Catalysis Communications 11 (2010) 763–767
Catalysis Communications
Fe-containing magnetic ionic liquid as an effective catalyst for the glycolysis
of poly(ethylene terephthalate)
b
b,
Hui Wang a, Ruiyi Yan a,b, Zengxi Li a, , Xiangping Zhang , Suojiang Zhang
*
*
a Graduate University of Chinese Academy of Sciences, Beijing 100049, China
b State Key Laboratory of Multiphase Complex System, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The depolymerization of poly(ethylene terephthalate) (PET) in ethylene glycol could be catalyzed by imi-
dazolium-based Fe-containing ionic liquid, 1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]-
FeCl4). This magnetic ionic liquid exhibits higher catalytic activity for the glycolysis of PET, compared
with FeCl3 or ionic liquid, 1-butyl-3-methylimidazolium chloride ([bmim]Cl). Investigation also shows
that the onset reaction temperature of the glycolysis process catalyzed by [bmim]FeCl4 is much lower,
being 140 °C. The proposed mechanism indicates that the high catalytic activity of [bmim]FeCl4 is attrib-
uted to the synergic effect of its cation and anion.
Received 11 December 2009
Received in revised form 2 February 2010
Accepted 9 February 2010
Available online 12 February 2010
Keywords:
Poly(ethylene terephthalate)
Magnetic ionic liquid
Catalysis
Ó 2010 Elsevier B.V. All rights reserved.
Glycolysis
Synergic effect
1. Introduction
the bis(hydroxyethyl) terephthalate (BHET) monomer [3]. How-
ever, it is difficult to separate the catalysts from the depolymerized
The amount of plastic production has been increasing signifi-
cantly year by year, with uses including fiber, packing, container,
building materials, etc. [1]. Plastics offer a tremendous conve-
nience for our life. However, the proliferation of plastic uses has
raised waste disposal issues. In recent years, disposal of waste
materials has come into focus as an environmental problem that
affects everyone. Poly(ethylene terephthalate) (PET) resin, a com-
mon form of plastics, has excellent characteristic features such as
thermal stability, clarity, transparency, light, and processability.
The amount of PET consumption has rising each year, used for pro-
ducing fibers, textiles, video and audio tapes, food packing and
containers [2]. With the increasing of PET consumption, its recy-
cling has received considerable attention for the ecological and
economic considerations.
Glycolysis of PET is one of the most widely studied processes for
PET degradation. This process is carried out most frequently using
ethylene glycol [3,4], diethylene glycol [5,6], propylene glycol [5,7],
and dipropylene glycol [6]. The glycolysis reaction is very sluggish
when performed without a catalyst. Traditionally, the glycolysis of
PET is catalyzed by metal acetates [3,8], titanium-phosphate [9],
solid superacids [10], metal oxides such as copper oxide [11], etc.
These catalysts show high catalytic activity, with good yield of
products. Thus, the property of the products would be influenced.
In our previous study, we have found that ionic liquids could cat-
alyze the depolymerization of PET in ethylene glycol [12]. But long
reaction time and large amount of catalyst were required for high
conversion of PET in the glycolysis catalyzed by ionic liquids such
as 1-butyl-3-methylimidazolium chloride ([bmim]Cl). Recently, we
have found that magnetic ionic liquid (MIL) has good catalytic
activity for the glycolysis of PET.
Magnetic ionic liquid is basically a kind of ionic liquid (IL). The
only difference between IL and MIL is that MIL is magnetic. MILs
have the unusual properties of ILs, including extremely low volatil-
ity, high thermal stability, nonflammability, high ionic conductiv-
ity, etc. Besides, they show a strong response to a magnetic field.
Hayashi et al. have found that 1-butyl-3-methylimidazolium tetra-
chloroferrate ([bmim]FeCl4) is nearly paramagnetic, having a large
magnetic susceptibility of 40.6 ꢀ 10ꢁ6 emu/g [13]. It is also re-
ported that magnetic ionic liquids could be separated from other
solvents by a combination of magnetic field and conventional
methods such as filtration, ultracentrifugation, and adsorption
[14]. [Bmim]FeCl4 has already been used in synthesis [15–17],
catalysis [18], etc. However, there is no report on the use of MIL
in the catalysis of depolymerization of PET.
In the present study, [bmim]FeCl4 was synthesized and used to
catalyze the depolymerization of PET in ethylene glycol. This mag-
netic ionic liquid shows better catalytic activity than metal salt,
FeCl3, or ionic liquid, [bmim]Cl.
* Corresponding authors. Tel.: +86 10 88256322; fax: +86 10 88256093.
1566-7367/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.