5-7 OCTOBERISFR2011

177

TOLEDO (SPAIN)

PRELIMINARY ASSESSMENT OF PLASTIC WASTE VALORIZATION VIASEQUENTIAL PYROLYSIS AND CATALYTIC REFORMING
J. Dufour1,2, D.P. Serrano1,2 and D. Iribarren1
1Instituto IMDEA Energía. 28933 – Mostoles, Spain
2Department of Chemical and Energy Technology, ESCET, Rey Juan Carlos University. 28933 – Mostoles, Spaine-mail:javier.dufour@imdea.org

Abstract
A lice cycle approach is followed to carry out a preliminary assessment of the energy and global warming performance ofa specific feedstock recycling alternative. Thus, cumulative energy demand and global warming potential indicators arecomputed for a production system that involves the supply of gasoline blending components from waste agriculturalpolyethylene films through sequential pyrolysis and catalytic reforming. Energy and global warming results suggest thesuitability of this system for plastic waste valorization, though actions to reduce the thermal energy demand are required.

Keywords: allocation; cumulative energy demand; feedstock recycling; global warming; life cycle assessment

1. Introduction
The wide range of applications for plastics has led to highconsumption levels of plastic materials worldwide. As aresult, the management of plastic wastes has arisen as a
key environmental issue that should be addressed on thebasis of a well-balanced choice of options, including reuse, mechanical recycling, chemical recycling(depolymerization), feedstock recycling, and energy
recovery [1]. In particular, feedstock recycling refers to avalorization strategy based on chemical and thermal
processes for the conversion of waste polymers intohydrocarbon products to be used as petrochemical
feedstocks [2]. Although only a low percentage of plastic
wastes are sent to feedstock recycling (due mainly tounfavorable investment costs), this management
alternative is expected to play a leading role in the futureowing to the potential attainment of economic andenvironmental advantages [3].
The present work uses a life cycle approach in order toassess the energy and global warming performance of a
specific feedstock recycling system based on thesequential pyrolysis and catalytic reforming (SPCR) of
waste agricultural polyethylene films to yield hydrocarbon
products [2].

2. Materials and MethodsComprehensive environmental analyses of energy
systems require the use of environmental management
tools provided with a life cycle approach. Among these,Life Cycle Assessment (LCA) is a standardized
methodology to assess the environmental aspects andpotential impacts associated with a product [4]. LCA
methodology was used herein to evaluate the productionof gasoline blending components through SPCR of waste
agricultural low density polyethylene (LDPE) films. Fig. 1
summarizes the scope of the analysis, from waste plastic

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reception to gasoline blendstock production. The
functional unit (FU) –i.e. quantified performance of theproduct system for use as the reference unit in the LCA
study– was defined as 1.00 kg of gasoline product forblending. Although this study focused on the gasoline
fraction, other energy co-products derive from the SPCR
system, viz. gas fraction (C1-C4 compounds), diesel
fraction, and char.

Fig. 1. Case study: SPCR of waste agricultural LDPE
films.
Table 1 gathers the main inventory data for the SPCR
system subject to evaluation. These data were adaptedfrom specific scientific literature [1,2], while secondary
data for background processes such as electricity
production or water supply were taken from the ecoinvent
database.
Two relevant categories were evaluated in thispreliminary LCA study: cumulative energy demand (CED)
and global warming potential (GWP). The term CED
refers here to the cumulative non-renewable fossil andnuclear energy demand computed according to Hischieret al. [5], while GWP was quantified by using the CML
method [6]. PRé Consultants’ SimaPro 7 software wasused for the computational implementation of theinventory.

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6th International Symposium on Feedstock Recycling of Polymeric Materials
1.80

Table 1. Simplified life cycle inventory for the SPCRsystem.

3. Results and Discussion
Since this case study involves a multifunctional system,
allocation was needed to distribute the CED and GWP
results among the different products in Table 1. A system
expansion approach based on the concept of avoided
burdens was followed [1]. Hence, -62.64 MJ eq (CED)
and 1.61 kg CO2 eq (GWP) were attributed to thegasoline product per FU. Turning to a whole systemperspective, a promising net energy ratio of 4.69 wasestimated according to the potential energy output of all
the products as a whole.
As shown in Fig. 2, a total negative CED value wascomputed for the gasoline product. This favorable result
is closely linked to the avoided burdens approach, which
considers co-products as substitutes for conventional
refinery products. The CED category was extremely
influenced by the energy discounts for the co-products.
30.00
15.00
0.00

CED (MJ eq)-15.00-30.00-45.00-60.00-75.00-90.00Fig. 2. Contributions to CED (results per FU).
As observed in Fig. 3, thermal energy production anddirect emissions to air arose as the main sources ofGWP. On the other hand, GWP discounts associatedwith the co-products significantly offset the greenhousegas emissions brought about by the assessed system.

interiores libro.indd 178

1.20
0.90

GWP (kg CO2 eq)

Inputs from the technosphere
Waste LDPE film
2.94
kg
Water
5.88
kg
Electricity energy
0.17
kWhThermal energy
17.52
MJ
Outputs to the technosphere: products
Gasoline fraction
1.00
kg
Diesel fraction
0.09kg
Gas fraction
1.50kgChar
0.03kgOutputs to the technosphere: wastes to treatment
Ash to landfilling
0.05kgSolid waste to incineration
0.14kgOutputs: direct emissions to air
1.01kg
CO2
0.88
g
NOx
5.88g
SO2

1.50

0.60
0.30
0.00

-0.30
-0.60
-0.90

Fig. 3. Contributions to GWP (results per FU).
Even though this preliminary assessment led toencouraging values for the CED and GWP indicators,
further aspects need to be evaluated. For instance, if amore thorough environmental assessment is desired,additional impact categories should be comprised (e.g.
ozone layer depletion, acidification, eutrophication, etc.).

4. Conclusions
The processing of waste agricultural LDPE films through
SPCR to produce gasoline blending components wasevaluated in terms of its life-cycle CED and GWP
indicators. An appropriate energy and global warming
performance was concluded, though improvement
actions are needed to minimize the thermal energy
demand. Further efforts are required to (i) gather specificinventory data from industrial or pilot scale experiences,(ii) evaluate alternative methodological choices, and (iii)
include additional impact categories.

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[3] J. Aguado, D.P. Serrano and J.M. Scola. Fuels fromwaste plastics by thermal and catalytic processes: Areview. Industrial & Engineering Chemistry Research 47(2008) 7982-7992.
[4] ISO 14040:2006. Environmental management – LifeCycle Assessment – Principles and framework,
International Organization for Standardization (2006).
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