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Yuan, XiangZhou,Fan, ShuMin,Choi, Seung Wan,Kim, Hyung-Taek,Lee, Ki Bong Elsevier 2017 APPLIED ENERGY Vol.195 No.-
<P>In this study, after conducting K2CO3-catalyzed steam gasification in a bench-scale bubbling fluidized bed reactor, the bench-scale recovery process of potassium catalyst was investigated by changing washing methods and operating parameters. The optimal potassium catalyst recovery efficiency (eta(k)) from MSJ gasified residue was 87.62%, achieved by utilizing a combined washing method in which the first wash was performed with N-2 limewater (0.25 mol ratio of Ca/K) and the last two washes were with CO2 water. The recovered potassium catalyst was re-loaded with MSJ coal and then was utilized for conducting the catalytic steam gasification in a lab-scale fixed bed reactor, in order to evaluate the performance of the recovered potassium catalyst from both experimental and kinetic aspects. Compared with the results obtained from fresh K2CO3, not only the trends of carbon conversion (X-c) were similar at each gasifying temperature, but also there was no obvious difference in volume percentage of gases produced. When the random pore model (RPM) was adopted, both reaction rate constant (K-RPM) and activation energy (Ea) remained similar. In addition, the lifecycle of the recovered potassium catalyst was studied. Finally, it can be concluded that the potassium catalyst was effectively and efficiently recovered from gasified residue and the recovered potassium catalyst had the same catalytic activity as fresh K2CO3, promoting the commercialization and development of the catalytic gasification process. (C) 2017 Elsevier Ltd. All rights reserved.</P>
Yuan, XiangZhou,Namkung, Hueon,Kang, Tae-Jin,Kim, Hyung-Taek Wiley-VCH Verlag GmbH Co., KGaA 2015 Energy technology Vol.3 No.5
<P> K<SUB>2</SUB>CO<SUB>3</SUB>-catalyzed steam gasification of low-rank coal in a fixed bed reactor was investigated in order to elucidate the effects of temperature and catalyst loading amounts on hydrogen yield. The optimum conditions for H<SUB>2</SUB>-rich syngas were 102.08 g kg<SUP>-1</SUP> coal at 1073 K with 20 wt % K<SUB>2</SUB>CO<SUB>3</SUB>; the carbon conversion <I>(X<SUB>C</SUB>)</I> reached 72.63 wt % and the cold gas efficiency (<I>η</I><SUB>CGE</SUB>) reached 87.05 %, simultaneously. However, at 1073 K the tar yield was too small to be ignored. Through Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), <I>t</I>-plot, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses of the gasification process, the surface area and micro-pore volume were found to reach a maximum value at 20 min, while the average pore size reached a maximum value at 10 min. <I>X<SUB>C</SUB></I> was promoted by the enlargement of average pore size and surface area, mainly caused by coal devolatilization. Potassium compounds tightly adhered to the surface and interpore sites of coal, capturing sulfur compounds to form K<SUB>2</SUB>SO<SUB>4</SUB>. </P>
Yuan, XiangZhou,Fan, ShuMin,Zhao, Liang,Kim, Hyung-Taek American Chemical Society 2016 ENERGY AND FUELS Vol.30 No.3
<P>The K2CO3-catalyzed steam gasification process of an Indonesian low-rank coal (Lanna coal) was studied, and the gasified residue was collected and used as a sample in the catalyst recovery process. The catalyst recovery process was mainly investigated by changing several operating parameters and washing methods, in order to evaluate the performance of the whole process. The shrinking core model was applicable to predict this gasification reactivity. H-2-rich syngas can reach 71.02 vol % at a gasification temperature of 800 degrees C with 20 wt % K2CO3 loading amount when the CO2 capture efficiency was 90%, and carbon conversion (X-C) reached 87.78% simultaneously. The potassium compounds in the gasified residue were found to coexist as K2CO3, K2SO4, and KAlSiO4. The optimal catalyst recovery efficiency (eta(K)) reached 84.69% by conducting three washes using the combined washing method. The variations of surface area, total pore volume, and average pore size under different washing methods were analyzed using Brunauer-Emmett-Teller and Barrett Joyner Halenda analyses after the catalyst recovery process was conducted. In addition, a new and advanced technology was developed that incorporates carbon capture, utilization, and storage with these two processes.</P>
Yuan, XiangZhou,Choi, Seung Wan,Jang, Eunji,Lee, Ki Bong Elsevier 2018 Chemical engineering journal Vol.336 No.-
<P><B>Abstract</B></P> <P>CF<SUB>4</SUB> is considered to be a significant global-warming compound and has a fairly long atmospheric lifetime, which exacerbates climate change. Adsorption is considered a promising technology for capturing CF<SUB>4</SUB> and appropriate adsorbent is one of key factors for successful development of adsorption method. In this study, CF<SUB>4</SUB> adsorption using microporous carbon materials was investigated from both equilibrium and kinetic perspectives. Petroleum coke (PC) was utilized for developing CF<SUB>4</SUB> adsorbents by carbonization and KOH-activation processes. The carbonization temperature and KOH/PC mass ratio were varied from 300 to 600 °C and from 1 to 3, respectively. Varying the carbonization temperature and KOH/PC mass ratio had a dramatic effect on the textual properties of the prepared samples. CF<SUB>4</SUB> adsorption was well fitted by the Langmuir isotherm model, and the CF<SUB>4</SUB> uptake was remarkably dominated by the surface area and pore volume of narrow micropores below 0.8 nm in diameter. The experimental CF<SUB>4</SUB> adsorption data were well described by the pseudo-second-order kinetic model, compared with the Elovich and intra-particle-diffusion models, and CF<SUB>4</SUB> adsorption appeared to be mainly controlled by physisorption. The PC450-K2 adsorbent, prepared using a carbonization temperature of 450 °C and a KOH/PC mass ratio of 2, exhibited the highest CF<SUB>4</SUB> adsorption uptake of 2.79 mol kg<SUP>−1</SUP> at 25 °C and 1 atm, in addition to good CF<SUB>4</SUB>/N<SUB>2</SUB> selectivity at relatively low CF<SUB>4</SUB> pressures, excellent recyclability, easy regeneration, and rapid adsorption-desorption kinetics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Microporous carbons were prepared from petroleum coke by carbonization and activation. </LI> <LI> The synthesized microporous carbon showed high CF<SUB>4</SUB> adsorption uptake. </LI> <LI> Fast adsorption-desorption kinetics and excellent cyclic stability were achieved. </LI> <LI> The effects of textural properties on CF<SUB>4</SUB> adsorption uptake were investigated. </LI> </UL> </P>