5-7 OCTOBERISFR2011

39

TOLEDO (SPAIN)

VALORIZATION OF WASTE TIRES BY PYROLYSIS IN A CONICAL SPOUTED BED
REACTOR
G. López, M. Amutio, M. Artetxe, A. Erkiaga, J. Alvarez and M. Olazar
1University of the Basque Country
Department of Chemical Engineering
P.O. Box 644 - E48080 (Bilbao)
e-mail: gartzen.lopez@ehu.es

Abstract
The pyrolysis of waste tires in continuous mode has been studied in a bench scale plant provided with a conical spouted
bed reactor, in the 425-600 ºC range. The properties of the pyrolysis products have been characterized using different
techniques for both the volatile and solid fraction. Continuous operation in the 425–600 ºC range gives way to a yield of
1.8–6.8 wt % of gases, 44.5–55.0 wt % of liquid fraction (C5–C10 range hydrocarbons, with a maximum yield of limoneneof 19.3 wt % at 425 ºC), 9.2–11.5 wt % of tar and 33.9–35.8 wt % of char. The high yield of limonene, the flexibility in theoperating conditions and the capacity for a continuous removal of the residual carbon black from the reactor are theadvantages of conical spouted bed technology.

Keywords: waste tire, pyrolysis, spouted bed, waste management, tire valorization

1. Introduction
The world generation of used tires in 2005 was over 2.5
million tones in North America, 2.5 million tones in
Europe and 0.5–1.0 million tones in Japan, which means
6 kg (the approximate weight of a tire) per inhabitant andyear [1]. Given that they are considered a hazardous
waste and there are regulations that forbid their landfill,considerable attention has been paid to waste tiremanagement.
Pyrolysis (heating to moderate temperatures in anoxygen free atmosphere) has good perspectives for
upgrading waste tires. Different technologies have been
applied to the tire pyrolysis process (apart fromthermogravimetric analysers and fast heating
microreactors used for kinetic studies), such as fixed bed
reactors [2], rotatory kilns, circulating fluid beds, bubbling
fluid beds [3], and vacuum moving beds. A conicalspouted bed reactor (CSBR) has been used in this study
for tire pyrolysis. This reactor is an alternative technology
to classical fluid beds for handling sticky and irregularmaterials. Certain features of the CSBR that make itsuitable for scrap tire pyrolysis are: cyclic particle
movement characteristic to spouted beds, bed
isothermicity, with a high heat transfer between phases,
which is essential for the treatment of a low conductivity
material such as rubber and finally short residence timeof volatiles, which minimizes secondary reactions andallows high yields of sensitive products, such aslimonene.

2. Materials and Methods
The tire material used in this work is a rubber free ofsteel and other tire carcass elements and has beeninteriores libro.indd 39

provided by Jenecan S.L. Its main components are:natural rubber (SMR 5CV), 29.59 wt %; styrenebutadiene rubber (SBR 1507), 29.59 wt %; carbon black(ISAF N220), 29.59 wt %. The materials have been
ground to a particle size below 1mmafter been frozen inliquid nitrogen. The low heating value is 38.8 MJ kg-1.
A bench scale plant provided with a conical spouted bed
reactor has been used to study the pyrolysis of waste
tires in the 425 to 600 ºC temperature range. For
operating under continuous conditions, the plant has asystem for feeding scrap tires, which is pneumaticallyactuated and is able to feed up to 300 g h-1 of tire. Prior
to entering the reactor, it is heated to the reaction
temperature by means of a preheater. The reactor is theunit’s main component, being a spouted bed of conicalgeometry with a cylindrical upper section. The volatile
products leave the reactor together with the inert gas andthe finest carbon black particles. These particles areretained in a high efficiency cyclone followed by asintered steel filter. The gases leaving this filter circulate
through a volatile condensation system consisting of acondenser and a coalescence filter.
In order to quantify volatile stream components, samples
have been taken at the reactor outlet and analyzed
online by means of a GC Agilent 6890 (HP-Ponacolumn). Furthermore, identification and quantification ofnoncondensable components has been carried out by
taking samples at the outlet of the condensation systemand sending them to a micro GC connected to a mass
spectrometer (Agilent 5975B). In order to identify thecomponents of the condensable fraction, the liquidobtained by product stream condensation has been

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6th International Symposium on Feedstock Recycling of Polymeric Materials

analyzed by GC/MS (Shimadzu UP-2010S provided witha HP-Pona column).

3. Results and Discussion
In order make easier the interpretation of the results, thepyrolysis products have been grouped into five fractions:Gas (C1–C4 hydrocarbons), non-aromatic liquid fraction(non-aromatic C5–C10 hydrocarbons), aromatic liquidfraction (single-ring C10- aromatic hydrocarbons), tar(which includes C11+ hydrocarbons, independently of
their aromatic or non-aromatic nature) and char orresidual carbon black. Figure 1 shows the evolution of
the yields of the different fractions with temperature in therange studied. As observed, there are some clear trends,
such as the increase in C1–C4 gas fraction withtemperature as a result of more severe thermal cracking
at high temperatures. The yields of gases obtained in a
spouted bed reactor are similar to those obtained byother authors in fluid bed reactors [3]. The gases
comprise mainly methane and C2–C4 olefins.
A significant increase in C10- aromatic compounds withtemperature has been obtained, from 13.1 wt % at 425ºC to 22.9 wt % at 600 ºC. This behaviour of C10aromatic fraction is due to Diels–Alder reactions that
promote the formation of aromatic compounds fromolefins. The gaseous and C10- aromatic fractions
increase with temperature and the yield of non-aromatic
C5–C10 fraction decreases, which is due to thermal
cracking and secondary reactions at high temperatures.
The heavy fraction, or tar, made up of C11+ components,
has no clear trend in the temperature range studied. The
amount of liquid fraction is almost constant up to atemperature of 500 ºC and then decreases at 600 ºC.
50
non aromatics C5-C10Yields (wt %)4030aromatics C10-tar C11+10gases
0400

450

500

550

4. Conclusions
The CSBR is suitable for obtaining high yields of liquid
at moderate temperatures. Temperature has animportant effect on product distribution by increasing thearomatization of the volatile fraction and the gas yield.
Moreover, the quality of the solid fraction (adulteratedcarbon black) is improved by operating at hightemperatures. The liquid fraction is of suitable quality for
its use as fuel or it can be an interesting feedstock for arefinery, especially for the hydrocracking process.
Pyrolysis oil contains interesting products in highconcentrations depending on the operating conditions,such as limonene.

References

char

20

gaseous products compared to other technologies.
Another difference involves the properties of the liquidfraction. Thus, the liquid obtained using this technology islighter than other ones due to the reduction in
repolymerization reactions as a consequence of the short
residence time of the pyrolysis primary products in thereactor.
It is noteworthy the high limonene yields obtained in thisprocess, the maximum yields have been obtained
operating at 425 ºC, reaching a yield of 20.4 wt %.
Limonene is an interesting chemical with numerous
industrial applications, such as the production ofindustrial solvents, resins and adhesives, as well as incosmetics.
The residual carbon black is made up mainly of carbon,hydrogen, and sulfur, with the sulfur content beingaround 3 wt %. This content corresponds to half of thesulfur contained in the tire. This sulfur content may limit
the applications of residual carbon blacks. The surface
area of the residual carbon black shows a clear trend toincrease with temperature, which gives way to a carbon
black with 116.3 m2 g-1 at 600ºC.

600650Temperature (ºC)

Fig. 1. Effect of temperature on the yield of the different
lumps in the 425-600 ºC range.

[1] M.B. Larsen, L. Schultz, P. Glarborg, L. SkaarupJensen, K. Dam-Johansen, F. Frandsen and U.
Herriksen. Devolatilization characteristics of large
particles of tyre rubber under combustion conditions.
Fuel 85 (2006)1335–1345.
[2] A.M. Cunliffe and P.T. Williams. Composition of oils
derived from the batch pyrolysis of tyres. J Anal Appl
Pyrolysis 44 (1998) 131–52.
[3] W. K aminsky and C. Mennerich. Pyrolysis ofsynthetic tire rubber in a fluidised-bed reactor to yield
1,3-butadiene styrene and carbon black. J Anal Appl
Pyrolysis 58 (2001) 803–811.

The CSBR is a suitable technology for obtaining highyields of liquid due its excellent performance. Thus, oneof the features of this reactor is the high heat transfer
between phases that allows for a high heating rate of thetire particle. Moreover, the residence time of the volatile
products in the reactor is very short (of the order ormilliseconds). Consequently, the cracking reactions ingas phase are largely avoided resulting in a low yield ofinteriores libro.indd 40

26/9/11 13:12:45

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6th International Symposium on Feedstock Recycling of Polymeric Materials

analyzed by GC/MS (Shimadzu UP-2010S provided witha HP-Pona column).

3. Results and Discussion
In order make easier the interpretation of the results, thepyrolysis products have been grouped into five fractions:Gas (C1–C4 hydrocarbons), non-aromatic liquid fraction(non-aromatic C5–C10 hydrocarbons), aromatic liquidfraction (single-ring C10- aromatic hydrocarbons), tar(which includes C11+ hydrocarbons, independently of
their aromatic or non-aromatic nature) and char orresidual carbon black. Figure 1 shows the evolution of
the yields of the different fractions with temperature in therange studied. As observed, there are some clear trends,
such as the increase in C1–C4 gas fraction withtemperature as a result of more severe thermal cracking
at high temperatures. The yields of gases obtained in aspouted bed reactor are similar to those obtained byother authors in fluid bed reactors [3]. The gases
comprise mainly methane and C2–C4 olefins.
A significant increase in C10- aromatic compounds withtemperature has been obtained, from 13.1 wt % at 425ºC to 22.9 wt % at 600 ºC. This behaviour of C10aromatic fraction is due to Diels–Alder reactions that
promote the formation of aromatic compounds fromolefins. The gaseous and C10- aromatic fractions
increase with temperature and the yield of non-aromatic
C5–C10 fraction decreases, which is due to thermal
cracking and secondary reactions at high temperatures.
The heavy fraction, or tar, made up of C11+ components,
has no clear trend in the temperature range studied. The
amount of liquid fraction is almost constant up to atemperature of 500 ºC and then decreases at 600 ºC.
50
non aromatics C5-C10Yields (wt %)4030aromatics C10-tar C11+10gases
0400

450

500

550

4. Conclusions
The CSBR is suitable for obtaining high yields of liquid
at moderate temperatures. Temperature has animportant effect on product distribution by increasing thearomatization of the volatile fraction and the gas yield.
Moreover, the quality of the solid fraction (adulteratedcarbon black) is improved by operating at hightemperatures. The liquid fraction is of suitable quality for
its use as fuel or it can be an interesting feedstock for arefinery, especially for the hydrocracking process.
Pyrolysis oil contains interesting products in highconcentrations depending on the operating conditions,such as limonene.

Referenceschar20gaseous products compared to other technologies.
Another difference involves the properties of the liquidfraction. Thus, the liquid obtained using this technology islighter than other ones due to the reduction inrepolymerization reactions as a consequence of the short
residence time of the pyrolysis primary products in thereactor.
It is noteworthy the high limonene yields obtained in thisprocess, the maximum yields have been obtained
operating at 425 ºC, reaching a yield of 20.4 wt %.
Limonene is an interesting chemical with numerous
industrial applications, such as the production ofindustrial solvents, resins and adhesives, as well as incosmetics.
The residual carbon black is made up mainly of carbon,hydrogen, and sulfur, with the sulfur content beingaround 3 wt %. This content corresponds to half of thesulfur contained in the tire. This sulfur content may limit
the applications of residual carbon blacks. The surface
area of the residual carbon black shows a clear trend toincrease with temperature, which gives way to a carbon
black with 116.3 m2 g-1 at 600ºC.

600650Temperature (ºC)

Fig. 1. Effect of temperature on the yield of the different
lumps in the 425-600 ºC range.

[1] M.B. Larsen, L. Schultz, P. Glarborg, L. SkaarupJensen, K. Dam-Johansen, F. Frandsen and U.
Herriksen. Devolatilization characteristics of large
particles of tyre rubber under combustion conditions.
Fuel 85 (2006)1335–1345.
[2] A.M. Cunliffe and P.T. Williams. Composition of oils
derived from the batch pyrolysis of tyres. J Anal Appl
Pyrolysis 44 (1998) 131–52.
[3] W. K aminsky and C. Mennerich. Pyrolysis ofsynthetic tire rubber in a fluidised-bed reactor to yield
1,3-butadiene styrene and carbon black. J Anal Appl
Pyrolysis 58 (2001) 803–811.

The CSBR is a suitable technology for obtaining highyields of liquid due its excellent performance. Thus, oneof the features of this reactor is the high heat transfer
between phases that allows for a high heating rate of thetire particle. Moreover, the residence time of the volatile
products in the reactor is very short (of the order ormilliseconds). Consequently, the cracking reactions in
gas phase are largely avoided resulting in a low yield ofinteriores libro.indd 40

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6th International Symposium on Feedstock Recycling of Polymeric Materials

plastic materials are chemically resistant against acids,
basics and alcohols. Mixtures, Table 2, have beenobtained mixing polyethylene pellets and wastes of thesame material with 25, 50 and 75 wt%. The stagnant bed
heights studied are in the range 0.05 - 0.35 m.
Table 1. Properties of the materials.

(kg/m3)size range
(mm)

923

2.7-5

3.5

0.95 0.34

940

2.7-5

3.5

0.92 0.36923

10x12x0.514x18x0.5

5.3

0.24 0.35

MaterialsLDPE
pellets
HDPE
pellets
LDPEwastes940

LDPE
wastesdoS(mm)

10x12x0.514x18x0.5

5.3

0.24 0.35

Table 2. Properties of the mixtures.
Material

LDPE
mixtures
HDPE
mixturessweight percent(kg/m3)

(wt%)

923

25, 50, 75

3.8 4.2 4.7

940

25, 50, 75

3.8 4.2 4.7

dS

mixture(mm)

3. Results and Discussion
The stable operating conditions of beds of polyethylene
wastes in spouted beds have been delimited in diagramsof stagnant bed height, Ho, against gas velocity, u.
0,25Ho (m)

Fixed
bed0,20

Spouted bed

0,15Transition

Classic0,100,05

Instablespouting

Dilutespouted bed

0,000481216u (m/s)

Fig. 2. Operating regimes in conical contactors.
Experimental conditions: = 36°; Do = 0.04 m and HDPEof d = 5.3 mm.
Sinteriores libro.indd 42

In Figure 2, the results plotted as an example correspondto a spouted bed contactor geometry ( = 36º; Do= 0.04m) and for a bed consisting of HDPE of 3.5 mm ofparticle diameter and for different values of the stagnant
bed height. The borders between the regimes, drawn
with solid lines, have been obtained experimentally foreach stagnant bed height. As it is observed, as gas
velocity is increased bed passes from fixed bed tospouted bed regime. It is noteworthy that the HDPE has
an instability region for low stagnant bed heights.
The experimental value of minimum spouting velocity isdetermined from the values of pressure drop by
decreasing slowly gas flow as the point when thepressure drop levels off and it increases as stagnant bed
height is increased and.

4. Conclusions
Gas inlet diameter and height of conical spouted bed
reactor have been obtained for thermal treatment ofpolyethylene pellets, wastes and their mixtures, in a wide
range of gas flow rate. Furthermore, it is determined thatmixtures improve bed performance in the transition
regime between conventional spouted bed and dilute
spouted bed regimes.
These results predict good perspectives for polyethylene
wastes recycling by this technology.

References[1] M. Olazar, M.J. San José, S. Alvarez, A. Morales andJ. Bilbao. Design in Conical Spouted Beds for theHandling of Low-Density Solids. Ind. Eng. Chem. Res.,
43(2004) 655-661.
[2] R. Aguado, M. Olazar, B. Gaisán, R. Prieto, and J.
Bilbao. Kinetic Study of Polyolefin Pyrolysis in a ConicalSpouted Bed Reactor. Ind. Eng. Chem. Res., 41(2002)
4559-4566.
[3] R. Aguado, M. Olazar, M.J. San José, B. Gaisán, andJ. Bilbao. Wax Formation in the Pyrolysis of Polyolefins
in a Conical Spouted Bed Reactor. Energy & Fuels,
16(2002) 1429-1437.
[4] G. Elordi, M. Olazar, G. Lopez, M. Amutio, M. Artetxe,
R. Aguado and J. Bilbao. Catalytic pyrolysis of HDPE incontinuous mode over zeolite catalysts in a conicalspouted bed reactor. J Anal Appl Pyrol. 85(2009) 345351.
[5] R. Aguado, R. Prieto, M.J. San José, S. Alvarez, M.
Olazar, and J. Bilbao. Defluidization modelling ofpyrolysis of plastics in a conical spouted bed reactor.
Chem. Eng. Process 44(2005) 231-235.
[6] M. Olazar, M.J. San José, A.T. Aguayo, J.M. Arandes
and J. Bilbao. Stable Operation Conditions for Gas-SolidContact Regimes in Conical Spouted Beds. Ind. Eng.
Chem. Res. 31(1992) 1784-1792.

Acknowledgements
This work was carried out with the financial support of theSpanish Ministry of Science and Innovation (ProjectTRA2009-0318 and Project CTQ2010-18697) and of theMinistry of the Basque Country (Project SA-2010/00097).

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