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High Selectivities in Hydrogenation of Halogenonitrobenzenes on Pd, Pt, or Raney Nickel as Catalysts
Published in John R. Kosak, Thomas A. Johnson, Catalysis of Organic Reactions, 2020
Georges Cordier, Jean Michel Grosselin, Rose Marie Bailliard
The hydrogenations were carried out in a 500-mL Hastelloy autoclave stirred by a rotary Rushton turbine (1200 rpm) to perform the reactions at the gas-liquid mass-transfer limit; i.e., a further increase in agitation did not improve the rate of reaction. Aqueous methanol, 10% water w/w, 200 mL, was used to suspend the catalyst. On closing the autoclave and purging repeatedly, first with nitrogen and then hydrogen, the catalyst and solvent mixture were heated to the selected temperature under the selected hydrogen pressure. When the desired temperature and pressure were reached, the halogenonitrobenzene (0.6 mole) dissolved in methanol (150 mL) was injected at a predetermined and constant feed rate. Depending on the halogenonitrobenzene type, we performed the hydrogenations either at 353 or 373 K under 20 bar total pressure.
Scaling Up and Scaling Down for Cell Culture Bioreactors
Published in Wei-Shou Hu, Cell Culture Bioprocess Engineering, 2020
Rushton disk turbines, which are often used with multiple installations in large reactors, are the predominant type used in microbial fermentation (Figure 12.3c). Rushton turbines are usually used with an air sparger placed directly underneath it. Gas bubbles from the sparger rise, hit the disk, and are directed outward. The blades, which rotate at a fast speed, then break the bubbles up.1 Very high-energy dissipation in the area immediately surrounding the blades causes a high degree of turbulence in the fluid, further contributing to bubble break-up. The agitation also creates a high shear zone surrounding the impeller that can potentially damage cells. Despite this, it has been shown that mammalian cells grown in suspension can proliferate well with a Rushton turbine-type impeller rotating at a moderate agitation rate. Many cells are perhaps more tolerant to fluid flow stress than commonly thought.
Solid–Liquid Systems
Published in Wioletta Podgórska, Multiphase Particulate Systems in Turbulent Flows, 2019
Precipitation is carried out in a stirred tank (T=0.242m) equipped with a six-blade Rushton turbine of diameter D=0.075m (clearance 0.075 m) and four baffles. The reactor containing initially 10 dm3 of A (barium chloride) solution is fed by B (sodium sulfate) of volume VB0 through a feed tube of diameter 1.5 mm (to avoid back-mixing). The feed point is either 5 mm below the initial liquid level and 60 mm from the tank axis, or near the impeller in the discharge stream (43 mm from the axis, 80 mm from the bottom). The volume ratio is defined as αv=V0VB0
Performance intensification of a stirred bioreactor for fermentative biohydrogen production
Published in Preparative Biochemistry and Biotechnology, 2018
E. I. Garcia-Peña, C. Niño-Navarro, I. Chairez, L. Torres-Bustillos, J. Ramírez-Muñoz, E. Salgado-Manjarrez
As mentioned above, power consumption is also a key issue in studying and designing stirred tanks. Initially, most of the studies were performed with traditional impellers, such as standard Rushton turbine, and down-(up-)pumping 45°-pitched blade turbines. Armenante and Chang[39] studied the power consumption in vessels agitated by one-, two-, or three-RDT under turbulent conditions. In this work it was found that the dissipated overall power was proportional to the off-bottom clearance of the lowest impeller and the impeller spacing. Recently, Wang et al.[23] demonstrated that, in gas–liquid systems, in configurations with two radial impellers, the costs of energy and the power input were higher than in systems composed by two axial impellers. Pv was almost three times higher than the one obtained of both axial impellers. Those results agree with the ones obtained in the present work and with those of Bouaifi and Roustan.[37]