Solvent-based depolymerization of polyolefins

Christiane Lederer

Research output: ThesisDoctoral Thesis


Increasing amounts of produced and discarded plastics, progressive hydrocarbon resource shortcomings and the intensifying legal situation in resource and waste management raise questions about enabling increased recycling quotes and the establishment of alternative recycling opportunities. The evaluated process concept of a solvent-based depolymerization of polyolefins could lead to a finally feasible chemical recycling of so-called hard-to-recycle plastic fractions rich in polyolefins. The targeted process is a non-catalytic thermal polymer cracking process at moderate temperatures for maximized liquid yields. The selected up-scalable tube reactor application was found to enable distinct residence times and sharp residence time distribution, which are essential for a favorable product distribution in thermal cracking, at moderate capital and operational expenses. Difficulties in processing of polymer melts, which originate from their high viscosity and their low thermal conductivity, can be ameliorated by incorporating a high-boiling solvent into the process. The chosen solvent is a heavy oil fraction with high aromatic contents produced at the fluid catalytic cracking (FCC) unit. The feedstock of the conducted test runs was virgin polymer granulate to avoid inaccuracies in balancing from inhomogeneous and poorly specified input materials. Products from a test run for virgin polypropylene granulate at a reaction temperature of approximately 390°C were described in comparison to solvent cracking products from baseline balances conducted at equal process conditions without polymer dosage. Generally, the generated amounts of the lighter product cuts increased significantly in comparison to the baseline product. Naphtha, kerosene and gasoil cut showed decreased aromatics contents. Detailed analysis of the naphtha cut show an increased ratio of linear substances, which signifies a higher product quality towards feedstock production for steam cracking. Furthermore a massive shift towards isomeric substances is visible both in paraffins and olefins, which is characteristic for polypropylene decomposition as well as C9 species as main product components. However, untypical for thermal polymer cracking is the low olefin content of 17 percent. A possible explanation is occurrence of secondary reactions from reactive olefins to more stable products. The conversion into liquid products was calculated to approximately 72 percent, whereas this calculation is influenced by the inaccuracy of the baseline product adjustment. In product balancing, the retardation of approximately 3 to 6 hours until significant product generation was detected, indicates a too small heating surface and hence reactor length.
Translated title of the contributionLösungsmittelbasierte Depolymerisation von Polyolefinen
Original languageEnglish
  • Lehner, Markus, Assessor A (internal)
  • Winter, Franz, Assessor B (external), External person
Publication statusPublished - 2013

Bibliographical note

embargoed until null


  • depolymerization
  • polyolefins
  • solvent
  • thermal cracking

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