Alcohols

7 marks · Hard

Only some of the ethene reacts in the industrial hydration process for ethanol.

(a)

Describe how unreacted ethene is dealt with in the hydration of ethene process.

[2 marks]

(b)

Explain how this affects the efficiency of ethanol production.

[2 marks]

(c)

Compare one disadvantage and one advantage of recycling unreacted ethene in this process to fermentation methods.

[3 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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(a) Unreacted ethene is separated and fed back into the reactor (recycled) instead of being wasted. · must show clear description of recycling

(b) Recycling increases efficiency by ensuring more ethene is eventually converted into ethanol, reducing raw material waste. · must show link to efficiency and reduced waste

(c) Advantage over fermentation: improves overall yield and efficiency, continuous processing is possible. Disadvantage: requires extra equipment/process for recovery and recycling; fermentation does not require this. · must show one advantage and one disadvantage, clear comparison to fermentation

Show mark scheme and worked solution

Marking points

B1 (a) · 2 marks · Clear description of the recycling of unreacted ethene

B2 (b) · 2 marks · Correct explanation of effect on process efficiency

B3 (c) · 2 marks · One valid advantage with proper comparison

B4 (c) · 1 mark · One valid disadvantage with proper comparison

Worked solution

a) In the hydration of ethene, unreacted ethene is not wasted—it is separated from the reaction mixture and recycled back through the reactor with fresh steam.

b) This recycling increases the efficiency of the process by converting more ethene to ethanol, reducing the waste of the starting material.

c) An advantage over fermentation is that recycling allows the process to be continuous and improves overall yield. A disadvantage is that it requires additional equipment for separating and recycling the ethene, increasing complexity and cost, whereas fermentation does not involve recycling reactants.