DEVELOPMENT OF AN UPSCALABLE RECYCLING PROCESS FOR POLYOLEFINSAND OTHER POST-CONSUMER PLASTIC FRACTIONS VIA SOLVENT-BASEDDEPOLYMERIZATION
Christiane Lederer, Markus Lehner
University of Leoben, Institute of Process Engineering, Franz-Josef-Straße 18, A-8700 Leoben, Austria
E-mail: christiane.lederer@unileoben.ac.atAbstract
A concept for chemical recycling of post-consumer plastics in a refinery surrounding was designed in order to develop aneconomically feasible and technically viable solution for resource-efficient usage of hydrocarbon products.
Thermal, non-catalytic depolymerization at moderate temperatures and pressures is meant to produce valuable refinery
feedstock with an outstanding C/H ratio at optimum operation costs.
Solvent-based polymer cracking in liquid-phase conditions realized in a tube reactor design should overcome process
difficulties originating from high viscosity and low thermal conductivity of polymer melts and lead to a stable, robust andcontrollable process with constant and optimized product qualities.
To evaluate the conceived theoretical findings, a continuous bench-scale pilot plant was designed and built at the pilot
plant facilities of OMV Refining and Marketing in Schwechat, Austria.
Polyethylene (PE), Polypropylene (PP), Polystyrene (PS) granulates and their mixtures were fed to the unit for studying
the base depolymerization kinetics and process behaviors. In later test series, several pretreated post-consumer plastic
fractions were used as feedstock to review the robustness of the process towards impurities and impact of compounding
and additive materials.

Keywords: chemical recycling, polyolefins, thermal cracking, solvent, refinery

1. Introduction

2. Materials and Methods

Chemical recycling of pure and mixed plastics has
undergone extensive research for decades.[1],[2]Decreasing available disposal volumes and politicalpressure towards reduction of landfilling, high crude oiland thus feedstock prices are nowadays economic andecological incentives for the development of recycling
technologies.
Major companies in chemical and oil and gas industry
developed a range of different technologies. Complex,CAPEX-intense reactor designs, such as fluidized beds
and rotary kilns were applied to overcome process
difficulties originating from high viscosity and low thermal
conductivity of polymer melts. High temperatureapplications and elaborated catalysts produced thefavored products but also caused high operation costs.
Simpler and more cost efficient designs led to poor andinconstant product qualities and low throughputs.
Early papers and articles written in the beginning 1990s
have already described the challenge of making thetechnology cost effective. 20 years later, crude oil pricesrose to about a five-fold, plastics world production
increased by some 180% and landfill bans were put inplace in various European countries.
This set of changed economic conditions can finally leadto the economic viability of depolymerization
technologies.

After intense literature studies and discontinuouslaboratory tests a continuous bench-scale pilot plant wasdesigned and constructed.
Compared to earlier works [3], the approach was to build
a fully continuous plant, also for purge products.
The aim was to find process parameters for ideal
cracking conditions into favourable products. Optimum
reaction temperatures and system pressures for solventbased liquid-phase cracking had to be developed andverified [4].
The tube reactor design provides plug flow conditions
and thus distinct retention times, next to a high andthrough multiple heating zones variable ratio of heattransfer surface to the reaction volume.
Process data is used to set up simulation models in orderto validate the economic and technical viability of theprocess and to allow scale-up approaches.
A moderate process temperature and pressure design
favours energy efficient operation; the non-catalytic
solvent based process avoids margins losses throughcatalyst regeneration or a spent catalyst application.
Target feedstock materials are fractions with polyolefin
contents as those represent the majority in pre-treated(e.g. NIR-sorted) post-consumer recycling materials.
In order to study the base depolymerization kinetics andprocess behavior pure virgin polyolefin granulates andtheir mixtures are used as feed stock materials for the

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

first test series. Later, several pre-treated post-consumer
plastics were fed to the unit to study the robustness ofthe process towards impurities and impact ofcompounding and additive materials.

3. Results and Discussion
Typical post-consumer plastic fractions are fed into theprocess using refinery heavy oil fractions as solvent andmatrix liquid and cracked in a tube reactor. The obtained
products are flashed from the residues and additive
substances and distilled into typical refinery feedstock
products. The remaining residues and solvent mixture isrecycled in a pump around system.

References[1] A. Tukker, Ing H. de Groot, Ir.L. Simons, Ir. S.
Wiegersma, Chemical Recycling of Plastics Waste (PVCand Other Resins), TNO-Report STB-99-55 Final, 1999,
European Commission, DG III.
[2] John Scheirs, Walter Kaminsky, Feedstock Recyclingand Pyrolysis of Waste Plastics, ISBN 0-470-02152-7.
[3] Katsuhide Murata, Y. Hirano, Y. Sakata, Md. Azhar
Uddin, Basic study on a continuous flow reactor forthermal degradation of polymers, Journal of Analyticaland Applied Pyrolysis, Vol.65 (2002), 71-90.
[4] Katsuhide Murata, Kenji Sato, Yusaku Sakata, Effectof pressure on thermal degradation of polyethylene,
Journal of Analytical and Applied Pyrolysis, Vol.71 (2004)
569-589.

The set of product analyses is adapted to typical testing
parameters of refinery feedstock and products, such as:
simulated TBP distillation
PIONA analyses for naphtha fractions
density and viscosities
aromatics
C/H ratio
An empirical and visual testing method for coke contentsfrom polymer cracking in the purge material formation
was developed.
Process temperatures and pressures are preferably
below 500°C and 20 bar_g.

4. Conclusions
This new process can provide an economically viable
solution for the chemical recycling of preferably
polyolefins as feedstock for refineries.
The solvent-based technology enables an upscalable
reactor design and controllability of reaction and flow
conditions throughout the cracking unit.
The obtained process data could be used to set up
simulation models in order to validate the economic andtechnical viability of the process and to allow scale-up
approaches.
Economic considerations assuming an upscaling to acommercial size unit and its integration in an existingrefinery are done.
The found conclusions were compared to state-of-the-art
technologies.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013