3.3.5.1 alcohol production

what are the two methods in which alcohols/ethanol can be produced industrially?

1. fermentation of glucose (for ethanol)

2. direct hydration of alkenes eg ethene in the presence of an acid catalyst

outline the method of fermenting glucose + give the equation

this process uses living yeast cells to convert sugars such as glucose into ethanol + carbon dioxide

describe + explain the conditions of the fermentation of glucose

• yeast → provides enzymes which are the catalyst

• 37℃ so that the enzymes do not denature (optimum temp)

• absence of O₂ (anaerobic respiration)

give 2 advantages of fermentation

• low energy input is required

• sugar cane is a renewable resource

the ethanol made from the fermentation of glucose is called a what?

a bio-fuel → derived from plants/animals

what is meant by carbon neutral?

no net emissions of carbon dioxide to the atmosphere

why is ethanol made from fermentation said to be carbon neutral?

the CO₂ released when it is burnt is balanced by the CO₂ taken in by the source plant during photosynthesis

what are the 3 processes that show carbon neutrality?

1. photosynthesis (growing of the crops)

2. fermentation (process of producing ethanol)

3. combustion (burning/using of ethanol)

using the equations of the 3 processes, show how fermentation of glucose is carbon neutral

6 moles released = 6 moles absorbed

why is the process not actually carbon neutral in reality?

because additional carbon dioxide will be made from other processes including burning fossil fuels for transportation + harvesting the sugar cane crops

give 6 disadvantages of fermentation

• low yield (15%)

• the product is impure → further distillation is required

• slow rate of reaction

• this is a batch process

• environmental issues with loss of habitats + deforestation to use land for producing crops

• the land could be used for food production (instead of fuel production)

ethanol is also produced industrially by…

the direct hydration of ethene using steam

give the equation for the production of ethanol from ethene

give the conditions for the direct hydration of alkenes eg ethene

• steam

• heat

• concentrated H₂SO₄

give 3 advantages of direct hydration of alkenes eg ethene

• high yield + purity

• fast rate of reaction

• this is a continuous process

give 2 disadvantages of direct hydration of alkenes eg ethene

• high energy input is required

• ethene is obtained from crude oil which is a non-renewable resource

what is the mechanism of the direct hydration of ethene?

electrophilic addition

draw the mechanism of the direct hydration of ethene to form ethanol (electrophilic addition)