Recycling technologies, classification

From the data presented in this overview, it seems obvious that there exists a clear hierarchy in PET-film recycling technologies. The most important criteria of classification are, first of all, the degree of purity of PET-scrap to be handled, and secondly, the economics of the process. 

The simplest technological systems with recycling flows are shown schematically in Fig. 1. In this, the scheme (a) corresponds to a closed milling circuit, and the scheme (b) to a network of classifiers, in which, the fine product of the first classifier has the repeated classification in the second apparatus. These basic elements can be a part of more complex circuits. First let us examine the closed circuit milling system. 

Finally, it should be noted that this classification is not complete but represents the authors present point of view based on the experience with the RD systems from above. Certainly, new patterns of behavior will be identified, when applying RD technology to more complex reaction systems or within more complex plant configurations involving mass and energy recycles. 

Density-Based Dry Method The most common density-based dry separation methods include air classification discussed above and several technologies drawn from mineral processing and metal recycling industries such as air table classifiers and gravity table separators. Polymer melt density can also be used. Most polymers are incompatible in the soUd or liquid state and liquefy at different temperatures [82]. This has resulted in the exploration of a developmental melt centrifuge technique to separate individual plastics from mixtures of plastics. The technique has been applied to the separation of plastics used in several automotive applications [83]. 

A 2011 study by Lithner et al. (2011) assessed the environmental and health hazards posed by plastics, based on the toxicity of their monomers. The classification is not inherent to the polymer as it is based primarily on residual monomer (with selected additives, plasticizer, and flame retardants). The ranking (see Table 8.8) can have relevance only for occupational exposures and in some food-contact uses of plastics. Also, future advances in residual monomer reduction technology and green substitution of additives can change the status of a polymer in this assessment. Where recyclabihty" is used as a ranking criterion, it generally refers to technical recyclabihty that has little to do with if the resin will in fact be recycled in practice. 

Some technologies produce fly ash, which should be recycled back into the gasifier. If this is not possible, it can be used as additive for concrete. Because fly ash has a very small particle size (<10 pm), a high fraction of cenospheres, and cementing properties, it is referred to as a valuable product for the cement industry. If such use is, however, not possible, it must be disposed with unfevorable classification [32]. 

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