Manufacture of Ethanol: Fermentation & Hydration
Chemistry: Cambridge International GCSE Supplement, topic 11.6.6
Manufacture of Ethanol: Fermentation & Catalytic Hydration
Ethanol is made by fermentation of glucose and catalytic hydration of ethene using yeast and acid catalysts.
Fermentation overview
- Fermentation produces ethanol using aqueous glucose.
- Yeast acts as a catalyst during fermentation.
- Temperature is kept between 25°C and 35°C.
- Oxygen is absent during this process.
- The process was discovered before 1850 and is traditional in brewing.
Fermentation process details
- Glucose breaks down into ethanol and carbon dioxide.
- The reaction is: C6H12O6 → 2C2H5OH + 2CO2.
- Yeast enzymes speed up fermentation.
- Fermentation stops if the temperature rises above 35°C.
- Ethanol yield is limited to about 15% due to yeast sensitivity.
Catalytic hydration overview
- Ethanol also forms by adding steam to ethene.
- Steam and ethene react at 300°C.
- Pressure is high, about 6000 kPa (60 atm).
- An acid catalyst, like phosphoric acid, speeds the reaction.
- This method started in the early 20th century for industrial ethanol.
Catalytic hydration process details
- Ethene (C2H4) and steam (H2O) form ethanol (C2H5OH).
- Reaction: C2H4 + H2O → C2H5OH.
- Acid catalyst helps break and form chemical bonds faster.
- The process allows large-scale ethanol manufacturing.
- It uses ethene from cracking hydrocarbons.
Comparing both methods
- Fermentation uses renewable glucose, is slower, and produces less pure ethanol.
- Catalytic hydration uses ethene, allowing continuous production at high purity.
- Fermentation of ethanol is important in food and drink.
- Catalytic hydration of ethanol is useful for fuel and industry.
- Both methods are key to the organic chemistry topic of alcohol manufacture.
Test yourself on Manufacture of Ethanol: Fermentation & Hydration
What is the ideal temperature range for the fermentation of glucose using yeast?