1. The source of water in petroleum products
(1) Water mixed in storage and use

In the process of storage, transportation, filling and use of petroleum products, due to various reasons and mixed water. If the container is not dry and there is residual water, the oil storage container is not tightly sealed or rain, snow and frost fall in the filling process, and the condensation of water vapor can make the petroleum products contain some water.

(2) Dissolve water in the air

Because petroleum products, especially light fuel oil, have a certain degree of solubility. With the increase of temperature, humidity and aromatic hydrocarbon content, the water solubility of light fuel oil increases gradually. Gasoline and kerosene hardly mix with water, but can still be dissolved in no more than 0.01% water.

2. The existence form of water in oil
(1) Suspended water
Water is suspended in the oil in the form of small droplets, forming a turbid emulsion or emulsion. This phenomenon occurs in heavy oil with large viscosity, and its protective film can be formed by naphthenic acid, colloidal substance, clay, etc. In this case, the water is difficult to precipitate and separate, and special dewatering methods must be used. For example, water-containing lubricants are often dehydrated by stirring hot oil with air flow or by vacuum drying. Among them, the use of vacuum drying method can avoid the oxidation of air.

An introduction to the determination of moisture in petroleum products

(2) Dissolve water

Water is uniformly dispersed among hydrocarbon molecules in a molecular state called dissolved water. The solubility of water in oil depends on the chemical composition and temperature of the oil. Alkanes, cycloalkanes and alkenes generally have weak ability to dissolve water, and aromatic hydrocarbons can dissolve more water. The higher the temperature, the more water dissolves in the oil. In general, the amount of dissolved water in gasoline, kerosene, diesel oil and certain light lubricants is small and cannot be detected by the Method for Determination of Moisture in Petroleum Products GB/T260-1977 (1988) and is negligible.

(3) Free water

The small water particles precipitated into larger water droplets precipitated from the oil and existed in the state of oil-water separation. Usually, the anhydrous oil analysis refers to the absence of free water and suspended water, and dissolved water is difficult to remove.

3, the harm of water in petroleum products
(1) Damage the low-temperature flow performance of oil products

If the aviation fuel contains water, it will increase its freezing point, cause the filter or oil pipeline to block, and even interrupt the oil supply, resulting in accidents. If the vehicle gasoline, vehicle diesel contains water, it is easy to freeze in winter, blocking the fuel oil system. In addition, the water in the fuel oil will bring inorganic salts into the cylinder, causing corrosion, carbon accumulation, and wear. Water in boiler fuel reduces combustion efficiency and increases corrosiveness.

An introduction to the determination of moisture in petroleum products

(2) Reduce the antioxidant properties of oil products

The water in the petroleum product dissolves the newly added antioxidants, speeding up the gumming process of the petroleum product (such as cracked gasoline and other fuels containing unsaturated hydrocarbons). The influence of moisture on the stability of fuel oil in storage is more significant. If there is water in the storage of gasoline, the rate of gum formation is much larger than when there is no water.

(3) Reduce the solubility of oil

If there is water in the solvent oil, the solubility and efficiency of the oil will be reduced.

(4) Reduce lubrication performance

If there is water in the lubricating oil, it freezes into ice particles in winter, blocking the oil pipeline and filter, and increasing the wear of the parts after some parts of the engine freeze. The presence of moisture also increases the corrosiveness and emulsification of lubricating oil.

(5) Reduce the dielectric properties of the oil

If there is water in the electrical oil, it will reduce its dielectric properties, and in serious cases, it will cause short circuit or even burn out the equipment.

An introduction to the determination of moisture in petroleum products
4, the significance of determining the moisture in the oil
Water content is one of the important indexes to evaluate the quality of petroleum products. The determination of oil moisture has the following significance:

Provide basis for the design of dehydration process according to the moisture content of the oil, determine the dehydration method. Evaluation of oil quality: moisture is one of the essential specifications in various petroleum product standards, and also serves as the main control index for the material in and out of the oil production device. Except for water-added fuels that require special treatment in order to save energy and protect the environment, moisture is generally not allowed in petroleum products.

5. Overview of moisture determination methods
Distillation method: A certain amount of sample is mixed with an anhydrous solvent, and its moisture content is determined by distillation and expressed as a percentage.