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

STUDY OF AN OIL RECOVERY SYSTEM
FOR WASTE PLASTIC
Zar Zar Hlaing*, Mariko Adachi, Shin Suzuki, Shoji Kodama and Hideki Nakagome
Graduate School of Engineering, Chiba University, Chiba 263-8522, Japan.
E-mail: zarzarhlaing2007@gmail.com
Abstract: Recently disposal in landfill sites has become a serious environmental problem
because of the increasing volume of waste deposal. A variety of large capacity processes forwaste plastic have been proposed from an environmental perspective. In this study, thermaldecomposition of waste plastics including polyethylene (PE), polypropylene (PP), polystyrene(PS) was made using a designed batch plant that is an external heat type thermal
decomposition batch type furnace capable of processing 500kg of waste plastic a day. The oil
product yield of three kinds of waste plastics by thermal decomposition was compared and thetrend of the recovery rate was analysed.
Key Words: liquefaction; polyethylene (PE); polypropylene (PP); polystyrene (PS);thermal decomposition; fuel1. Introduction
Plastic has become something which is essential to our lives and 15,000,000 tons is
produced annually in Japan. The quantity of waste plastic is 10,000,000 tons annually, which
accounts for 67% of general waste. Therefore, recycling technology for plastic waste isrequired. Decomposition of waste plastic into fuel oil is one of the treatment methods thathave been proposed for waste plastic recycling as an energy source. In this study, PE, PP, PS
and their mixtures were thermally decomposed using a designed batch plant. After thereaction, the resulting oil recovery rates for various conditions were examined.
2. Experiments
2.1 MaterialsThe samples employed were PE, PP, PS and their mixtures. PE and PP were pure plasticpellets and PS was ingot. The mixed plastic was actual waste plastic from food packaging andindustrial waste such as films, packs, etc.

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2.2 Apparatus
The process of oil recovery from waste plastic is shown in Fig. 1. This small-sized waste
plastic liquefaction plant is manufactured by MAEDA Seisakusho Co., Ltd., and designed totreat PE, PP, PS and mixtures of these substances. It is an external heat type batch typefurnace which has two tubular reactors of diameter 70cm and length 200cm and capable ofprocessing 500kg of waste plastic a day. It is quite easy to run and once the reaction is started,
it is possible to run it almost automatically through to completion. The sample is heated anddecomposed in this device, separating into liquid product, the residue and gas.

Exhaust gas

Off GasCoolercooling water

waste plastics

Pyrolysis
oiltank

Water

waste plastics
fuel
Pyrolysis oven

Pyrolysis
oilFig. 1 The small-sized waste plastic liquefaction plant
2.3 Experimental Method
The quantity of samples was 250~500kg, and the temperature set was 500~590℃, thereaction time was 6 to 10 hours and the product yield was measured. Two sample lots
consisting of the same amounts of material were put in the two batch type reactors under astandard pressure N2 atmosphere. After nitrogen substitution, nitrogen was stopped andoperation was started. The plant was to be stopped when the quantity of the produced gas
decreased. The recovery rate of oil and a residual substance was measured after cooling, andthe rate of gas recovery was calculated in total.
3. Results and Discussion
The thermal decomposition product yield of PE, PP, PS and their mixtures are shown in
Tab.1.M-1,M-2 and M-3 show the single material experiment using PP, PS, PE. M-4, M-5
and M-6 shows the results from of two plastic mixtures and M-7, M-8, M-9 and M-10 shows
the results from three plastic mixtures.
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The 5th ISFR (October 11-14, 2009, Chengdu, China)
Tab. 1 The sample constitution and product distribution
Run NO
M-1
M-2
M-3
M-4
M-5
M-6
M-7
M-8
M-9Set Temp Sample Quantity（℃）（Kg)
500200560
300
545257570
99.7
570
158.5
590
140570
202
560
234
420
200

PE

PP

00
100080431626
50

1000062
20
053
37
25

PS（％）
0
100
0
370
57
313725Gas

OilResidue

7.5
5
37
20
24
15
20
18
9.5

93
94
63
77
82
77
74
77
90.5

0.1
10
3.4
3.2
8
6
5
0.1

Fig.2 shows a graph of product yield of the three single material separately. In case of PPand PS after thermal decomposition, more than 90% was collected as the liquid product, but
in case of PE thermal decomposition, liquid yield was 63% and the gas product was abundant.

100%

Products yield( % )80%60%

GasResidueOil

40%
20%0%PPPSPE

Fig.2 The effect of 3P single unit for products yield
Supposing that the additive rule applies, the recovery rate of produce yield of mixture of
2 and 3 plastics was calculated and was compared with the values actually observed. (Fig.3and Fig.4)- 54 -Product yield

PARTⅠ PYROLYSIS

Fig.3 The effect of two plastic mixtures on product yieldIn case of the mixtures of PE and PP (M-5), PE and PS (M-6) , when calculated values
are compared to the observed value, the additive rule relatively applies, although the residue
increased and the liquid product decreased a little.
However, in case of the mixture of PP and PS (M-4), the observed value is below thecalculated value.
There is the similar trend in the experiment of mixtures of three plastics. However, inM-7 and M-8, the residue increased but the gas is half the calculated value and the liquid
decreased. When M-9 is compared with the calculated value, the liquid has increased.

Fig.4 The effect of three plastic mixtures on product yield- 55 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
In the case of mixed plastics, there is no strong correlation in particular in mixing rate
and a liquid yield. As the whole, a liquid yield is lower than a calculated value, and theobserved value has much residue. It is possible that the yield of the pure plastics used for thecalculated value is too high as a reason. Especially the liquid yield of PP and PS is over 90%.
It is necessary to verify the difference between the reaction conditions at this time, and thereaction conditions of other experiments. Moreover, in the case of M9, the liquid yield of theobserved value is higher than a calculated value. Only in the case of M9, the liquid yield of
the observed value is higher than a calculated value.Let it be a future subject to carry out
comparison examination of the reaction conditions of M9 with the reaction conditions ofother experiments. The reaction conditions of each experiment will be verified from now on,and it will search for the reaction conditions for the improvement in a liquid yield.
Tab. 2 Analysis of Produced Oil

Flash point(℃)
Density(g/cm3)
Ash(%)
Element analysis(%)
CHNSOPS
32/32
1.0
0.0
90.8
9.0
0.2
8.0
0.1

PE-PS mixed PE-PP mixed PE-PP-PS mixed Heavy oil
9.0
4.5/4.5
-7.0
>40
0.9
0.8
0.9
0.70～0.95
0.0
0.0
0.0
88.6
10.1
0.9
0.0
0.6

85.7
13.4
0.9
0.5

88.3
11.8
0.0
0.0
0.0

82.0～87.0
11.7～14.7
0～1.0
0.1～3.0
0～0.1

Tab. 2 shows the analysis of the produced oil. Because it resembles the features of heavy
oil, liquid product derives from waste plastics can be used for power generation or as a fuelfor boilers.
4. Conclusion
PE, PP and PS were decomposed in an external heat type batch type furnace of500kg/day of practical scale and the recovery rate of product oil was compared for both thesingle unit and the mixtures. The tendency of formation oil recovery factor of two plastic
mixtures and three plastic mixtures was analysed on the basis of the result of actual scrap
material processing data.
(1) The small-sized waste plastic liquefaction plant which is used for this research is able toprocess each single material and to process the mixtures.
(2) In the observation, formation oil yield in case of the single material with PP and PS is 90%,
but PE is low at of 60% output generation, while gas formation ratio is high.
(3) In the case of mixed plastics, there is no strong correlation between the mixing rates andthe liquid yield. As a whole, the actual liquid yield is lower than the calculated value, and- 56 -PARTⅠ PYROLYSIS
greater residue was observed. It is possible that the yield of the pure plastics (PP and PS)
used for the calculated value was too high.
(4) Only M-9 showed a liquid yield that is higher than the calculated value.
(5) In this research, the relationship between the mixing rates of plastics and the product yield
was observed. In the future, in addition to this, the temperature conditions in the reactor
will be verified.
(6) Thermal decomposition formation oil yield of the mixtures averaged approximately 75%.
According to the analysis of the formation oil, it was verified that it is usable as analternate fuel.
References[1] G. bairi, M. Adachi, N. Akaishi, S. Kodama,T. Imai, T. Kamo, H. Nakakome. FSRJ 9th
debate preliminary report collection, 2006, 70, 7.
[2] Corporation plastic processing promotion association, 2007 http://pwmiwww.tandb.co.jp/
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