Alcohol production Flashcards
Wha
What will we produce if we react Z-pent-2-ene with water?
pentan-2-ol or pentan-3-ol
These are examples of
addition reactions bcs we are adding a molecule (water) can also be called hydration reaction
& when a molecule loses water it’s a dehydration reaction
How do industries carry out hydration reaction?
- they add the alkene in its gas phase into the reactor
- they add water in the form of steam (g)
- add an acid catalyst (H+) to start the reaction
What can sulfuric acid act as?
electrophile
What happens if we react propene with water using sulfuric acid as our catalyst knowing that sulfuric acid acts as an electrophile?
carbon carbon bond breaks and a carbon hydrogen bond forms
causing H-O to break
making the electron pair go to Oxygen making it a long pair
Between these 2 molecules (propen-2-ene and propen-1-ene) what molecule would likely form
First molecule (propen-2-ene) as secondary carbocations are more stable than primary carbocations meaning the secondary carbocation would form majority of the time
Knowing that secondary is more stable, what would happen next in the mechanism?
because we are also reacting water
a water bond would form between the carbocation like this
arrow telling us C—O bond forms
What happens next after water bonds with the molecule of propene
The Lone pair attracts one of the H+ ions and forms a bond breaking the H—O bond
The complete mechanism memorise
from propene to propan-2-ol
- catalyst H forms a bond with the double bond of carbon forming a carbocation
- carbocation forms a bond with water
- lone pair of catalyst forms a bond of one Hydrogen and that hydrogen breaks the bond with oxygen
Because sulfuric acid is a reagent at the beginning of the reaction and a product at the end, its acting as a
catalyst
because H2SO4 (sulfuric acid) is acting as an electrophile, this is an example
of electrophilic addition reaction
mechanism of all reactions using sulfuric acid
How do we simplify this to make it easier rather than writing whole sulfuric acid out?
H+
What’s the most appropriate mechanism for this reaction?
As the acid wasn’t specified this is the correct answer
What’s wrong with this mechanism?
1) arrow is the other way around
2) Oxygen is missing a lone pair
3) Oxygen is missing a + bcs it has 3 bonds
What’s the equation for this reaction
CH2=CHCH2CH2CH3+H2O <=> CH3CH(OH)CH2CH2CH3
What’s the equation for the hydration of butene?
C4H8 + H2O <=> C4H9OH
What do we do when writing equations for ethene, propene and ethanol?
we just write their molecular formula as they don’t have position isomer
What’s the equation for the hydration of propene to propan-1-ol
C3H6 + H2O <=> CH3CH2CH2OH
Industries use a degree of 300 celsius which is a compromised temperature why is that so?
this reaction is exothermic as stated (-45 kJmol)
so if we lower the temperature the equilibrium position will shift to the right
and increase the yield of ethanol
However low temperatures also decrease the rate of reaction so industries use 300 as a compromise between yield and rate
Why does ethanol form in this reaction?
& when does it form a liquid
because of the high temperature which causes the ethanol to come out as a gas
it forms a liquid when it leaves the reactor and enters the condenser when it’s a liquid
To produce ethanol from ethene industries use
H3PO4 (phosphoric) as a catalyst
compromised Temperature of 300
compromised Pressure if 6000 kPA
What’s the equation for the hydration of ethene?
C2H4 + H2O <=> C2H5OH
What’s the equation for the hydration of but-2-ene to butan-2-ol?
A
which of these molecules is the major product in the dehydration reaction of pent-1-ene?
and why
C
to form pentan-1-ol, a primary carbocation intermediate must form. however to form pentan-2-ol, a secondary carbocation must form.
what do catalyst do industries use to produce ethanol from ethene.
what are the conditions?
catalysts use Phosphoric acid H3PO4
they use compromised temperatures between 300 and 600
and compromised pressures between 5000 and 10000
Why do industries use compromised temperatures and pressure when producing ethanol from ethene?
The higher the pressure, the more dangerous the conditions, the higher the yield of ethanol, the more expensive the conditions
The higher the temperature, the lower the ethanol yield, the faster the rate of reaction, the more expensive the conditions
The reaction of ethene with water is exothermic. industries use a compromised temperature for ethanol because high temperatures increase the rate of reaction but lower the yield of ethanol.
In the reaction of ethene with water, there are 2 moles of reactants and one mole of product. Industries use a compromise pressure because high pressure increase the yield of ethanol but they also increase the risk of explosion
How can else can ethanol be produced?
By fermentation where ethanol can be produced from sugar
To produce ethanol from sugar we add warm water to sugar and add a single cell fungus (yeast) and make sure that there’s no oxygen in the system so we seal the mixture
we call ethanol produced from fermentation a biofuel
leave the mixture to produce ethanol and carbon dioxide
why do we can ethanol produced from fermentation a biofuel?
because it’s made from biological resources
What’s the sugar called in fermentation?
Sucrose
When sucrose is added to warm water what does it break into?
it breaks into 2 molecules
glucose and fructose
Out of the sugars it broke down in,
what forms ethanol in the process of fermentation?
glucose reacts to form ethanol and carbon dioxide
What is the balanced equation for fermentation?
What in yeast makes the glucose break down
enzymes produce by yeast catalyst reaction of glucose to produce ethanol and carbon dioxide
Above a certain concentration, ethanol is toxic to yeast. So what concentration do we need?
To keep our yeast alive and working we need a low concentration of ethanol
We do this by removing ethanol when it’s formed.
What can we use to seperate ethanol from the reaction?
distillation,
because ethanol has a lower boiling point than our sugars solution. We seperate ethanol from out reaction mixture using distillation
What do we need to ensure during fermentation?
that there’s no oxygen present in the system
fermentation is carried out in the absence of oxygen
What are the conditions of fermentation reactions?
we carry them out in the absence of water and keep the temperatures between 25-40 degrees celsius
Ethanol produced by hydration is made from
crude oil which is a non renewable fossil fuel
ethanol produced from fermentation is made from
plants which are renewable
Why is the equipment used for fermentation much cheaper?
to produce ethanol from hydration we need to extract it from the ground, then undergoes fractional distillation and then cracked which are all expensive requirements
whereas to produce ethanol from fermentation we just need to grow and harvest the plants and produce yeast
so overall fermentation is much cheaper equipment wise
Compared to fermentation, why is hydration less sustainable?
Fermentation only requires plants which won’t run out, whilst hydration requires crude oil which will run low
so fermentation is more sustainable
Compared to hydration and fermentation, which one is energy sufficient
hydration requires temperatures of 300 C and 6000 kPA
whereas fermentation only requires 25-40 degree and standard pressure conditions
meaning we need far less energy to manage fermentation and cost will be way cheaper
What are the advantages of hydration compared to fermentation?
Temperatures used for fermentation (25-40) is much lower than hydration (300) meaning hydration will have a higher rate of reaction so hydration produces ethanol quicker than fermentation (slower)
when we produce ethanol from fermentation we produce ethanol and carbon dioxide whereas if we produce ethanol from hydration we just produce ethanol meaning hydration has a higher atom economy (100%) so hydration is more efficient at producing ethanol than fermentation ( <100%)
when fermentation (batch process) is being done we need to clean it each time so we need to manually stop and keep going & only collect ethanol in batches whereas hydration when ethene is added to water in the reactor n reacts with acid catalyst ethanol is seperated and condensed and any remaining ethene or steam returns to the reactor so it means it can run continuously without stopping hydration = continuous process which is another reason why its faster
compare fermentation and hydration,
what process is better?
fossil fuel will run out
in the long term fermentation is better
what’s the molecular form for glucose
C6H12O6
when fuels completely combust what does it form?
CO2 and H2O
What is carbon neutral defined as in terms of biofuels
No overal CO2 emission into the atmosphere
What’s the equation for photosynthesis
6CO2 + 6H2O —> C6H12O6 + 6O2
What’s the equation of fermentation
C6H12O6 —> 2C2H5OH + 2CO2
What’s the equation for complete combustion
2C2H5OH + 6O2 —> 4CO2 + 6H2O
What if we combine all photosynthesis, fermentation and complete combustion equation what would it look like ?
bcs of the repeat Carbon dioxide
bio-ethanol is carbon neutral
but in reality it’s not completely due to CO2 being released during fertiliser production, when it’s transported and when plants are harvested
state the meaning of the term biofuel
biological resources 
