The Separation Phase

The Separation Phase

After the transesterification reaction in biodiesel production, the resultant mixture contains both biodiesel (esters) and glycerol, among other minor constituents. To obtain pure biodiesel, the separation of these major components is vital. Let’s dive into the separation phase, its significance, and the methods employed.

Why is Separation Important?

After transesterification, the biodiesel produced isn’t yet in a form that can be directly used as fuel. The mixture contains biodiesel, unreacted alcohol, catalyst residues, soap, and glycerol. Glycerol, in particular, has a higher density than biodiesel and can be separated to purify the biodiesel.

Methods of Separation

1. Gravity Separation

Since glycerol is denser than biodiesel, allowing the mixture to settle can lead to natural separation due to gravity.

Process: The transesterified mixture is transferred to a settling tank, where it’s left undisturbed for several hours to days. Biodiesel floats to the top, while glycerol settles at the bottom.

2. Centrifugation

For faster and more efficient separation, centrifuges can be used.

Process: The mixture is introduced into a centrifuge, which spins at high speeds. The centrifugal force pushes the denser glycerol outward, separating it from the biodiesel.

3. Decantation

In decantation, the top layer of biodiesel is carefully poured off, leaving the glycerol behind.

Process: After allowing the mixture to settle (gravity separation), the biodiesel layer is carefully decanted into another container, ensuring no mixing or disturbance of the glycerol layer.

4. Post-Separation Steps

  • Washing: The separated biodiesel might still contain traces of catalyst, alcohol, or soap. It is washed with warm water or specialized solutions to remove these contaminants.
  • Drying: Post-washing, it’s essential to remove any water from the biodiesel. This is done using drying equipment or by allowing the biodiesel to settle and naturally separate from the water.

5. Equipment Used in Separation

  • Settling Tanks: Large tanks designed to hold the mixture undisturbed for gravity separation.
  • Centrifuges: Machines that use centrifugal force for rapid separation of mixtures.
  • Decanters: Containers from which biodiesel can be poured off, leaving glycerol behind.

6. Considerations for Efficient Separation

  • Temperature: Maintaining an optimal temperature can aid in efficient separation.
  • Purity of Reactants: Ensuring the transesterification phase had minimal contaminants will reduce the complexities of the separation process.
  • Time: Adequate settling time should be given for gravity separation to ensure complete separation.


The separation phase in biodiesel production is pivotal to ensure the purity and quality of the final biodiesel product. Implementing the right methods and equipment ensures that the biodiesel produced meets or exceeds industry standards, readying it for further refining or direct use.