Production process of polyacrylamide
In 1893, Moureu et al. made PAM,1954 at low temperature for the first time.China started the industrial production of PAM in the early 1960s. In 1962, Shanghai Tianyuan Chemical Factory built the first polyacrylamide production device in China to produce water-solvent products.Both PAM and its derivatives are homopolymers or copolymers made from the free radical polymerization of acrylamide (AM).The specific methods mainly include: aqueous solution polymerization, reverse phase emulsion polymerization, reverse phase microemulsion polymerization, suspension polymerization, precipitation polymerization, radiation polymerization, etc.The common requirement for the product is controllable relative molecular quality, less soluble in water and residual monomer, and less stable product quality.Easy to use and reduce cost, is the direction of the development of polyacrylamide production technology today.
Aqueous solution polymerization method
Aqueous solution polymerization is the longest production history method of PAM, which is safe and economical, and is still the main production technology of PAM.The AM aqueous solution can be polymerized using almost all radical initiation methods at appropriate temperatures, and the polymerization process follows the law of the general radical polymerization reaction.The most commonly used ones in industry are the thermal decomposition and redox causes of initiators, including the structure and molecular weight of polymerization products.
Aqueous solution polymerization is simple, less environmental pollution, high polymer yield and high relatively molecular quality.At present, the research of aqueous solution polymerization has been deep, but there are some disadvantages, the quality score of the polymerization solution is low (about 10%, based on the total quality); in the process of making dry powder, high temperature drying and shear can easily degrade the polymer chain, reducing the solubility and flocculation of the powder products.
Antiphase emulsion polymerization
Antiphase emulsion polymerization adds the monomer aqueous solution to the oil phase in a certain proportion, dispersed in the oil medium with the emulsion polymerization under the action of the initiator. The resulting product is the colloidal dispersion of stable water-soluble polymer particles in the oil, namely type W/O emulsion, and obtains powder PAM. after dehydration through cozeolite distillationThe reverse phase emulsion polymerization system includes: water soluble AM monomers, water soluble cation or anionic functional monomers, initiator, W/O emulsifier, water phase, continuous phase and additives, etc.
The dynamics of the AM reverse phase emulsion polymerization and the properties of the resulting polymer depend on the type and concentration of the emulsifier and the initiator, the nature of the solvent used as a dispersant, the temperature, and the mixing speed.Compared with PAM emulsion produced by water and dry powder products, the emulsion is dissolved fast, high and narrow relative molecular mass, less residual monomer, small viscosity, large polymerization rate, easy heat control and large-scale production. However, this method requires a large number of organic solvents, slightly higher production cost and complex technology.
Antiphase microemulsion polymerization
Although antiphase emulsion polymerization has its advantages, there is still a low average relatively molecular mass of the product, wide particle size distribution and easy condensation, so people change from conventional reverse phase emulsion polymerization to reverse phase microemulsion polymerization.Microemulsion is an identical, thermodynamically stable, transparent, or translucent colloidal dispersion system consisting of oil, water, emulsifiers, and auxiliary emulsifiers, with a dispersion phase size of a nanoscale.Compared with antiphase emulsion polymerization, the emulsion prepared by reverse phase microemulsion polymerization is more stable, more uniform latex particle size distribution, high relative molecular quality, good transparency, small latex beam particle size, narrow diameter distribution and fast reaction rate.The reverse phase microemulsion polymerization system is mainly composed of four basic components: monomer aqueous solution, oil phase, emulsifier and initiator, and the polymer particles containing oil and water are obtained through polymerization.
Antiphase emulsion polymerization is particularly valued by offshore oil production, which is a direction of AM copolymer synthesis.But its industrial production is limited because the ratio of surfactants required for polymerization to monomers is too high.
Suspended polymerization is usually used by strong mixing to disperse the monomer or monomer mixture in the medium, and become small particles for repolymerization.The key of the process is the control of the dispersion phase particle size, and the main factors that determine the particle size are the mixing and dispersion stabilizer.If the surface tension of inorganic salts (e. g., NaCl, Na2CO3) is added to the polymerization process, increasing suspension stability and has little impact on the polymerization process, but adding a small amount of single, binary or multiple carboxylates, the molecular weight of the product usually increases, polymerization rate decreases, and suspension polymerization method can be used to produce powdery products.In suspended polymerization, the polymerization reaction is performed in a monomer droplet suspended in water, so essentially each droplet can be considered a small bulk polymerization reactor, the difference is that the monomer droplets are small, well dispersed in water, easy to exclude polymerization heat than bulk polymerization.The suspension polymerization process is simple, the polymerization heat is easy to eliminate, the operation and control are convenient, the polymer is easy to separate, wash and dry, the products are also pure, uniform and stable, and can be directly used directly for processing and forming.However, because a large amount of organic solvents are used in suspension polymerization, the production operation is not very safe. The recovery of organic solvents is a difficult problem in suspension polymerization, and the suspension polymerization cost is high, so suspension polymerization is not widely used in China.
Precipitation polymerization method
AM allows precipitate polymerization when organic solvents, or even entirely organic, are added to an aqueous solution.During this polymerization reaction, once PAM is generated, the reaction system appears in two phases, so it is called precipitation polymerization.The polymer obtained by precipitation polymerization has relatively low relative molecular weight, because the organic solvent used in polymerization is a lively AM. Moreover, when the polymer chain grows to a certain length, thus restricts the further growth of the molecular chain, but the PAM molecular weight distribution is narrow, few residual monomer, small viscosity, easy polymer heat distribution, and easy polymer separation and drying.
Spread polymerization is a particular type of precipitation aggregation that was first proposed by researchers at British ICI in the early 1970s.Its monomers, stabilizer and initiator are dissolved in the medium, and the reaction is homogeneous system before the reaction begins, but the generated polymer is insoluble in the medium. After the polymer chain reaches the critical chain long, it precipitate from the medium.Unlike precipitation polymerization, the precipitated polymer chains do not form powder or bulk polymers, but gather into small particles that are stably suspended in the medium with the aid of dispersants to form a stable dispersion system similar to the polymer emulsion.
Radiation polymerization method
Radiation polymerization belongs to a kind of bulk polymerization, or a polymerization system with only monomers and an initiator, without other solvents or diluents.AM aqueous solution is polymerized under radiation. In 30% aqueous solution of acrylamide, additives such as ethyldiamine tetraacetate are added. removal of oxygen is polymerization by γ -ray radiation from Co60 source, and then PAM. after granulation, drying and crushingThe advantages of radiation polymerization are low energy consumption, easy reaction control, simple production process, high product purity; the disadvantage is difficult to obtain high linear molecules and high polymerization products, large equipment investment and wide molecular weight distribution of products.Radiation polymerization of AM aqueous solution caused by Co60γ- -ray has been industrialized but of very small scale. The product obtained from this method is suitable for desert transformation.
Other aggregation methods
In addition to the above methods, high-quality and multifunctional PAM products can also be prepared by grafting copolymerization, composite action, and plasma polymerization.AM, sodium acrylate is often copolymerized with starch medium to prepare high absorbent resin, or co-copolymer with other macromolecular monomers, thereby branching AM/AA on some class of films, such as nylon film, polyurethane film, etc., for special occasions.Shang Zhenping synthesized the terminal acrylamide (β-aminoacrylic acid) macromolecule monomer, and used the oxidation-reduction reaction system of iron sulfate and isopropylene hydrogen peroxide to trigger the co-polymerization reaction of AM, sodium acrylic acid and polymer (β-aminoacrylic acid) macromolecule monomer, and synthesized the grafting co polymer of poly (sodium acrylamide co acrylate) -g-polymer (β-aminoacrylic acid), obtaining the anionic PAM copolymer drive with good salt resistance.