15.2 - Ethanol Production

Question 1

Carbon neutrality of ethanol:

Answer 1

However, the overall process is not entirely carbon neutral due to:

• The fossil fuels used to produce fertilisers for the crops.
• The energy consumed by farm machinery during planting and harvesting.
• The transportation of both the feedstock and the final ethanol product.

These activities contribute additional CO2emissions, indicating that while the fermentation process recycles CO2, it does not eliminate the reliance on fossil fuels entirely. Therefore, ethanol production through fermentation, while beneficial in reducing some carbon emissions, cannot be considered completely carbon neutral.

Question 2

Disadvantages of bioethanol (2):

Answer 2

1. Engine modifications- Some engines may require adjustments to efficiently use fuels with high ethanol content.
2. Competition for land - Using agricultural land for fuel production can reduce the area available for food crops.

Question 3

Advantages of bioethanol (2):

Answer 3

1. Renewable- Produced from crops that can be replanted and harvested repeatedly.
2. Lower net CO2emissions- The crops used for ethanol production absorb CO2from the atmosphere during their growth phase, which can offset some of the emissions from fuel use.

Question 4

What are biofuels

Answer 4

renewable fuels derived from recently living biological materials, such as plants, algae, or organic waste

Question 5

Following fermentation, how is ethanol separated?

Answer 5

fractional distillation

Question 6

Conditions for fermentation reaction

Answer 6

• Anaerobic conditions are used to ensure yeast performs anaerobic respiration. If oxygen was present, yeast would respire aerobically instead, producing ethanoic acid instead of ethanol.
• A temperature of 30-40°C is used because this is the optimal range for the yeast enzymes to function. Temperatures above 40°C would begin to denature the enzymes.

Question 7

What happens in the fermentation of yeast?

Answer 7

In the fermentation reaction, yeast enzymes break down glucose into ethanol and carbon dioxide.

Question 8

Fermentation of yeast in production of ethanol (overall reaction):

Answer 8

C6H12O6(aq)➔ 2C2H5OH(aq)+ 2CO2(g)

Question 9

Industrial conditions of the production of ethanol

Answer 9

Industrially, this reaction is typically carried out by mixing ethene with steam at a temperature of 300°C and a pressure of 60 atm, using solid phosphoric(V) acid as the catalyst.

Question 10

Reaction mechanism of ethene into ethanol

Answer 10

1. The formation of a carbocation occurs when the pi bond of ethene breaks and a proton (H+) attaches to one of the carbon atoms.
2. A water molecule then attaches itself to the positively charged carbocation.
3. Finally, a proton (H+) is lost from the newly attached water molecule, resulting in the formation of the ethanol molecule.

Question 11

Hydration reaction of ethene

Answer 11

C2H4(g)+ H2O(g)➔ C2H5OH(l)

Question 12

How is ethene typically obtained

Answer 12

cracking of crude oil which breaks down larger hydrocarbon chains into smaller and more useful ones

Question 13

How can ethanol be produced?

Answer 13

Ethanol can be produced industrially through the chemical reaction known as hydration, where water (H2O) is added to ethene (C2H4) in the presence of an acid catalyst