Polypropylene Carbonate Production

The process under analysis comprises four major sections: (1) Polymerization; (2) Phase Separation; (3) Monomers Separation; and (4) Pelletizing & Finishing.

Polymerization. Fresh carbon dioxide (CO2) feed is mixed with recycled CO2 from Monomers Separation. Propylene oxide feed is also mixed with a recovered stream. Both reactants are treated for moisture removal. Part of the propylene oxide treated feed is fed to the polymerization reactor outlet to dissolve the polymer solution obtained. The remainder is mixed with catalyst and CO2 feed, forming a liquid solution that is transferred to the prepolymerization reactor. The prepolymerization reaction effluent is fed to the polymerization reactor, where the polymer solution is obtained.

Phase Separation. The polymer solution is contacted with a material that binds to the catalyst and allows its removal via filtration. The catalyst-free solution is subjected to gradual pressure decrease, so that unreacted monomers can be released. Once the monomers are removed, the polymer melt is transferred to the Pelletizing & Finishing. Released monomers are routed to the Monomers Separation.

Monomers Separation. Unreacted monomers are fed to two consecutive distillation columns, from which three streams are obtained. A high-purity propylene oxide stream is recycled to the Feed Preparation and mixed with fresh feed. A carbon dioxide-rich stream (also containing propylene oxide) is also recycled to the feed preparation. Another stream, comprising heavy ends generated as side-products, is discharged from the process.

Pelletizing & Finishing. The polymer melt is fed to a pelletizing system, where it is homogenized and pelletized. Subsequently, the pellets are packed in bags before being stored in warehouses.