Recovery of phenols from bisphenol A polycarbonate in the presence of MgO
G. Grause, R. Kaerrbrant, T. Kameda, T. Yoshioka*
Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki-aza, Aoba-ku, Sendai, Miyagi 9808579, Japane-mail: yoshioka@env.che.tohoku.ac.jp; phone & fax: +81-22-795-7212

Abstract
Polycarbonate was hydrolyzed and pyrolyzed in the presence of MgO as bed material of a fluidized bed reactor. Pyrolysis
was carried out at 480 °C and hydrolysis between 350 and 500 °C. Pyrolysis resulted mainly in residue, while significant
amounts of phenols were obtained from hydrolysis. The highest BPA yield (26 wt%) was achieved at 400 °C. At lower
temperatures more phenol and IPP were obtained as products from the fission of BPA, probably because of the reducedhydrolysis rate. At higher temperatures, BPA was degraded and high phenol yields were obtained. At any temperature,
about 40 wt% of high boiling products were observed, indicating the volatilization of oligomeric material.

Keywords: Chemical recycling; Monomer recovery; Fluidized bed

1. Introduction
Poly(bisphenol A carbonate) (PC) is the most usedpolymer within the family of polycarbonates. PC is
produced in large volumes and in Japan alone made up
for 3.4% of the total thermoplastic resin production for thefirst four months of 2012 [1]. PC is generally used for its
transparency, strength, and heat resistance. It is used
e.g. in the production of optical storage media, reusable
water bottles, and automobile headlights.
PC can be recycled by both mechanical and chemicalmethods. Mechanical recycling is applicable forcontrolled and cleaned waste streams, but falls short if
the waste is of a more inhomogeneous type. Due to theester bonds of PC, hydrolysis is a common approach forchemical recycling. However, water as a solvent in thehydrolysis of PC requires subcritical conditions at highpressure, making the process uneconomical. The use oforganic solvents often lead to problems in the separation
stage and solvent treatment requires special efforts. Also,
the use of solvents in the case of impurities might result
in contaminated recyclate.
As an alternative to liquid systems, this work focuses onhigh temperature steam and MgO as a catalyst. MgO
was previously found to be effective in promoting thedegradation of PC into compounds such as
isopropenylphenol (IPP), bisphenol A (BPA), and phenol[2] using a fixed bed reactor. In order to investigate thereaction under real processing conditions, a fluidized bed
reactor was used. In contrast to a fixed bed, a fluidized
bed is characterized by high heat transfer, ensuring morestable reaction conditions and a uniform temperature
profile.

2. Materials and Methods
The materials used for this investigation were PC(Panlite® AD-5504, Teijin) and MgO (beads 98%, Sigma-Aldrich). The PC was ground and sieved to obtain aparticle size of less than 0.5 mm, while the bed material(MgO) was ground and the fraction with a particle size
between 0.3 and 0.5 mm was used.

Fig. 1. Fluidized bed plant.
Experiments under hydrolysis conditions were performed
between 350 and 500 °C in a laboratory scale fluidized
bed plant (Fig. 1). One experiment under pyrolysis
conditions was carried out at 480 °C in the same plant.
Under hydrolysis conditions the fluidizing gas was madeup from steam. A small side stream of N2 (0.5 l min-1,room pressure and temperature) was used to keep
reaction gas from entering the feeders. Under pyrolysis
conditions the reaction was performed in N2 atmosphere.
An overpressure of around 5 kPa was maintained in bothexperiments in order to prevent air from entering theplant. PC was fed at a speed of 100 g h-1 and theproducts were condensed in a series of coolers.
Solid products from the hydrolysis were separated into
organic and inorganic compounds by continuous
extraction using diethyl ether; distillation at reducedpressure was used for pyrolysis products, resulting in alow (bp < 290 °C) and a high boiling fraction (bp >290 °C). Liquid and gaseous products were analyzed byGC-FID, while the H2 content of the gaseous fraction wasdetermined by GC-TCD. For the qualitative analysis, the

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

retention times of compounds from the GC-FID werecompared with those from GC-MS equipped with thesame type of column, using the same temperature
program.

3. Results and Discussion

polycondensation modifier, indicating a average molar
weight of about 10,000 g mol-1. At any temperature,
about 40 wt% left the reactor in the form of high boilingproducts. It can be assumed that volatile oligomericmaterial left the reactor before the hydrolysis wascompleted. Only CO2 was observed in the gas phase at
any temperature.
a)Fig. 2. Product distribution.
b)
3.1

Fluidized bed pyrolysis

The pyrolysis reaction at 480 °C yielded 14.4 wt% gas,29.9 wt% low boiling oil, 16.7 wt% high boiling oil and 39wt% solid residue (Fig 2). The gas mainly consisted of
CO2 and CO. Other gaseous products were methane,hydrogen, ethylene, ethane, propylene, propyne andbutenes. All were found in levels of less than 0.5 wt% of
the total organic input.
More than one hundred different products were found in
the low boiling oil (Fig. 3a). However, only a few werefound in a significant amount. Main products werephenols. Small amounts of other aromatic compounds
were also found. The amount of heavy oil and residue
was problematic as the high viscosity of the oil caused
plugging in coolers, resulting in problems in the reactor
operation. The residue also had a strong negative effectupon the reaction as it caused defluidization of the bedmaterial.
3.2

Fluidized bed hydrolysis

Compared with the pyrolysis, far less residue wasobtained from the hydrolysis of PC (Fig. 2). Almost
20 wt% of unreacted material was found in the reactor at350 °C, suggesting a low reaction rate at thattemperature. About 40 wt% of low boiling products wasfound at any temperature, consisting of phenols. The
highest BPA recovery (26 wt%) was achieved at 400 °C.
At 350 °C, BPA was degraded to phenol and IPP,
probably because of the slow hydrolysis rate, resulting ina longer residence time of PC in the reactor. At highertemperatures, the degradation of BPA was accelerated
and more phenol was found. Also IPP was degraded,
resulting in a rising phenol yield [2]. The tert-butylphenol
yield was independent from the temperature. It can beassumed that tert-butylphenol was present as

Fig. 3. Composition of the low boiling phase: a) pyrolysis
at 480 °C, b) hydrolysis.

4. Conclusions
The use of steam hydrolysis in a MgO filled fluidized bed
reactor for the chemical recycling of PC showed apromising way to increase the amount of phenolicproducts. The reduced amount of residue produced in
the reactor allows a long utilization of the catalyst before
deactivation. In contrast, pyrolysis of PC caused
defluidization and large amounts of high boiling products
and residue were produced. 400 °C was found to be themost promising temperature for PC hydrolysis. At a lowertemperature, the hydrolysis rate is too slow and BPA
fission occurs before hydrolysis. At higher temperatures,
BPA is degraded before it can leave the reactor.

References[1] http://www.jpif.gr.jp/english/statistics/monthly/2012/20
12_production_materials_e.htm , accessed 120719.
[2] G. Grause, K. Sugawara, T. Mizoguchi, T. Yoshioka.
Polym. Degrad. Stab. 94 (2009) 1119–1124.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013