CONTRIBUTION OF POLYOLEFINS, POLYSTYRENE AND CELLULOSICMATERIALS TO THE QUALITY OF PACKAGING WASTE PYROLYSIS PRODUCTS
I. de Marco*, A. Lopez-Urionabarrenechea, A. Adrados, B.M. Caballero, and M.F. Laresgoiti
Chemical and Environmental Engineering Department - School of Engineering of Bilbao.
Alda de Urquijo s/n – 48013 Bilbao - SPAIN
e-mail: isabel.demarco@ehu.es

Abstract
Three of the main components of municipal packaging wastes (polyolefins, polystyrene and paper/cardboard), as well as areal sample coming from a municipal packaging waste sorting plant, have been pyrolyzed, at 500 ºC in a fixed bed reactor.
Polyolefins yield mainly alkenes, polystyrene generates mainly aromatics (> 60% styrene) and paper/cardboard gives rise
to a lot of water (> 75%), oxygenated compounds, char and CO2. The real sample liquids contain an aqueous and anorganic phase, this later much more similar to PS liquids than to polyolefins liquids. There are beneficial interactions
among the components which promote aromatics generation and prevent char and long-chain alkenes formation.
Keywords: pyrolysis, packaging wastes, polyolefins, polystyrene, cellulosic wastes

Introduction
One of nowadays most important waste is packaging
waste. In the European Union about 18 million tonnes ofthis waste are generated each year. All over the world
different initiatives for valorising packaging waste arebeing launched. In Europe the 2004/12/EC Packing andPackaging Directive obliges to recycle at least 55 % of
packaging waste. In many European countries packaging
wastes are selectively collected in at least three types ofmunicipal containers: one for glass, one for paper andcardboard and one for plastic and metallic packaging.
Since the later contains a mixture of materials, in order torecycle them it is previously necessary to separate themin sorting plants were the waste is separated in different
fractions (steel, aluminum, tetrabrick©, different plastics),
which are then sent to recycling companies. In suchplants there is a fraction left which is not worthwhilefurther separating, ant it is frequently incinerated orlandfilled. Such rejected fraction is mainly composed ofplastics, but also contains some tetrabrick©, aluminumand steel, which has not been possible to recover, andsome mistaken materials (paper, glass, non-packagingplastics), which should have not been placed in themetallic and plastic packaging municipal container. In
order to increase recycling rates and fulfill therequirements of the 2004/12/EC Directive, recycling ofsuch rejected fraction becomes a necessity, and sincemechanical separation and recycling is not technically or
economically viable, feedstock recycling is a very
appropriate technique for such waste rejected stream. In
this work pyrolysis of the main components of suchstream, individually, as well as of a whole real samplefrom a Spanish sorting plant has been investigatedExperimental procedure
Characteristics of the samples pirolyzed
The amount and composition of rejected fractions comingfrom packaging waste sorting plants, vary significantly
depending on the characteristics and efficiency of thesorting facility and also depending on the inhabitants

habits and on the time of the year. Along three years theauthors have collected up to seven samples of rejected
stream coming from a sorting industrial plant where thepackaging wastes of the province of Biscay (north ofSpain) are sorted. Table 1 shows the main types ofmaterials that composed such samples and theirconcentration range. A detailed description of such
samples has been presented elsewhere [1]Table 1.- Main type of materials in rejected streams froma packaging waste sorting plant
Concentration
Material
range
Plastics
33 - 97(PE, PP, PS, PET, other polymers)

Cellulosic materials(paper, tetrabrick©, wood, clothes, etc.)

Inorganics(glass, ceramics, metals, batteries, etc.)≈0 - 44≈0 - 45

Others(multimaterial packages, medical waste,printed circuit boards, etc)

≈0 - 5

It can be seen that there is a wide variation in the
proportion of each type of material. Rejected streams
from sorting plants should be mainly composed ofplastics, however due to inefficiency or malfunction of thesorting plant, and also due to the fact that mistaken
materials (toys, paper, clothes, etc) are frequently placedin the municipal plastic and metallic packaging container,a significant and unpredictable proportion of non-plastic
materials can be present in such streams, as it occurs in
the case studied in this work. Plastics and cellulosic
material are the components which can be transformed
into liquids and gases in pyrolysis processes. Table 2
shows the concentration range (in an inorganics-freebasis) of the main types of polymers contained in theabove mentioned samples. It can be seen that the mostabundant components are polyolefins, polystyrene, andcellulosic materials. Therefore the quality of pyrolysis
products will be mainly determined by these components.
In this work a polyolefin (PE/PP=50/50) sample, a PS

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013Table 2.- Types of polymers in real rejected streams froma packaging waste sorting plant (inorganics-free basis)
Range
Specificcomposition
composition
Materialof severalof the sample
samples
pyrolyzed
Polyolefins (PE + PP)
27 - 75
27,5Polystyrene (PS )6 - 2510,7Polyethylene
2-9
8,1
terephthalate (PET)
Polyvinyl chloride (PVC)≈0 - 4
1,6
Other plastics≈0 - 104,0Cellulosic materials≈0 - 60
48,1
sample, a paper/cardboard sample and a real rejected
sample from a packaging sorting plant (composition
presented in table 2), have been pyrolyzed. Solid, liquidand gaseous products wher thoroughly characterized.
Pyrolysis experiments
The pyrolysis experiments were carried out with 100 g ofsample, at 500 ºC, for 30 minutes once reached reaction
temperature, in nitrogen atmosphere, and using an
unstirred stainless steel 3.5 dm3 reactor, which washeated at 20 ºC min-1. Pyrolysis liquids and solids wereweighed after the experiment to determined their yield in
weight %, while gas yield was calculated by difference

Results and Discussion
The solid, liquid and gas yields obtained in the pyrolysis
experiments are presented in table 3.
Table 3.- Pyrolysis yields (weight % inorganic free basis)
LiquidGas
Solid
Material
Organic Aqueous (by diff)
Polyolefins055,2044,8Polystyrene
0,797,50
1,8Cellulosic
34,1
5,0
29.8
31.1
13,4
41,4
14,6
30,7
Real sample
aaaa(19,0a(32,5)(16,6)(31,8

Theoretical mathematical yield calculated according to the sample
composition and to the pyrolysis yield of the individual components

It can be seen that the behavior of the 3 materials
pyrolyzed is completely different. On the first place it
must be mentioned that the cellulosic material yields
important proportions of aqueous phase and of solid(char), while polyolefins do not produce neither aqueous
phase nor char, and polystyrene does not yield aqueous
phase but generates a very low proportion of char.
Secondly it can be seen that polyolefins give rise tocomparable proportions of gases and liquids, while
polystyrene is converted almost completely to liquids. As
far as the real sample is concerned, table 3 includes (inbrackets) the pyrolysis yields calculated according to theproportions of the components in the sample and thepyrolysis yields of the individual components; in suchcalculation the effect of PET, PVC and “other plastics”
has been neglected, it has been considered as if thesample were only composed of polyolefins (31,9 %),polystyrene (12,4 %) and cellulosic materials (55,7 %).
Comparing real and theoretical yields it can be seen that
there are some kind of beneficial interactions when thematerials are pyrolyzed together, since less char andmore organic liquids, than the theoretical value areobtained. An explanation to this fact may be thathydrogen rich free radicals coming from the polymers
somewhat inhibit the recombination of the hydrogen
depleted free radicals coming from cellulosic materials
that tend to form char. Nevertheless it must be born inmind that the other components which have not been
considered, may also have an influence, and also thatmetals present in the real sample may also have somekind of catalytic effect.
A summary of the characteristics of the pyrolysis liquids
is presented in table 4. GC/MS and elemental analyses
showed that there are clear differences among thequality of such liquids. Those derived from polyolefins aremainly composed of alkenes and cycloalkanes and havea significant proportion of >C13 compounds, which gives
them a wax-like consistency. Those derived from PS are
low viscosity liquids, mainly composed of aromatics andwith an styrene content > 60%. Liquids from cellulosic
wastes are mainly composed of water (up to 78 %), thisis corroborated by its low carbon content and extremely
high H/C ratio, mixed with some organic oxygenatedcompounds (phenols, ketones, carboxylic acids, etc.).
Concerning the real sample, the results reported in table
4 correspond to the organic phase. They are more similar
to PS liquids than to PE/PP ones, so the interactions
among the different waste components prevents theformation of long-chain-alkenes and promotes aromatics
formation (toluene+styrene+ethyl-benzene was > 55%).
The aqueous phase of the real sample liquids wasequivalent to that of the cellulosic liquids: it was mainlycomposed of oxygenated compounds. Concerning
pyrolysis gases, they are mainly composed ofhydrocarbons in the case of PE/PP and PS, while thecellulosic derived gases have a very high COx content (>70 vol %) and the real sample gases contain comparable
proportions of hydrocarbons and of COx.
Table 4.- Characteristics of pyrolysis liquids
PE+PP PS Cellulosic RealºMaterial
C (wt%)
81,791,97,189,1
H(wt%)
12,5
7,810,59,3
H/C atomic
1,8
1,0
17,81,2
HHV (MJ kg-1)
45,341,42,741,4
Aromatics
19,296,58,096,6Non Aromatics
71,6090,23,4
No identified
9,23,52,80C5-C945,385,1n.d.
75,1C10-C1326,71,2n.d.
17,7> C13
18,810,2n.d.
7,2a Characteristics of the organic phasen.d. not determined

References[1] A. Lopez-Urionabarrenechea et al. Applied Energy 98,(2012) 524-53.

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