1. Introduction Physical anhydride, also known as phthalic anhydride, is an important organic chemical raw material, widely used as a raw material and intermediate in plasticizers, resins, pharmaceuticals, dyes, and pesticides. At room temperature, phthalic anhydride crystallizes as a flaky white solid with a melting point of 131.6℃. The industrial production of phthalic anhydride employs the gas-phase catalytic oxidation method with o-xylene. This process is carried out under flammable, explosive, high-temperature, and toxic conditions, with oxidation temperatures reaching as high as 440℃. The purification temperature of liquid phthalic anhydride is also as high as 180-250℃. During production, if liquid phthalic anhydride splashes onto the skin, in addition to burns, it easily absorbs water to form highly corrosive phthalic acid. Gaseous phthalic anhydride is highly irritating; inhalation can cause coughing, sore throat, mucous membrane congestion, and red, swollen, and tearing eyes, posing a significant health hazard. Under open flame conditions, it can also lead to serious accidents such as combustion and explosion. Therefore, phthalic anhydride plants have very high technical requirements, and most key equipment is imported. For example, phthalic anhydride pumps, domestic equipment generally chooses products from German company KSB and American company DURCO, all of which are jacketed mechanical seal centrifugal pumps. However, due to the physicochemical properties of phthalic anhydride, this type of pump has a short seal life, high maintenance costs, and during equipment maintenance, phthalic anhydride poses significant hazards to human health and the environment. [b]2 Defects of Mechanical Seal Centrifugal Pumps[/b] Based on the physicochemical properties of phthalic anhydride and its hazards to human health and the environment, bellows mechanical seals are often selected for phthalic anhydride pumps to ensure a good sealing effect. However, since phthalic anhydride is a high-melting-point substance, during start-up and shutdown, the temperature at the mechanical seal is often lower than the melting point of the material, resulting in a small amount of phthalic anhydride solidification or crystal precipitation. The bellows will gradually lose its elasticity due to blockage and other reasons, leading to friction pair failure and pump leakage. Secondly, during the operation of the phthalic anhydride pump, the accumulation of crystals on the bellows surface causes axial bending, resulting in bellows breakage or uneven sealing compression. The high-temperature aging of the auxiliary sealing ring reduces its compensability, leading to seal failure and leakage. Third, because the phthalic anhydride oxidation reaction is carried out within the explosive limits of o-xylene, it is highly dangerous, and there are many occasional accidents in the equipment. The service life of the mechanical seal of the phthalic anhydride pump is often greatly shortened due to frequent start-up and shutdown. Fourth, when the pump is repaired, the temperature at the mechanical seal chamber of the pump body is far below the melting point of phthalic anhydride, and the medium being transported has completely solidified in the mechanical seal chamber. Thus, the entire sealing assembly, including the bushing, must be replaced. Even a set of domestically produced bellows mechanical seals of the same type costs around 5,000 yuan, indicating that the maintenance cost of this equipment is relatively high. Moreover, the material is very harmful to operators and the environment, making it necessary to replace it with a suitable seal-less pump. [b]3 Advantages of Jacketed Magnetic Pumps[/b] When choosing a static seal pump to replace a dynamic seal centrifugal pump, the first consideration is the canned motor pump, which is a commonly used seal-less pump. However, it has the disadvantages of high-temperature media on the operation of the canned motor and the difficulty in determining whether there is an unmelted solid medium at the sliding bearing before the initial start-up. Therefore, it is not suitable for transporting high-melting-point phthalic anhydride products. In contrast, the magnetically driven seal-less pump can meet the above conditions. First, considering that the conveyed material may crystallize or solidify due to the drop in pump chamber temperature, a heat jacket design is added to the volute pump body and isolation sleeve. The very small gap between the isolation sleeve and the internal rotor is a crucial technical requirement. The two jacket sections must provide consistent insulation or heating, ensuring complete heat absorption. Even in the tiny gaps of the sliding bearings and at the tail of the isolation sleeve, the material must remain completely molten to prevent damage to critical components of the magnetic pump. The heat transfer medium is typically steam. It is important to note that the insulation jacket must ensure absolute separation between the conveyed medium and the heat transfer medium to prevent phthalic anhydride from combining with water vapor to form phthalic acid with a higher melting point, which could clog the pipes. A well-designed heat jacket for the magnetic pump can achieve the same jacket heating effect as a centrifugal pump. Second, during the internal circulation process, the fluidity of the conveyed phthalic anhydride decreases due to the drop in temperature. The auxiliary impeller at the tail creates a high-speed flow zone in the small space, preventing potential blockages. Simultaneously, when the pump stops, liquid will not accumulate at the tail of the magnetic pump area, ensuring thorough emptying and preventing difficulties in restarting due to material solidification. This is significantly better than the liquid accumulation defects caused by centrifugal pump shutdown. Furthermore, based on operational experience with pumps conveying high-melting-point substances, the medium should be completely emptied after the pump stops running. This prevents damage to the equipment due to volume changes in material form and improves efficiency during preheating before startup, ensuring uniform temperature rise. Similarly, before starting a magnetic pump, the rotor can be manually rotated to check for blockages. Only after confirming everything is correct should material be fed, the pump warmed up, and the pump started, effectively ensuring the reliability of the pump startup. In summary, the jacketed magnetic pump fully meets the process conditions for phthalic anhydride production. Replacing the dynamically sealed centrifugal pump significantly reduces the pump leakage and maintenance rate. [b]4 Comparison of Operating Costs of Mechanical Seal Pumps and Sealless Magnetic Pumps 5 Conclusion[/b] As long as the emptying and preheating processes of the jacketed magnetic pump are carefully observed, ensuring easy manual rotation without damaging the sliding bearings and isolation sleeves, this type of pump is superior to mechanical seal pumps. It not only significantly reduces maintenance costs but also simplifies operation, facilitating continuous operation of the unit, while reducing operator injury and environmental pollution. This allows for the further application of this type of sealless magnetic pump to the production of similar products, such as DMT and tar.