The production steps of polyacrylamide are two steps:
Monomer production technology: When producing acrylamide monomer, acrylonitrile is used as the raw material, and hydrated under the action of a catalyst to generate a crude product of acrylamide monomer. After flash evaporation and refining, refined acrylamide monomer is obtained. This monomer is the raw material for the production of polyacrylamide.
Acrylonitrile + (water catalyst/water) → synthesis → crude acrylamide → flash evaporation → refining → refined acrylamide.
According to the development history of catalysts, monomer technology has gone through three generations:
The first generation is sulfuric acid catalytic hydration technology. The disadvantages of this technology are low acrylonitrile conversion rate, low acrylamide product yield and low by-products, which brings a great burden to refining. In addition, due to the strong corrosiveness of the catalyst sulfuric acid, the equipment cost is high, which increases the production cost; the second generation is binary or ternary skeleton copper catalytic production technology. The disadvantage of this technology is that metal copper ions that affect polymerization are introduced into the final product, thereby increasing the cost of post-processing refining; the third generation is microbial nitrile hydratase catalytic production technology. This technology has mild reaction conditions and is carried out at room temperature and pressure. It has the characteristics of high selectivity, high yield and high activity. The conversion rate of acrylonitrile can reach 100%, the reaction is complete, and there are no by-products and impurities. The product acrylamide does not contain metal copper ions, and no ion exchange is required to remove the copper ions generated during the production process, which simplifies the process flow. In addition, gas chromatography analysis shows that the acrylamide product contains almost no free acrylonitrile and has high purity, which is particularly suitable for the preparation of ultra-high relative molecular mass polyacrylamide and non-toxic polyacrylamide required by the food industry.
The microbial catalytic acrylamide monomer production technology was first developed by Japan in 1985, where a 6,000 t/a acrylamide plant was built. Russia also mastered this technology later. In the 1990s, Japan and Russia successively built 10,000-ton microbial catalytic acrylamide plants. my country is the third country in the world to have this technology after Japan and Russia. The activity of the microbial catalyst is 2857 international biochemical units, which has reached the international level. my country's microbial catalytic acrylamide monomer production technology was developed by the Shanghai Pesticide Research Institute through three five-year plans, namely the "Seventh Five-Year Plan", "Eighth Five-Year Plan" and "Ninth Five-Year Plan". The microbial catalyst nitrile hydratase was screened in 1990. It was obtained by seed culture of 163 strains isolated from the soil at the foot of Mount Tai and 145 strains isolated from the soil in Wuxi. The nitrile hydratase was code-named Norcardia-163. This technology has been put into production in Rugao, Jiangsu, Nanchang, Jiangxi, Shengli Oilfield and Wanquan, Hebei, with excellent quality, reaching the quality indicators for producing ultra-high relative molecular mass polyacrylamide. It indicates that my country's microbial catalytic acrylamide technology has reached the international advanced level.
Polymerization technology: Polyacrylamide production uses acrylamide aqueous solution as raw material, and carries out polymerization reaction under the action of initiator. After the reaction is completed, the polyacrylamide block generated is cut, granulated, dried, and crushed to finally obtain the polyacrylamide product. The key process is the polymerization reaction. In the subsequent processing process, attention should be paid to mechanical cooling, thermal degradation and cross-linking to ensure the relative molecular mass and water solubility of polyacrylamide.
