Characterization of Styrene Recovery from the Pyrolysis of Waste

Catalytic and thermal degradation of waste expandable polystyrene (WEPS) have been studied in a semi-batch reactor with continuous flow of nitrogen to...
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Energy & Fuels 2003, 17, 1576-1582

Characterization of Styrene Recovery from the Pyrolysis of Waste Expandable Polystyrene Jong Jin Park,* Kwinam Park, Ji-Soo Kim,† Sanjeev Maken, Hocheol Song, Hochul Shin, Jin-Won Park, and Myung-Jae Choi‡ Department of Chemical Engineering, Yonsei University, 134 Sodaemoon-ku Shinchon-dong, Seoul, Korea 120-749 Received April 24, 2003

Catalytic and thermal degradation of waste expandable polystyrene (WEPS) have been studied in a semi-batch reactor with continuous flow of nitrogen to achieve greater oil yield and maximize styrene monomer recovery. Effect of temperature, nature of catalyst and its size, reaction time of catalytic pyrolysis, and effect of repyrolysis have been also investigated. Higher reaction temperature favors the oil yield and also decreases the reaction time with maximum styrene selectivity (76.31 wt %) at 450 °C. Among the catalysts studied, solid base BaO is found to be the most efficient and increases the styrene selectivity (84.29 wt %) significantly at a reaction temperature of 350 °C in comparison to thermal and acid catalytic degradation. Modified catalyst Fe-A/Al (A ) basic material) also shows better activity than Fe2O3 or Fe/Al. Increase in the size of the catalyst and repyrolysis decrease the oil yield, and styrene production also decreases on repyrolysis.

Introduction The total amount of plastic consumed by Korea was about 14 000 ton per day in 2001.1 It forms 22 wt % of the total MSW of Korea. Because of their versatility, their relatively low cost, and technological advances made in the plastics industry, this amount will continue to grow in the future. The abundance of the plastic material, their nonbiodegradability, and lack of landfill sites, on the other hand, created an environmental problem.2-5 Stringent environmental regulations are being imposed by the industrialized nations to control the detrimental environmental impact of waste plastic. In 1995, the law of disposal had been established to regulate the amount of waste disposal in Korea.6 The recycling of waste plastic appears to be the only solution to this problem.4-7 There are three main methods of recyclingsreprocessing, incineration, and resource recovery. Reprocessing involves melting and reforming waste plastic into secondary products. This results in plastics with inferior physical properties and production * Corresponding author. Phone: 82-2-364-1807. Fax: 82-2-312-6401. E-mail: [email protected], [email protected]. † Institute of Technical Development, Doha Industry Co., 1183 Songhuyn-ri Jinrae-myun, Kimhae, Korea. ‡ Advanced Technology Division, Korea Research Institute of Chemical Technology, 100 Jang-dong, Yusong, Taejon, Korea, 305-600. (1) Lee, C. H. State of the Art Report on Waste Recycling Technical Trend, Ministry of Science and Technology, Korea, 2000; pp 37-70. (2) Puente, G.; Klocker, C.; Sedran, U. Appl. Catal. B: Environmental 2002, 36, 279-285. (3) Fouhy, K.; Kim, I.; Moore, S. Culp, E. Chem. Eng. 1993, 100, 30-33. (4) Shelley, S.; Fouhy, K.; Moore, S. Chem. Eng. 1992, 99, 30-35. (5) Woo, O. S.; Broadbelt, L. J. Catal. Today 1998, 40, 121-140. (6) Second National Waste Management Plan, Ministry of Environment, Korea, 2002; pp 50-92. (7) Kim, J. R.; Yoon, J. H.; Park, D. W. Polym. Degrad. Stab. 2002, 76, 61-67.

of another waste. Thus, this method is not an ultimate solution to this problem. Incineration involves the recovery of plastic waste as energy; however, the loss of a chemical source, production of dioxin and other hazardous gases, and the negative public acceptance of incinerating MSW have limited its use. Resource recovery involves converting waste polymers to valuable chemicals and corresponding monomers. Thus, resource recovery is one of the promising alternatives to reprocessing, incineration, or dumping for the treatment of plastic waste, and thermal degradation of waste plastics has become a subject of considerable industrial and academic interest in the recent years.8-12 Thermal pyrolysis converts waste plastic into fuel, the converted fuels or chemicals could be merged in standard petrochemical or petroleum refining industry operation, and the recovered monomer can be used to produce new polymer. There are six main plastics which occur in Korean municipal solid waste. These are high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl-chloride (PVC), and polyethylene-terephthalate (PET). LDPE and PS was about 30 wt % of the total plastic production of (8) Kaminsky, W.; Sinn, H. Petrochemical Processing for Recycling Plastics. In Recycling and Recovery of Plastics; Brandrup, M., Bittner, W., Michaeli, G., Menges, G., Eds.; Hanser: Munich, 1996; pp 434443. (9) Carniti, P.; Gervasini, A.; Beltrame, P.; Audisio, G.; Bertini, F. Appl. Catal. A: General 1995, 127, 139-155. (10) Kaminsky, W. Pyrolysis of Polymers. In Emerging Technologies in Plastic Recycling; Andrews, G. D., Subramanian, P. M., Eds.; American Chemical Society: Philadelphia, 1992; pp 60-72. (11) Wampler, T. P. Instrumentation and Analysis. In Applied Pyrolysis Handbook; Wampler, T. P., Ed.; Marcel Dekker, Inc.: New York, 1995; pp 31-35. (12) Broadbelt, J. L.; Chu, A.; Klein, M. T. Polym. Degrad. Stab. 1994, 45, 57-70.

10.1021/ef030102l CCC: $25.00 © 2003 American Chemical Society Published on Web 10/17/2003

Styrene Recovery from the Pyrolysis of WEPS

Korea in the year 2001.14 In our earlier work,13 pyrolysis of LDPE was studied, and it was found that catalytic pyrolysis with an additive increases the efficiency; molecular weight distribution could also be controlled by using a different additive. In this paper, waste expandable polystyrene (WEPS) is selected because the WEPS collecting system is well managed in Korea and it constitutes about 13 wt % of the total plastic produced in Korea.14 Catalytic and thermal pyrolysis of PS was investigated by many workers in order to increase monomer recovery. Styrene monomer is relatively easy to recover from PS due to its low activation energy.15 It was reported that acid-catalyzed pyrolysis of PS produces more benzene, toluene, and ethylbenzene than styrene monomer in comparison to thermal pyrolysis.9 On the other hand, selectivity of styrene was found to be high in the case of base-catalyzed pyrolysis of PS.16 Lee et al. also studied the pyrolysis of PS in a semibatch reactor with continuous flow of nitrogen17 and found that an increase of acidity of catalyst and reaction time increased the production of ethylbenzene whereas high reaction pyrolysis temperature favored the selectivity of polystyrene to styrene. About 78 wt % yield of styrene monomer was also reported at a pyrolytic temperature of 600 °C using a fluidized bed reactor with nitrogen as carrier gas.18 Styrene selectivity was reported to increase during pyrolysis of PS in the presence of poly(R-methylstyrene).5 In the present work, we studied the thermal and catalytic degradation of WEPS in a semi-batch reactor with a continuous flow of nitrogen. Effect of temperature, nature of catalyst, its size and reaction time, and effect of repyrolysis have been investigated in order to maximize the styrene recovery from WEPS at low pyrolytic temperature. Experimental Methods In this experiment, WEPS collected from the waste plastic collection center at Garack-Dong Agriculture and Marine market (South Korea) and GPPS from SK Chemicals Corp. have been used. The catalysts used in the pyrolysis are Al2O3, ZrO2, Fe2O3, ZnO, and BaO (90% Acros) and modified Fe/Al and Fe-A/Al (A) basic material impregnated to Fe/Al). Pyrolysis has been carried out in a semi-batch reactor with a continuous flow of nitrogen as a carrier gas. The schematic diagram of the reactor is shown in Figure 1. It consists of a three-neck round-bottomed flask of 1.0 L capacity with a PID temperature controller (KT-1130, Chino, Korea). WEPS is crushed into 3 cm2 pieces and is put into port 1 of the reactor and mixed at 50 rpm. The mixture is then activated and heated to the desired temperature in a 1.0 kW heating mantle with a PID controller. Nitrogen gas is continuously fed (30 mL/min) to the reactor as a carrier gas to prevent the oxidation and reforming of thermally degraded gases. In the batch reactor, the desired temperature is achieved within 3 min and the (13) Park, J. J.; Park, K.; Park, J. W.; Kim, D. C. Korean J. Chem. Eng. 2002, 19, 658-662. (14) Korea Petrochemical Handbook; Korea Petrochemical Industry Association, Korea, 2001; pp 43-46. (15) Flynn, J. H.; Florin, R. E. Degradation and Pyrolysis Mechanism. In Pyrolysis and GC in Polymer Analysis; Liebman, S. A., Levy, E. J., Eds.; Marcel Dekker, Inc.: New York, 1985; pp 149-208. (16) Zhang, Z.; Hirose, T.; Nishio, S.; Morioka, Y.; Azuma, N.; Ueno, A.; Ohikita, H.; Okada, M. Ind. Eng. Chem. Res. 1995, 34, 4514-4519. (17) Lee, S. Y.; Yoon, J. H.; Kim, J. R.; Park, D. W. J. Anal. Appl. Pyrol. 2002, 64, 71-83. (18) Liu, Y.; Qiam, J.; Wang, J. Fuel Process. Technol. 2000, 63, 4555.

Energy & Fuels, Vol. 17, No. 6, 2003 1577 Table 1. Elemental Analysis of the Raw Materials plastic

Mwa

carbon hydrogen nitrogen sulfur oxygen ash

GPPS 223,380 91.60 WEPS 159,475 91.33 a

8.07 8.07

0.00 0.04

0.15 0.03

0.00 0.00

0.18 0.53

Weight-average molecular weight; unit: wt %.

amount of product formed is less than 2.0 wt %. Thus, ignoring the initial stage, the reaction can be considered as an isothermal reaction. Reaction temperature is then maintained for desired reaction time. Degraded gases are made to pass through a condenser maintained at 145 °C to prevent condensation as shown in Figure 1. Finally, thermally pyrolyzed gases pass through water condenser at 4 °C to collect degraded liquid oil, and light gases are collected in a liquid nitrogen trap. In the case of catalytic pyrolysis, the catalyst is mixed (1.0 wt %) with WEPS and then put into the reactor flask. A quantity of 200 g of WEPS or GPPS is used for every pyrolysis. Analysis Method. For qualitative analysis of oil product, GC/MSD (HP-5890, FID, capillary column, HP-1) is used. Sampled liquid (2 µL) produced from pyrolysis is injected and the obtained results are then compared with predetermined pure compound (benzene, toluene, ethylbenzene, methylstyrene, styrene, styrene-dimer) data to identify the component of degraded oil. Methylene chloride is used as a diluent to make calibration curves of six main components. GC (HP-6890, FID, capillary column, HP-1) is used for quantitative analysis. Internal standard method is used for accurate quantitative analysis, and hexane is used as an internal standard as it does not interfere with components of the oil. An internal standard method eliminates the need for accurate injections since hexane (reference standard) is included in each oil sample.

Results and Discussion Thermogravimetric Study. The thermogravimetric weight loss curve (TG, wt %) for thermal degradation of GPPS and WEPS and weight loss derivative curve (DTG, %/min) for GPPS are shown in Figure 2. The heating rate is 10 °C/min and almost identical curves are observed for GPPS and WEPS. It has been found from the TG curve that pyrolysis is activated around 380 °C, and rate of thermal decomposition is at its peak at 430 °C, i.e., DTG peak temperature. Elemental analysis of GPPS and WEPS also shows (Table 1) that two polymers have different molecular weights with almost the same carbon/hydrogen ratio equal to one. A similar type of thermal decomposition behavior was also reported by Miranda et al.19 and Kiran et al.20 Effect of Reaction Temperature. A sample of WEPS is pyrolyzed in the temperature range 350-480 °C and GPPS at 450 °C. Effect of temperature on the oil yield is shown in Figures 3 and 4, and composition (wt %) of aromatics in the liquid products for non catalytic degradation of WEPS and GPPS at various temperatures are tabulated in Table 2. For the same reaction time, oil yield is always higher in WEPS than GPPS at 450 °C, and styrene selectivity is also better in WEPS than GPPS (Table 2). Reaction time for 80 wt % oil yield at 450 °C is 14 min more in the case of GPPS than WEPS. The effect of reaction temperature on styrene selectivity and oil yield for degradation of WEPS is also shown in Figure 4. Oil yield increases from 24.3 to 96.7 wt % (19) Miranda, R.; Yang, J.; Roy, C.; Vasile, C. Polym. Degrad. Stab. 2001, 72, 469-491. (20) Kiran, N.; Ekinsi, E.; Snape, C. E. Resour. Conserv. Recycl. 2001, 29, 279-283.

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Figure 1. Schematic diagram of the pyrolysis reactor. Table 2. Composition (wt %) and Oil Yield (wt %) of the Product Oil for Non Catalytic Pyrolysis of WEPS at Various Reaction Temperaturesa temperature (°C)

B

T

EB

St

350 400 450 480 450(GPPS)

0.14 tr tr tr tr

4.41 2.42 2.08 1.07 2.64

2.24 1.72 1.40 0.16 0.76

76.60 73.07 76.31 49.41 65.53

total m-St dimer others oil yield 5.41 4.24 6.96 3.61 9.52 9.66 2.89 8.82 8.50 0.70 9.55 39.11 2.30 17.91 10.87

24.32 88.43 95.10 96.70 92.50

a B(benzene), T(toluene), EB(ethylbenzene), St(styrene), m-St(Rmethylstyrene), dimer(styrene-dimer, C16H14).

with an increase in reaction temperature from 350 to 480 °C, and styrene selectivity which is about 76 wt % up to 450 °C decreases sharply to 49.4 wt % at 480 °C (Table 1). This decrease in styrene selectivity takes place with an increase in styrene dimer production from 4.24 to 9.55 wt % (Figure 5) and other chemical production (6.96 to 39.11 wt %) (Table 2). Also the production of toluene (4.41 to 1.07 wt %), ethylbenzene (2.24 to 0.16 wt %), and R-methylstyrene (5.41 to 0.71 wt %) decreases with same rise in pyrolysis temperature (Figure 5). Our results are comparable with the studies reported in the literature.8,17,21,22 Martinkat et al. reported21 the oil yield of 99.7 wt % with 60 wt % styrene monomer

Figure 2. TG and DTG curves of plastic samples at a heating rate of 10 °C/min.

and 25 wt % for other aromatics, and Woo et al. also recovered 58 wt % styrene from thermal degradation of (21) Mertinkat, J.; Kirsten, A.; Predel, M.; Kaminsky, W. J. Anal. Appl. Pyrol. 1999, 49, 87-95.

Styrene Recovery from the Pyrolysis of WEPS

Energy & Fuels, Vol. 17, No. 6, 2003 1579

Figure 4. Effects of reaction temperature on the oil yield and styrene selectivity of noncatalytic pyrolysis.

Figure 3. Effects of reaction temperature on the oil yield of noncatalytic pyrolysis.

PS at 350 °C after 60 min of time and for Xf ) 0.433.22 An oil yield of 81.7 wt % with 70.08 wt % styrene selectivity was reported by Lee et al.,17 and 76.8 wt % styrene recovery at 580 °C was also reported by Kaminsky and Sinn.8 Thermal degradation of PS starts with a random initiation to form polymer radicals,23 the main products being styrene and its corresponding dimers and trimers. Effect of Catalyst. Effect of the nature of the catalyst on the pyrolysis of WEPS has been investigated using various catalysts to maximize the styrene monomer selectivity and oil yield at low reaction temperature. To achieve this, reaction temperature of 350 °C and seven catalysts such as BaO, ZnO, Fe2O3, ZrO2, Al2O3, Fe-A/Al and Fe/Al are selected for catalytic pyrolysis of WEPS. A comparison of oil yield for catalytic and non catalytic pyrolysis of WEPS has been shown in Figures 6 and 7. Composition and oil yield (wt %) for catalytic and non catalytic pyrolysis of WEPS for 50 wt % conversion (Xf ) 0.5) at 350 °C are summarized in Table (22) Woo, S. O.; Ayala, N.; Broadbelt, L. J. Catal. Today 2000, 55, 161-171. (23) Jellinek, H. H. G. J. Polym. Sci. 1949, 4, 13-36.

Figure 5. Effect of reaction temperature on selectivity of oil components in noncatalytic pyrolysis. Table 3. Composition (wt %) and Oil Yield (wt %) of Liquid Product from Catalytic Pyrolysis of WEPS at 350 °C for Xf ) 0.5 catalyst

B

T

EB

thermal BaO ZnO ZrO2 Al2O3 Fe2O3 Fe/Al Fe-A/Al

0.17 0.11 tr 0.21 0.19 tr 0.16 0.08

5.41 1.37 2.07 6.39 5.69 2.54 5.55 3.09

3.30 0.20 0.13 4.86 3.83 0.82 3.68 1.12

a

St

total m-St dimer others oil yield

71.88 9.32 1.40 84.29 0.81 9.52 82.15 4.08 5.54 71.34 10.64 0.31 69.76 10.19 0.51 69.07 2.45 13.34 70.52 10.81 0.67 77.66 6.25 5.10

6.52 3.70 6.03 6.25 9.83 11.78 8.61 6.72

24.32 73.20 53.80 34.24 29.73 28.73 35.49 46.41

Fe(Fe2O3), Al(Al2O3), A (basic material).

3. In comparison to the non catalytic degradation, catalytic pyrolysis shows better conversion and oil yield increases in catalytic pyrolysis (Figure 6) in the following order: BaO > ZnO > Fe-A/Al > Fe/Al > ZrO2 > Al2O3 > Fe2O3 > thermal. Styrene selectivity also increases in the case of BaO, ZnO, and Fe-A/Alcatalyzed pyrolysis (Figure 7) but decreases for other catalysts. The decreasing order of styrene selectivity (Figure 7) is: BaO > ZnO > Fe-A/Al > thermal > ZrO2 > Fe/Al2O3 > Al2O3 > Fe2O3.

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Figure 7. Effect of the nature of the catalyst on the oil yield and styrene selectivity.

Figure 6. Effect of the nature of the catalyst on the oil yield.

Our results are in good agreement with the results reported by Jhang et al.16 for solid acid- and basecatalyzed pyrolysis of polystyrene. The increased oil yield and styrene selectivity for BaO-catalyzed degradation and decreased production of benzene, toluene, and ethylbenzene can be explained on the reaction mechanism suggested by Jhang et al. In the case of acidcatalyzed (Al2O3) pyrolysis of WEPS, a carbenium ion is formed due to the attack of the proton associated with the acid site of the catalyst on the reactive branched phenyl group. These phenyl groups may undergo β-scission of C-C bonds in the polystyrene main chain followed by hydrogen transfer. This results in the formation of styrene, methylstyrene, ethylbenzene, benzene, and toluene. Further cracking and hydrogenation of styrene yielded in the presence of Al2O3 may increase the amount of benzene, toluene, and ethylbenzene and decrease the styrene production. In base-catalyzed (BaO) pyrolysis, the value of styrene selectivity and oil yield is quite high with a low yield of

benzene, toluene, ethylbenzene, and methylstyrene, and a considerable amount of dimer (9.52 wt %). In the presence of BaO, pyrolysis starts with formation of the carboanion by the adsorption of a proton from PS on the base site of the catalyst which results in the formation of styrene. Some transition metal oxides have also been reported24 to have many base sites, and oil yield during the pyrolysis of WEPS on these metal oxides may also contain small amounts of benzene, toluene, and ethylbenzene as observed in ZnO (Table 3). To increase the catalytic activity of catalyst and improve the selectivity of styrene in this experiment, Fe2O3, which is cheap and abundant in nature, is modified by precipitating it with alumina (Fe/Al) and also impregnated with some basic material such as KOH. Catalytic pyrolysis is also studied by using Fe2O3, Fe/Al, and Fe-A/Al2O3. It has been observed that modification of catalysts Fe2O3 by Al2O3 and impregnation with basic material increase the oil yield from 28.73(Fe2O3) to 35.49(Fe/Al) and to 46.41(Fe-A/Al2O3), and styrene selectivity also increases from 69.07(Fe2O3) to 70.52(Fe/Al) and to 77.66(Fe-A/Al2O3). Thus BaO catalyst is a most efficient catalyst for pyrolysis of WEPS, and maximum styrene selectivity (84.29 wt %) (24) Cornell, G.; Dumesic, J. A. J. Catal. 1987, 105, 285-290.

Styrene Recovery from the Pyrolysis of WEPS

Energy & Fuels, Vol. 17, No. 6, 2003 1581

Table 4. Effects of Catalyst (Fe2O3) Size on the Composition (wt %) of Product Oil from Pyrolysis of WEPS at 350 °C size (µm) 38 48 150

B

T

EB

St

0.05 2.10 0.60 77.70 0.08 2.20 0.72 77.60 0.15 5.01 2.93 77.01

total m-St dimer others oil yield 3.02 3.30 8.99

7.19 6.30 1.40

9.38 9.80 4.45

54.4 50.0 31.4

Table 5. Effect of Reaction Time on the Composition (wt %) of Degraded Oil from Catalytic (BaO) Pyrolysis of WEPS at 350 °C time (min)

B

T

EB

St

15 30 45 86

0.11 tr tr tr

1.37 1.51 2.11 4.73

0.20 0.26 0.52 2.02

84.29 78.01 71.66 58.74

total m-St dimer others oil yield 0.81 2.29 4.24 8.60

9.52 12.54 14.78 12.29

5.14 7.24 7.42 16.28

30.49 45.27 59.15 80.54

Table 6. Effect of Repyrolysis on Oil Composition (wt %) and Its Yield (wt %) component

Tr ) 390 °C (first)

Tr ) 390 °C (second)

Tr ) 430°C (second)

B T EB St m-St dimer others total oil yield

0.00 1.75 0.51 62.03 1.91 7.73 26.07 83.30

0.07 5.77 16.02 23.84 7.34 6.28 40.68 41.40

0.32 5.06 9.79 36.51 6.07 5.70 36.55 54.60

and high oil yield (73.20 wt %) can be achieved even at low pyrolytic temperature, i.e., 350 °C Effect of Catalyst Size. Catalytic pyrolysis of WEPS is investigated at reaction temperature 350 °C using different sizes of Fe2O3 catalyst (38, 48, 150 µm). The effect of catalyst size on oil yield and composition of oil is shown in Table 4. A decrease in catalyst size shows better conversion, and oil yield increases by 23 wt % with a decrease in catalyst size from 150 to 38 µm. Also the amount of benzene, toluene, ethylbenzene, and R-methylstyrene decreases with a decrease in the size of catalyst. This increase in oil yield may be due to the increased surface area of small-sized catalyst which increases the catalytic activity. Effect of Reaction Time on Catalytic Pyrolysis. WEPS is pyrolyzed at 350 °C with BaO(1.0 wt %), and the product oil is analyzed at different reaction times. The compositions of oils along with oil yields are reported in Table 5. Oil yield increases (30.49 to 80.54 wt %) with an increase in reaction time from 15 to 86 min, but styrene selectivity decreases from 84.29 to 58.74 for the same temperature change. The amount of styrene in the produced oil is maximum within 15 min of the reaction time. Thus, it is found that reaction time must be shortened for enhancement of styrene selectivity. Similar trends of styrene selectivity and oil yield for catalytic pyrolysis of PS were also reported by Lee et al. 17 Effect of Repyrolysis. WEPS is pyrolyzed at 390 °C, and the oil product contains 62.03 wt % styrene. This oil product is now divided into two parts and repyrolyze at temperatures 390 and 430 °C. Results of analysis of oils are reported in Table 6 and shown in Figure 9. On repyrolysis, styrene selectivity decreases by 41.9 (390 °C) and 28.7 (430 °C). It is clear from Table 6 that, on

Figure 8. Effect of reaction time on styrene selectivity and oil yield for BaO-catalyzed pyrolysis.

Figure 9. Effect of repyrolysis on oil yield.

repyrolysis, styrene monomer decomposes into lower molecules and also production of other aromatics increases. Conclusion TGA study of WEPS and GPPS reveals that pyrolysis is activated around 380°C and the rate of thermal degradation is maximum at 430 °C. Maximum styrene selectivity (76.31 wt %) with oil yield (95.1 wt %) is achieved during the non catalytic pyrolysis of WEPS at 450 °C. The rate of thermal degradation of WEPS is found to be higher than GPPS at 450 °C, and styrene production is also more by 11 wt % in the case of WEPS. Higher pyrolytic temperature decreases the reaction time considerably (Figure 3) and also decreases the production of benzene, toluene, ethylbenzene, and Rmethylstyrene, but increases the oil yield greater than 95 wt % (Table 2). The nature of the catalyst, its size, and reaction time of catalytic pyrolysis affect greatly the oil yield, production of styrene, as well as other aromatic components of oils. While the basic catalyst (BaO) increases the oil yield by 49 wt % and styrene selectivity by 13 wt %, acidic catalyst (Al2O3) decreases the styrene

1582 Energy & Fuels, Vol. 17, No. 6, 2003

production by 2 wt % and oil yield is also low (29.73 wt %). Modification of catalyst (Fe2O3) by coprecipitation with alumina (Fe/Al) and by impregnation with some basic material (Fe-A/Al) improve its efficiency and increase the oil yield by 17.68 wt % and styrene selectivity by 8.59 wt %. Decrease in catalyst size also increases the oil yield but has no considerable effect on styrene production. An increase in reaction time during

Park et al.

catalytic pyrolysis also increases the oil yield but at the cost of styrene. Oil yield as well as styrene selectivity decreases on repyrolysis of already pyrolyzed WEPS, and the decrease in oil yield is less if the reaction temperature during repyrolysis is higher.

EF030102L