Energy and Power Engineering, 2010, 2, 95-102
doi:10.4236/epe.2010.22014 Published Online May 2010 (http://www.SciRP.org/journal/epe)
95
Co-liquefaction of Coal and Used Tire in
Supercritical Water
Kwanruthai Onsri1, Pattarapan Prasassarakich1,2, Somkiat Ngamprasertsith1,2*
1Fuels Research Center, Department of Chemical Technology, Faculty of Science,
Chulalongkorn University, Bangkok, Thailand
2Center for Petroleum, Petrochemicals and Advance Materials, Chulalongkorn University,
Bangkok, Thailand
Received December 19, 2009; revised January 8, 2010; accepted March 3, 2010
Abstract
The co-liquefaction of lignite coal and used tire was performed in a 250-ml batch reactor, in supercritical
water under a nitrogen atmosphere to investigate the effects of temperature (380-440℃), water/feedstock
ratio (4/1-10/1 (wt./wt.)) and the % used tire content in the feedstock (0-100 wt.%) on the conversion effi-
ciency, liquid yield and oil composition attained. The maximum conversion and oil yield were 67 and 50%,
respectively, obtained at 400℃ at 1 min, with water/feedstock ratio of 10/1 and 80% used tire content. The
distillation characteristics of the oil products, analyzed by simulated distillation gas chromatography, re-
vealed that the oil composition depended significantly on the reaction temperature. The co-liquefaction of
coal and used tire yielded a synergistically increased level of oil production. Moreover, the total conversion
level obtained with co-liquefaction alone was almost equal to those obtained in the presence of either Fe2O3
or NiMo as catalysts, under the same conditions. Therefore, supercritical water is a good medium for the
dissolution of the volatile matter from a coal and used tire matrix.
Keywords: Co-liquefaction, Coal, Used Tire, Supercritical Water
1. Introduction
In recent years, the growth in tire consumption has con-
tinued to expand concomitantly leading to the problem of
the disposal of an ever increasing number of essentially
non-biodegredable but flammable spent scrap tires with-
out causing environmental pollution (including combus-
tion). With in excess of 3.0 million tons per year of waste
tires being produced in just the USA and Japan alone [1],
this has become a major challenge. Indeed, currently
perhaps only 60-70% of all used tires are recycled, and
evens this requires the use of environmentally and eco-
nomically costly processes including the use of solvents
like n-hexane, toluene and tetralin [2,3]. Used tires are
comprised of vulcanized natural and synthetic rubbers,
zinc, sulfur and carbon black and, as such, contain poly-
meric aromatic structures that are somewhat similar to
those in coal. Hence, the well-developed techniques used
in coal utilization should theoretically be applicable to
the pyrolytic destruction of waste tires and there has been
an increasing amount of attention paid to the co-utiliza-
tion of coal and waste tires. Indeed, given that coal liq-
uefaction is enhanced by the addition of crude oil [4]
which is a source of rubber constituents in tires, the co-
liquefaction of coal and used tires is of obvious interest.
A number of different concepts for the degradation of
spent tires in the presence of coal have hitherto contrib-
uted to the background knowledge. The processing of
used tire and/or coal have been subjected to thermal py-
rolysis and supercritical extraction using toluene, helium,
nitrogen and water. Mastral et al. [5] investigated subbi-
tuminous coal-tire hydroprocessing and reported that oil
formation and total solid conversion reached 45% and
70%, respectively, at a reaction temperature of 400℃,
with a coal: tire ratio of 0.5 and 10 MPa initial hydrogen
pressure. Moreover, the presence of rubber tire had a
positive effect as an additive for coal hydropyrolysis and
this was more relevant when tire feeds were coprocessed.
In a similar vein, synergistic effects including increased
total conversion levels and the yields of oil and asphal-
tene were attained during the simultaneous hydrogenoly-
sis of coal and tire were reported [2-9]. Joung et al. [3]

K. ONSRI ET AL. 96
studied the thermolysis of scrap tire using supercritical
toluene (T > 318.6℃, P > 4.06 MPa) and cyclohexane
under a nitrogen atmosphere and reported that the con-
version level reached 100% for toluene once the critical
state of toluene was reached (350℃). Indeed, tempera-
ture was far more important than other variables includ-
ing pressure for the complete dissolution of tire materials.
However, moving away from organic solvents as the
hydrogen donor to the cheaper and environmentally
friendlier water, the potential of supercritical water
(SCW) was first evaluated by Funazukuri et al. [10] who
reported that SCW was almost as effective as toluene for
tire liquefaction, attaining around 57% of tire solids to
oils. Finally, Park and Gloyna [11] reported that the liq-
uefaction of used rubber tire by using SCW under a he-
lium atmosphere attained a conversion and liquid yield
level of 89% and 68%, respectively.
The type of solvent used is likely to play a key role as
it acts as a medium to aid in the transport of hydrogen, as
a heat transfer medium reactant (including hydrogen do-
nor) and dissolution media to transport rubber and espe-
cially coal liquefaction products out of the matrix. How-
ever, previous research works have reported that SCW
(T > 374℃, P > 22 MPa) is an alternative approach for
the conversion of coal and tire into liquid products [10,
11]. The use of SCW as the reaction solvent can change
the reaction rate, equilibrium, and principal reaction
pathway, specifically around the critical point, because
of the significant variation in water properties [12]. Thus
SCW can dissolve hydrocarbons whose dielectric con-
stant is widely variable. In addition, the use of SCW as
opposed to organic solvents serves to both reduce the
cost and avoid the problems associated with the removal
of the solvent from the products. The separation of the
liquid extracted from coal and organic solvents typically
requires a tedious procedure to achieve any degree of
completion and product purity, and is both economically
and environmentally costly [13].
In this study, coal and used tire co-liquefaction were
conducted in SCW under a N2 atmosphere and the effects
of the reaction temperature, the water/feedstock ratio, %
used tire content in feedstock and the presence of catalysts
on the co-liquefaction efficiency were investigated and
are discussed with reference to the product composition.
2. Experiment Apparatus and Procedure
2.1. Material and Chemicals
The lignite coal used in this study was obtained from the
Mae Moh lignite mine in Lampang province, northern
Thailand. The used tire was obtained from Union Patta-
nakij Ltd. They were grounded, sieved (particle size is in
range of 250-850 micron), dried at 110℃ overnight and
then kept in the desiccator. The proximate and ultimate
Table 1. Proximate and ultimate analysis of coal and used
tire.
Coal Used tire
Proximate analysis (wt.% db1)
Ash 21.6 3.5
Fixed carbon 59.4 67.8
Volatile matter 19.1 28.7
Moisture (original sample, %) 17.7 1.1
Ultimate analysis (wt.% daf 2)
Carbon 66.4 85.8
Hydrogen 5.1 8.0
Nitrogen 2.6 0.5
Sulfur 4.6 1.5
Oxygen (by difference) 21.3 4.3
H/C atomic ratio 0.9 1.1
Heating value (MJ/kg) 21.3 33.6
1 db = dry basis, 2 daf = dry ash-free basis
analysis of lignite and used tire are presented in Table 1.
Other chemicals were: Tetrahydrofuran (THF) (+
99.99%) purchased from Fisher Chemicals, Dichloro-
methane (CH2Cl2) and Anhydrous sodium sulfate pur-
chased from CARLO ERBA and Carbon disulfide (CS2)
(99%) purchased from Merck.
2.2. Procedure
The experimental scheme for co-liquefaction of coal and
used tire constituent is summarized in Figure 1 and
schematic of apparatus is shown in Figure 2. The
co-liquefaction reactions were carried out in a 250-ml
reactor (Parr reactor model 4843). The reactor filled with
water under nitrogen atmosphere. The water-filling con-
tent (percentage water volume to reactor volume) was
15-17% which this amount of water caused the pressure
approaching 24-25 MPa at the desired temperature (380
-440℃). The calculated amounts of coal and used tire
were loaded in the reactor at the specific ratio.
The reactor was heated to the desired temperature, above
the water critical temperature at a heating rate of 5℃/min,
and held at this temperature for 1 min. The reactor was
then cooled to room temperature and the products trans-
ferred by washing into, and extracted with THF, in an
ultrasonic bath. After the THF extraction, the product
mixture was filtered to separate solid from liquid, and the
solid residue was dried for 4 h in an oven at 110℃ to
remove the residual solvent. The liquid products were
separated into both oil and aqueous phases by CH2Cl2
using a separation funnel. Anhydrous sodium sulfate was
added to the isolated oil phase to remove the trace

K. ONSRI ET AL. 97
amounts of residual water remaining in the oil phase and
then evaporated in a vacuum rotary evaporator at 60℃
and 400 mmHg to remove the CH2Cl2 and THF solvent
residues. The evaporated liquid (oil) was weighed to
calculate the liquid yield. The total conversion, liquid
and gas yields and solid residue levels were calculated by
the following expressions:
The liquid product was analyzed by Simulated Distil-
lation Gas Chromatography (SIM/DIS GC, Varian
Model CP-3800) according to ASTM D2887. Star Simu-
lated Distillation version 5.5 software was used for data
collection and processing. The liquid was dissolved in
1% (v/v) CS2 and a 15 m × 0.25 mm Cp-SIL5CB column
was used for separation. The oven temperature was raised
from 30 to 370℃ at a constant heating rate of 20℃/min.
The distillation curve was evaluated to fractions as fol-
lows: IBP-200℃, gasoline; 200-250℃, kerosene; 250-
350℃, light gas oil; 350-370℃, gas oil; and 370℃-FBP,
long residue.
% Conversion = 100[(Wdaf – WRT)/Wdaf]
% Liquid yield = 100[Wliq/Wdaf]
% Solid residue = 100[WRT/Wdaf]
% Gas yield = 100 - % Liquid yield - % Solid residue
where: Wdaf = wt. of dry-ash free coal and used tire
mixture, WRT = wt. of dry-ash free residue remaining
after THF solvent wash and dry, Wliq = wt. of liquid. All
experiments were conducted in duplicate.
The gaseous product was analyzed by Gas Chromato-
graph with a Thermal Conductivity Detector (GC-TCD,
Shimadzu GC-2014). The GC-TCD conditions were as
follows: 90℃ injection temperature; He carrier gas; Po-
rapak Q column and 50℃ column temperature.
2.3. Product Analysis
In this study, the raw coal and used tire was analyzed for
proximate analysis, total sulfur and determined the heat-
ing value by ASTM D2492, D3177 and D2015, respec-
tively. The carbon, hydrogen and oxygen were per-
formed using a CHN analyzer (Leco CHN-2000).
3. Results and Discussion
3.1. Preliminary Study
In the initial stage of study co-liquefaction of coal and
used tire, the factorial design was used to analyze the
significant process variables. Three variables such as
temperature, water/feedstock ratio (wt./wt.) and used tire
content in feedstock (wt.%) were chosen. Each of the
variables was coded at two levels: -1 and +1 as shown in
Table 2 and the average 23 (= 8) experimental results
including % conversion and % liquid yield of 2 replica-
tions were showed in Table 3.
Liquefaction
Coal and used tire Water
Gas
THF extraction
Insoluble
Residue
Soluble
CH
2
Cl
2
Oil Water phase
SIM/DIS GC
G
C TCD
N
2
Init. Pres. : 1 atm
4/1 10/1
380-440℃ 1-30 min
The analysis using the 2-level factorial design method
was based on an evaluation of variance ratios. Such
comparison helped to determine whether or not signifi-
cant difference existed among the means of several
groups of observation. It was assumed that each group
followed a normal distribution and its trend of the re-
sponse between ranges of studied variables is linear. The
F-test (95% confidence limits) method was used. The
calculated results were showed in Table 4. These results
showed that only temperature had effect on % conver-
sion, while all three variables (temperature, Water/feed-
stock (wt./wt.) ratio and % used tire in feedstock) had
effect on % liquid yield.
Figure 1. Experimental scheme.
However, the effect of reaction time on the product
distribution of the co-liquefaction was not studied, be-
Table 2. Factorial design of experiments.
Factor Level
-1 +1
Temperature (℃), A 380 440
Water/feedstock ratio (wt./wt.), B 4/1 10/1
% Used tire content in feedstock (wt.%), C 20 80
Figure 2. Schematic diagram of the apparatus. (1) N2 gas
cylinder. Parr reactor model 4843 consisted of; (2) Heater;
(3) 250-ml high temperature and pressure reactor; (4)
Temperature and pressure controller.
(1) (2)
(3) (4)

K. ONSRI ET AL. 98
Table 3. Experimental results obtained from factorial design for co-liquefaction experiments.
Factorial Factor % Conversion % Liquid
Design* Temperature Water/feedstock % Used tire content yield
(℃), A Ratio (wt./wt.), B in feedstock (wt.%), C
(1) 380 4/1 20 53.9 15.0
a 440 4/1 20 62.6 24.9
b 380 10/1 20 56.3 25.5
ab 440 10/1 20 63.4 28.6
c 380 4/1 80 53.2 26.6
ac 440 4/1 80 62.4 36.0
bc 380 10/1 80 60.0 40.2
abc 440 10/1 80 68.2 41.6
* Reaction conditions are denoted according to statistical nomenclature;
e.g. ab represents high levels of factors A and B and low levels of C and D (see Table 2)
Table 4. Analysis of variance for co-liquefaction experi-
ments. (a) for % conversion; (b) for % liquid yield.
Source of Sum of Degrees of Mean F0
Variation Square Freedom Square
A 137.74 1 137.74 37.21*
B 30.69 1 30.69 8.29
AB** 0.90 1 0.90 0.24
C 7.29 1 7.29 1.97
Error 11.10 3 3.70
Total 187.73 7
(a)
Source of Sum of Degrees of Mean F0
Variation Square Freedom Square
A 70.92 1 70.92 9.13*
B 138.83 1 138.83 17.87*
C 315.63 1 315.63 40.63*
Error 31.07 4 7.77
Total 556.45 7
(b)
* Significant in F-test with 95% confidence limits, F0.05,1,3 = 10.13 (F0 >
F0.05,1,3)
* Significant in F-test with 95% confidence limits, F0.05,1,4 = 7.71 (F0 >
F0.05,1,4)
** Two-factor interaction effects of factors A and B (see Table 2)
cause the results from initial experiments of liquefaction
of the used tire, as shown in Figure 3, showed that the
reaction time (elapsed time after the temperature reached
the desired temperature) did not affect the product dis-
tribution. Moreover, the previous studies [14-16] re-
ported that the coal and some polymers including rubber
67.4 67.5 67 .6 67.6
54.1 53.653.1 53.0
32.6 32.5 32.4 32. 4
14.5 14.5 14. 0
13.3
0
20
40
60
80
100
01020
time, (min)
% wt (daf)
30
% conversion% liquid% solid % gas
Time
Figure 3. The effect of temperature on the distribution of
products for used tire liquefaction. (Temperature 420℃;
water/feedstock ratio of 10/1).
and plastics can be decomposed and give the highest oil
yield within 1 min. Thus, we used the reaction time of 1
min for all of co-liquefaction experiments.
3.2. The Effect of Temperature
Thermal cracking is the principal reaction in SCW and
the effect of temperature on thermal cracking is impor-
tant. Thermogravimetric analysis curves revealed the
weight loss of used tire when pyrolyzed at a constant
heating rate of 10℃/min within a temperature range of
25-900℃ under a nitrogen atmosphere (Figure 4). The
decomposition of used tire begins in earnest near 380℃
and is essentially completely decomposed at 480℃.
Therefore, the chosen temperature range for all subse-
quent co-liquefaction experiments was 380-440℃. Fig-
ure 5 summarizes the variation in product yield with
reaction temperature at a reaction time of 1 min, a wa-
ter/feed stock ratio of 10/1 and a substrate composition
C
opyright © 2010 SciRes. EPE

K. ONSRI ET AL.99
0
20
40
60
80
100
0100 200 300 400 500 600 700 800 900
Temperature (℃)
Figure 4. Thermogravimetric analysis curve of used tire.
40.0
26.6
68.2
66.8
66.3
60.0
41.6
44.1
50.0
40.2
33.7 33.3 31.8
22.6
16.4
19.8
0
20
40
60
80
100
380 400420 440
temperature, (oC)
% wt (daf)
% conversion% liquid% solid% gas
Figure 5. The effect of temperature on the distribution of
products for co-liquefaction. (Reaction time 1 min; wa-
ter/feedstock ratio of 10/1; 80% used tire content in feed-
stock).
of 80% used tire. The yield of liquid product increased
from that obtained at 380℃ to a maximum level at 400℃
and thereafter decreased with further temperature in-
creases. At lower temperature, the liquid could be ex-
tracted from coal, the used tire was decomposed and then
yielded the heavy liquid products. However, with in-
creasing reaction temperatures, the residue yield de-
creased because of the further thermal decomposition of
heavy liquid product and solid residue could be took
place and resulted in decreased liquid and residue yields
at temperatures above 400℃ and a concomitant increase
in gas yields.
The total conversion level, which increased with tem-
perature rises from 380 to 400℃, did not significantly
change with further temperature increases from 400 to
440℃, whilst the liquid yield was decreased, presumably
via the decomposition of long chained hydrocarbons into
gaseous products. Moreover, the total conversion at-
tained at 400℃ was almost equal to that attained at 440℃
some 8 min later. Therefore, it can be concluded that the
optimum temperature and reaction time was 400℃ and 1
min.
3.3. The Effect of Water/Feedstock Ratio
Remaining weigh
t
(%)
The effect of varying the water/feedstock ratio on the
yield of products attained at 400℃ with a reaction time
of 1 min and 80% used tire content is summarized in
Figure 6. Whilst the yield of gas remained stable, the
liquid oil yield was slightly increased with increasing
water content and reached 50% at the maximum wa-
ter/feedstock ratio of 10/1 whilst the levels of residual
solids were concomitantly decreased. The mechanism of
coal pyrolysis starts with SCW diffusing into the coal
matrix and acting as a medium for the dissolution of coal
fragments. At the supercritical state, the static dielectric
constant of water decreases dramatically, leading to the
miscibility of nonpolar organic compound with SCW [15,
17,18]. The products from coal pyrolysis can dissolve
and disperse in the SCW and, as a result, the conversion
of coal is enhanced in the presence of water.
Moreover, the water gas shift reaction (CO + H2O 
CO2 + H2) occurs as a side reaction during coal and used
tire conversion in SCW. The CO produced from par-
tial-oxidation of oxygen-contained functional groups of
coal and then reacts with water in SCW to produce car-
bon dioxide and hydrogen. The appearance of carbon
dioxide in the gas product was shown in Figure 7. In-
creasing the water/feedstock ratio in partial-oxidation of
coal in SCW causes the equilibrium to favor carbon di-
oxide and hydrogen production leading to higher rates
and levels of reactive intermediate hydrogen production,
which is the actual hydrogenation agent [12]. The gener-
ated hydrogen reacts with free radicals produced from
the thermal cracking of coal and used tires, and so liquid
products are increased.
Temperature (℃)
50.0
33.7
16.4
66.3
65.3
63.3
61.4
45.0 47.0 48.9
34.736.7
38.6
16.4 16.3 16.4
0
20
40
60
80
100
1234
Water/feedstock ratio
% wt (daf)
% conversion% liquid% solid % gas
4/1 6/1 8/1 10/1
Figure 6. The effect of the water/feedstock ratio on the dis-
tribution of products from co-liquefaction of coal and used
tire. (Reaction time 1 min; temperature 400℃; 80% used
tire content in feedstock).

K. ONSRI ET AL. 100
12.5 17.2
8.4 3.0
26. 0
33.0
0
20
40
60
80
100
CH4C2H4 C3H6C4H10 CO2Other
sion of coal and the oil yield obtained. For example, the
total conversion and oil yield obtained from using 80%
used tire content in feedstock were both synergistically
higher than with only coal or tires alone under the same
conditions.
%wt (daf)
3.5. Analysis of the Liquid Products Obtained
The liquid products obtained from the co-liquefaction
were divided into gasoline, kerosene, light gas oil, gas oil
and long residue by using Simulated Distillation Gas
Chromatography (SIM/DIS GC). The effect of varying
the reaction temperature, water/feedstock ratio and %
used tire content in feedstock on the oil product compo-
sition are summarized in Figure 9. The temperature and
% used tire content in feedstock have a detectable effect
upon the oil composition with the content of gasoline and
kerosene being increased whilst long residues were de-
creased with both increasing temperature and % used tire
content in feedstock. In contrast, the water/feedstock
ratio had no discernable effect on the oil composition.
The more severe thermolysis and depolymerization of
the coal and used tire seen with increasing temperature
and % used tire content in feedstock thus resulted in an
increased yield of lighter and intermediate compounds at
the expense of the higher MW compounds.
CH4 C2H4 C
2H6 C 4H10 CO 2 Other
Figure 7. The effect of % used tire content in feedstock on
the distribution of gas products obtained from their co-
liquefaction. (Reaction time 1 min; temperature 400℃;
water/feedstock ratio of 10/1).
3.4. The Effect of the % Used Tire Content in
Feedstock
The effect of varying the amount of used tire content in
feedstock on the product composition attained at 400℃
with a water/feedstock ratio of 10/1 and a reaction time
of 1 min are summarized in Figure 8. The liquid yield
attained was increased from 39.1 to 50.0% as the used
tire content in feedstock was increased from 20 to 80 wt.%.
Because the depolymerization of used tires occurs easier
than that for coal, likely due to the simpler structure of
the tires, the thermal cracking of tire to form free radicals
and water-gas shift reaction are stabilized by those pro-
duced during coal cracking. This results in a more effi-
cient co-liquefaction process with coal and used tire rela-
tive to the liquefaction seen with only coal under the
same conditions.
3.6. The Effect of Catalysts
Moreover, these results show that adding used tire to
the coal liquefaction process increases the total conver-
63.9
22.7
46.8
36.1
31.0
17.0
66.3
63.9 63.2
62.2
60.9
53.6
38.3
42.1 43.8 45.6 50.0
33.7
36.1
36.8
37.8
46.4
39.1
22.5 20.1 19.4 18.3 16. 4
0
20
40
60
80
100
0 20406080100
% used tire
% wt (daf)
% conversion% liquid% solid % gas
The effect of using two established coal liquefaction
catalysts, 2.5% (w/w) Fe2O3 and NiMo (Ni: 0.2 wt% db
coal, Mo: 0.6 wt% db coal) particles, on the co-liquefac-
tion of coal and tires was evaluated. Catalyst loading of
the coal was prepared by an in situ impregnation method
[19,20]. The co-liquefaction in SCW with or without
catalysts was performed at 400℃ for 1 min, with a wa-
ter/feedstock ratio of 10/1, and 80% used tire content in
feedstock.
The total conversion obtained in the presence of either
of the two catalysts was almost equal to that obtained in
their absence (Figure 10). However, the gas yield was
increased significantly in the presence of either catalyst,
with a concomitant reduction in oil yield. Thus, the cata-
lysts perform further thermal cracking to give lighter
liquid products. However, considering the absence in
changes in total conversion, for solid to oil conversion
(i.e. % oil yield), it can be concluded that the process
does not require either catalyst or additive.
4. Conclusions
In this work, the total conversion and liquid yield ob-
tained from the co-liquefaction of coal and waste tire
attained were 66 and 50%, respectively, at the optimum
reaction condition of 400℃ for 1 min, with wa-
Figure 8. The effect of the % used tire content in feedstock
on the distribution of products obtained from their co-liq-
uefaction. (Reaction time 1 min; temperature 400℃; wa-
ter/feedstock ratio of 10/1).

K. ONSRI ET AL. 101
45.440.740
.446.541.040 .837.831.031.4
40.0
32.932
.8
5.2
6.05.3
5.1
5.95.45.6
5.65.3
5.1
6.25.4
27.4
27.227.6
27.2
27.927.7
26.4
26.926.9
27.3
26.926.6
5.8
5.4
5.3
6.46.09.0
10.19.5
7.5
10.010.2
16.219.321.315.918.820.121.226.426.920.124.025.0
6.8
0%
20%
40%
60%
80%
100%
long residuegas oillight gas oilkerosene gasoline
water:feedstock 4:1water:feedstock 10:1water:feedstock 4:1water:feedstock 10:1
20%80%20%80% 100%100%20%80%20%80%
100%100%
Liquid product distribution (%wt)
%used tire
content
380℃ 380℃ 440℃ 440℃
Figure 9. The effect of temperature, water/feedstock ratio, and % used tire content in feedstock upon the composition of liq-
uid products obtained from co-liquefaction.
33.732.632.6
50 42.647.2
16.424.820.2
0%
20 %
40 %
60 %
80 %
100%
No catalystsFe2O3NiMo
Product Distribution (%w
t
Solid yieldLiquid yieldGas yield
Fe2O3
Product Distribution (%wt)
Figure 10. The effect of catalyst upon the distribution of
products obtained from co-liquefaction of coal and used tire.
The calculated total conversion (%) is in parenthesis above
each bar. (400oC for 1 min, water/feedstock ratio of 10/1,
80% used tire content in feedstock).
ter/feedstock ratio of 10/1 and 80% used tire content.
The total conversion increased with increasing tempera-
ture whilst liquid yields obtained increased with increas-
ing temperature, water/feedstock ratio and % used tire
content in feedstock. Moreover, as reported in other sys-
tems, the addition of used tire to the coal co-liquefaction
had a synergistic effect, whilst the key factor affecting
the liquid product composition was temperature. SCW is
a suitable medium to extract the volatile matter from
waste tire, as a tire-coal matrix, without the need to use
catalysts, long reaction times or organic solvents. There-
fore, the co-liquefaction of coal and used tire in SCW is
an attractive way for reducing waste tires by means of
giving a moderate oil yield without the need for envi-
ronmentally and economically costly long reaction times
and chemical solvents, but rather provides rapid and easy
separation of the oil product from all the other residual
components.
5. Acknowledgements
This work was supported by Center for Petroleum, Pet-
rochemicals and Advanced Materials and Graduate
School, Chulalongkorn University.
6
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