15.2 Ethanol production Flashcards
Why are alcohols important in industry
Eg methanol
They are used as intermediates, as they are easily made and converted into other compounds
Methanol is made from natural gas
What is ethanol used for
It is used as an intermediate in the manufacture of other organic chemicals
Eg perfume, cosmetics, drinks, detergents, drugs
How is ethanol made in industry
What conditions
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
What is the mechanism for the production of ethanol from crude oil
. 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, as this H+ takes an electron from it so leaves it positively charged
. 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 an electron from it is given to the carbon.
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.
How is ethanol made by fermentation
Give equation
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
C6H12O6 —> 2C2H5OH + 2CO2
What are the conditions for fermentation of carbohydrates to produce ethanol
. 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
Why is it necessary that there is no oxygen present in reaction vessel
It may oxidise ethanol to ethanoic acid (the acid in vinegar)
How can we get ethene from ethanol
Is this a good method? Evaluate
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
So provide H+ ion
. In ethanol, the lone pair on the oxygen can go to a H+ ion
. So the oxygen has a positive charge
. So the C-O bond must break and the electrons go from the bond to the oxygen as they are attracted to the positive charge of the oxygen.
. 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 products are ethene and a H+ and water
What are the differences between hydration and fermentation methods of producing ethanol
.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
Why is ethanol made by fermentation a carbon neutral fuel
. When the plants are grown, they absorb carbon dioxide from the air
. So when the ethene made from it is burned after the ethanol is made by fermentation, the same amount of CO2 is released as was absorbed originally
