Kinetic Study on Steam Gasification of E-waste in the Presence of Carbonates○ Shangzhong ZHANG1, Yoichi KODERA2, Hideki NAKAGOME3, Kunio YOSHIKAWA1, Tohru KAMO2
1

Tokyo Institute of Technology;2

National Institute of Advanced Industrial Science and Technology (AIST); 3Chiba University

Steam gasification of a phenolic board in the presence of molten carbonate was studied as a means torecover useful metals effectively from electronic waste (E-waste), and to convert plastic fraction into clean
fuel gas. Experimentally observed hydrogen formation rates indicated the gasification of finely pulverized
phenolic board particles (≤0.15 mm) was well shown by a homogeneous kinetic model. On the other hand,
the gasification of relatively large phenolic board particles has progressed through two differenthydrogen-producing gasification processes: the initial homogeneous gasification in outer layer of the charinto which carbonate and steam infiltrated and the later gasification on surface of the char after the outerlayer was consumed.

Key words: E-waste; Steam gasification; Phenolic board; Molten carbonate; Particle size

1. Introduction
E-waste contains a lot of useful resources such as precious

carbonate (LNK-carbonate) was prepared by mixing equal weightsof three pure carbonates (lithium carbonate, sodium carbonate andmetal and rare metal. Effective recovery technologies of them arepotassium carbonate, Wako Pure Chemical Industries, Ltd.).

attracting attentions [1, 2], because serious shortages of these

2.2 Experimental procedure

resources are expected in the near future. Currently metals have

Fig. 1 is a schematic outline of the experimental apparatus forbeen recovered from the e-waste by incinerating its plastic fraction

steam gasification. The equipment comprised a gas introduction

without recovering energy. Such simple incineration not onlysystem, sample feeding port, preheater, reactor (inner diameter: 32

wastes useful organic resources, but also produces serious airmm, height: 125 mm), product cooling system, and analysis system.

pollution[1, 3]. To recover resources effectively and to reduce theThe LNK-carbonate (30 g) was loaded in the reactor vessel andenvironmental load caused by E-waste, it is desirable to develop

heated to the designated temperature at 20 °C/min under nitrogentechnologies that can obtain useful metals from the E-waste andgas flowing at 40 ml/min.

can use plastic fraction as energy resources effectively.
In this study, steam gasification of a phenolic board wascarried out in the presence of molten carbonates. Influence ofsample particle sizes on hydrogen formation rate in the steam
gasification was studied by using some kinetics models.

2. Experimental
2.1 Samples
A phenolic board (PL-1102, Sumitomo Bakelite Co. Ltd.) wasused as a model material of practical electronic phenolic circuitboards. It was crushed and classified by size using sieves of various
mesh sizes: 0.15 mm, 0.25 mm, 1.00 mm and 2.00 mm. A eutectic

Fig. 1 Schematic diagram of steam gasification apparatus.

After the reactor temperature reached the experimental

gasification reaction to occur uniformly throughout the solid

condition, a mixture of ultra-pure water (0.26 g/min) and nitrogensample. On the other hand, in the steam gasification of largegas (40 liter/min) was introduced through a pipe heated at 500 °C

phenolic board particles (d ≥ 1.00 mm), three different

and squirted into the molten carbonate from the bottom of thehydrogen-producing reactions were observed: initial rapid pyrolysis,reactor vessel. The sample was dropped into the reactor through thehomogeneous-model gasification and the shrinking-core model

feeder placed on the top of the reactor. The gas flow rate wasgasification. When the particle size (d) is larger than tmax, the rate ofmeasured by an integrated gas meter, and the gaseous sample washydrogen formation during the initial 20 min matched well with theanalyzed every five minutes using a rapid gas chromatographhomogeneous model, because the main reaction occurred in the(Varian CP-4900).

outer layer of depth of tmax infiltrated by molten carbonate. After
this layer was consumed by gasification, the reaction occurred only

3. Results and discussion
Hydrogen formation rates measured in the steam gasificationon the outer surface of the core, and the hydrogen formation rate
was matched well with the shrinking core model.

of various phenolic particle sizes were shown in Fig. 2. In thesteam gasification of the small phenolic particle (<0.15 mm), thelogarithmic hydrogen formation rate decreased almost linearly withtime that was agreement with the predictive values fromhomogeneous model. In the gasification of phenolic board of
1.0–2.0 mm, initial hydrogen formation rates were lower than thatwere observed in using fine particle sample, and the logarithmichydrogen formation rates decreased almost linearly until 20 min.

Fig. 3. Schematic of the reaction processes proposed for large andsmall particles in the steam gasification.

However, the steam gasification rate constants derived from slopeof the graph in Fig. 2 decreased after 20 min. From theseexperimental results, we proposed new reaction mechanism asshown in Fig. 3.

4. Conclusion
In the steam gasification of sufficiently small phenolic board
particles in the presence of molten carbonate, gasification occurred
uniformly throughout the sample particles. On the other hand, inthe steam gasification of relatively large phenolic board particles,
the reaction proceeded though three steps: rapid pyrolysis,
homogeneous model gasification and the shrinking core modelgasification.

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Fig. 2 Logarithmic hydrogen formation rates from steam
gasification among various particle sizes.

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