Glycerol wash

From Biopowered
Jump to: navigation, search

Glycerol wash is the process of mixing the waste glycerine from previous reactions before the biodiesel reaction. This has a variety of benefits.


  • Lowers titration/acid value of the oil
  • Lowers the water content of the oil
  • Frees biodiesel trapped in the glycerol by-product.
  • Can release methanol from the glycerol layer.


This method is only possible if you have access to glycerol by-product from a previous biodiesel reaction, this is not possible on your first batch.

The method below assumes you have a GL Processor reactor or similar, although this can be adapted to alternate designs.

  • Fill your reactor with feedstock as normal, although ensure you have enough space for the glycerine to be added.
  • Heat feedstock to ~65°C
  • Inject glycerine into the reactor using the venturi. Typically the full amount of glycerine from the previous batch is used.
  • Mix for at least 30 minutes, although longer will improve the result.
  • Turn off all pumps. If you are using NaOH derived glycerine, drain the lower pipe work whilst still hot, and allow the processor contents to settle for at least 30 minutes.
  • Drain off the lower glycerine layer, until oil starts to appear.
  • Mix then take a sample for titration.

Please note the amount of glycerine drained off can differ to the amount originally loaded into the reactor This can be greater if water has been absorbed into the glycerine, or lower if biodiesel and methanol have been released into the oil.


It is very important to titrate after the pre-treat (unless you are using the two stage process with no titration) as the main effect it has is that of reducing the acid value/titration value of the oil, Failure to titrate after may result in excess soap production during the reaction stage.


If you do not currently de-meth with the glycerine present AKA whole batch demeth then methanol will be present in the waste glycerine and care should be taken to limit exposure to the vapours. Residual catalyst will be from the last reaction, and so will be highly corrosive so wear protective clothing and eye wear.


Methanol is both highly flammable and toxic, take great care when dealing with this hazardous material. Glycerine will contain residual catalyst from the previous reaction, and so should be treated with care as it is highly corrosive. Ensure you wear long sleeve clothing and wear eye protection.

See also

Mon 19:15, 26 March 2011 (UTC)