Depolimerización De Pet

J. of Supercritical Fluids 62 (2012) 226–231

Contents lists available at SciVerse ScienceDirect

The Journal of Supercritical Fluids
journal homepage: www.elsevier.com/locate/supflu

Catalytic depolymerization of polyethylene terephthalate
in hot compressed water
Yingping Liu, Meixian Wang, Zhiyan Pan ∗
Department of Environmental Engineering, Zhejiang University of Technology, 18 RoadChaowang, Hangzhou, Zhejiang 310032, PR China

article

info

Article history:
Received 27 May 2011
Received in revised form 2 November 2011
Accepted 3 November 2011
Keywords:
Hot compressed water
Polyethylene terephthalate
Catalytic depolymerization
Terephthalic acid
Zinc acetate

abstract
Zinc acetate (Zn(Ac)2 ) catalyzed depolymerization of polyethylene terephthalate (PET) inhot compressed
water (HCW) was carried out in a batch autoclave reactor, as a potential method for chemical recycling
of waste PET. The effects of the ratio of Zn(Ac)2 to PET (0–3%), temperature (220–300 ◦ C), and reaction
time (5–60 min) were investigated. The optimal conditions for complete catalytic depolymerization of
PET were temperature 240 ◦ C, pressure 3.2 MPa, reaction time 30 min,and Zn(Ac)2 /PET ratio 1.5%. The
main products of catalytic depolymerization were identified and quantified as terephthalic acid and ethylene glycol by Fourier-transform infrared spectroscopy, high-performance liquid chromatography, gas
chromatography/mass spectrometry, and gas chromatography. The maximum yield of terephthalic acid
reached 90.5%. The phase behavior of PET with or without acatalyst in water during heating and cooling
was studied in a fused-silica capillary reactor. According to the phase change data, the temperature of
PET dissolution in HCW to form a homogeneous aqueous solution was decreased by adding Zn(Ac)2 .
© 2011 Elsevier B.V. All rights reserved.

1. Introduction
Polyethylene terephthalate (PET) is a thermoplastic polyester
with characteristics of highstrength, low density, low permeability
to gases (mainly CO2 ), and good aesthetic appearance (high lighttransmittance, smooth surface). PET is widely used for containers
for soda water, fruit juices, and carbonated drinks. In recent years,
the excessive use of PET in various industries has caused pollution
that has attracted worldwide attention [1,2]. As a result of recycling laws promulgated bymany nations, there is a growing need
for the development of post-consumer PET goods to ameliorate the
environmental impact and increase resource conservation [3]. At
the present time, PET is recycled mainly by mechanical and chemical methods [4]. Chemical recycling, through depolymerization of
PET into its monomers, is an ideal recycling method because, in
principle, PET can be recycledindefinitely [3].
Water is an ecologically safe substance that is widespread
throughout nature. The important studies by Franck’s research
group [5–7] of the properties of hot compressed water (HCW, here
sub-critical and supercritical water above 200 ◦ C and at sufficiently
high pressure) and its mixing behavior [7–9] highlighted the opportunity to use these extraordinary properties for chemicalreactions.
Some studies of the hydrolysis of PET have been reported. Depolymerization of PET to terephthalic acid (TPA) and ethylene glycol
(EG) in water at high temperatures (>250 ◦ C) has been investigated

∗ Corresponding author. Tel.: +86 571 88320061; fax: +86 571 88320061.
E-mail address: panzhiyan@zjut.edu.cn (Z. Pan).
0896-8446/$ – see front matter © 2011 Elsevier B.V. All rightsreserved.
doi:10.1016/j.supflu.2011.11.001

by Sato’s research group [10–12]. For the purpose of monomer recycling, Sato et al. [10] found that the yield of TPA increased to 97%
with increasing reaction temperature up to 420 ◦ C, and the maximum yield of EG achieved was 60% at 300 ◦ C. PET was completely
depolymerized in water after 10 min at 300 ◦ C, and the depolymerization of PET was enhanced...