PARTⅠ PYROLYSISPYROLYSIS OF POST-CONSUMED WASTE PLASTICS FORTHE RECOVERY OF BTX-AROMATICS USING A
FLUIDIZED BED REACTOR
Su-Hwa Jung, Min-Hwan Cho, Joo-Sik Kim*
Faculty of Environ. Eng., Univ. of Seoul, 90 Jeonnong-Dong, Dongdaemun-Gu,Seoul 130-743, Korea.E‐mail: joosik@uos.ac.kr
Abstract: Waste plastics have been usually disposed on landfill sites or been utilizedenergetically, for instance, incineration. Modern Society, however, requires reasonable
alternatives to cope effectively with needs for energy- and environmental conservation.
Researchers consider the pyrolysis of plastic wastes to be an alternative, and intensive
researches have been carried out [1]. Via pyrolysis, plastic wastes can be converted into
chemical feedstock which can be used to produce new valuable products such as oils andgases of high caloric value. In this study, fractions of waste polypropylene and polyethylene
and mixed waste plastics, were pyrolyzed in a laboratory scale pyrolysis plant equipped with afluidized bed reactor and a char removal system, under different conditions. In experiments,
the influence of the reaction temperature, the feed rate, and the kind of fluidizing medium on
the product spectrum was investigated to optimize reaction conditions for the maximum
recovery for BTX-aromatics. Pyrolysis of the PP fraction produced oils up to 43 wt% of theproduct. With respect to the PE fraction, the maximum oil yield was above 60 wt% of theproduct. The target compound was BTX aromatics, whose amount in the oils reached 53 wt%
for the PP fraction and 32 wt% for the PE fraction. The oils that were obtained in theexperiments almost had no metal and chlorine contents.
1. Introduction
Waste plastics cause considerable problems in the world due to their large volume andthe difficulty of treating them. Incineration and landfill, which are traditional treatment
methods for waste plastics, cannot solve the problem regarding the treatment of plastic wastes
because suitable depots are expensive and because incineration stimulates the emission ofharmful gases [1]. Furthermore, waste plastics can only be partly recycled into new products
due to their contamination [2].
A promising treatment process for waste plastics is pyrolysis. The thermal and catalyticpyrolysis of waste plastics into fuel-like hydrocarbons or monomer under different conditions
has been well investigated by some researchers [3-5]. The pyrolysis of the polyolefin plastics- 73 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
LDPE, HDPE, and PP yields an oil product consisting mainly of alkenes, alkanes, andalkadienes; a gas product consisting of hydrogen, alkanes, and alkenes; and negligible char
[6,7]. Many researches on the pyrolysis of waste plastics have been carried out in a fluidized
bed reactor. Pyrolysis in a fluidized bed reactor, which offers high heat and mass transfer andconsequently almost a constant temperature, provides a more uniform spectrum of products
due to the shorter residence times in the reactor. As a result of the uniformity of the productspectrum, the possibility of applying the process at a relatively small scale gives rise to awider range of investment alternatives [8].
The annual generation of waste plastics in Korea currently amounts to 4.6 million
ton/year, and is continually increasing. Polypropylene and polyethylene are the main
components of such plastic wastes. In this study, three waste fractions of polypropylene,polyethylene, and mixed plastics, were pyrolyzed in a pyrolysis plant equipped with afluidized bed reactor and a char removal system. The aim of this study was to find out theoptimal temperature for a high yield of BTX aromatics and to reduce the chlorine content in
the pyrolysis oils by applying additives, such as CaO, Ca(OH)2, rice straw and oyster shell.
2. Experiments
2.1 Feed material
Three pellet-type fractions of waste plastics, polypropylene, polyethylene and mixed,
were used in the experiments. To capture HCl liberated during pyrolysis, CaO, Ca(OH)2, ricestraw and oyster shell were premixed with waste plastics. The main properties of the feedmaterials including chlorine contents are shown in Tab. 1.
Tab. 1 Specifications of feed material
Proximateanalysis(wt.%)PP

Moisture
Volatile
matterFixedcarbonPE

Mixed

Ultimateanalysis(wt.%)

PPPE

Mixed

0.15

0.1

1.37

C

80.3

81.8

79.85

95.08

98.87

92.9

H

13.2

13.6

12.26

1.22

0.04

1.14

O

1.7

1.9

5.08

3.55

0.99

4.59

Cl0.060.01

1.13

Ashaaby difference- 74 -PARTⅠ PYROLYSIS
2.2 Pyrolysis plant and Procedure
The pyrolysis plant consisted mainly of a feeding system, a fluidized bed reactor, a charremoval system, a quench system, and a gas-circulating system. The feeding system wasequipped with two screw feeders with variable feed rates, so they would input uniformly. Thereactor, which was indirectly heated by electricity, was made of a sus-316 steel tube with aheight of 300 mm and an inner diameter of 80 mm. The reaction temperature was determinedbased on the average value taken from the three thermocouples in the reactor. The gas
distributor was made of steel, with 49 bending tubes designed to prevent the fluidizing quartz
sand (0.4 mm) from falling through the plate. The char removal system was made up of acyclone and a hot filter designed to capture particles bigger than 10 and 2 µm, respectively.
The quench system, which was cooled to -30 °C using ethanol, consisted of four glasscondensers for the precipitation of oil and of an electrostatic precipitator by which theaerosols were captured. The non-condensable gas was recycled using a compressor, and wasused as the fluidizing gas. During the pyrolysis, the non-condensable gas was sampled, using
teflon gas bags (2L) at 10 min intervals, to analyze their composition. The excess gas wasburned in a flare stack to regulate the pressure. A schematic diagram of the pyrolysis plant isshown in Fig. 1.

Fig. 1 Schematic diagram of the pyrolysis plant.
2.3 Reaction Conditions
In each experiment, the input of the feed material was 0.5 kg, and 1.5 kg quartz sand wasused as the fluidized bed material. The experiments from Run1 to Run4 for all the fractions
were performed to determine the influence of the reaction temperature on the aromatics yield.
To achieve a high yield of BTX aromatics, reaction temperatures ranging from 660 °C to 780°C were selected. The reaction conditions of the experiments are shown in Tab.2.
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The 5th ISFR (October 11-14, 2009, Chengdu, China)

Tab. 2 Reaction conditions
Polypropylene
Parameters

Reaction
temperature(°C)
Feed rate(g/min)Flow rate(NL/min)

Polyethylene

MixedRun
1Run
2Run
3Run
4Run
1Run
2Run3Run
4Run
1Run2Run
3Run
4668

703

727

746

660

680

704

728

677

710

735

773

4.5

4.5

4.5

4.5

5.2

5.2

5.2

5.2

6.7

6.7

6.7

6.7

29

28

27

26

292828

27

53

50

48

46

3. Results and Discussions
3.1 Organic Mass Balance
In establishing organic mass balance, the product oil and char yields were determined byweighing after the pyrolysis experiments. The amount of gas production was calculated, alongwith the gas density and the measured gas volume. Thereafter, distillation with the product oil
was conducted to separate the light oil from the viscose residue. The light distilled oil and theviscose fraction were designated as oil and distillation residues, respectively. Finally, the charand distillation residues were burnt in a furnace to find out the amount of organic mass inthem. The organic mass balance from Run1 to Run4 is shown in Tab. 3.
Tab. 3 Organic Mass Balance of the Pyrolysis Experiments
Product

Polypropylene

Mixed

Polyethylene

Run1 Run2 Run3 Run4 Run1 Run2 Run3 Run4 Run1 Run2 Run3 Run4Oil

43.1

35.9

34.7 29.6

60.9

56.6

43.6

38.2

35.2

32

29.725.9Gas

54.4

57

61.7 65.9

36.6

42.8

54.6

59.3

57.8

61.2

61.9

64.4

Char2

6.9

3.1

4

0.7

0.3

0.3

25

4.5

6.3

7.2

Distillation
residue

0.5

0.2

0.5

0.5

1.8

0.3

1.5

0.5

1.9

2.3

2.1

2.5

3.2 Chlorine Content in Pyrolysis Oil
Additives, such as CaO, Ca(OH)2, oyster shell and rice straw, was pre-mixed with mixed
waste plastics that contains relatively high amount of chlorine in them. Fig. 2 presents theeffect of the various additives on the chlorine content. It can be seen that CaO, Ca(OH)2 and- 76 -PARTⅠ PYROLYSIS
oyster shell were significantly influence on the chlorine removal but rice straw was slightlydecreased.

Fig. 2 Effect of additives on the chlorine content
4. Conclusions
Pyrolysis of waste plastics (PP, PE and mixed fractions) was carried out in a fluidized
bed reactor equipped with a char removal system, under various reaction temperatures. The
oil that was obtained in the experiments consisted of aliphatics and mono- and polyaromaticcompounds. For the target compounds (BTX aromatics), up to 53 wt% was obtained for thePP fraction in the oil, and up to 32 wt% for the PE fraction, up to 51 wt% was obtained for themixed fraction in the oil. For PP and PE fractions, it was found that the concentration of BTX
aromatics in the oil increased along with the reaction temperature but the mixed fraction wasslightly decreased at the reaction temperature 773°C. The main compounds of the pyrolysis
gas were methane, ethene, ethane, propene, butadiene, and butane, and the maximum heating
value of the gas obtained in both cases was about 50 MJ/kg. Therefore, the pyrolysis gas
seems to be appropriate for use as a heating source in a pyrolysis plant. Ethene and propene, if
separated from the other gas components, can be utilized as chemical feedstock for theproduction of polyolefin. The oils that were obtained in the experiments almost had no metalcontent. The metals were concentrated in the char and in the distillation residue. In addition,
the amount of chlorine in the oil was below 10 ppm for both the PP and PE fractions. Due tothe lower metal and chlorine contents of the oil, it seems that the environmental problems
caused by the burning of the oil would not be serious. Chlorine content of mixed fraction wasdecreased about up to 50 ppm by addition of additives (CaO, Ca(OH)2 and oyster shell). Thechar and distillation residue produced in the experiments consisted mainly of inorganics,- 77 -

The 5th ISFR (October 11-14, 2009, Chengdu, China)
whose utilization remains a challenge. Pyrolysis char, however, has potential for use in roadsurfacing and as a building material.
Acknowledgement
The authors express great thanks for financial support from the Korea Energy
Management Corporation (“New & Renewable Energy R & D project”).
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[4] M. R. Hernandez, A. N.Garcia, A. Marcilla, J. Anal. Appl. Pyrolysis, 2007,78, 272-281.
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