Polyacrylamide (PAM) production involves using acrylamide aqueous solution as raw material. Under the action of an initiator, a polymerization reaction is carried out. After the reaction is completed, the generated polyacrylamide gel blocks are cut, granulated, dried and crushed to finally obtain polyacrylamide products. The core process is the polymerization reaction. During the subsequent treatment, attention should be paid to mechanical cooling, thermal degradation and cross-linking
And ensure the relative molecular mass and water solubility of polyacrylamide.
Acrylamide + water (initiator/polymerization)→ polyacrylamide gel block → Granulation → drying → crushing → polyacrylamide product
So, what are the polyacrylamide polymerization technologies?
The early disc polymerization and kneader polymerization processes of polyacrylamide polymerization technology have been phased out. Currently, the conical reactor polymerization process is mostly adopted.
With the development of technology, polyacrylamide has the common features of controllable molecular weight, easy solubility in water and low residual monomers, which makes the product quality uniform, stable, easy to use and reduces production costs
It has become the pursuit target of market demand and also the direction of development for polyacrylamide production technology.
In industry, aqueous solution polymerization, reversed-phase emulsion polymerization, reversed-phase suspension polymerization and solid-state polymerization are usually adopted according to different characteristics and demands to obtain various types of products.
1. Aqueous solution polymerization method
Homogeneous aqueous solution polymerization is the oldest method for the production of flocculant PAM. It uses water-soluble inorganic peroxides and oxidation-reduction initiation systems or water-soluble azo initiators. There is no need to recover solvents, and the product can be used directly. As water is used as the solvent, the system has few impurities and the chain transfer constant from monomers to water-based solvents is extremely small. Therefore, this method has the characteristics of good product purity and high molecular weight.
2. Dispersed gatherings are legal
The preparation of polyacrylamide by dispersion polymerization can be further classified into four types: reversed-phase emulsion polymerization, reversed-phase microemulsion polymerization, suspension polymerization and precipitation polymerization.
(1) The reversed-phase emulsion polymerization method involves dispersing the aqueous solution of monomers in a continuous oil medium with the aid of water-in-oil (W/O) emulsifiers, initiating polymerization, and the resulting product is water-soluble
The colloidal dispersion of submicroscopic polymer particles (100nm to 1000nm) in oil, that is, W/O type latex.
(2) Reversed-phase microemulsion polymerization method In recent years, on the basis of the theory and technology of reversed-phase emulsion polymerization, the reversed-phase microemulsion polymerization method has emerged. Currently, there are reports on the reversed-phase microemulsion polymerization of AM and the copolymerization of AM with other monomers. Microemulsions generally refer to an isotropic, clear and transparent colloid dispersion system with a particle size ranging from 8nm to 80nm, which is thermodynamically stable. Water-soluble polymer microemulsions produced by various methods have the characteristics of uniform particle size and good stability.
(3) In the presence of a dispersion stabilizer, acrylamide aqueous solution can be dispersed in an inert organic medium for suspension polymerization. The particle size of the product is generally within
1.0um to 500um. When the particle size of the product is between 0.1nm and 1.0nm, it is called columnar polymerization. In suspension polymerization, acrylamide aqueous solution at Span-60, inorganic ammonides, fats
In the presence of dispersion stabilizers such as sodium acetate or cellulose acetate, stable suspensions are formed in gasoline, xylene, and tetrachloroethylene, initiating post-polymerization.
(4) Precipitation polymerization method: This acrylamide polymerization is carried out in an organic solvent or a mixed solution of water and organic substances. These media are solvents for monomers but non-solvents for the polymer polyacrylamide. Therefore, at the beginning of the polymerization, the reaction mixture is homogeneous. However, during the polymerization process, once the flocculant PAM is formed, it precipitates out, resulting in two phases in the reaction system. Therefore
Polymerization occurs in a heterogeneous system and is called precipitation polymerization.
3. Solid-state polymerization method (also known as radiation method
Acrylamide (AM) can undergo solid-state polymerization reactions initiated by radiation. Acrylamide crystals can undergo polymerization at a higher temperature by continuously irradiating them with Y-rays at 0 to 60℃ and then removing the radiation source. It can also polymerize under ultraviolet light. The polymerization reaction occurs on the crystal surface, so its thickness becomes the controlling factor. The polymerization rate is lower than that of Y-ray irradiation, so the polymer is highly branched and has a low molecular weight. In addition, when the temperature rises, the polymer may undergo transformation. Moreover, this method itself is very difficult to dissipate heat, and the molecular weight distribution of the obtained product is very wide. Therefore, it has not yet been carried out on a large scale in industrial production and is only at the laboratory research stage.
