Mixed plastics thermal degradation

Gels Small round surface defects that resembles distorted plastic Poor mixing of plastic, thermal degradation of plastic at the barrel walls, un-melted plastic... 

This comprehensive article supplies details of a new catalytic process for the degradation of municipal waste plastics in a glass reactor. The degradation of plastics was carried out at atmospheric pressure and 410 degrees C in batch and continuous feed operation. The waste plastics and simulated mixed plastics are composed of polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene, and polyethylene terephthalate. In the study, the degradation rate and yield of fuel oil recovery promoted by the use of silica alumina catalysts are compared with the non-catalytic thermal degradation. 9 refs. lAPAN... 

Polymer Degradation and Stability 53,No.2, 1996,p.l89-97 THERMAL DEGRADATION OF MIXED PLASTIC WASTE TO AROMATICS AND GAS... 

W. Kaminsky, B. Schlesselmann and C. M. Simon, Thermal degradation of mixed plastic waste to aromatics and gas. Polymer Degradation and Stability, 53, 189-197 (1996). 

T. Bhaskar, M. A. Uddin, K. Murai, J. Kaneko, K. Hamano, T. Kusaba, A. Muto and Y. Sakata, Comparison of thermal degradation products from real municipal waste plastic and model mixed plastics. J. Analytical and Applied Pyrolysis, 70, 579-587, (2003). 

W. Kaminsky and H. Sinn, Pyrolytic techniques, In Recycling and Recovery of Plastics, J. Brandrup et al. (eds), Hanser Publishers, New York, pp. 435-444, 1996. W. Kaminsky, B. Schiesselmann and C. M. Simon, Thermal degradation of mixed plastic waste to aromatics and gas, Polymer Degradation and Stability, 53, 189-197 (1996). 

The thermal degradation of PE mixed with polyethylene terephthalate (PET) and PE only degradation were compared. The presence of small amounts of PET is quite possible with the mixture of PE, PP, and PS, which is generally considered as municipal waste plastics. The yields of product gases, liquids and residues from the degradation of PET and the mixtures of PET and PE in ratios of 1 9 and 2 8 are shown in Table 18.4. Unlike PE or PVC, no liquid products could be obtained from the degradation of PET. The decomposition of PET proceeds with the production of a large amount of pale yellow... 

Table 18.7 Product yields and properties of liquid product from PVC mixed PP/PE/PS plastic degradation using Ca-C (6 consecutive runs) and thermal degradation. (Reproduced with permission from the American Chemical Society)...

The thermal degradation of mixed plastics (weight ratio PP/PE/PS/PVC/HlPS-Br = 3 3 2 1 1) was carried out under atmospheric pressure in a batch process at 430°C and... 

Figure 18.18 C-NP gram of liquid products obtained during real MWP and model mixed plastics (3P/PVC and 3P/PVC/PET) thermal degradation at 430°C. (Reproduced with permission from Elsevier)...

During the pyrolysis of mixed waste plastic, one of the main problems associated with the feedstock recycling is the presence of plastic containing hetroatoms, e.g. PVC, ABS, PVDC, etc. Efforts are made to remove the heteroatoms before pyrolysis. Chlorine can be removed either by thermal degradation or by using a catalyst. The HCl generated in the process can be used as industrial hydrochloric acid. 

Shiraga and Uddin [6] carried out thermal and catalytic degradation of mixed plastic containing PVC. The solid acid catalyst employed in this study is silica-alumina with a chlorine sorbent such as goethite hydrated Iron Oxide FeO (OH). The dechlorination ability effects of contact mode, liquid phase contact, (LP) or vapor phase contact (VP) were studied. Dechlorination results show that the vapor phase contact was more effective for chlorine removal. 

The pyrolysis process for waste recycling is frequently done at larger scale than analytical pyrolysis. However, analytical pyrolysis studies are performed independently for the understanding and the optimization of such processes [10,16-19]. Also, model mixtures can be used in parallel with real samples. For example, the comparison of thermal degradation products from real municipal waste plastic and model mixed plastics can help understand the compounds generated in waste incinerators. In one such study [20], analytical pyrolysis of real municipal plastic waste obtained from Sapporo, Japan and model mixed plastics was carried out at 430 °C in atmospheric pressure by batch operation. The chlorinated hydrocarbons found in degradation liquid products of poly(ethylene)/poly(propylene)/ poly(styrene)/poly(vinyl chloride) and other polymeric mixtures were monitored. It was determined that the presence of poly(ethylene terephthalate), in addition to chlorinated plastics in the waste, facilitates... 

As a final consideration, it is relevant to discuss the behaviour of mixtures of different plastics. In fact, one possible process for recovering valuable chemical and petrochemical products from plastic waste is the stepwise thermal degradation of polymer mixtures. This potentially allows the step-by-step simultaneous separation of the different fractions generated by the polymers of the blend. The effect of the mixing scale of PE and PS and their interactions in the melt on the basis of several hypotheses was recently investigated (Faravelli et al., 2003). The first and simplest approach was a completely segregated model which... 

Thermal processes are mainly used for the feedstock recycling of addition polymers whereas, as stated in Chapter 2, condensation polymers are preferably depolymerized by reaction with certain chemical agents. The present chapter will deal with the thermal decomposition of polyethylene, polypropylene, polystyrene and polyvinyl chloride, which are the main components of the plastic waste stream (see Chapter 1). Nevertheless, the thermal degradation of some condensation polymers will also be mentioned, because they can appear mixed with polyolefins and other addition polymers in the plastic waste stream. Both the thermal decomposition of individual plastics and of plastic mixtures will be discussed. Likewise, the thermal coprocessing of plastic wastes with other materials (e.g. coal and biomass) will be considered in this chapter. Finally, the thermal degradation of rubber wastes will also be reviewed because in recent years much research effort has been devoted to the recovery of valuable products by the pyrolysis of used tyres. 

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