Polymeric Cracking of Waste Polyethylene Terephthalate to Chemicals and Energy

Polyethylene terephthalate (PET) is a widely used thermo-plastic. 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 iso-thermal 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. IMPLICATIONS Plastic solid waste (PSW) represents up to 8% by wt and 20% by volume of household waste. Landfill disposal wastes valuable energy and chemical feedstock. Incineration for energetic valorization (waste-to-energy) is applied for ∼50% of PSW. To date, research focuses increasingly on pyrolysis, which has the advantage over incineration of producing value-added chemicals, even from commingled or mixed feedstock. The process gains in efficiency and yield if PSW fractions are collected separately or presegregated. The cost of separate collection is easily overcome by the value of the pyrolysis products. The pyrolysis of polyethylene terephthalate is developed as an example of the above.