Winter waxing

In winter (or in a convenient freezer) some waxing in biodiesel may be observed as either suspended flakes or a white/yellow creamy layer at the bottom of containers.

Solids found at the bottom of a batch of biodiesel in the winter

Feedstock related waxing

Turning vegetable oils into biodiesel lowers the overall melt point of the liquid, that is to say that the resultant fuel will still be liquid at temperatures where the source oil would have become solid. However, making biodiesel from feedstocks containing high melt components such as palm oil will inevitably result in higher melt points in the final fuel. These components are commonly referred to as High Melt Point Esters (HMPEs).

Process related waxing

An incomplete reaction, or a partial reverse reaction (such as by removing too much methanol while following the Whole Batch Demeth method) can result in biodiesel that is rich in monoglycerides and diglycerides. These often cause cloudyness in the methanol when performing a 3/27 test.

Mono and diglycerides have an elevated melt point. During summer, they well go undetected as they remain liquid, but in winter a layer of cream may form during settling.

Surviving waxing winter

Additives such as petrol typically do not prevent wax formation, though the level may be reduced. Treatment is by water washing or separation.

Water washing

As mono and diglycerides are highly hygroscopic, they can be removed by Water Washing with cold water. The initial level of in the produced fuel may also be reduced by doing a cold Water Prewash before settling soaps.

The same is likely to be true of waxes from HMPEs, as the cold water will assist their solidification.

Separation by settling

If water it not used in your process and the fuel is only gravity settled after demething, liquid biodiesel can be drawn from the top of a settled batch, and the creamy liquid at the bottom put into the next batch for reprocessing. Only a very small amount of methanol and catalyst will be required to complete their conversion to fatty acid methyl esters, so treat them as already converted biodiesel in the batch, or follow the two stage process without any changes.

Separation by filtering

Waxes may be separated by gravity filtering through sheets, or by centrifuging.

Pressure filtering, for example with a pump through 10" filter elements, may only remove a small amount of wax - the rest will be extruded through the filter element by the pump's pressure and still be present in the fuel.

• Waxing
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  Wax at bottom of barrel

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  A closer look at the ball formation

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  Wax balls on the side of a barrel

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  Waxes after bio is filtered off

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  Wax forming around the coil of a beer chiller

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  A closer look

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  Severe waxing. Source Bionoob

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  Severe waxing. Source Bionoob

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  Severe waxing. Source Bionoob

See also

• MSDS - Biodiesel