Polyvinylpyrrolidone PVP synthesis technology

The preparation process of PVP includes the synthesis of monomer NVP and polymer PVP. During the synthesis of monomer NVP, the key techniques include the synthesis and purification of monomer. In the synthetic process of polymer PVP, the key technologies mainly involve polymerization technology and drying technology.

Acetylene method and gamma-butyrolactone method
Acetylene process is the mainstream NVP production process at present, with high maturity. The method takes acetylene and formaldehyde as starting materials, and obtains NVP monomer through multi-step reaction.
Firstly, the PVP monomer NVP is produced by the acetylene method through the synthesis of 1, 4-butanediol (BDO), and then through catalytic dehydrogenation to ring, ammonolysis and acetylene addition.
Acetylene process has the advantages of mature technology, cheap and easy to obtain raw materials, and suitable for large-scale industrial production. However, the acetylene process is long, the investment of fixed assets is large, the operating conditions are strict, and the main raw material acetylene has the characteristics of explosion risk.
Therefore, only enterprises with a certain scale, high management level, control technology, research and development strength, perfect sales network and after-sales service can choose this method. At present, only BASF, Ashland and a few large domestic manufacturers use acetylene to produce NVP.
Gamma-butyrolactone method is suitable for small and medium-sized enterprises, but its yield is low. The method involves the reaction of γ-butyrolactone with ethanolamine to produce hydroxyethyl pyrrolidone (NHP), the amylysis product, and then the target monomer NVP is produced directly or indirectly by dehydration in the presence of a dehydration catalyst.
The direct dewatering method of γ-butyrolactone requires high temperature (350-400℃), high energy consumption, and the lack of ideal dewatering catalyst at present limits the development of this process.
γ-butyrolactone indirect dewatering method has toxic and irritating by-products in the production process, the production process involves the absorption of harmful substances, the process becomes complicated and difficult to control, and the general equipment utilization rate is low, and the NVP yield is lower than the acetylene method.
NVP monomer purification technology: NVP reaction liquid in the distillation process will produce by-products, reduce the content of active components in the monomer, affect the yield of NVP. Therefore, the level of monomer purification technology directly affects the purity of NVP, and then affects the quality of polymer.
At present, the purity of NVP monomer can be increased to 99.50% by the commonly used vacuum distillation method, and the purity of monomer can be increased to more than 99.90% by the method of step crystallization. The future development direction is to use lower temperature, low energy monomer separation methods, such as molecular distillation technology, to improve the separation efficiency and reduce the generation of by-product impurities.
The polymerization techniques of PVP include homopolymerization, copolymerization and crosslinking polymerization. The polymerization process conditions (such as initiator, polymerization method, polymerization temperature, polymerization time, etc.) have a decisive effect on the structure and molecular weight of the polymerization products.
1, homopolymerization (PVP-K) : Homopolymerization refers to the polymerization of only NVP a monomer, the product is polyethylene pyrrolidone (PVP). The molecular weight and K value of PVP homopolymer are different, and its properties and applications are also different. A full range of PVP homopolymer products from ultra-low molecular weight K12 to ultra-high molecular weight K120 have been developed.
2, copolymerization (PVP-A) : copolymerization refers to the co-polymerization of NVP monomer with other unsaturated monomers with vinyl structure, and the product is a polymer compound with both NVP structural units and other copolymerizing monomer structural units. At present, PVP/VA (vinyl acetate copolymer) is the only large-scale copolymer variety.
3, cross-linked polymerization (PVP-P) : Cross-linked polymerization refers to the self-crosslinking reaction of NVP monomer or the cross-linked copolymerization reaction of NVP monomer and crosslinking agent (containing multiple unsaturated base compounds), the product is polyvinylpyrrolidone cross-linked polymer (PVPP).
Depending on the degree of crosslinking, PVPP can appear as super absorbent resins (low crosslinking), water absorbent gels (medium crosslinking), and insoluble substances (high crosslinking). PVPP has been used in food and medicine.
PVP complex technology: PVP complex refers to the complex compound formed by the combination of PVP and other chemical substances with a certain bond type. Among them, the production of PVP-I (PVP and iodine complex) has been very mature. A few companies also produce PVP-H2O2 complexes.
Drying technology of PVP polymer: Ordinary molecular weight PVP polymer is usually spray drying. For high molecular weight PVP products that cannot be dehydrated by spray drying (such as K60, K90, K120, etc.), the main manufacturers generally use open scraper drying.
However, this method consumes high energy, easily reduces the degree of polymerization of the product, and can lead to cross-contamination between the material, the operator and the operating environment. The future development direction is to gradually adopt low polymerization degradation, no cross contamination, low energy consumption of low temperature vacuum continuous drying method.