Petroleum products and chemical testing

Distillation characteristics

Distillation is a physical method for separating liquid mixtures on the basis of their different boiling temperatures. It is used in industry mainly in oil processing and in the food industry in the production of spirits. The mixture of substances is heated until it reaches the desired boiling and evaporation temperature of the separated substance. These vapours are transferred to the condenser, where their condensation occurs, and the separated substance is then collected in liquid form.

Flash point

The flash point is the lowest temperature at which a flammable liquid substance, under well-defined test conditions, develops a quantity of flammable vapour which, when an initial source is brought near (e.g. a flame or a spark), it is able to burn briefly (max. 5 seconds) and go out again.

Impurity content

Freezing point

Solidification occurs when liquids cool down to freezing temperature. The freezing temperature varies for different substances. The freezing temperature for crystalline substances is the same as the melting point. The freezing temperature depends on the type of substance and the pressure. The heat which the liquid gives off on freezing is called the latent heat of fusion and it is the same as the latent heat of melting for the same substance. The opposite of freezing is melting, in which the solid is converted into liquid.

Turbidity point

The turbidity point is the temperature at which crystalline paraffin turbidity first appears in the liquid when cooled under specified test conditions. The sample is cooled at the specified rate and periodically tested. The temperature at which turbidity occurs at the bottom of the test vessel is recorded as the turbidity point or paraffin deposition temperature (TVP).

Limit temperature of filterability

The limit temperature at which diesel is still capable of penetrate a test sieve with apertures of 45 micrometres (0,045 mm) without completely interrupting the fuel supply due to the excluded paraffin particles is called the filterability temperature. It is indicated by the CFPP symbol      (Cold Filter Plugging Point).

Viscosity, viscosity index of petroleum products, viscosity number

The viscosity of the liquid is its resistance to flow and it is very much affected by temperature. As the temperature increases, viscosity decreases, i.e. the liquid behaves more as a liquid. The temperature dependence of kinematic viscosity can be compared using a viscosity index. It basically describes the change in viscosity with temperature.

The determination of the viscosity index is based on two types of oils with the same initial viscosity and strongly different changes in viscosity when temperature rises. Oils showing a strong temperature dependency are assigned a viscosity index of 0, while oils with a lower change in viscosity are assigned a viscosity index of 100.

Corrosion by action on metals

Extractable substances