Lumped Kinetics for Homogeneous Reactions of n-Hexadecane and n-Decene as Model Compounds for PE Pyrolysis Primary Tars

Osvalda Senneca,Teresa Tucciullo

doi:10.3390/en13205466

Abstract

The focus of this paper is to establish a lumped kinetic scheme for secondary reactions of tar produced from pyrolysis of plastics or polymer-based wastes. Notably, the focus is not on the detailed yield of all reaction intermediates and products but on the propensity to form soot. Based on the assumption that that primary tar from pyrolysis of plastic wastes is mostly formed by aliphatics which can undergo progressive aromatization to polycyclic aromatic hydrocarbons (PAHs) and soot, a reaction network with 198 species and 6307 reactions proposed by Ranzi and coworkers was lumped into a very simple five reaction mechanism. The lumped kinetic model has been used to predict PAHs and soot formation in different conditions and proved to be a good alternative to comprehensive kinetic models up for relatively low temperature and short residence times (of up to 1 min at 1200 K, up to 1 s at 1400 K). At higher temperature/longer residence times, the simplified model still provides reasonable qualitative trends but the amount of PAHs and soot is underestimated. The timescale of aromatization under inert conditions appears similar for all the alkanes and alkenes examined and also the yields in main reaction products seem to scale well with the number of carbon and hydrogen atoms of the parent alkane/alkene. Evolution of the young aliphatic tar into large aromatics is prevented as long as gaseous oxygen being available for oxidation. The lumped kinetic model has been used to highlight the effect of different modes of oxygen feeding and of incomplete mixing of fuel and oxygen on the formation of PAH and soot.

Highlights

Based on the assumption that that primary tar from pyrolysis of plastic wastes is mostly formed by aliphatics which can undergo progressive aromatization to polycyclic aromatic hydrocarbons (PAHs) and soot, a reaction network with 198 species and 6307 reactions proposed by Ranzi and coworkers was lumped into a very simple five reaction mechanism
In order to check the ability of the simplified kinetics of scheme in Figure 1, to predict PAHs and soot formation, calculations have been performed in MATLAB of the fate of nC16H34 at different
In order to check the ability of the simplified kinetics of scheme in Figure 1, to predict PAHs and soot formation, calculations have been performed in MATLAB of the fate of nC16 H34 at different temperature and holding times

Summary

Introduction

Several well-known technologies for pyrolysis and gasification—such as entrained flow reactors, fluidized beds, rotary kilns, and fire grates—are nowadays receiving renewed attention as possible solutions to the problem of wastes disposal and for energetic exploitation of biomass and wastes.Within this context, considerable attention has been devoted to thermal recovery of plastic wastes [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24].processing of non-conventional fuels is not straightforward. Several well-known technologies for pyrolysis and gasification—such as entrained flow reactors, fluidized beds, rotary kilns, and fire grates—are nowadays receiving renewed attention as possible solutions to the problem of wastes disposal and for energetic exploitation of biomass and wastes Within this context, considerable attention has been devoted to thermal recovery of plastic wastes [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. PAHs increase with pyrolysis temperature [25,26,27,28].

Objectives

Methods

Results

Discussion

Conclusion