Alcohol production (3.3.5.1)

How are alcohols produced by hydration and what are the conditions?

Alcohols can be produced industrially via the hydration of alkenes. It proceeds by an electrophilic addition.

Mechanism:

Conditions:

Temperature - 600K

Pressure - 6000-7000 kPa

Catalyst - H₃PO₄

Equation:

How is ethanol produced by fermentation and what are the conditions?

Ethanol can be produced industrially via the fermentation of glucose. In this process, enzymes break down the starch from crops into sugar, which is then fermented into alcohol.

Equation:

C₆H₁₂O_{6 (aq)} → 2C₂H₅OH _(aq) + 2CO_{2 (g)}

Glucose →ethanol + carbon dioxide

Conditions:

• Absence of oxygen (so fermentation can occur)

• Presence of yeast

• Temperature is 37 - 40°C (optimum for enzymes)

What are the pros and cons of hydration of ethene for ethanol production?

Pros:

• It is a continuous process so quicker

• High percentage yield

• Low labour requirements as few workers need to operate system

• Process doesn’t use up farming land

Cons:

• It is energy intensive due to high temperature and pressure

• Produce from a nonrenewable resource (crude oil)

What are the pros and cons of the fermentation of glucose for ethanol production?

Pros:

• Cheaper than hydration as carried out at lower temperatures

• Produced from renewable resources

Cons:

• It must be fermented in batches so the reaction vessels have to be emptied, cleaned and restocked repeatedly, making it a slow process

• Low percentage yield as high concentrations of ethanol are toxic to yeast cells (why its a batch process) so fractional distillation is needed to purify final product

• Land used for growing biomass for fermentation is also needed for food production

What is biofuel and how can ethanol be turned into it?

Biofuel - fuel made from biomass

Ethanol produced via fermentation can be fractionally distilled and can be used as biomass (since it is made from sugars). It is said to be carbon neutral as the CO₂ given out is equal to the CO₂ taken in by the crops when they are growing. However it can be argued it isn’t carbon neutral as purification of the final product requires energy from fossil-fuel power stations.