Biodiesel
Lajoy Tucker
Teacher
Contents
What is Biodiesel?
Biodiesel is a renewable fuel made by chemically modifying vegetable oils or animal fats (which are triglycerides) through a reaction with alcohol in the presence of a catalyst.
- It is a mixture of methyl esters (or ethyl esters) of long-chain fatty acids.
Biodiesel Transesterification Explainer Video
Triglyceride Structure
Triglycerides are esters formed from:
Glycerol (propane - 1, 2, 3 - triol)
Three fatty acids (long-chain carboxylic acids)
General formula:
Formation of a triglyceride molecule:
Making Biodiesel – Transesterification Reaction
The triglyceride reacts with methanol in the presence of a strong base catalyst (commonly or ) to form:
3 methyl esters (biodiesel)
Glycerol (by-product)
The mechanism for this reaction is NOT needed on the AQA specification, only the equation and structures below are needed.
Advantages of Biodiesel | Disadvantages of Biodiesel |
Renewable (made from plant sources) | Uses farmland so creates competition with farmers |
Biodegradable | Higher emissions than petroleum diesel |
Carbon neutral | Expensive to store as it requires high temperatures |
Produces low when burned | Requires a lot of methanol which may come from fossil fuels |
Comparison to Other Fuels
Property | Biodiesel | Petroleum Diesel |
Source | Renewable (plants) | Non-renewable (crude oil) |
Biodegradability | Biodegradable | Non-biodegradable |
Emissions | Lower (theoretically carbon neutral) | Higher |
Emissions | Low | High |
Practice Question
Question 1 (4 marks)
State two advantages and two disadvantages of using biodiesel compared to fossil fuels.
Mark Scheme:
Advantages:
Renewable (1)
Biodegradable / less harmful if spilled (1)
Disadvantages:
Requires agricultural land, potentially competing with food crops (1)
Poor performance in cold temperatures (1)
Question 2 (2 marks)
Suggest why the production of biodiesel might not be fully carbon neutral.
Mark Scheme:
Fossil fuels may be used in the farming, harvesting, and transport of crops (1)
Methanol used may be derived from fossil fuels (1)