An in situ methylation of toluene using syngas over bifunctional mixture of Cr2O3/ZnO and HZSM-5

Authors:  Seulah Lee, Donguk Kim, Jihye Lee, Yeseul Choi, Young-Woong Suh, Changq Lee, Tae Jin Kim, Seong Jun Lee, Jung Kyoo Lee

Abstract:
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/Al₂O₃ = 30) in a fixedbed 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.

Keywords:
Syngas
Toluene methylation
Methanol synthesis catalyst
Cr₂O₃/ZnO
HZSM-5
Bifunctional catalyst
Xylenes production

Published in: Applied catalysis A: General  (Volume 466, Pages 1-314, 10 September 2013)

Publisher: Elsevier  

ISSN Information: 0926-860X

An in situ methylation of toluene using syngas over bifunctional mixture of Cr2O3/ZnO and HZSM-5

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