5-7 OCTOBERISFR2011

105

TOLEDO (SPAIN)

INFLUENCE ON RAPID HYDROPYROLYSIS OF POLYETHYLENE BY
COEXISTENCE OF COAL
K. Kawasaki1, H. Yasuda2, S.Sajima1, O. Yamada2, M. Kaiho2 and H. Nakagome1
1 Graduate School & Faculty of Engineering, Chiba University, Chiba, JAPAN 263-8522
2 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, JAPAN 305-8569

e-mail:Kawasaki_kazuaki@graduate.chiba-u.jp

Abstract
Hydrogasification is a process to produce methane which substitutes natural gas from coal. It has been considered todiversify feedstock of hydrogasification other than coal. Waste plastics mixed with coal were seems to be suitable materials
as a means of feedstock. Hydrogasification of polyethylene singly and a mixture of the coal and polyethylene (50:50) werecarried out. Synergistic effect was observed when polyethylene was mixed with coal for raw materials, increasing in yield ofmethane. From the change in the temperature monitored inside the reactor, heat of reaction seemed to be dominant for thesynergistic effect. Heat of exothermic hydrogenation of polyethylene may supplement the heat of endothermic pyrolysis ofcoal to enhance the overall reaction. In this study, the ratio of polyethylene and coal mixture was varied to clarify the mixing
effect. The amounts of products were analyzed and reaction enhancement affected by mixing was discussed from themethane yield. As a result, synergistic effect was observed when the ratio of polyethylene and coal mixture was varied.

Keywords: Rapid hydropyrolysis, Hydrogasification, Polyethylene, Coal, Mixture

1. Introduction
Coal hydrogasification is a process to produce methane
which substitutes natural gas. It has been considered todiversify feedstock of hydrogasification other than coal.
Waste plastics mixed with coal were seems to be suitablematerials as a means of feedstock. In a previous study,hydrogasification of polyethylene singly were carried out.
As a result, a large quantity of methane and benzene wereproduced from polyethylene singly used. It was understoodthat polyethylene could be used as a raw material ofhydrogasification. Hydrogasification of a mixture of the coaland polyethylene (50:50) were carried out. As a result, alarge quantity of methane was produced. Therefore, it canbe expected to produce methane in high efficiency whenwaste plastic and coal mixture is used as a feedstock forhydrogasification(1). From the change in the temperaturemonitored inside the reactor, heat of reaction seemed to be
dominant for the synergistic effect. In this study, the ratio ofpolyethylene and coal mixture was varied to clarify themixing effect. The change in polyethylene reaction bymixing with coal was discussed.

In this study, a unique batch reactor was used for rapidhydrogenation(2). The reactor consist of threea main
components, sample feeder, reaction chamber and gasreservoir. Prior to reaction, the sample was loaded in thesample tube and was kept at room temperature. The
reaction chamber filled with gas for reaction atmosphere
under the condition where the reaction pressure waspreheated to the reaction temperature and the sample tube
was driven into preheated chamber just before the reaction
started. From the sample tube, the sample was blown into
the reaction chamber and started the reaction. The reaction
was started with blowing sample to reaction chamber after
the sample tube was let down by air-cylinder. After a settime, the product gas was moved immediately to the gasreservoir. The gas production in the reservoir wasdetermined and obtained a part of product gas by thesyringe. The compositions of the product were analyzed
with GC-TCD, GC-FID and GC-MS.

sample tubesample

2. Materials and Methods
Japanese Taiheiyo coal (C 75.93, H 6.46, N 1.31, O+S
16.27 wt%(daf)), polyethylene, and those mixture wereused for the samples. The amount of samples for coal
singly (100:0) was 0.67g, polyethylene singly (0:100) was
0.61g, mixture (25:75) was mixed coal 0.17g andpolyethylene 0.52g. Reaction experiment was carried out at
1073K under 7Mpa of hydrogen pressure. The reaction
time was set at 1 second to 80 seconds.

interiores libro.indd 105

reactionchambervacuum pumpgas
reservoir

Fig. 1 Outline of apparatus

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6th International Symposium on Feedstock Recycling of Polymeric Materials

3. Results and Discussion
1.)Product distribution
Major products from coal and polyethylene mixture(25:75)
by rapid hydropyrolysis experiment were methane,benzene, C2HX and C3HX. Product distribution as carbon
conversion of major hydrogasification products frommixture (25:75) is shown in Fig. 2. Carbon conversion wascalculated by dividing amount of carbon in each product byamount of carbon in the mixture(25:75). Methane increased
linearly with reaction time. Benzene increased from 1
second to 20 seconds, following by decreasing to 80
second with convex upward. Their tendency is similar to
those tendency with using coal singly or a mixture (50:50)
as the samples(1).
2.)Synergistic effect on methane production
Comparison between experiment value of methan yield( )and a predicted value are shown in Fig. 3. Dasheddotted line ”(0)” indicates values calculated on theassumption that synergistic effect isn’t observed.
Comparing experiment value with a predicted value,experiment value exceeds a predicted value in a wholetime. This tendency is similar to a mixture (50:50).
Therefore, synergistic effect was observed when the ratioof polyethylene and coal mixture was varied.
From the change in the temperature monitored inside thereactor, heat of reaction seemed to be dominant for thesynergistic effect. Heat of exothermic hydrogenation ofpolyethylene may supplement the heat of endothermic
pyrolysis of coal to enhance the overall reaction. Then, it
was validated that the reaction of polyethlene is enhancedby mixing with coal. Another values ware calculated basedon a hypothesis that only the reaction of coal is enhanced,
the reaction of polyethylene isn’t enhanced. Each dash line
in Fig. 3 shows synergistic effect rate of the coal 0.4-1.0
are based on above hypothesis. “0.4” means 40% moremethane produced from coal than “(0)”. In the case of “1.0”as a same manner of calculation, all carbon in coal will
convert to methane.
As a result, experiment value in 1 second indicated a value
close to synergistic effect rate of the coal 0.9. Experimentvalue in 2 seconds indicated a value close to “0.8”.
Experiment value in 5 seconds indicated a value close to“0.6”. Experiment value in 20 seconds indicated a value
close to “1.0”. But experiment value in 80 seconds exceeds
a predicted value of synergistic effect rate of the coal 1.0.
Synergistic effect rate of the coal 1.0 indicate a value
calculated on the assumption that coal completely carbon
conversion to methane. Therefore, it seems that theexperiment value cannot be reproduced by above
hypothesis. Not only coal reaction but also polyethylene
reaction was suggested to be enhanced. Therefore, it could
be understood that the reaction of polyethylene enhancedby mixing coal.

4. Conclusions
In this study, the ratio of polyethylene and coal mixture
was varied to clarify the mixing effect. The amounts ofinteriores libro.indd 106

products were analyzed and reaction enhancement
affected by mixing was discussed from the methane yield.
As a result, synergistic effect was observed when the ratioof polyethylene and coal mixture was varied.
Experiment values and predicted values baed on ahypothesis were compared. As a result, an experimentvalue exceeds a predicted value. It was suggest that not
only coal reaction but also polyethylene reaction seemed to
be enhanced.

Fig. 2
Carbon conversion to major hydrogasification products
from coal and polyethylene mixture[25:75].

Fig. 3 Comparison between experiment value andpredicted values synergistic effect rate of the coal 0.4-1.0.

References[1]Yasuda, et al., Fuel, 83 (2004), 2251-2254.
[2]Yasuda, et al., 2nd ISFR (2002), A59.

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