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Polyethylene terephthalate (PET) is a widely used thermoplastic. PET residues represent on average 7.6 wt% of the different polymer wastes in Europe. Pyrolysis of these wastes is attracting increasing interest, and PET is a potential candidate for this thermal process. The paper measures and discusses the kinetics of the pyrolysis reaction in terms of the reaction rate constants as determined by dynamic thermogravimetric analysis, with special emphasis on the required heating rate to obtain relevant results. The product yields and compositions are also determined. Gaseous products represent 16 -18 wt%. The amounts of condensables and carbonaceous residue are a function of the operating mode, with slow pyrolysis producing up to 24 wt% of carbonaceous residue. Major condensable components are benzoic acid, monovinyl terephthalate, divinyl terephthalate, vinyl benzoate, and benzene. The present paper complements previous literature findings by (1) the study of the influence of the heating rate on the reaction kinetics in dynamic pyrolysis tests, (2) the isothermal investigation in a fluidized bed reactor to pyrolyze PET, and (3) the assessment of upgrading and recovery of the products. The paper concludes with a proposed reactor recommendation for PET pyrolysis, in either the bubbling or circulating fluidized bed operating mode.

The disposal of waste plastics has become a major worldwide environmental problem. The USA, Europe and Japan generate annually about 50 million tons of post-consumer plastic waste, previously landfilled, generally considered as a non-sustainable and environmentally questionable option. Landfill sites and their capacity are, moreover, decreasing rapidly, and legislation is stringent. Several European Directives and US legislation concern plastic wastes and the required management. They are briefly discussed in this paper. New processes have emerged, i.e., advanced mechanical recycling of plastic waste as virgin or second grade plastic feedstock, and thermal treatments to recycle the waste as virgin monomer, as synthetic fuel gas, or as heat source (incineration with energy recovery). These processes avoid land filling, where the non-biodegradable plastics remain a lasting environmental burden. The paper reviews these alternative options through mostly thermal processing (pyrolysis, gasification and waste-to-energy). Additional research is, however, still needed to confirm the potential on pilot and commercial scale. [Acknowledgments. The research was partly funded by the Fundamental Research Funds for the Central Universities RC1101 (PR China) and partly funded by Project KP/09/005 (SCORES4CHEM Knowledge Platform) of the Industrial Research Council of the KU Leuven (Belgium).

The paper starts by reviewing the increasing production of waste and the growing importance of its thermal treatment, which aims at volume reduction of the waste, at the destruction, capture, and concentration of hazardous substances, and at the recovery of energy (WtE).

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The disposal of plastic solid waste (PSW) has become a major worldwide environmental problem. New sustainable processes have emerged, i.e. either advanced mechanical recycling of PSW as virgin or second grade plastic feedstock, or thermal treatments to recycle the waste as virgin monomer, as synthetic fuel gas, or as heat source (incineration with energy recovery). These processes avoid land filling, where the non-biodegradable plastics remain a lasting environmental burden. Within the thermal treatments, gasification and pyrolysis gain increased interest. Gasification has been widely studied and applied for biomass and coal, with results reported and published in literature. The application to the treatment of PSW is less documented. Gasification is commonly operated at high temperatures (> 600℃ to 800℃) in an air-lean environment (or oxygen-deficient in some applications): the air factor is generally between 20% and 40% of the amount of air needed for the combustion of the PSW. Gasification produces mostly a gas phase and a solid residue (char and ashes). The use of air introduces N2 in the product gases, thus considerably reducing the calorific value of the syngas, because of the dilution. The paper will review the existing literature data on PSW gasification, both as the result of laboratory and pilot-scale research. Processes developed in the past will be illustrated. Recently, the use of a sequential gasification and combustion system (at very high temperatures) has been applied to various plastic-containing wastes, with atmospheric emissions shown to be invariably below the legal limits. Operating results and conditions will be reviewed in the paper, and completed with recent own lab-scale experimental results. These results demonstrate that gasification of PSW can be considered as a first order reaction, with values of the activation energy in the order of 187 to 289 kJ/mol as a function of the PSW nature.

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