PARTⅡ GASIFICATIONINFLUENCE OF THE MIXED MOLTEN CARBONATECOMPOSITION FOR HYDROGEN FORMATION BY STEAMGASIFICATION OF WASTE MATERIALS
Tohru Kamo*1, Yuriko Egami2, Hajime Yasuda1, and Hideki Nakagome2
1

National Institute of Advanced Industrial Science and Technology (AIST),
16-1 Onogawa, Tsukuba 305-8569, Japan.
2
Chiba University, Faculty of Engineering, 1-33 Yayoi-cho,Inage-ku, Chiba-shi 263-8522, Japan.
E-mail: tohru-kamo@aist.go.jp

Abstract: Hydrogen is important as an energy source of a fuel cell and an energy storage
medium. The hydrogen production process by using the steam reforming of naphtha or thepartial oxidation of heavy hydrocarbon resources has already put in practical use. However,these processes are not suitable for hydrogen formation from waste materials, anddevelopment of small and high efficient new technology is expected.
The steam gasification of carbon residue was promoted in the presence of carbonates.
Particularly, rate of the gasification was accelerated significantly by using mixed carbonates.
The activation energy of the reaction with carbonates was smaller than that observed withoutcarbonates. The effects of the mixed carbonates were caused not only by increasing ofphysical-contact-efficiency due to fluidization of molten salt, but also by increasing catalytic
activity of the carbonates.
1. Introduction
A lot of useful resources, for instance gold, palladium, copper, and some rare metals, areused in electric devices. It is very important to recover these metals from the end-of-lifeelectric devices, and to secure indispensable strategy materials to electronic industry.
However, only a few electric devices such as mobile phones containing many noble metals, orsome household appliances on which recovery duty is imposed by law have been disposed,
because recovery metals from the end-of-life devices require high cost. The demand of rare
metals is increasing rapidly, and we are anxious about future short supply of them. The
end-of-life electric devices contain a lot of rare-metals. However, we cannot recover them by
the conventional copper smelter. Moreover, plastics recovered from the end-of-life electric
devices cannot be used as a feedstock or a fuel, because they are contaminated by toxic
halogen compounds or heavy metals.

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The 5th ISFR (October 11-14, 2009, Chengdu, China)
Our research group is developing the new technology to recover useful resources fromthe end-of-life electric devices efficiently by steam gasification. In our process, neither ofmanual recovery of the circuit-boards nor pulverizing of the boards is necessary, because allplastics parts are gasified by steam at the presence of molten carbonate. Toxic halogenatedcompounds hardly remain in gaseous or solid products, because bromine or chlorine isrecovered as safe and stable inorganic salt. All plastic parts used in the electric devices, forinstance circuit-board, insulation materials, case, can be converted into hydrogen and carbon
dioxide mainly. We can use the gas products as energy for operating this process, and convert
the surplus gaseous products into electricity by using a gas engine or a fuel cell.
In this work, I introduced influences of molten carbonate composition on steam
gasification of activated carbon used as a model compound of organic solid waste.
2. Experiment
In the most of ourN2
experiments,
activatedFiltercarbon (ALDRICH, 20-40
P ressure
Therm ogauge
P ressurecouplemesh) was used. The
keepingvalve
activated carbon (0.4 g) andTherm alinsulation
Furnacemixed carbonates (8.0 g)
R eactor
G as-liquid
were charged in a reactor
separator
3(30 cm ). Outline of oursemi-batch reactor was W ater D egasser P um p P reheater
C ooling
shown in Fig.1 Detail ofFig.1 Outline of apparatus
the apparatus was describedin our previous paper [1].
Ultra pure water (0.2~1.3 g/min) and nitrogen gas (200~300 cm3/min) were introduced into
the reactor through a preheater. Most of the experiments were carried out at 700 °C under 0.1~ 3.0 MPa. Each melting point of three
Na2CO3858℃
carbonates (sodium carbonate (Na2CO3),potassium carbonate (K2CO3), and lithium
800℃

carbonate (Li2CO3)) is more than 700 ℃.

700℃

600℃
However, the melting points of the500℃
carbonate decrease easily by mixing other400℃
carbonates as shown in Fig. 2 [2]. The
Li2CO3
partial steam pressure was controlled by
K2CO3726℃
898℃
changing the flow ratio of water andnitrogen gas. Gaseous product was Fig. 2 Melting point of mixed carbonates
sampled for every constant period andanalysed by a rapid analysis gas chromatograph (GL Science Micro GC-CP4900). Because- 114 -PARTⅡ GASIFICATION
steam gasification was assumed to be pseudo first order reaction, gasification rate (k, 1/min)
was derived from convertion (Xt) and reaction time (t) by using equation (1).
kt = ln(1－Xt) (1)3. Results and discussion
Hydrogen and carbon dioxide were produced mainly under our experimental condition.
Carbon monoxide and methane were detected as trace products. Production rate of hydrogenand carbon dioxide derived from steam gasification of the activated carbon at the presence ofProduction rate (m mol/min)various carbonate at 700 ℃ under 0.1 MPa are shown in Fig. 3. Slight formation of2.0

H2H2
CO21.0

CO2H2 CO2H2
CO20.0060

120 0Reaction time (min)60
120
120 060
120 0
Reactiontime(min)Reaction time (min)Reaction time (min)60

Na2CO3K2CO3Li2CO3Fig. 3 Effects of carbonate for steam gasification of activated carbon at 700 °C.
hydrogen or methane was observed without carbonates. On the other hand, production rates ofhydrogen and carbon dioxide increased significantly at the presence of sodium carbonate orpotassium carbonate. The experimental results show that these carbonates have catalytic
effect for the steam gasification. Amount of hydrogen formed in this steam gasification wasalmost twice amount of carbon dioxide. From the production ratio of hydrogen and carbon
dioxide, chemical reaction formula of the steam gasification is summarized to (1). At thepresence of lithium carbonate, carbon dioxide was observed dominantly in early stages of thegasification. Hydrogen increased gradually with reaction time and exceeded the amount ofcarbon dioxide in 50 minute of reaction. Thermodynamic equilibrium calculation indicatedthat approximately 10% of lithium carbonate decomposes to lithium hydroxide at 700 °C inexcessive steam. We estimated that the carbon dioxide observed in early stages of the reaction
was derived from lithium carbonate.
C + 2H2O →2H2 + CO2(1)- 115 -The 5th ISFR (October 11-14, 2009, Chengdu, China)

0.10

0.100.10) 0.08
ni/m
1( 0.06k) 0.08
nim/1( 0.06k) 0.08
nim/(1 0.06k0.04
0.02

0.04

0.2

0.4

0.6

0.8

0.00
0.0

1.0

K2CO3 /(K2CO3+Li2CO3) mol ratio

0.04
0.02

0.02

0.00
0.0

Fig.4k(1/min)

0.12k(1/min)

0.12k(1/min)

0.12

0.2

0.4

0.6

0.8

1.0

0.00
0.0

0.2

0.4

0.6

0.8

1.0

Na2CO 3 /(Na2CO3 +Li2CO3) mol ratio K2CO3 /(K2CO3 +Na2CO3) mol ratio

Effects of carbonate compositions for gasification rate. (700 °C, 0.1 MPa)

The rates of gasification observed at 700 °C under 0.1 MPa (partial steam pressure 0.09MPa) in the presence of various carbonate mixture were shown in Fig.4. In the presence oflithium carbonate alone, the gasification rate was only 0.31/min. However, the gasification
rate increased in proportion to the concentration of the potassium in the carbonate mixture,and it was 0.94 1/min at the presence of potassium carbonate alone. On the steam gasificationin the mixture of carbonates, sodium carbonate and lithium carbonate or sodium carbonate
and potassium carbonate, the maximum gasification rate was observed at 75% of sodium
carbonate in the carbonate mixtures.
Effect of partial steam pressure in the gasification carried out under 8.0MPa was shownin Fig.5. The gasification rate increased in proportion to the partial steam pressure at thepresence of three-carbonate-mixture (K2CO3/Na2CO3/Li2CO3=2/4/4 mol ratio). On the other
hand, effect of total pressure in the gasification was shown in Fig.6. The gasification wascarried at a constant flow ratio of nitrogen and steam under various total pressures. Rate of thegasification increased with the total pressure gradually. However, the rate closed to a constantvalue at higher pressure than 0.4 MPa.

0.100.10)
ni/m(10.05k0.05k(1/min)

k(1/min)

0.10
0.10

0.00
0.00

0.00
0.00

0.0

0.2

0.4

0.6

Partial steam pressure (MPa)Fig.5 Effects of partial steam pressure forgasification rate (700 °C, Ptotal: 0.8 MPa)

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ni/m
(10.050.05
k0.0

0.2

0.4

0.6

0.8

1.0Total pressure (MPa)Fig.6 Effects of total pressure forgasification rate (700 °C, Psteam/ Ptotal: 0.9)

PARTⅡ GASIFICATION
4. Conclusions
Activated carbon was converted into hydrogen and carbon dioxide almost completely bysteam gasification at the presence of mixed carbonate at 700 °C under 0.1-0.8 MPa. At thepresence of carbonate, the gasification of the activated carbon was accelerated significantly.
The gasification rate increased with partial steam pressure and total pressure, respectively.
These experimental results suggest that, we can convert various plastics used in electric
devices into hydrogen and carbon dioxide even under atmospheric pressure by choosing
proper mixed carbonate.
References[1] T. Kamo, K. Takaoka, J. Otomo, H. Takahashi, Fuel, 2006, 85, 1052-1059.
[2] J. R. Selman, H. C. Maru, Advanced in Molten Salt Chemistry, 1981, 202.

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