Published June 1998
Aliphatic polyketones are semicrystalline thermoplastics composed of CO and olefins. The compounds are formed by the copolymerization of CO with an olefinic hydrocarbon, preferably ethylene. Small amounts of propylene, when added to the copolymer, improve the physical properties of the thermoplastic product, which is now produced on an industrial scale.
Several companies, including Shell, BP Chemicals, GE Plastics, and BFGoodrich, have been researching the commercial production of polyketones for a decade. BP Chemicals, GE Plastics, and BFGoodrich are working on pilot plants, whereas Shell Chemicals constructed the world's first commercial polyketones plant in 1996 at Carrington, United Kingdom; the plant has a nameplate capacity of 44 million lb/yr (20,000 t/yr). Shell Chemical Company, the U.S. subsidiary of Royal Dutch Shell, announced plans in 1997 to build the world's second polyketones plant of 55.2 million lb/yr (25,000 t/y) capacity at its site in Geismar, Louisiana. Plant operations are expected to begin in 1999.
Shell uses a proprietary palladium-based catalyst system for the liquid-phase (or gas-phase) terpolymerization reaction of CO, ethylene, and propylene. The catalyst system is prepared in a solvent by reacting a palladium salt with a bidentate phosphorus ligand. A catalyst modifier such as trifluoroacetic acid or p-toluene-sulfonic acid is also added to the palladium complex. Polymerization takes place in a liquid reaction medium, preferably methanol, at 45-50 bar (653-725 psia) and 78-90°C (172-194°F). The reaction products are cooled and depressurized to flash unconverted CO and olefins, which are recycled to the process. The insoluble copolymer is concentrated and separated from the mother liquor by a solid-liquid separation technique. The copolymer product is then dried and bagged. Solvent is recovered through distillation or evaporation and recycled to the process. Reaction by-products and spent catalyst are discharged from the bottom of a distillation column/evaporator. These waste streams are sent for recovery of associated palladium.
PEP's process scheme relies on patents assigned to Shell; however, our design—for a 55.2 million lb/yr (25,000 t/yr) capacity plant for polyketone production, at a 0.9 stream factor, in the U.S. Gulf Coast region—may not exactly reflect Shell's manufacturing practices at its plants. Nevertheless, the Review gives a reliably accurate idea of the process and its economics.