This article provides a comprehensive understanding of water content determination in petroleum products, including sources, forms, hazards, and methods of measurement. It emphasizes the importance of accurate water content analysis for ensuring product quality and preventing performance issues in various industries such as petroleum, chemicals, power, and more.
1. Sources of Water Content in Petroleum Products:
(1) Water Contamination during Storage and Transportation
Water can get mixed into petroleum products during storage, transportation, refueling, and usage due to various reasons. Residual moisture in containers, inadequate sealing of storage tanks, ingress of rain, snow, or frost during refueling, as well as condensation of water vapor, can all lead to the presence of water in petroleum products.
(2) Dissolved Moisture from Air
Petroleum products, especially light fuels, have a certain degree of water solubility. With increasing temperature, humidity in the air, and aromatic hydrocarbon content, the water solubility of light fuels also increases. Gasoline and kerosene do not readily mix with water but can contain up to 0.01% dissolved water.
2. Forms of Water Presence in Oil Products:
(1) Suspended Water
Water is suspended in the form of small droplets in the oil, forming cloudy emulsions or colloids. This phenomenon commonly occurs in high-viscosity heavy oils, with protective films formed by cyclic acids, colloidal substances, clays, and more. In such cases, water is difficult to separate by sedimentation and requires special dehydration methods. For example, air agitation and heating or vacuum drying methods are used to remove water from water-containing lubricating oils.
(2) Dissolved Water
Water is uniformly dispersed in molecular form among hydrocarbon molecules, known as dissolved water. The solubility of water in oil depends on the chemical composition of the oil and temperature. Alkanes, cycloalkanes, and olefins generally have weaker water solubility, while aromatics can dissolve more water. Higher temperatures result in greater dissolved water content in oil. In general, gasoline, kerosene, diesel, and some light lubricating oils have minimal dissolved water content, often below the detectable limit as per the “Method for Determining Water Content in Petroleum Products” GB/T260-1977 (1988).
(3) Free Water
Precipitated micro-water particles aggregate into larger droplets and settle out of the oil, resulting in an oil-water separation state. The term “water-free” in oil analysis generally refers to the absence of free and suspended water; dissolved water is difficult to remove.
3. Harms of Water Content in Petroleum Products:
(1) Impairment of Low-Temperature Flow Performance
Water in aviation fuels can elevate their freezing point, leading to filter or pipeline blockages and even fuel supply interruptions, causing accidents. Vehicle gasoline and diesel containing water can freeze in winter, obstructing fuel systems. Furthermore, water in fuel oil carries inorganic salts into cylinders, causing corrosion, increased carbon deposits, and heightened wear. Water in boiler fuel reduces combustion efficiency and increases corrosiveness.
(2) Degradation of Antioxidant Properties
Water in petroleum products can dissolve added antioxidants, accelerating the gum formation process in fuels like cracked gasoline and other unsaturated hydrocarbon-containing fuels. Water significantly affects the stability of stored fuel oils; gasoline stored with water forms gum faster than when water-free.
(3) Reduction of Oil Solubility
Solvent oils with water experience reduced solubility and efficiency.
(4) Diminution of Lubricating Properties
Water in lubricating oils can freeze into ice particles in winter, blocking fuel pipelines and filters, and increased component wear upon freezing in certain engine parts. Water presence also heightens lubricating oil corrosiveness and emulsification properties.
(5) Deterioration of Dielectric Properties
Water in electrical insulating oils lowers their dielectric properties and can lead to short circuits or even equipment damage.
4. Significance of Water Content Determination in Oil Products:
Water content is a crucial quality parameter for evaluating petroleum products. Determining water content holds the following significance:
Provides a basis for designing dehydration processes.
Evaluates oil product quality: Water content is an essential specification in various petroleum product standards and a primary control parameter for material in/out of oil production facilities.
Prevents the presence of water in petroleum products, except for specially treated water-containing fuels for energy saving and environmental protection.
Overview of Water Content Determination Methods:
Distillation Method: Involves distillation of a sample mixed with water-free solvent to determine water content as a percentage.
Karl Fischer Coulometric Titration Method: Utilizes the relationship between the number of water molecules and the charge according to electrolytic law for determining water content. This method is sensitive, precise, and suitable for trace analysis of low water content samples.
5. Overview of Water Content Determination Methods:
Distillation Method: Involves distillation of a sample mixed with water-free solvent to determine water content as a percentage.
