Cloud point

In the petroleum industry, cloud point refers to the temperature below which wax in diesel or biowax in biodiesels forms a cloudy appearance. The presence of solidified waxes thickens the oil and clogs fuel filters and injectors in engines. The wax also accumulates on cold surfaces (producing, for example, pipeline or heat exchanger fouling) and forms an emulsion with water. Therefore, cloud point indicates the tendency of the oil to plug filters or small orifices at cold operating temperatures.

An everyday example of cloud point can be seen in olive oil stored in cold weather. Olive oil begins to solidify at around 4 °C, whereas winter temperatures in temperate countries can often be colder than 0 °C. In these conditions, olive oil begins to develop white, waxy clumps of solidified oil that sink to the bottom of the container.

In crude or heavy oils, cloud point is synonymous with wax appearance temperature (WAT) and wax precipitation temperature (WPT).

The cloud point of a nonionic surfactant or glycol solution is the temperature at which the mixture starts to phase-separate, and two phases appear, thus becoming cloudy. This behavior is characteristic of non-ionic surfactants containing polyoxyethylene chains, which exhibit reverse solubility versus temperature behavior in water and therefore "cloud out" at some point as the temperature is raised. Glycols demonstrating this behavior are known as "cloud-point glycols" and are used as shale inhibitors. The cloud point is affected by salinity, being generally lower in more saline fluids.

The test oil is required to be transparent in layers 40 mm in thickness (in accordance with ASTM D2500). The wax crystals typically first form at the lower circumferential wall with the appearance of a whitish or milky cloud. The cloud point is the temperature at which these crystals first appear.

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Wikipedia