Polyethylene pyrolysis

Industrial Engineering Chemistry Research 37, No.7, July 1998, p.2582-91 POLYETHYLENE PYROLYSIS THEORY AND EXPERIMENTS FOR MOLECULAR WEIGHT DISTRIBUTION KINETICS Sezgi N A Cha W S Smith J M McCoy B J California,University... 

A. Marcilla, M. Beltran, and J. A. Conesa, Catalyst addition in polyethylene pyrolysis thermogravimetric study, J. Anal. Appl. Pyrolysis 58-59, 117 (2001). 

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]. 

The study of polyethylene thermal decomposition is important in relation to the polymer resistance to heating [2], to various attempts to use waste containing polyethylene as a combustible or as a source of other useful materials [3-7], or to environmental issues when polyethylene is burned [8]. Various other studies on polyethylene pyrolysis were reported [9-22], etc. 

Numerous studies have been performed on polyethylene pyrolysis [22-41]. These studies include flash pyrolysis in He, in air, in the presence of various catalysts, in the presence of steam, under pressure, etc. Also, besides analytical pyrolysis, some of the studies were performed at slow heating rates that better simulate pyrolysis in industrial incinerators. Most frequently, the analysis of polyethylene pyrolysates has been done using GC/MS. However, other techniques also were applied, such as pyrolysis field ionization mass spectrometry [42]. 

Thermal decomposition of polyethylene in an inert atmosphere starts at about 280° C and occurs mainly following fragmentation and dehydrogenation reactions, the fragmentation being predominant at temperatures below 600° C (see Section 2.2). Hydrocarbons, from 2 carbon atoms up to 90 carbons, were identified in pyrolysates. Three types of fragment molecules are the most common, namely alkenes, alkanes, and a,(B-dienes. Traces of other hydrocarbons also are formed during pyrolysis. Some reactions typical for polyethylene pyrolysis are shown below ... 

Figure 6.1.2. Pyrogram from a Py-GC/MS analysis of high-density polyethylene. Pyrolysis done on 0.4 mg material at 60(f C in He, with the separation on a Carbowax type column.

After the sharp drop in the mass via temperature curve due to polyethylene pyrolysis, the remaining mass does not usually remain constant with temperature. Rather, the curve continues to gradually decrease. The point of time or temperature for switching over to synthetic air gas flow can therefore affect the measurement result of the carbon black content. Such measurement conditions must be observed to achieve comparable results. Comparing the measurement results with measurements obtained by con-... 

Sablier M, Sala M, Kitahara Y, Takahashi S, Fujii T. Influenee of eopper chloride for the formation of aromatie eompounds during polyethylene pyrolysis. J Anal Appl Pyr. 2010 89 178 82. 

Phosphoms-containing additives can act in some cases by catalyzing thermal breakdown of the polymer melt, reducing viscosity and favoring the flow or drip of molten polymer from the combustion zone (25). On the other hand, red phosphoms [7723-14-0] has been shown to retard the nonoxidative pyrolysis of polyethylene (a radical scission). For that reason, the scavenging of radicals in the condensed phase has been proposed as one of several modes of action of red phosphoms (26). 

Pyrolysis characteristics of polyethylene using waste catalysts... 

Nonvolatile compounds cannot be analysed unless pyrolysis or derivatisation converts them to a condition amenable to GC. Derivatisation GC (or LC) has been used for several components such as erucamide (imidi-sation for volatility), fatty amines (aromatic amidation for UV detectability), and polyethylene oxides (esterification for both volatility and detectability) [178]. The surface concentration of erucamide on extruded LLDPE films was determined quantitatively by surface washings with ether, followed by evaporation, dissolution... 

A proposed expansion of the corporation s polyethylene production capacity will require additional ethylene monomer as a feedstock. It is suggested that the ethylene be produced by the pyrolysis of a propane stream that is available at axrate of 7000 lb/hr. 

The two polymer substrates investigated as part of the study of DBDPO mixtures were polypropylene (PP) and linear high density polyethylene (HDPE). while both PP and HDPE decompose by similar random chain scission, radical mechanisms, chain transfer occurs much more teadily during the pyrolysis of PP because of the presence of the tertiary hydrogens. In addition, only primary chain end radicals are formed when the HDPE chain cleaves homolytically. Therefore, a comparison of the PP/DBDPO and the HDPE/DBDPO mixtures volatile product distributions was undertaken. 

J.A. Conesa, R. Font, A. Marcilla, Comparison between the pyrolysis of types of polyethylenes in a fluidized bed reactor, Energy Fuels 11 (1997) 126-136. 

P.T. Williams, E.A. Williams, Fluidised bed pyrolysis of low density polyethylene to produce petrochemical feedstock, J. Anal. Appl. Pyrolysis 51 (1999) 107-126. 

The pyrolysis unit in Centralis converts 100 tires per hour (about one ton, assuming each tire weighs 20 pounds) to 600 pounds of carbon black, 90 gallons of oil, and 30 therms (8000 ft3) of vapor gas. In addition to tire rubber, Conrad s unit has been used to pyrolyze substances as diverse as rice hulls, nut shells, biomass (including wood, paper, and compost), and plastics (including polyester, polyethylene, and propylene).1... 

L. Ballice, Classification of volatile products evolved during temperature-programmed co-pyrolysis of low-density polyethylene (LDPE) with polypropylene (PP). Fuel, 81(9),1233-1240 (2002). 

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