Ethanol production Flashcards
What are the two ways to make ethanol?
Hydrating alkenes and fermenting sugars
What is the standard industrial method for producing alcohols?
Hydrate an alkene
What are the conditions for hydrating an ethene?
Hydrate using steam
Acid catalyst - solid phosphoric acid catalyst concentrated
300 degrees Celsius
60 atm
What is the general equation for a hydration of an alkene?
CnH2n + H2O + (acid catalyst) -> CnH2n+1OH
What is hydration the opposite mechanism of?
Dehydration
What is the equation for the hydration of ethene?
CH2=CH2 + H2O -> CH3CH2OH
Is the hydration of an alkene reversible or irreversible?
Reversible
Although the yield of the hydration of an alkene is low (5%), what can be done to improve this?
The unreacted ethene gas can be recycled which causes the yield to become 95%
Why will producing ethanol by fermentation become important in the future?
Ethene comes from crude oil and supplies may run out in the future
What type of process is fermentation?
Exothermic
What carries out fermentation?
Yeast in anaerobic conditions
What is the equation for fermentation?
C6H12O6(aq) -> 2C2H5OH (aq) +2CO2 (g)
What condition is needed for fermentation?
Anaerobic conditions
How does fermentation work?
The yeast produce enzymes which convert glucose into ethanol and carbon dioxide
What is the optimum temperature for the enzymes in fermentation to work at?
30-40 degrees celsius
What happens to the enzymes if the temperature is too high?
They will become denatured and the reaction will no longer work
What happens if the temperature is too low?
The reaction will be too slow
At what percentage of ethanol does the yeast die?
15%
What is used to increase the concentration of the ethanol?
Fractional distillation
What is the rate of reaction for the hydration of ethene?
Very fast
What is the rate of reaction for fermentation?
Very slow
What is the quality of the product from the hydration of ethene?
Pure
What is the quality of the product from fermentation?
Very impure - needs further processing with fractional distillation which increases costs and time
What is the raw material used in the hydration of ethene?
Ethene from oil which is a finite resource
What is the raw material used in fermentation?
Glucose/sugars - renewable resource
What is the process and the costs like for the hydration of ethene?
Continuous process
Expensive equipment needed
Low labour costs
What is the process and the costs like for fermentation?
Batch process
Cheap equipment
High labour costs
What is a biofuel?
A fuel thats made from biological material thats recently died
What are advantages of using biofuel?
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
What are disadvantages of biofuel?
- 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
What is carbon-neutral?
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
What are three equations to support the idea that ethanol as a biofuel is carbon neutral and explain them?
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)
What do the three equations show?
6 moles of CO2 are taken in and 6 moles are then given out = carbon neutral
Why might ethanol as a biofuel not be carbon neutral?
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
