5-7 OCTOBERISFR2011

171

TOLEDO (SPAIN)ENVIRONMENTAL EVALUATION OF GLYCOLYSIS AND HYDROLYSIS OF PETWASTE USING LIFE CYCLE ASSESSMENT
M. Calero1, J.L. Martí1, B. Ferreira1, M. Arieta2, L. Martínez3, and A. Aguado3
1ITENE. C/Albert Einstein, 1. 46980 Paterna (Valencia)
2GAIKER. Parque Tecnológico, Edificio 202, 48.170 - Zamudio – Bizkaia
3CARTIF. Parque Tecnológico de Boecillo, 205.47151 Boecillo. Valladolide-mail:mcalero@itene.com

Abstract
The concern about alternative plastic end-of-life management processes as well as the decrease of environmental impacts isincreasing in the last few years. Two different feedstock recycling processes (glycolysis and hydrolysis) for the recovery of
PET are compared in this paper from an environmental point of view using the LCA methodology. A cradle-to-gate approachand Eco-Indicator 99 has been used to assess environmental impacts. Avoided impacts from the production of BHET inglycolysis and TPA in hydrolysis have been considered. Electricity in both end-of-life processes is the main responsible ofimpacts for most categories. This is due to that laboratory data such as energy consumption of the equipment has been usedin the analysis. In addition, ethylene glycol and hydrochloric acid in glycolysis and hydrolysis respectively, have relevant
impacts for respiratory effects on humans caused by organic substances category. Glycolysis presents a better
environmental profile than hydrolysis. However, results of glycolysis and hydrolysis environmental impacts are quite similar.

Keywords: Feedstock recycling, Plastic, environmental impact, LCA, End-of-life

1. Introduction
The production and consumption of plastic products hasbeen increasing around 9% since 1950 [1], being thedemand from European converters 45 million tonnes in2009, with 8% corresponding to PET. The packaging
sector is the largest application for plastics, with a market
share of 40.1% [2]. Although plastic end-of-life
management improves yearly, 11.2 million tonnes ofdomestic post-consumer plastic waste were disposed atlandfill in 2009 [2]. Hard coloured, multilayer or highly
contaminated PET is included in this waste landfilled,
since their mechanical recycling doesn’t allow getting a
good-quality secondary raw material. Therefore,
feedstock recycling processes, like glycolysis andhydrolysis, have been studied in PROQUIPOL project inorder to give an added value to this PET packaging
waste, obtaining bis (hydroxyethyl) terephtalate (BHET)and Purified Terephthalate Acid (TPA) respectively.
Environmental impacts of both processes have been
compared using Life Cycle Analysis (LCA) methodology.
These LCA results are included in this paper.

2. Materials and Methods
The environmental assessment of the two end-of-life
options was made through LCA using a cradle-to-gateapproach. Environmental impacts were assessed
according to the Eco-Indicator 99 v 2.1 methodology inIndividualist (I) perspective.
The goal and scope of the LCA was to assess andcompare main environmental impacts of two feedstock

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recycling processes, hydrolysis and glycolysis, for PET
packaging waste.
The functional unit of the study is to feedstock recycle
100g of PET waste.
The origin of the PET waste used both for hydrolysis andglycolysis was the domestic packaging waste stream
from Spain. This study does not include impacts
associated to the generation of the PET waste.
Sub-processes considered in glycolysis were shredding,glycolysis, extraction-filtration, crystallization-filtration anddrying. For hydrolysis, shredding, hydrolysis, filtration,
precipitation-filtration and drying were the sub-processes
included.
Compilation of primary data for glycolysis was gatheredfrom CARTIF and for hydrolysis from GAIKER
laboratories. In addition, Ecoinvent data base was usedas secondary data.
Since monomer and acid were formed from both
feedstock recycling processes, avoided impacts wereincluded in the analysis as a bonus for both end-of-life
options. BHET and TPA industrial manufacturing werethe processes avoided for glycolysis and hydrolysis,
respectively.

3. Results and Discussion
Results of the LCA for glycolysis and hydrolysis of PET
waste were first analysed separately and subsequently,
compared one to another.
Figure 1 shows the relative contribution to environmental
impacts for each input on the glycolysis of the PET life
cycle.

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6th International Symposium on Feedstock Recycling of Polymeric Materials
LCA Impact assessment
PET Glycolysis

LCA Impact Assessment PET Glycolysis & Hydrolysis

100%

100%

80%80%60%

BHET

60%

Water

Glycolys is

Liquid Nitrogen

40%

Ethylene glycol

Hydrolys is
40%

Electricity
20%

20%
0%

0%
Carcinogens-20%
Carcinogens

Resp. organics

Resp. inorganics

Climate change

Radiation

Ozone layer

Ecotoxicity

Acidification/
Eutrophication

Land use

Resp. organics

M inerals

Resp.
inorganics

Climate change

Radiation

Ozone layer

Ecotoxicity

A cidif ication/
Eutrophication

Land use

Minerals

Im pact Cate gor ie s

Im pa ct Ca te gorie s

Fig.1 Environmental impacts of the glycolysis of PET
waste.

Fig.2 Environmental impacts of the hydrolysis of PETwaste.

Electricity is the process which causes the majority of theimpacts in most of the categories and its contribution issimilar to all of them except for respiratory effects onhumans caused by organic substances category (fromnow on respiratory organics). These impacts are due toemissions generated in the combustion of coal and lignite
used during electricity production. In respiratory organics
category, main impacts are caused by the electricity andthe Ethylene glycol (EG) which generates non-methane
volatile organic compounds, ethene and methane
emissions from Ethylene production.
The input which influences in the second placeenvironmental impacts of glycolysis is the EG for
respiratory organics and inorganics, climate change,acidification/eutrophication and use of minerals
categories. Whereas for carcinogenic, radiation, ozone
layer, ecotoxicity and land use categories it is liquid
nitrogen (N2) and specifically, due to electricity requiredfor its manufacturing.
Negative values show avoided impacts from themonomer of BHET obtained in the glycolysis of the PET.
For respiratory organics, avoided impacts of BHET
represent 18% of the total for this impact category.
Figure 2 shows, for each input on the hydrolysis of thePET life cycle, the relative contribution to environmentalimpacts.

Hydrolysis of PET waste has greater impact thanglycolysis for most impact categories, although thesedifferences are no too large.
In order to facilitate comprehension of results, impact
categories have being aggregated. In carcinogenic,
respiratory of organic and inorganics, radiation,
ecotoxicity, acidification/eutrophication and land use
categories, hydrolysis present slightly higher impacts
than glycolysis. In ozone layer category differences arehigher due to Hydrochloric acid production whereas in
respiratory organics, differences are caused by EG
production. In climate change and minerals, impacts
among glycolysis and hydrolysis are similar though foreach of them, have different sources.

LCA Impact assessment
PET Hydrolysis
100%

80%

60%

TPA
Water
Sodium hydroxide40%Hydrochloric acidElectricity

20%

0%

-20%
Carcinogens

Resp. organics

Resp. inorganics

Climate changeRadiation

Ozone layer

Ecotoxicity

Acidification/Eutrophication

Land use

M inerals

Impact Categories

Fig.2 Environmental impacts of the hydrolysis of PET
waste.
Electricity is again the main responsible of the impacts
for all impact categories. Ozone layer is the sole impact
category which is influenced by other process
significantly which is caused by the Hydrochloric acidproduction process.
For all impact categories, Sodium Hydroxyle has an
impact of less than 1,5% of the total.
Avoided impacts are shown in Figure 2 as negative
figures. For respiratory organics, avoided impacts
represent 23% out of the total and are due to TPA
production from Paraxilene.
Finally, both feedstock recycling processes werecompared in order to analysed which present higher
environmental impacts.
Figure 3 shows the comparison of environmental impacts
among glycolysis and hydrolysis.

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4. Conclusions
Glycolysis presents lower environmental impacts thanhydrolysis of PET packaging waste. However it should
be highlighted that these differences are not relevant for
many impact categories.
The majority of the impact in all categories is caused byelectricity consumption of equipment used since bothglycolysis and hydrolysis processes have been carriedout at laboratory scale. Energy consumption of lab
equipment is much higher than industrial machinery. Thisfact has been identified and it is actually being studied.
On the other hand, the solvent used for glycolysis (EG)and the Hydrochloric acid for hydrolysis have around
20% of the total impact in respiratory organics category.
Nevertheless, it should be considered that EG impact
can be recovered by evaporation and reusing in further
glycolysis processes.
Next steps in Proquipol project will be scaling feedstock
recycling process throughout pilot trials. Then,
environmental impacts closer to industrial conditions areexpected.

References[1] Eurostat / PlasticsEurope Market Research Group(PEMRG), "European Union (EU27) Plastics Industry
Production"[2] PlasticsEurope "Plastics – the Facts 2010. An
analysis of European plastics production, demand andrecovery for 2009"

Acknowledgement
This research has been done in the framework of theproject “Development of sustainable chemical processes
for the conversion of polymeric waste into resources(Proquipol) PID-560620-2009-4” funded by the Ministryof Science and Innovation of Spain.

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