PARTⅤ SOLVOLYSISSOLVOLYSIS OF ON-LINE IDENTIFIED AND
REFUSED HIGHLY COLOURED AND COMPLEX PETPOST-CONSUMER WASTE BOTTLES AND PACKAGES
S.Arnaiz*1, A.Asueta1, M.Arieta-araunabeña1, D.Manjón1, R.López-Fonseca2,
J.I.Gutiérrez-Ortiz2, I.Duque2
12

GAIKER-IK4 Technological Centre, E-48170 Zamudio (Spain)
Chemical Engineering Department, Faculty of Science and Technology, The BasqueCountry University - UPV/EHU, P.O. Box 644, Bilbao E-48080, Spain.
E-mail: arnaiz@gaiker.esAbstract: The relevancy of this paper is based on the global scientific understanding andtechnical approach to the use of on-line polymer identification for sorting PET post-consumer
waste bottles and packages in two fractions and their coupling with the requirements of theirsubsequent recovery steps. The fraction containing light coloured and monomaterial PET will
be derived to mechanical recycling and the one having highly coloured and complex
multilayered PET to feedstock recycling.This work is focused to go in deep in that need andtry to correlate inlet feed properties, reaction parameters and catalyst selection with exit
stream conditioning requirements and product quality.
1. Introduction
Nowadays, due to the general awareness about environmental issues in the society, it isnecessary the improvement of technologies for the treatment and recycling of plastic wastes.
PET consumption worldwide almost has doubled during the last years, having passed from 5
million tonne in the year 2000 to near 10 million tonne in the year 2006, being soft drink andmineral water bottles have been the applications in which major growths have been registered.
In the same way that the consumption has increased, the waste generation and its collection,sorting and recycling, supported by the integrated waste management systems, have presented
the same trend, so that in the year 2005 almost 2.5 million tonne were collected in the wholeworld, and it is foreseen that in year 2010, this quantity will reach on 4 million tonne [1].
Additionally to material itself demand, needs of content preservation have been
responsible for the development of barrier materials and marketing strategies favoured theintroduction of high coloured materials associated to brands and quality perception. Currently,
one emerging challenge associated to PET recycling, is to provide a suitable treatment to thehighly coloured and complex multilayered post-consumer waste fractions of PET. Bothfractions are not convenient to be mixed with transparent and slightly coloured PET and- 215 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
hence does not exist for them a different alternative to disposal. These fractions are notappropriate for mechanical recycling because derived products present limitations either incolour, transparency or intrinsic viscosity, restricting their applications and value. In
accordance with this, the present work proposes feedstock recycling as alternative ofmanagement for this non mechanically recoverable fractions, even though this option has not
begun to apply until recent dates and at preset only covers the treatment of 0.4% of the total
plastic waste collected in Europe.
In this work, NIR spectroscopy and other on-line techniques have been applied forsorting the post-consumer waste streams of PET bottles and packages in two fractions, one
containing the slightly coloured and monomaterial PET, to be mechanically recycled and theother one the high coloured and complex multilayered PET to be derived towards feedstockrecycling. Additionally, the study PET glycolysis process has done. The reaction consists ofthe degradation of polymer at temperatures in the range of 180-240°C, atmospheric pressure,with an excess of ethylene glycol (EG) and the presence of a catalyst which promote theformation of bis(hydroxyethyl) terephtalate (BHET) [2]. In principle, glycolysis conditions
allows to use reduced amounts of reagents as well as low operation temperatures andpressures when compared with other methods such as methanolysis or thermal degradation[3-5], while hydrolysis under alkaline or acid conditions involve serious environmental
problems associated with corrosion and management of the liquid effluent [6]. BHET, after
adequate purification, is used in PET synthesis, or in the production of other polyesters,
polyurethanes, plasticizers, epoxy resins, additives for textiles and biocompatible materials[7-12]. These numerous applications, in turn, provide an economical flexibility when using
the raw monomer for the most profitable option upon demand.
2. Experimental
2.1 Materials
During this research work a virgin PET (Lighter S93 PET Copolymer) supplied byEQUIPOLYMERS and samples of highly coloured and complex multilayered post-consumer
PET wastes provided by ECOEMBES, the Spanish integrated management system for thelight packaging waste, have been used. The information related with PET materials is shownat Tab.1.
Post-consumer PET waste bottles and packages have been grinded to 5 mm flakes and,in order to avoid dirtiness effects at reaction tests, cleaned with diluted caustic soda, rinsed
with water and dried. PET clean flakes have been milled by using a cryogenic mill to 250 µmto minimise diffusion controlled regimes at reactor. The solvent, EG (ehylene glycol 99%),
has been purchased from ALDRICH and Zn(Ac)2·2 H2O (zinc acetate dihydrate 99.5%), thecatalyst, from PANREAC. Trying to simulate reaction conditions expected to be found atindustrial plants, reagents have been used directly without any further purification.

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PARTⅤ SOLVOLYSIS
Tab.1 PET materials tested in glycolysis reactions
OriginVirginPost-consume

Post-consume

Post-consume

Post-consume

Post-consume

Post-consume

NatureNaturalHighly-col
ouredHighly-coloured

Highly-colouredHighly-colouredHighly-colouredMulti-layered

ColourTransparent

Blue

SilverGreenWhite

Mixed

Amber

Application

PelletBottles

Bottles

Bottles

Bottles

VariousBottlesContent---Water

Soft drinkSoft drink

Various

Various

Beer

Photo

2.2 Automatic identification tests
A commercial automatic identification and sorting system, the UnisortÒ manufactured
by RTT Systemtechnik, has been used for the post consumer waste PET packages
identification and sorting tests. The system comprises: an acceleration belt, an identification
belt, a sensor head with 32 probes, two nozzle groups for classification by blowing air, acollecting hood and an operation and control unit. Identification tests have been carried out
with representative samples of post-consumer PET wastes in order to measure separation andpurity rates.
2.3 Glycolysis of PET
Glycolysis experiments have been carried out in a 250 mL, a three necked, flat bottom
glass reactor equipped with thermometer and condenser operated at atmospheric pressure. A
stirrer is incorporated to the tank to assure proper mixing and turbulence. In all runs, 30 g ofPET together with 1% catalyst by weight basis were charged to the reaction system. Firstly, aset of reactions with virgin PET have been carried out to assess the influences of time,
temperature and EG/PET ratio and select the appropriate conditions for the depolymerisationof post-consumer highly coloured or complex multilayered PET. Recovery of product after
each glycolysis run has been completed by adding boiling water into the reactor, keeping themixture at 100°C during 20 min and stirring vigorously. Once BHET oligomers are
precipitated, the mixture has been filtrated and the recovered liquid has been refrigerated at5°C during 5 h to assure BHET precipitation. After the filtration to separate BHET from EG,
BHET has been dried at 60-80°C during 3 h for later analysis.
2.4 Analysis of glycolysis products
A FTIR spectrophotometer (Nicolet Protegé 460 Model) has been used to identify thechemical structure of BHET. Samples were mixed with KBr (2:100) and the mixture wasconverted into a disc by mean of a press, applying a pressure of 3.5·104 N·cm-2. A DSC- 217 -The 5th ISFR (October 11-14, 2009, Chengdu, China)(Mettler Toledo DSC822e Model), has been used for thermal analysis of BHET. Samples
were heated from room temperature to 350°C with a heating rate of 10°C/min under anitrogen stream of 15 mL/min.
3. Results and discussion
3.1 Automatic identification tests
Representative samples of the plastic fraction coming from the post consumer lightpackaging waste stream collected by ECOEMBES has been studied by means of a NIR
spectrometer. The NIR spectra of both plastic materials (PET, HDPE, PVC, LDPE, PP, PS)
and non-plastic materials (wood, paper, aluminium film), usually found due to theirapplication at packaging, have been recorded and examined. As shown at Fig. 1 and Fig. 2 ,PET spectrum presents a distinctive peak at 1,657 nm which made possible to differentiate
packaging materials including this polymer from the others.

Fig. 1 PET and other polymers spectra

Fig. 2 PET and no-polymers spectra

On-line identification of the PET fraction and subsequent automatic sorting of it, withhigh yield and purity, has been possible using the UnisortÒ system. Recognition highly
coloured and multilayered PET materials haves not been successful by NIR. Image analysis
and colour sorting technology is proposed for the segregation of those fractions in a second
separation step.
3.2 Glycolysis reactions
Time, temperature and PET/EG ratio have been chosen as the independent variables forthe glycolysis study, setting catalyst/PET ratio on 1% by weigh. Run #1 at Tab. 2 has been
carried out using virgin PET for studying the evolution of BHET yield with time. Reaction
progress at 20 min, 40 min, 1, 2, 3, 4, 5 and 8 h is shown on the curve at Fig. 3. Run #2 hasbeen used to compare reaction rate without catalyst that has been confirmed slower. Although
run #1 verified that catalysed reaction reached equilibrium after 2 h, in order to shorten
duration of preliminary work, it has been selected a time of 1 h to determine the influence of
the independent variables. Runs #1, #3 and #4 have been respectively carried out at 165, 180- 218 -PARTⅤ SOLVOLYSISand 196°C and confirmed the need for operating at the maximum reachable temperature that,in practice, corresponds to the closest one to the boiling point of glycol at atmosphericpressure. The achieved BHET yields at a given time with temperature are represented at Fig. 4.
Finally, runs #5 and #6 have been completed at 1:4.5 and 1:6.75 PET/EG molar ratios andverified that the 1:9 is the value required for getting a reasonable BHET yield as plotted
at.Fig.5.Runs #7 to #12 at Tab. 2 are the glycolysis of the highly coloured and complex
multilayered post-consumer PET wastes after 2 h at 196°C and 1:9 PET/EG ratio. After
representing at Fig.6 the BHET yields it has been found that the PET nature does not havesignificant influence but on the cases of white and multilayered materials.
Tab. 2 Glycolysis reactions with virgin PET and post-consumer waste PET
Runt (h)T (°C)

PETNature

PET (g)

PET/EG(mol/mol)

ZnAc2/PET(w/w)

BHET
yield (%)

#18196

Virgin

30

1:91%

79.06

#28196

Virgin30

1:9---67.74#31165

Virgin

30

1:91%

46.99

#41180Virgin

30

1:91%

78.77

#11196

Virgin

30

1:91%

79.99

#51196

Virgin

30

1:41%

61.96

#61196Virgin30

1:6.75

1%75,70#12196

Virgin30

1:91%

79.32

#72196

Blue30

1:91%

76.16

#82196Grey30

1:91%80.20#92196

Green30

1:91%

78.37

#102196

White30

1:91%

72.99

#112196

Brown

30

1:91%

80.46

#122

196

Multilayered

30

1:91%

69.86

3.3 Analysis of glycolysis products
DSC and FTIR analysis of BHET produced after the glycolysis of highly coloured andcomplex multilayered post-consumer waste streams of PET at runs #7 to #12 are illustrated inFig. and Fig. and compared with the one derived from virgin PET at run #1. In bothfigures, curves have been shifted to provide a better comparison. According to previous DSC
analysis, in which melting temperature of BHET and dimmer have been verified to be around
110°C and 170°C respectively, it has been assumed that main glycolysis product is BHET. On
the other hand, regarding FTIR studies it has been confirmed that, for a pure BHET, theabsorptions at 3.400, 3.000-2.800, 1.750 and 1100 cm-1 are respectively due to -OH, C-H,- 219 -The 5th ISFR (October 11-14, 2009, Chengdu, China)

100

1008080

BHET yield, %60
1% ZnAc2/PET40

Non catalyzed

2060
40
200024608160

170Time, hFig. 3 Time effect on BHET yield (virgin
PET glycolysis at T=196°C, PET/EG=1/9)8080BHET yield, %

100

200

60
40
2080,579,1 76,2 80,2 78,473,069,960
40200PET/EG (mol/mol)

Fig. 5 PET/EG ratio effect on BHET yield(virgin PET glycolysis at T=196°C, t=1 h)

50

100

150

200

250300350Whi

1:9Virgen

1:6,75teBrowMnultilaye
red01:4,5Blue

BHET yield, %190

Fig. 4 Temperature effect on BHET yield(virgin PET glycolysis at PET/EG=1/9, t=1 h)

1000180
Temperature, ºC

GreyG
reen

BHET yield, %C=O and C-O verifying that infrared spectra of glycolysis products correspond with the
BHET one.

Fig. 6 PET nature effect on BHET yield(glycolysis at T=196°C, PET/EG=1/9, t=2 h)

400

40

BHET of PET virgin-5

BHET of PET blue

3BHET of PET grey
BHET of PET greenAbs.

Wg-1-10-15

BHET of PET white

2

BHET of PET brown

BHET of PET virgin
BHET of PET blue

-20

BHET of PET grey

1

BHET of PET green-25

BHET of PET white
BHET of PET brown-30
T (ºC)BHET of PET multilayer

Fig. 7 DSC thermal analysis curves of BHET

00500

1000

1500

2000

2500

3000

3500

40004500

cm-1

Fig. 8 IR analysis curves of BHET

4. Conclusions
On-line NIR identification tests of PET materials for their subsequent automatic sorting
have been carried out by means of a commercial system. Results have shown that NIR is afeasible technology for sorting a PET fraction from other non-polymer and polymer based- 220 -PARTⅤ SOLVOLYSIS
materials at packaging waste stream but fails on the recognition highly coloured andmultilayered PET fractions among them that will requires image analysis and/or colour
sorting technologies for its segregation.
The glycolysis of virgin PET has been carried out under atmospheric pressure, with anexcess of ethylene glycol as chemical agent and zinc acetate dihydrate as catalyst. The
influence of glycolysis time, temperature and PET/EG ratio has been investigated, showingthat conversion rate depends significantly on these factors. The main products have been
BHET and oligomers. Once defined suitable operating conditions, highly coloured andcomplex multilayered post-consumer PET wastes have been depolymerised, getting BHET
yields up to 80%. These values have been similar to the one coming from virgin PET,
demonstrating that PET nature and colour has less influence on BHET yield than expected.
The DSC and FTIR results have verified that the BHET products derived from highly
coloured and complex multilayered post-consumer waste streams of PET have beenequivalent to the one derived from virgin PET. As a first step in a large project, glycolysis has
been verified as a promising option for the recycling of these non-mechanically recoverable
PET wastes that probably can be recycled by glycolysis as a mixture of highly coloured andcomplex PET materials.
Acknowledgments
The authors wish to acknowledge the confidence and economic support of the Spanish
Ministry of Science and Innovation to this work by financing the GLICOPLAST Project“Reference CTQ2008-06868-C02-02” and the supply of actual post-consumer waste samplesof PET by ECOEMBES.
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