Paraformaldehyde (Vacuum Rake Dryer Process) Plant

Paraformaldehyde, produced via the vacuum drying method, ensures high purity (formaldehyde content ≥95%) and low moisture (≤1.5%) due to its low-temperature and low-pressure process. It is widely used in pharmaceuticals (slow-release disinfectants), agrochemicals (glyphosate synthesis), synthetic resins (urea/phenolic resins), electronic materials, and textile treatment, particularly suited for heat-sensitive and high-value applications.

Key Application:

Plywood Adhesives: Paraformaldehyde is used in urea-formaldehyde resins to produce waterproof adhesives for plywood and particleboard.
Herbicide Glyphosate: Acts as an intermediate in synthesizing glyphosate (e.g., Roundup®), a globally used herbicide.
Medical Disinfection Tablets: Slow-release formaldehyde tablets sterilize medical equipment or enclosed spaces (e.g., laboratories).
Electronic Encapsulants: High-purity paraformaldehyde modifies epoxy resins for semiconductor packaging materials.
Textile Anti-Wrinkle Treatment: Reacts with cellulose to improve wrinkle resistance and durability of cotton fabrics.
Water Treatment Biocide: Gradually releases formaldehyde to control microbes in industrial cooling water systems.
3D Printing Resins: Serves as a crosslinker to enhance mechanical strength and precision of UV-curable resins.

Introduction

50% formaldehyde solution is pumped into scraper evaporator via flow meter, the falling film evaporator concentrated to 60% flowed into the still kettle. In the kettle it continuously gets heated by the 0.4 MPa steam in the coil and evaporates and dehydrates, when the concentration reaches 75%, put high concentrated formaldehyde into the rake dryer with vacuum. Further get heated and stirred in the rake dryer, get vacuum dehydrated and dry, finally it makes paraformaldehyde. The product gets unloaded from the dryer discharge hole, and then it is put into packer by rubbing board conveyor for package.

Technical Features

The main feature of Raking drying process with scraper is the simple process and little investment. The plant is batch operation, composed with several independent operating unit. When any unit has fault, others will not be affected.

The process is with advantage of vacuum drying as well as stirring drying. The energy saving and less investment of the equipment makes no big loss under normal circumstances.

Process Characteristics

Low-Temperature and Low-Pressure Operation
- Conducted under reduced pressure (vacuum), significantly lowering the evaporation temperature of water (typically <60°C) to avoid thermal decomposition or degradation of heat-sensitive materials like paraformaldehyde.
Controlled Drying Environment
- Low-Oxygen Atmosphere: Reduced oxygen content minimizes oxidation risks, suitable for oxidation-prone or flammable materials.
- Closed System: High sealing prevents leakage of harmful gases (e.g., formaldehyde), enhancing operational safety.
Batch Production
- Primarily batch operation, ideal for small-scale, high-value products or scenarios requiring strict quality control.
Slower Drying Speed
- Compared to continuous processes like spray drying, vacuum drying is slower but achieves more thorough drying with lower residual moisture (≤1%).
Broad Applicability
- Suitable for pastes, blocks, or high-viscosity materials, with strong adaptability to material forms.

Process Advantages

High Product Quality
- High Purity: Low-temperature drying reduces thermal decomposition byproducts and formaldehyde volatilization, ensuring higher purity (formaldehyde content ≥95%).
- Thermal Stability: Prevents chain breakage of paraformaldehyde caused by high temperatures, ensuring stability during storage and transportation.
Protection of Heat-Sensitive Components
- Low-temperature conditions protect thermally sensitive materials (e.g., low-degree-polymerization paraformaldehyde), preventing thermal degradation or discoloration.
Thorough Moisture Removal
- Efficient water evaporation under vacuum results in low product moisture content (≤1.5%), reducing caking risks.
Reduced Environmental Pollution
- Closed systems allow recovery of volatile formaldehyde gas, minimizing workshop air pollution and raw material loss.
Operational Flexibility
- Precise control of drying parameters (vacuum level, temperature, time) to meet requirements for products with varying degrees of polymerization.

Applicable Scenarios

High-Value Products: Pharmaceutical-grade or electronic-grade paraformaldehyde requiring extreme purity and stability.
Small-Batch Production: Experimental or customized orders needing flexible parameter adjustments.
Heat-Sensitive Materials: Low-polymerization products prone to decomposition at high temperatures.

Paraformaldehyde specification

S/N	Item	Process index	Note
1	PFA content	92~96% w/w	Normally 95%
2	Formic acid	＜0.03%
3	Melting range	120~170℃
4	Ash content	＜100 ppm
5	Appearance	White powder
6	Methanol content	＜1 wt%
7	Free water	＜1 wt%
8	Iron content	＜2 ppm