Making ethanol by the hydration of ethene
5 marks · HardIn the industrial process to make ethanol from ethene, only some of the ethene reacts in a single pass through the reactor.
Explain what happens to the ethene that does not react during one pass through the reactor.
Describe one advantage of recycling the unreacted ethene in this process.
Suggest what effect not recycling unreacted ethene would have on the overall yield of ethanol.
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Show answer
(a) The unreacted ethene is separated from the mixture and fed back into the reactor to react again with steam. · must show Separation of unreacted ethene, Recycling/return to reactor
(b) Recycling unreacted ethene increases the total amount of ethanol produced, as more ethene is given the chance to react. It improves efficiency and makes better use of raw materials. · must show Increases yield, Improves efficiency/better use of resources
(c) The overall yield of ethanol would be lower. · must show Lower overall yield
Common mistakes: Saying unreacted ethene forms a byproduct; Not linking recycling to yield; Mixing up why recycling is done
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Mentions the unreacted ethene is separated or collected after the reaction.
A1 (a) · 1 mark · Explains that the unreacted ethene is recycled or sent back through the reactor.
M2 (b) · 1 mark · States that recycling increases the amount of ethanol produced (increases yield) or maximises use of ethene.
A2 (b) · 1 mark · Explains that recycling ethene improves efficiency or makes better use of resources.
B1 (c) · 1 mark · States that not recycling would lead to a lower overall yield of ethanol.
Worked solution
(a) After the reaction, not all the ethene reacts with steam. The unreacted ethene is separated from ethanol and water, then recycled by being sent back into the reactor to react again.
(b) Recycling unreacted ethene increases the yield of ethanol since it allows more of the ethene to be converted into product, which improves efficiency and reduces waste of raw materials.
(c) If unreacted ethene is not recycled, the overall yield of ethanol would be lower because less ethene would be turned into ethanol.