Energy & Fuels 2003, 17, 75-80
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Liquefaction of Mixed Plastics Containing PVC and Dechlorination by Calcium-Based Sorbent Thallada Bhaskar,† Md. Azhar Uddin,†,| Jun Kaneko,† Toshiaki Kusaba,† Toshiki Matsui,‡ Akinori Muto,† Yusaku Sakata,*,† and Katsuhide Murata§ Department of Applied Chemistry, Faculty of Engineering, Okayama University, 3-1-1 Tsushima Naka, 700-8530 Okayama, Japan, Toda Kogyo Co., Ltd., Hiroshima 739-0652, Japan, and K. Murata Research Inc., Ichihara 290-0006, Japan Received April 10, 2002
The pyrolysis of PVC-containing mixed plastics (PVC/PP/PE/PS) was carried out at 430 °C under atmospheric pressure by semibatch operation using a carbon composite of calcium carbonate sorbent (Ca-C) and also in the absence of sorbent (thermal). An amount of 4 g of Ca-C sorbent was used for consecutive 6 batches (each batch 10 g plastic) of the mixed plastic (PVC/PP/PE/ PS:1/3/3/3) pyrolysis process. Hydrogen chloride and chlorinated hydrocarbons were produced during the pyrolysis of the mixed plastics containing PVC (PVC/PP/PE/PS). The Ca-C sorbent captured the hydrogen chloride evolved from the pyrolysis process. The theoretical sorbent capacity (71%) was utilized by repeatedly using the same sorbent for up to 5 consecutive batch processes without chlorine compounds in liquid products. The chlorinated hydrocarbons observed in the liquid products were obtained during run 5 (theoretical sorbent capacity 89%) and also during run 6 (theoretical sorbent capacity 106%). The hydrocarbons produced during the pyrolysis process reacted with the sorbent (during run 5) and yielded the chlorinated hydrocarbons in liquid products. X-ray diffraction studies revealed that the calcium carbonate sorbent was converted into calcium chloride during the pyrolysis process. The calcium-based sorbent was successfully utilized for the removal of chlorine content (inorganic and organic) from the pyrolysis process (PVC/PP/PE/PS:1/3/3/3) and produced halogen-free liquid products for 4 consecutive batch processes. The liquid products can be used as a fuel oil or feedstock in refinery.
Introduction In today’s modern world, plastics provide a fundamental contribution to all activities such as agriculture, automobile industry, electricity and electronics, building materials, packing, and so on. Increased production of plastic leads to generation of enormous amounts of waste, particularly in more industrialized countries, as they are not biodegradable when buried in landfills. Mechanical recycling can be performed solely on single polymer plastic waste because a market can be found only if the recycled products match the original products as closely as possible in quality. Incineration of plastic waste to produce heat may be a possibility, but its organic content would totally be destroyed and converted only into CO2 and H2O. In addition, depending on its nature, combustion may produce pollutants such as light hydrocarbons, nitrous and sulfur oxides, dusts, dioxins, and other toxins that have a highly negative impact on the environment. New pathways in plastic recycling and the current status of plastics recycling has been recently highlighted * Corresponding author. Tel: +81-86-251-8081. Fax: +81-86-2518082. E-mail:
[email protected]. † Okayama University. ‡ Toda Kogyo Co., Ltd. § K. Murata Research Inc. | Present address: Process Safety and Environment Protection Group School of Engineering, The University of Newcastle Callaghan, NSW 2308, Australia.
by Kaminsky et al.1 The development of different viable recycling technologies for plastic waste materials is becoming increasingly important. There is growing interest in thermolysis and catalytic polymer degradation as methods of producing various fuel fractions from polymer wastes. Pyrolysis is one of the best methods for preserving valuable petroleum resources in addition to protecting the environment by limiting the volume of nondegradable waste. Pyrolysis of waste plastics is favored because of the high rates of conversion into oil, which can be obtained. The gaseous products coming from the pyrolysis process with high caloric value may be used as fuel in the process. Recycling by pyrolysis has high potential for heterogeneous waste materials, which cannot be economically separated. There has been a plethora of research work published on the pyrolysis of waste plastics into fuel. Pyrolysis involves the thermal degradation of organic matter in an oxygen-free environment. Kaminsky2 studied the thermal cracking of PE in a fixed bed reactor over the temperature range 500-600 °C. At temperatures below 550 °C, high yields of useful products with low yields of gas and aromatics were obtained. Ding et al.3,4 have (1) Kaminsky, W.; Hartmann, F. Angew. Chem., Int. Ed. 2000, 39, 331. (2) Kastner, H.; Kaminsky, W. Hydrocarbon Process. 1995, 74, 109. (3) Ding, W.; Liang, J.; Anderson, L. L. Energy Fuels 1997, 11, 1219. (4) Ding, W.; Liang, J.; Anderson, L. L. Fuel Process. Technol. 1997, 51, 47.
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studied hydrocracking of PE using HZSM-5 and metalloaded hybrid catalysts prepared from HZSM-5 and silica-alumina. HZSM-5 produced more aromatic hydrocarbons, whereas hybrid catalysts (especially Niloaded) showed higher hydroisomerization ability. An interesting result was that the liquid products obtained over hybrid catalysts were clean and white or light yellow with a gasoline like smell, while the liquids produced from thermal cracking and over HZSM-5 were brown red with a strong unpleasant smell. Agudo et al.5 investigated the effect of β-zeolite on the degradation of PP, LDPE, and HDPE at 400 °C in a batch reactor. It was observed that degradation of HDPE affords a high selectivity of C5-C12 products (70 wt %), whereas in the cracking of LDPE and PP, selectivity to gasoline is reduced (64 wt %) and higher proportions of lighter products C1-C4 are obtained. The solid superacidcatalyzed depolymerization-liquefaction (DL) reactions of high-density polyethylene, isotactic polypropylene, and cis-polybutadiene sample were investigated by Shabtai et al.6 Dehydrochlorination of plastic mixtures was studied by Bockhorn et al.7-9 They explained that those stepwise low-temperature pyrolysis mixtures of PVC, polystyrene, and polyethylene have been separated into hydrogen chloride, the monomer of polystyrene, and aliphatic compounds from polyethylene decomposition. The degree of conversion of chlorine from PVC into hydrogen chloride at the low temperature (330 °C) is about 99.6%.7-9 In our earlier studies,10-12 we reported on the catalytic degradation of PP and PE by silica-alumina catalyst in a semi-batch reactor and showed that silica-alumina was effective in increasing the degradation rate and yield of oil products. The studies13,14 were on the effect of catalyst type on polymer degradation and we observed that catalysts with strong acid sites such as zeolite accelerated the degradation of PP and PE into gases, which resulted in low liquid yields. We have also reported on the thermal and catalytic degradation of individual PE/PVC, PP/PVC, and PS/PVC by silica-alumina catalysts and dechlorination by iron oxides (FeOOH and Fe3O4 sorbents).15,16 The purpose of this study is to investigate the degradation of PE, PP, PS, and PVC mixed plastics and removal of inorganic (HCl) and also chlorinated hydrocarbon compounds produced during the degradation process by a novel calcium carbonate-carbon composite sorbent (Ca-C). The study also concentrated on the (5) Aguado, J.; Serrano, D. P.; Escola, J. M.; Garagorri, E.; Fernandez, J. A. Polym. Degrad. Stab. 2000, 69, 11. (6) Shabtai, J.; Xiao, X.; Zmierczak, W. Energy Fuels 1997, 11, 76. (7) Bockhorn, H.; Hornung, A.; Hornung, U.; Jakobstroer, P.; Kraus. M. J. Anal. Appl. Pyrolysis 1999, 49, 97. (8) Bockhorn, H.; Hornung, A.; Hornung, U. J. Anal. Appl. Pyrolysis 1998, 46, 1. (9) Hornung, A.; Bockhorn, H.; Hornung, U. Chem. Eng. Technol. 1998, 9, 21. (10) Sakata, Y.; Uddin, Md. A.; Muto, A.; Narazaki, L.; Murata, K.; Kaji, M. Polym. Recycl. 1996, 2, 309. (11) Sakata, Y.; Uddin, Md. A.; Muto, A.; Murata, K. Chem. Lett. 1996, 245. (12) Uddin, Md. A.; Koizumi, K.; Murata, K.; Sakata, Y. Polym. Degrad. Stab. 1997, 56, 37. (13) Sakata, Y.; Uddin, Md. A.; Muto, A. J. Anal. Appl. Pyrolysis 1999, 51, 135. (14) Sakata, Y.; Uddin, Md. A.; Muto, A.; Koizumi, K.; Kanada, Y.; Murata, K. J. Anal. Appl. Pyrolysis 1997, 43, 15. (15) Shiraga, Y.; Uddin, Md. A.; Muto, A.; Narazaki, M.; Sakata, Y.; Murata, K. Energy Fuels 1999, 13, 428. (16) Uddin, Md. A.; Sakata, Y.; Shiraga, Y.; Muto, A.; Murata, K. Ind. Eng. Chem. Res. 1999, 38, 1406.
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Figure 1. Schematic experimental setup for PP/PE/PS mixed with PVC degradation at 430 °C and dechlorination at 350 °C.
maximum utilization of theoretical sorbent capacity for HCl by repeatedly using the same sorbent for consecutive 6 batch runs (each run consisted of 10 g of mixed plastic consisting PVC:PP:PE:PS with 1:3:3:3 weight ratio) of PVC-mixed PP/PE/PS plastics. The mixed plastic ratio has been selected on the basis of the composition of municipal plastic waste. Experimental Section Materials. The high-density polyethylene (PE) was obtained from Mitsui Chemical Co. Ltd., Japan; polypropylene (PP) from Ube Chemical Industries Co. Ltd., Japan; polystyrene (PS) from Asahi Kasei Industries Co., Ltd., Japan; and poly(vinyl chloride) (PVC) from Geon Chemical Co. Ltd., Japan. The grain sizes of PP, PE, PS, and PVC were about 3 mm × 2 mm. The calcium carbonate-carbon composite sorbent (CaC) was cooperatively developed with Toda Kogyo Co., Ltd., Hiroshima, Japan. Preparation of Ca-C. About 90 wt % of CaCO3 was mixed with 10 wt % of phenol resin by mechanical kneading; during the kneading process 20% of water was added to the mixture and pellet formation was accomplished by molding method. The prepared sorbent was calcined at 500 °C for 1 h in an inert atmosphere. The finished sorbent designated as Ca-C (calcium carbonate-carbon composite) and had a surface area of 40 m2 g-1. Powder X-ray diffraction analysis confirmed the presence of CaCO3 phase in Ca-C. Experimental Procedure. Pyrolysis of PP/PE/PS mixed with PVC was carried out in a glass reactor (length: 32 cm; i.d. 2 cm) under atmospheric pressure by batch operation with identical experimental conditions and temperature program. Briefly, 10 g of mixed plastics [weight ratio: (PVC/PP/PE/PS ) 1/3/3/3)] was loaded into the reactor for degradation in vaporphase contact with Ca-C. The fresh PP/PE/PS and PVC grains were well mixed and used for degradation. The Ca-C (1 mm av. diam.) was loaded into the another reactor (dechlorination reactor) (Figure 1) and the sorbent bed temperature was kept at 350 °C. In a typical run, after setting the reactor, the reactor was purged with nitrogen gas at a flow rate of 10 mL/min and held at 120 °C for 60 min to remove the physically adsorbed water from the sorbent and plastic sample. The reactor temperature was increased to the degradation temperature (430 °C) at a heating rate of 3 °C/min [(degradation reactor temperature program, room temperature (rate 3 °C/min) f 120 °C (rate 3 °C/min; hold 60 min) f 430 °C]. The dechlorination reactor temperature (350 °C) was increased linearly at a heating rate of 5 °C/min [(dechlorination reactor temperature
Liquefaction of Mixed Plastics Containing PVC program, room temperature f 350 °C (rate 5 °C/min)]. In a similar way, the thermal degradation of plastics was carried out in the absence of sorbent. A schematic diagram of the experimental setup is shown in Figure 1. Waste plastic bed temperature was taken as the temperature of the degradation, and the sorbent bed temperature was taken for the dechlorination process (Figure 1). The gaseous products were condensed (using a cold water condenser; Figure 1) into liquid products and trapped in a measuring jar. An amount of 80 mL of 1 M NaOH was used for NaOH trap (container capacity 100 mL). The weight of a reactor including the mixed plastics was measured before and after the degradation process. The weight difference (X) between before and after the degradation was considered as liquid and gas yields. The residue [(plastic feed (10 g) - X] was the difference between plastic feed and liquid & gas yields. There is very small amount of liquid products on the reactor walls and on the sidearm. Analysis Procedure. The quantitative analysis of the liquid products (collected once at the end of experiment) was performed using a gas chromatograph equipped with a Flame Ionization Detector (FID; YANACO G6800; column, 100% methyl silicone; 50 m × 0.25 mm × 0.25 µm; temperature program, 40 °C (hold 15 min) f 280 °C (rate 5 °C/min; hold 37 min) to obtain the quantity of hydrocarbons and carbon number distribution of the liquid products. The distribution of chlorine compounds and the quantity of halogen content (organic) in liquid products were analyzed by a gas chromatograph equipped with atomic emission detector (AED; HP G2350A; column, HP-1; cross-linked methyl siloxane; 25 m × 0.32 mm × 0.17 µm). 1,2,4-Trichlorobenzene was used as the internal standard for the quantitative determination of the chlorine content using the GC-AED analysis. The Cl content in the NaOH trap (Figure 1) was analyzed using an ion chromatograph (DIONEX, DX-120 Ion Chromatograph). The main liquid products were also analyzed by a gas chromatograph with a mass selective detector [GC-MSD; HP 5973; column, HP-1; cross-linked methyl siloxane, 25 m × 0.32 mm × 0.17 µm; temperature program, 40 °C (hold 10 min) f 300 °C (rate 5 °C/min) hold for 10 min] for the identification of various chlorinated hydrocarbons in liquid products. The composition of the liquid products was characterized using C-NP grams (C stands for carbon and NP from normal paraffin) and Cl-NP gram (Cl stands for chlorine). The curves were obtained by plotting the weight percent of Cl, which was in the liquid products, against the carbon number of the normal paraffin determined by comparing the retention times from GC analysis using a nonpolar column. In this GC column, peaks for the hydrocarbons appear in order of increasing boiling points.
Results and Discussion The pyrolysis of mixed plastics containing PVC (PVC/ PP/PE/PS) was carried out under atmospheric pressure in a batch process using Ca-C sorbent and also thermal degradation (no sorbent). The products of mixed plastic degradation were classified into three groups: gas, liquid, and degradation residue. Table 1 shows the yield of products (gas, liquid, and residues) and average carbon number (Cnp) and density of liquid products obtained during thermal degradation and also using Ca-C sorbent. The thermal degradation (PVC/PP/PE/ PS at 430 °C) produced liquid products (63 wt %), with the average carbon number of 10.4 and density 0.79 g/cm3. The liquid product obtained during the degradation with Ca-C sorbent was about 67 (run 1) and 75 wt % (run 5). There is no appreciable change in the Cnp and density of liquid products obtained during both thermal degradation and degradation using Ca-C sor-
Energy & Fuels, Vol. 17, No. 1, 2003 77 Table 1. Product Yields and Properties of Liquid Product from PVC Mixed PP/PE/PS [10 g] Plastic Degradation Using Ca-C [consecutive 6 runs] and Thermal Degradationa degradation and run number using Ca-C thermal 1 2 3 4 5 6
yield of degradation products [wt %] liquid products liquid [L]
gas [G]b
residue [R]
Cnpc
density (g/cm3)
63 67 65 67 69 75 70
24 23 22 21 21 15 20
13 10 13 12 10 10 10
10.4 10.8 10.7 10.7 10.9 10.8 10.6
0.79 0.80 0.79 0.79 0.80 0.81 0.80
a Weight ratio: PVC:PP:PE:PS ) 1:3:3:3; weight of Ca-C: 4 g; degradation temp: 430 °C; dechlorination temp: 350 °C. b G ) 100 - (L + R). c Cnp ) average carbon number of liquid products based on C-NP gram.
Table 2. Chlorine Content in PVC Mixed PP/PE/PS [10 g] Plastic Degradation Liquid Products Using Ca-C [consecutive 6 runs] and Consumed Theoretical Sorbent Capacity for Each Runa degradation and run number using Ca-C
chlorine content in liquid products (ppm)
consumed theoretical capacity of CaCO3 [%]
thermal 1 2 3 4 5 6
360 0 0 0 0 150 3000
18 35 53 71 89 106
a Weight ratio: PVC:PP:PE:PS ) 1:3:3:3; weight of Ca-C: 4 g; degradation temp: 430 °C; dechlorination temp: 350 °C.
bent (Table 1). The gaseous products obtained during the thermal degradation were approximately same as with the degradation using sorbent (Table 1). There is no appreciable change in amount of residue for the thermal degradation and also degradation using sorbent from run 1 to run 4. Roy et al.18 reported on the vacuum pyrolysis of commingled plastics (HDPE/LDPE/PP/PS) containing PVC at a final temperature of 500 °C and under a total pressure of 2 kPa. During their vacuum pyrolysis studies, the pyrolysis oil contained 12 ppm Cl on a pyrolysis oil basis. Pyrolysis under vacuum reduces the incidence of secondary reactions in comparison to slow pyrolysis at atmospheric pressure.18 The total chlorine content in liquid products obtained during thermal degradation, degradation using Ca-C sorbent, and also consumed theoretical capacity of Ca-C sorbent during each run of mixed plastic degradation were presented in Table 2. As can be seen from Table 2, 360 ppm of chlorine content was found in liquid products obtained during thermal degradation. However, the chlorine content is zero (not detected) from run 1 to run 4 by using Ca-C sorbent (4 g), indicating that the chlorine compounds (inorganic and organic) were completely removed from the liquid products. The theoretical consumption capacity of CaCO3 was calculated as follows. In the present study, 1 g of PVC (for each batch 1 g of PVC) and 4 g of CaCO3 (the same (17) Williams, E. A.; Williams, P. T. J. Anal. Appl. Pyrolysis 1997, 40-41, 347. (18) Miranda, R.; Pakdel, H.; Roy, C.; Vasile, C. Polym. Degrad. Stab. 2001, 73, 47.
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sorbent repeatedly used for run 1 to run 6) sorbent was used for the experimental investigation. A 1-g amount of PVC contains 0.524 g of Cl and 4 g of CaCO3 can consume 2.92 g of Cl (1 g CaCO3 can react with 0.73 g Cl). Table 2 shows that Ca-C sorbent consumed all the chlorine for run 1, indicating that about 18% (0.524/ 2.92 × 100) of theoretical sorbent capacity was utilized. In a similar way, the theoretical consumed sorbent capacity was calculated for run 2 to run 6. The chlorine content in the aqueous NaOH trap was analyzed by ion chromatograph. During thermal degradation about 92 wt % of HCl (gaseous) was found in the NaOH trap, about 3 wt % of chlorine was observed in the residue, and the remaining 5 wt % might be in the gaseous products collected in the Teflon bag (Figure 1). The degradation using Ca-C sorbent showed that there is no chlorine in oil from run 1 to run 4. However, there is a small amount of chlorine in the NaOH trap during run 3 (0.33 wt %) and run 4 (1.21 wt %). The degradation for run 5 and run 6 showed the presence of chlorine in oil (Table 2) and also in the NaOH trap (run 5 ) 1.68 and run 6 ) 55.3 wt %). Meszaros19 reported the pyrolysis of municipal plastic waste (MPW) containing 3% of PVC in an auger kiln reactor (Conrad recycling process). Lime was used to trap the HCl evolved, which resulted in liquid products with 25 ppm of chlorine. In the present process, the inorganic chlorine compounds (HCl) were captured by the Ca-C sorbent and the chlorinated hydrocarbons produced during the PVC mixed plastic pyrolysis process were dehydrohalogenated by Ca-C. About 71% of the theoretical HCl sorption capacity of Ca-C was utilized for the 4 batches of the PVC mixed PP/PE/PS plastic pyrolysis process. The chlorine content of 150 ppm was observed during run 5 of the degradation, and the chlorine content increased from 150 to 3000 ppm (run 6), which is higher than the thermal degradation. It clearly indicates that the sorbent cannot be used in the process after 71% of theoretical capacity (Table 2). The presence of a higher content of chlorinated hydrocarbons during run 6 (3000 ppm) than that of thermal degradation (360 ppm) might be due to the hydrocarbons produced during the pyrolysis process reacting with the calcium chloride (CaCO3 converted to CaCl2 during the process) and forming the chlorinated hydrocarbons in the liquid products. This process is an additional process other than forming the chlorinated hydrocarbons by reaction of free hydrogen chloride with hydrocarbons produced during the thermal degradation. In the present study, we were able to utilize about 71% of its theoretical capacity (upto 4 batch processes) without chlorine compounds in the liquid products. Williams and Williams17 studied the pyrolysis of municipal plastic waste (MPW) in a fluidized bed reactor at atmospheric pressure. A dreschel bottle of deionized water was used in order to trap the evolved HCl, but only 27.5% of the HCl was trapped. Bockhorn et al.8 studied the pyrolysis of a PVC/PS/PE (1:6:3 by weight) mixture in three circulated-sphere reactors arranged in a cascade and they detected 44 ppm of chlorine in oil from the third reactor, which mainly contained aliphatic (19) Meszaros, M. W. In ACS Symposim series 609; Andrews, G. D., Subramanian, P. M., Eds.; American Chemical Society: Washington, DC, 1996; Chapter 15, p 170.
Bhaskar et al.
Figure 2. C-NP gram of liquid products obtained during PP/ PE/PS mixed with PVC thermal degradation and degradation using Ca-C sorbent.
Figure 3. Cl-NP gram of liquid products obtained during PP/ PE/PS mixed with PVC thermal degradation and degradation using Ca-C sorbent.
compounds. However, the chlorine content in the oil from the second reactor was still high at 210 ppm (by weight). The liquid products were characterized by a Normal Paraffin gram (NP-gram) proposed by Murata and Makino et al.20 Figure 2 illustrates the C-NP gram of the liquid products obtained by analyzing their gas chromatogram. The carbon numbers in the abscissa of the NP-gram are equivalent to retention time (from gas chromatogram) of the corresponding normal paraffin and the ordinate shows the weight percent of the corresponding hydrocarbons [g(Cl)/g(Oil) × 100 wt %]. The hydrocarbon amount (C6-C11) during the thermal degradation and degradation using Ca-C sorbent was 47 wt %. As with the C-NP gram, the carbon number distribution of chlorinated hydrocarbons [weight percent of chlorine ) g(Cl)/g(Oil) × 100 wt %] in the liquid product was prepared from the gas chromatogram obtained using a gas chromatograph with an atomic emission detector (GC-AED). The weight percents of chlorinated hydrocarbons are presented in a Cl-NP gram in Figure 3. The hydrocarbons containing the chlorine were distributed in the range of C6-C11. The liquid products were analyzed by GC-MS to identify the (20) Murata, K.; Makino, M. Nippon Kagaku Kaishi 1975, 1, 192-200.
Liquefaction of Mixed Plastics Containing PVC
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Figure 4. GC-AED chromatograms of chlorine compounds for PP/PE/PS mixed with PVC thermal degradation and degradation using Ca-C; b, internal standard for chlorine (1,2,4-trichlorobenzene); 2, 2-chloro-2-phenylpropane; º, R-chloroethylbenzene; 9, 2-chloro-2-methylpentane; O, 2-chloro-2-methylpropane.
compounds. Both the chlorine content and concentration of chlorine-containing organic compounds in liquid products were determined by gas chromatography with an atomic emission detector (GC-AED), which provides a selective detection of Cl in the liquid products. The selective chlorine compounds analyzed by GC-AED chromatograms are presented in Figure 4. The presence of chlorinated compounds during the thermal degradation and degradation with sorbent (run 5 to run 6) was observed. 2-Chloro-2-phenylpropane was the major chlorine compound observed during thermal degradation (Figure 4a) and also during run 6 (Figure 4d). 2-Chloro2-methylpropane, 2-chloro-2-methylpentane, and R-chloroethylbenzene was also identified during 5 and 6 runs (Figure 4c and Figure 4d). The formation of chlorinated hydrocarbons might be due to either of the following reactions: Cl radicals produced by the thermal degradation of PVC reacting with cracked hydrocarbon species or free hydrogen chloride reacting with cracked hydrocarbon species. We suggest the latter, i.e., that organic compounds are produced by the reaction between hydrogen chloride originating from PVC and the hydrocarbons obtained from the degradation of PE, PP, and PS.16 The chlorinated hydrocarbons formed during the pyrolysis of commingled plastics were different from those obtained during the thermal decomposition of pure PVC. However, the hydrocarbons produced in the oil fraction were similar to those identified during the pyrolysis of single plastics.18 The representative X-ray diffraction patterns of the Ca-C before and after the degradation experiment are shown in Figure 5. The X-ray diffraction pattern before
Figure 5. X-ray diffraction patterns of Ca-C sorbent before and after the pyrolysis: (a) before degradation (peaks due to CaCO3), and (b) after degradation (peaks due to CaCl2‚nH2O, n ) 2, 4).
degradation indicates the presence of CaCO3 phase (Figure 5a) but after degradation the CaCl2.nH2O (where n ) 2, 4) phase (Figure 5b) peaks were observed, indicating the sorption of chlorine by CaCO3. Conclusions It was demonstrated that the pyrolysis of PVC containing PP/PE/PS mixed plastics (degradation at 430 °C) using Ca-C sorbent was carried out into halogen free liquid products (dechlorination at 350 °C). The Ca-C sorbent was used successfully for the consecutive
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6 batch processes and obtained the halogen-free liquid products up to 4 run by utilizing 71% of sorbent theoretical HCl sorption capacity. The use of the same sorbent beyond its experimental sorption capacity produced more chlorinated compounds than the thermal degradation. The liquid products obtained during this process can be used as fuel oil or feedstock in refinery. The use of the novel Ca-C sorbent for the real municipal waste plastic pyrolysis plant at Mizushima, Japan, is under progress.
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Acknowledgment. The authors thank New Energy Development Organization (NEDO), Japan, for financial support to carry out this research work under the Chugoku regional consortium project (2000-2003). We are grateful to Dr. K. Nagata (Industrial Technology Center of Okayama Prefecture)and Dr. Y. Kusano (Kurashiki University of Science and Arts, Japan) for their valuable discussions. EF020091G
