Quimico

D. Spaseska, M. Civkaroska
Journal of the University of Chemical Technology and Metallurgy, 45, 4, 2010, 379-384

ALKALINE HYDROLYSIS OF POLY(ETHYLENE TEREPHTHALATE) RECYCLED
FROM THE POSTCONSUMER SOFT-DRINK BOTTLES
D. Spaseska, M. Civkaroska
Faculty of Technology and Metallurgy
“SS Cyril and Methodius” University of Skopje
Republic of Macedonia

Received 30 June 2010
Accepted 28September 2010

ABSTRACT
The post consumer Poly (ethylene terephthalate)PET) recycling science was initiated by the fact that this polymer
was non-degradable in nature, since its molecules were too large to decompose. There has been a growing need, however,
for a chemical recycling process as one of the most successful method for post-consumer PET transformation into
monomers. The solution ofthis problem seems to be in the creation of remunerative processes, for which post-consumer
PET is used as a source material.
This paper presents a review of works that cover PET waste recycling with alkaline hydrolysis of post-consumer
bottles for their depolymerization to monomers (terephthalic acid). The process is carried out with sodium hydroxide and
trioctyl methyl ammonium bromide(TOMAB) as catalyst within a relatively short time and temperature.
A mathematical model of PET recycling has been derived according to the definition of a 23 factorial experimental
design. The influence of the main factors on the alkaline hydrolysis conversion of the PET, as expressed by the yield of
terepthalic acid (TPA), in ascending order, includes the process temperature and the amount ofcatalyst, but the hold-up
time is negligible.
Keywords: PET recycling, hydrolysis conversion, terephthalic acid, factorial experimental design, mathematical
model of the process, hydrolysis time, amount of catalyst, hydrolysis temperature.

INTRODUCTION
Plastics make up a high proportion of waste the
volume and range of which increases dramatically. Although plastics make up between 5 mass %and 15% mass
of municipal solid waste it comprises 20-30 % of the
volume [1]. Most plastics are non-degradable and take
a long time to decompose, possibly up to hundreds of
years – although no one knows for certain as plastics
have not existed for long enough, since they started to
be land filled.
PET is one of the versatile engineering plastics
that are widely used in manufacturing of highstrength
fibers, audio and video tapes and various types of packaging, mainly soft drink bottles and jars [2-4]. The
majority of the world PET production is for synthetic
fibers (in excess of 60 %) with bottle production accounting for around 30 % of global demand. One of the
main reasons for the widespread use of PET is the pos-

sibility for producing a number of different grades over
abroad range of molecular masses in a single
multiproduct polymerization plant [5]. A very important feature of PET, decisive in the choice of its wide
application in the manufacture of packaging for the food
industry is that it does not have any side effects on the
human beings. It should be pointed out, that PET does
not create a direct hazard to the environment but, due
to its substantialfraction by volume in the waste stream
and its high resistance to the atmospheric and biological agents, it is seen as a noxious material [2]. Therefore, the recycling of PET does not only serve as a partial solution to the solid waste problem but also contributes to the conservation of raw petrochemical products and energy.
The huge amounts of PET products cause serious environmental pollution,because commonly PET
content reaches about 12 % in municipal plastic waste
showing a slow rate of natural decomposition [1,6]. PET

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Journal of the University of Chemical Technology and Metallurgy, 45, 4, 2010

recycling is very important for at least two main reasons: firstly, to reduce the increasing volumes of plastic
waste and secondly - to generate value-added materials
from...