Intermediate pyrolysis of scrap tires in a fixed bed reactor and activation of thepyrolysis char using CO2: Characteristics of pyrolysis products and activated char
Gyung-Goo Choi, Seung-Jin Oh, and Joo-Sik Kim
Department of Energy and Environmental System Engineering, University of Seoul, 90 Jeonnong-Dong,
Dongdaemun-Gu, Seoul 130-743, Republic of Korea
e-mail : tigerguinam@naver.com

Abstract
Four carbonized chars were obtained from the intermediate pyrolysis of waste tires in a fixed bed reactor at different reaction
temperatures (between 500 and 800 °C) in a N2 atmosphere. Gas, liquid and char were product fractions. The liquid wasagain distilled to give a light oil (pryolysis oil) and distillation residue. The chars obtained were again activated using carbon
dioxide at 950 °C with different activation time. The solids (carbonized char and activated char) and liquid (or pyrolysis oil)generated in each experiment were characterized by various analytic techniques. To describe the behavior of sulfur during
thermal degradation, elemental analysis of liquids and carbonized chars were performed. Pyrolysis oils were also
investigated by gas chromatography/mass spectrometer (GC/MS) to determine their compositions qualitatively andquantitatively. Carbonized chars and activated chars produced were characterized using gas (nitrogen) phase adsorption.
Results revealed that pyrolysis temperature and activation time significantly affected the pore structure and BET surface areaof activated chars. The maximum surface area of activated char produced in the experiment was about 440 m2/g.
Keyword: Intermediate pyrolysis, Scrap tire, Carbon dioxide, Activated char

1. Introduction
As a result of the great increase in the use ofautomobiles, the production of scrap tires has alsoincreased. Over 5 million tons of scrap tires are disposed
annually worldwide [1]. Due to their durability, thedisposal and reprocessing of scrap tires are difficult, andthey are also immune to biological degradation. Landfillof scrap tires needs lots of site, and fire problem also
exist. Important application of scrap tires is their use as afuel. However, high emissions of hazardous gas during
their combustion need expensive gas filtering systems.
As a method of scrap tire treatment, pyrolysis offers analternative route for high potential energy recovery, while
being environmentally friendly.
Oil fraction, one of pyrolysis products, can be used as analternative fuel and chemical feedstock in industrial
processes. Pyrolytic char could be upgraded to activatedchar through activation process. The resultant activatedchars can be used as pollutant adsorbents in both gas
phase and liquid phase separation processes [2].
In this work, a fraction of scrap tires were pyrolyzed in a
fixed bed reactor. The main goal of this study was toinvestigate the influence of reaction temperature on thecharacteristics of pyrolysis products and the influence ofreaction temperature and activation time on thecharacteristics of activated char.

2. Materials and Methods
Material. Scrap tires of 1-2 mm in size was used to as
the feed material of the intermediate pyrolysis. The
elemental compositions of a scrap tire sample were 82.3

wt.% carbon, 7.1 wt.% oxygen, 0.5 wt.% nitrogen and 2.5
wt.% sulfur, respectively.
Pyrolysis plant and procedure. Fig.1 shows theintermediate pyrolysis plant.

Fig. 1 Intermediate pyrolysis plant
The pyrolysis plant consisted mainly of a fixed bed
reactor, cyclone and quenching system. The fixed bed
reactor, which was indirectly heated by electricity, wasmade of a 316 SS with a height of 410 mm and an innerdiameter of 83 mm. The cyclone designed to capture theparticle size bigger than 10 µm. The quenching system
consisted of one steel condenser which was watercooled at 10 °C and one impactor separator which cancapture larger molecular weight in pyrolysis vapor. Thelatter part of the quenching system was electrostatic
precipitator that can capture an aerosol phase in thepyrolysis vapor. Non-condensable gas passed throughinto bent line and burned using a Bunsen burner.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

Nitrogen or carbon dioxide gas passed into the fixed bed
reator through a pre-heater to keep the reaction
temperature constant.
Pyrolysis conditions. In each experiment, 50 g of scrap
tires was put into the reactor. Subsequently the reactorwas heated at a heating rate of 10 °C/min until the desire
temperature (500, 600, 700 and 800 °C) reached, andthen held for 2 hr. In the intermediate pyrolysis, the flowrate of nitrogen gas was fixed at 5 NL/min.
Activation conditions. The resultant carbonized chars
from the intermediate pyrolysis were continuouly heatedat a heating rate of 10 °C/min up to 950 °C at the flow of
5 NL/min of carbon dioxide. The activation time wasvaried between 1 and 3 h.
Analysis of products. After pyrolysis, the liquid andsolid fractions were recovered. The liquid fraction wasdistillated to analyze its components with GC/MS. The
distillation of liquid was carried on a laboratory scale
apparatus under reduced pressure (210 °C, 13.3 Kpa).
After the distillation of liquid, a light fraction, which wasanalyzed by GC-MS, and a viscous fraction wereobtained. In this study, the light fraction and the viscousfraction were designated as pyrolysis oil and distillation
residue,respectively.
This
distillation
conditioncorresponded to the boiling point of 9H-fluorene (boilingpoint = 295 °C at atmospheric pressure). The applied
capillary column for GC-MS was a HP-5MS, and helium
was used as the carrier gas. After each activation
process, mass loss was calculated by burn-off. Activatedchars obtained from activation of carbonized char werecharacterized from nitrogen adsorption isotherms at 77 K
using BEL, Belsorp-mini II. The each value of surface
area, pore size distributions, mesopore and micropore
volume was obtained noted data using Brunauer-EmmetTeller (BET) equipment.

3. Results and Discussion
Pyrolysis product. In each experiment, the liquid andchar yields were determined by weighing them after eachexperiment. The gas yield was calculated by difference.
The effect of reaction temperature on the yields ofpyrolysis products was presented in Table 1.
Table 1. Yields of pyrolysis products with the reaction
temperature.
Reaction temperature (°C)
500
600
700
800

Liquid40.7 ± 2.47
34.7 ± 1.58
33.5 ± 1.25
33.1 ± 2.20

Yield (wt.o /o )Char
36.7 ± 0.08
36.6 ± 0.15
37.0 ± 0.22
36.8 ± 0.08

Gas
22.6 ± 1.01
28.7 ± 1.08
29.5 ± 1.21
30.1 ± 2.69

Elemental compositions of liquid and solid were detectedby elemental analysis. The result is presented in Table 2.
Table 2. Elemental analysis of liquid and solid fractions.
Elementcomposition (wt.o /o )C
H
LiquidN
SCH
Solid aN
S

500
84.0 ± 0.00
10.0 ± 0.00
1.8 ± 0.00
4.2 ± 0.00
94.3 ± 0.13
0.6 ± 0.10
0.5 ± 0.03
4.6 ± 0.00

Reaction temperature (°C)
600
70078.6 ± 0.00
83.9 ± 0.00
8.2 ± 0.00
8.4 ± 0.00
3.7 ± 0.00
2.2 ± 0.00
9.5 ± 0.00
5.5 ± 0.00
94.0 ± 0.09
97.4 ± 0.09
0.4 ± 0.01
0.4 ± 0.01
0.5 ± 0.07
0.2 ± 0.01
5.1 ± 0.00
2.0 ± 0.00

800
84.6 ± 0.00
8.7 ± 0.00
2.0 ± 0.00
4.7 ± 0.00
97.1 ± 0.02
0.4 ± 0.04
0.2 ± 0.03
2.3 ± 0.00

aAsh free

GC-MS analysis revealed that the pyrolysis oils consisted
mainly of aromatic hydrocarbons such as styrene,
xylenes, 2-methylnaphtalene and 1,2,3-trimethylindene.
Other major components in the oils were limonene which
could be used as an important commercial chemical. Inthe GC-MS analysis, it was also found that a decrease in
the yield of aliphatic compounds with increasing reaction
temperature, accompanied by an increase in thecontents of aromatic compounds. This result was due tothe fact that the monomer recyclization occured throughDiels-Alder reaction mechanism at higher reaction
temperatures. The limonene yield was also raised due tothe depolymerization of natural rubber by β-scission ofdouble bonds. [3].
Activated char. Activation was carried out to develop theporosity of carbonized char. As can be seen in Table 2,
the pyrolysis temperature and activation time significantly
affected the pore structure and BET surface area ofactivated chars. The maximum BET surface area ofactivated char produced was about 440 m2/g.
Table 3. Textural parameters of activated char.
P_500
AC_500_1
AC_500_2
AC_500_3
P_600
AC_600_1
AC_600_2
AC_600_3
P_700
AC_700_1
AC_700_2
AC_700_3
P_800
AC_800_1
AC_800_2
AC_800_3

Pyrolysis
temperature
(°C)
500
500
500
500
600
600
600
600
700
700
700
700
800
800
800
800

Activation
tempe rature
(°C)
950
950
950
950
950
950
950
950
950
950
950
950

Activatio ntime (hr)Burno ff (o/ o)

SBET(m2/g)

Vmicro(cm 3/g )V mes o(cm3/g)

123
12
3
12312
3

Control
21.5
33.0
44.8
Control
21.6
32.7
43.2
Control
17.5
32.9
42.2
Control
18.5
31.8
42.7

73.5
202.8
313.0
437.1
77.6
240.3
332.9
420.1
71.6
182.4
335.7
389.1
70.9
198.4
274.5
349.1

0.00220.04610.08760.12240.0047
0.0613
0.09880.1245N.D a
0.04030.10680.1268N.D
0.05550.07190.09020.18290.01100.76800.04420.61130.26091.07190.13990.18060.00920.55060.10550.46300.06540.65680.17300.35050.01670.49620.15220.29100.00990.31680.00480.36450.07760.22690.00380.60360.11150.70910.2716
a. No t dete cted

V mac ro(cm3/g)

4. Conclusions
In this study, a fraction of scrap tires were pyrolyzed in a
fixed bed reactor at various temperatures. The yield ofgas increased with increasing reaction temperature;
whereas the liquid yield decreased. A distillation of liquid
was conducted to give rise to two fractions, pyrolysis oiland distillation residue.The chemical compositions of thepyrolysis oil were complex, and it was mainly composedof aromatic and aliphatic compounds. The contents ofaromatic hydrocarbons increased with increasing
reaction temperature. The maximum surface area ofactivated char produced in the experiment was high witha value of about 440 m2/g. The activated char appeared
to be used as an adsorbent of liquid pollutants such as
phenol and dyes.

References[1] P.P.M. Fung, W.H. Cheung and G. McKay.
Systematic analysis of carbon dioxide activation of waste
tire by factorial design. Chinese journal of chemicalengineering 20 (2012) 497–504.
[2] N. Antoniou. and A. Zabaniotou. Features of anefficient and environmentally attractive used tyres
pyrolysis with energy and material recovery. Renewable
and sustainable energy reviews 20 (2013) 539–558.
[3] Adrian M. Cunliffe, Paul T. Williams. Composition ofoils derived from the batch pyrolysis of tyres. Journal ofanalytical and applied pyrolysis 44 (1998) 131-152.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013