Ethanol can be produced by two different industrial methods: fermentation of glucose and the hydration of ethene. Evaluate these two methods of producing ethanol, considering the raw materials used and the conditions required.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethanol is an important industrial chemical used as a fuel and solvent. It can be manufactured from renewable or non-renewable sources depending on the method chosen.
Model answer (5 marks)
Fermentation uses glucose (from crops, sugar cane or starch) – a renewable feed‑stock – whereas the hydration of ethene uses ethene derived from crude oil, a non‑renewable resource.
Fermentation is carried out at low temperatures (≈25–37 °C) and atmospheric pressure, using yeast (enzymes) as a catalyst. It is a batch process, so the rate of production is relatively slow and the product is a dilute aqueous solution of ethanol that must be distilled to give a useful product.
Hydration of ethene is performed at high temperature (≈150–200 °C) and high pressure (≈10–20 bar) with a strong acid catalyst (e.g. phosphoric acid). It is a continuous process, giving a high purity ethanol directly and a much higher production rate.
In terms of sustainability, fermentation is preferable because it uses renewable raw materials and operates under mild conditions, reducing energy input and environmental impact. However, from an economic point of view the ethene hydration route is more efficient: it produces a purer product, requires less downstream processing and can be run continuously, giving a higher overall yield per unit time.
Fermentation is carried out at low temperatures (≈25–37 °C) and atmospheric pressure, using yeast (enzymes) as a catalyst. It is a batch process, so the rate of production is relatively slow and the product is a dilute aqueous solution of ethanol that must be distilled to give a useful product.
Hydration of ethene is performed at high temperature (≈150–200 °C) and high pressure (≈10–20 bar) with a strong acid catalyst (e.g. phosphoric acid). It is a continuous process, giving a high purity ethanol directly and a much higher production rate.
In terms of sustainability, fermentation is preferable because it uses renewable raw materials and operates under mild conditions, reducing energy input and environmental impact. However, from an economic point of view the ethene hydration route is more efficient: it produces a purer product, requires less downstream processing and can be run continuously, giving a higher overall yield per unit time.
Examiner tips
- Mention renewable vs non‑renewable raw materials first; give temperature/pressure differences; note batch vs continuous; state purity and downstream processing; finish with a clear overall judgement.
Common mistakes
- Confusing the temperature/pressure conditions of the two processes; claiming fermentation is faster; ignoring the need for distillation after fermentation.
Mark scheme (5 marks)
- Fermentation uses glucose (from crops/sugar cane/starch) which is a renewable resource, whereas hydration of ethene uses ethene derived from crude oil which is a non-renewable resource.
- Fermentation occurs at low temperatures (around 25–37 °C / room temperature) whereas hydration of ethene requires high temperatures and high pressures.
- Fermentation uses yeast (enzymes) as a catalyst and is a batch process, which makes it slower and produces a lower rate of production compared to hydration.
- Hydration of ethene produces a higher purity ethanol directly, whereas fermentation produces a dilute solution of ethanol that requires further processing (distillation) to purify it.
- Overall judgement: fermentation is more sustainable/better for the environment due to use of renewable raw materials and lower energy conditions, but hydration is more economically efficient due to higher purity and faster continuous production.
Key terms in this question
Related
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