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Daejeon, South Korea

Jeong S.W.,Sungkyunkwan University | Kim J.,Catalyst Process R and nter | Lee D.H.,Sungkyunkwan University
Chemical Engineering Science

The effect of operating variables (reaction temperature, space velocity, and partial pressure of the carbon source) on carbon yield was determined for synthesizing MWCNTs by catalytic chemical vapor deposition using ethylene as the carbon source in a batch type fluidized bed reactor. Stable fluidization was maintained using the MWCNT agglomerate as the initial bed material and MWCNTs with high selectivity were synthesized. The optimal reaction temperature for the maximum carbon yield was 983K and the apparent activation energy was 102kJ/mol. The maximum carbon yield occurred at the space velocity of 136h-1. The carbon yield increased with increasing partial pressure of ethylene. However, the synthesis reaction of MWCNTs did not proceed at partial pressures above 0.63. A correlation is proposed to predict the yield of MWCNTs. © 2015 Elsevier Ltd. Source

Lee S.C.,Sungkyunkwan University | Jang J.T.,Sungkyunkwan University | Kim J.,Catalyst Process R and nter | Bae J.W.,Sungkyunkwan University | And 2 more authors.
Science of Advanced Materials

CH4 decomposition and CO2 gasification with activated carbon (AC) were concurrently conducted to stably produce syngas at 800-950°C. With a CH4/CO2 feed ratio of 1 or less, both reaction rates remained nearly constant with time, while the CH4 decomposition rate decreased significantly at higher ratios. As the CH4/CO2 ratio increased from 0.3 to 3, the weight loss of AC decreased from 28% to less than 1% under the reaction conditions investigated. Even though the CH4 decomposition rate was close to or greater than the CO2 gasification rate, the H2/CO ratio in the product gas was less than 1 (~0.9), which is consistent with the thermodynamic prediction. The reaction orders with respect to CH4 and CO2 for the concurrent reactions were 0.52 and 0.58, respectively. The activation energies for CH4 decomposition and CO2 gasification were 108.3 and 75.1 kJ/mol, respectively, which suggest that the surface carbon atoms exposed after CO liberation by CO2 gasification are more active for both reactions than before CO liberation. Based on these results, stable operating conditions were recommended. © 2016 by American Scientific Publishers. Source

Lee S.,Dong - A University | Kim D.,Dong - A University | Lee J.,Dong - A University | Choi Y.,Dong - A University | And 5 more authors.
Applied Catalysis A: General

The in situ methylation of toluene using syngas (in situ methylation hereafter) was studied to produce xylenes over bifunctional catalysts comprising Cr2O3/ZnO (CrZ) and HZSM-5 (SiO2/Al 2O3 = 30) in a fixed-bed down-flow reactor at 460 psig. In this study, three basic aspects in the in situ methylation were investigated: (1) the catalytic activity of CrZ as the methanol synthesis catalyst with respect to the equilibrium conversion, (2) the evaluation of catalytic synergies in the in situ methylation over bifunctional catalyst, and (3) the effect of the ratio of catalytic functions regarding the ratio of methanol synthesis catalyst to HZSM-5, and their intimacy. The CrZ catalyst exhibited very low CO conversion to methanol in the methanol synthesis reaction, which is controlled by the equilibrium. However, the bifunctional mixture of CrZ and HZSM-5 catalysts exhibited significant catalytic synergies in the in situ methylation in terms of catalytic activity and product selectivities, with about a 10-times-higher CO conversion rate, and 2- to 3-times-higher toluene conversion and xylene production rates compared to the monofunctional catalysis of methanol synthesis and toluene disproportionation, respectively. The in situ methylation also gave rise to higher catalytic performance than in typical toluene methylation conducted with a molar feed ratio of methanol/toluene of 0.5. The catalytic synergy was manifested when both metallic and acidic functions were brought into close intimacy with a weight ratio of CrZ/HZSM-5 close to one in the in situ methylation. © 2013 Elsevier B.V. All rights reserved. Source

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