Steam gasification of low rank coals with ion-exchanged sodium catalysts prepared using natural soda ash

Yuu Hanaoka, Enkhsaruul Byambajav, Takemitsu Kikuchi, Naoto Tsubouchi, Yasuo Ohtsuka

研究成果: Conference contribution

抜粋

Ion exchange reactions of brown and sub-bituminous coals with natural soda ash, which is composed of > 99 % Na2CO3, have been studied at 20 - 40 °C without any pH-adjusting reagents, and the pyrolysis and subsequent steam gasification of the resulting Na-exchanged coals has been carried out with a fixed bed quartz reactor mainly at 700 °C. When the Na+ concentration and pH of an aqueous mixture of each coal and the soda ash are monitored in the ion exchange process, these factors decrease both at a larger rate with the brown coal that contains a higher content of COOH groups, showing that the ion exchange of Na+ with the H+ of the COOH takes place predominantly. About 65 % of the COOH can be exchanged with Na+ ions under the optimized conditions, irrespective of the coal type. The reactivity of these raw coals in steam at 700 °C is almost the same to be low, and char conversions are less than 20 mass % even after 2 h reaction. The exchanged Na promotes remarkably the gasification of both coals at this temperature, but the rate profile is different: The conversion for the brown coal increases linearly with increasing time and reaches almost 100 % at 1 h, whereas it needs approximately 2 h for the sub-bituminous coal to be gasified completely. The temperature dependency of the conversion with this coal reveals that the use of the Na catalyst can lower reaction temperature by about 120 °C, and the Arrhenius plots of the initial specific rate show that apparent activation energies are estimated to be 190 and 120 kJ/mol without and with the catalyst, respectively. The SEM-EPMA and XRD measurements of Na-bearing chars recovered after the pyrolysis and gasification suggest that the Na catalysts are finely dispersed at the initial stage of the reaction but that they may be deactivated by the formation of sodium silicates at high char conversions of more than 90 % even at a low temperature of 700 °C.

元の言語English
ホスト出版物のタイトル27th Annual International Pittsburgh Coal Conference 2010, PCC 2010
ページ1793-1801
ページ数9
出版物ステータスPublished - 2010
イベント27th Annual International Pittsburgh Coal Conference 2010, PCC 2010 - Istanbul, Turkey
継続期間: 2010 10 11 → …

出版物シリーズ

名前27th Annual International Pittsburgh Coal Conference 2010, PCC 2010
3

Other

Other27th Annual International Pittsburgh Coal Conference 2010, PCC 2010
Turkey
Istanbul
期間10/10/11 → …

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geotechnical Engineering and Engineering Geology

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  • これを引用

    Hanaoka, Y., Byambajav, E., Kikuchi, T., Tsubouchi, N., & Ohtsuka, Y. (2010). Steam gasification of low rank coals with ion-exchanged sodium catalysts prepared using natural soda ash. : 27th Annual International Pittsburgh Coal Conference 2010, PCC 2010 (pp. 1793-1801). (27th Annual International Pittsburgh Coal Conference 2010, PCC 2010; 巻数 3).