Microwave pyrolysis plastic wastes

Industrial Engineering Chemistry Research 40, No.22, 31st Oct. 2001, p.4749-56 MICROWAVE-INDUCED PYROLYSIS OF PLASTIC WASTES... 

Microwave pyrolysis of plastic (or plastic-containing) wastes is a relatively new area that has been studied only in the last decade or so. Because of this, there is considerably less information in the scientific literature compared with other approaches to the pyrolysis of plastics. Also, there is a substantial amount of information contained in patents, which suggests that the development of microwave pyrolytic processes has been more intuitive rather than strictly scientific. This chapter will summarize the developments in this area that are described both in scientific and commercial literature. 

As mentioned in Section 2.2.1, the recovery of clean aluminium from real plastic-containing wastes has been one of the main focuses of the research into microwave pyrolysis. With the semi-batch apparatus shown in Figure 21.3, experiments were performed using toothpaste tube laminate and depulped drink carton laminate (a Tetra Pak ... 

Mixing carbon with microwave-transparent materials, particularly plastics, and subjecting the mix to microwave radiation, is a very efficient way to heat up such materials, increasing their bulk temperature to a point where pyrolysis occurs. In this chapter the main characteristics of a number of microwave pyrolysis processes, for plastics and other materials, have been introduced, showing that these processes combine the advantages of microwave heating with the commercial and environmental opportunities intrinsic to the pyrolysis of wastes. 

Scientific studies have found that the differences between microwave and conventional pyrolysis go beyond the obvious difference in the source of heat. Other differences arise from the very high rates of heat transfer from the microwave-absorbent to the waste, the amount heat received by the primary pyrolytic products once they leave the absorbent bed and the highly reducing environment. These three aspects have been shown to have an important effect in the final products since they modify the extent of secondary and tertiary reactions. Moreover, the scientific studies have shown that a nonthermal microwave effect in these processes is unlikely to exist. Tests have showed the potential of the microwave-induced pyrolysis process for the treatment of real plastic-containing wastes and it is believed that a commercial process could be developed, for example, to recover clean aluminium from plastic/aluminium laminates. Other materials, in particular tyres, coal and medical wastes are very good candidates to be treated/recycled using microwave pyrolysis and there have been a considerable number patents filed with this goal in mind. 

C. Ludlow-Palafox and H. A. Chase, Pyrolysis of plastic wastes using a microwave induced pyrolysis process. 6th World Congress of Chemical Engineering, Melboume, Australia 2001. 

C. Ludlow-Palafox, H.A. Chase, Microwave-induced pyrolysis of plastic wastes. Ind. Eng. Chem. Res. 40(22), 4749-4756 (2001)... 

The use of various pretreatments of the plastic wastes such as chemical soaking, heat treatments, microwave, and plasma treatments, etc. in conjunction with the pressurized method might be attractive areas for future research. Co-pyrolysis with other wastes such as food wastes is also plausible. Much work has been carried out on other pressurized carbonization methods such as biomass hydrothermal carbonization [111, 112]. If an industrial process is to emerge from the research, the combined use of various carbon sources would be attractive for economy-of-scale purposes. Producing porous carbons for further applications from plastic wastes would not only yield useful products from cheap precursors, but it would also help reduce the problems associated with the ever-growing plastic waste stream. 

Patent US 6,152,306 describes a whole plant for the reduction of municipal solid waste, including plastics. The plant is said to include a microwave reduction chamber in which pyrolysis presumably occurs. However the document did not contain any detail regarding the chemical reactions or the mechanisms involved [123]. 

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