Ethanol production and biofuels

What are the two methods used to produce ethanol?

• Hydrating alkenes (opposite of dehydration of alcohols)

• Fermentation of sugars

Which method of alcohol production is preferred in industry?

Hydration of alkenes in steam with the presence of an acid catalyst.

What conditions are required for the hydration of alkenes?

• 300 degrees celsius

• pressure of 60 atm

• solid phosphoric acid catalyst

What is the general equation for the hydration of alkenes?

CnH2n + H2O -> <- CnH2n+1OH

Draw the mechanism for the reaction between ethene and steam (textbook pg. 238).

XXX.

What type of process is fermentation and what is an equation for it?

• Exothermic process carried out by yeast in anaerobic conditions

• C6H12O6(aq) --yeast, 30/40 degrees--> 2C2H5OH(aq) + 2CO2(g)

How does fermentation work and why is a temp of 30/40 degrees celsius required for it?

• An enzyme produced by yeast converts glucose into ethanol and carbon dioxide

• The enzyme's optimum temp is between 30 and 40 degrees celsius

Is the product produced by fermentation very pure?

No:

• at 15% ethanol conc the yeast dies

• fractional distillation is needed to increase ethanol conc

Which of fermentation and hdyration is faster and produced more pure product?

Hydration

Which of fermentation and hydration is a continuous process and which is a batch process?

• Hydration is a continuous process (expensive equipment but low labour costs).

• Fermentation is a batch process (cheap equipment but low labour costs).

What is a biofuel?

A fuel made from biological material that has recently died, such as ethanol produced during fermentation from sugarcane.

What are the advantages of biofuels?

• Renewable resources

• Considered by some to be carbon neutral as the amount of CO2 released in combustion is balanced by the CO2 absorbed during growth

What is an argument that supports the idea that ethanol is a carbon-neutral biofuel?

• Photosynthesis eq: 6CO2 +6H2O -> C6H12O6 +6O2

• Fermentation eq: C6H12O6 -> 2CO2 + 2C2H5OH

• Combustion eq: 2C2H5OH + 6O2 -> 4CO2 + 6H2O

When combined, exactly 6 moles of carbon dioxide are given in and exactly 6 moles of carbon dioxide are given out.

What is an argument suggesting that carbon dioxide is not a carbon neutral biofuel?

Fossil fuels will need to be burned to power the machinery used to harvest, transport and fertilise the crops etc. So more carbon dioxide is eventually released than absorbed.

What are the disadvantages of biofuel use?

• Ethical issue with using land to grow crops for fuel instead of for food production

• Areas may be deforested to provide space for crop growth for biofuels

• Fossil fuels added to soil can pollute waterways

• Logistical/infrastructural issues with a complete switch from fossil fuels to biofuels