Open Journal of Applied Sciences, 2013, 3, 413-420
Published Online November 2013 (http://www.scirp.org/journal/ojapps)
Open Access OJAppS
Studying the Utilization of Plastic Waste by Chemical
Chemical Engineering Department, Engineering Faculty, Inonu University, Malatya, Turkey
Received November 19, 2012; revised January 8, 2013; accepted January 18, 2013
Copyright © 2013 Adil Koç. This is an open access article distributed under the Creative Commons Attribution License, which per-
mits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The rapid increase in the use of plastic materials in the recent years led to the accumulation of excessive amounts of
plastic waste. The so-called thermoplastics such as PE, PP, PS, PVC and PET as well as materials that are derived from
these are the type of plastic that is most used and consequently creates most of the waste. In this study, the original and
waste forms of PE and PP plastic types have been chosen for thermal and catalytic degradation. As process parameter,
410˚C - 450˚C temperature interval and 600 mL/min constant flow rate nitrogen gas have been chosen as the carrier gas
and the reaction time was considered to be 90 minutes for all experiments. Liquid products collected in experiments
were separated by means of fractioned distillation process. For purposes of determining product distribution, the frac-
tions, which were separated by distillation, were diluted in an appropriate solution for analysis of GC/MS. In the study
conducted, it has been observed that the liquid product distribution obtained mainly consists of a mixture of saturated
and unsaturated (heptane, heptane, octane, nonane, dodecane, etc.) hydrocarbons.
Keywords: Waste Plastics; Chemical Recycling; Catalyst
Nowadays plastic materials have become an indispensa-
ble part of social life and the fact that they generate ex-
cessive amounts of waste causes large economic losses.
For purposes of recovering these plastic materials various
pyrolysis techniques (thermal, catalytic, inert atmosphere,
oxygen environment, under high pressure pyrolysis, etc.)
have been developed. Due to its unique structure and
properties (cheap, high resistance against impact, easy
processing, etc.), polyethylene is used more commonly in
comparison to other plastic types such as PP, PS, PET,
PVC and consequently more waste is formed [1-5]. In a
plastic degradation study, it has been reported that the
reaction products consist of a hydrocarbon mixture such
as water insoluble saturated and unsaturated petrochemi-
cal raw material and that the distribution of molecular
weights of these products is determined. By applying
thermo-gravimetric method and thermal degradation tech-
nique, oxygenated and non-oxygenated polymers were
degraded in a reactor consisting of different sections [6,
7]. In these studies some kinetic parameters were deter-
mined and it has been claimed that the liquid products
obtained especially by degeneration of oxygenated poly-
mers were alcohol, alkene, ether (ethoxymethane, ethoxy
ethane, methoxy methane, etc.), aldehydes, CO and CO2.
In some studies it has been shown that when waste plas-
tic mixture pyrolysis is implemented in hydrogen at-
mosphere and gas oil by using synthetic zeolite (Co-Ac,
DHC) catalysts, a high rate of liquid product was ob-
tained [6,8]. Due to the fact that products similar to fuel
and petrochemical raw material quality can be generated
through thermal and catalytic pyrolysis of plastic waste,
these are considered to be important recovery methods.
In the study of HDPE plastics pyrolysis, one group of
researchers has been reported to have obtained liquid
product in C5-C28 carbon range consisting of high rate
of paraffin and aromatic component mixture [9-13]. PE
plastics were pyrolyzed in different reactors for purposes
of analyzing pyrolytic medium and it has been reported
that residence time and reaction temperature are parame-
ters that are effective on degradation mechanism [14,15].
Some original and waste plastic types such as PE, PP, PS
were pyrolyzed and it has been reported that alkene/ par-
affin ratio was an important parameter in pyrolysis of
plastic mixture [16,17]. Additionally, in the same study,
it has been claimed that the reaction rate constant in-
creased significantly by increasing the amount of PS in
the mixture. In Japan, a plastic waste recycling plant was
opened in the year of 1997, and it has been indicated that
plastic waste could be used in blast furnace applications,
coke oven applications and gasification processes .
In plastic pyrolysis studies, conducted in continuous tu-
bular flow reactor, it was reported that a liquid mixture of
wide carbon number such as gasoline, refinery raw mate-
rial and similar liquid chemicals was obtained . In
some studies it has been reported that new products were
formed when the long chain making up the polymeric
substance is broken in pyrolysis of a polymer [19-21].
Furthermore, it has been indicated that the pyrolysis
mechanism could be brought to light as such and asserted
that kinetic parameters could be determined with the help
of this mechanism. Due to the fact that plastic material
could stay a very long time without degradation in the
environment, great effort has been expanded for the pro-
duction of biodegradable polymer materials especially in
recent years [22-26]. In a study involving the thermal and
BaCO3catalytic pyrolysis of HDPE material, it has been
reported that the liquid products obtained at 450˚C tem-
perature and 0.1 catalyst/plastic ratio display the proper-
ties similar to gasoline, kerosene and fuel oil [27,28]. In
the subject matter study, catalytic and thermal degrada-
tion of HDPE and PP were studied and the effects of
some factors such as catalysts and temperature on degra-
dation products were analyzed. In pyrolysis studies, the
yield of the liquid product obtained was determined and
the characterization of this liquid product was elucidated
by GC/MS analysis.
2.1. Experimental Equipment and Raw
In this study HDPE and PP samples, which are in origi-
nal (F12, which named by producer) and waste form
(milk bottles, shampoo bottles, detergent bottles, etc.)
were degraded under atmospheric conditions in a cylin-
drical horizontal furnace reactor. The furnace operates on
the basis of a temperature controlled system containing a
heating zone that is 50 mm in diameter and 450 mm long.
A glass reactor of 40 mm diameter with 350 mL operat-
ing capacity was placed in the furnace. The reaction tem-
perature of the glass reactor is controllable (Figure 1).
The detailed schematic presentation of reactor has
shown in Figure 2. The reactor has three parts, where the
reaction area and inner and outer contact of reactor. The
feed into reactor was batch operation than established the
center of oven which its temperature was settled previ-
For purposes of measuring the temperature of the fur-
nace and the reaction environment, thermocouples were
placed at different places, and with the help of these
thermocouples the temperature profiles of the furnace and
reaction zone were determined. In experimental studies,
nitrogen gas was selected as the carrier gas and in order
to establish an inert environment and it was maintained
constantly at 600 mL/min flowrate. The gas-vapor mix-
ture emitted by the reactor was passed through a pre-
cooler with air cooling and the liquefied products were
collected in containers that were placed in salt-ice bath
(approximately −16˚C). The same system was also used
for catalytic degradation studies in addition to thermal
degradation. By using SiO2support material, Co and Mo
catalysts were prepared in different percent ratios (by
weight) to be used in catalytic degradation experiments
of HDPE and PP plastics. The effects of environmental
conditions on the collected liquid product yield and char-
acterization for catalytic and thermal degradation were
2.2. Catalyst Preparation
Co and Mo cracking catalysts were prepared with the
purpose of using them in experimental studies. A specific
percentage ratio of each catalyst (by weight) was taken in
the amount calculated according to the salts with high
solubility in water for this purpose, and after dissolving
gas cylinder, 2. Oven, 3. Reactor, 4. Reaction area,
5. Ice-salt bath, 6. Heater oven command panel, 7. Catalyst
Figure 1. Experimental set-up.
Open Access OJAppS
A. KOÇ 415
Figure 2. Detailed reactor scheme.
in water it was adsorbed onto the support material. To
prepare Cobalt (Co) catalyst cobalt-II-nitrate hexa-hy-
drate salt [Co(NO3)26H2O], and to prepare molybdenum
(Mo) catalyst ammonium molybdate tetra hydrate
[(NH4)6Mo7O24·4H2O] sale was selected. To prepare cata-
lysts of different percentage ratios (1%, 5% 10%, by
weight) the salts indicated were placed in a beaker in the
ratios calculated. Later on the salt was dissolved in dis-
tilled water and finally added to SiO2 salt solution that
was used as support material and dried in oven at 110˚C.
After a waiting period of approximately 24 - 36 hours,
the catalyst was placed in 110˚C oven for purposes of
removing its water and its water was evaporated. Finally
the catalyst was subjected to calcination process to achieve
its form for use.
2.3. Calcination of Catalyst
After the removal of its water and being dried, raw cata-
lyst was let stand in a muffle furnace at different tem-
peratures and for different time periods. To serve this
purpose the standing periods indicated in the following
table was applied (Table 1). At the end of the standing
period the catalyst, which was removed from the hot
oven, was cooled in a desiccator and stored in glass jars
for experimental studies.
The SEM-EDX compound content of Co-Mo catalyst
was presented in Table 2. We can see in this table that
this catalyst is formed of Co, Mo and SiO2, which is a
support material. And the detailed estimation of form of
this catalyst is shown in Figure 3 too.
3. Result and Discussion
The effects of different environmental conditions on the
liquid product were analyzed in experimental studies,
and their iodine numbers were attempted to be deter-
mined with the purpose of determining how unsaturated
liquid products were. The liquid products collected in the
coolers located at the outlet of the reactor were subjected
to distillation process under atmospheric conditions in
order to be able to determine the boiling point distribu-
tion. Later, the same liquid fractions were prepared for
GC/MS analysis by being dissolved in a suitable solvent
and the characterization of liquid products were deter-
mined by GC/MS analysis. In thermal and catalytic deg-
radation experiments of PP and HDPE plastics, nitrogen
Table 1. Catalyst calcinations and temperature periods.
Catalysts Co or Mo
Temperatures, ˚C 350 450 550 600
Waited time, min. 60 90 120 60
Table 2. The SEM-EDX compound content of Co-Mo cata-
11:05:48 HV: 20.0 kV Puls th.: 6.16 kcps
ElANSeries unn. C
[at%] Error [%]
Si14K-series10.50 15.03 37.46 0.5
Co27K-series0.86 1.23 1.47 0.1
Mo42L-series58.49 83.73 61.07 2.1
Total: 69.85 100.00 100.00
gas was selected as the carrier gas and it was maintained
constant at 600 mL/min while the experiment tempera-
ture interval was set to 410˚C - 450˚C.
At 425˚C temperature, the effects of catalyst/plastic
ratio on PP-HDPE degradation products were examined
and the change shown in Figure 4 was obtained. Ac-
cording to Figure 4, the liquid product yield displays an
increase with the increase in catalyst/plastic ratio (in-
creases approximately from 60% to 82% (by weight)). In
contract to this there were no significant changes in the
number of iodine and residue amounts (what is left over
in the reactor after degradation) and while the iodine
number remained approximately around 53 g/100g of
liquid, the residue amount was 4%. The fact that the io-
dine number did not change significantly means that the
ratio of unsaturated liquid products under these environ-
mental conditions did not change much. (The iodine
number provides information as to the ratio of unsatu-
rated components available in the environment and this
has been determined analytically as per ASTM D4607-94
standard). From the same figure, we can see that the
highest liquid yield was obtained when the catalyst/plas-
tic ratio is 0.2. This means that in this plastic degradation
study, if for each 5 grams of plastic 1 gram of catalyst is
used, the highest liquid yield would be obtained. And this
value has been determined to be 82% (by weight). This
demonstrated that using a catalyst would yield more of
the liquid product in comparison to the conditions where
a catalyst is not used.
Changes in the liquid product yield and iodine number
against catalyst/plastic ratio are provided in Figure 5 for
catalytic degradation of HDPE at 450˚C temperature.
According to Figure 5, the highest liquid product and
lowest residue amounts were obtained at 0.1 catalyst/
plastic ratio. Furthermore, we can see from Figure 5 that
maximum residue and liquid amounts are approximately
12% and 77% (by weight) respectively at 450˚C tem-
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1 2 3 4 5 6 7 8
Co Co Mo Mo Si O
Figure 3. The SEM-EDX presentation of Co-Mo catalyst.
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A. KOÇ 417
Figure 4. The variation of liquid products, residue and io-
dine numbers of PP-HDPE mixture degradation with cata-
lyst/plastic ratio at 425˚C temperature.
Figure 5. The variation of degradation products of LDPE
and iodine numbers with catalyst/plastic ratio at 450˚C tem-
perature and 0.1 catalyst/plastic ratio. However, we can
say that the highest iodine number was determined for
0.03 catalyst/plastic ratio at the same temperature, and
under these conditions, more unsaturated liquid product
was obtained in comparison to other catalyst/plastic ra-
tios. Accordingly, if it is desired to obtain higher amounts
of unsaturated liquid product, the use of a catalyst/plastic
ratio of 0.03 would be required.
The change in the reaction products and iodine number
with temperature in degradation of HDPE at 1/10 cata-
lyst/plastic ratio are provided in Figure 6. According to
Figure 6, the liquid product yield increased with the
temperature in the degradation of HDPE and the highest
liquid yield of approximately 78% was obtained at 440˚C
temperature. However, it was also observed that the
amount of residue decreases with the increases in tem-
perature and the highest residue amount is obtained at the
lowest study temperature of 410˚C. This means that the
HDPE degradation study is not deliberate at low tem-
400 410 420430 440 450
Figure 6. The variation of amount of liquid products, resi-
due and iodine numbers of degradation of LDPE with tem-
perature at 1/10 catalyst/plastic ratio.
peratures even if a catalyst is used. It can be observed
that the iodine number does not change much with the
temperature and remains at approximately 56 g/100g of
liquid at all temperatures. For this reason the saturation
of liquid products did not show much change as the
catalyst/plastic ratio remained constant. However, it must
be noted that the saturation of liquid products as shown
in Figure 5 above was determined to change on the basis
of the catalyst/plastic ratio.
It has been determined that the boiling point distribu-
tion of the distilled product of liquid products obtained in
the catalytic degradation of HDPE at 450˚C temperature,
changes with the changes in the catalyst/plastic ratio as
shown in Table 3. It can be said that, the boiling tem-
perature range at maximum catalyst/plastic ratio of 3/30
is 130˚C - 250˚C, while the boiling temperature range is
revealed to be 80˚C - 250˚C for the liquid products at
catalyst/plastic ratio of 1/30. Therefore, the boiling tem-
perature of liquid products obtained at higher cata-
lyst/plastic ratios is higher. Moreover, the liquid products
in possession of lower boiling temperatures at lower cata-
lyst/plastic ratios seem to be obtained in a wider range of
boiling point temperature.
The temperature distribution during fractioned distilla-
tion of liquid products obtained in the study of PP Deg-
radation at different temperatures (425˚C and 450˚C) is
shown in Figure 7. According to Figure 7, while the
approximate boiling point of the product when the con-
densation starts during the distillation of the liquid prod-
uct obtained at 425˚C is 65˚C, this temperature for the
liquid product obtained at the temperature of 450˚C is
77˚C. At the beginning of distillation, the distillate tem-
perature obtained showed a rapid increase and in ap-
proximately 10 minutes reached 175˚C levels. After this
temperature level, a significant change did not occur dur-
ing distillation in the distillation temperature of the liquid
product obtained at 425˚C. However in the distillation of
the liquid product, which was obtained at 450˚C, an in-
crease has been observed after the 25th minute and the
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distillate temperature increased to 215˚C by the end of
the distillation process.
Distillation process was applied to determine the dis-
tribution of the liquid product obtained by catalytic deg-
radation of PP at 425˚C temperature. After distillation
samples were obtained from these fractions and they
were dissolved in a suitable solvent (such as CCI4) and
subjected to GC/MS analysis. The chromatogram dis-
played a change as shown in Figure 7 and the results are
summarized in Table 4. When the Table 4 and chroma-
togram (Figure 8) are evaluated together, it can be seen
that the liquid product obtained includes a high rate of
Table 3. The effect of catalyst/plastic ratio on distillation
range of HDPE degradation at 450˚C temperature.
Catalyst/Plastic ratio Distillation part, %w BP range, ˚C
3/30 39 130-255
1/30 33 80-250
Figure 7. The variation of distillation temperature of liquid
products of PP degradation at different temperatures.
saturated (paraffin) structure components and that addi-
tionally there are unsaturated (olefin) hydrocarbon mixtures
with aromatic structure.
It is possible to comment on the carbon atom number
of the degradation product of PP plastics degraded at
425˚C by evaluating Table 5 and Figure 9 together. Ac-
cording to Figure 9, the carbon atom number distribution
is between C5-C18 range, while C8-C12 carbon num-
bered products are higher in concentration. From Table 5
Table 4. The product distribution of catalytic degradation
of HDPE at 425˚C temperature conditions.
Peak numberRetention timeCompound name
1 4.35 1-Heptene
2 4.51 2,4-Dimethyl, Heptane
3 5.22 1-Octene
4 4.21 Nonane
5 5.25 Cyclopropane, 1-methl, 2-penthyl
6 5.11 n-Decane
7 4.25 n-Undecane
8 4.69 Cyclopropane,
9 4.89 o-Xylene
10 5.92 n-Dodecane
11 5.12 1-Dodecene
12 5.33 1-Cyclododecane
13 5.92 Benzene, 1-3-5 Trymethyl
14 6.32 Tetradecane
15 5.24 Tetradecene
16 4.57 Pentadecane
17 5.85 Hexadecane
18 6.32 Heptadecane
19 6.56 Octadecene
Figure 8. The GC/MS chromatogram of catalytic degradation products of PP at 425˚C temperature.
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A. KOÇ 419
Table 5. The product group distribution of catalytic degra-
dation of HDPE at 425˚C temperature by GC/MS analysis.
Compound group Peak area (in percentage)
Pick area, (in percentage)
Carbon atom number
Figure 9. The variation of carbon atom numbers of catalytic
degradation of PP at 425˚C temperature.
it can be seen that there are small amounts of aromatic
components (10.81%) in the degradation products ob-
tained at 425˚C, while products of paraffin quality are
available at highest amounts (46.26 %).
The catalytic degradation of HDPE and PP shows us that
in different catalyst/plastic ratios the amount and struc-
ture of liquid products are different. So the iodine num-
ber is an interesting parameter for unsaturated compounds
determination. In this study, the unsaturated products are
important part of the degradation products. In our later
studies, the evolution of unsaturated product which they
obtained in thermal or catalytic degradation processes
will be investigated.
This work had been supported by UNIBAP 2011/45 Re-
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