs of fertilizer, pesticides, and water.
udZRL/SadvkogOeQxAzr9Wryk+AWLOVAvznkQxoLYEomTRci9veYIRiYMdp+6Xu6YV/8gd+URHAz8mp+GfsO9ydXQMA5x00/	Bioethanol made by breaking down cellulose in plants; a difficult process that has yet to be scaled up to meet large production goals.
SaD+FvsSWfbYhf05hy0zVjFYj/CK8TTuCtnyKJmGW4EkAplwm+bcxoTETFYn6oOrMl0AnZlI/YdMBPooPScTYnn1WUWcRsj0	The amount of carbon released during the first 50 years of land clearing for biofuel feedstocks.
CIvpddi4tuXoLnzFhbWYhrEEbIpYymbn02BW2OcgkE/6PPQCZDmY/61KUcmYit6ty0iG9UDGvUmiJspewGOwdHS6ylsAEOn5	The storage of carbon in a form that does not readily release the carbon to the atmosphere or water.

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Question 29.1

yE1D2tg3idvp+yyC9BfpvgUsgyEkallzW/oh/YyD4GEipJ2rhOQzMnGVowJyBlRH1tupVmcxdCUpOpgD3WgEomJecT9ei9byuxLYm133MRXU5wHQlFOYWRqoba3TYwwG5ntXb65V4EQVcBXlapHhPaxhhBExmNIoW4ZAmpk+TBnzxrU6PTTjHHK9nzGyPiW1qpno9Gtn7g4wCl4ytb6IDrOGa8v58++Wny4Bbq6/xjMfQbZLRbfd3Xh4OFHchqgy+gVEUH8mjDpzd7qHBmpB9H5+JHno3UbRZUoz9i1rJZExfqdawtczVum3fEGfK86oU/ummIWVwHjk711hvPTRE8Poc+WCDYUJdFiOu0WdvI28uTSrVzzJQ0LQAMBRy/y6onEDaoNLUENpjSzu3DTNM/jnqSSEapl6gMZDo2e6jEeA/hm525xYITLkgXs=

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Question 29.2

ITicPSCCsySdVYNtdNcBMPT5kyx2DxJFK/qCOWMjESCm/lgW33UnpecQycARWJMuZCuJX6LXQZw8OlWQHfvJxseoL5YPJW2phCXUQNj/ZRQhmU1ZbnOUpVtWoeFRqd6tFug2tll2MBx4HVglWvEZ8TyoCLpH0C7R

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Question 29.3

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Question 29.4

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Question 29.5

Match the numbers in the diagram above to the items listed below. Note that more than one number may correspond to a description.

Feedstock:

1: aFyLQOV9P9qF6KzY 2: 6Tla4sTC7UhhcmHA 8: aFyLQOV9P9qF6KzY 9: 6Tla4sTC7UhhcmHA

Enzymes are added:

3: aFyLQOV9P9qF6KzY 5: 6Tla4sTC7UhhcmHA 10: 6Tla4sTC7UhhcmHA 11: aFyLQOV9P9qF6KzY

By-product:

2: 6Tla4sTC7UhhcmHA 6: aFyLQOV9P9qF6KzY 10: 6Tla4sTC7UhhcmHA 12: aFyLQOV9P9qF6KzY

Heating to kill microbes:

4: aFyLQOV9P9qF6KzY 5: 6Tla4sTC7UhhcmHA 7: 6Tla4sTC7UhhcmHA 10: 6Tla4sTC7UhhcmHA

Increases surface area for reaction:

2: aFyLQOV9P9qF6KzY 7: 6Tla4sTC7UhhcmHA 9: aFyLQOV9P9qF6KzY 10: aFyLQOV9P9qF6KzY

Yeast is added to ferment sugars:

3: 6Tla4sTC7UhhcmHA 5: aFyLQOV9P9qF6KzY 7: 6Tla4sTC7UhhcmHA 11: 6Tla4sTC7UhhcmHA

By-product typically used for making animal feed:

1: 6Tla4sTC7UhhcmHA 6: aFyLQOV9P9qF6KzY 10: 6Tla4sTC7UhhcmHA 12: 6Tla4sTC7UhhcmHA

By-product typically used for producing electricity:

1: 6Tla4sTC7UhhcmHA 6: 6Tla4sTC7UhhcmHA 10: 6Tla4sTC7UhhcmHA 12: aFyLQOV9P9qF6KzY

Ethanol separated from watery mixture:

3: 6Tla4sTC7UhhcmHA 5: 6Tla4sTC7UhhcmHA 7: aFyLQOV9P9qF6KzY 11: 6Tla4sTC7UhhcmHA

Distillation:

3: 6Tla4sTC7UhhcmHA 5: 6Tla4sTC7UhhcmHA 7: aFyLQOV9P9qF6KzY 11: 6Tla4sTC7UhhcmHA

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Question 29.6

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Both numbers 3 and 11 are enzyme-addition steps used to break the feedstocks down into simpler molecules (sugars) that can be fermented by yeast into ethanol. The substrates, however, are different in numbers 3 and 11 (starch vs. cellulose), so different enzymes would have to be used.

Question 29.7

Thought Question: Refer back to the first graph in Infographic 29.4 (above). The spent grain by-product from corn fermentation (number 6) is what that makes up most of the nonfuel products listed in the legend.

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Part 1: This was a difficult question. The feed is listed as an energy source because it could potentially be burned as a direct biomass energy source.

Part 2: Both of the first methods (including spent grain energy in total energy outputs or subtracting it from energy inputs) would tend to make the energy output from corn seem higher, and that would inflate the EROEI. Not including spent grain energy would tend to deflate EROEI.