Making ethanol by fermentation
4 marks · NormalDescribe the two main methods used to produce ethanol industrially.
State one condition needed for the hydration of ethene to make ethanol.
Suggest one reason why hydration of ethene is used in some countries instead of fermentation.
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(a) Ethanol is made by fermentation of sugars with yeast at 30–40°C and no air (anaerobic conditions), or by hydration of ethene with steam at high temperature and pressure using a catalyst.
(b) High temperature (e.g. about 300°C) or use of a catalyst (phosphoric acid), or high pressure.
(c) Hydration of ethene is fast or produces pure ethanol, or uses available petroleum feedstock.
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Marking points
M1 (a) · 1 mark · Describes fermentation method for ethanol production.
M2 (a) · 1 mark · Describes hydration of ethene method for ethanol production.
B1 (b) · 1 mark · States any correct condition for hydration of ethene (temperature, pressure, catalyst).
B2 (c) · 1 mark · Gives a correct reason why hydration of ethene is used (faster, pure product, uses oil feedstock, etc).
Worked solution
a) Ethanol can be made by fermenting sugars with yeast at 30–40°C and without air, or by reacting ethene with steam at 300°C and 60 atmospheres pressure with a catalyst.
b) One condition is high temperature (about 300°C).
c) Hydration of ethene gives pure ethanol quickly, or uses oil-derived ethene where sugar may not be available.