Determine the freezing point of oil

The freezing point in oil

• The freezing point is usually considered to be the temperature at which a substance changes from a liquid to a solid state of aggregation, i.e. the substance can no longer flow. Strictly speaking, it means the temperature at which a substance changes into a crystalline phase.
• Since oil does not have a crystalline phase, there are various terms that have to do with the changes in the state of oil when it is cold. There is the pour point, that is the temperature at which it no longer flows, which is specified in DIN 51597 mentioned pour point, this is the temperature that is slightly above and at which the oil is just barely flows.
• In connection with aviation fuels, which are technically a mineral oil, the term freezing point (FRP) is used in a different context. This is about the lowest temperature at which this fuel is still completely liquid, i.e. no paraffin has crystallized out. The freezing point is the temperature at which some components of the oil solidify. Similarly, cooking oil is usually referred to as freezing point when it comes to the temperature at which this oil flocculates and becomes milky.
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• Diesel drivers may have already made the experience that when it is very cold there are crystals in the pipes that prevent the engine from starting. This is because diesel attracts water and it freezes, which often happens long before the actual diesel oil solidifies. This freezing has nothing to do with the freezing point of oil.

So before we can figure out the specific freezing point temperature, you need to determine which change will be considered freezing. So whether it should be about the pour point (no longer flowable) or the FRP, which relates to the flocculation.

Determination of the pour point or of the FRP

1. Store the oil at different temperatures in order to have an approximate idea at which temperature to start the experiments.
2. Then it is best to adhere to the DIN standard. Set up different cooling baths, each with a temperature difference of 3 ° C. For example 9 ° C, 6 ° C, 3 ° C, 0 ° C, - 3 ° C etc.
3. Fill a sample of the oil of which you want to determine the freezing point into a test tube and place it in the warmest of the cooling baths. Wait for the sample to cool to temperature.
4. Remove the test tube. To determine the FRP, you need to look for a cloudiness of the oil, to determine the pour point, slowly tilt the glass horizontally. If the oil is still flowing, the pour point has not been reached. In order to be able to carry out an exact measurement, the oil must not have changed at this temperature, so it must have remained fluid and clear.
5. Now put it in the next colder bath. Take out the sample. If this is now cloudy, then put the sample in the warmer bath. Wait until it has reached the temperature. Look at the sample again. If it is still cloudy, put it in an even warmer band. The freezing point is reached when the oil is clear again. Assuming it became cloudy at 0 ° C and clear again at 6 ° C, then the freezing point is 6 ° C.

If you want to determine the pour point, you have to put the oil sample in ever colder baths until the point is finally reached that it no longer flows. Aviation fuel is usually between 9 ° C and 12 ° C between the pour point and the freezing point. The freezing point, which is literally translated as the freezing point, is not the point at which the entire sample becomes solid, but rather the point at which individual substances flocculate into a solid state of aggregation.