Predicting the distribution of thermal pyrolysis of high density polyethylene products using a mechanistic model

Original Article
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Abstract

The increase of the plastic wastes has urged finding different solutions for their recycling. Thermal pyrolysis is a suitable solution for refining the combination of different plastics. The main goal of this research is developing a model to predict the distribution of products obtained from pyrolysis. To do this a mechanism model based on free radical mechanism is developed. In this model some kinetic stages are used including initiation, scission, abstraction, aromatic making and radical combination. After determining the kinetic constants, the equations were solved in MATLAB software. The results were compared with experimental results from a conical spouted bed reactor (CSBR) in temperature (500–900 °C) and residence time (0.016–0.032 s). the results show that the model can predict the experimental observation for different temperatures and residence time and estimate the amount of low and high density products in a way that the increase of that gas fraction increase and high density products decrease. Also in all the situation the amount of olefin fraction is more than paraffin and diolefin.

Keywords

Polyethylene Pyrolysis Mechanistic model Temperature Residence time 

List of symbols

Arn

molar flow of n carbon atoms aromatic (mol/m3)

Dn

molar flow of n carbon atoms diolefin (mol/m3)

Kf

kinetic constant of H-abstraction reaction (m3/mol s)

Kpp

kinetic constant of initial scission reaction (s− 1)

Kr

kinetic constant of H-abstraction reaction (m3/mol s)

Kt

kinetic constant of termination reaction (m3/mol s)

K1ar

kinetic constant of production of aromatics 1reaction (m3/mol s)

K2ar

kinetic constant of production of aromatics 2reaction (m3/mol s)

Kβ

kinetic constant of β-scission reaction (s− 1)

On

molar flow of n carbon atoms olefin (mol/m3)

Pn

molar flow of n carbon atoms paraffin (mol/m3)

r

rate of production of i via β-scission (mol/m3 s)

riArn

rate of production of i via aromatization (mol/m3 s)

rif

rate of production of i via H-abstraction (mol/m3 s)

ripp

rate of production of i via initial scission (mol/m3 s)

rir

rate of production of i via H-abstraction (mol/m3 s)

rit

rate of production of i via termination (mol/m3 s)

rj

rate of production of the j reaction (kg/m3 s)

RDn

molar flow of n carbon atoms radical diolefin (mol/m3)

ROn

molar flow of n carbon atoms radical olefin (mol/m3)

RPn

molar flow of n carbon atoms radical paraffin (mol/m3)

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Copyright information

© Springer International Publishing Switzerland 2017

Authors and Affiliations

  1. 1.Department of Chemical Engineering, School of Engineering, Tehran North BranchIslamic Azad UniversityTehranIran
  2. 2.Faculty of EngineeringIran Polymer and Petrochemical Institute (IPPI)TehranIran

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