Thermal oil, previously known as "thermal carrier oil" in GB/T 4016-1983 "Petroleum Product Terminology," is a type of oil with good thermal stability used for indirectly transferring heat. Due to its even heating, precise temperature control, ability to produce high temperatures at low steam pressure, effective heat transfer, energy-saving, and ease of transportation and operation, it has been widely used in various applications in recent years, with increasing usage and demand.
Low-melting thermal oil of biphenyl and biphenyl ether type, this type of thermal oil is composed of 26.5% biphenyl and 73.5% biphenyl ether. The melting point is 12°C. Dowtherm, the earliest synthetic aromatic thermal oil used worldwide, boasts excellent thermal stability and high operating temperatures up to 400°C. This product is heat-resistant in organic heat carriers due to the absence of alkyl side chains connected to the benzene ring. The low freezing point (12.3°C) allows for economic use within a boiling temperature range of 256~258°C at room temperature. This is because both substances have high melting points (biphenyl <71°C, biphenyl ether <28°C). There is no concentration of any component during the low-melting evaporation process, and the liquid properties remain unchanged. However, due to the combined ether in diphenyl ether, prolonged use at high temperatures (350°C) can produce phenolic substances, which have low corrosiveness and can cause corrosion to carbon steel and other materials when in contact with water.
Alkyl biphenyl ether thermal oil is connected by an ether group between two benzene rings, with two isomers having two methyl groups. This mixed thermal oil has low kinematic viscosity and good fluidity at low temperatures, making it suitable for cold regions in the north. It is recommended for use at temperatures not exceeding 330°C, with a freezing point of -54°C, and has a longer service life than mineral oil and alkyl benzene thermal oil. Base ether-type thermal oil is commonly used both domestically and internationally, and there are also domestic manufacturers producing this high-temperature thermal oil.
Alkyl biphenyl thermal oil is a type of thermal oil that consists of compounds with alkyl side chains attached to the biphenyl ring. It is formed by combining short-chain alkyls (ethyl, isopropyl) with the biphenyl ring, with the type and quantity of alkyls determining its properties. The more alkyl groups, the poorer the thermal stability. Among these products, thermal oils synthesized from isopropyl para- and meta- isomers (isomers) with biphenyl have excellent quality, with a boiling point >330°C and good thermal stability, making them ideal for use in the range of 300~340°C.
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