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.
Contents
Turning vegetable oils into biodiesel lowers the overall melt point of the liquid - the produced fuel will still be liquid at temperatures where the source oil will be solid. However, making biodiesel from oils 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).
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 the warm days of summer they remain liquid and their presence may go undetected. In winter a layer of cream can form after a few days of settling.
Surviving winter waxing
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 emulsifiers, they can be removed by Water Washing.
Cold water washing may also help remove waxes caused by HMPEs, as the cold will assist their solidification. However not all HMPEs may be washed out, as they are less dense than water.
Separation by settling
The initial level of waxes in the produced fuel may also be reduced by doing a Water Prewash before settling soaps.
If water it not used in your process at all, and the fuel is only gravity settled after demething, liquid biodiesel can be drawn from the top of a settled batch.
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.
Reprocessing
If you believe the waxes are from monoglycerides rather than HMPEs, then the creamy liquid at the bottom can be 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.
If the waxes are from HMPEs, then reprocessing will have no effect, beyond melting them (they will reform on settling again).
TODO: Possible to differentiate between HMPEs and monoglycerides by 50:50 shake test with water or cloudy 3/27? Further testing required.
- Waxing
Wax at bottom of barrel
A closer look at the ball formation
Wax balls on the side of a barrel
Waxes after bio is filtered off
Wax forming around the coil of a beer chiller
A closer look
Severe waxing. Source Bionoob
Severe waxing. Source Bionoob
Severe waxing. Source Bionoob
