Polyolefins pyrolysis

A considerable number of reports regarding the formation of compounds that may represent a health hazard are related to the formation of polycyclic aromatic hydrocarbons (PAHs) during industrial pyrolysis processes (recycling of waste, incineration, etc.). This interest is particularly geared toward the study of polyolefins pyrolysis and synthetic and natural rubber pyrolysis. The formation of PAHs during polyethylene pyrolysis has been reported frequently in literature [6, 12] and is further discussed in Section 6.1. The formation of PAHs during tire pyrolysis is also of considerable concern. The concentrations of some components in the oils generated from the pyrolysis of used tires as a function of temperature are indicated in Table 5.3 1 [13]. 

In particular, PB and PMP are inert materials and usually present no health hazard. PMP is employed extensively for a number of medical and food packaging appHcations. Several grades conform to FDA regulations and to the health standards of other countries. Flammability of polyolefin resins is equal to that of PP, around 2.5 cm /min (ASTM D635). However, during combustion or pyrolysis, smoke, fumes, and toxic decomposition products are formed and can pose a health hazard. 

Macromolecular Symposia Vol.135, Dec. 1998, p. 175-82 NEW CHEMICAL RECYCLING METHODOLOGIES HYDROUS PYROLYSIS TO RECOVER MONOMERS FROM POLYOLEFINS Audisio G Bertini F Beltrame P L Bergamasco L Castelli A... 

The use of pyrolysis for the recycling of mixed plastics is discussed and it is shown that fluidised bed pyrolysis is particularly advantageous. It is demonstrated that 25 to 45% of product gas with a high heating value and 30 to 50% of an oil rich in aromatics can be recovered. The oil is found to be comparable with that of a mixture of light benzene and bituminous coal tar. Up to 60% of ethylene and propylene can be produced by using mixed polyolefins as feedstock. It is suggested that, under appropriate conditions, the pyrolysis process could be successful commercially. 23 refs. 

This paper diseusses in detail the option of fluidised-bed reaetors to eraek mixed plastics waste into valuable raw materials, under the headings thermal cracking for feedstocks, pyrolysis of polyolefins, and other options. 7 refs. 

Recycling plastics back to hydrocarbons (tertiary recycling) may offer significant promise. Three different options currently being evaluated for the tertiary recycling of polyolefins - refinery recycling, pyrolysis and depolymerisation - are discussed. 

Pyrolysis GC/MS is limited in application to those studies in which the compounds formed are capable of being analysed by GC, that is it is only reasonably suitable for low molecular weight products. Many synthetic polymers degrade (pyrolyse) by processes that may simply be described as either random scission (e.g., polyolefins), unzipping to produce mostly monomers (e.g., PMMA)... 

The difference of the polyolefins and the PVC in the catalytic degradation can be seen in Fig. 3 the decomposition of PVC takes place at least in two steps, the first is due to the release of HC1 with 300 °C characteristic temperature, the second peak corresponds to the pyrolysis of the residual hydrocarbon framework (440 - 470 °C temperature range). 

W.J. Hall, N.M.M. Mitan, T. Bhaskar, A. Muto, Y. Sakata, and P.T. Williams, The co-pyrolysis of flame retarded high impact polystyrene and polyolefins, /. Anal. Appl. Pyrolysis, 80(2) 406-415, October 2007. 

FIGURE 26.4 Probability for flame spread versus heat release capacity of compounds. (Cogen, J.M. et al., Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen free flame retardant polyolefin compounds, Fire Mater., 2009, 33, 33-50.)... 

The results of an interesting study on copyrolysis of naphtha and added polyolefins or their kinetics and degradation products were presented at the Analytical and Applied Pyrolysis meeting at Alicante [12] (Table 1.3). The product yields from cracking (450°C) of LDPE and PP are quite different, with more liquid fraction from PP ... 

Distinction should be made between monomers, specific petrochemicals, and more or less typical oil fractions, produced by mixed plastics pyrolysis. Potential pyrolysis products from polyolefins are naphtha, kerosene, or gas-oil. These are blends of numerous different... 

Pyrolysis treatments are interesting regarding the aforementioned plastic refuse makeup. Other successful treatments for feedstock recycling of condensation polymers (PET, ABS, etc.), that allows for the depolymerization and recovery of their constituent monomers (e.g. hydrolysis, alcoholysis, methanolysis, etc.), cannot be applied for polyolefin plastics recycling. In contrast, pyrolysis of polyolefins yields valuable hydrocarbon mixtures of... 

T. P. Wampler, Thermometric behavior of polyolefins, J. Anal. Appl. Pyrolysis 15, 187, 1989. 

Figure 4.1 Cracking and pyrolysis of waste polyolefin processing, main products and their application [1]. (Reproduced by permission of Hydrocarbon Processing)...

M. Predel and W. Kaminsky, Pyrolysis of mixed polyolefins in a fluidized - bed reactor and on a pyro-GC/MS to yield ahphatic waxes. Polymer Degradation and Stability, 70, 373 (2000). 

W. Kaminsky, and B. Schlessehnann, C. Simon, Olefins from polyolefins and mixed plastics by pyrolysis, J. Anal. Appl. PyroL, 32, 19 (1995). 

C. M. Simon, W. Kaminsky, B. Schlesselmann, Pyrolysis of polyolefins with steam to yield olefins, J. Anal Appl Pyrol, 38, 75 (1996). 

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