Chemistry
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Production of Ethanol

Production of Ethanol

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Ethanol is a type of alcohol that has many uses in our daily lives. It's made up of two carbons, and it's really important to understand how it's made. In organic chemistry, we learned that the root name 'eth-' means it has two carbons, and the suffix '-ol' means it has the hydroxyl functional group '-OH'. To help you understand more about ethanol, here's a table summarising its structural properties.

What are the uses of ethanol?

The main uses of alcohol include:

As a solvent in cosmetics.

As an intermediate in the manufacture of drugs, detergents, inks, and coatings.

As biofuel.

Let's move on to ethanol production.

What is the production process of ethanol?

There are two main ways in which ethanol is produced.

Fermentation of glucose Hydration of ethene

Fermentation of glucose

To make ethanol, yeasts convert plant carbohydrates like sugar cane or sugar beet into ethanol through a process called fermentation. This process takes place in a fermenter with specific environmental conditions. Most breweries use this process to make alcoholic beverages.

The secret to making ethanol is yeast. Yeast contains enzymes that convert glucose in plant carbohydrates into ethanol through anaerobic respiration. Anaerobic respiration is when glucose is broken down to create energy (ATP) without using oxygen.

Glucose ethanol carbon dioxide

Effective fermentation requires specific conditions to be successful. These conditions are listed below, along with an explanation of why they're important.

  • Temperature: Yeast works best at specific temperatures. If it's too hot, the yeast will die, and if it's too cold, the yeast won't be active enough to ferment the glucose.
  • pH: Yeast also needs a specific pH range to work effectively. If the pH is too high or low, the yeast won't be able to do its job.
  • Nutrients: Yeast needs specific nutrients to carry out fermentation, including nitrogen and phosphorus.

Once the fermentation process reaches 15 percent, the enzymes involved in anaerobic respiration are denatured, which stops the fermentation process.

To separate the ethanol from the water, a process called fractional distillation is used. This process separates the components of a solution based on their boiling points. Ethanol has a lower boiling point than water, which allows it to be separated from the water. Here's a simplified diagram of the apparatus used in fractional distillation.

Apparatus for fractional distillation
Apparatus for fractional distillation

In addition to fermentation, the hydration of ethene is another method used to produce ethanol in industry.

The chemical equation for the hydration of ethene is as follows:

C2H4 + H2O → CH3CH2OH

This reaction is reversible, which means the reaction conditions are important in order to maximize the equilibrium shift to the right-hand side. Steam is added during this reaction, and the carbon-carbon double bond in ethene becomes a single bond.

Even though the ethanol produced via hydration is pure in theory, it still needs to undergo fractional distillation to obtain pure ethanol. This is because there may be condensed steam inside the collecting vessel, which can mix with the ethanol and contaminate it.

How do hydration and fermentation compare?

The table below summarizes the differences between ethanol production via fermentation and hydration:

FermentationHydrationRaw materialsGlucose from plantsEthene from crude oilReaction typeBiologicalChemicalPurity of productLowerHigherRate of reactionSlowerFasterCostLowerHigher

Despite the higher purity and faster rate of reaction of the hydration method, the fermentation method is more widely used for ethanol production due to its lower costs and environmental-friendliness.

Ethanol is increasingly being used as a biofuel, replacing petrol as an environmentally friendly resource. In the UK, unleaded petrol now contains 10 percent ethanol. This helps to reduce greenhouse gas emissions and dependence on non-renewable resources.

What is a biofuel?

Biofuels are fuels derived from biomass such as plants. Biofuel is advantageous over crude oil for its renewable properties - it is naturally replenished at the rate we use it. In terms of using ethanol as a renewable resource, the crops where the plant carbohydrates are sourced (sugarcane, for example) can be sowed again once the existing batches have been harvested.

Combustion of ethanol biofuel

You may wonder about the chemical reaction associated with ethanol acting as a fuel. Similar to that of petrol, the chemical reaction that allows ethanol to generate energy is combustion, whose equation is as follows:

2C2H5OH   + 6O2    -> 4CO2        +   6H2O

ethanol      oxygen  carbon dioxide      water

Study tip: Complete combustion always involves oxygen and releases carbon dioxide and water. What differs is the starting molecule (i.e., octane or ethanol), as well as the number of moles of oxygen, carbon dioxide and water required to ensure a balanced chemical equation.

Advantages of using ethanol as a biofuel

There are arguments for and against using ethanol as a biofuel.

One argument for using ethanol as a biofuel is its carbon neutrality. Using ethanol from biomass as a fuel has no net release of carbon dioxide, as the amount of carbon dioxide released equals the amount taken in by the plants during photosynthesis. This helps to reduce greenhouse gas emissions and dependence on non-renewable resources.

Another benefit of using ethanol as a fuel is that it releases fewer pollutants. The combustion of ethanol is "cleaner" than the combustion of fossil fuels, as there are no end products containing sulfur or nitrogen oxides, which are pollutants that cause acid rain and respiratory conditions.

In terms of the production of ethanol biofuel, the fermentation of plant carbohydrates into ethanol is cheap, easy to store, and distribute.

However, there are also arguments against using ethanol as a biofuel. One argument is that it can lead to increased food prices, as the crops used to produce ethanol compete with those used for food. This can have a negative impact on food security, especially in developing countries where food is already scarce.

Another argument is that the production of ethanol can have negative environmental impacts, such as deforestation and soil erosion. This is because large areas of land are needed to grow crops for ethanol production, which can lead to the destruction of natural habitats and loss of biodiversity.

Furthermore, the production of ethanol requires large amounts of water, which can lead to water scarcity issues in areas where water resources are already limited. In addition, the use of fertilizers and pesticides in crop production can lead to water pollution and other environmental problems.

Overall, while there are benefits to using ethanol as a biofuel, there are also potential drawbacks that need to be considered. It is important to weigh the pros and cons carefully before deciding whether or not to use ethanol as a biofuel.

Disadvantages of using ethanol as a biofuel

It is important to consider the practical implications of using ethanol as a biofuel, rather than just focusing on theoretical arguments. One concern is the energy used in the harvesting and transportation of crops, which may come from non-renewable sources, and is not considered in the carbon neutrality argument. Additionally, the rapid combustion of ethanol biofuel may not be balanced by the rate of crop growth, leading to potential imbalances in the carbon cycle.

Furthermore, the production of ethanol as a biofuel can have negative environmental impacts, such as deforestation, which can lead to habitat loss and reduced biodiversity. The burning of rainforests for agriculture releases greenhouse gases, worsening global warming. The use of manpower for biofuel production may also lead to reduced manpower in food agriculture, potentially causing global food shortages.

Finally, the distillation of the fermented mixture used to produce ethanol is not only costly but may also require non-renewable energy sources, further adding to the environmental impact of ethanol production.

Overall, while there are potential benefits to using ethanol as a biofuel, it is important to carefully consider the practical implications and potential drawbacks of its production and use.

Production of Ethanol

Is ethanol the same as isopropyl alcohol?

Ethanol and isopropyl alcohol are two different alcohols. Ethanol is a primary alcohol, contains two carbons and has the structural formula CH3CH2OH. In contrast, isopropyl alcohol is branched, contains three carbons, and has the structural formula CH3CH(OH)CH3.

What is the role of anaerobic respiration of yeast in fermentation?

It is through anaerobic respiration of glucose that ethanol is produced as a byproduct.

Why can’t simple distillation be used to purify ethanol?

Ethanol produced by fermentation consists of two liquids, whereas simple distillation is used when purifying a liquid containing a dissolved solvent (for example, seawater).

Can all acids be used in the hydration of ethene to ethanol?

Strong acids, commonly phosphoric acid (and sometimes sulfuric acid) are used in the hydration process.

Since rainforests are cleared for the production of biofuel, does that mean that the growth of biofuel crops happens in the tropics?

Yes. For instance, sugar cane used in the production of biofuel is commonly grown in Brazil.

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