Polyethylene terephthalate pyrolysis

The following section reviews the literature data summarizing the behaviour during carbonization of five individual polymers, i.e. polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). Eor each polymer, results will first be presented for flash pyrolysis then for slow pyrolysis by the isothermal and dynamic methods. 

The pyrolysis of polyethylene terephthalate produces a gas consisting mainly of carbon dioxide and carbon monoxide, due to the high oxygen content of the original plastic... 

Figure 11.5 Fourier transform infrared spectra of the oils/waxes derived from the pyrolysis of polyvinyl chloride, polystyrene and polyethylene terephthalate...

Figure 11.8 Molecular weight distribution of the oils derived from the fluidized-bed pyrolysis of polystyrene, polyvinyl chloride and polyethylene terephthalate...

The price of baled HDPE with up to 2% impurities has fluctuated from 7-10 cents/lb two years ago to about 30 cents/lb recently. If the plastic used in the pyrolysis process did not require this limit, the cost could be considerably lower. (Unseparated waste plastic can be valued as low as negative 2 cents/lb, which accounts for landfilling cost or tipping fee.) Consequently, the run with HDPE was repeated, except the plastic was 96 wt% HDPE and 4 wt% waste polyethylene terephthalate from soft-drink bottles. Pyrolysis yields are given in Table 13.1, showing a 385°C- - yield, based on plastic, of 42.4 wt%. 

Figure 15.3 Thermal cracking mechanism for polyethylene terephthalate. Note under mild conditions terephthalic acid predominates, but under more severe pyrolysis conditions the terephthalic acid decomposes to benzoic acid and benzene...

Polyethylene terephthalate (PET). At temperatnres above 300°C PET pyrolysis proceeds via a random-chain scission of the ester links to yield a mixture of terephthalic acid monomer and vinyl ester oligomers [47], The presence in the monomer of oxygen and a benzene ring imphes that the decomposition prodncts contain aromatic and oxygenated carbon componnds, like CO2, ketones and aldehydes [27],... 

A special case in terms of application of rotary kiln technology is the pyrolysis of mono fractions such as styrene, PMMA, polycarbonate, or polyethylene terephthalate. Polymethylmethacrylate is an example illustrate the advantages in using fluidized beds or rotary kilns. The feed material does not have a heteroatom problem and the pyrolysis product can easily be handled as a monomer source instead of feedstock. Therefore the... 

Pyrolysis and reforming of several types of common plastics (polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polyurethane, and polycarbonate) were studied qualitatively, using a micro-reactor interfaced with a MBMS. Each type of plastic pyrolyzed at 550-750°C. This was followed by steam reforming of vapors in a fixed bed of C-11 NK catalyst at 750-800°C. The composition of the product gas (mass spectrum) was observed for different values of the steam-to-carbon mtio and space velocity that changed depending on the size of plastic samples. Preliminary tests showed that at process conditions similar to those used for reforming natural gas, polymers were almost completely converted to hydrogen and carbon oxides. 

Polyester fibers are composed of linear chains of polyethylene terephthalate (PET), which produces benzene, benzoic acid, biphenyl, and vinyl terephthalate on pyrolysis. Acrylic fibers comprise chains made up of acrylonitrile units, usually copolymerized with less than 15% by weight of other monomers, e.g., methyl acrylate, methyl methacrylate, or vinylpyrrolidone. Thermolysis results in the formation of acrylonitrile monomer, dimers, and trimers with a small amount of the copolymer or its pyrolysis product. In this case, the acrylic is Orion 28, which contains methyl vinyl pyridine as comonomer. Residual dimethyl formamide solvent from the manufacturing process is also found in the pyrolysis products. Cotton, which is almost pure cellulose, comprises chains of glucose units. The pyrolysis products of cellulose, identified by GC/MS, include carbonyl compounds, acids, methyl esters, furans, pyrans, anhydrosugars, and hydrocarbons. The major pyrolysis products are levoglucosan (1,6-anhydro-B-D-glucopyranose) and substituted furans. 

Polymers like polyoxymethylene (POM) and polyethylene terephthalate (PTFE, Teflon), do not form hydrocarbon compounds during combustion and do not exhibit an inclination towards formation of soot. Polyolefins, which form predominantly aliphatic hydrocarbons during pyrolysis, are less inclined to form soot than others like PS, styrene copolymers or ABS, which produce aromatic hydrocarbon [131]. 

Bhaskar T, Mitan NM, Onwudili J, Muto A, Williams P, Sakata Y (2010) Effect of polyethylene terephthalate (PET) on the pyrolysis of brominated flame retardant-containing high-impact polystyrene (HIPS-Br). J Mater Cycles Waste Manage 10(4) 332-340... 

Parra JB, Ania CO, Arenillas A, Rubiera F, Pis JJ, Palacios JM (2006) Stractural changes in polyethylene terephthalate (PET) waste materials caused by pyrolysis and CO2 activation. Adsorpt Sci Technol 24(5) 439 149... 

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