Comparing the two methods of producing ethanol
3 marks · NormalA factory can produce ethanol by either fermentation or hydration of ethene. Each method has a different efficiency and energy requirement, as shown in the table below.
| Method | Percentage Yield (%) | Energy Input per Tonne Ethanol (kJ) |
|---|---|---|
| Fermentation | 60 | 2,500 |
| Hydration of ethene | 95 | 6,000 |
Calculate the amount of ethanol (in tonnes) produced from 1000 tonnes of raw material by each method.
Fermentation
Hydration of ethene
Which method requires less energy per tonne of ethanol produced? Show how you use the data to decide.
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.
Show answer
(a(i)) 600 tonnes
(a(ii)) 950 tonnes
(b) Fermentation requires less energy per tonne of ethanol. Energy used per tonne is 2,500 kJ (fermentation) vs 6,000 kJ (hydration). · must show comparison based on energy input per tonne
Common mistakes: Swapping yields for each method; Calculating yield in percent not tonnes
Show mark scheme and worked solution
Marking points
M1 (a(i)) · 1 mark · Correct use of percentage yield to find the mass of ethanol produced by fermentation: tonnes.
M2 (a(ii)) · 1 mark · Correct use of percentage yield to find the mass of ethanol produced by hydration: tonnes.
B1 (b) · 1 mark · Correct decision and comparison showing fermentation uses less energy per tonne, with supporting data from the table.
Worked solution
a) To calculate the amount of ethanol produced by each method, multiply the mass of raw material by the yield (as a decimal).
Fermentation: tonnes ethanol
Hydration of ethene: tonnes ethanol
b) From the table: Fermentation uses 2,500 kJ per tonne of ethanol. Hydration of ethene uses 6,000 kJ per tonne.
Fermentation requires less energy per tonne of ethanol produced.