Typically, four process factors can lead to adhering on the walls of stainless steel reactors:
Due to the excessive sulfate content in urea, adding it during the latter stages of the resin condensation reaction is akin to introducing a hardener, which accelerates the cross-linking of the resin into a network structure. If not addressed promptly, the resin may solidify within the reaction vessel. Therefore, it is crucial to use standard industrial urea as a raw material in production, ensuring that the sulfate content in urea is limited to less than 0.01%.
When the control of temperature, pressure, and other胶 making process indicators is unstable or fluctuates excessively, the polymerization process of the resin is uneven, which is prone to cause sticking to the wall. Therefore, during production operations, the pressure and temperature should be increased slowly. Generally, introduce about 0.15Mpa of steam and maintain for 2 to 3 minutes before slowly increasing the pressure and temperature. The increase rate should be around 0.1 to 0.15Mpa per minute.
3. Low cooling medium temperature in the釜 wall or sudden temperature drop leads to a significant difference in temperature between the釜 wall and the material, causing adhesive residue on the釜 wall of the contact stainless steel reaction釜. Therefore, both heating and cooling should be conducted within a reasonable temperature difference range. Typically, the steam usage temperature should be less than 180°C, the temperature difference thermal shock should be less than 120°C, and the cooling shock should be less than 90°C. At the same time, attention should be given to determining the appropriate inlet and outlet temperatures of the cooling medium to maintain balanced operation.
4. When the reaction liquid temperature is below 80°C, if ammonium chloride is used as a catalyst, due to its fast reaction rate, the pH value may not be displayed. As the temperature rises, the pH value drops rapidly, the reaction rate accelerates, and the polycondensation reaction becomes too vigorous, leading to gel formation and sticking to the walls. Additionally, if the polycondensation reaction time is too long, the resin's molecular weight is high, and the viscosity is too high, sticking to the walls is also likely to occur. Therefore, it is important to properly control the temperature and time of the polycondensation reaction during operation and to terminate the reaction promptly. Generally, it is advisable to keep the reaction liquid temperature within 95°C.
