Alcohols (3.3.5)

Alkenes can converted to alcohols on an industrial scale by reacting with steam in the presence of an acid catalyst.

Conditions in industry:

• Catalyst: Concentrated phosphoric acid () on silica

• Temperature: Around

• Pressure: Approximately

Ethanol can be produced industrially by fermenting glucose using yeast under specific conditions. This biological process is essential for producing alcoholic beverages and biofuels.

Glucose () is converted into ethanol () and carbon dioxide ().

Ethanol produced industrially through fermentation is purified using fractional distillation and subsequently utilised.

This process ensures high-purity ethanol suitable for energy applications.

For efficient industrial fermentation of glucose:

• Yeast must be present. This catalyses the conversion of glucose to ethanol.

• An anaerobic environment is required for efficient production of ethanol. Absence of oxygen is crucial to direct the metabolic pathway towards fermentation and ethanol production rather than aerobic respiration, which would produce and reduce the yield of ethanol.

• An optimal temperature range of maintains yeast activity without denaturing the enzymes and maximises fermentation rate.

• An optimal range of 4.0–4.5 ensures yeast enzyme viability and efficient fermentation.

• Adequate nutrients (nitrogen, vitamins, minerals) to support yeast growth and metabolism must be present.

Together these conditions minimise cost and optimises yield.

Biofuel refers to a type of fuel that is derived from biological materials (biomass) and is considered renewable and sustainable.

Unlike fossil fuels, which are finite, biofuels are produced from biological sources and can be replenished.

Ethanol produced by fermentation is often touted as a carbon neutral fuel.

This concept is based on the carbon cycle, where the released during ethanol combustion is offset by the absorbed during the growth of the biomass used to produce ethanol.

Supporting equations for carbon neutrality are:

1. Photosynthesis (carbon fixation)
Plants absorb carbon dioxide from the atmosphere to produce glucose and oxygen.

2. Fermentation (ethanol production)
Yeast converts glucose into ethanol and carbon dioxide.

3. Combustion (ethanol as fuel)
Burning ethanol releases carbon dioxide and water.

Over the duration of the process, the amount of released during fermentation and combustion is equal to the amount consumed by photosynthesis.

The argument for the carbon neutrality of ethanol from fermentation as a fuel is:

There are several factors that invalidate the statement that ethanol produced from biomass is a carbon neutral fuel.

1. Energy required for planting, harvesting, processing, transportation, and distillation often comes from fossil fuels, adding to emissions..
2. Deforestation may be required to clear land for biofuel crops, reducing the number of trees that can absorb . This results in a net decrease in absorption.
3. Production and application of fertilisers consumes energy and causes release of nitrous oxide, another potent greenhouse gas.
4. Residual biomass decomposition can release methane, another potent greenhouse gas.

Biofuels are a promising renewable alternative to fossil fuels. When deciding on the appropriateness of biofuels as an energy source, environmental and ethical factors must be considered.

Biofuels can lower emissions compared to fossil fuels, however, production processes may release other more potent, greenhouse gases, such as nitrous oxides and methane.

Large areas of land are required for planting crops for biofuel production. This can lead to deforestation and remove sites for food crop cultivation. Land for biofuel production can also compete with sites to build housing.

High water requirements for growing biofuel crops can strain local water resources. This can be mitigated by sustainable irrigation infrastructure.

Monocultures for biofuels reduce biodiversity and disrupt ecosystems.

can be used along the arrow or as a balanced reagent in a chemical equation to represent the oxidising agent.

Elimination reactions remove atoms or small groups from a molecule, resulting in the formation of a double bond.

A key example of an elimination reaction is the elimination of water from an alcohol to form an alkene.

Alkenes produced via acid-catalysed elimination of alcohols serve as valuable monomers for synthesising polymers, offering an alternative to those derived from crude oil.

Alkenes can be derived from biomass, such as plant-based alcohols, reducing reliance on fossil fuels. Compared to fossil fuels, biomass is renewable and has a lower carbon footprint.