Biodiesel and the biofuel debate

Overview

Transesterification of vegetable oil, the sodium hydroxide catalyst, filtering, glycerol separation and washing, excess methanol, the advantages and disadvantages of biodiesel, oil palm, land use in developing countries and indirect land-use change.

What you need to know

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Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is biodiesel?

   Model answer

   Biodiesel is a fuel made of methyl esters of fatty acids, produced from vegetable oils or animal fats. Biodiesel can be used in diesel engines, usually blended with fossil diesel.

2. 2

   Give the word equation for making biodiesel from vegetable oil.

   Model answer

   The word equation is triglyceride + methanol → methyl esters + glycerol. One triglyceride reacts with three methanol molecules to form three methyl esters, in a reaction called transesterification.

3. 3

   What is the role of sodium hydroxide in biodiesel manufacture?

   Model answer

   Sodium hydroxide is the catalyst. Sodium hydroxide is first dissolved in methanol to form sodium methoxide, which speeds up the reaction.

4. 4

   Outline the main stages in making biodiesel from vegetable oil.

   Model answer

   The oil is filtered and dried, then warmed with methanol containing dissolved sodium hydroxide. The glycerol is separated off, and the biodiesel is washed and dried.

5. 5

   Why is waste cooking oil filtered and dried before it is made into biodiesel?

   Model answer

   Food particles must be removed so they do not contaminate the fuel. Water reacts with the catalyst and oil to form soap, which lowers the yield.

6. 6

   How is glycerol separated from biodiesel?

   Model answer

   Glycerol is denser than biodiesel and does not mix with it. The mixture is left to settle, and the glycerol layer is drained from the bottom.

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