Intensifying micromixing in a semi-batch reactor using a Rushton turbine

Reactor Engineering in Large Scale Animal Cell Culture

“…Probes can do so and therefore pH homogeneity was investigated in the same 8 m 3 (T = 2 m) bioreactor and in a transparent, geometrically similar, scaled-down vessel of 0.61 m diameter (Langheinrich and Nienow 1999). In addition, other work on chemical reactors has shown distinct advantages from feeding close to impellers when chemical reactions, especially involving acid or base, are under consideration (Nienow et al 1997;Assirelli et al 2005). Therefore, since it was found that pH excursions from the mean value with addition to the top surface were very large, additions close to the impeller were also made and both sparged and unsparged runs were studied.…”

“…It was concluded that 'during scale-up, agitation rate should be increased to minimise the magnitude and duration of pH perturbations as much as possible and alkali should be added to a well-mixed region of the vessel'. Another way of reducing the magnitude and duration of pH perturbations in addition to agitation intensity and feed position is to use a lower concentration solution for pH control, a well-known strategy when handling fast chemical reactions (Assirelli et al 2005). As a measure of how carefully pH control must be carried out even at the bench-scale, Ozturk (1996) showed a picture taken of a poorly agitated bioreactor in which a viscous 'snow-ball' close to the addition point of concentrated alkali had formed.…”

“…'Cleaning-in-place' can perhaps be resolved by adding some CIP fluid through the subsurface feed pipe (though if it can not, the use of an up-pumping hydrofoil should help mixing (Nienow and Bujalski 2004) if, in spite of the obvious problems it causes, surface addition is employed). Also, the use of less concentrated reagents can be considered (Assirelli et al 2005). (c) Install an over-powered variable speed motor with respect to oxygen demand and control speed on dissolved O 2 .…”

Flow Instabilities in Mechanically Agitated Stirred Vessels

“…For instance for a Rushton turbine (RT) they appear as a pair, behind the lower and the upper sides of the impeller blade, and provide a source of turbulence that can improve mixing. Assirelli et al (2005) have shown how micro-mixing efficiency can be enhanced when a feeding pipe stationary with the impeller is used to release the fed reactant in the region of maximum dissipation rate behind the trailing vortices. Such trailing vortices may also play a crucial role in determining gas accumulation behind impeller blades in gas-liquid applications, thus affecting pumping and power dissipation capacity of the impeller.…”

On the use of the Iodide Iodate Reaction Method for assessing mixing times in continuous flow mixers

“…Among those are the concentration of the acid injected, 2,4 the acid feed point, 2,4,5 the acid feed time, 2,4 the geometry of the mixing accessory, 4 and the stirrer speed. 2,[4][5][6] Later, the reaction scheme was applied for characterizing mixing in continuous flow devices, 7 where two flows were combined in the device in a flow ratio of 1:1. One feed contained sulfuric acid in a rather low concentration; the other feed contained the other reactants.…”