Bioethanol crops and industrial production, starch hydrolysis, fermentation and its equation and conditions, distillation and dehydration, esterification, an ethanol yield calculation, and measuring the heat energy of ethanol.

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Key term

What is bioethanol?

Key term

Which crops are used to make bioethanol?

Key term

Outline how bioethanol is made from biomass on an industrial scale.

Questions from this subtopic

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1
What is bioethanol?
Model answer
Bioethanol is ethanol, C₂H₅OH, made by fermenting sugars from plant material. Bioethanol is blended with petrol or used alone in adapted engines.
2
Which crops are used to make bioethanol?
Model answer
Sugar cane and sugar beet supply sugar directly, while maize and wheat supply starch. Wood and straw can be used once their cellulose is broken down.
3
Outline how bioethanol is made from biomass on an industrial scale.
Model answer
The feedstock is milled, and its starch or cellulose is broken down into sugars. Yeast ferments the sugars, then the ethanol is distilled and dehydrated.
4
Why must starch be hydrolysed before fermentation?
Model answer
Yeast cannot ferment starch directly. Enzymes such as amylase break starch down into glucose, which yeast can use.
5
Give the equation for the fermentation of glucose.
Model answer
The equation is C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Enzymes in yeast convert each glucose molecule into two ethanol and two carbon dioxide molecules.
6
What conditions does fermentation need?
Model answer
Fermentation needs yeast, a sugar solution, warmth of about 25–35°C and no oxygen. A higher temperature denatures the yeast's enzymes.

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