Ethanol production

Question 1

What are the two ways to make ethanol?

Answer 1

Hydrating alkenes and fermenting sugars

Question 2

What is the standard industrial method for producing alcohols?

Answer 2

Hydrate an alkene

Question 3

What are the conditions for hydrating an ethene?

Answer 3

Hydrate using steam
Acid catalyst - solid phosphoric acid catalyst concentrated
300 degrees Celsius
60 atm

Question 4

What is the general equation for a hydration of an alkene?

Answer 4

CnH2n + H2O + (acid catalyst) -> CnH2n+1OH

Question 5

What is hydration the opposite mechanism of?

Answer 5

Dehydration

Question 6

What is the equation for the hydration of ethene?

Answer 6

CH2=CH2 + H2O -> CH3CH2OH

Question 7

Is the hydration of an alkene reversible or irreversible?

Answer 7

Reversible

Question 8

Although the yield of the hydration of an alkene is low (5%), what can be done to improve this?

Answer 8

The unreacted ethene gas can be recycled which causes the yield to become 95%

Question 9

Why will producing ethanol by fermentation become important in the future?

Answer 9

Ethene comes from crude oil and supplies may run out in the future

Question 10

What type of process is fermentation?

Answer 10

Exothermic

Question 11

What carries out fermentation?

Answer 11

Yeast in anaerobic conditions

Question 12

What is the equation for fermentation?

Answer 12

C6H12O6(aq) -> 2C2H5OH (aq) +2CO2 (g)

Question 13

What condition is needed for fermentation?

Answer 13

Anaerobic conditions

Question 14

How does fermentation work?

Answer 14

The yeast produce enzymes which convert glucose into ethanol and carbon dioxide

Question 15

What is the optimum temperature for the enzymes in fermentation to work at?

Answer 15

30-40 degrees celsius

Question 16

What happens to the enzymes if the temperature is too high?

Answer 16

They will become denatured and the reaction will no longer work

Question 17

What happens if the temperature is too low?

Answer 17

The reaction will be too slow

Question 18

At what percentage of ethanol does the yeast die?

Answer 18

15%

Question 19

What is used to increase the concentration of the ethanol?

Answer 19

Fractional distillation

Question 20

What is the rate of reaction for the hydration of ethene?

Answer 20

Very fast

Question 21

What is the rate of reaction for fermentation?

Answer 21

Very slow

Question 22

What is the quality of the product from the hydration of ethene?

Answer 22

Pure

Question 23

What is the quality of the product from fermentation?

Answer 23

Very impure - needs further processing with fractional distillation which increases costs and time

Question 24

What is the raw material used in the hydration of ethene?

Answer 24

Ethene from oil which is a finite resource

Question 25

What is the raw material used in fermentation?

Answer 25

Glucose/sugars - renewable resource

Question 26

What is the process and the costs like for the hydration of ethene?

Answer 26

Continuous process Expensive equipment needed Low labour costs

Question 27

What is the process and the costs like for fermentation?

Answer 27

Batch process Cheap equipment High labour costs

Question 28

What is a biofuel?

Answer 28

A fuel thats made from biological material thats recently died

Question 29

What are advantages of using biofuel?

Answer 29

Biofuels are renewable resources More sustainable They only release the same amount of carbon dioxide that was taken in when the crop plant was growing - carbon neutral

Question 30

What are disadvantages of biofuel?

Answer 30

- When land is being used to grow crops for fuel, it cant be being used to grow food - Trees may be cut down to create more land - deforestation destroys habitats and trees cut down are burnt which releases more carbon dioxide - Fertilisers are often added and this means that waterways can be polluted - Practical issues with switching from fossil fuels to biofuel

Question 31

What is carbon-neutral?

Answer 31

When the fuel is burnt produced from the plant only releases the same amount of carbon dioxide which they took in in the first place

Question 32

What are three equations to support the idea that ethanol as a biofuel is carbon neutral and explain them?

Answer 32

1 ) 6CO2 + H2O -> C6H12O6 + 6O2 (6 moles of carbon dioxide taken In to produce 1 mole of glucose during photosynthesis) 2) C6H12O6 -> 2C2H5OH + 2CO2 ( 2 moles of carbon dioxide are made when 1 mole of glucose is converted into 2 moles of ethanol) 3) 2C2H5OH + 6O2 -> 4CO2 + 6H2O (4 moles of carbon dioxide are made when 2 moles of ethanol are completely burned)

Question 33

What do the three equations show?

Answer 33

6 moles of CO2 are taken in and 6 moles are then given out = carbon neutral

Question 34

Why might ethanol as a biofuel not be carbon neutral?

Answer 34

Fossil fuels need to be burnt to power the machinery to make the fertilisers for the crops and power the machinery to harvest them. Refining and transporting biofuels also needs energy