15.2 Ethanol production

Question 1

Why are alcohols important in industry

Eg methanol

Answer 1

They are used as intermediates, as they are easily made and converted into other compounds

Methanol is made from natural gas

Question 2

What is ethanol used for

Answer 2

It is used as an intermediate in the manufacture of other organic chemicals

Eg perfume, cosmetics, drinks, detergents, drugs

Question 3

How is ethanol made in industry

What conditions

Answer 3

HYDRATION
React ethene (made by cracking crude oil) with steam, so water is added across the double bond

. 300 degrees

. 60 atm

Use phosphoric acid catalyst

Question 4

What is the mechanism for the production of ethanol from crude oil

Answer 4

. From the acid catalyst, there are H+ ions, so the double bond breaks and the electrons in it go to the H+
So the H joins onto the molecule and a carbocation is formed as there is still one carbon only bonded to 3 things

. Then, a water molecule: The oxygen on it has two lone pairs, put only one is needed which will go to the carbocation so the water molecule will bind to the molecule

. The oxygen has a + charge on it as it is bonded to 3 things so the pair of electrons goes from the O-H bond to the oxygen, breaking the OH bond.

. So now the oxygen has a lone pair of electrons, and a molecule of ethanol is formed, and a H+ ion as it broke off.

Question 5

How is ethanol made by fermentation

Answer 5

During fermentation, carbohydrates from plants are broken down into sugars and are then converted into ethanol by the action of the enzymes in yeast

The carbohydrates come from crops eg sugar cane and sugar beet

Question 6

What are the conditions for fermentation of carbohydrates to produce ethanol

Answer 6

. Anaerobic conditions, so there must be no oxygen present
So air is kept out of fermentation vessels because it may oxidise ethanol to ethanoic acid (the acid in vinegar)

. Once the fermentation mixture contains 15% ethanol, the enzymes can’t function anymore and fermentation stops

.The reaction is slow at low temperatures, but the enzymes are denatured if the temperature is too high
. So a compromise temperature is used

Question 7

How can we get ethene from ethanol

Is this a good method? Evaluate

Answer 7

It is a renewable method, as biofuel is used
However, to grow the crops is taking us space that could be used to grow food, so food prices increase

. Dehydrate ethanol made from fermentation of sugar

. In ethanol, the lone pair on the oxygen can go to a H+ ion

. So the oxygen has a positive charge

. So the C-H bond from the other carbon (without the oxygen) breaks and the electrons go to the bond between the two carbons

. So the C-O bond must break and the electrons go from the bond to the oxygen

So the products are ethene and a H+ and water

Question 8

What are the differences between hydration and fermentation methods of producing ethanol

Answer 8

.In hydration, rate of reaction is faster than in fermentation which has a slow rate of reaction

. The products from hydration are pure, whilst in fermentation the products need to be processed

. Hydration is a continuous process, whilst fermentation is a batch process

. Hydration needs expensive equipment, but there is a low labour cost
Whilst fermentation has low equipment cost but high labour cost

. Hydration is non renewable, from crude oil
Whilst fermentation is renewable, biomass that can be regrown