Paraformaldehyde CAS 30525-89-4 PFA

S1. Ingredients: First, add urotropine with a mass content of 0.8% to a 37% formaldehyde solution. Then, the 37% formaldehyde solution mixed with urotropine is heated to about 55 degrees, and the solution is continuously stirred to make the solution in a uniform state.

S2. Evaporation and concentration: The 37% formaldehyde solution is transported to a falling film evaporator and a steam separator in turn with a centrifugal pump for concentration. In the falling film evaporator, the 37% formaldehyde solution is concentrated to 58%, and in the evaporation separator The 58% formaldehyde solution is purely separated from the formaldehyde vapor; the formaldehyde solution with a concentration of 58% is transported from the steam separator to the concentration kettle for secondary concentration; the formaldehyde solution with a concentration of 58% is concentrated to the concentration again in the concentration kettle was 79%.

S3. Spray granulation: spray granulation is carried out in a spray granulation tower through two-stage concentrated formaldehyde solution. The above-mentioned concentrated 79% formaldehyde solution is transported to the spray granulation device through a high-pressure pump, and the material is fed from the top of the granulation tower, and nitrogen is introduced into the tower. Can prevent dust explosion and high oxygen concentration. In addition, the temperature in the spray tower was 120°C, the spray angle was kept at 30° from the vertical direction, and the temperature of the nitrogen gas introduced into the tower was 40°C. Finally, the gas discharged from the spray granulation tower is separated by a cyclone to remove the solid-phase paraformaldehyde carried by it, and the separated paraformaldehyde is sent to a vibrating far-infrared dryer to be dried to the finished paraformaldehyde. The gas from the cyclone separator can be sent to the washing, separation and purification equipment to remove the gas-phase formaldehyde component in the gas, and then discharged to the atmosphere, and the dried paraformaldehyde is further sent to the vibrating far-infrared dryer for drying;

S4. Far-infrared drying: The paraformaldehyde after spray granulation and solidification is dried in a vibrating far-infrared dryer to further remove the bound water contained in the paraformaldehyde. A two-stage heating method is adopted, including a first-stage drying section. and secondary drying section. The temperature of the primary drying section is controlled at 60° C., and it is dried to paraformaldehyde with a mass content of 90%. The temperature of the secondary drying section is controlled at 80°C, and the paraformaldehyde is finally dried to a finished product with a weight content of 93%. Finally, N2 with a temperature of 30°C is passed into the vibration far-infrared dryer as the cooling after drying. medium to cool the finished paraformaldehyde. In addition, the gas discharged from the vibrating far-infrared dryer can be separated and removed by the cyclone to remove the carried solid-phase paraformaldehyde, and the separated paraformaldehyde can directly enter the finished paraformaldehyde. The gas from the cyclone separator can enter the washing, separation and purification equipment together with the gas discharged from the cyclone separator used to process the gas of the granulation operation unit to remove the gas-phase formaldehyde components in the gas, and then discharge to the atmosphere.

Concentrate the aqueous solution containing 37% of formaldehyde in vacuo at 65°C to obtain a concentrated aqueous solution of paraformaldehyde containing 80% of formaldehyde, add the suspension at a concentration of 1.5%, and the manufacturing method of the suspension is to disperse the magnesium oxide fine powder into In methanol, obtain a methanol suspension with a magnesium oxide concentration of 50 ppm, then add it to an extruder to obtain 2-5mm particles, add the particles to a dryer, and dry for 60 minutes to make a solid content of 80% The paraformaldehyde can be made into 92% paraformaldehyde after drying for 120 minutes, and its output is 400kg/hr.

A process for producing paraformaldehyde, the detailed process steps are as follows:

1. The formaldehyde solution (45-50% by mass) passes through the intermediate tank under the condition of heat preservation throughout the whole process. The whole process is heated by steam to keep the temperature above 60 °C, and the formaldehyde solution in the intermediate tank is continuously pumped by the pump. Circulation to prevent formaldehyde polymerization; formaldehyde solution is pumped into the device area.

2. The formaldehyde solution (concentration by mass percentage 45-50%) enters the first-stage evaporator to evaporate the formaldehyde vapor. The first-stage evaporator is a tubular evaporator, and the evaporation temperature is kept between 75-85 °C; the formaldehyde vapor enters the first-stage separator, In the case of ensuring that the temperature of the material does not decrease, the separation process maintains a vacuum condition. The 7% dilute aldehyde is taken away by vacuuming and sent to the absorption device, and the separated concentrated aldehyde (75-85% by mass) is pumped into the second-stage concentration device.

3. The second-stage concentration device is a steam-heated thin-film evaporator, and the formaldehyde solution (with a mass percentage concentration of 75-85%) is sent to the second-stage concentration thin-film evaporator for second-stage concentration. The thin film evaporator is heated by steam, and the interior is stirred evenly by a stirring paddle to prevent the polymerization of concentrated aldehydes. Vacuum conditions were maintained throughout the concentration process. The concentrated aldehyde concentration after concentration is 90-95% (mass percentage), wherein 34% of the dilute aldehyde is taken away by vacuuming and sent to the absorption device. Concentrated formaldehyde is sent to the spray granulation device through a pump;

4. The concentrated formaldehyde solution in the second stage is spray-dried in a spray granulation tower to further remove the free moisture that is easier to remove in the paraformaldehyde. The concentrated concentrated aldehyde in the second stage should be pressurized into the spray granulation device through a high-pressure pump. The spray granulation device used is a spray granulation tower. The material is fed from the top of the spray granulation tower. Precise adjustment of temperature and spray angle, the temperature is 90-150°C, and the spray angle is kept at 0-45° to the vertical direction to produce paraformaldehyde with the most optimized particle size, viscosity and continuity. The entire spraying process must be carried out in nitrogen flow, which not only plays the role of drying, but also prevents dust explosion and high oxygen concentration. Among them, the dilute formaldehyde gas and its dilute aldehyde powder are sent to the absorption tower for absorption, and the dried paraformaldehyde enters the fluidized bed drying device;

5. The paraformaldehyde after spray granulation and solidification enters the fluidized bed drying device to further remove the bound water contained in the paraformaldehyde. The fluidized bed drying device is a vibrating fluidized bed, and the dried paraformaldehyde passes through a bucket. The hoist enters the PF middle tank and is ready for packaging.