Polypropylene production process
Polypropylene resin is one of the four general-purpose thermoplastic resins (polyethylene, polyvinyl chloride, polypropylene, polystyrene). It is produced by polymerization with propylene as raw material and ethylene as comonomer.
The process methods used in the production of polypropylene in the world are mainly divided into the following categories according to categories: solvent method, solution method, liquid phase bulk method (including liquid phase and gas phase combination) and gas phase bulk method. The characteristics of each process are introduced as follows:
Solvent polymerization
Solvent method (also known as slurry method or slurry method, slurry method) is the earliest polypropylene production process. However, due to the deashing and solvent recovery processes, the process is long and complicated. Since the 1980s, the solvent method has become stagnant and gradually replaced by the liquid bulk method.
Process characteristics: (1) Propylene monomer is dissolved in an inert liquid-phase solvent (such as hexane), and the solvent is polymerized under the action of a catalyst, and the polymer is suspended in the solvent in the state of solid pellets, and a tank-type stirring reactor is used; (2) There are deashing and solvent recovery processes, the process is long and complicated, the equipment investment is large, and the energy consumption is high. However, the production is easy to control and the product quality is good; (3) The polypropylene particles are separated by centrifugal filtration and then boiled, dried and extruded to granulate.
solution polymerization
Process features: (1) Using high-boiling straight-chain hydrocarbons as solvent and operating at a temperature higher than the melting point of polypropylene, all the obtained polymers are dissolved in the solvent and are homogeneously distributed; (2) The solvent is evaporated by high temperature stripping method Obtain molten polypropylene, and then extrude and granulate to obtain pellet products; (3) There is only one American Kodak company as the manufacturer.
liquid bulk method
The liquid-phase gas-phase combined type, liquid-phase bulk polypropylene production process is a new process developed in the middle and late stages of polypropylene production. The production process comes seven years after polypropylene industrial production began in 1957.