Potassium hydroxide is a strong base, which can be widely used in electroplating or chemical raw materials. However, when we use it, we will find that the color of some products turns black. This is because there are some mistakes in the process of production. Let's have a detailed understanding of the reasons why the color of products turns black.
1. Nitrogen sealing equipment is needed after start-up
When the equipment is in micro positive pressure state, it can effectively avoid air entering the system. Therefore, during the production, the equipment is sealed with nitrogen after feeding, and the device at the nitrogen inlet is always in a high temperature and strong alkali state. Oxygen entering will aggravate the corrosion of nickel material, and then increase the nickel content, resulting in black color.
2. Ability control
The capacity should be controlled in the range of 60% ~ 100% of the rated output. In the evaporator, if the feed rate is too small, the liquid film in the evaporator will be too thin to break, resulting in dry wall area, which will make the pipe bear greater thermal stress, thus aggravating stress corrosion. When the liquid feed volume is too large, the liquid can not form a normal film or the film is too thick. In the heating process, the liquid often can not be fully heat transfer, so it can not reach the temperature required for boiling, so it can not be fully evaporated, which will lead to the concentration process can not be well carried out, or even can not be carried out. If the flow rate is too large or too small, the equipment will be damaged and the nickel material will be corroded, which will increase the nickel content in potassium hydroxide and make it black.
3. Reduce the times of starting and stopping
Try to reduce the number of start-up and shut-down of the equipment, because each start-up, the feed alkali will wash away a layer of nickel oxide layer which plays a protective role on the surface of nickel material, and then continue to wash and corrode the lower layer of nickel material, so it is inevitable to produce black alkali in the process of start-up. Measures such as extending the time of steam purging system can be taken to reduce the amount of black alkali during start-up as much as possible.
4. Purge the equipment with steam before start-up
Clean the system with steam before start-up to ensure sufficient pressure and purging time. Purging can not only preheat the equipment and reduce the thermal stress during feeding, but also purge the residual alkali in the pipeline during purging; it can also exhaust the air in the system through purging to reduce the oxygen content as far as possible; at the same time, it can reduce the erosion and corrosion of nickel equipment during feeding, reduce the nickel content and prevent blackening.
The above is the reason why the color of potassium hydroxide turns black when it is made. The main reason is that the output of potassium hydroxide is not well controlled when it is made, and the equipment can not be cleaned up, resulting in the color of the product turns black when it is made.