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1TOLEDO (SPAIN)

TRENDS AND PERSPECTIVES IN FEEDSTOCK RECYCLING OF POLYMERIC
MATERIALS
J.M.N. van Kasteren and Q.Zhou
Eindhoven University of Technology, Eindhoven Energy Institute, PO Box 513, 5600 MB Eindhoven, The Netherlands
e-mail: j.m.n.v.kasteren@tue.nl

Abstract
This paper provides up-to-date information on the technological trends regarding polymer feedstock recycling, paying special
attention to materials such as biomass, biodegradable polymers and thermosets, and the development and application ofnew processes for feedstock recycling of polymeric materials.

Keywords: Feedstock recycling; Waste polymers; Recycling

1. Introduction
The plastic production increased from 1.5 million tonnes
in 1950 to 230 million tonnes in 2009 with the growth rateof around 9% a year on average [1]. As plastics aresynthesized from non-renewable resources and are
generally non-biodegradable, plastics should be properly
managed in order to prevent serious environmental
waste issues. For a sustainable use of polymers anecessary requisite is closing the material loop by either
reuse or recycling. An attractive potential technology inthis case, which can provide beside environmental also
economical benefits is feedstock recycling.
Also known as chemical recycling, feedstock recyclingrefers to techniques used to break down plastic polymers
into their constituent monomers, which in turn can beused again in refineries, or petrochemical and chemicalproduction. A variety of treatments may be included
under this category including chemical depolymerisation,
gasification, thermal cracking and catalytic conversion[2].
Some lifecycle assessments show that feedstock
recycling from mixed plastic waste has goodenvironmental performance [3]. However, the rate offeedstock recycling for post-consumer plastic waste in
the EU in 2008 is only 0.3% (0.07 Mt), and it shows no or
little growth from 1995 to 2008 compared withmechanical recycling and energy recovery due to a
combination of technological and economic reasons(Fig.1) [4].

In order to compete with other recycling methods, the key
success factor for feedstock of recycling will be lowering
processing cost in combination with producing highvalue-added products.

2. New Trends on Feedstock Recycling
2.1 Emerging sectors
2.1.1Biomass
Recently natural polymers such as lignocellulosic
biomass, which is the most abundant and inexpensive
sustainable source of carbon, have been considered as afeedstock for the production of renewable fuels andcommodity chemical feedstocks. One typical example isby combining fast pyrolysis with zeolite catalyzedhydroprocessing, lignocellulosic biomass can beconverted into high value chemicals like light olefins andaromatic hydrocarbons (Fig.2) [5].

Fig. 2. Production of olefins, aromatic hydrocarbons,diols, and gasoline range alcohols from the integrated
catalytic processing of pyrolysis oil [5].

Fig.1 Plastic recovery options in EU-15, 1996-2008[4]interiores libro.indd 1

2.1.2
Biodegradable polymers
Biodegradable plastics are supposed to be completely
broken down by micro-organisms in the environment into
non-toxic compounds. However, the microbial
degradation of some biodegradable polymers such as
PLA is limited to a few species of microorganisms [6].

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6th International Symposium on Feedstock Recycling of Polymeric Materials

Large-scale consumption of PLA products will lead to an
excess of PLA waste, which will be difficult to be treatedby biodegradation either in composting plants or in thenatural environment. Moreover, recyclers complain that
PLA is often indiscernible from the polyethylene
terephthalate (PET), and even small amounts of PLA
contamination in a PET recycling stream can affect thepolyester's properties. Therefore, it is necessary to findefficient recycling methods for biodegradable polymers. If
you can recover the polymer pure it is possible to convert
PLA back to lactic acid/lactide (Fig.3) [7].

2.2 New processes
2.2.1
Solar driven gasification
Solar-driven gasification uses concentrated solarradiation as the energy source to produce syngas, which
offers an attractive alternative to conventional auto
thermal processes. The advantages of this processinclude [9]:z Produce high-quality synthesis gas with higher
output per unit of feedstock and lower specific
CO2 emissionsz Elimination of an air separation unitz Storing intermittent solar energy in transportableand dispatchable chemical form.
The prototype solar reactors have been experimentallydemonstrated, yielding high carbon conversions andreasonable solar-to-fuel energy conversion efficiencies(Fig.5) [9].

Fig.3 Cradle-to-cradle concept for PLA [7].
For mixtures of polymer feedstock recycling can deliver agood alternative.
2.1.3
Thermosetting polymers
Recycling of thermosets has been an important point on
the agenda for the composite industry for a long period.
Due to the crosslinked state, composites are neither
fusible nor soluble and cannot be treated by simple
methods. New technology that can make the recycling
structurally possible is to bring reversible crosslinking decrosslinking functions to the thermosets (Fig.4) [8].
This function can be activated as function of certain
process parameters: e.g. temperature and/or light.

Fig.4. Scheme of the Diels-Alder (DA) and Retro-DielsAlder (RDA) reactions between PK-furan and bismaleimide [8].

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Fig. 5 Modeling schematics for the three solar reactor
concepts: (a) indirectly irradiated packed-bed; (b) directlyirradiated vortex-flow, and (c) indirectly irradiatedentrained flow [9].
2.2.2
Combination processes
Combinations of feedstock recycling methods areneeded to produce high-value products with lower
content of impurities instead of single methods. E.g. apyrolysis-gasification process has been used to producehydrogen [10]; ABS has been treated using a tandemhydrolysis-pyrolysis method, which has the advantage ofhigh denitrogenation efficiency under mild reaction
conditions and decrease of the probability of forming
complicated nitrogen-containing compounds during
pyrolysis (Fig.6) [11]; Another example is polystyrene
and PET which can be converted to biodegradable
polymer polyhydroxyalkanoate (PHA) using a two-steppyrolysis-biosynthesis method [12,13]. In the frst step thepolymers are converted into oil which can then be usedas feedstock for the bio synthesis method.

Fig.6 A two-step process for thermochemical recycling ofABS [11].

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2.2.3
Environmental-friendly process
When treating waste plastics, the environmental impactof the process should be considered. The developmentof environment-friendly methods for feedstock recycling
is an area of considerable importance. The use of volatileand toxic solvents should be avoided, and the process
should not produce other pollutions. New trend is to use
so-called green solvents such as poly (ethylene glycol)(PEG) [14] and ionic liquids for chemical recycling. They
have been shown to be effective for efficientdechlorination of PVC at atmospheric pressure (Figure 7)[15].

Figure 7. Plausible mechanism for [BMIM]Cl-enhanced
dehydrochlorination of PVC [15].

3. Conclusions
In summary, this paper provides latest developments inthe area of feedstock recycling of polymers, paying
special attention to materials such as biomass,biodegradable polymers and thermosets.
Feedstock recycling of polymeric materials is still in its
infancy. New combinations of both existing andpromising technologies can meet the challenge andcompetition with existing mechanical recycling andenergy recovery. The key factor to this is to both improvethe cost efficiency of the processes and the production ofhigh value end products.

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