Detailed mechanistic modeling of high-density polyethylene pyrolysis: Low molecular weight product evolution

A detailed, mechanistic model for high-density polyethylene pyrolysis was created based on the modeling framework developed in our previous work and was used to study the time evolution of low molecular weight products formed. Specifically, the role that unzipping, backbiting, and random scission reaction pathways play in the evolution of low molecular weight species was probed. The model tracked 151 species and included over 11,000 reactions. Rate parameters were adapted from our previous work, literature values, and regression against experimental data. The model results were found to be in excellent agreement with experimental data for the evolution of condensable low molecular weight products. The time evolution curves of specific low molecular weight products indicated that the random scission pathway was important for all species, while the backbiting pathway played a complementary role. Net rate analysis was used to further elucidate the competition between the pathways. Net rate analysis of end-chain radicals showed that the unzipping pathway was not competitive with the other pathways, as expected based on experimental yields of ethylene. The random scission pathway was found to be controlling, with the backbiting pathway playing a more minor role for product formation. By comparing the net rates for formation of specific mid-chain radicals via intramolecular hydrogen shift reactions, the contribution of the backbiting pathway was shown to vary, with radicals formed via the most facile x,x + 4-intramolecular hydrogen transfer reactions being favored.

[1]  M. Poutsma.  Reexamination of the Pyrolysis of Polyethylene: Data Needs, Free-Radical Mechanistic Considerations, and Thermochemical Kinetic Simulation of Initial Product-Forming Pathways , 2003 .

[2]  Valerio Cozzani,et al.  Kinetic modeling of polyethylene and polypropylene thermal degradation , 1997 .

[3]  S. L. Madorsky,et al.  Pyrolysis of polyisobutene (Vistanex), polyisoprene, polybutadiene, GR-S, and polyethylene in a high vacuum , 1949 .

[4]  Binary mixture pyrolysis of polypropylene and polystyrene: A modeling and experimental study , 2005 .

[5]  J. Smith,et al.  Continuous kinetics for thermal degradation of polymer in solution , 1995 .

[6]  J. Smith,et al.  Polyethylene Pyrolysis: Theory and Experiments for Molecular-Weight-Distribution Kinetics , 1998 .

[7]  H. Jellinek.  Thermal degradation of polystyrene and polyethylene. Part III , 1949 .

[8]  L. Broadbelt,et al.  Modeling the Evolution of the Full Polystyrene Molecular Weight Distribution during Polystyrene Pyrolysis , 2003 .

[9]  S. Benson,et al.  Thermochemical Kinetics: Methods for the Estimation of Thermochemical Data and Rate Parameters , 1976 .

[10]  Neil A. Dotson,et al.  Polymerization Process Modeling , 1995 .

[11]  Warren E. Stewart,et al.  Parameter estimation from multiresponse data , 1992 .

[12]  J. Scheirs,et al.  Feedstock recycling and pyrolysis of waste plastics : converting waste plastics into diesel and other fuels , 2006 .

[13]  L. Broadbelt,et al.  Mechanistic modeling of polymer pyrolysis: Polypropylene , 2003 .

[14]  L. Broadbelt,et al.  Reaction pathways to dimer in polystyrene pyrolysis: A mechanistic modeling study , 2008 .

[15]  M. G. Evans,et al.  Inertia and driving force of chemical reactions , 1938 .

[16]  Y. Tsuchiya,et al.  Thermal decomposition products of polyethylene , 1968 .

[17]  S. Nguyen,et al.  Limitations in the Synthesis of High Molecular Weight Polymers via Nitroxide-Mediated Controlled Radical Polymerization: Experimental Studies , 2003 .

[18]  L. Broadbelt,et al.  Quantum chemical investigation of low-temperature intramolecular hydrogen transfer reactions of hydrocarbons. , 2006, The journal of physical chemistry. A.

[19]  Robert Simha,et al.  The depolymerization of polymethylene and polyethylene , 1954 .

[20]  L. Broadbelt,et al.  Binary Interactions between High-Density Polyethylene and 4-(1-Naphthylmethyl)bibenzyl during Low-Pressure Pyrolysis , 2000 .

[21]  B. J. McCoy.  Continuous‐mixture kinetics and equilibrium for reversible oligomerization reactions , 1993 .

[22]  R. Masel,et al.  An Extension of the Marcus Equation for Atom Transfer Reactions , 1999 .

[23]  Tiziano Faravelli,et al.  Gas product distribution from polyethylene pyrolysis , 1999 .

[24]  Tiziano Faravelli,et al.  Detailed kinetic modeling of the thermal degradation of vinyl polymers , 2007 .

[25]  Y. Tsuchiya,et al.  Thermal decomposition products of polymethylene , 1968 .

[26]  David P. Serrano,et al.  Feedstock recycling of plastic wastes , 1999 .

[27]  B. J. McCoy,et al.  Distribution kinetics of thermolytic macromolecular reactions , 2001 .

[28]  Sabine Beuermann,et al.  Rate coefficients of free-radical polymerization deduced from pulsed laser experiments , 2002 .

[29]  J. Ceamanos,et al.  Modelling of the pyrolysis of high density polyethylene: Product distribution in a fluidized bed reactor , 2007 .

[30]  B. J. McCoy,et al.  Distribution kinetics for polymer mixture degradation , 1999 .

[31]  Linda J. Broadbelt,et al.  Detailed mechanistic modeling of polymer degradation : application to polystyrene , 2001 .

[32]  J. K. Gillham,et al.  Pyrolysis‐molecular weight chromatography: A new on‐line system for analysis of polymers. II. Thermal decomposition of polyolefins: Polyethylene, polypropylene, polyisobutylene , 1976 .

[33]  Linda J. Broadbelt,et al.  Mechanistic Modeling of Polymer Degradation: A Comprehensive Study of Polystyrene , 2002 .

[34]  B. J. McCoy,et al.  Distribution kinetics of radical mechanisms: Reversible polymer decomposition , 1997 .