Negative Impact of High Stirring Speed in Laboratory-Scale Three-Phase Hydrogenations
Bibliographic record
Abstract
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/CaCO 3 . 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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".