POM: Ethanol - Use and Manufacture

Question 1

How do I convert ethanol to ethylene?

Answer 1

Ethanol is dehydrated by heating it with a catalyst (concentrate h2s04) which breaks the c-oh and c-h bond, allowing the formation of double bond and water.

Question 2

What is formula for the dehydration of ethanol?

Answer 2

C2H50H (l) –> C2H4 (g) + H2O (l)

Catalyst: concentrate h2s04

Question 3

How do i convert ethylene to ethanol?

Answer 3

It is through hydration.
This involves the addition of a water molecule to ethylene.

Hydratation also needs heat and a catalyst (dilute h2s04) which opens the double bond and allows water to attach.

Water itself is not reactive enough to break the ethylene double bond.

Question 4

What is the formua for the hydration of ethanol?

Answer 4

C2H4 + H20 (l) –> C2H5OH (l)

Question 5

How is ethanol able to act as a solvent for polar and non-polar substances?

Answer 5

Ethanol has a unique molecular structure as it has both polar and non-polar ends.

The -OH group is the polar hydroxyl end, which interacts with other polar molecules through dipole-dipole forces or hydrogen bonds. Therefore it dissolves in water.

THe CH3CH2– is the non-polar alkyl chain end, which interacts with non-polar substances through DISPERSION forces.

Question 6

What are some uses of ethanol as a solvent?

Answer 6

Motor fuel supplement
Costmetics (perfumes)
External pharmaceuticals (antiseptics
Food colourings and dyes
Industrially = paints, oils

Question 7

What is the chemical equation for the fermentation of glucose to ethanol?

Answer 7

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

Fermentation is a process in which glucose is broken down to ethanol and carbon dioxide by the action of enzymes present in yeast.

Question 8

Describe the conditions under which fermentation of sugars is promoted

Answer 8

A suitable microorganism such as yeast (supplies enzyme zymase)
A suitable temperature (around 37°C)
Anaerobic conditions
Ethanol concentration is kept about 15% as yeast cannot function effectively above this concentration

Question 9

Summarise the chemistry of the fermentation process

Answer 9

1. Yeast is added to mashed biomass
2. Enzymes in the mixture convert and starch or sucrose into glucose or fructose
3. Yeast use their enzymes to convert glucose or fructose into ethanol and carbon dioxide

Fractional distillation is required to obtain higher ethnol concentrations as yeast dies after 15%

Question 10

Outline the use of ethanol as a fuel and explain why it can be called a renewable resource.

Answer 10

Ethanol is able to undergo combustion so it can be used as a fuel.

Ethanol is a renewable resource as it is manufactured from carbohydrates such as glucose and starch that are produced by synthesis in plants. Also, the products of it’s combustion (C02 and H2O) are reactants needed by plants for photosynthesis

Question 11

What is the chemical formula of the combustion of ethanol?

Answer 11

C2H5OH (l) + 3O2 (g) –> 2CO2 + 3H2O (g)

Question 12

What are the advantages of using ethanol as a fuel?

Answer 12

• It is a renewable resource that is derived from biomass.

– It undergoes complete combustion more readily than fossil fuels:
 The oxygen atom in the ethanol molecule ensures that less oxygen is needed for complete combustion. Also contains less carbon than octane, the major component of petrol.
 It produces only carbon dioxide and water as by-products.

 Cleaner and more efficient fuel that has reduced greenhouse gas emissions.

Question 13

What are the disadvantages of using ethanol as a fuel?

Answer 13

• Lower heat of combustion. Does not release as much energy
  on complete combustion. -
• Therefore ethanol is more expensive than petrol.
  – Engines must be modified to run on high ethanol mixtures (e.g. E25).
  – Large areas of arable land are needed to grow crops to use in the production of ethanol,
• Leads to environmental problems such as soil
  erosion, deforestation, fertiliser runoff and salinity.
  – Disposal of fermentation wastes in the production of ethanol also presents major environmental issues.

Question 14

What is the evaluation of using ethanol as a fuel?

Answer 14

Currently, ethanol has potential as an alternative fuel and a future replacement for fossil fuels, particularly for transport.

However, further research into developing more efficient methods of ethanol production is required before it can become an economically viable proposition.

Question 15

Why is ethanol considered ‘greenhouse neutral’?

Answer 15

Because CO2 produced when it burns is balanced by the CO2 used in photosynthesis to produce crops to
be later converted to ethanol.

However, significant energy input is required for the production of fertilisers and the distillation process.

This comes from the combustion of fossil fuels, which leads to the release of carbon dioxide.

Nevertheless, the combustion of ethanol does have a lower greenhouse impact compared with the combustion of petrol.

Question 16

How is ethanol currently being used as an alternative car fuel?

Answer 16

thanol is mainly used (mixed with petrol) as a fuel to supplement petrol supplies. Petrol containing 10% ethanol can be used in normal petrol engines without engine modification.

In Australia, ethanol is generally considered an uneconomic proposition due to the high costs of production.