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Negative Impact of High Stirring Speed in Laboratory-Scale Three-Phase Hydrogenations
Date
2014-11-19
Author
Ayrancı Tansık, İnci
Shen, Jing
Semagina, Natalia
Metadata
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Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License
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An increase in stirring speed is generally considered to be an a priori means of reducing external mass-transfer limitations in fast three-phase hydrogenations that are performed in a stirred tank. We provide experimental evidence for a 300-mL stirred reactor that, above a certain impeller speed, the efficiency of gas-liquid mass-transfer decreases, resulting in the decreased reaction rate. The phenomenon is attributed to the high degree of gas recirculation with large cavities behind the blades. The recirculation may decrease hydrogen concentration in the remainder of the tank, thus decreasing the concentration gradient that controls mass transfer. The model reaction in this work was 2-methyl-3-butyn-2-ol semihydrogenation with Lindlar catalyst Pd-Pb/CaCO3. The test impellers were a Rushton turbine, a down-pumping pitched blade turbine, and up-pumping A340 impellers. The kinetic experiments were combined with the measurement of volumetric gas-liquid mass-transfer coefficient, flow pattern analysis and impeller power demand calculations. Although the study does not include kinetic analysis, it provides guidance to the three-phase reaction system analysis that the highest stirring speed may enhance mass-transfer limitations and should not be used without caution.
Subject Keywords
Mass-transfer
,
Reactors
,
Turbıne
URI
https://hdl.handle.net/11511/41632
Journal
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
DOI
https://doi.org/10.1021/ie5017927
Collections
Department of Chemical Engineering, Article
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İ. Ayrancı Tansık, J. Shen, and N. Semagina, “Negative Impact of High Stirring Speed in Laboratory-Scale Three-Phase Hydrogenations,”
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
, pp. 18091–18094, 2014, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/41632.