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2011

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TOLEDO (SPAIN)ADVANCES IN THE RECYCLING OF PLASTIC WASTES FOR METALLURGICAL
COKE PRODUCTION
M.A. Diez and R. Alvarez
Instituto Nacional del Carbón, INCAR-CSIC, Apartado 73, 33080-Oviedo. Spain.
e-mail: madiez@incar.csic.esAbstract
This paper is intended to provide useful knowledge on the use of plastic wastes for carbonization with coking blends in orderto produce metallurgical coke. It focuses on the influence of the composition of plastic wastes on the pressure generated
during the coking process and on the quality of the cokes produced in a semipilot coke oven. Several binary, ternary andmulticomponent plastic mixtures of two types of thermoplastics, polyolefins (HDPE, LDPE and PP) and aromatic polymers(PS and PET) are used. It is shown that polyolefins may be employed to maintain the coke quality parameters but they havea negative effect on the generation of coking pressure, while plastics of the aromatic type such as PS and PET can be used
to balance the generation of coking pressure. In light of the results, a relative proportion of polyolefins:aromatic polymers
close to 65:35 w/w under the conditions applied in this study may be considered an optimum proportion for counteracting thegeneration of pressure during the coking process and for maintaining or enhancing the quality of the cokes. These results
confirm previous findings using a different coal blend and multicomponent plastic wastes.

Keywords: Plastic wastes, recycling, coal, coking, metallurgical coke

1. Introduction

2. Materials and Methods

The environmental challenge of developing a recyclingoriented society requires the implementation andpromotion of the law of the 3Rs (reduce, reuse andrecycling) in order to minimize the environmental impact
of wastes in landfill sites and to conserve our naturalresources [1,2]. In recent years, the recycling of plastics
from municipal wastes has increased via different routes
including mechanical recovery, feedstock recycling andenergy recovery. As a consequence, the amount ofplastic household wastes dumped in landfill sites hasdecreased, but the amount of plastics disposed of in thisway still continues to be a major problem and otheralternatives need to be implemented. New strategies forrecycling plastic wastes are of great importance,
especially if they can be incorporated into consolidated
industrial processes that offer a stable and continuousroute. The feedstock recycling of plastic wastes in
integrated steel industries could contribute to theexpansion of plastic recycling via two routes: a) the blastfurnace where plastics are injected as a reducing agent[3,4]; and b) coke ovens as additives to coal blends forthe production of coke [5-9]. Both recycling alternatives
have been industrially implemented [3,5,6], where thelocal conditions and quality criteria allow it. In light of thedifferent effect of each type of thermoplastics present inmunicipal wastes upon the properties of coal, the coking
process and the coke quality [7-9], we have focused ourattention on optimizing the relative proportion of two wellestablished plastic groups in the wastes: polyolefins(HDPE, LDPE and PP) and polyaromatics (PS and PET).

Co-carbonization tests of an industrial coal blend (B:VM= 23.9 wt% db, Gieseler fluidity = 517 ddpm), used by
the steel industry in coke manufacture, with a plastic
waste addition of 2 wt% (of both individual and mixedplastics) were carried out in a movable-wall coke-oven of
17 kg capacity. By means of this oven it is possible tomeasure the force exerted by the charge on the ovenwall during the carbonization process (coking pressure)and to obtain a large enough quantity of coke for it to be
characterized by the standard methods used by the steel
industry. The plastic wastes were provided by theSpanish recycling company Abornasa. The bulk densities
were kept in the 756±20 kg/m3 range on a dry basis. Thequality of the resultant cokes for use in a blast furnace
was assessed in terms of reactivity to CO 2 at 1100 ºC for
2 h (CRI) and mechanical strength after reaction withCO2 (CSR index) by the NSC method, following theASTM D5341 standard procedure.

interiores libro.indd 21

3. Results and Discussion
When HDPE is added to the coal blend at an addition
rate of 2 wt%, the pressure generated during the coking
process (Pc) increases from about 5 kPa in the case of
the coal blend with no plastic waste added up to 39 kPa.
This pressure value is extremely high and exceeds thesafety limit established for cokemaking in this type ofoven (maximum limit value of 20 kPa under theexperimental conditions applied). A similar effect isobserved for the binary mixture of LDPE and PP (37 kPa)
and a muticomponent waste containing 95 % polyolefins(38 kPa). However, when PET is added to HDPE in

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6th International Symposium on Feedstock Recycling of Polymeric Materials

different proportions (75:25, 65:35 50:50, 25:75) and tothe LDPE+PP binary mixture (50:50), the coking
pressure decreases until it reaches safe values. Fromthese results, it is evident that there is a dependence
between the percentage of total polyolefins in the waste
and the coking pressure (Fig. 1), confirming that theincrease in coking pressure is linked to polyolefins andthat the relative proportion of polyolefins:polyaromatics inthe waste is critical for obtaining safe blends forcokemaking. These results provide a useful basis for theoptimization of the composition of plastic wastes forcokemaking in order to ensure that a force as low as
possible is exerted on the wall during the process. On thebasis of previous results [9], the maximum limit of 65 wt%
was established as a safe quantity of polyolefins in a
waste for ensuring a safe coking pressure.
500.0209 Xpolyolefins

Pc = 4.8918 er = 0.9822

Coking pressure (kPa)

Coal blend
Series HDPE

40

Although the coal blend characteristics, small variations
in bulk density and heating rate may also have an effecton coking pressure, there is a clear relationship between
the amount of polyolefins in the waste and the maximum
permissible value of coking pressure. Some of the plastic
mixtures tested may not give a realistic picture ofmunicipal plastic wastes, but they nevertheless allow us
to affirm that the optimum amount of polyolefins in awaste for ensuring optimal coking pressure and goodquality is around 65 wt%.

Acknowledgements
The authors thank the European Commission for financial
support in the RFCS Programme (Contract number: RFSR-CT2005-00001) and the Spanish Ministry of Science andInnovation (project CTM2004-03254). We also thank Abornasa
and ArcelorMittal in Spain for participating in the project

References

Series LDPE+PPwaste M95302010001020304050607080
Polyolefins in the waste (wt%)

90

100

Fig. 1. Relationship between the quantity of polyolefins in
the waste and the coking pressure.
Before analyzing the coke quality parameters, it isimportant to point out that the values of the CRI and CSRof the cokes produced in the semipilot oven do notnumerically match those obtained in industrial cokeovens. However, a comparison between cokes reveals
differences that emerge as a consequence of the effectof the plastic wastes (Fig. 2).
60

CRI and CSR (%)

4. Conclusions

5655

5457

59

55

565655555040313232323234333365HDPE
CRI502510050LDPE+PP95M953332100753020100
B802 B761coal blend

CSRFig. 2. Variation of CRI and CSR of cokes produced fromblends of coal and plastic wastes.
The reference coke B was produced from the coal blend
at two different bulk densities, 802 and 761 kg/m 3 db. Ingeneral, although the plastic wastes added are different,
the resulting cokes are quite similar, indicating that thereactivity to CO2 (CRI) and the mechanical strength ofthe partially-gasified coke (CSR) are not greatly affected.

interiores libro.indd 22[1] Plastic Waste Management Institute, An Introduction
to Plastic Recycling, Report 2009. Available at
http://www.pwmi.or.jp[2] Association of Plastics Manufacturers (APME).
Plastics-the Facts 2010. An analysis of European plastic
production, demand and recovery for 2009. Available at:
http:\\www.plasticseurope.org.
[3] J. Janz and W. Weiss, Injection of waste plastics into
the blast furnace of Stahlwerke Bremen, Proc. 3rd
European Cokemaking Cong., pp. 114-119, CRM-VDEh,Gent, Belgium, 1996.
[4] F. Hanrot, D. Sert, J. Delinchant, R. Pietruck, T.
Bürgler, A. Babich, M. Fernández, R. Alvarez and M.A.
Diez, CO2 mitigation for steelmaking using charcoal andplastics wastes as reducing agents and secondary raw
materials, In: A. López, F. Puertas, F.J. Alguacil and A.
Guerrero., Proc. 1st Spanish National Conf. on Advancesin Materials Recycling and Eco–Energy. Recimat 09,
paper S05-4, Madrid, Spain, 12-13 November 2009.
Available at: http://hdl.handle.net/10261/18433.
[5] S. Nomura and K. Kato, Basic study on separate
charge of coal and waste plastics in coke oven chamber,
Fuel 84 (2005) 429-434.
[6] S. Nomura and K. Kato, The effect of plastic size oncoke quality and coking pressure in the co-carbonizationof coal/plastic in coke oven, Fuel 85 (2006), 47-56.
[7] M.A. Diez, R. Alvarez, S. Melendi and C. Barriocanal,
Feedstock recycling of plastic wastes/oil mixtures incokemaking, Fuel 88 (2009) 1937-1944.
[8] S. Melendi, M.A. Diez R. Alvarez and C. Barriocanal,
Plastic wastes, lube oils and carbochemical products as
secondary feedstocks for blast-furnace coke production,
Fuel Processing Technology 92 (2011) 471-478.
[9] S. Melendi, M.A. Diez R. Alvarez and C. Barriocanal,
Relevance of the composition of municipal plastic wastes
for metallurgical coke production, Fuel 90 (2011) 14311438.

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TOLEDO (SPAIN)

AUTO SHREDDER RESIDUE SEPARATION AND PYROLYSIS
A. Santini1, Luciano Morselli1, Fabrizio Passarini1, Ivano Vassura1, David Serrano2,3, Javier
Dufour2,3
1 University of Bologna – Dept. Industrial Chemistry and Materials, viale Risorgimento 4, I-40136, Bologna, Italy.
2 Department of Chemical and Energy Technology, ESCET, Universidad Rey Juan Carlos, c/Tulipán s/n, 28933 Móstoles,Madrid, Spain
3 Instituto IMDEA Energy c/Tulipán s/n, 28933 Móstoles, Madrid, Spaine-mail:ale.santini@unibo.it

Abstract
This work deals with auto shredder residue (ASR or car fluff) refining since Directive 2000/53/EC claims for 85% material
recycling from end-of-life vehicles (ELVs) in 2015. Plastics amount at about 10%by weight of modern cars and their use islikely to increase due to lightweight requirements and design freedom concerning colors and shapes. Current ELVs metal
content is around 70% and with pretreatment 75% recycling rate can be easily achieved. ASR represents the remaining
25% ELV mass, and plastics are a rough 35% of the total car fluff. Plastics separation and recycling is thus strategic inorder to meet ELVs Directive targets. In this work, floatation and sieving are used as ASR pretreatment. Pyrolysis of eachobtained fraction has been carried on in order to evaluate which fraction is more suitable to feedstock recycling andwhether pyrolysis could be used as recycling technique in ELV management. Results show that PP/PE mixture hashighest conversion rate. Pyrolysis can be exploited to liberate metals and recover them from the char as well. Finally, if
light plastics mix oil could be refined in a “waste to chemicals” optic, ELVs Directive targets can be achieved withpyrolysis.

Keywords: Auto shredder residue (ASR); pyrolysis; plastic separation; plastics recycling

1. Introduction
This work deals with auto shredder residue (ASR or carfluff) refining since Directive 2000/53/EC claims for 85%
material recycling from end-of-life vehicles (ELVs) in2015. Plastics amount at about 10% (by weight) ofmodern cars and their use is likely to increase due tolightweight requirements and design freedom concerning
colors and shapes. Current ELVs metal content is around
70% and with pretreatment 75% recycling rate can beeasily achieved. ASR represents the remaining 25% ELVmass, and polimers consist of little less than 50% of thetotal car fluff.

Plastics separation and recycling is thus strategic inorder to meet ELVs Directive targets. In this work,
floatation and sieving are used as ASR pretreatment.
Pyrolysis of each obtained fraction has been carried on inorder to evaluate which fraction is more suitable tofeedstock recycling and whether pyrolysis could be used
as recycling technique in ELV management

2. Materials and Methods
Two density stage floatation has been used to sort
plastics from the non-organic matrix. The Pyrolysis
reactor consists of a semi-continuous reactor provided
with a helicoidal stirrer [2]. In a typical experiment, 10-15
grams of the chosen sample were loaded into thereactor. Products were collected as light and heavy oils
in two coolers and gases in a Tedlar bag. Solid residue
was recovered once the reactor cooled down as well andmetal content weighted. Oils and gases were thenanalyzed with GC-MS to identify products. Authors
decided to carry out also some runs using ananocrystalline HZSM-5 zeolite catalyst placed in thereactor together with the plastic-rich samples.

3. Results and Discussion

Fig. 1. Car fluff composition [1].

interiores libro.indd 23

Results show that PP/PE mixture has highest
conversion rate. Pyrolysis can be exploited to liberate
metals and recover them from the char as well.
Moreover, catalyst enhanced cracking by cutting
down hydrocarbons chains shorter, and producing

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6th International Symposium on Feedstock Recycling of Polymeric Materials

more gases and lighter compounds in the oil. Finally,
if light plastics mix oil could be refined in a “waste tochemicals” optic, ELVs Directive targets can beachieved with pyrolysis.

4. Conclusions
Catalytic refining of the pyrolysis oil (and gases) remains
the bottleneck of the “waste-to-chemicals” recycling inEurope, as well as an interesting field to develop
research. Although in industrial applications they are
currently used for generating heat, gaseous products
could be also refined and exploited as chemicals in orderto enhance ELVs recycling rate.

References[1] Santini, A., Morselli, L., Passarini, F., Vassura, I., DiCarlo, S., Bonino F., End-of-Life Vehicles management:
Italian material and energy recovery efficiency, Waste
Management.
[2] Serrano, D.P, Aguado, J., Escola, J.M ., Rodrıguez,J.M., Morselli, L., Orsi, R., Thermal and catalytic cracking
of a LDPE–EVA copolymer mixture, Journal of Analyticaland Applied Pyrolysis, Volumes 68-69, August 2003,
Pages 481-494.

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