Steam Hydrolysis of Poly(bisphenol A carbonate) in a Fluidized Bed

Article pubs.acs.org/IECR

Steam Hydrolysis of Poly(bisphenol A carbonate) in a Fluidized Bed Reactor Guido Grause,* Rikard Kar̈ rbrant, Tomohito Kameda, and Toshiaki Yoshioka* Graduate School of Environmental Studies, Tohoku University, Aramaki Aza Aoba 6-6-07, Aoba-ku, Sendai 980-8579, Japan ABSTRACT: Poly(bisphenol A carbonate) (PC) was hydrolyzed in a benchtop fluidized bed reactor and compared with the pyrolysis of PC. Hydrolysis resulted in bisphenol A (BPA) and the cleavage of BPA in the formation of phenol and pisopropenylphenol (IPP). Experiments were carried out using MgO or quartz sand (SiO2) as bed materials in a temperature range between 350 and 500 °C. It was found that the combination of bed material and temperature has a significant impact on the product distribution. High BPA yields between 40% and 45% were obtained with MgO at 400 °C and with SiO2 at 500 °C. Moreover, the reaction in the presence of SiO2 at 400 °C led to phenol and IPP yields of 34% and 32%, respectively. Compared with pyrolysis at 480 °C, residue and high-boiling-fraction quantities were reduced. The reaction pathway is also discussed.

1. INTRODUCTION Poly(bisphenol A carbonate) (PC) is the most widely used polymer in the family of polycarbonates. The overall production of PC in 2010 was 3.4 Mt, corresponding to 1.5% of the total thermoplastic production (225 Mt).1 The demand for polycarbonate has steadily increased over the years owing to the introduction of new products, such as optical discs and casings for electronic devices, requiring the high-quality optical and physical properties of PC. After-life treatment of PC can be achieved in different ways. Mechanical recycling requires the lowest effort; however, recycled PC shows a deterioration in its mechanical and optical properties.2 Chemical recycling is an alternative if the material is contaminated or degraded to such a degree that mechanical recycling is no longer an option. During pyrolysis, heat is applied under an inert atmosphere to break down the polymer into smaller units. However, this process is of limited use for PC, since this reaction favors low-value products such as CO, CO2, and carbonaceous residues.3,4 Achilias et al.5 reported a product distribution at 550 °C of 6.6/63.0/30.4 (gas/liquid/ residue (wt %)) and 8.6/80.4/11 from the pyrolysis of pure PC and compact disks, respectively. Pyrolysis in a fluidized bed pilot plant at 710 °C resulted in a product distribution of 26.5/ 46.4/24.6/2.5 (gas/liquid/residue/water (wt %)).3 In an attempt to utilize the large amounts of residue produced for a constructive purpose, Méndez-Liñań et al.6 modified and analyzed the residue with the intention of obtaining a gasstorage medium. Efforts have been aimed at the chemical fission of the carbonate bond (Scheme 1), as it is susceptible to several types of chemical attacks. Some reported processes are hydrolysis,7−9 methanolysis,10−13 and ammonolysis. 14−16 The aim of solvolytic processes, in general, is the recovery of bisphenol A (BPA); in some cases, urea14 or dimethylcarbonate10 are obtained as carbonic acid derivatives. High yields of BPA were achieved in supercritical ammonia14 or during PC methanolysis in ionic liquids at moderate temperatures below 100 °C.13 Since the phenyl groups of PC are linked by a quaternary carbon, the carbonate bond is protected by the rigidity of the macromolecular backbone, providing some resistance if a © 2014 American Chemical Society

solvolytic process is carried out. The resistance of PC to solvolytic processes makes it necessary to dissolve or at least swell the PC surface before it is readily solvolyzed. Toluene, dioxane, tetrahydrofuran, and other solvents10,12 were used to enhance swelling in methanol. The toxicity of many of the solvents used is also a source of concern.2 Moreover, solvolysis processes are problematic since a complex separation system is necessary for the removal of solvents, products, and additives. Hydrolysis was carried out at various conditions. Huang et al.9 explored the reaction in high-temperature water and obtained a BPA yield of 31% after 45 min at 300 °C. Tagaya et al.17 investigated the reaction between 230 and 430 °C in the presence of Na2CO3. However, although many phenolic products could be obtained, BPA was mostly degraded.18,19 Reduction of the reaction temperature can be achieved by microwave-supported alkaline hydrolysis in the presence of a phase-transfer catalyst.20 High BPA yields of more than 95% were also achieved during the hydrolysis of PC when employing ionic liquids.21,22 Watanabe et al.8 depolymerized PC at 300 °C with high-pressure steam and obtained a yield of 80%. A similar yield was achieved by Grause et al.7 at the same temperature at atmospheric pressure in the presence of MgO as a catalyst. However, polystyrene and phosphate-based flame retardants present in real waste samples reduced the reaction rate.23 On the basis of the results obtained in a quartz-glass tube reactor,7,23 we investigated in the present work the upscaling of this process in a benchtop fluidized bed reactor with a capacity of 100 g of plastic/h.

2. EXPERIMENTAL SECTION 2.1. Materials. Polycarbonate (Panlite AD-5504) was obtained from Teijin Ltd. (Osaka, Japan) and ground to a particle size below 0.5 mm. MgO was received from SigmaReceived: Revised: Accepted: Published: 4215

December 17, 2013 February 12, 2014 February 27, 2014 February 27, 2014 dx.doi.org/10.1021/ie404263a | Ind. Eng. Chem. Res. 2014, 53, 4215−4223

Industrial & Engineering Chemistry Research

Article

Scheme 1. Methanolysis, Hydrolysis, and Ammonolysis of PC

Figure 1. Benchtop fluidized bed plant: (1) N2 inlet, (2) sample vessel, (3) screw feeders, (4) flow controllers, (5) preheater, (6) steam generator, (7) water pump, (8) water tank, (9) fluidized bed reactor, (10) cyclone, (11) air-cooled steel cooler, (12) impact precipitator, (13) ethanol-cooled glass coolers, (14) electrostatic precipitator, (15) gas pump, (16) valve, (17) gas meter, and (18) gas sampling/outlet.

Table 1. Experimental Conditions experiment

1

2

3

4

5

6

7

bed material fluidizing gas temp of fluidized bed (°C) temp of freeboard (°C) PC input (g) feeding time (min) feed rate (g/h) N2 flow (L/min) steam flow (g/min) residence time (s) pressure before fluidized bed (kPa) pressure freeboard (kPa)

MgO N2 480 478 89 25 212 20.2 2.8 8.7 5.1

MgO steam 359 403 111 121 55 0.5 6.4 2.9 7.4 1.8

MgO steam 404 414 197 116 102 0.5 6.0 3.0 6.9 2.7

MgO steam 447 434 137 56 146 0.5 5.9 2.8 5.7 1.1

MgO steam 499 474 80 45 106 0.5 5.5 2.8 6.0 2.7

sand steam 399 394 96 75 77 0.5 9.3 2.0 8.8 1.8

sand steam 499 494 199 215 56 0.5 7.9 2.0 9.2 1.6

2.2. Pyrolysis and Hydrolysis Experiments. The benchtop fluidized bed plant with a capacity of 100 g h−1 of organic material, which was used in these experiments, has been described in detail elsewhere.24 The apparatus consisted of a steel reactor equipped with an input system and heater (Figure 1). Products exited the reactor with the gas flow, and product separation was achieved using a cyclone for inorganic dust and a steel cooler, an impact precipitator, two ethanol-cooled glass coolers, and an electrostatic precipitator for condensable products. It was decided that the steel cooler would be cooled by air only in order to avoid the solidification of products within the apparatus by rapid cooling. Precipitation of solid product can cause clogging in the coolers and dangerous

Aldrich in the form of large beads with a MgO content of 98%. The beads were crushed to a particle size between 0.3 and 0.5 mm. Since MgO is a quite soft material, only a small fraction of the material ended up as the required particle size, and most of it was converted into fine dust. BPA was purchased from Aldrich, and naphthalene, phenol, diethyl ether, and tertbutylphenol were purchased from Kanto Chemicals. Gases used for the determination of retention times were purchased from GL Sciences, and Karl−Fischer reagents were purchased from Sigma−Aldrich. The solvents used for analytical purposes were of analytical grade. Deionized water was produced by an Advantec RFD240HA deionizer. 4216

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Table 2. Product Distribution of Organic Compounds with Respect to PC Inputa MgO pyrolysis gases (wt %) carbon dioxide carbon monoxide methane hydrogen other gases phenols (wt %) phenol methylphenols ethylphenols isopropenylphenol isopropylphenol tert-butylphenol BPA other phenols aromatics (wt %) benzene styrene other aromatics unknown high-boiling compounds (wt %) residue (wt %) total a

sand steam

steam

steam

480 °C

359 °C

404 °C

447 °C

499 °C

399 °C

499 °C

14.5 12.5 1.4 0.4 + 0.1 27.8 17.1 2.8 1.5 0.5 4.4 1.3 + 0.2 1.1 0.1 0.1 0.9 1.0 16.7 39.0 100

5.8 5.8 + + − + 53.4 13.3 + + 6.5 0.1 2.8 30.7 − + − − + 3.9 13.6 19.7 97

9.3 9.3 + + + + 53.0 8.1 0.1 0.1 1.4 0.2 3.0 40.1 + 0.1 − − 0.1 3.1 21.8 12.5 100

11.6 11.6 + + − + 51.4 11.4 + + 6.5 0.2 2.5 30.8 + + − − + 2.2 17.6 10.1 93

8.3 8.3 + + − + 42.1 14.8 0.1 + 1.2 0.4 2.3 20.4 3 + − − − 1.8 37.8 7.4 98

20.5 20.3 + + − 0.2 55.6 25.1 + + 17.0 0.5 2.2 9.7 0.9 0.2 − − 0.2 0.4 16.6 16.3 110

16.4 16.2 0.1 0.1 + + 57.3 9.2 0.7 0.4 6.5 0.7 2.4 36.9 0.4 0.1 − − 0.1 1.0 26.3 8.3 109

+, traces below 0.1%; −, not detected.

2.3. Analytical Methods. Gases were analyzed by gas chromatography coupled with a flame ionization detector (GCFID; GL Science GC4000, Tokyo, Japan) equipped with a methanizer for the quantification of carbon oxides using a Varian CP-PoraBOND Q column (temperature program, 40 °C (5 min) → 5 °C/min → 180 °C (5 min)). Hydrogen was quantified using a gas chromatograph coupled with a thermoconductivity detector (GC-TCD; GL Science GC323) and equipped with a packed stainless steel column filled with activated carbon (temperature program, 50 °C (5 min) → 10 °C/min → 150 °C (5 min)) by comparing the hydrogen peak area with that of carbon dioxide. The appearance of condensable products varied depending on the reaction conditions. Only the pyrolysis experiment in a nitrogen atmosphere gave a liquid product fraction, which was distilled by employing a vacuum in order to separate lowboiling compounds (bp < 300 °C) from high-boiling compounds. Phenols derived from hydrolysis experiments gave at any time solid products and an aqueous phase. Organic compounds were separated from water and inorganic impurities after acidification with 1 M HCl solution by liquid−liquid extraction with diethyl ether for 6 h. Pyrolysis oil and extracted products were identified by gas chromatography coupled with a mass-selective detector (GC-MS; Hewlett−Packard; GC, HP6890; MS, HP5973) and quantified by GC-FID (GL Science GC4000). For both GC-MS and GC-FID, the same type of column (GL Science InertCap5MS/Sil) and the same temperature program (50 °C (5 min) → 10 °C/min → 320 °C (10 min)) were used. Since BPA showed degradation on the GC column, BPA determination was carried out using a highperformance liquid chromatograph (HPLC) from JASCO (pump, PU-2089; oven, 2060; detector, UV-2075; Easton,

pressure increases, which was prevented by using an impact precipitator after the steel cooler for the removal of phenolic compounds. After the separation of condensable products, exhaust gas volume was quantified, and the gas was disposed in a draft. Gas samples were taken in regular intervals. Additionally, the reactor was equipped with a steam generator consisting of a copper coil heated to 250 °C. The water feed was maintained by a peristaltic pump connected to a polypropylene vessel as a water reservoir located on a balance for monitoring the mass flow. For each experiment, the reactor was filled with 470 g of bed material. The sample vessel held 200 g of PC for each experiment, for an estimated reaction time of 2 h. Before the experiment, the plant was sealed and checked for leaks. The maximum pressure loss allowed was 1 kPa h−1 at an initial pressure of 10 kPa. Operating pressures were in the range of 1− 15 kPa depending on the location of the pressure sensor. The plant was then purged with nitrogen to remove oxygen. Simultaneously, heating was started, and after the desired reactor temperature was reached, nitrogen flow was gradually replaced by steam. In addition, one experiment was carried out in a nitrogen atmosphere under pyrolytic conditions. PC feed was started after steady conditions were achieved. Experimental conditions are given in Table 1. The outgoing gas was sampled up to four times per experiment by gas-bag collection spread out evenly over the course of the experiment. The total amount of gas produced was calculated by measuring the total volume of gas leaving the plant and subtracting the nitrogen going into the plant. After input was stopped, both steam flow and reaction temperature were maintained until products were no longer visually observed. 4217



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MD, USA) with a JASCO CrestPak C18S column and 80:20 (v/v) methanol/water as the mobile phase at 25 °C. Solid products from the hydrolysis experiments were also analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy (Shimadzu, AXIMA-CFR Plus) with 2,5-dihydroxybenzoic acid (DHBA) as a matrix. The water contents of the products were determined using Karl− Fischer titration (Metrohm, 870 KF Titrino plus) with both water standard and titer solutions obtained from Fluka (Hydranal). Scanning electron microscope (SEM) images (TOPCON ABT-32, Tokyo, Japan) of the bed material before and after the experiment were carried out after coating the sample with platinum. X-ray diffraction (XRD) was carried out using a Rigaku RINT-2200 VHF+/PC (Tokyo, Japan) diffractometer in the range of 2θ = 3−90°. 2.4. Definitions. The main findings are presented as the mass fractions of the obtained products and the yields of the most important phenolic compounds. An individual compound is reported as its percent mass fraction, Xi, defined as Xi /(wt %) = 100 ×

mi mPCin

Scheme 2. Pyrolysis Reaction of PC

(1)

where mi and mPCin are the mass of compound i and the PC input. The yield Yi of a phenolic compound i was calculated by Yi /% = 100 ×

Scheme 3. Hydrolysis of PC

ni ,obtained ni ,theoretical

(2)

where ni,obtained and ni,theoretical denote the number of moles present in the product and in the case of the complete conversion of the introduced PC sample, respectively.

3. RESULTS AND DISCUSSION 3.1. Pyrolysis. Pyrolysis of PC was carried out at 480 °C in a nitrogen atmosphere (Table 2). This reaction is already wellinvestigated and was only conducted for comparison in the present study. Results were in compliance with earlier investigations.2,3,5 Main products were residue (39 wt %) and high-boiling compounds (16.7 wt %) as the result of pyrolytic condensation reactions forming mainly condensed ring systems from the carbonate group as described by Puglisi et al.25 (Scheme 2). These reactions do not lead to low molecular weight products; rather, chain fission is achieved by breaking the BPA propylidene bridge, resulting in phenol as the main product of the phenol fraction and various alkylated phenolic products. BPA was detected only in traces. Also observed besides phenols were some aromatic hydrocarbons. The product gas consisted mainly of carbon dioxide and carbon monoxide, along with methane and hydrogen as minor products. The high amount of residue produced caused defluidization of the bed and problems related to the control of the reaction temperature. 3.2. Steam Hydrolysis with MgO. In previous investigations,7,23 a more rapid degradation of PC was demonstrated in a steam atmosphere as a result of the hydrolysis of the carbonate ester group. This reaction is strongly accelerated by MgO and results in the formation of BPA and carbon dioxide (Scheme 3). Thermally labile BPA might be degraded to phenol and isopropenylphenol (IPP). IPP is further decomposed to phenol.18,19

In the present work, the amount of residue was reduced and the phenol fraction doubled in the temperature range between 359 and 447 °C compared with the pyrolysis reaction at 480 °C (Table 2). Over the whole temperature range, BPA was the main component of the phenolic fraction, reaching a maximum at 404 °C. Phenol and IPP were observed as BPA degradation products in smaller amounts. Noteworthy is the constant presence of tert-butylphenol over the whole temperature range; the compound is not a degradation product of BPA, and was probably added during production as a molecular weight modifier. Other phenolic products and aromatic hydrocarbons were negligible. The highest BPA fraction was obtained at 404 °C. At higher and lower temperatures, BPA degradation was observed and phenol and IPP were obtained instead. The composition of the phenolic fraction at 359 °C resembled strongly that obtained at 447 °C. At the higher temperatures, the pyrolytic degradation of PC took place as the result of the enhanced pyrolysis 4218



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Figure 2. MALDI-TOF-MS spectra for high-boiling products obtained from the hydrolysis of PC in the presence of MgO at (a) 404 and (b) 499 °C. Molar weight numbers in the spectra refer to the protonated molecules.

sensitive, it was expected that the amount of IPP would decrease with the temperature, while the phenol amount should increase by the degradation of BPA and IPP. In fact, the highest amount of IPP was observed at the lowest temperature of 359 °C. Caused by the slow hydrolysis rate at this temperature, high amounts of phenol were also obtained. With increasing hydrolysis rate, amounts of phenol and IPP decreased at 404 °C. At higher temperatures, more IPP was degraded and phenol was formed. The exceptional low amount of IPP at 404 °C

reaction rate. At the lower temperature, the reduced hydrolysis reaction rate caused the agglomeration of unreacted PC in the fluidized bed, preventing contact between the PC and steam, thus promoting pyrolysis. Finally, at 499 °C, only half of the BPA obtained at 404 °C was recovered. Pyrolysis was apparent by the decreasing phenolic fraction and amount of IPP. Differences in the reaction rates of hydrolysis, BPA fission, and IPP degradation had a strong influence on the resulting amount of phenol and IPP. Since IPP is rather temperature4219



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with particle size and crystal structure remaining unchanged. However, small particles were removed with the gas flow from the MgO surface (Figure 3).

might be the result of IPP being retained in the PC melt by the still high viscosity at this temperature. These assumptions are supported by observations made for both the residue and high-boiling fractions. Compared with pyrolysis at 480 °C, hydrolysis reduced the residue fraction significantly; however, the temperature also played an important role in the residue reduction. The highest amount of residue (19.7 wt %) was obtained at the lowest temperature of 359 °C, which was caused by the low reaction rate at this temperature. As temperature was increased, fewer residues were observed, reaching a minimum of 7.4 wt % at 499 °C. This finding is indicative of a more efficient chain length reduction from PC macromolecules to the volatile species, which contributed to the high-boiling fraction. There was a tendency toward an increased high-boiling fraction in conjunction with the temperature; MALDI-TOF-MS investigations of the fractions from 404 and 499 °C showed the occurrence of various pyrolytic degradation products (Figure 2). Low molecular weight products below 300 Da were easily attributed to compounds identified by Puglisi et al.25,26 However, with increasing molecular weight, the number of possible congeners increased exponentially and the identification of specific degradation products was not possible. It became clear, though, that PC oligomers were not present in the high-boiling fraction, and therefore, carbonate esters were completely degraded by either hydrolysis or pyrolysis. Only one peak might indicate the presence of an unreacted carbonate group (m/z = 363, BPA ptolyl carbonate−H+). At all temperatures, the product gas consisted solely of CO2 with traces of other gases and did not give any information about degradation pathways. The hydrolytic fission of PC likely occurred at the MgO surface. MgO itself is very resistant against chemical attack; however, the presence of basic hydroxide groups at the particle surface can be assumed. Thermogravimetric (TG) experiments showed the dehydration of Mg(OH)2 between 350 and 400 °C.27 In a steam atmosphere, this range shifts to higher temperatures, allowing MgO to take part in the water transfer in which first a hydroxyl group is added to the carbonate group leading to fission of the ester and in a second step CO2 is released (Scheme 4). SEM images and XRD did not show any alterations to the bed material prior to and after the reaction,

Figure 3. XRD and SEM of MgO bed material (a) prior to and (b) after the experiment at 404 °C.

3.3. Steam Hydrolysis with SiO2. Steam hydrolysis in the presence of SiO2 as the bed material at 399 and 499 °C resulted in the same product compounds as in the presence of MgO. However, the product distribution showed significant differences. At both temperatures, the fraction of phenols was higher than in the presence of MgO. While MgO resulted at 400 °C mainly in the recovery of BPA, in the presence of SiO2 the BPA amount was below 10 wt %. Therefore, BPA degradation products, phenol and IPP, were recovered in 25.1% and 17.0%, respectively. All other conditions investigated resulted in less IPP. Interestingly, at 499 °C, BPA recovery reached 36.9 wt %, almost the same level as in the presence of MgO at 404 °C. At any temperature, phenolic byproducts resulting from the fission of BPA, such as phenol, and IPP, increased compared with MgO. Differences in the behaviors of these two bed materials are probably related to their surface properties. While MgO is rather a basic material, SiO2 is considered to be rather acidic. It seems that MgO facilitated the occurrence of stronger hydrolytic reactions than SiO2. High BPA yields and low molar IPP/phenol ratios (Figure 4) suggest this idea, since the degradation of IPP is also considered a hydrolytic reaction (Scheme 5).19 On the contrary, SiO2 promoted the pyrolytic fission of the BPA propylidene bridge, which might occur in the PC melt, resulting in smaller chain fragments (Figure 5). When viscosity decreases and volatility of fragments increases, an improved contact with the steam phase also allows for enhanced hydrolysis. This reaction might occur by electrophilic substitution (Scheme 6), where a proton from the SiO2 surface is transferred to one of the phenylene groups. Subsequently, the

Scheme 4. Hydrolysis Mechanism of PC in the Presence of MgO

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Scheme 6. Fission of BPA by Electrophilic Substitution in the Presence of SiO2

Figure 4. Molar IPP/phenol ratio depending on the experimental conditions.

Scheme 5. Degradation of IPP in the Presence of MgO

present case, only a slight increase in isopropylphenol was observed in the presence of SiO2, caused by the low hydrogen content of PC. At low temperatures, BPA is already degraded before the carbonate groups are hydrolyzed. At high temperatures, larger fragments are volatilized and hydrolyzed in the gas phase, explaining the high BPA amount at 499 °C.

4. CONCLUSION Steam hydrolysis in a fluidized bed offers the possibility to obtain valuable products that cannot otherwise be achieved by pyrolysis or solvolytic processes. Solvolysis allows the recovery of bisphenol A and other phenolic products from high-quality PC. However, PC rich in additives or fillers is difficult to process in this way. Fluidized bed technology offers the opportunity of separating organic hydrolysis products from inorganic materials without extensive separation technology, which may compensate the lower product yields as a result of competitive pyrolytic reactions. Moreover, MgO is used as a filler for PC and can be applied directly in the hydrolysis of PC. The highest BPA yields of 45 and 41% were obtained with MgO at 404 °C and SiO2 at 499 °C, respectively (Figure 6). Moreover, in the presence of SiO2 at 399 °C, yields of 34% for phenol and 32% of IPP were achieved. Parameters are still not optimized; higher yields and less pyrolytic products are expected by reducing the feed rate.

Figure 5. PC degradation on a SiO2 surface. At low temperatures, volatilization is slow and little BPA is obtained. At high temperatures, fast volatilization prevents BPA from undergoing decomposition.

propylidene bridge is cleaved and the proton returns to the SiO2 surface. Similar reactions are observed during the pyrolysis of polystyrene.28 In general, acid catalysts increase the alkane yield and reduce the alkene yield by hydrogen transfer. In the 4221



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(3) Kaminsky, W.; Predel, M.; Sadiki, A. Feedstock recycling of polymers by pyrolysis in a fluidised bed. Polym. Degrad. Stab. 2004, 85, 1045−1050. (4) Yoshioka, T.; Sugawara, K.; Mizoguchi, T.; Okuwaki, A. Chemical Recycling of Polycarbonate to Raw Materials by Thermal Decomposition with Calcium Hydroxide/Steam. Chem. Lett. 2005, 34, 282− 283. (5) Achilias, D. S.; Antonakou, E. V.; Koutsokosta, E.; Lappas, A. A. Chemical recycling of polymers from waste electric and electronic equipment. J. Appl. Polym. Sci. 2009, 114, 212−221. (6) Méndez-Liñań , L.; López-Garzón, F. J.; Domingo-García, M.; Pérez-Mendoza, M. Carbon Adsorbents from Polycarbonate Pyrolysis Char Residue: Hydrogen and Methane Storage Capacities. Energy Fuels 2010, 24, 3394−3400. (7) Grause, G.; Sugawara, K.; Mizoguchi, T.; Yoshioka, T. Pyrolytic hydrolysis of polycarbonate in the presence of earth-alkali oxides and hydroxides. Polym. Degrad. Stab. 2009, 94, 1119−1124. (8) Watanabe, M.; Matsuo, Y.; Matsushita, T.; Inomata, H.; Miyake, T.; Hironaka, K. Chemical recycling of polycarbonate in high pressure high temperature steam at 573 K. Polym. Degrad. Stab. 2009, 94, 2157−2162. (9) Huang, Y.; Liu, S.; Pan, Z. Effects of plastic additives on depolymerization of polycarbonate in sub-critical water. Polym. Degrad. Stab. 2011, 96, 1405−1410. (10) Hu, L.-C.; Oku, A.; Yamada, E. Alkali-catalyzed methanolysis of polycarbonate. A study on recycling of bisphenol A and dimethyl carbonate. Polymer 1998, 39, 3841−3845. (11) Piñero-Hernanz, R.; García-Serna, J.; Cocero, M. J. Nonstationary model of the semicontinuous depolymerization of polycarbonate. AlChE J. 2006, 52, 4186−4199. (12) Liu, F.-S.; Li, Z.; Yu, S.-T.; Cui, X.; Xie, C.-X.; Ge, X.-P. Methanolysis and Hydrolysis of Polycarbonate Under Moderate Conditions. J. Polym. Environ. 2009, 17, 208−211. (13) Liu, F.; Li, L.; Yu, S.; Lv, Z.; Ge, X. Methanolysis of polycarbonate catalysed by ionic liquid [Bmim][Ac]. J. Hazard. Mater. 2011, 189, 249−254. (14) Mormann, W.; Spitzer, D. Ammonolysis of Polycarbonates with (Supercritical) Ammonia: An Alternative for Chemical Recycling. Advances in Polycarbonates; American Chemical Society: Washington, DC, USA, 2005; Vol. 898, pp 244−261. (15) Arai, R.; Zenda, K.; Hatakeyama, K.; Yui, K.; Funazukuri, T. Reaction kinetics of hydrothermal depolymerization of poly(ethylene naphthalate), poly(ethylene terephthalate), and polycarbonate with aqueous ammonia solution. Chem. Eng. Sci. 2010, 65, 36−41. (16) Hatakeyama, K.; Kojima, T.; Funazukuri, T. Chemical recycling of polycarbonate in dilute aqueous ammonia solution under hydrothermal conditions. J. Mater. Cycles Waste Manage. 2014, in press (DOI: 10.1007/s10163-013-0151-8). (17) Tagaya, H.; Katoh, K.; Kadokawa, J.; Chiba, K. Decomposition of polycarbonate in subcritical and supercritical water. Polym. Degrad. Stab. 1999, 64, 289−292. (18) Hunter, S. E.; Savage, P. E. Kinetics and Mechanism of pIsopropenylphenol Synthesis via Hydrothermal Cleavage of Bisphenol A. J. Org. Chem. 2004, 69, 4724−4731. (19) Hunter, S. E.; Felczak, C. A.; Savage, P. E. Synthesis of pisopropenylphenol in high-temperature water. Green Chem. 2004, 6, 222−226. (20) Tsintzou, G.; Achilias, D. Chemical Recycling of Polycarbonate Based Wastes Using Alkaline Hydrolysis Under Microwave Irradiation. Waste Biomass Valorization 2013, 4, 3−7. (21) Song, X.; Liu, F.; Li, L.; Yang, X.; Yu, S.; Ge, X. Hydrolysis of polycarbonate catalyzed by ionic liquid [Bmim][Ac]. J. Hazard. Mater. 2013, 244−245, 204−208. (22) Li, L.; Liu, F.; Li, Z.; Song, X.; Yu, S.; Liu, S. Hydrolysis of polycarbonate using ionic liquid [Bmim][Cl] as solvent and catalyst. Fibers Polym. 2013, 14, 365−368. (23) Grause, G.; Tsukada, N.; Hall, W. J.; Kameda, T.; Williams, P. T.; Yoshioka, T. High-value products from the catalytic hydrolysis of polycarbonate waste. Polym. J. 2010, 42, 438−442.

Figure 6. Product yields at different conditions.

The presence of MgO accelerated the hydrolysis of PC in the melt and high BPA yields were obtained at a low temperature of 400 °C. Higher temperatures caused the fission of BPA into phenol and IPP, the latter of which was further degraded in the presence of MgO. The influence of SiO2 mainly caused the fission of the BPA propylidene bridge, producing volatile fragments that were hydrolyzed in the steam phase. This behavior resulted, at a low temperature of 400 °C, in the slow volatilization of fragments and the degradation of BPA into phenol and IPP. Especially, IPP was recovered in high yields at these conditions. At a high temperature of 500 °C, the fast volatilization of PC allowed the recovery of high BPA yields. The present hydrolytic process using a fluidized bed reactor allows for the production of different target compounds from PC, depending on the reaction conditions: BPA can be reused for the production of PC; phenol is an important feedstock for various plastics; the possibilities of use for IPP are still not investigated, but it contains two functional groupsa double bond for polymerization and an aromatic alcohol group for esterification or phenol resin formationwhich might be applied for the connection of polymers with polyesters or phenol resins. This process is aimed for PC containing high amounts of fillers and other additives, which cannot be treated otherwise.

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AUTHOR INFORMATION

Corresponding Authors

*(G.G.) Tel./Fax: +81-22-795-7212. E-mail: [email protected]. tohoku.ac.jp. *(T.Y.) Tel./Fax: +81-22-795-7211. E-mail: [email protected]. tohoku.ac.jp. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was partially supported by the Ministry of Education, Science, Sports, and Culture, Grand-in-Aid for Scientific Research (A), 30241532, 2009. Furthermore, it was partly conducted by the Division of Multidisciplinary Research on the Circulation of Waste Resources endowed by the Sendai Environmental Development Co., Ltd.

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REFERENCES

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