Le traitement des déchets polymères : la valorisation énergétique ou chimique
Treatment of Polymer Wastes: Chemical Or Energy Upgrading
Institut Français du Pétrole
Une protection accrue de l'environnement requiert la mise en place de nouvelles techniques fiables et économiques de traitement des déchets polymères. Parmi les diverses méthodes envisagées pour la réutilisation ou l'élimination des polymères usagés, les recyclages énergétiques et chimiques peuvent apporter des solutions satisfaisantes et complémentaires au recyclage de la matière. Cet article fait le point sur l'état d'avancement des techniques de valorisation énergétique et chimique des rejets de polymères et il propose une analyse critique des traitements actuels.
Increased environmental protection requires the installation of new treatment techniques for polymer wastes. Competitive industrial facilities are not available from the economic standpoint for recycling spent plastic and rubber wastes in the form of materials, especially when mixtures are involved. It is only by using other treatment method for the chemical or energy upgrading of polymers, as a supplement to the recycling of materials, that it should be possible to make a significant reduction in the amount of spent polymers currently being scrapped. The energy upgrading of wastes by incineration with energy recovery or by pyrolysis with the formation of fuels in an interesting approach for a great many countries. When no reuse is possible, the energy content of the material is upgraded before the subsequent scrapping of an ultimate residue that is reduced to its incompressible minimum after having been inerted. There are currently several technical solutions for incineration furnaces and the treatment of the fumes produced, which meet the more and more severe requirements concerning environmental protection. Incineration systems with energy recovery can recover about 8000 thermies per ton of unsorted plastics. They already have an important position, albeit a varying one, from one European country to another (Table 6). They should develop considerably further in the years to come. The pyrolysis or controled thermolysis of polymer wastes is a future route for the recovery of upgradable products in the form of gaseous, liquid or solid fuels, and sometimes in the form of oligomers or monomers. Pyrolysis systems preferably use rotary reactors or a fluidised bed with a view to obtaining a more uniform composition of the products. Chemical upgrading holds an intermediate position between the recycling of materials and energy recycling. It consists in chemically decomposing macromolecules, e. g. by cracking or hydrocracking, hydrolysis, alcoholysis, saponification, etc., with a view to obtaining products or monomers that can be reused for manufacturing new polymers. Chemical recycling is eminently suitable, in particular, for polyolefins, polyesters, polyurethanes and polyamides. To conclude, as our understanding of the effects of incineration improves and as further progress is made in the technological field, incineration with energy recovery should make up a more widely accepted alternative solution for increasing the recycling of polymers. In the medium term, it is thought that pyrolysis, and, more probably, low-temperature thermolysis will be the main routes for the recycling of spent polymers with a view to recovering upgradable raw materials with sufficient degrees of purity. However, the economic cost effectiveness of such processes remains to be proved on the industrial scale. Most experts think that the technology of cracking is potentially the most advantageous among all chemical recycling techniques, but that another 5 to 10 years will be needed for the transformation of polyolefin wastes into refinery feedstocks, to be marketed and industrially applied.
© IFP, 1992