Hydrocarbon processing monomer recovery

R.W. Baker and M.L. Jacobs, Improve Monomer Recovery from Polyolefin Resin Degassing, Hydrocarbon Process. 75, 49 (1996). 

Baker, R.W. and Jacobs, M. (1996) Improved monomer recovery from polyolefin resin degassing. Hydrocarbon Processing, 75(3), 49. 

The slurry process is the oldest and still widely used method for manufacturing polymers of ethylene, propylene and higher a-olefins. In this process, the monomer dissolves in the polymerisation medium (hydrocarbon diluent) and forms a solid polymer as a suspension containing ca 40 wt-% of the polymer the polymerisation occurs below the melting point of the polymer. In slurry polymerisation, the temperature ranges from 70 to 90 °C, with the ethylene pressure varying between 7 and 30 atm. The polymerisation time is 1-4 h and the polymer yield is 95-98 %. The polymer is obtained in the form of fine particles in the diluent and can be separated by filtration. Removal of the catalyst residues from the polymer can be achieved by the addition of alcohol (isopropanol, methanol), followed by recovery and extraction of the catalyst residues. The polymer is freed from diluent by centrifuging and then dried. In the case of polypropylene manufacture, the atactic fraction remains in the diluent [28,37]. 

One approach we tried was a suspension process. The lactone monomer containing an initiator such as a phosphine was stirred at 60°-100°C in a long-chain hydrocarbon oil ( Shell Ondina oil 33) in which it was essentially insoluble. Although polymer with a high bulk density was obtained in quantitative yields, the particles contained hydrocarbon oil that had to be removed by a hot organic wash (heptane) after recovery by filtration. 

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