Production and types of coated asphalt

Currently, the preparation techniques for coated asphalt at home and abroad mainly involve oxidation and thermal condensation. The raw materials are divided into coal-based asphalt and petroleum-based asphalt, while the main preparation methods include vacuum flash evaporation, air oxidation, oxidative cross-linking, and thermal condensation. In the vacuum flash evaporation method, the raw material, ethylene tar, is first subjected to sedimentation pretreatment to remove the coarse components. It is then heated to 460°C in a reactor for thermal treatment, yielding a heated product. This heated product is subsequently separated and purified, and the purified product is subjected to continuous vacuum flash evaporation at a vacuum level of 100 Pa. Continuous stirring is carried out during this flash evaporation process, and ultimately, asphalt specifically suitable for coating lithium batteries is obtained. Air oxidation method: The raw material used is purified polycondensed asphalt (RPP), with an industrial softening point of 80°C, a toluene-insoluble content of 20.07%, a quinoline-insoluble content of 0.39%, and a coking value of 50.87%). The raw materials are heated to 290–320°C in a high-pressure reactor, where they react at a constant temperature for a certain period of time. Stirring is continued throughout the heating process, and an appropriate amount of air is introduced as an oxidizing agent. After the reaction is complete, the resulting asphalt is the coated asphalt. The oxidative cross-linking method involves first mixing coal tar pitch with an extractant for extraction, followed by placing the mixture in a sedimentation tank for preliminary sedimentation. After allowing it to stand and separate for 12 hours, the upper light-phase mixed oil is sent to a distillation tower. Adjust the vacuum level of the distillation column to -0.09 MPa and control the distillation temperature. The solvent in the light-phase mixed oil and the light components in the pitch are extracted, yielding refined medium-temperature pitch with a softening point of 115–120°C and quinoline insolubles below 0.01%. The refined medium-temperature asphalt is poured into the oxidation/crosslinking reactor. The temperature is then raised, and air is evenly introduced into the material through an air distributor at the bottom of the reactor (the air must be preheated before entering the distributor). Meanwhile, the material is stirred to ensure thorough contact between the air and the asphalt. Once the temperature reaches the set point, it is maintained at this level for a certain period of time to produce coated asphalt. The resulting high-softening-point coated asphalt exhibits a high degree of aromatic condensation, few branched chains, and excellent thermal stability; it is therefore a high-quality coated asphalt product. The production method via heat shrinkage involves mixing medium-temperature coal tar pitch with a stabilizer in an environment filled with nitrogen as a protective gas. It is then heated to 350–380°C and fed into a rapid heater, where the temperature is raised to 410–450°C within 1–5 seconds to initiate the polymerization reaction. After that, the temperature is lowered to 290–340°C for extraction using an extractant; followed by centrifugal separation and drying of the solid phase to obtain mesophase carbon microsphere products. The mother liquor is subjected to distillation in a tower to recover the extractant, while the residue at the bottom of the tower is used as coating asphalt.