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

COKE DEPOSITION ON THE REACTOR SURFACE
IN WASTE TIRE PYROLYSIS
Jeong-Geol Na, Ho Se Lee, Chang Hyun Ko Soo Hyun Chung*Climate Change Technology Research Division, Korea Institute of Energy Research,Daejeon 305-343, Korea.
Waste tire is mainly composed of natural and synthetic rubber and regarded as renewableenergy resource since it has 9,000 kcal/kg of calorific value. Approximately 270,000 tonnesof scrap tires are generated in Korea each year and most of them are recycled with energy byincineration. For national energy security, it is necessary to diversify use of waste tires. The
contents of volatile matters are high in waste tires and therefore oil production by pyrolysis
could be one of the attractive options of energy recovery from waste tires.
The formation of coke deposits is a major problem in waste tire pyrolysis. The
mechanism of coke formation is as follows: Reactor tube is heated indirectly and the metals
such as iron and nickel in the reactor surface catalyze dehydrogenation reaction. Then,pyrolysis vapors recovered from waste tires lose their hydrogen atoms and carbons aredeposited on the reactor surface. Carbon blacks in tires for giving wear resistance and wet
traction could worsen the situation. Coke formation reduces products yields, increases energy
consumption and shortens life time of reactor. Fig. 1 shows a reactor tube after waste tire
pyrolysis. This obstacle has delayed commercialization of the process and it is necessary todevelop a technology for suppression of coke deposition on reactor surface.
In this study, the behavior of coke formation in pyrolysis reactor was investigated. Waste
tire pyrolysis experiments have been carried out at various reaction temperatures and cokeformation was observed using a coking sampler. Also, ceramic coatings on metal surface wereattempted for suppression of coke deposition.

Fig. 1 Reactor tube after
waste tire pyrolysis- 64 -Fig. 2 Coking sampler

PARTⅠ PYROLYSIS
A coking sampler was specially designed in order to simulate the environment nearheating surface where coke formation is severe. Coking sampler is composed of a reactor tube,
a tray for uploading metal plates and a heating furnace (Fig. 2). Eight SUS304 plates (1 by 1cm) were loaded with the position in tray and they were covered with 30 grams of waste tires.
The tray was inserted into the reactor tube and heated to 400, 500 and 600℃ in N2
atmosphere, after which the temperature was kept at the set point for 1 hour. Then, thereaction tube was cooled to 200 ℃ by flowing N2 gas and the tray was pulled out of the tube.
Coke formation was determined from the weight difference before and after the reaction of
the metal plates. To investigate the effect of unvolatilized oils on coke formation, two samples
were wiped with acetone and the weights were measured. The experiments were repeated tentimes to get accumulated amounts of coke formation.
The amounts of coke formation at various temperatures are summarized in Tab. 1. The
coke formation at 400℃ seemed insignificant. On the other hands, the accumulated cokeamounts at 500 ℃ (87.1 g/m2) and 600 ℃ (85.5 g/m2) were comparable. The difference incolor change can be seen in the metal surface after pyrolysis as shown in Fig. 3. Some
deposits on the surface seem to be unvolatilized oils rather than coke particles for which theweight difference of the plates wiped by acetone (position 1 and 2) was lower than that ofother samples. The tendency of coke formation increased near the outlet due to active contact
with pyrolysis vapors.
Tab. 2 Accumulated amounts of coke formation on SUS304 metal plates
Temperature/℃
Position
400

500

600

1

2.0

27.0

7.0

2

2.0

36.0

94.0

30.0

131.0

57.0

40.0

73.0

42.0

50.0

59.0

77.0

60.0

32.0

137.0

70.0

97.0

79.0

89.0

131.0

121.0

Average

1.6

87.185.5- 65 -The 5th ISFR (October 11-14, 2009, Chengdu, China)(a) Before reaction(b) after reaction

Fig. 3 Metal plates before and after pyrolysis
The ceramic coating on metal surface was conducted for suppression of dehydrogenation
reaction. For efficient coating, SUS304 metal plates were pretreated in three steps. [1]sonication with acetone, [2] 0.1 M nitric acid treatement and [3] calcination at 300 ℃ in air.
The pretreated plates were coated by dip-coating method in silica or alumina solution andtheir coking tendencies were determined using the coking sampler at 500 ℃. The coatedplates were loaded at the position of outlet part of the tray.
Tab. 2 shows that coke deposition could be repressed by ceramic coating. Theaccumulated coke amounts at 500 ℃ with coated plates were lower than 25 g/m2 whereas
the amounts of the plates without coating were 87.1 g/m2. Particularly, the coking amounts ofthe sample with all of pretreatments including washing, oxidation and calcination were 2 g/m2.
It is noteworthy that the coated plates were on the outlet part where coking formation wasvigorous.
Tab. 2 Accumulated amounts of coke formation on SUS304 metal plates
Coke amounts

Coating material

Pre-treatment condition

87.1

No coating

Coke amounts at 500 ℃

114SiO2Acetone washing

28Al2O3Acetone washing

323SiO2Acetone washing followed by 0.1 N nitricacid treatment

48Al2O3Acetone washing followed by 0.1 N nitricacid treatment

54SiO2

62Al2O3- 66 -Acetone washing, 0.1 N nitric acid treatment
followed by calcination at 300 ℃
Acetone washing, 0.1 N nitric acid treatment
followed by calcination at 300 ℃

PARTⅠ PYROLYSIS
In conclusion, the metal plates coated with ceramic material was proof against coke
deposition probably owing to inhibition of dehydrogenation and this method would offer away for stable operation of waste tire pyrolysis.
References[1] A. G. Wysiekierski, G. Fisher, C. M. Schillmoller, Hydrocarbon Processing, 1999,78, 97.
[2] K. Y. Grace Chan, F. Inal, S. Senkan, Industrial & Engineering Chemistry Res.,
1998, 37, 901.
[3] J. R. Rostrup-Nielsen, Catalysis Today, 1997, 37, 225.

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