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

CHARACTERISTICS OF BY-PRODUCTS ANDDIOXIN EMISSION FROM PYROLYSIS PROCESS FORURETHANE/STYROFOAM WASTE OF ELECTRIC
HOME APPLIANCES
Sung-Jin Cho1, Ki-Heon Kim2, Hae-Young Jung1, Oh-Jun Kwon2, Yong-Chil Seo*1
1

Dept. of Environmental Engineering, YIEST, Yonsei University, Wonju, R.O.Korea
National Institute of Environmental Research, Environmental Research Complex,Incheon, R.O.Korea
Tel.: +82-33-760-2438, fax: +82-33-763-5224
E-mail: seoyc@yonsei.ac.kr

2

Abstract: EU directive RoHS (Restriction of Hazardous Substances) prohibits marketing ofelectrical home appliances containing harmful substances such as lead, cadmium, mercury,chromium (VI), Polybrominated biphenyls (PBBs), and Polybrominated diphenyl ethers(PBDE). The enactment of RoHS was a big shock to Asian companies and especially to
Japanese companies as they have supplied major portion of their products to the global market.
Influenced by RoHS, most countries enacted the regulations and laws related to prohibiting
the use of such substances in the home appliances. The recycling rate of home appliancessuch as washing machine, TV, and air condition is currently above 90%, which is mostly
recycled in waste treatment/recycling facilities. In case of refrigerator and washing machine
all parts are recycled except urethane/styrofoam (14.36%). During recovery process, therefrigerant (CFCs) from the refrigerator is first recovered. After then copper, iron, aluminum,plastic, and rubber are separated and pass through the crushing and grinding process. The
reclaimed metals are almost recycled. Urethane/Styrofoam mixture is collected from urethane
separation device. The mixture ratio of urethane and styrofoam is usually 8.6:1, which aredifficult to separate. So, in most of the countries, the mixture is disposed of in landfill or isdirectly incinerated.
In this study, we evaluated the recycling possibility of urethane/styrofoam by a pyrolysis
process to generate any usable products such as syngas and use of residue as sorbent-activatedcarbon. A series of pyrolysis and carbonization experiments for the mixture sample werecarried out at various temperatures, and product gas, carbon characteristics and loss ofignition were analyzed to observe the characteristics of products and the feasibility of suchtechnology utilization.

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1. Introduction
According to Korean Association of Electronics Environment (KAEE), 1,438.5 thousand
units of refrigerators, 1,146.7 thousand units of washing machine, 885.6 thousand units oftelevision, 326.8 thousand units of air conditioner were discarded in 2006. The recycling rateof air conditioner, washing machine and TV is above 90%. All parts of these appliances arerecycled except urethane/styrofoam mixture which is mainly generated from refrigerators.
Since the separation of urethane/styrofoam from refrigerator is difficult, it is shredded and theportion of steel is recovered with leaving the mixture of urethane/styrofoam as residues. Then
most of them are sent to cement kilns to be burnt as auxiliary fuel or are disposed of at landfill.
Considering the limited land availability and environmental problems associated to landfilling,others treatment methods such as pyrolysis are to be evaluated for urethane/styrofoam
disposal. In this study, we evaluated the recycling possibility of urethane/styrofoam using
pyrolysis process. A series of pyrolysis and carbonization experiments were carried out atvarious temperatures. Yield of by-products, dioxin emission characteristics were alsoanalyzed. The characteristics of by-products: char, gas and oil were studied to evaluate thefeasibility of such technology utilization.
2. Experimental
2.1 Sampling of urethane/styrofoam waste
Urethane/styrofoam waste is the last material that remains after collecting valuablematerials (recyclable parts, valuable metals: Cu, Ni, Au and so on) from electric/electronichome appliance wastes (especially refrigerator, washing machine) at recycling facility.
Samples were collected after crushing and pulverizing process to feed samples
homogeneously and to reduce error during experiments.
2.2 Pyrolysis reactor and operational procedure
Fig. 1 presents a schematic diagram of lab-scale pyrolysis system. The feeder in thesystem was designed to operate in semi-batch mode. Reduction atmosphere in reactor wasmaintained by purging N2. Char was collected in crucibles (5). For collecting oil, two coolingsystems were used. Firstly, cool water was continuously circulated in the condenser (8) forcooling. And secondly, cooled by ice in the impinger train. As pyrolysis gas passes through 4
impinger sets with ice in the bottom, oil was condensed and collected. Gas samples werecollected in Tedlar bag for further analysis. Experiments were carried out at input rate ofurethane/styrofoam of 7g per 30 seconds, and pyrolysis temperature experimented wasvarying from 500 to 800 oC.
By-products (gas, oil, and char) generated at each pyrolysis experimental temperature
were evaluated carefully by observing the mass distribution to estimate the yield of them. The
characteristics of generated gas, oil, and char were studied. Dioxin in exhaust gas was
sampled and analysed by Korean standard methods.
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3

4

86

72

1

591011

1- nitrogen supply; 2- nitrogen controller; 3- feeder; 4- reactor #1; 5- reactor #2; 6- cyclone;
7- residue collector; 8- condenser #1; 9- condenser #2; 10- pump; 11- Tedlar bagFig. 1 Schematic diagram of lab scale pyrolysis system
HHV (High Heating Value) of oil was analyzed using bomb calorimeter (AC-350,LECO). SEM (Scanning Electron Microscope) analysis of char was done in SEM analyzer(JSm-5410, JEOL). Adsorption capacity of char and activated carbon were measured using
KS M1802 (Korean standard method: activated carbon experiment method). Adsorption
amount (Q) and decolorization capability (M) was calculated using residual concentration ofmethylene blue, and residual concentration was calculated from calibration curve.
Tab. 1 Equation of adsorption and decolorization① Adsorption amount② Decolorization capability

Q = ((1,200-C)*25/1,000)/S
Q = Methylene blue adsorption amount(mg/g)C = Methylene blue residual concentration(mg/L)
S = mass of sample (g)1,200 = Methylene blue concentration (mg/L)

M = Q/1.2
M = Methylene blue decolorization
capability (mL/g)
Q = Methylene blue adsorption amount(mg/g)
1.2 = Methylene blue liquids concentration(g/L)

3. Results and discussion
3.1 Yield of gas, oil and char, and HHV of oil
Yield result of by-products generated at each experimental temperature is presented inFig. 2. As pyrolysis temperature increased, residue mass of char decreased. But oil mass andgas showed opposite tendency with increasing products by temperatures. At 500oC, weightloss was minimum (about 70 wt.%), and was maximum at 800 oC, (about 90 wt.%). Oil and- 60 -PARTⅠ PYROLYSIS
gas mass was related with each other, that is, oil mass was high at higher cooling efficiency ofcondenser. Temperature of circulating water at condenser and ice impinger set were almost
same during these experiments. As temperature was higher, HHV of oil was higher as shownin Fig.3, which ranged from 6,000 to 8,000 kcal/kg.
3.2 Dioxin emission in exhaust gas
Dioxins concentration in gas leaving from the process at different pyrolysis temperature
is presented in Fig. 4. At 500 oC, 600 oC, 700 oC, 800 oC, dioxins concentrations were 946.999
ng-TEQ/Sm3, 38.449ng-TEQ/Sm3, 24.493ng-TEQ/Sm3, 4.756ng-TEQ/ Sm3, respectively. At
the temperature of 500 oC, the formation of dioxins was high since it could be closed tosynthesized temperature zone as known as de novo synthesis reaction. Concentration
percentage ratio of 2,3,7,8-isomer at different pyrolysis temperature is presented in Fig. 5.
Among isomers, 2,3,4,7,8-PeCDF in PCDFs was 20-40%; 1,2,3,7,8-PeCDD in PCDDs was10-30%. Higher portion of PCDFs was synthesized than PCDDs in all the experimental
pyrolysis temperatures since pyrolysis reaction was done in reduced condition.

100

10,000
char

8,000

oil

HHV, kcal/kg

wt.%

80gas

60
40
20

6,000
4,000
2,000

00500℃

600℃

700℃

800℃

500℃Fig. 2 Yield of gas, oil and char

800℃

80
PCDFs

PCDFs

800

PCDDs60

PCDDs

PCDFs+PCDDs

600%

3700℃

Fig. 3 High heating value of oil

1,000ngWHO-TEQ/Sm600℃

40400
20200
00500℃

600℃

700℃

Fig. 4 PCDDs/Fs concentration withpyrolysis temp.

800℃

500℃

600℃

700℃

800℃

Fig. 5 Percentage concentration distributionof PCDDs/Fs

3.4 Absorption ability of char
Fig. 6 shows the SEM result of urethane carbide produced as char. As temperature washigher, fineness of pore was increased, size of pore was smaller. However, the difference
between them was negligible. Also, absorption capacity of carbide pyrolyzed at different
temperatures was similar.

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

500℃

600℃

700℃

800℃

Fig. 6 SEM result of urethane carbide
Calibration curve (Fig. 7) is made using absorbance with methylene-blue concentration.
Using this, adsorption amount and decolorization capability was calculated. The adsorption
capacity and its decolorization were calculated relatively to activated carbon, considering thevalue for activated carbon as 100%. The relative adsorption was 99.16 to 99.85% anddecolorization was 99.81 to 99.85%. The various char samples obtained from different
pyrolysis temperatures did not show big differences with its adsorption capacity. The
adsorption and decolorization capacity of char was almost similar with activated carbon. Thisshows that the char from pyrolysis of urathane/styrofoam wastes can be used as sorbent.

0.8

101
Relative absorption

y = 0.2346x2

R = 0.9742

Relative decolorization
Activated carbon

0.4%

absorbance

0.61000.2

000.5

11.5

Me thylenblue concentration, mg/L

Fig. 7 Calibration curve

299500℃

600℃

700℃

800℃Fig. 8 Evaluation of absorption anddecolorization of char relative to AC

4. Conclusions
Recycling possibility using the prolysis of urethane/styrofoam wastes generated fromdismantling plants of home electric appliances was evaluated at a bench scale apparatus. Withchanging pyrolysis temperatures, yield of different phase products, dioxin content in gas, andproperties of char were observed for utilization of products. As pyrolysis temperature
increased, residue mass of char decreased while yields of oil and gas products increased. As
temperature was higher, HHV of oil was higher, which ranged from 6,000 to 8,000 kcal/kg.
At 500 oC, 600 oC, 700 oC, 800 oC, dioxin concentrations in gas were 946.999 ng-TEQ/Sm3,38.449ng-TEQ/Sm3, 24.493ng-TEQ/Sm3, 4.756ng-TEQ/ Sm3, respectively. So less dioxin is
generally formed in pyrolysis process, however the dioxin synthesis reaction could beoccurred at the temperature around 500 oC or less with a little amount of oxygen existing. For- 62 -PARTⅠ PYROLYSIS
produced char, as temperature was higher pore fineness increased and size of pore wassmaller. However the difference between them was negligible. Absorption capacity of char,pyrolyzed at different temperatures, was similar. The relative adsorption of char to activatedcarbon commercially available was 99.2 to 99.8% and decolorization showed about 99.8%.
Thus, the adsorption and decolorization capacity of char was almost similar with activatedcarbon. Further feasibility studies including economic evaluation will be made prior to utilize
pyrolysis technology to recover energy or usable by-products with the construction of a pilot
scale plant.
Acknowledgement
This work was sponsored by Brain Korea-21 (BK-21) project and the project related toASR handling supported by Korean Ministry of Knowledge Economy (MKE).
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