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Alcohol production




AQA Content

Explain the meaning of the term biofuel
Justify the conditions used in the production of ethanol by fermentation of glucose
Write equations to support the statement that ethanol produced by fermentation is a carbon neutral fuel and give reasons why this statement is not valid
Outline the mechanism for the formation of an alcohol by the reaction of an alkene with steam in the presence of an acid catalyst
Discuss the environmental (including ethical) issues linked to decision making about biofuel use.

Specification Notes

Fractional distillation is used to obtain a concentrated ethanol solution.
Ethanol is used as a fuel and solvent.


Industrial production

1. Hydration of ethene - an addition reaction between steam and ethene
Good for rich countries with oil reserves
solid phosphoric acid catalyst
~ 70 atmospheres.

2. Fermentation of sugars (glucose).
Good for warm climate, oil poor countries
Yeast (zymase).
anaerobic conditions (prevent the oxidation of ethanol to ethanoic acid)

Mechanism outline

A hydrogen (with a partial ∂+ charge) is attracted to the double bond of the alkene - the pi part of the bond breaks and electrons make a new bond with the hydrogen.

Electrons in the hydrogen-oxygen bond move onto the oxygen and a carbocation is formed:
The carbocation reacts with a lone pair on a molecule of water.

A hydrogen is removed from the oxygen by reaction with the H2PO4- ion. The catalyst is now reformed and ethanol is forned.


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