Industrial Chemistry

Based on Lucarelli's Essential Chemistry Chapter 15

Green Chemistry

Developing chemical processes that are more agreeable to the health of humanity and the natural world.

Principles of Green Chemistry

• Preventing waste

• Atom economy

• Reduce hazards

• Reduce toxicity

• Use safer or no solvents

• Energy efficiency

• Use renewable resources

• Keep the process simple as possible

• Use catalysts

• Monitor and reduce pollution

• Use fewer harmful chemicals

What are the benefits of using enzymes?

They reduce unwanted side reactions, and can reduce energy consumption due to not working at high temperatures.

Biofuels

Fossil fuel alternatives made from biomass

Benefits of biofuels

• Renewable

• Reduced toxicity

• Carbon neutral*

• Do not contain sulphur

• Produce less soot [this is due to increased O content] (though they do produce more NO_x)

Examples of biofuels

Biodiesel and bioethanol (produced via fermentation, not from ethene)

Biodiesel

Methyl or Ethyl esters of fatty acids

Uses of ethanol

Feedstock for chemical reactions, fuel replacement, hand sanitiser, solvent

What plants are good sources of biomass for fermenting ethanol?

Sugarcane, grapes (for wine), wheat (for beer), corn, sugar beet

How is ethanol fermented from molasses (sugar refining byproduct)?

Warm conditions of 25-37ºC are used, as well as a pH of 3-5. As the reaction is exothermic, heat must be removed from the reaction vessel. The reaction involves using yeast to convert glucose into ethanol via anaerobic respiration, until the alcohol concentration gets too high, killing the yeast. The ethanol can then be distilled.

How is ethanol synthesised from ethene?

Steam is added to ethene gas at a 5:3 mole ratio in the presence of H₃PO₄ catalyst. The reaction is exothermic but a temperature of 300ºC is used to maximise rate, while the pressure is 6-7 atm. Through reactant recycling, a yield of approximately 95% is possible.

What is transesterification?

The carboxylic acid part of an ester swapping from one alcohol to another

How does base-catalysed transesterification of triglycerides produce biodiesel?

1. Remove all foreign matter, water, and free fatty acids to prevent soap formation (fatty acids may be treated via alcohol esterification, with H₂SO₄ catalyst)

2. Add excess methanol or ethanol along with a NaOH or KOH catalyst, and heat the reaction vessel to 60ºC

3. The yield of this process may be as high as 98%, the products form two layers, with biodiesel on top and glycerol on the bottom (glycerol is a useful by-product)

4. Wash the biodiesel with warm water to remove residual catalyst

5. Remove the water from the biodiesel

What are some potential advantages of replacing the hydroxide catalyst with lipase?

1. Operating at lower temperatures

2. Operating at milder pH

3. It can catalyse the transesterification of both fatty acids and triglycerides

4. Lipase does not catalyse side reactions, e.g. saponification

5. It simplifies product purification and reduces waste water

6. Reduces energy usage for heating and refining

What are the disadvantages of lipase vis-a-vis conventional catalysts?

1. It is slower acting

2. It is quite a bit dearer

3. It is difficult to recover after the reaction, and so more must be bought for each batch of biodiesel

4. It is inhibited by high concentrations of alcohol

What is ammonia used to make?

Fertiliser, polymers, explosives, and cleaning agents

What are the conditions used in the Haber process?

150-350 atm of pressure, 350-550ºC (compromise as the reaction is exothermic), 3:1 ratio of H_2(g) to N_2(g), and an iron catalyst. The reactants are recycled to improve yield.