3.12 describe the dehydration of ethanol to ethene, using aluminium oxide

If you have ethanol and you want ethene, you can dehydrate it. This is done by removing water from the ethanol and is known as a dehydration reaction. 

Method
Ethanol vapour is passed over a hot catalyst (aluminium oxide, Al2O3)


NOTE: The catalyst is used as it provides a large surface area for the reaction to take place, meaning the reaction will be quick(ish)

3.11 evaluate the factors relevant to the choice of method used in the manufacture of ethanol, for example the relative availability of sugar cane and crude oil

Producing ethanol by reacting ethene and steam is relatively cheap (as, right now, ethane is quite cheap and not much is wasted). However, ethene is produced from crude oil which is a finite source, soon it will become fairly expensive as it gets rarer and in the end it will run out, meaning ethanol will no longer be able to be made using ethene and steam.

An advantage of making ethanol by fermenting sugars is that all 'reactants' are renewable (sugar and yeast). It also can be produced at a much lower temperature. However, the ethanol you get from fermenting sugars is not as concentrated as when you react steam with ethene (basically, its super weak). This needs to be distilled to increase its strength and it also needs to be purified. So, although its simpler, its also a lot more hassle.

3.10 describe the manufacture of ethanol by the fermentation of sugars, for example glucose, at a temperature of about 30ºC

Another method of producing ethanol is by fermentation. The raw material for fermentation is sugar (e.g. glucose), which is converted into ethanol using yeast. This process is done at 30ºC.

3.9 describe the manufacture of ethanol by passing ethene and steam over a phosphoric acid catalyst at a temperature of about 300ºC and a pressure of about 60-70 atm

Ethene will react with steam to produce ethanol. This reaction will take place at 300ºC with a pressure of 60-70 atm. This process is very slow, so a catalyst of phosphoric acid is used.

NOTE: atm stands for atmospheres