To produce polypropylene-based polymers, including homopolymer polypropylene (PP), random, heterophasic impact and specialty dual composition copolymers, using Spherizone process technology.
The Spherizone process is LyondellBasell’s new proprietary gas-loop reactor technology based on a Multi-Zone Circulating Reactor (MZCR) concept. Inside the reactor (1) the growing polymeric granule is continuously recirculating between two interrelated zones, where two distinct and different fluodynamic regimes are realized. In the first zone (1a), the polymer is kept in a fast fluidization regime; when leaving this zone, the gas is separated and the polymer crosses the second zone (1b) in a packed-bed mode and is then reintroduced in the first zone. A complete and massive solid re-circulation is obtained between the two zones.
The gas composition with respect to the chain terminator (hydrogen) and to the comonomer can be altered between the two zones of the MZCR. This is accomplished by injecting monomers from the external system (2) in one or more points of the second zone (1b) and so two or more different polymers (MFR and/or comonomer type and content) can grow on the same granule.
While the granules recycle through the multiple zones, different polymers are generated in an alternate and cyclic way via continuous polymerization. This allows the most intimate mixing of different polymers, giving a superior homogeneity of the final product. Unreacted monomer is mostly recovered at intermediate pressure (3) and recycled back to the MZC reactor through a compressor, while polymer can be fed to a fluidized gas- phase reactor (4) operated in series (optional) where additional copolymer can be added to the product from the gas loop.
From the intermediate separator/second reactor, the polymer is discharged to a receiver (5), the unreacted gas is recovered, while the polymer is sent to a proprietary unit for monomer steam stripping and catalyst deactivation (6). The removed residual hydrocarbons are recycled to the reaction. While the polymer is dried by a closed-loop nitrogen system (7) and, now free from volatile substances, the polymer is sent to additives incorporation step (8).
Products: The process can produce a broad range of propylene-based polymers, including mono- and bimodal (medium/wide/very wide molecular weight distribution) homopolymer PP, high stiffness homopolymers, random copolymers and terpolymers, high-clarity random copolymers as well as two compositions copolymer/random copolymer, twin-random
or random/heterophasic copolymer). Conventional heterophasic impact copolymers (with improved stiffness/impact balance) can be produced with the second additional gas phase reactor, with ethylene/ propylene rubber content up to 40%.