The 5th ISFR (October 11-14, 2009, Chengdu, China)

HYDROLYSIS OF POLYCARBONATE USING
A FLUIDIZED BED REACTOR
Toshiro Tsuji*, Toshiaki Sugawara
Graduate School of Engineering, Hokkaido University
N13-W8, Kita-Ku, Sapporo 060-8628, Japan
E-mail: ttsuji@eng.hokudai.ac.jp
Abstract: The hydrolysis of polycarbonate was investigated to recycle the monomer ofBisphenol-A (BPA). Experiments were carried out with a laboratory scale sand bed fluidized
by superheated steam. The yield and the selectivity of BPA were examined under various
conditions such as bed materials, temperatures and feed rates. The production rate of BPA
increased with increasing temperature whereas the selectivity of BPA decreased withincreasing temperature. By using olivine sand as a bed material, the hydrolysis rate increased
remarkably due to the catalytic effect by minerals in the sand. When the olivine sand was used,
the yield of BPA increased with temperature up to 350 °C, and at the temperatures higher than
350 °C, the yield of BPA decreased due to the decomposition of BPA.
1. Introduction
Polycarbonate (PC) is one of the most widely used engineering plastics with high impact
strength, strong heat resistance and excellent electrical and optical properties. Its production
has been increasing in recent years, and this trend will continue. So, the developing of its
effective recycling method is desirable for conserving natural resources. Until now, manystudies about the degradation of PC have been reported. The examples include thedecomposition by alcohol in a liquid phase[1], the degradation in super critical water[2,3] andthe degradation by steam[4-6]. PC has the structure that BPAs are connecting through esterbond. This ester bond is easily broken by hydrolysis at high temperature, and the degradation
is promoted by the presence of alkaline earth metals[4,6]. In this study, we performed thehydrolysis of PC with a fluidized sand bed as a reactor to recover the BPA effectively. The
mixing of PC polymer with sand effectively increases the reaction surface of polymer withsteam. Also, the minerals in the sand revealed a remarkable catalytic effect on the hydrolysisof PC. Therefore the reaction can occur with steam at atmospheric pressure without any
organic solvent or expensive high-pressure vessel.

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2. Experimental
2.1 Material
The Polycarbonate used in this experiment was PC pellet (CALIBRETM 200-20,Sumitomo Dow Ltd.). The PC pellet was about 3 mm in size and was used without any
preparation. The bed materials used were silica sand, river sand and olivine sand produced inHokkaido prefecture.
2.2 Equipment and procedure
The experiments were carried out using a laboratory scale fluidized bed reactor with aninside diameter of 52 mm and a height of 600 mm (Fig.1). The reactor was heated to theprogrammed temperature from outside by an electric heater. Silica sand (130 g), river sand(135 g) and olivine sand(154g) were used as bed materials. Steam was generated by anelectrical heating tube and was preheated up to about 500 °C. In order to prevent steam fromflowing into a feeder unit, nitrogen gas was continuously sent into the feeder with a flow rateof 200 ml/min. PC pellets were continuously fed into the reactor for 15 min. The experimental
parameters such as amount of the feed material and reaction temperature are listed in Tab. 1.
The hydrolysis of PC occurs in the fluidized bed, and the vaporized product gas and steam
mixture leave the reactor and condenses in a cooling trap chilled with iced water. After eachexperiment, the solid products were filtered from the condensed water and were dried in avacuum for a whole day and night. The gas product was collected in a gasbag which wasreplaced at intervals of ten minutes.
N2
Polycarbonate
PID controller

FeederGasbag
Water out
Condenser

Distilled water
Steam generator

Water inSteamIce water bath
Fluidized bed

Fig.1 Schematic view of fluidized bed reactor- 85 -The 5th ISFR (October 11-14, 2009, Chengdu, China)

Tab. 1 Experimental conditions
Experiment

Run 1

Run 2

Run 3

Fluidized bed temperature [°C]400400400

silica sandolivine sandriver sand

5.9

7.0

6.5

0.39

0.46

0.44

Ratio of feed to bed material [h ]

0.18

0.18

0.19

Water throughput [g / min]

109.4

9.3

Steam flow rate [l / min]

1212

12

Bed material
Total weight of fed PC [g]Feed rate [g / min]-1

2.3 Analysis of reaction products
The solid products were classified into crystalline fraction and resinoid fraction that wasa thick sticky liquid. Each of them was weighed by a balance and dissolved in 1-hexanol(Wako Pure Chemical Industries Ltd.). The products contained in the water were extractedwith 1-hexanol. The 1-hexanol solutions were quantitatively analyzed by GC-FID (GC-17A,Shimadzu Ltd.) with a capillary column (ULBON HR-1, Shinwa Chemical Industries Ltd.).
The qualitative analysis was carried out by GC-MS (GC: GC-17A, Shimadzu Ltd., MS:QP5000, Shimadzu Ltd.). The gas fraction was analyzed by GC-TCD (GC-9A, ShimadzuLtd.). Residue was defined as the difference of all determined products to 100-wt%.
3. Results and Discussion
The experiments were conducted using three different bed materials. Fig.2 shows thesum of the yield of each component based on the total amounts of PC fed into the reactor. The
main components are Bisphenol-A, Carbon dioxide, Phenol and p-Isopropenylphenol.
Bisphenol-A was the largest composition (component?) in every experiment. Most of thegaseous product was carbon dioxide. Its yield ranged from 16 to 18 wt% and the bed materials
did not make much difference. From the result of these products, primary reactions of thehydrolysis of PC were considered to be described by following two equations.
CH3OO
CH3nO

Polycarbonate (PC)CH3HOOH+CO2(1)CH3Bisphenol-A (BPA)
CH3CH3HOOH
CH3Bisphenol-A (BPA)- 86 -HO+OH

CH2

p-Isopropenylphenol

Phenol(2)

PARTⅠ PYROLYSIS

100

Yield [wt%]

80
60
40

Residue

Othersp -Cresolp -Ethylphenolp -Isopropenylphenol

20Carbon dioxide

Phenolp -Isopropylphenol

p -tert-ButhylphenolBisphenol-A0Run 1Run 2Run 3

Fig.2 Product yield of thehydrolysis of PC (400 °C)

110.8
Composition [-]Composition [-]0.80.6
0.4
0.2
00.6
0.4
0.20Run 1

Run 2

Run 3

Fig.3 Composition of the crystalline solid

Run 1

Run 2Run 3

Fig.4 Composition of thewater-soluble products

Among the solid product, the ratios of crystalline solid to resinoid solid were 0.45, 1,0.62 for silica sand, olivine sand and river sand respectively. When the bed material wasolivine sand (Run 2), the solid product was almost crystalline product. And it contained about
25wt% of p-Isopropenylphenol as shown in Fig. 5 whereas for the bed material of silica sand,the content of BPA was 94 %. As a result, the component yields for silica sand (RUN 1) andolivine sand (RUN2) were not so much different as shown in Fig. 2.
From the comparison of Run 1 and Run 3, the effect of river sand on the hydrolysis
products was considered. In Run 3, both the ratio of p-isopropenylphenol in the crystalline
solid and the ratio of phenol in the water increased. Though the reason for this is not clear,some minerals such as magnesium and calcium in river sand might have accelerated thedegradation of BPA.
The main liquid product desolved in the water was phenol as shown in Fig.4. However,someamounts of p-cresol, p-ethylphenol, p-isopropylphenol, p-isopropenylphenol,p-tert-buthylphenol, BPA were also found to be desolved in the water.
Fig. 5 shows the curves of the production of carbon dioxide versus time. This figure
shows that the production rate (Equation (1)) for the case of olivine sand is much larger thanthat for the case of silica sand or river sand. This may be due to the catalytic effect by theminerals contained in the olivine sand.
- 87 -The 5th ISFR (October 11-14, 2009, Chengdu, China)

Production of carbon dioxide [mol%]Both the hydrolysis reaction rate and the product component changed with temperature.
When the olivine sand was used as a bed material, the yield of BPA increased withtemperature up to 350 °C, however, at the temperatures higher than 350 °C, the yield of BPA
decreased due to the decomposition of BPA as described in Equation (2). Therefore, themaximum yield of BPA was about 58 wt% at 350 °C .
100
Silica sand80

Olivine sandRiver sandFeed6040
20002040
T ime [min]6080

Fig.5 Production of carbon dioxide vs. time (350°C)
4. Conclusions
Polycarbonate (PC) was successfully hydrolyzed in the fluidized sand bed which is very
effective to accelerate the reaction rate by increasing reaction surface. The hydrolysis reaction
rate increased with temperature. However the selectivity of BPA decreased with increased
temperature due to the degradation reaction (Equation (2)). The production rate and theselectivity were also strongly affected by the bed materials used. Especially olivine sand,which contains a large amount of magnesium and some other minerals, showed strong
catalytic effect. The maximum yield of BPA was 58wt% in this experiment when the olivine
sand was used as the bed material.
Reference[1] A. Oku et al. Polymer, 2000,41, 6749-6753.
[2] I. Okajima et al., Kagakukougaku Ronbunshu(Japanese), 2002,28, 553.
[3] H. Tagaya et al., Polymer Degradation and Stability,1999,64,289-292.
[4] T. Yoshioka et al., Chemistry Letters, 2005, 34(3), 282.
[5] T. Masuda et al., Polymer Degradation and Stability,1999, 58, 315-320.
[6] G. Grause et al., ISFR2007 proceedings, 2007,129-136.

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