Experimental investigation and modeling of a polyolefin pyrolysis process

Research output: ThesisDoctoral Thesis

Abstract

Increasing application of plastics as short life span products like packaging, bags and foils leads to a growth of stock of post-consumer plastics which have to be recycled to ensure sustainable resource management. In a previous study, a solvent-based pyrolysis process 'ReOil' as tertiary treatment route for polyolefins was developed to recover valuable hydrocarbons. The novel introduction of a organic carrier liquid improves processability of the polymer melt by viscosity reduction and heat transfer enhancement. The aim of this work was to increase understanding of the underlying cracking reaction mechanisms and their influencing factors as foundation to optimize the technical process and to build an integrated reactor simulation model. For this purpose, after an extensive literature review, a continuous laboratory plant called 'Flash' was developed and used to degrade LDPE commingled with solvent in a plug flow reactor, varying the process parameters systematically. The effect of the alterations of polymer content, pressure, temperature and residence time on the gaseous and liquid product yields and qualities gave information about the potential adjusting screws. It was observed that rises in polymer content, pressure, temperature and residence time lead to higher light liquid production at the cost of heavy products. Due to the experimental setup, interdependences between the single process parameters have to be considered during evaluation of the influencing factors. For example, an increase in pressure causes a lower vapor fraction in the reactor and consequently residence time elongations, which can explain the increase in conversion at higher pressure levels. The differences in degradation behavior between the most common plastic types were investigated performing thermogravimetric analyses at constant heating rates, which offer clues of the relative thermal stability depending on the chemical structure. The results of virgin polymer granulate and post-consumer waste components were compared. Additionally, the analysis of polymer, solvent and mixtures of both showed that interactions between plastics and carrier medium cannot be ruled out. The measured yields of residence time test runs were further used to develop a lumped kinetic model, which simplifies complex reaction networks by lumping together chemical compounds according to their physical or chemical properties. A reaction scheme consisting of four pseudo-species with different boiling ranges, which can undergo six different reaction pathways among them, was developed, tested and found to describe the occurring behavior sufficiently.
Translated title of the contributionExperimental investigation and modeling of a polyolefin pyrolysis process
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Lehner, Markus, Assessor A (internal)
  • Winter, Franz, Assessor B (external), External person
Publication statusPublished - 2018

Bibliographical note

embargoed until 11-05-2023

Keywords

  • plastic pyrolysis
  • lumped kinetic modeling

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